Merge tag 's390-6.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux

[linux-block.git] / fs / btrfs / extent_io.c

// SPDX-License-Identifier: GPL-2.0

#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/bio.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/page-flags.h>
#include <linux/sched/mm.h>
#include <linux/spinlock.h>
#include <linux/blkdev.h>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include <linux/prefetch.h>
#include <linux/fsverity.h>
#include "misc.h"
#include "extent_io.h"
#include "extent-io-tree.h"
#include "extent_map.h"
#include "ctree.h"
#include "btrfs_inode.h"
#include "bio.h"
#include "check-integrity.h"
#include "locking.h"
#include "rcu-string.h"
#include "backref.h"
#include "disk-io.h"
#include "subpage.h"
#include "zoned.h"
#include "block-group.h"
#include "compression.h"
#include "fs.h"
#include "accessors.h"
#include "file-item.h"
#include "file.h"
#include "dev-replace.h"
#include "super.h"
#include "transaction.h"

static struct kmem_cache *extent_buffer_cache;

#ifdef CONFIG_BTRFS_DEBUG
static inline void btrfs_leak_debug_add_eb(struct extent_buffer *eb)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        unsigned long flags;

        spin_lock_irqsave(&fs_info->eb_leak_lock, flags);
        list_add(&eb->leak_list, &fs_info->allocated_ebs);
        spin_unlock_irqrestore(&fs_info->eb_leak_lock, flags);
}

static inline void btrfs_leak_debug_del_eb(struct extent_buffer *eb)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        unsigned long flags;

        spin_lock_irqsave(&fs_info->eb_leak_lock, flags);
        list_del(&eb->leak_list);
        spin_unlock_irqrestore(&fs_info->eb_leak_lock, flags);
}

void btrfs_extent_buffer_leak_debug_check(struct btrfs_fs_info *fs_info)
{
        struct extent_buffer *eb;
        unsigned long flags;

        /*
         * If we didn't get into open_ctree our allocated_ebs will not be
         * initialized, so just skip this.
         */
        if (!fs_info->allocated_ebs.next)
                return;

        WARN_ON(!list_empty(&fs_info->allocated_ebs));
        spin_lock_irqsave(&fs_info->eb_leak_lock, flags);
        while (!list_empty(&fs_info->allocated_ebs)) {
                eb = list_first_entry(&fs_info->allocated_ebs,
                                      struct extent_buffer, leak_list);
                pr_err(
        "BTRFS: buffer leak start %llu len %lu refs %d bflags %lu owner %llu\n",
                       eb->start, eb->len, atomic_read(&eb->refs), eb->bflags,
                       btrfs_header_owner(eb));
                list_del(&eb->leak_list);
                kmem_cache_free(extent_buffer_cache, eb);
        }
        spin_unlock_irqrestore(&fs_info->eb_leak_lock, flags);
}
#else
#define btrfs_leak_debug_add_eb(eb)                     do {} while (0)
#define btrfs_leak_debug_del_eb(eb)                     do {} while (0)
#endif

/*
 * Structure to record info about the bio being assembled, and other info like
 * how many bytes are there before stripe/ordered extent boundary.
 */
struct btrfs_bio_ctrl {
        struct bio *bio;
        int mirror_num;
        enum btrfs_compression_type compress_type;
        u32 len_to_oe_boundary;
        btrfs_bio_end_io_t end_io_func;

        /*
         * This is for metadata read, to provide the extra needed verification
         * info.  This has to be provided for submit_one_bio(), as
         * submit_one_bio() can submit a bio if it ends at stripe boundary.  If
         * no such parent_check is provided, the metadata can hit false alert at
         * endio time.
         */
        struct btrfs_tree_parent_check *parent_check;

        /*
         * Tell writepage not to lock the state bits for this range, it still
         * does the unlocking.
         */
        bool extent_locked;

        /* Tell the submit_bio code to use REQ_SYNC */
        bool sync_io;
};

static void submit_one_bio(struct btrfs_bio_ctrl *bio_ctrl)
{
        struct bio *bio;
        struct bio_vec *bv;
        struct inode *inode;
        int mirror_num;

        if (!bio_ctrl->bio)
                return;

        bio = bio_ctrl->bio;
        bv = bio_first_bvec_all(bio);
        inode = bv->bv_page->mapping->host;
        mirror_num = bio_ctrl->mirror_num;

        /* Caller should ensure the bio has at least some range added */
        ASSERT(bio->bi_iter.bi_size);

        if (!is_data_inode(inode)) {
                if (btrfs_op(bio) != BTRFS_MAP_WRITE) {
                        /*
                         * For metadata read, we should have the parent_check,
                         * and copy it to bbio for metadata verification.
                         */
                        ASSERT(bio_ctrl->parent_check);
                        memcpy(&btrfs_bio(bio)->parent_check,
                               bio_ctrl->parent_check,
                               sizeof(struct btrfs_tree_parent_check));
                }
                bio->bi_opf |= REQ_META;
        }

        if (btrfs_op(bio) == BTRFS_MAP_READ &&
            bio_ctrl->compress_type != BTRFS_COMPRESS_NONE)
                btrfs_submit_compressed_read(inode, bio, mirror_num);
        else
                btrfs_submit_bio(bio, mirror_num);

        /* The bio is owned by the end_io handler now */
        bio_ctrl->bio = NULL;
}

/*
 * Submit or fail the current bio in the bio_ctrl structure.
 */
static void submit_write_bio(struct btrfs_bio_ctrl *bio_ctrl, int ret)
{
        struct bio *bio = bio_ctrl->bio;

        if (!bio)
                return;

        if (ret) {
                ASSERT(ret < 0);
                btrfs_bio_end_io(btrfs_bio(bio), errno_to_blk_status(ret));
                /* The bio is owned by the end_io handler now */
                bio_ctrl->bio = NULL;
        } else {
                submit_one_bio(bio_ctrl);
        }
}

int __init extent_buffer_init_cachep(void)
{
        extent_buffer_cache = kmem_cache_create("btrfs_extent_buffer",
                        sizeof(struct extent_buffer), 0,
                        SLAB_MEM_SPREAD, NULL);
        if (!extent_buffer_cache)
                return -ENOMEM;

        return 0;
}

void __cold extent_buffer_free_cachep(void)
{
        /*
         * Make sure all delayed rcu free are flushed before we
         * destroy caches.
         */
        rcu_barrier();
        kmem_cache_destroy(extent_buffer_cache);
}

void extent_range_clear_dirty_for_io(struct inode *inode, u64 start, u64 end)
{
        unsigned long index = start >> PAGE_SHIFT;
        unsigned long end_index = end >> PAGE_SHIFT;
        struct page *page;

        while (index <= end_index) {
                page = find_get_page(inode->i_mapping, index);
                BUG_ON(!page); /* Pages should be in the extent_io_tree */
                clear_page_dirty_for_io(page);
                put_page(page);
                index++;
        }
}

void extent_range_redirty_for_io(struct inode *inode, u64 start, u64 end)
{
        struct address_space *mapping = inode->i_mapping;
        unsigned long index = start >> PAGE_SHIFT;
        unsigned long end_index = end >> PAGE_SHIFT;
        struct folio *folio;

        while (index <= end_index) {
                folio = filemap_get_folio(mapping, index);
                filemap_dirty_folio(mapping, folio);
                folio_account_redirty(folio);
                index += folio_nr_pages(folio);
                folio_put(folio);
        }
}

/*
 * Process one page for __process_pages_contig().
 *
 * Return >0 if we hit @page == @locked_page.
 * Return 0 if we updated the page status.
 * Return -EGAIN if the we need to try again.
 * (For PAGE_LOCK case but got dirty page or page not belong to mapping)
 */
static int process_one_page(struct btrfs_fs_info *fs_info,
                            struct address_space *mapping,
                            struct page *page, struct page *locked_page,
                            unsigned long page_ops, u64 start, u64 end)
{
        u32 len;

        ASSERT(end + 1 - start != 0 && end + 1 - start < U32_MAX);
        len = end + 1 - start;

        if (page_ops & PAGE_SET_ORDERED)
                btrfs_page_clamp_set_ordered(fs_info, page, start, len);
        if (page_ops & PAGE_SET_ERROR)
                btrfs_page_clamp_set_error(fs_info, page, start, len);
        if (page_ops & PAGE_START_WRITEBACK) {
                btrfs_page_clamp_clear_dirty(fs_info, page, start, len);
                btrfs_page_clamp_set_writeback(fs_info, page, start, len);
        }
        if (page_ops & PAGE_END_WRITEBACK)
                btrfs_page_clamp_clear_writeback(fs_info, page, start, len);

        if (page == locked_page)
                return 1;

        if (page_ops & PAGE_LOCK) {
                int ret;

                ret = btrfs_page_start_writer_lock(fs_info, page, start, len);
                if (ret)
                        return ret;
                if (!PageDirty(page) || page->mapping != mapping) {
                        btrfs_page_end_writer_lock(fs_info, page, start, len);
                        return -EAGAIN;
                }
        }
        if (page_ops & PAGE_UNLOCK)
                btrfs_page_end_writer_lock(fs_info, page, start, len);
        return 0;
}

static int __process_pages_contig(struct address_space *mapping,
                                  struct page *locked_page,
                                  u64 start, u64 end, unsigned long page_ops,
                                  u64 *processed_end)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(mapping->host->i_sb);
        pgoff_t start_index = start >> PAGE_SHIFT;
        pgoff_t end_index = end >> PAGE_SHIFT;
        pgoff_t index = start_index;
        unsigned long pages_processed = 0;
        struct folio_batch fbatch;
        int err = 0;
        int i;

        if (page_ops & PAGE_LOCK) {
                ASSERT(page_ops == PAGE_LOCK);
                ASSERT(processed_end && *processed_end == start);
        }

        if ((page_ops & PAGE_SET_ERROR) && start_index <= end_index)
                mapping_set_error(mapping, -EIO);

        folio_batch_init(&fbatch);
        while (index <= end_index) {
                int found_folios;

                found_folios = filemap_get_folios_contig(mapping, &index,
                                end_index, &fbatch);

                if (found_folios == 0) {
                        /*
                         * Only if we're going to lock these pages, we can find
                         * nothing at @index.
                         */
                        ASSERT(page_ops & PAGE_LOCK);
                        err = -EAGAIN;
                        goto out;
                }

                for (i = 0; i < found_folios; i++) {
                        int process_ret;
                        struct folio *folio = fbatch.folios[i];
                        process_ret = process_one_page(fs_info, mapping,
                                        &folio->page, locked_page, page_ops,
                                        start, end);
                        if (process_ret < 0) {
                                err = -EAGAIN;
                                folio_batch_release(&fbatch);
                                goto out;
                        }
                        pages_processed += folio_nr_pages(folio);
                }
                folio_batch_release(&fbatch);
                cond_resched();
        }
out:
        if (err && processed_end) {
                /*
                 * Update @processed_end. I know this is awful since it has
                 * two different return value patterns (inclusive vs exclusive).
                 *
                 * But the exclusive pattern is necessary if @start is 0, or we
                 * underflow and check against processed_end won't work as
                 * expected.
                 */
                if (pages_processed)
                        *processed_end = min(end,
                        ((u64)(start_index + pages_processed) << PAGE_SHIFT) - 1);
                else
                        *processed_end = start;
        }
        return err;
}

static noinline void __unlock_for_delalloc(struct inode *inode,
                                           struct page *locked_page,
                                           u64 start, u64 end)
{
        unsigned long index = start >> PAGE_SHIFT;
        unsigned long end_index = end >> PAGE_SHIFT;

        ASSERT(locked_page);
        if (index == locked_page->index && end_index == index)
                return;

        __process_pages_contig(inode->i_mapping, locked_page, start, end,
                               PAGE_UNLOCK, NULL);
}

static noinline int lock_delalloc_pages(struct inode *inode,
                                        struct page *locked_page,
                                        u64 delalloc_start,
                                        u64 delalloc_end)
{
        unsigned long index = delalloc_start >> PAGE_SHIFT;
        unsigned long end_index = delalloc_end >> PAGE_SHIFT;
        u64 processed_end = delalloc_start;
        int ret;

        ASSERT(locked_page);
        if (index == locked_page->index && index == end_index)
                return 0;

        ret = __process_pages_contig(inode->i_mapping, locked_page, delalloc_start,
                                     delalloc_end, PAGE_LOCK, &processed_end);
        if (ret == -EAGAIN && processed_end > delalloc_start)
                __unlock_for_delalloc(inode, locked_page, delalloc_start,
                                      processed_end);
        return ret;
}

/*
 * Find and lock a contiguous range of bytes in the file marked as delalloc, no
 * more than @max_bytes.
 *
 * @start:      The original start bytenr to search.
 *              Will store the extent range start bytenr.
 * @end:        The original end bytenr of the search range
 *              Will store the extent range end bytenr.
 *
 * Return true if we find a delalloc range which starts inside the original
 * range, and @start/@end will store the delalloc range start/end.
 *
 * Return false if we can't find any delalloc range which starts inside the
 * original range, and @start/@end will be the non-delalloc range start/end.
 */
EXPORT_FOR_TESTS
noinline_for_stack bool find_lock_delalloc_range(struct inode *inode,
                                    struct page *locked_page, u64 *start,
                                    u64 *end)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
        const u64 orig_start = *start;
        const u64 orig_end = *end;
        /* The sanity tests may not set a valid fs_info. */
        u64 max_bytes = fs_info ? fs_info->max_extent_size : BTRFS_MAX_EXTENT_SIZE;
        u64 delalloc_start;
        u64 delalloc_end;
        bool found;
        struct extent_state *cached_state = NULL;
        int ret;
        int loops = 0;

        /* Caller should pass a valid @end to indicate the search range end */
        ASSERT(orig_end > orig_start);

        /* The range should at least cover part of the page */
        ASSERT(!(orig_start >= page_offset(locked_page) + PAGE_SIZE ||
                 orig_end <= page_offset(locked_page)));
again:
        /* step one, find a bunch of delalloc bytes starting at start */
        delalloc_start = *start;
        delalloc_end = 0;
        found = btrfs_find_delalloc_range(tree, &delalloc_start, &delalloc_end,
                                          max_bytes, &cached_state);
        if (!found || delalloc_end <= *start || delalloc_start > orig_end) {
                *start = delalloc_start;

                /* @delalloc_end can be -1, never go beyond @orig_end */
                *end = min(delalloc_end, orig_end);
                free_extent_state(cached_state);
                return false;
        }

        /*
         * start comes from the offset of locked_page.  We have to lock
         * pages in order, so we can't process delalloc bytes before
         * locked_page
         */
        if (delalloc_start < *start)
                delalloc_start = *start;

        /*
         * make sure to limit the number of pages we try to lock down
         */
        if (delalloc_end + 1 - delalloc_start > max_bytes)
                delalloc_end = delalloc_start + max_bytes - 1;

        /* step two, lock all the pages after the page that has start */
        ret = lock_delalloc_pages(inode, locked_page,
                                  delalloc_start, delalloc_end);
        ASSERT(!ret || ret == -EAGAIN);
        if (ret == -EAGAIN) {
                /* some of the pages are gone, lets avoid looping by
                 * shortening the size of the delalloc range we're searching
                 */
                free_extent_state(cached_state);
                cached_state = NULL;
                if (!loops) {
                        max_bytes = PAGE_SIZE;
                        loops = 1;
                        goto again;
                } else {
                        found = false;
                        goto out_failed;
                }
        }

        /* step three, lock the state bits for the whole range */
        lock_extent(tree, delalloc_start, delalloc_end, &cached_state);

        /* then test to make sure it is all still delalloc */
        ret = test_range_bit(tree, delalloc_start, delalloc_end,
                             EXTENT_DELALLOC, 1, cached_state);
        if (!ret) {
                unlock_extent(tree, delalloc_start, delalloc_end,
                              &cached_state);
                __unlock_for_delalloc(inode, locked_page,
                              delalloc_start, delalloc_end);
                cond_resched();
                goto again;
        }
        free_extent_state(cached_state);
        *start = delalloc_start;
        *end = delalloc_end;
out_failed:
        return found;
}

void extent_clear_unlock_delalloc(struct btrfs_inode *inode, u64 start, u64 end,
                                  struct page *locked_page,
                                  u32 clear_bits, unsigned long page_ops)
{
        clear_extent_bit(&inode->io_tree, start, end, clear_bits, NULL);

        __process_pages_contig(inode->vfs_inode.i_mapping, locked_page,
                               start, end, page_ops, NULL);
}

static void end_page_read(struct page *page, bool uptodate, u64 start, u32 len)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);

        ASSERT(page_offset(page) <= start &&
               start + len <= page_offset(page) + PAGE_SIZE);

        if (uptodate) {
                if (fsverity_active(page->mapping->host) &&
                    !PageError(page) &&
                    !PageUptodate(page) &&
                    start < i_size_read(page->mapping->host) &&
                    !fsverity_verify_page(page)) {
                        btrfs_page_set_error(fs_info, page, start, len);
                } else {
                        btrfs_page_set_uptodate(fs_info, page, start, len);
                }
        } else {
                btrfs_page_clear_uptodate(fs_info, page, start, len);
                btrfs_page_set_error(fs_info, page, start, len);
        }

        if (!btrfs_is_subpage(fs_info, page))
                unlock_page(page);
        else
                btrfs_subpage_end_reader(fs_info, page, start, len);
}

/* lots and lots of room for performance fixes in the end_bio funcs */

void end_extent_writepage(struct page *page, int err, u64 start, u64 end)
{
        struct btrfs_inode *inode;
        const bool uptodate = (err == 0);
        int ret = 0;

        ASSERT(page && page->mapping);
        inode = BTRFS_I(page->mapping->host);
        btrfs_writepage_endio_finish_ordered(inode, page, start, end, uptodate);

        if (!uptodate) {
                const struct btrfs_fs_info *fs_info = inode->root->fs_info;
                u32 len;

                ASSERT(end + 1 - start <= U32_MAX);
                len = end + 1 - start;

                btrfs_page_clear_uptodate(fs_info, page, start, len);
                btrfs_page_set_error(fs_info, page, start, len);
                ret = err < 0 ? err : -EIO;
                mapping_set_error(page->mapping, ret);
        }
}

/*
 * after a writepage IO is done, we need to:
 * clear the uptodate bits on error
 * clear the writeback bits in the extent tree for this IO
 * end_page_writeback if the page has no more pending IO
 *
 * Scheduling is not allowed, so the extent state tree is expected
 * to have one and only one object corresponding to this IO.
 */
static void end_bio_extent_writepage(struct btrfs_bio *bbio)
{
        struct bio *bio = &bbio->bio;
        int error = blk_status_to_errno(bio->bi_status);
        struct bio_vec *bvec;
        u64 start;
        u64 end;
        struct bvec_iter_all iter_all;

        ASSERT(!bio_flagged(bio, BIO_CLONED));
        bio_for_each_segment_all(bvec, bio, iter_all) {
                struct page *page = bvec->bv_page;
                struct inode *inode = page->mapping->host;
                struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
                const u32 sectorsize = fs_info->sectorsize;

                /* Our read/write should always be sector aligned. */
                if (!IS_ALIGNED(bvec->bv_offset, sectorsize))
                        btrfs_err(fs_info,
                "partial page write in btrfs with offset %u and length %u",
                                  bvec->bv_offset, bvec->bv_len);
                else if (!IS_ALIGNED(bvec->bv_len, sectorsize))
                        btrfs_info(fs_info,
                "incomplete page write with offset %u and length %u",
                                   bvec->bv_offset, bvec->bv_len);

                start = page_offset(page) + bvec->bv_offset;
                end = start + bvec->bv_len - 1;

                end_extent_writepage(page, error, start, end);

                btrfs_page_clear_writeback(fs_info, page, start, bvec->bv_len);
        }

        bio_put(bio);
}

/*
 * Record previously processed extent range
 *
 * For endio_readpage_release_extent() to handle a full extent range, reducing
 * the extent io operations.
 */
struct processed_extent {
        struct btrfs_inode *inode;
        /* Start of the range in @inode */
        u64 start;
        /* End of the range in @inode */
        u64 end;
        bool uptodate;
};

/*
 * Try to release processed extent range
 *
 * May not release the extent range right now if the current range is
 * contiguous to processed extent.
 *
 * Will release processed extent when any of @inode, @uptodate, the range is
 * no longer contiguous to the processed range.
 *
 * Passing @inode == NULL will force processed extent to be released.
 */
static void endio_readpage_release_extent(struct processed_extent *processed,
                              struct btrfs_inode *inode, u64 start, u64 end,
                              bool uptodate)
{
        struct extent_state *cached = NULL;
        struct extent_io_tree *tree;

        /* The first extent, initialize @processed */
        if (!processed->inode)
                goto update;

        /*
         * Contiguous to processed extent, just uptodate the end.
         *
         * Several things to notice:
         *
         * - bio can be merged as long as on-disk bytenr is contiguous
         *   This means we can have page belonging to other inodes, thus need to
         *   check if the inode still matches.
         * - bvec can contain range beyond current page for multi-page bvec
         *   Thus we need to do processed->end + 1 >= start check
         */
        if (processed->inode == inode && processed->uptodate == uptodate &&
            processed->end + 1 >= start && end >= processed->end) {
                processed->end = end;
                return;
        }

        tree = &processed->inode->io_tree;
        /*
         * Now we don't have range contiguous to the processed range, release
         * the processed range now.
         */
        unlock_extent(tree, processed->start, processed->end, &cached);

update:
        /* Update processed to current range */
        processed->inode = inode;
        processed->start = start;
        processed->end = end;
        processed->uptodate = uptodate;
}

static void begin_page_read(struct btrfs_fs_info *fs_info, struct page *page)
{
        ASSERT(PageLocked(page));
        if (!btrfs_is_subpage(fs_info, page))
                return;

        ASSERT(PagePrivate(page));
        btrfs_subpage_start_reader(fs_info, page, page_offset(page), PAGE_SIZE);
}

/*
 * Find extent buffer for a givne bytenr.
 *
 * This is for end_bio_extent_readpage(), thus we can't do any unsafe locking
 * in endio context.
 */
static struct extent_buffer *find_extent_buffer_readpage(
                struct btrfs_fs_info *fs_info, struct page *page, u64 bytenr)
{
        struct extent_buffer *eb;

        /*
         * For regular sectorsize, we can use page->private to grab extent
         * buffer
         */
        if (fs_info->nodesize >= PAGE_SIZE) {
                ASSERT(PagePrivate(page) && page->private);
                return (struct extent_buffer *)page->private;
        }

        /* For subpage case, we need to lookup buffer radix tree */
        rcu_read_lock();
        eb = radix_tree_lookup(&fs_info->buffer_radix,
                               bytenr >> fs_info->sectorsize_bits);
        rcu_read_unlock();
        ASSERT(eb);
        return eb;
}

/*
 * after a readpage IO is done, we need to:
 * clear the uptodate bits on error
 * set the uptodate bits if things worked
 * set the page up to date if all extents in the tree are uptodate
 * clear the lock bit in the extent tree
 * unlock the page if there are no other extents locked for it
 *
 * Scheduling is not allowed, so the extent state tree is expected
 * to have one and only one object corresponding to this IO.
 */
static void end_bio_extent_readpage(struct btrfs_bio *bbio)
{
        struct bio *bio = &bbio->bio;
        struct bio_vec *bvec;
        struct processed_extent processed = { 0 };
        /*
         * The offset to the beginning of a bio, since one bio can never be
         * larger than UINT_MAX, u32 here is enough.
         */
        u32 bio_offset = 0;
        int mirror;
        struct bvec_iter_all iter_all;

        ASSERT(!bio_flagged(bio, BIO_CLONED));
        bio_for_each_segment_all(bvec, bio, iter_all) {
                bool uptodate = !bio->bi_status;
                struct page *page = bvec->bv_page;
                struct inode *inode = page->mapping->host;
                struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
                const u32 sectorsize = fs_info->sectorsize;
                u64 start;
                u64 end;
                u32 len;

                btrfs_debug(fs_info,
                        "end_bio_extent_readpage: bi_sector=%llu, err=%d, mirror=%u",
                        bio->bi_iter.bi_sector, bio->bi_status,
                        bbio->mirror_num);

                /*
                 * We always issue full-sector reads, but if some block in a
                 * page fails to read, blk_update_request() will advance
                 * bv_offset and adjust bv_len to compensate.  Print a warning
                 * for unaligned offsets, and an error if they don't add up to
                 * a full sector.
                 */
                if (!IS_ALIGNED(bvec->bv_offset, sectorsize))
                        btrfs_err(fs_info,
                "partial page read in btrfs with offset %u and length %u",
                                  bvec->bv_offset, bvec->bv_len);
                else if (!IS_ALIGNED(bvec->bv_offset + bvec->bv_len,
                                     sectorsize))
                        btrfs_info(fs_info,
                "incomplete page read with offset %u and length %u",
                                   bvec->bv_offset, bvec->bv_len);

                start = page_offset(page) + bvec->bv_offset;
                end = start + bvec->bv_len - 1;
                len = bvec->bv_len;

                mirror = bbio->mirror_num;
                if (uptodate && !is_data_inode(inode) &&
                    btrfs_validate_metadata_buffer(bbio, page, start, end, mirror))
                        uptodate = false;

                if (likely(uptodate)) {
                        loff_t i_size = i_size_read(inode);
                        pgoff_t end_index = i_size >> PAGE_SHIFT;

                        /*
                         * Zero out the remaining part if this range straddles
                         * i_size.
                         *
                         * Here we should only zero the range inside the bvec,
                         * not touch anything else.
                         *
                         * NOTE: i_size is exclusive while end is inclusive.
                         */
                        if (page->index == end_index && i_size <= end) {
                                u32 zero_start = max(offset_in_page(i_size),
                                                     offset_in_page(start));

                                zero_user_segment(page, zero_start,
                                                  offset_in_page(end) + 1);
                        }
                } else if (!is_data_inode(inode)) {
                        struct extent_buffer *eb;

                        eb = find_extent_buffer_readpage(fs_info, page, start);
                        set_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags);
                        eb->read_mirror = mirror;
                        atomic_dec(&eb->io_pages);
                }

                /* Update page status and unlock. */
                end_page_read(page, uptodate, start, len);
                endio_readpage_release_extent(&processed, BTRFS_I(inode),
                                              start, end, PageUptodate(page));

                ASSERT(bio_offset + len > bio_offset);
                bio_offset += len;

        }
        /* Release the last extent */
        endio_readpage_release_extent(&processed, NULL, 0, 0, false);
        bio_put(bio);
}

/*
 * Populate every free slot in a provided array with pages.
 *
 * @nr_pages:   number of pages to allocate
 * @page_array: the array to fill with pages; any existing non-null entries in
 *              the array will be skipped
 *
 * Return: 0        if all pages were able to be allocated;
 *         -ENOMEM  otherwise, and the caller is responsible for freeing all
 *                  non-null page pointers in the array.
 */
int btrfs_alloc_page_array(unsigned int nr_pages, struct page **page_array)
{
        unsigned int allocated;

        for (allocated = 0; allocated < nr_pages;) {
                unsigned int last = allocated;

                allocated = alloc_pages_bulk_array(GFP_NOFS, nr_pages, page_array);

                if (allocated == nr_pages)
                        return 0;

                /*
                 * During this iteration, no page could be allocated, even
                 * though alloc_pages_bulk_array() falls back to alloc_page()
                 * if  it could not bulk-allocate. So we must be out of memory.
                 */
                if (allocated == last)
                        return -ENOMEM;

                memalloc_retry_wait(GFP_NOFS);
        }
        return 0;
}

/*
 * Attempt to add a page to bio.
 *
 * @bio_ctrl:       record both the bio, and its bio_flags
 * @page:           page to add to the bio
 * @disk_bytenr:    offset of the new bio or to check whether we are adding
 *                  a contiguous page to the previous one
 * @size:           portion of page that we want to write
 * @pg_offset:      starting offset in the page
 * @compress_type:  compression type of the current bio to see if we can merge them
 *
 * Attempt to add a page to bio considering stripe alignment etc.
 *
 * Return >= 0 for the number of bytes added to the bio.
 * Can return 0 if the current bio is already at stripe/zone boundary.
 * Return <0 for error.
 */
static int btrfs_bio_add_page(struct btrfs_bio_ctrl *bio_ctrl,
                              struct page *page,
                              u64 disk_bytenr, unsigned int size,
                              unsigned int pg_offset,
                              enum btrfs_compression_type compress_type)
{
        struct bio *bio = bio_ctrl->bio;
        u32 bio_size = bio->bi_iter.bi_size;
        u32 real_size;
        const sector_t sector = disk_bytenr >> SECTOR_SHIFT;
        bool contig = false;

        ASSERT(bio);
        /* The limit should be calculated when bio_ctrl->bio is allocated */
        ASSERT(bio_ctrl->len_to_oe_boundary);
        if (bio_ctrl->compress_type != compress_type)
                return 0;


        if (bio->bi_iter.bi_size == 0) {
                /* We can always add a page into an empty bio. */
                contig = true;
        } else if (bio_ctrl->compress_type == BTRFS_COMPRESS_NONE) {
                struct bio_vec *bvec = bio_last_bvec_all(bio);

                /*
                 * The contig check requires the following conditions to be met:
                 * 1) The pages are belonging to the same inode
                 *    This is implied by the call chain.
                 *
                 * 2) The range has adjacent logical bytenr
                 *
                 * 3) The range has adjacent file offset
                 *    This is required for the usage of btrfs_bio->file_offset.
                 */
                if (bio_end_sector(bio) == sector &&
                    page_offset(bvec->bv_page) + bvec->bv_offset +
                    bvec->bv_len == page_offset(page) + pg_offset)
                        contig = true;
        } else {
                /*
                 * For compression, all IO should have its logical bytenr
                 * set to the starting bytenr of the compressed extent.
                 */
                contig = bio->bi_iter.bi_sector == sector;
        }

        if (!contig)
                return 0;

        real_size = min(bio_ctrl->len_to_oe_boundary - bio_size, size);

        /*
         * If real_size is 0, never call bio_add_*_page(), as even size is 0,
         * bio will still execute its endio function on the page!
         */
        if (real_size == 0)
                return 0;

        return bio_add_page(bio, page, real_size, pg_offset);
}

static void calc_bio_boundaries(struct btrfs_bio_ctrl *bio_ctrl,
                                struct btrfs_inode *inode, u64 file_offset)
{
        struct btrfs_ordered_extent *ordered;

        /*
         * Limit the extent to the ordered boundary for Zone Append.
         * Compressed bios aren't submitted directly, so it doesn't apply to
         * them.
         */
        if (bio_ctrl->compress_type == BTRFS_COMPRESS_NONE &&
            btrfs_use_zone_append(btrfs_bio(bio_ctrl->bio))) {
                ordered = btrfs_lookup_ordered_extent(inode, file_offset);
                if (ordered) {
                        bio_ctrl->len_to_oe_boundary = min_t(u32, U32_MAX,
                                        ordered->file_offset +
                                        ordered->disk_num_bytes - file_offset);
                        btrfs_put_ordered_extent(ordered);
                        return;
                }
        }

        bio_ctrl->len_to_oe_boundary = U32_MAX;
}

static void alloc_new_bio(struct btrfs_inode *inode,
                          struct btrfs_bio_ctrl *bio_ctrl,
                          struct writeback_control *wbc, blk_opf_t opf,
                          u64 disk_bytenr, u32 offset, u64 file_offset,
                          enum btrfs_compression_type compress_type)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct bio *bio;

        bio = btrfs_bio_alloc(BIO_MAX_VECS, opf, inode, bio_ctrl->end_io_func,
                              NULL);
        /*
         * For compressed page range, its disk_bytenr is always @disk_bytenr
         * passed in, no matter if we have added any range into previous bio.
         */
        if (compress_type != BTRFS_COMPRESS_NONE)
                bio->bi_iter.bi_sector = disk_bytenr >> SECTOR_SHIFT;
        else
                bio->bi_iter.bi_sector = (disk_bytenr + offset) >> SECTOR_SHIFT;
        btrfs_bio(bio)->file_offset = file_offset;
        bio_ctrl->bio = bio;
        bio_ctrl->compress_type = compress_type;
        calc_bio_boundaries(bio_ctrl, inode, file_offset);

        if (wbc) {
                /*
                 * Pick the last added device to support cgroup writeback.  For
                 * multi-device file systems this means blk-cgroup policies have
                 * to always be set on the last added/replaced device.
                 * This is a bit odd but has been like that for a long time.
                 */
                bio_set_dev(bio, fs_info->fs_devices->latest_dev->bdev);
                wbc_init_bio(wbc, bio);
        }
}

/*
 * @opf:        bio REQ_OP_* and REQ_* flags as one value
 * @wbc:        optional writeback control for io accounting
 * @disk_bytenr: logical bytenr where the write will be
 * @page:       page to add to the bio
 * @size:       portion of page that we want to write to
 * @pg_offset:  offset of the new bio or to check whether we are adding
 *              a contiguous page to the previous one
 * @compress_type:   compress type for current bio
 *
 * The will either add the page into the existing @bio_ctrl->bio, or allocate a
 * new one in @bio_ctrl->bio.
 * The mirror number for this IO should already be initizlied in
 * @bio_ctrl->mirror_num.
 */
static int submit_extent_page(blk_opf_t opf,
                              struct writeback_control *wbc,
                              struct btrfs_bio_ctrl *bio_ctrl,
                              u64 disk_bytenr, struct page *page,
                              size_t size, unsigned long pg_offset,
                              enum btrfs_compression_type compress_type,
                              bool force_bio_submit)
{
        struct btrfs_inode *inode = BTRFS_I(page->mapping->host);
        unsigned int cur = pg_offset;

        ASSERT(bio_ctrl);

        ASSERT(pg_offset < PAGE_SIZE && size <= PAGE_SIZE &&
               pg_offset + size <= PAGE_SIZE);

        ASSERT(bio_ctrl->end_io_func);

        if (force_bio_submit)
                submit_one_bio(bio_ctrl);

        while (cur < pg_offset + size) {
                u32 offset = cur - pg_offset;
                int added;

                /* Allocate new bio if needed */
                if (!bio_ctrl->bio) {
                        alloc_new_bio(inode, bio_ctrl, wbc, opf, disk_bytenr,
                                      offset, page_offset(page) + cur,
                                      compress_type);
                }
                /*
                 * We must go through btrfs_bio_add_page() to ensure each
                 * page range won't cross various boundaries.
                 */
                if (compress_type != BTRFS_COMPRESS_NONE)
                        added = btrfs_bio_add_page(bio_ctrl, page, disk_bytenr,
                                        size - offset, pg_offset + offset,
                                        compress_type);
                else
                        added = btrfs_bio_add_page(bio_ctrl, page,
                                        disk_bytenr + offset, size - offset,
                                        pg_offset + offset, compress_type);

                /* Metadata page range should never be split */
                if (!is_data_inode(&inode->vfs_inode))
                        ASSERT(added == 0 || added == size - offset);

                /* At least we added some page, update the account */
                if (wbc && added)
                        wbc_account_cgroup_owner(wbc, page, added);

                /* We have reached boundary, submit right now */
                if (added < size - offset) {
                        /* The bio should contain some page(s) */
                        ASSERT(bio_ctrl->bio->bi_iter.bi_size);
                        submit_one_bio(bio_ctrl);
                }
                cur += added;
        }
        return 0;
}

static int attach_extent_buffer_page(struct extent_buffer *eb,
                                     struct page *page,
                                     struct btrfs_subpage *prealloc)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        int ret = 0;

        /*
         * If the page is mapped to btree inode, we should hold the private
         * lock to prevent race.
         * For cloned or dummy extent buffers, their pages are not mapped and
         * will not race with any other ebs.
         */
        if (page->mapping)
                lockdep_assert_held(&page->mapping->private_lock);

        if (fs_info->nodesize >= PAGE_SIZE) {
                if (!PagePrivate(page))
                        attach_page_private(page, eb);
                else
                        WARN_ON(page->private != (unsigned long)eb);
                return 0;
        }

        /* Already mapped, just free prealloc */
        if (PagePrivate(page)) {
                btrfs_free_subpage(prealloc);
                return 0;
        }

        if (prealloc)
                /* Has preallocated memory for subpage */
                attach_page_private(page, prealloc);
        else
                /* Do new allocation to attach subpage */
                ret = btrfs_attach_subpage(fs_info, page,
                                           BTRFS_SUBPAGE_METADATA);
        return ret;
}

int set_page_extent_mapped(struct page *page)
{
        struct btrfs_fs_info *fs_info;

        ASSERT(page->mapping);

        if (PagePrivate(page))
                return 0;

        fs_info = btrfs_sb(page->mapping->host->i_sb);

        if (btrfs_is_subpage(fs_info, page))
                return btrfs_attach_subpage(fs_info, page, BTRFS_SUBPAGE_DATA);

        attach_page_private(page, (void *)EXTENT_PAGE_PRIVATE);
        return 0;
}

void clear_page_extent_mapped(struct page *page)
{
        struct btrfs_fs_info *fs_info;

        ASSERT(page->mapping);

        if (!PagePrivate(page))
                return;

        fs_info = btrfs_sb(page->mapping->host->i_sb);
        if (btrfs_is_subpage(fs_info, page))
                return btrfs_detach_subpage(fs_info, page);

        detach_page_private(page);
}

static struct extent_map *
__get_extent_map(struct inode *inode, struct page *page, size_t pg_offset,
                 u64 start, u64 len, struct extent_map **em_cached)
{
        struct extent_map *em;

        if (em_cached && *em_cached) {
                em = *em_cached;
                if (extent_map_in_tree(em) && start >= em->start &&
                    start < extent_map_end(em)) {
                        refcount_inc(&em->refs);
                        return em;
                }

                free_extent_map(em);
                *em_cached = NULL;
        }

        em = btrfs_get_extent(BTRFS_I(inode), page, pg_offset, start, len);
        if (em_cached && !IS_ERR(em)) {
                BUG_ON(*em_cached);
                refcount_inc(&em->refs);
                *em_cached = em;
        }
        return em;
}
/*
 * basic readpage implementation.  Locked extent state structs are inserted
 * into the tree that are removed when the IO is done (by the end_io
 * handlers)
 * XXX JDM: This needs looking at to ensure proper page locking
 * return 0 on success, otherwise return error
 */
static int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
                      struct btrfs_bio_ctrl *bio_ctrl,
                      blk_opf_t read_flags, u64 *prev_em_start)
{
        struct inode *inode = page->mapping->host;
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        u64 start = page_offset(page);
        const u64 end = start + PAGE_SIZE - 1;
        u64 cur = start;
        u64 extent_offset;
        u64 last_byte = i_size_read(inode);
        u64 block_start;
        struct extent_map *em;
        int ret = 0;
        size_t pg_offset = 0;
        size_t iosize;
        size_t blocksize = inode->i_sb->s_blocksize;
        struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;

        ret = set_page_extent_mapped(page);
        if (ret < 0) {
                unlock_extent(tree, start, end, NULL);
                btrfs_page_set_error(fs_info, page, start, PAGE_SIZE);
                unlock_page(page);
                goto out;
        }

        if (page->index == last_byte >> PAGE_SHIFT) {
                size_t zero_offset = offset_in_page(last_byte);

                if (zero_offset) {
                        iosize = PAGE_SIZE - zero_offset;
                        memzero_page(page, zero_offset, iosize);
                }
        }
        bio_ctrl->end_io_func = end_bio_extent_readpage;
        begin_page_read(fs_info, page);
        while (cur <= end) {
                unsigned long this_bio_flag = 0;
                bool force_bio_submit = false;
                u64 disk_bytenr;

                ASSERT(IS_ALIGNED(cur, fs_info->sectorsize));
                if (cur >= last_byte) {
                        iosize = PAGE_SIZE - pg_offset;
                        memzero_page(page, pg_offset, iosize);
                        unlock_extent(tree, cur, cur + iosize - 1, NULL);
                        end_page_read(page, true, cur, iosize);
                        break;
                }
                em = __get_extent_map(inode, page, pg_offset, cur,
                                      end - cur + 1, em_cached);
                if (IS_ERR(em)) {
                        unlock_extent(tree, cur, end, NULL);
                        end_page_read(page, false, cur, end + 1 - cur);
                        ret = PTR_ERR(em);
                        break;
                }
                extent_offset = cur - em->start;
                BUG_ON(extent_map_end(em) <= cur);
                BUG_ON(end < cur);

                if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags))
                        this_bio_flag = em->compress_type;

                iosize = min(extent_map_end(em) - cur, end - cur + 1);
                iosize = ALIGN(iosize, blocksize);
                if (this_bio_flag != BTRFS_COMPRESS_NONE)
                        disk_bytenr = em->block_start;
                else
                        disk_bytenr = em->block_start + extent_offset;
                block_start = em->block_start;
                if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
                        block_start = EXTENT_MAP_HOLE;

                /*
                 * If we have a file range that points to a compressed extent
                 * and it's followed by a consecutive file range that points
                 * to the same compressed extent (possibly with a different
                 * offset and/or length, so it either points to the whole extent
                 * or only part of it), we must make sure we do not submit a
                 * single bio to populate the pages for the 2 ranges because
                 * this makes the compressed extent read zero out the pages
                 * belonging to the 2nd range. Imagine the following scenario:
                 *
                 *  File layout
                 *  [0 - 8K]                     [8K - 24K]
                 *    |                               |
                 *    |                               |
                 * points to extent X,         points to extent X,
                 * offset 4K, length of 8K     offset 0, length 16K
                 *
                 * [extent X, compressed length = 4K uncompressed length = 16K]
                 *
                 * If the bio to read the compressed extent covers both ranges,
                 * it will decompress extent X into the pages belonging to the
                 * first range and then it will stop, zeroing out the remaining
                 * pages that belong to the other range that points to extent X.
                 * So here we make sure we submit 2 bios, one for the first
                 * range and another one for the third range. Both will target
                 * the same physical extent from disk, but we can't currently
                 * make the compressed bio endio callback populate the pages
                 * for both ranges because each compressed bio is tightly
                 * coupled with a single extent map, and each range can have
                 * an extent map with a different offset value relative to the
                 * uncompressed data of our extent and different lengths. This
                 * is a corner case so we prioritize correctness over
                 * non-optimal behavior (submitting 2 bios for the same extent).
                 */
                if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags) &&
                    prev_em_start && *prev_em_start != (u64)-1 &&
                    *prev_em_start != em->start)
                        force_bio_submit = true;

                if (prev_em_start)
                        *prev_em_start = em->start;

                free_extent_map(em);
                em = NULL;

                /* we've found a hole, just zero and go on */
                if (block_start == EXTENT_MAP_HOLE) {
                        memzero_page(page, pg_offset, iosize);

                        unlock_extent(tree, cur, cur + iosize - 1, NULL);
                        end_page_read(page, true, cur, iosize);
                        cur = cur + iosize;
                        pg_offset += iosize;
                        continue;
                }
                /* the get_extent function already copied into the page */
                if (block_start == EXTENT_MAP_INLINE) {
                        unlock_extent(tree, cur, cur + iosize - 1, NULL);
                        end_page_read(page, true, cur, iosize);
                        cur = cur + iosize;
                        pg_offset += iosize;
                        continue;
                }

                ret = submit_extent_page(REQ_OP_READ | read_flags, NULL,
                                         bio_ctrl, disk_bytenr, page, iosize,
                                         pg_offset, this_bio_flag,
                                         force_bio_submit);
                if (ret) {
                        /*
                         * We have to unlock the remaining range, or the page
                         * will never be unlocked.
                         */
                        unlock_extent(tree, cur, end, NULL);
                        end_page_read(page, false, cur, end + 1 - cur);
                        goto out;
                }
                cur = cur + iosize;
                pg_offset += iosize;
        }
out:
        return ret;
}

int btrfs_read_folio(struct file *file, struct folio *folio)
{
        struct page *page = &folio->page;
        struct btrfs_inode *inode = BTRFS_I(page->mapping->host);
        u64 start = page_offset(page);
        u64 end = start + PAGE_SIZE - 1;
        struct btrfs_bio_ctrl bio_ctrl = { 0 };
        int ret;

        btrfs_lock_and_flush_ordered_range(inode, start, end, NULL);

        ret = btrfs_do_readpage(page, NULL, &bio_ctrl, 0, NULL);
        /*
         * If btrfs_do_readpage() failed we will want to submit the assembled
         * bio to do the cleanup.
         */
        submit_one_bio(&bio_ctrl);
        return ret;
}

static inline void contiguous_readpages(struct page *pages[], int nr_pages,
                                        u64 start, u64 end,
                                        struct extent_map **em_cached,
                                        struct btrfs_bio_ctrl *bio_ctrl,
                                        u64 *prev_em_start)
{
        struct btrfs_inode *inode = BTRFS_I(pages[0]->mapping->host);
        int index;

        btrfs_lock_and_flush_ordered_range(inode, start, end, NULL);

        for (index = 0; index < nr_pages; index++) {
                btrfs_do_readpage(pages[index], em_cached, bio_ctrl,
                                  REQ_RAHEAD, prev_em_start);
                put_page(pages[index]);
        }
}

/*
 * helper for __extent_writepage, doing all of the delayed allocation setup.
 *
 * This returns 1 if btrfs_run_delalloc_range function did all the work required
 * to write the page (copy into inline extent).  In this case the IO has
 * been started and the page is already unlocked.
 *
 * This returns 0 if all went well (page still locked)
 * This returns < 0 if there were errors (page still locked)
 */
static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
                struct page *page, struct writeback_control *wbc)
{
        const u64 page_end = page_offset(page) + PAGE_SIZE - 1;
        u64 delalloc_start = page_offset(page);
        u64 delalloc_to_write = 0;
        /* How many pages are started by btrfs_run_delalloc_range() */
        unsigned long nr_written = 0;
        int ret;
        int page_started = 0;

        while (delalloc_start < page_end) {
                u64 delalloc_end = page_end;
                bool found;

                found = find_lock_delalloc_range(&inode->vfs_inode, page,
                                               &delalloc_start,
                                               &delalloc_end);
                if (!found) {
                        delalloc_start = delalloc_end + 1;
                        continue;
                }
                ret = btrfs_run_delalloc_range(inode, page, delalloc_start,
                                delalloc_end, &page_started, &nr_written, wbc);
                if (ret) {
                        btrfs_page_set_error(inode->root->fs_info, page,
                                             page_offset(page), PAGE_SIZE);
                        return ret;
                }
                /*
                 * delalloc_end is already one less than the total length, so
                 * we don't subtract one from PAGE_SIZE
                 */
                delalloc_to_write += (delalloc_end - delalloc_start +
                                      PAGE_SIZE) >> PAGE_SHIFT;
                delalloc_start = delalloc_end + 1;
        }
        if (wbc->nr_to_write < delalloc_to_write) {
                int thresh = 8192;

                if (delalloc_to_write < thresh * 2)
                        thresh = delalloc_to_write;
                wbc->nr_to_write = min_t(u64, delalloc_to_write,
                                         thresh);
        }

        /* Did btrfs_run_dealloc_range() already unlock and start the IO? */
        if (page_started) {
                /*
                 * We've unlocked the page, so we can't update the mapping's
                 * writeback index, just update nr_to_write.
                 */
                wbc->nr_to_write -= nr_written;
                return 1;
        }

        return 0;
}

/*
 * Find the first byte we need to write.
 *
 * For subpage, one page can contain several sectors, and
 * __extent_writepage_io() will just grab all extent maps in the page
 * range and try to submit all non-inline/non-compressed extents.
 *
 * This is a big problem for subpage, we shouldn't re-submit already written
 * data at all.
 * This function will lookup subpage dirty bit to find which range we really
 * need to submit.
 *
 * Return the next dirty range in [@start, @end).
 * If no dirty range is found, @start will be page_offset(page) + PAGE_SIZE.
 */
static void find_next_dirty_byte(struct btrfs_fs_info *fs_info,
                                 struct page *page, u64 *start, u64 *end)
{
        struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private;
        struct btrfs_subpage_info *spi = fs_info->subpage_info;
        u64 orig_start = *start;
        /* Declare as unsigned long so we can use bitmap ops */
        unsigned long flags;
        int range_start_bit;
        int range_end_bit;

        /*
         * For regular sector size == page size case, since one page only
         * contains one sector, we return the page offset directly.
         */
        if (!btrfs_is_subpage(fs_info, page)) {
                *start = page_offset(page);
                *end = page_offset(page) + PAGE_SIZE;
                return;
        }

        range_start_bit = spi->dirty_offset +
                          (offset_in_page(orig_start) >> fs_info->sectorsize_bits);

        /* We should have the page locked, but just in case */
        spin_lock_irqsave(&subpage->lock, flags);
        bitmap_next_set_region(subpage->bitmaps, &range_start_bit, &range_end_bit,
                               spi->dirty_offset + spi->bitmap_nr_bits);
        spin_unlock_irqrestore(&subpage->lock, flags);

        range_start_bit -= spi->dirty_offset;
        range_end_bit -= spi->dirty_offset;

        *start = page_offset(page) + range_start_bit * fs_info->sectorsize;
        *end = page_offset(page) + range_end_bit * fs_info->sectorsize;
}

/*
 * helper for __extent_writepage.  This calls the writepage start hooks,
 * and does the loop to map the page into extents and bios.
 *
 * We return 1 if the IO is started and the page is unlocked,
 * 0 if all went well (page still locked)
 * < 0 if there were errors (page still locked)
 */
static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode,
                                 struct page *page,
                                 struct writeback_control *wbc,
                                 struct btrfs_bio_ctrl *bio_ctrl,
                                 loff_t i_size,
                                 int *nr_ret)
{
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        u64 cur = page_offset(page);
        u64 end = cur + PAGE_SIZE - 1;
        u64 extent_offset;
        u64 block_start;
        struct extent_map *em;
        int saved_ret = 0;
        int ret = 0;
        int nr = 0;
        enum req_op op = REQ_OP_WRITE;
        const blk_opf_t write_flags = wbc_to_write_flags(wbc);
        bool has_error = false;
        bool compressed;

        ret = btrfs_writepage_cow_fixup(page);
        if (ret) {
                /* Fixup worker will requeue */
                redirty_page_for_writepage(wbc, page);
                unlock_page(page);
                return 1;
        }

        /*
         * we don't want to touch the inode after unlocking the page,
         * so we update the mapping writeback index now
         */
        wbc->nr_to_write--;

        bio_ctrl->end_io_func = end_bio_extent_writepage;
        while (cur <= end) {
                u64 disk_bytenr;
                u64 em_end;
                u64 dirty_range_start = cur;
                u64 dirty_range_end;
                u32 iosize;

                if (cur >= i_size) {
                        btrfs_writepage_endio_finish_ordered(inode, page, cur,
                                                             end, true);
                        /*
                         * This range is beyond i_size, thus we don't need to
                         * bother writing back.
                         * But we still need to clear the dirty subpage bit, or
                         * the next time the page gets dirtied, we will try to
                         * writeback the sectors with subpage dirty bits,
                         * causing writeback without ordered extent.
                         */
                        btrfs_page_clear_dirty(fs_info, page, cur, end + 1 - cur);
                        break;
                }

                find_next_dirty_byte(fs_info, page, &dirty_range_start,
                                     &dirty_range_end);
                if (cur < dirty_range_start) {
                        cur = dirty_range_start;
                        continue;
                }

                em = btrfs_get_extent(inode, NULL, 0, cur, end - cur + 1);
                if (IS_ERR(em)) {
                        btrfs_page_set_error(fs_info, page, cur, end - cur + 1);
                        ret = PTR_ERR_OR_ZERO(em);
                        has_error = true;
                        if (!saved_ret)
                                saved_ret = ret;
                        break;
                }

                extent_offset = cur - em->start;
                em_end = extent_map_end(em);
                ASSERT(cur <= em_end);
                ASSERT(cur < end);
                ASSERT(IS_ALIGNED(em->start, fs_info->sectorsize));
                ASSERT(IS_ALIGNED(em->len, fs_info->sectorsize));
                block_start = em->block_start;
                compressed = test_bit(EXTENT_FLAG_COMPRESSED, &em->flags);
                disk_bytenr = em->block_start + extent_offset;

                /*
                 * Note that em_end from extent_map_end() and dirty_range_end from
                 * find_next_dirty_byte() are all exclusive
                 */
                iosize = min(min(em_end, end + 1), dirty_range_end) - cur;
                free_extent_map(em);
                em = NULL;

                /*
                 * compressed and inline extents are written through other
                 * paths in the FS
                 */
                if (compressed || block_start == EXTENT_MAP_HOLE ||
                    block_start == EXTENT_MAP_INLINE) {
                        if (compressed)
                                nr++;
                        else
                                btrfs_writepage_endio_finish_ordered(inode,
                                                page, cur, cur + iosize - 1, true);
                        btrfs_page_clear_dirty(fs_info, page, cur, iosize);
                        cur += iosize;
                        continue;
                }

                btrfs_set_range_writeback(inode, cur, cur + iosize - 1);
                if (!PageWriteback(page)) {
                        btrfs_err(inode->root->fs_info,
                                   "page %lu not writeback, cur %llu end %llu",
                               page->index, cur, end);
                }

                /*
                 * Although the PageDirty bit is cleared before entering this
                 * function, subpage dirty bit is not cleared.
                 * So clear subpage dirty bit here so next time we won't submit
                 * page for range already written to disk.
                 */
                btrfs_page_clear_dirty(fs_info, page, cur, iosize);

                ret = submit_extent_page(op | write_flags, wbc,
                                         bio_ctrl, disk_bytenr,
                                         page, iosize,
                                         cur - page_offset(page),
                                         0, false);
                if (ret) {
                        has_error = true;
                        if (!saved_ret)
                                saved_ret = ret;

                        btrfs_page_set_error(fs_info, page, cur, iosize);
                        if (PageWriteback(page))
                                btrfs_page_clear_writeback(fs_info, page, cur,
                                                           iosize);
                }

                cur += iosize;
                nr++;
        }
        /*
         * If we finish without problem, we should not only clear page dirty,
         * but also empty subpage dirty bits
         */
        if (!has_error)
                btrfs_page_assert_not_dirty(fs_info, page);
        else
                ret = saved_ret;
        *nr_ret = nr;
        return ret;
}

/*
 * the writepage semantics are similar to regular writepage.  extent
 * records are inserted to lock ranges in the tree, and as dirty areas
 * are found, they are marked writeback.  Then the lock bits are removed
 * and the end_io handler clears the writeback ranges
 *
 * Return 0 if everything goes well.
 * Return <0 for error.
 */
static int __extent_writepage(struct page *page, struct writeback_control *wbc,
                              struct btrfs_bio_ctrl *bio_ctrl)
{
        struct folio *folio = page_folio(page);
        struct inode *inode = page->mapping->host;
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        const u64 page_start = page_offset(page);
        const u64 page_end = page_start + PAGE_SIZE - 1;
        int ret;
        int nr = 0;
        size_t pg_offset;
        loff_t i_size = i_size_read(inode);
        unsigned long end_index = i_size >> PAGE_SHIFT;

        trace___extent_writepage(page, inode, wbc);

        WARN_ON(!PageLocked(page));

        btrfs_page_clear_error(btrfs_sb(inode->i_sb), page,
                               page_offset(page), PAGE_SIZE);

        pg_offset = offset_in_page(i_size);
        if (page->index > end_index ||
           (page->index == end_index && !pg_offset)) {
                folio_invalidate(folio, 0, folio_size(folio));
                folio_unlock(folio);
                return 0;
        }

        if (page->index == end_index)
                memzero_page(page, pg_offset, PAGE_SIZE - pg_offset);

        ret = set_page_extent_mapped(page);
        if (ret < 0) {
                SetPageError(page);
                goto done;
        }

        if (!bio_ctrl->extent_locked) {
                ret = writepage_delalloc(BTRFS_I(inode), page, wbc);
                if (ret == 1)
                        return 0;
                if (ret)
                        goto done;
        }

        ret = __extent_writepage_io(BTRFS_I(inode), page, wbc, bio_ctrl, i_size,
                                    &nr);
        if (ret == 1)
                return 0;

done:
        if (nr == 0) {
                /* make sure the mapping tag for page dirty gets cleared */
                set_page_writeback(page);
                end_page_writeback(page);
        }
        /*
         * Here we used to have a check for PageError() and then set @ret and
         * call end_extent_writepage().
         *
         * But in fact setting @ret here will cause different error paths
         * between subpage and regular sectorsize.
         *
         * For regular page size, we never submit current page, but only add
         * current page to current bio.
         * The bio submission can only happen in next page.
         * Thus if we hit the PageError() branch, @ret is already set to
         * non-zero value and will not get updated for regular sectorsize.
         *
         * But for subpage case, it's possible we submit part of current page,
         * thus can get PageError() set by submitted bio of the same page,
         * while our @ret is still 0.
         *
         * So here we unify the behavior and don't set @ret.
         * Error can still be properly passed to higher layer as page will
         * be set error, here we just don't handle the IO failure.
         *
         * NOTE: This is just a hotfix for subpage.
         * The root fix will be properly ending ordered extent when we hit
         * an error during writeback.
         *
         * But that needs a bigger refactoring, as we not only need to grab the
         * submitted OE, but also need to know exactly at which bytenr we hit
         * the error.
         * Currently the full page based __extent_writepage_io() is not
         * capable of that.
         */
        if (PageError(page))
                end_extent_writepage(page, ret, page_start, page_end);
        if (bio_ctrl->extent_locked) {
                /*
                 * If bio_ctrl->extent_locked, it's from extent_write_locked_range(),
                 * the page can either be locked by lock_page() or
                 * process_one_page().
                 * Let btrfs_page_unlock_writer() handle both cases.
                 */
                ASSERT(wbc);
                btrfs_page_unlock_writer(fs_info, page, wbc->range_start,
                                         wbc->range_end + 1 - wbc->range_start);
        } else {
                unlock_page(page);
        }
        ASSERT(ret <= 0);
        return ret;
}

void wait_on_extent_buffer_writeback(struct extent_buffer *eb)
{
        wait_on_bit_io(&eb->bflags, EXTENT_BUFFER_WRITEBACK,
                       TASK_UNINTERRUPTIBLE);
}

static void end_extent_buffer_writeback(struct extent_buffer *eb)
{
        clear_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags);
        smp_mb__after_atomic();
        wake_up_bit(&eb->bflags, EXTENT_BUFFER_WRITEBACK);
}

/*
 * Lock extent buffer status and pages for writeback.
 *
 * May try to flush write bio if we can't get the lock.
 *
 * Return  0 if the extent buffer doesn't need to be submitted.
 *           (E.g. the extent buffer is not dirty)
 * Return >0 is the extent buffer is submitted to bio.
 * Return <0 if something went wrong, no page is locked.
 */
static noinline_for_stack int lock_extent_buffer_for_io(struct extent_buffer *eb,
                          struct btrfs_bio_ctrl *bio_ctrl)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        int i, num_pages;
        int flush = 0;
        int ret = 0;

        if (!btrfs_try_tree_write_lock(eb)) {
                submit_write_bio(bio_ctrl, 0);
                flush = 1;
                btrfs_tree_lock(eb);
        }

        if (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags)) {
                btrfs_tree_unlock(eb);
                if (!bio_ctrl->sync_io)
                        return 0;
                if (!flush) {
                        submit_write_bio(bio_ctrl, 0);
                        flush = 1;
                }
                while (1) {
                        wait_on_extent_buffer_writeback(eb);
                        btrfs_tree_lock(eb);
                        if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
                                break;
                        btrfs_tree_unlock(eb);
                }
        }

        /*
         * We need to do this to prevent races in people who check if the eb is
         * under IO since we can end up having no IO bits set for a short period
         * of time.
         */
        spin_lock(&eb->refs_lock);
        if (test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags)) {
                set_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags);
                spin_unlock(&eb->refs_lock);
                btrfs_set_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN);
                percpu_counter_add_batch(&fs_info->dirty_metadata_bytes,
                                         -eb->len,
                                         fs_info->dirty_metadata_batch);
                ret = 1;
        } else {
                spin_unlock(&eb->refs_lock);
        }

        btrfs_tree_unlock(eb);

        /*
         * Either we don't need to submit any tree block, or we're submitting
         * subpage eb.
         * Subpage metadata doesn't use page locking at all, so we can skip
         * the page locking.
         */
        if (!ret || fs_info->nodesize < PAGE_SIZE)
                return ret;

        num_pages = num_extent_pages(eb);
        for (i = 0; i < num_pages; i++) {
                struct page *p = eb->pages[i];

                if (!trylock_page(p)) {
                        if (!flush) {
                                submit_write_bio(bio_ctrl, 0);
                                flush = 1;
                        }
                        lock_page(p);
                }
        }

        return ret;
}

static void set_btree_ioerr(struct page *page, struct extent_buffer *eb)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;

        btrfs_page_set_error(fs_info, page, eb->start, eb->len);
        if (test_and_set_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags))
                return;

        /*
         * A read may stumble upon this buffer later, make sure that it gets an
         * error and knows there was an error.
         */
        clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);

        /*
         * We need to set the mapping with the io error as well because a write
         * error will flip the file system readonly, and then syncfs() will
         * return a 0 because we are readonly if we don't modify the err seq for
         * the superblock.
         */
        mapping_set_error(page->mapping, -EIO);

        /*
         * If writeback for a btree extent that doesn't belong to a log tree
         * failed, increment the counter transaction->eb_write_errors.
         * We do this because while the transaction is running and before it's
         * committing (when we call filemap_fdata[write|wait]_range against
         * the btree inode), we might have
         * btree_inode->i_mapping->a_ops->writepages() called by the VM - if it
         * returns an error or an error happens during writeback, when we're
         * committing the transaction we wouldn't know about it, since the pages
         * can be no longer dirty nor marked anymore for writeback (if a
         * subsequent modification to the extent buffer didn't happen before the
         * transaction commit), which makes filemap_fdata[write|wait]_range not
         * able to find the pages tagged with SetPageError at transaction
         * commit time. So if this happens we must abort the transaction,
         * otherwise we commit a super block with btree roots that point to
         * btree nodes/leafs whose content on disk is invalid - either garbage
         * or the content of some node/leaf from a past generation that got
         * cowed or deleted and is no longer valid.
         *
         * Note: setting AS_EIO/AS_ENOSPC in the btree inode's i_mapping would
         * not be enough - we need to distinguish between log tree extents vs
         * non-log tree extents, and the next filemap_fdatawait_range() call
         * will catch and clear such errors in the mapping - and that call might
         * be from a log sync and not from a transaction commit. Also, checking
         * for the eb flag EXTENT_BUFFER_WRITE_ERR at transaction commit time is
         * not done and would not be reliable - the eb might have been released
         * from memory and reading it back again means that flag would not be
         * set (since it's a runtime flag, not persisted on disk).
         *
         * Using the flags below in the btree inode also makes us achieve the
         * goal of AS_EIO/AS_ENOSPC when writepages() returns success, started
         * writeback for all dirty pages and before filemap_fdatawait_range()
         * is called, the writeback for all dirty pages had already finished
         * with errors - because we were not using AS_EIO/AS_ENOSPC,
         * filemap_fdatawait_range() would return success, as it could not know
         * that writeback errors happened (the pages were no longer tagged for
         * writeback).
         */
        switch (eb->log_index) {
        case -1:
                set_bit(BTRFS_FS_BTREE_ERR, &fs_info->flags);
                break;
        case 0:
                set_bit(BTRFS_FS_LOG1_ERR, &fs_info->flags);
                break;
        case 1:
                set_bit(BTRFS_FS_LOG2_ERR, &fs_info->flags);
                break;
        default:
                BUG(); /* unexpected, logic error */
        }
}

/*
 * The endio specific version which won't touch any unsafe spinlock in endio
 * context.
 */
static struct extent_buffer *find_extent_buffer_nolock(
                struct btrfs_fs_info *fs_info, u64 start)
{
        struct extent_buffer *eb;

        rcu_read_lock();
        eb = radix_tree_lookup(&fs_info->buffer_radix,
                               start >> fs_info->sectorsize_bits);
        if (eb && atomic_inc_not_zero(&eb->refs)) {
                rcu_read_unlock();
                return eb;
        }
        rcu_read_unlock();
        return NULL;
}

/*
 * The endio function for subpage extent buffer write.
 *
 * Unlike end_bio_extent_buffer_writepage(), we only call end_page_writeback()
 * after all extent buffers in the page has finished their writeback.
 */
static void end_bio_subpage_eb_writepage(struct btrfs_bio *bbio)
{
        struct bio *bio = &bbio->bio;
        struct btrfs_fs_info *fs_info;
        struct bio_vec *bvec;
        struct bvec_iter_all iter_all;

        fs_info = btrfs_sb(bio_first_page_all(bio)->mapping->host->i_sb);
        ASSERT(fs_info->nodesize < PAGE_SIZE);

        ASSERT(!bio_flagged(bio, BIO_CLONED));
        bio_for_each_segment_all(bvec, bio, iter_all) {
                struct page *page = bvec->bv_page;
                u64 bvec_start = page_offset(page) + bvec->bv_offset;
                u64 bvec_end = bvec_start + bvec->bv_len - 1;
                u64 cur_bytenr = bvec_start;

                ASSERT(IS_ALIGNED(bvec->bv_len, fs_info->nodesize));

                /* Iterate through all extent buffers in the range */
                while (cur_bytenr <= bvec_end) {
                        struct extent_buffer *eb;
                        int done;

                        /*
                         * Here we can't use find_extent_buffer(), as it may
                         * try to lock eb->refs_lock, which is not safe in endio
                         * context.
                         */
                        eb = find_extent_buffer_nolock(fs_info, cur_bytenr);
                        ASSERT(eb);

                        cur_bytenr = eb->start + eb->len;

                        ASSERT(test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags));
                        done = atomic_dec_and_test(&eb->io_pages);
                        ASSERT(done);

                        if (bio->bi_status ||
                            test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags)) {
                                ClearPageUptodate(page);
                                set_btree_ioerr(page, eb);
                        }

                        btrfs_subpage_clear_writeback(fs_info, page, eb->start,
                                                      eb->len);
                        end_extent_buffer_writeback(eb);
                        /*
                         * free_extent_buffer() will grab spinlock which is not
                         * safe in endio context. Thus here we manually dec
                         * the ref.
                         */
                        atomic_dec(&eb->refs);
                }
        }
        bio_put(bio);
}

static void end_bio_extent_buffer_writepage(struct btrfs_bio *bbio)
{
        struct bio *bio = &bbio->bio;
        struct bio_vec *bvec;
        struct extent_buffer *eb;
        int done;
        struct bvec_iter_all iter_all;

        ASSERT(!bio_flagged(bio, BIO_CLONED));
        bio_for_each_segment_all(bvec, bio, iter_all) {
                struct page *page = bvec->bv_page;

                eb = (struct extent_buffer *)page->private;
                BUG_ON(!eb);
                done = atomic_dec_and_test(&eb->io_pages);

                if (bio->bi_status ||
                    test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags)) {
                        ClearPageUptodate(page);
                        set_btree_ioerr(page, eb);
                }

                end_page_writeback(page);

                if (!done)
                        continue;

                end_extent_buffer_writeback(eb);
        }

        bio_put(bio);
}

static void prepare_eb_write(struct extent_buffer *eb)
{
        u32 nritems;
        unsigned long start;
        unsigned long end;

        clear_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags);
        atomic_set(&eb->io_pages, num_extent_pages(eb));

        /* Set btree blocks beyond nritems with 0 to avoid stale content */
        nritems = btrfs_header_nritems(eb);
        if (btrfs_header_level(eb) > 0) {
                end = btrfs_node_key_ptr_offset(eb, nritems);
                memzero_extent_buffer(eb, end, eb->len - end);
        } else {
                /*
                 * Leaf:
                 * header 0 1 2 .. N ... data_N .. data_2 data_1 data_0
                 */
                start = btrfs_item_nr_offset(eb, nritems);
                end = btrfs_item_nr_offset(eb, 0);
                if (nritems == 0)
                        end += BTRFS_LEAF_DATA_SIZE(eb->fs_info);
                else
                        end += btrfs_item_offset(eb, nritems - 1);
                memzero_extent_buffer(eb, start, end - start);
        }
}

/*
 * Unlike the work in write_one_eb(), we rely completely on extent locking.
 * Page locking is only utilized at minimum to keep the VMM code happy.
 */
static int write_one_subpage_eb(struct extent_buffer *eb,
                                struct writeback_control *wbc,
                                struct btrfs_bio_ctrl *bio_ctrl)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        struct page *page = eb->pages[0];
        blk_opf_t write_flags = wbc_to_write_flags(wbc);
        bool no_dirty_ebs = false;
        int ret;

        prepare_eb_write(eb);

        /* clear_page_dirty_for_io() in subpage helper needs page locked */
        lock_page(page);
        btrfs_subpage_set_writeback(fs_info, page, eb->start, eb->len);

        /* Check if this is the last dirty bit to update nr_written */
        no_dirty_ebs = btrfs_subpage_clear_and_test_dirty(fs_info, page,
                                                          eb->start, eb->len);
        if (no_dirty_ebs)
                clear_page_dirty_for_io(page);

        bio_ctrl->end_io_func = end_bio_subpage_eb_writepage;

        ret = submit_extent_page(REQ_OP_WRITE | write_flags, wbc,
                        bio_ctrl, eb->start, page, eb->len,
                        eb->start - page_offset(page), 0, false);
        if (ret) {
                btrfs_subpage_clear_writeback(fs_info, page, eb->start, eb->len);
                set_btree_ioerr(page, eb);
                unlock_page(page);

                if (atomic_dec_and_test(&eb->io_pages))
                        end_extent_buffer_writeback(eb);
                return -EIO;
        }
        unlock_page(page);
        /*
         * Submission finished without problem, if no range of the page is
         * dirty anymore, we have submitted a page.  Update nr_written in wbc.
         */
        if (no_dirty_ebs)
                wbc->nr_to_write--;
        return ret;
}

static noinline_for_stack int write_one_eb(struct extent_buffer *eb,
                        struct writeback_control *wbc,
                        struct btrfs_bio_ctrl *bio_ctrl)
{
        u64 disk_bytenr = eb->start;
        int i, num_pages;
        blk_opf_t write_flags = wbc_to_write_flags(wbc);
        int ret = 0;

        prepare_eb_write(eb);

        bio_ctrl->end_io_func = end_bio_extent_buffer_writepage;

        num_pages = num_extent_pages(eb);
        for (i = 0; i < num_pages; i++) {
                struct page *p = eb->pages[i];

                clear_page_dirty_for_io(p);
                set_page_writeback(p);
                ret = submit_extent_page(REQ_OP_WRITE | write_flags, wbc,
                                         bio_ctrl, disk_bytenr, p,
                                         PAGE_SIZE, 0, 0, false);
                if (ret) {
                        set_btree_ioerr(p, eb);
                        if (PageWriteback(p))
                                end_page_writeback(p);
                        if (atomic_sub_and_test(num_pages - i, &eb->io_pages))
                                end_extent_buffer_writeback(eb);
                        ret = -EIO;
                        break;
                }
                disk_bytenr += PAGE_SIZE;
                wbc->nr_to_write--;
                unlock_page(p);
        }

        if (unlikely(ret)) {
                for (; i < num_pages; i++) {
                        struct page *p = eb->pages[i];
                        clear_page_dirty_for_io(p);
                        unlock_page(p);
                }
        }

        return ret;
}

/*
 * Submit one subpage btree page.
 *
 * The main difference to submit_eb_page() is:
 * - Page locking
 *   For subpage, we don't rely on page locking at all.
 *
 * - Flush write bio
 *   We only flush bio if we may be unable to fit current extent buffers into
 *   current bio.
 *
 * Return >=0 for the number of submitted extent buffers.
 * Return <0 for fatal error.
 */
static int submit_eb_subpage(struct page *page,
                             struct writeback_control *wbc,
                             struct btrfs_bio_ctrl *bio_ctrl)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
        int submitted = 0;
        u64 page_start = page_offset(page);
        int bit_start = 0;
        int sectors_per_node = fs_info->nodesize >> fs_info->sectorsize_bits;
        int ret;

        /* Lock and write each dirty extent buffers in the range */
        while (bit_start < fs_info->subpage_info->bitmap_nr_bits) {
                struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private;
                struct extent_buffer *eb;
                unsigned long flags;
                u64 start;

                /*
                 * Take private lock to ensure the subpage won't be detached
                 * in the meantime.
                 */
                spin_lock(&page->mapping->private_lock);
                if (!PagePrivate(page)) {
                        spin_unlock(&page->mapping->private_lock);
                        break;
                }
                spin_lock_irqsave(&subpage->lock, flags);
                if (!test_bit(bit_start + fs_info->subpage_info->dirty_offset,
                              subpage->bitmaps)) {
                        spin_unlock_irqrestore(&subpage->lock, flags);
                        spin_unlock(&page->mapping->private_lock);
                        bit_start++;
                        continue;
                }

                start = page_start + bit_start * fs_info->sectorsize;
                bit_start += sectors_per_node;

                /*
                 * Here we just want to grab the eb without touching extra
                 * spin locks, so call find_extent_buffer_nolock().
                 */
                eb = find_extent_buffer_nolock(fs_info, start);
                spin_unlock_irqrestore(&subpage->lock, flags);
                spin_unlock(&page->mapping->private_lock);

                /*
                 * The eb has already reached 0 refs thus find_extent_buffer()
                 * doesn't return it. We don't need to write back such eb
                 * anyway.
                 */
                if (!eb)
                        continue;

                ret = lock_extent_buffer_for_io(eb, bio_ctrl);
                if (ret == 0) {
                        free_extent_buffer(eb);
                        continue;
                }
                if (ret < 0) {
                        free_extent_buffer(eb);
                        goto cleanup;
                }
                ret = write_one_subpage_eb(eb, wbc, bio_ctrl);
                free_extent_buffer(eb);
                if (ret < 0)
                        goto cleanup;
                submitted++;
        }
        return submitted;

cleanup:
        /* We hit error, end bio for the submitted extent buffers */
        submit_write_bio(bio_ctrl, ret);
        return ret;
}

/*
 * Submit all page(s) of one extent buffer.
 *
 * @page:       the page of one extent buffer
 * @eb_context: to determine if we need to submit this page, if current page
 *              belongs to this eb, we don't need to submit
 *
 * The caller should pass each page in their bytenr order, and here we use
 * @eb_context to determine if we have submitted pages of one extent buffer.
 *
 * If we have, we just skip until we hit a new page that doesn't belong to
 * current @eb_context.
 *
 * If not, we submit all the page(s) of the extent buffer.
 *
 * Return >0 if we have submitted the extent buffer successfully.
 * Return 0 if we don't need to submit the page, as it's already submitted by
 * previous call.
 * Return <0 for fatal error.
 */
static int submit_eb_page(struct page *page, struct writeback_control *wbc,
                          struct btrfs_bio_ctrl *bio_ctrl,
                          struct extent_buffer **eb_context)
{
        struct address_space *mapping = page->mapping;
        struct btrfs_block_group *cache = NULL;
        struct extent_buffer *eb;
        int ret;

        if (!PagePrivate(page))
                return 0;

        if (btrfs_sb(page->mapping->host->i_sb)->nodesize < PAGE_SIZE)
                return submit_eb_subpage(page, wbc, bio_ctrl);

        spin_lock(&mapping->private_lock);
        if (!PagePrivate(page)) {
                spin_unlock(&mapping->private_lock);
                return 0;
        }

        eb = (struct extent_buffer *)page->private;

        /*
         * Shouldn't happen and normally this would be a BUG_ON but no point
         * crashing the machine for something we can survive anyway.
         */
        if (WARN_ON(!eb)) {
                spin_unlock(&mapping->private_lock);
                return 0;
        }

        if (eb == *eb_context) {
                spin_unlock(&mapping->private_lock);
                return 0;
        }
        ret = atomic_inc_not_zero(&eb->refs);
        spin_unlock(&mapping->private_lock);
        if (!ret)
                return 0;

        if (!btrfs_check_meta_write_pointer(eb->fs_info, eb, &cache)) {
                /*
                 * If for_sync, this hole will be filled with
                 * trasnsaction commit.
                 */
                if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync)
                        ret = -EAGAIN;
                else
                        ret = 0;
                free_extent_buffer(eb);
                return ret;
        }

        *eb_context = eb;

        ret = lock_extent_buffer_for_io(eb, bio_ctrl);
        if (ret <= 0) {
                btrfs_revert_meta_write_pointer(cache, eb);
                if (cache)
                        btrfs_put_block_group(cache);
                free_extent_buffer(eb);
                return ret;
        }
        if (cache) {
                /*
                 * Implies write in zoned mode. Mark the last eb in a block group.
                 */
                btrfs_schedule_zone_finish_bg(cache, eb);
                btrfs_put_block_group(cache);
        }
        ret = write_one_eb(eb, wbc, bio_ctrl);
        free_extent_buffer(eb);
        if (ret < 0)
                return ret;
        return 1;
}

int btree_write_cache_pages(struct address_space *mapping,
                                   struct writeback_control *wbc)
{
        struct extent_buffer *eb_context = NULL;
        struct btrfs_bio_ctrl bio_ctrl = {
                .extent_locked = 0,
                .sync_io = (wbc->sync_mode == WB_SYNC_ALL),
        };
        struct btrfs_fs_info *fs_info = BTRFS_I(mapping->host)->root->fs_info;
        int ret = 0;
        int done = 0;
        int nr_to_write_done = 0;
        struct folio_batch fbatch;
        unsigned int nr_folios;
        pgoff_t index;
        pgoff_t end;            /* Inclusive */
        int scanned = 0;
        xa_mark_t tag;

        folio_batch_init(&fbatch);
        if (wbc->range_cyclic) {
                index = mapping->writeback_index; /* Start from prev offset */
                end = -1;
                /*
                 * Start from the beginning does not need to cycle over the
                 * range, mark it as scanned.
                 */
                scanned = (index == 0);
        } else {
                index = wbc->range_start >> PAGE_SHIFT;
                end = wbc->range_end >> PAGE_SHIFT;
                scanned = 1;
        }
        if (wbc->sync_mode == WB_SYNC_ALL)
                tag = PAGECACHE_TAG_TOWRITE;
        else
                tag = PAGECACHE_TAG_DIRTY;
        btrfs_zoned_meta_io_lock(fs_info);
retry:
        if (wbc->sync_mode == WB_SYNC_ALL)
                tag_pages_for_writeback(mapping, index, end);
        while (!done && !nr_to_write_done && (index <= end) &&
               (nr_folios = filemap_get_folios_tag(mapping, &index, end,
                                            tag, &fbatch))) {
                unsigned i;

                for (i = 0; i < nr_folios; i++) {
                        struct folio *folio = fbatch.folios[i];

                        ret = submit_eb_page(&folio->page, wbc, &bio_ctrl,
                                        &eb_context);
                        if (ret == 0)
                                continue;
                        if (ret < 0) {
                                done = 1;
                                break;
                        }

                        /*
                         * the filesystem may choose to bump up nr_to_write.
                         * We have to make sure to honor the new nr_to_write
                         * at any time
                         */
                        nr_to_write_done = wbc->nr_to_write <= 0;
                }
                folio_batch_release(&fbatch);
                cond_resched();
        }
        if (!scanned && !done) {
                /*
                 * We hit the last page and there is more work to be done: wrap
                 * back to the start of the file
                 */
                scanned = 1;
                index = 0;
                goto retry;
        }
        /*
         * If something went wrong, don't allow any metadata write bio to be
         * submitted.
         *
         * This would prevent use-after-free if we had dirty pages not
         * cleaned up, which can still happen by fuzzed images.
         *
         * - Bad extent tree
         *   Allowing existing tree block to be allocated for other trees.
         *
         * - Log tree operations
         *   Exiting tree blocks get allocated to log tree, bumps its
         *   generation, then get cleaned in tree re-balance.
         *   Such tree block will not be written back, since it's clean,
         *   thus no WRITTEN flag set.
         *   And after log writes back, this tree block is not traced by
         *   any dirty extent_io_tree.
         *
         * - Offending tree block gets re-dirtied from its original owner
         *   Since it has bumped generation, no WRITTEN flag, it can be
         *   reused without COWing. This tree block will not be traced
         *   by btrfs_transaction::dirty_pages.
         *
         *   Now such dirty tree block will not be cleaned by any dirty
         *   extent io tree. Thus we don't want to submit such wild eb
         *   if the fs already has error.
         *
         * We can get ret > 0 from submit_extent_page() indicating how many ebs
         * were submitted. Reset it to 0 to avoid false alerts for the caller.
         */
        if (ret > 0)
                ret = 0;
        if (!ret && BTRFS_FS_ERROR(fs_info))
                ret = -EROFS;
        submit_write_bio(&bio_ctrl, ret);

        btrfs_zoned_meta_io_unlock(fs_info);
        return ret;
}

/*
 * Walk the list of dirty pages of the given address space and write all of them.
 *
 * @mapping:   address space structure to write
 * @wbc:       subtract the number of written pages from *@wbc->nr_to_write
 * @bio_ctrl:  holds context for the write, namely the bio
 *
 * If a page is already under I/O, write_cache_pages() skips it, even
 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 * and msync() need to guarantee that all the data which was dirty at the time
 * the call was made get new I/O started against them.  If wbc->sync_mode is
 * WB_SYNC_ALL then we were called for data integrity and we must wait for
 * existing IO to complete.
 */
static int extent_write_cache_pages(struct address_space *mapping,
                             struct writeback_control *wbc,
                             struct btrfs_bio_ctrl *bio_ctrl)
{
        struct inode *inode = mapping->host;
        int ret = 0;
        int done = 0;
        int nr_to_write_done = 0;
        struct folio_batch fbatch;
        unsigned int nr_folios;
        pgoff_t index;
        pgoff_t end;            /* Inclusive */
        pgoff_t done_index;
        int range_whole = 0;
        int scanned = 0;
        xa_mark_t tag;

        /*
         * We have to hold onto the inode so that ordered extents can do their
         * work when the IO finishes.  The alternative to this is failing to add
         * an ordered extent if the igrab() fails there and that is a huge pain
         * to deal with, so instead just hold onto the inode throughout the
         * writepages operation.  If it fails here we are freeing up the inode
         * anyway and we'd rather not waste our time writing out stuff that is
         * going to be truncated anyway.
         */
        if (!igrab(inode))
                return 0;

        folio_batch_init(&fbatch);
        if (wbc->range_cyclic) {
                index = mapping->writeback_index; /* Start from prev offset */
                end = -1;
                /*
                 * Start from the beginning does not need to cycle over the
                 * range, mark it as scanned.
                 */
                scanned = (index == 0);
        } else {
                index = wbc->range_start >> PAGE_SHIFT;
                end = wbc->range_end >> PAGE_SHIFT;
                if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
                        range_whole = 1;
                scanned = 1;
        }

        /*
         * We do the tagged writepage as long as the snapshot flush bit is set
         * and we are the first one who do the filemap_flush() on this inode.
         *
         * The nr_to_write == LONG_MAX is needed to make sure other flushers do
         * not race in and drop the bit.
         */
        if (range_whole && wbc->nr_to_write == LONG_MAX &&
            test_and_clear_bit(BTRFS_INODE_SNAPSHOT_FLUSH,
                               &BTRFS_I(inode)->runtime_flags))
                wbc->tagged_writepages = 1;

        if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
                tag = PAGECACHE_TAG_TOWRITE;
        else
                tag = PAGECACHE_TAG_DIRTY;
retry:
        if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
                tag_pages_for_writeback(mapping, index, end);
        done_index = index;
        while (!done && !nr_to_write_done && (index <= end) &&
                        (nr_folios = filemap_get_folios_tag(mapping, &index,
                                                        end, tag, &fbatch))) {
                unsigned i;

                for (i = 0; i < nr_folios; i++) {
                        struct folio *folio = fbatch.folios[i];

                        done_index = folio->index + folio_nr_pages(folio);
                        /*
                         * At this point we hold neither the i_pages lock nor
                         * the page lock: the page may be truncated or
                         * invalidated (changing page->mapping to NULL),
                         * or even swizzled back from swapper_space to
                         * tmpfs file mapping
                         */
                        if (!folio_trylock(folio)) {
                                submit_write_bio(bio_ctrl, 0);
                                folio_lock(folio);
                        }

                        if (unlikely(folio->mapping != mapping)) {
                                folio_unlock(folio);
                                continue;
                        }

                        if (wbc->sync_mode != WB_SYNC_NONE) {
                                if (folio_test_writeback(folio))
                                        submit_write_bio(bio_ctrl, 0);
                                folio_wait_writeback(folio);
                        }

                        if (folio_test_writeback(folio) ||
                            !folio_clear_dirty_for_io(folio)) {
                                folio_unlock(folio);
                                continue;
                        }

                        ret = __extent_writepage(&folio->page, wbc, bio_ctrl);
                        if (ret < 0) {
                                done = 1;
                                break;
                        }

                        /*
                         * the filesystem may choose to bump up nr_to_write.
                         * We have to make sure to honor the new nr_to_write
                         * at any time
                         */
                        nr_to_write_done = wbc->nr_to_write <= 0;
                }
                folio_batch_release(&fbatch);
                cond_resched();
        }
        if (!scanned && !done) {
                /*
                 * We hit the last page and there is more work to be done: wrap
                 * back to the start of the file
                 */
                scanned = 1;
                index = 0;

                /*
                 * If we're looping we could run into a page that is locked by a
                 * writer and that writer could be waiting on writeback for a
                 * page in our current bio, and thus deadlock, so flush the
                 * write bio here.
                 */
                submit_write_bio(bio_ctrl, 0);
                goto retry;
        }

        if (wbc->range_cyclic || (wbc->nr_to_write > 0 && range_whole))
                mapping->writeback_index = done_index;

        btrfs_add_delayed_iput(BTRFS_I(inode));
        return ret;
}

/*
 * Submit the pages in the range to bio for call sites which delalloc range has
 * already been ran (aka, ordered extent inserted) and all pages are still
 * locked.
 */
int extent_write_locked_range(struct inode *inode, u64 start, u64 end)
{
        bool found_error = false;
        int first_error = 0;
        int ret = 0;
        struct address_space *mapping = inode->i_mapping;
        struct page *page;
        u64 cur = start;
        unsigned long nr_pages;
        const u32 sectorsize = btrfs_sb(inode->i_sb)->sectorsize;
        struct btrfs_bio_ctrl bio_ctrl = {
                .extent_locked = 1,
                .sync_io = 1,
        };
        struct writeback_control wbc_writepages = {
                .sync_mode      = WB_SYNC_ALL,
                .range_start    = start,
                .range_end      = end + 1,
                /* We're called from an async helper function */
                .punt_to_cgroup = 1,
                .no_cgroup_owner = 1,
        };

        ASSERT(IS_ALIGNED(start, sectorsize) && IS_ALIGNED(end + 1, sectorsize));
        nr_pages = (round_up(end, PAGE_SIZE) - round_down(start, PAGE_SIZE)) >>
                   PAGE_SHIFT;
        wbc_writepages.nr_to_write = nr_pages * 2;

        wbc_attach_fdatawrite_inode(&wbc_writepages, inode);
        while (cur <= end) {
                u64 cur_end = min(round_down(cur, PAGE_SIZE) + PAGE_SIZE - 1, end);

                page = find_get_page(mapping, cur >> PAGE_SHIFT);
                /*
                 * All pages in the range are locked since
                 * btrfs_run_delalloc_range(), thus there is no way to clear
                 * the page dirty flag.
                 */
                ASSERT(PageLocked(page));
                ASSERT(PageDirty(page));
                clear_page_dirty_for_io(page);
                ret = __extent_writepage(page, &wbc_writepages, &bio_ctrl);
                ASSERT(ret <= 0);
                if (ret < 0) {
                        found_error = true;
                        first_error = ret;
                }
                put_page(page);
                cur = cur_end + 1;
        }

        submit_write_bio(&bio_ctrl, found_error ? ret : 0);

        wbc_detach_inode(&wbc_writepages);
        if (found_error)
                return first_error;
        return ret;
}

int extent_writepages(struct address_space *mapping,
                      struct writeback_control *wbc)
{
        struct inode *inode = mapping->host;
        int ret = 0;
        struct btrfs_bio_ctrl bio_ctrl = {
                .extent_locked = 0,
                .sync_io = (wbc->sync_mode == WB_SYNC_ALL),
        };

        /*
         * Allow only a single thread to do the reloc work in zoned mode to
         * protect the write pointer updates.
         */
        btrfs_zoned_data_reloc_lock(BTRFS_I(inode));
        ret = extent_write_cache_pages(mapping, wbc, &bio_ctrl);
        submit_write_bio(&bio_ctrl, ret);
        btrfs_zoned_data_reloc_unlock(BTRFS_I(inode));
        return ret;
}

void extent_readahead(struct readahead_control *rac)
{
        struct btrfs_bio_ctrl bio_ctrl = { 0 };
        struct page *pagepool[16];
        struct extent_map *em_cached = NULL;
        u64 prev_em_start = (u64)-1;
        int nr;

        while ((nr = readahead_page_batch(rac, pagepool))) {
                u64 contig_start = readahead_pos(rac);
                u64 contig_end = contig_start + readahead_batch_length(rac) - 1;

                contiguous_readpages(pagepool, nr, contig_start, contig_end,
                                &em_cached, &bio_ctrl, &prev_em_start);
        }

        if (em_cached)
                free_extent_map(em_cached);
        submit_one_bio(&bio_ctrl);
}

/*
 * basic invalidate_folio code, this waits on any locked or writeback
 * ranges corresponding to the folio, and then deletes any extent state
 * records from the tree
 */
int extent_invalidate_folio(struct extent_io_tree *tree,
                          struct folio *folio, size_t offset)
{
        struct extent_state *cached_state = NULL;
        u64 start = folio_pos(folio);
        u64 end = start + folio_size(folio) - 1;
        size_t blocksize = folio->mapping->host->i_sb->s_blocksize;

        /* This function is only called for the btree inode */
        ASSERT(tree->owner == IO_TREE_BTREE_INODE_IO);

        start += ALIGN(offset, blocksize);
        if (start > end)
                return 0;

        lock_extent(tree, start, end, &cached_state);
        folio_wait_writeback(folio);

        /*
         * Currently for btree io tree, only EXTENT_LOCKED is utilized,
         * so here we only need to unlock the extent range to free any
         * existing extent state.
         */
        unlock_extent(tree, start, end, &cached_state);
        return 0;
}

/*
 * a helper for release_folio, this tests for areas of the page that
 * are locked or under IO and drops the related state bits if it is safe
 * to drop the page.
 */
static int try_release_extent_state(struct extent_io_tree *tree,
                                    struct page *page, gfp_t mask)
{
        u64 start = page_offset(page);
        u64 end = start + PAGE_SIZE - 1;
        int ret = 1;

        if (test_range_bit(tree, start, end, EXTENT_LOCKED, 0, NULL)) {
                ret = 0;
        } else {
                u32 clear_bits = ~(EXTENT_LOCKED | EXTENT_NODATASUM |
                                   EXTENT_DELALLOC_NEW | EXTENT_CTLBITS);

                /*
                 * At this point we can safely clear everything except the
                 * locked bit, the nodatasum bit and the delalloc new bit.
                 * The delalloc new bit will be cleared by ordered extent
                 * completion.
                 */
                ret = __clear_extent_bit(tree, start, end, clear_bits, NULL,
                                         mask, NULL);

                /* if clear_extent_bit failed for enomem reasons,
                 * we can't allow the release to continue.
                 */
                if (ret < 0)
                        ret = 0;
                else
                        ret = 1;
        }
        return ret;
}

/*
 * a helper for release_folio.  As long as there are no locked extents
 * in the range corresponding to the page, both state records and extent
 * map records are removed
 */
int try_release_extent_mapping(struct page *page, gfp_t mask)
{
        struct extent_map *em;
        u64 start = page_offset(page);
        u64 end = start + PAGE_SIZE - 1;
        struct btrfs_inode *btrfs_inode = BTRFS_I(page->mapping->host);
        struct extent_io_tree *tree = &btrfs_inode->io_tree;
        struct extent_map_tree *map = &btrfs_inode->extent_tree;

        if (gfpflags_allow_blocking(mask) &&
            page->mapping->host->i_size > SZ_16M) {
                u64 len;
                while (start <= end) {
                        struct btrfs_fs_info *fs_info;
                        u64 cur_gen;

                        len = end - start + 1;
                        write_lock(&map->lock);
                        em = lookup_extent_mapping(map, start, len);
                        if (!em) {
                                write_unlock(&map->lock);
                                break;
                        }
                        if (test_bit(EXTENT_FLAG_PINNED, &em->flags) ||
                            em->start != start) {
                                write_unlock(&map->lock);
                                free_extent_map(em);
                                break;
                        }
                        if (test_range_bit(tree, em->start,
                                           extent_map_end(em) - 1,
                                           EXTENT_LOCKED, 0, NULL))
                                goto next;
                        /*
                         * If it's not in the list of modified extents, used
                         * by a fast fsync, we can remove it. If it's being
                         * logged we can safely remove it since fsync took an
                         * extra reference on the em.
                         */
                        if (list_empty(&em->list) ||
                            test_bit(EXTENT_FLAG_LOGGING, &em->flags))
                                goto remove_em;
                        /*
                         * If it's in the list of modified extents, remove it
                         * only if its generation is older then the current one,
                         * in which case we don't need it for a fast fsync.
                         * Otherwise don't remove it, we could be racing with an
                         * ongoing fast fsync that could miss the new extent.
                         */
                        fs_info = btrfs_inode->root->fs_info;
                        spin_lock(&fs_info->trans_lock);
                        cur_gen = fs_info->generation;
                        spin_unlock(&fs_info->trans_lock);
                        if (em->generation >= cur_gen)
                                goto next;
remove_em:
                        /*
                         * We only remove extent maps that are not in the list of
                         * modified extents or that are in the list but with a
                         * generation lower then the current generation, so there
                         * is no need to set the full fsync flag on the inode (it
                         * hurts the fsync performance for workloads with a data
                         * size that exceeds or is close to the system's memory).
                         */
                        remove_extent_mapping(map, em);
                        /* once for the rb tree */
                        free_extent_map(em);
next:
                        start = extent_map_end(em);
                        write_unlock(&map->lock);

                        /* once for us */
                        free_extent_map(em);

                        cond_resched(); /* Allow large-extent preemption. */
                }
        }
        return try_release_extent_state(tree, page, mask);
}

/*
 * To cache previous fiemap extent
 *
 * Will be used for merging fiemap extent
 */
struct fiemap_cache {
        u64 offset;
        u64 phys;
        u64 len;
        u32 flags;
        bool cached;
};

/*
 * Helper to submit fiemap extent.
 *
 * Will try to merge current fiemap extent specified by @offset, @phys,
 * @len and @flags with cached one.
 * And only when we fails to merge, cached one will be submitted as
 * fiemap extent.
 *
 * Return value is the same as fiemap_fill_next_extent().
 */
static int emit_fiemap_extent(struct fiemap_extent_info *fieinfo,
                                struct fiemap_cache *cache,
                                u64 offset, u64 phys, u64 len, u32 flags)
{
        int ret = 0;

        /* Set at the end of extent_fiemap(). */
        ASSERT((flags & FIEMAP_EXTENT_LAST) == 0);

        if (!cache->cached)
                goto assign;

        /*
         * Sanity check, extent_fiemap() should have ensured that new
         * fiemap extent won't overlap with cached one.
         * Not recoverable.
         *
         * NOTE: Physical address can overlap, due to compression
         */
        if (cache->offset + cache->len > offset) {
                WARN_ON(1);
                return -EINVAL;
        }

        /*
         * Only merges fiemap extents if
         * 1) Their logical addresses are continuous
         *
         * 2) Their physical addresses are continuous
         *    So truly compressed (physical size smaller than logical size)
         *    extents won't get merged with each other
         *
         * 3) Share same flags
         */
        if (cache->offset + cache->len  == offset &&
            cache->phys + cache->len == phys  &&
            cache->flags == flags) {
                cache->len += len;
                return 0;
        }

        /* Not mergeable, need to submit cached one */
        ret = fiemap_fill_next_extent(fieinfo, cache->offset, cache->phys,
                                      cache->len, cache->flags);
        cache->cached = false;
        if (ret)
                return ret;
assign:
        cache->cached = true;
        cache->offset = offset;
        cache->phys = phys;
        cache->len = len;
        cache->flags = flags;

        return 0;
}

/*
 * Emit last fiemap cache
 *
 * The last fiemap cache may still be cached in the following case:
 * 0                  4k                    8k
 * |<- Fiemap range ->|
 * |<------------  First extent ----------->|
 *
 * In this case, the first extent range will be cached but not emitted.
 * So we must emit it before ending extent_fiemap().
 */
static int emit_last_fiemap_cache(struct fiemap_extent_info *fieinfo,
                                  struct fiemap_cache *cache)
{
        int ret;

        if (!cache->cached)
                return 0;

        ret = fiemap_fill_next_extent(fieinfo, cache->offset, cache->phys,
                                      cache->len, cache->flags);
        cache->cached = false;
        if (ret > 0)
                ret = 0;
        return ret;
}

static int fiemap_next_leaf_item(struct btrfs_inode *inode, struct btrfs_path *path)
{
        struct extent_buffer *clone;
        struct btrfs_key key;
        int slot;
        int ret;

        path->slots[0]++;
        if (path->slots[0] < btrfs_header_nritems(path->nodes[0]))
                return 0;

        ret = btrfs_next_leaf(inode->root, path);
        if (ret != 0)
                return ret;

        /*
         * Don't bother with cloning if there are no more file extent items for
         * our inode.
         */
        btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
        if (key.objectid != btrfs_ino(inode) || key.type != BTRFS_EXTENT_DATA_KEY)
                return 1;

        /* See the comment at fiemap_search_slot() about why we clone. */
        clone = btrfs_clone_extent_buffer(path->nodes[0]);
        if (!clone)
                return -ENOMEM;

        slot = path->slots[0];
        btrfs_release_path(path);
        path->nodes[0] = clone;
        path->slots[0] = slot;

        return 0;
}

/*
 * Search for the first file extent item that starts at a given file offset or
 * the one that starts immediately before that offset.
 * Returns: 0 on success, < 0 on error, 1 if not found.
 */
static int fiemap_search_slot(struct btrfs_inode *inode, struct btrfs_path *path,
                              u64 file_offset)
{
        const u64 ino = btrfs_ino(inode);
        struct btrfs_root *root = inode->root;
        struct extent_buffer *clone;
        struct btrfs_key key;
        int slot;
        int ret;

        key.objectid = ino;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = file_offset;

        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                return ret;

        if (ret > 0 && path->slots[0] > 0) {
                btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0] - 1);
                if (key.objectid == ino && key.type == BTRFS_EXTENT_DATA_KEY)
                        path->slots[0]--;
        }

        if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
                ret = btrfs_next_leaf(root, path);
                if (ret != 0)
                        return ret;

                btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
                if (key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY)
                        return 1;
        }

        /*
         * We clone the leaf and use it during fiemap. This is because while
         * using the leaf we do expensive things like checking if an extent is
         * shared, which can take a long time. In order to prevent blocking
         * other tasks for too long, we use a clone of the leaf. We have locked
         * the file range in the inode's io tree, so we know none of our file
         * extent items can change. This way we avoid blocking other tasks that
         * want to insert items for other inodes in the same leaf or b+tree
         * rebalance operations (triggered for example when someone is trying
         * to push items into this leaf when trying to insert an item in a
         * neighbour leaf).
         * We also need the private clone because holding a read lock on an
         * extent buffer of the subvolume's b+tree will make lockdep unhappy
         * when we call fiemap_fill_next_extent(), because that may cause a page
         * fault when filling the user space buffer with fiemap data.
         */
        clone = btrfs_clone_extent_buffer(path->nodes[0]);
        if (!clone)
                return -ENOMEM;

        slot = path->slots[0];
        btrfs_release_path(path);
        path->nodes[0] = clone;
        path->slots[0] = slot;

        return 0;
}

/*
 * Process a range which is a hole or a prealloc extent in the inode's subvolume
 * btree. If @disk_bytenr is 0, we are dealing with a hole, otherwise a prealloc
 * extent. The end offset (@end) is inclusive.
 */
static int fiemap_process_hole(struct btrfs_inode *inode,
                               struct fiemap_extent_info *fieinfo,
                               struct fiemap_cache *cache,
                               struct extent_state **delalloc_cached_state,
                               struct btrfs_backref_share_check_ctx *backref_ctx,
                               u64 disk_bytenr, u64 extent_offset,
                               u64 extent_gen,
                               u64 start, u64 end)
{
        const u64 i_size = i_size_read(&inode->vfs_inode);
        u64 cur_offset = start;
        u64 last_delalloc_end = 0;
        u32 prealloc_flags = FIEMAP_EXTENT_UNWRITTEN;
        bool checked_extent_shared = false;
        int ret;

        /*
         * There can be no delalloc past i_size, so don't waste time looking for
         * it beyond i_size.
         */
        while (cur_offset < end && cur_offset < i_size) {
                u64 delalloc_start;
                u64 delalloc_end;
                u64 prealloc_start;
                u64 prealloc_len = 0;
                bool delalloc;

                delalloc = btrfs_find_delalloc_in_range(inode, cur_offset, end,
                                                        delalloc_cached_state,
                                                        &delalloc_start,
                                                        &delalloc_end);
                if (!delalloc)
                        break;

                /*
                 * If this is a prealloc extent we have to report every section
                 * of it that has no delalloc.
                 */
                if (disk_bytenr != 0) {
                        if (last_delalloc_end == 0) {
                                prealloc_start = start;
                                prealloc_len = delalloc_start - start;
                        } else {
                                prealloc_start = last_delalloc_end + 1;
                                prealloc_len = delalloc_start - prealloc_start;
                        }
                }

                if (prealloc_len > 0) {
                        if (!checked_extent_shared && fieinfo->fi_extents_max) {
                                ret = btrfs_is_data_extent_shared(inode,
                                                                  disk_bytenr,
                                                                  extent_gen,
                                                                  backref_ctx);
                                if (ret < 0)
                                        return ret;
                                else if (ret > 0)
                                        prealloc_flags |= FIEMAP_EXTENT_SHARED;

                                checked_extent_shared = true;
                        }
                        ret = emit_fiemap_extent(fieinfo, cache, prealloc_start,
                                                 disk_bytenr + extent_offset,
                                                 prealloc_len, prealloc_flags);
                        if (ret)
                                return ret;
                        extent_offset += prealloc_len;
                }

                ret = emit_fiemap_extent(fieinfo, cache, delalloc_start, 0,
                                         delalloc_end + 1 - delalloc_start,
                                         FIEMAP_EXTENT_DELALLOC |
                                         FIEMAP_EXTENT_UNKNOWN);
                if (ret)
                        return ret;

                last_delalloc_end = delalloc_end;
                cur_offset = delalloc_end + 1;
                extent_offset += cur_offset - delalloc_start;
                cond_resched();
        }

        /*
         * Either we found no delalloc for the whole prealloc extent or we have
         * a prealloc extent that spans i_size or starts at or after i_size.
         */
        if (disk_bytenr != 0 && last_delalloc_end < end) {
                u64 prealloc_start;
                u64 prealloc_len;

                if (last_delalloc_end == 0) {
                        prealloc_start = start;
                        prealloc_len = end + 1 - start;
                } else {
                        prealloc_start = last_delalloc_end + 1;
                        prealloc_len = end + 1 - prealloc_start;
                }

                if (!checked_extent_shared && fieinfo->fi_extents_max) {
                        ret = btrfs_is_data_extent_shared(inode,
                                                          disk_bytenr,
                                                          extent_gen,
                                                          backref_ctx);
                        if (ret < 0)
                                return ret;
                        else if (ret > 0)
                                prealloc_flags |= FIEMAP_EXTENT_SHARED;
                }
                ret = emit_fiemap_extent(fieinfo, cache, prealloc_start,
                                         disk_bytenr + extent_offset,
                                         prealloc_len, prealloc_flags);
                if (ret)
                        return ret;
        }

        return 0;
}

static int fiemap_find_last_extent_offset(struct btrfs_inode *inode,
                                          struct btrfs_path *path,
                                          u64 *last_extent_end_ret)
{
        const u64 ino = btrfs_ino(inode);
        struct btrfs_root *root = inode->root;
        struct extent_buffer *leaf;
        struct btrfs_file_extent_item *ei;
        struct btrfs_key key;
        u64 disk_bytenr;
        int ret;

        /*
         * Lookup the last file extent. We're not using i_size here because
         * there might be preallocation past i_size.
         */
        ret = btrfs_lookup_file_extent(NULL, root, path, ino, (u64)-1, 0);
        /* There can't be a file extent item at offset (u64)-1 */
        ASSERT(ret != 0);
        if (ret < 0)
                return ret;

        /*
         * For a non-existing key, btrfs_search_slot() always leaves us at a
         * slot > 0, except if the btree is empty, which is impossible because
         * at least it has the inode item for this inode and all the items for
         * the root inode 256.
         */
        ASSERT(path->slots[0] > 0);
        path->slots[0]--;
        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        if (key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY) {
                /* No file extent items in the subvolume tree. */
                *last_extent_end_ret = 0;
                return 0;
        }

        /*
         * For an inline extent, the disk_bytenr is where inline data starts at,
         * so first check if we have an inline extent item before checking if we
         * have an implicit hole (disk_bytenr == 0).
         */
        ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_file_extent_item);
        if (btrfs_file_extent_type(leaf, ei) == BTRFS_FILE_EXTENT_INLINE) {
                *last_extent_end_ret = btrfs_file_extent_end(path);
                return 0;
        }

        /*
         * Find the last file extent item that is not a hole (when NO_HOLES is
         * not enabled). This should take at most 2 iterations in the worst
         * case: we have one hole file extent item at slot 0 of a leaf and
         * another hole file extent item as the last item in the previous leaf.
         * This is because we merge file extent items that represent holes.
         */
        disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, ei);
        while (disk_bytenr == 0) {
                ret = btrfs_previous_item(root, path, ino, BTRFS_EXTENT_DATA_KEY);
                if (ret < 0) {
                        return ret;
                } else if (ret > 0) {
                        /* No file extent items that are not holes. */
                        *last_extent_end_ret = 0;
                        return 0;
                }
                leaf = path->nodes[0];
                ei = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_file_extent_item);
                disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, ei);
        }

        *last_extent_end_ret = btrfs_file_extent_end(path);
        return 0;
}

int extent_fiemap(struct btrfs_inode *inode, struct fiemap_extent_info *fieinfo,
                  u64 start, u64 len)
{
        const u64 ino = btrfs_ino(inode);
        struct extent_state *cached_state = NULL;
        struct extent_state *delalloc_cached_state = NULL;
        struct btrfs_path *path;
        struct fiemap_cache cache = { 0 };
        struct btrfs_backref_share_check_ctx *backref_ctx;
        u64 last_extent_end;
        u64 prev_extent_end;
        u64 lockstart;
        u64 lockend;
        bool stopped = false;
        int ret;

        backref_ctx = btrfs_alloc_backref_share_check_ctx();
        path = btrfs_alloc_path();
        if (!backref_ctx || !path) {
                ret = -ENOMEM;
                goto out;
        }

        lockstart = round_down(start, inode->root->fs_info->sectorsize);
        lockend = round_up(start + len, inode->root->fs_info->sectorsize);
        prev_extent_end = lockstart;

        btrfs_inode_lock(inode, BTRFS_ILOCK_SHARED);
        lock_extent(&inode->io_tree, lockstart, lockend, &cached_state);

        ret = fiemap_find_last_extent_offset(inode, path, &last_extent_end);
        if (ret < 0)
                goto out_unlock;
        btrfs_release_path(path);

        path->reada = READA_FORWARD;
        ret = fiemap_search_slot(inode, path, lockstart);
        if (ret < 0) {
                goto out_unlock;
        } else if (ret > 0) {
                /*
                 * No file extent item found, but we may have delalloc between
                 * the current offset and i_size. So check for that.
                 */
                ret = 0;
                goto check_eof_delalloc;
        }

        while (prev_extent_end < lockend) {
                struct extent_buffer *leaf = path->nodes[0];
                struct btrfs_file_extent_item *ei;
                struct btrfs_key key;
                u64 extent_end;
                u64 extent_len;
                u64 extent_offset = 0;
                u64 extent_gen;
                u64 disk_bytenr = 0;
                u64 flags = 0;
                int extent_type;
                u8 compression;

                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
                if (key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY)
                        break;

                extent_end = btrfs_file_extent_end(path);

                /*
                 * The first iteration can leave us at an extent item that ends
                 * before our range's start. Move to the next item.
                 */
                if (extent_end <= lockstart)
                        goto next_item;

                backref_ctx->curr_leaf_bytenr = leaf->start;

                /* We have in implicit hole (NO_HOLES feature enabled). */
                if (prev_extent_end < key.offset) {
                        const u64 range_end = min(key.offset, lockend) - 1;

                        ret = fiemap_process_hole(inode, fieinfo, &cache,
                                                  &delalloc_cached_state,
                                                  backref_ctx, 0, 0, 0,
                                                  prev_extent_end, range_end);
                        if (ret < 0) {
                                goto out_unlock;
                        } else if (ret > 0) {
                                /* fiemap_fill_next_extent() told us to stop. */
                                stopped = true;
                                break;
                        }

                        /* We've reached the end of the fiemap range, stop. */
                        if (key.offset >= lockend) {
                                stopped = true;
                                break;
                        }
                }

                extent_len = extent_end - key.offset;
                ei = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_file_extent_item);
                compression = btrfs_file_extent_compression(leaf, ei);
                extent_type = btrfs_file_extent_type(leaf, ei);
                extent_gen = btrfs_file_extent_generation(leaf, ei);

                if (extent_type != BTRFS_FILE_EXTENT_INLINE) {
                        disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, ei);
                        if (compression == BTRFS_COMPRESS_NONE)
                                extent_offset = btrfs_file_extent_offset(leaf, ei);
                }

                if (compression != BTRFS_COMPRESS_NONE)
                        flags |= FIEMAP_EXTENT_ENCODED;

                if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
                        flags |= FIEMAP_EXTENT_DATA_INLINE;
                        flags |= FIEMAP_EXTENT_NOT_ALIGNED;
                        ret = emit_fiemap_extent(fieinfo, &cache, key.offset, 0,
                                                 extent_len, flags);
                } else if (extent_type == BTRFS_FILE_EXTENT_PREALLOC) {
                        ret = fiemap_process_hole(inode, fieinfo, &cache,
                                                  &delalloc_cached_state,
                                                  backref_ctx,
                                                  disk_bytenr, extent_offset,
                                                  extent_gen, key.offset,
                                                  extent_end - 1);
                } else if (disk_bytenr == 0) {
                        /* We have an explicit hole. */
                        ret = fiemap_process_hole(inode, fieinfo, &cache,
                                                  &delalloc_cached_state,
                                                  backref_ctx, 0, 0, 0,
                                                  key.offset, extent_end - 1);
                } else {
                        /* We have a regular extent. */
                        if (fieinfo->fi_extents_max) {
                                ret = btrfs_is_data_extent_shared(inode,
                                                                  disk_bytenr,
                                                                  extent_gen,
                                                                  backref_ctx);
                                if (ret < 0)
                                        goto out_unlock;
                                else if (ret > 0)
                                        flags |= FIEMAP_EXTENT_SHARED;
                        }

                        ret = emit_fiemap_extent(fieinfo, &cache, key.offset,
                                                 disk_bytenr + extent_offset,
                                                 extent_len, flags);
                }

                if (ret < 0) {
                        goto out_unlock;
                } else if (ret > 0) {
                        /* fiemap_fill_next_extent() told us to stop. */
                        stopped = true;
                        break;
                }

                prev_extent_end = extent_end;
next_item:
                if (fatal_signal_pending(current)) {
                        ret = -EINTR;
                        goto out_unlock;
                }

                ret = fiemap_next_leaf_item(inode, path);
                if (ret < 0) {
                        goto out_unlock;
                } else if (ret > 0) {
                        /* No more file extent items for this inode. */
                        break;
                }
                cond_resched();
        }

check_eof_delalloc:
        /*
         * Release (and free) the path before emitting any final entries to
         * fiemap_fill_next_extent() to keep lockdep happy. This is because
         * once we find no more file extent items exist, we may have a
         * non-cloned leaf, and fiemap_fill_next_extent() can trigger page
         * faults when copying data to the user space buffer.
         */
        btrfs_free_path(path);
        path = NULL;

        if (!stopped && prev_extent_end < lockend) {
                ret = fiemap_process_hole(inode, fieinfo, &cache,
                                          &delalloc_cached_state, backref_ctx,
                                          0, 0, 0, prev_extent_end, lockend - 1);
                if (ret < 0)
                        goto out_unlock;
                prev_extent_end = lockend;
        }

        if (cache.cached && cache.offset + cache.len >= last_extent_end) {
                const u64 i_size = i_size_read(&inode->vfs_inode);

                if (prev_extent_end < i_size) {
                        u64 delalloc_start;
                        u64 delalloc_end;
                        bool delalloc;

                        delalloc = btrfs_find_delalloc_in_range(inode,
                                                                prev_extent_end,
                                                                i_size - 1,
                                                                &delalloc_cached_state,
                                                                &delalloc_start,
                                                                &delalloc_end);
                        if (!delalloc)
                                cache.flags |= FIEMAP_EXTENT_LAST;
                } else {
                        cache.flags |= FIEMAP_EXTENT_LAST;
                }
        }

        ret = emit_last_fiemap_cache(fieinfo, &cache);

out_unlock:
        unlock_extent(&inode->io_tree, lockstart, lockend, &cached_state);
        btrfs_inode_unlock(inode, BTRFS_ILOCK_SHARED);
out:
        free_extent_state(delalloc_cached_state);
        btrfs_free_backref_share_ctx(backref_ctx);
        btrfs_free_path(path);
        return ret;
}

static void __free_extent_buffer(struct extent_buffer *eb)
{
        kmem_cache_free(extent_buffer_cache, eb);
}

int extent_buffer_under_io(const struct extent_buffer *eb)
{
        return (atomic_read(&eb->io_pages) ||
                test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags) ||
                test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
}

static bool page_range_has_eb(struct btrfs_fs_info *fs_info, struct page *page)
{
        struct btrfs_subpage *subpage;

        lockdep_assert_held(&page->mapping->private_lock);

        if (PagePrivate(page)) {
                subpage = (struct btrfs_subpage *)page->private;
                if (atomic_read(&subpage->eb_refs))
                        return true;
                /*
                 * Even there is no eb refs here, we may still have
                 * end_page_read() call relying on page::private.
                 */
                if (atomic_read(&subpage->readers))
                        return true;
        }
        return false;
}

static void detach_extent_buffer_page(struct extent_buffer *eb, struct page *page)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        const bool mapped = !test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);

        /*
         * For mapped eb, we're going to change the page private, which should
         * be done under the private_lock.
         */
        if (mapped)
                spin_lock(&page->mapping->private_lock);

        if (!PagePrivate(page)) {
                if (mapped)
                        spin_unlock(&page->mapping->private_lock);
                return;
        }

        if (fs_info->nodesize >= PAGE_SIZE) {
                /*
                 * We do this since we'll remove the pages after we've
                 * removed the eb from the radix tree, so we could race
                 * and have this page now attached to the new eb.  So
                 * only clear page_private if it's still connected to
                 * this eb.
                 */
                if (PagePrivate(page) &&
                    page->private == (unsigned long)eb) {
                        BUG_ON(test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
                        BUG_ON(PageDirty(page));
                        BUG_ON(PageWriteback(page));
                        /*
                         * We need to make sure we haven't be attached
                         * to a new eb.
                         */
                        detach_page_private(page);
                }
                if (mapped)
                        spin_unlock(&page->mapping->private_lock);
                return;
        }

        /*
         * For subpage, we can have dummy eb with page private.  In this case,
         * we can directly detach the private as such page is only attached to
         * one dummy eb, no sharing.
         */
        if (!mapped) {
                btrfs_detach_subpage(fs_info, page);
                return;
        }

        btrfs_page_dec_eb_refs(fs_info, page);

        /*
         * We can only detach the page private if there are no other ebs in the
         * page range and no unfinished IO.
         */
        if (!page_range_has_eb(fs_info, page))
                btrfs_detach_subpage(fs_info, page);

        spin_unlock(&page->mapping->private_lock);
}

/* Release all pages attached to the extent buffer */
static void btrfs_release_extent_buffer_pages(struct extent_buffer *eb)
{
        int i;
        int num_pages;

        ASSERT(!extent_buffer_under_io(eb));

        num_pages = num_extent_pages(eb);
        for (i = 0; i < num_pages; i++) {
                struct page *page = eb->pages[i];

                if (!page)
                        continue;

                detach_extent_buffer_page(eb, page);

                /* One for when we allocated the page */
                put_page(page);
        }
}

/*
 * Helper for releasing the extent buffer.
 */
static inline void btrfs_release_extent_buffer(struct extent_buffer *eb)
{
        btrfs_release_extent_buffer_pages(eb);
        btrfs_leak_debug_del_eb(eb);
        __free_extent_buffer(eb);
}

static struct extent_buffer *
__alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start,
                      unsigned long len)
{
        struct extent_buffer *eb = NULL;

        eb = kmem_cache_zalloc(extent_buffer_cache, GFP_NOFS|__GFP_NOFAIL);
        eb->start = start;
        eb->len = len;
        eb->fs_info = fs_info;
        init_rwsem(&eb->lock);

        btrfs_leak_debug_add_eb(eb);
        INIT_LIST_HEAD(&eb->release_list);

        spin_lock_init(&eb->refs_lock);
        atomic_set(&eb->refs, 1);
        atomic_set(&eb->io_pages, 0);

        ASSERT(len <= BTRFS_MAX_METADATA_BLOCKSIZE);

        return eb;
}

struct extent_buffer *btrfs_clone_extent_buffer(const struct extent_buffer *src)
{
        int i;
        struct extent_buffer *new;
        int num_pages = num_extent_pages(src);
        int ret;

        new = __alloc_extent_buffer(src->fs_info, src->start, src->len);
        if (new == NULL)
                return NULL;

        /*
         * Set UNMAPPED before calling btrfs_release_extent_buffer(), as
         * btrfs_release_extent_buffer() have different behavior for
         * UNMAPPED subpage extent buffer.
         */
        set_bit(EXTENT_BUFFER_UNMAPPED, &new->bflags);

        ret = btrfs_alloc_page_array(num_pages, new->pages);
        if (ret) {
                btrfs_release_extent_buffer(new);
                return NULL;
        }

        for (i = 0; i < num_pages; i++) {
                int ret;
                struct page *p = new->pages[i];

                ret = attach_extent_buffer_page(new, p, NULL);
                if (ret < 0) {
                        btrfs_release_extent_buffer(new);
                        return NULL;
                }
                WARN_ON(PageDirty(p));
                copy_page(page_address(p), page_address(src->pages[i]));
        }
        set_extent_buffer_uptodate(new);

        return new;
}

struct extent_buffer *__alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info,
                                                  u64 start, unsigned long len)
{
        struct extent_buffer *eb;
        int num_pages;
        int i;
        int ret;

        eb = __alloc_extent_buffer(fs_info, start, len);
        if (!eb)
                return NULL;

        num_pages = num_extent_pages(eb);
        ret = btrfs_alloc_page_array(num_pages, eb->pages);
        if (ret)
                goto err;

        for (i = 0; i < num_pages; i++) {
                struct page *p = eb->pages[i];

                ret = attach_extent_buffer_page(eb, p, NULL);
                if (ret < 0)
                        goto err;
        }

        set_extent_buffer_uptodate(eb);
        btrfs_set_header_nritems(eb, 0);
        set_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);

        return eb;
err:
        for (i = 0; i < num_pages; i++) {
                if (eb->pages[i]) {
                        detach_extent_buffer_page(eb, eb->pages[i]);
                        __free_page(eb->pages[i]);
                }
        }
        __free_extent_buffer(eb);
        return NULL;
}

struct extent_buffer *alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info,
                                                u64 start)
{
        return __alloc_dummy_extent_buffer(fs_info, start, fs_info->nodesize);
}

static void check_buffer_tree_ref(struct extent_buffer *eb)
{
        int refs;
        /*
         * The TREE_REF bit is first set when the extent_buffer is added
         * to the radix tree. It is also reset, if unset, when a new reference
         * is created by find_extent_buffer.
         *
         * It is only cleared in two cases: freeing the last non-tree
         * reference to the extent_buffer when its STALE bit is set or
         * calling release_folio when the tree reference is the only reference.
         *
         * In both cases, care is taken to ensure that the extent_buffer's
         * pages are not under io. However, release_folio can be concurrently
         * called with creating new references, which is prone to race
         * conditions between the calls to check_buffer_tree_ref in those
         * codepaths and clearing TREE_REF in try_release_extent_buffer.
         *
         * The actual lifetime of the extent_buffer in the radix tree is
         * adequately protected by the refcount, but the TREE_REF bit and
         * its corresponding reference are not. To protect against this
         * class of races, we call check_buffer_tree_ref from the codepaths
         * which trigger io after they set eb->io_pages. Note that once io is
         * initiated, TREE_REF can no longer be cleared, so that is the
         * moment at which any such race is best fixed.
         */
        refs = atomic_read(&eb->refs);
        if (refs >= 2 && test_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
                return;

        spin_lock(&eb->refs_lock);
        if (!test_and_set_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
                atomic_inc(&eb->refs);
        spin_unlock(&eb->refs_lock);
}

static void mark_extent_buffer_accessed(struct extent_buffer *eb,
                struct page *accessed)
{
        int num_pages, i;

        check_buffer_tree_ref(eb);

        num_pages = num_extent_pages(eb);
        for (i = 0; i < num_pages; i++) {
                struct page *p = eb->pages[i];

                if (p != accessed)
                        mark_page_accessed(p);
        }
}

struct extent_buffer *find_extent_buffer(struct btrfs_fs_info *fs_info,
                                         u64 start)
{
        struct extent_buffer *eb;

        eb = find_extent_buffer_nolock(fs_info, start);
        if (!eb)
                return NULL;
        /*
         * Lock our eb's refs_lock to avoid races with free_extent_buffer().
         * When we get our eb it might be flagged with EXTENT_BUFFER_STALE and
         * another task running free_extent_buffer() might have seen that flag
         * set, eb->refs == 2, that the buffer isn't under IO (dirty and
         * writeback flags not set) and it's still in the tree (flag
         * EXTENT_BUFFER_TREE_REF set), therefore being in the process of
         * decrementing the extent buffer's reference count twice.  So here we
         * could race and increment the eb's reference count, clear its stale
         * flag, mark it as dirty and drop our reference before the other task
         * finishes executing free_extent_buffer, which would later result in
         * an attempt to free an extent buffer that is dirty.
         */
        if (test_bit(EXTENT_BUFFER_STALE, &eb->bflags)) {
                spin_lock(&eb->refs_lock);
                spin_unlock(&eb->refs_lock);
        }
        mark_extent_buffer_accessed(eb, NULL);
        return eb;
}

#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
struct extent_buffer *alloc_test_extent_buffer(struct btrfs_fs_info *fs_info,
                                        u64 start)
{
        struct extent_buffer *eb, *exists = NULL;
        int ret;

        eb = find_extent_buffer(fs_info, start);
        if (eb)
                return eb;
        eb = alloc_dummy_extent_buffer(fs_info, start);
        if (!eb)
                return ERR_PTR(-ENOMEM);
        eb->fs_info = fs_info;
again:
        ret = radix_tree_preload(GFP_NOFS);
        if (ret) {
                exists = ERR_PTR(ret);
                goto free_eb;
        }
        spin_lock(&fs_info->buffer_lock);
        ret = radix_tree_insert(&fs_info->buffer_radix,
                                start >> fs_info->sectorsize_bits, eb);
        spin_unlock(&fs_info->buffer_lock);
        radix_tree_preload_end();
        if (ret == -EEXIST) {
                exists = find_extent_buffer(fs_info, start);
                if (exists)
                        goto free_eb;
                else
                        goto again;
        }
        check_buffer_tree_ref(eb);
        set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);

        return eb;
free_eb:
        btrfs_release_extent_buffer(eb);
        return exists;
}
#endif

static struct extent_buffer *grab_extent_buffer(
                struct btrfs_fs_info *fs_info, struct page *page)
{
        struct extent_buffer *exists;

        /*
         * For subpage case, we completely rely on radix tree to ensure we
         * don't try to insert two ebs for the same bytenr.  So here we always
         * return NULL and just continue.
         */
        if (fs_info->nodesize < PAGE_SIZE)
                return NULL;

        /* Page not yet attached to an extent buffer */
        if (!PagePrivate(page))
                return NULL;

        /*
         * We could have already allocated an eb for this page and attached one
         * so lets see if we can get a ref on the existing eb, and if we can we
         * know it's good and we can just return that one, else we know we can
         * just overwrite page->private.
         */
        exists = (struct extent_buffer *)page->private;
        if (atomic_inc_not_zero(&exists->refs))
                return exists;

        WARN_ON(PageDirty(page));
        detach_page_private(page);
        return NULL;
}

static int check_eb_alignment(struct btrfs_fs_info *fs_info, u64 start)
{
        if (!IS_ALIGNED(start, fs_info->sectorsize)) {
                btrfs_err(fs_info, "bad tree block start %llu", start);
                return -EINVAL;
        }

        if (fs_info->nodesize < PAGE_SIZE &&
            offset_in_page(start) + fs_info->nodesize > PAGE_SIZE) {
                btrfs_err(fs_info,
                "tree block crosses page boundary, start %llu nodesize %u",
                          start, fs_info->nodesize);
                return -EINVAL;
        }
        if (fs_info->nodesize >= PAGE_SIZE &&
            !PAGE_ALIGNED(start)) {
                btrfs_err(fs_info,
                "tree block is not page aligned, start %llu nodesize %u",
                          start, fs_info->nodesize);
                return -EINVAL;
        }
        return 0;
}

struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
                                          u64 start, u64 owner_root, int level)
{
        unsigned long len = fs_info->nodesize;
        int num_pages;
        int i;
        unsigned long index = start >> PAGE_SHIFT;
        struct extent_buffer *eb;
        struct extent_buffer *exists = NULL;
        struct page *p;
        struct address_space *mapping = fs_info->btree_inode->i_mapping;
        u64 lockdep_owner = owner_root;
        int uptodate = 1;
        int ret;

        if (check_eb_alignment(fs_info, start))
                return ERR_PTR(-EINVAL);

#if BITS_PER_LONG == 32
        if (start >= MAX_LFS_FILESIZE) {
                btrfs_err_rl(fs_info,
                "extent buffer %llu is beyond 32bit page cache limit", start);
                btrfs_err_32bit_limit(fs_info);
                return ERR_PTR(-EOVERFLOW);
        }
        if (start >= BTRFS_32BIT_EARLY_WARN_THRESHOLD)
                btrfs_warn_32bit_limit(fs_info);
#endif

        eb = find_extent_buffer(fs_info, start);
        if (eb)
                return eb;

        eb = __alloc_extent_buffer(fs_info, start, len);
        if (!eb)
                return ERR_PTR(-ENOMEM);

        /*
         * The reloc trees are just snapshots, so we need them to appear to be
         * just like any other fs tree WRT lockdep.
         */
        if (lockdep_owner == BTRFS_TREE_RELOC_OBJECTID)
                lockdep_owner = BTRFS_FS_TREE_OBJECTID;

        btrfs_set_buffer_lockdep_class(lockdep_owner, eb, level);

        num_pages = num_extent_pages(eb);
        for (i = 0; i < num_pages; i++, index++) {
                struct btrfs_subpage *prealloc = NULL;

                p = find_or_create_page(mapping, index, GFP_NOFS|__GFP_NOFAIL);
                if (!p) {
                        exists = ERR_PTR(-ENOMEM);
                        goto free_eb;
                }

                /*
                 * Preallocate page->private for subpage case, so that we won't
                 * allocate memory with private_lock hold.  The memory will be
                 * freed by attach_extent_buffer_page() or freed manually if
                 * we exit earlier.
                 *
                 * Although we have ensured one subpage eb can only have one
                 * page, but it may change in the future for 16K page size
                 * support, so we still preallocate the memory in the loop.
                 */
                if (fs_info->nodesize < PAGE_SIZE) {
                        prealloc = btrfs_alloc_subpage(fs_info, BTRFS_SUBPAGE_METADATA);
                        if (IS_ERR(prealloc)) {
                                ret = PTR_ERR(prealloc);
                                unlock_page(p);
                                put_page(p);
                                exists = ERR_PTR(ret);
                                goto free_eb;
                        }
                }

                spin_lock(&mapping->private_lock);
                exists = grab_extent_buffer(fs_info, p);
                if (exists) {
                        spin_unlock(&mapping->private_lock);
                        unlock_page(p);
                        put_page(p);
                        mark_extent_buffer_accessed(exists, p);
                        btrfs_free_subpage(prealloc);
                        goto free_eb;
                }
                /* Should not fail, as we have preallocated the memory */
                ret = attach_extent_buffer_page(eb, p, prealloc);
                ASSERT(!ret);
                /*
                 * To inform we have extra eb under allocation, so that
                 * detach_extent_buffer_page() won't release the page private
                 * when the eb hasn't yet been inserted into radix tree.
                 *
                 * The ref will be decreased when the eb released the page, in
                 * detach_extent_buffer_page().
                 * Thus needs no special handling in error path.
                 */
                btrfs_page_inc_eb_refs(fs_info, p);
                spin_unlock(&mapping->private_lock);

                WARN_ON(btrfs_page_test_dirty(fs_info, p, eb->start, eb->len));
                eb->pages[i] = p;
                if (!PageUptodate(p))
                        uptodate = 0;

                /*
                 * We can't unlock the pages just yet since the extent buffer
                 * hasn't been properly inserted in the radix tree, this
                 * opens a race with btree_release_folio which can free a page
                 * while we are still filling in all pages for the buffer and
                 * we could crash.
                 */
        }
        if (uptodate)
                set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
again:
        ret = radix_tree_preload(GFP_NOFS);
        if (ret) {
                exists = ERR_PTR(ret);
                goto free_eb;
        }

        spin_lock(&fs_info->buffer_lock);
        ret = radix_tree_insert(&fs_info->buffer_radix,
                                start >> fs_info->sectorsize_bits, eb);
        spin_unlock(&fs_info->buffer_lock);
        radix_tree_preload_end();
        if (ret == -EEXIST) {
                exists = find_extent_buffer(fs_info, start);
                if (exists)
                        goto free_eb;
                else
                        goto again;
        }
        /* add one reference for the tree */
        check_buffer_tree_ref(eb);
        set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);

        /*
         * Now it's safe to unlock the pages because any calls to
         * btree_release_folio will correctly detect that a page belongs to a
         * live buffer and won't free them prematurely.
         */
        for (i = 0; i < num_pages; i++)
                unlock_page(eb->pages[i]);
        return eb;

free_eb:
        WARN_ON(!atomic_dec_and_test(&eb->refs));
        for (i = 0; i < num_pages; i++) {
                if (eb->pages[i])
                        unlock_page(eb->pages[i]);
        }

        btrfs_release_extent_buffer(eb);
        return exists;
}

static inline void btrfs_release_extent_buffer_rcu(struct rcu_head *head)
{
        struct extent_buffer *eb =
                        container_of(head, struct extent_buffer, rcu_head);

        __free_extent_buffer(eb);
}

static int release_extent_buffer(struct extent_buffer *eb)
        __releases(&eb->refs_lock)
{
        lockdep_assert_held(&eb->refs_lock);

        WARN_ON(atomic_read(&eb->refs) == 0);
        if (atomic_dec_and_test(&eb->refs)) {
                if (test_and_clear_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags)) {
                        struct btrfs_fs_info *fs_info = eb->fs_info;

                        spin_unlock(&eb->refs_lock);

                        spin_lock(&fs_info->buffer_lock);
                        radix_tree_delete(&fs_info->buffer_radix,
                                          eb->start >> fs_info->sectorsize_bits);
                        spin_unlock(&fs_info->buffer_lock);
                } else {
                        spin_unlock(&eb->refs_lock);
                }

                btrfs_leak_debug_del_eb(eb);
                /* Should be safe to release our pages at this point */
                btrfs_release_extent_buffer_pages(eb);
#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
                if (unlikely(test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags))) {
                        __free_extent_buffer(eb);
                        return 1;
                }
#endif
                call_rcu(&eb->rcu_head, btrfs_release_extent_buffer_rcu);
                return 1;
        }
        spin_unlock(&eb->refs_lock);

        return 0;
}

void free_extent_buffer(struct extent_buffer *eb)
{
        int refs;
        if (!eb)
                return;

        refs = atomic_read(&eb->refs);
        while (1) {
                if ((!test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags) && refs <= 3)
                    || (test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags) &&
                        refs == 1))
                        break;
                if (atomic_try_cmpxchg(&eb->refs, &refs, refs - 1))
                        return;
        }

        spin_lock(&eb->refs_lock);
        if (atomic_read(&eb->refs) == 2 &&
            test_bit(EXTENT_BUFFER_STALE, &eb->bflags) &&
            !extent_buffer_under_io(eb) &&
            test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
                atomic_dec(&eb->refs);

        /*
         * I know this is terrible, but it's temporary until we stop tracking
         * the uptodate bits and such for the extent buffers.
         */
        release_extent_buffer(eb);
}

void free_extent_buffer_stale(struct extent_buffer *eb)
{
        if (!eb)
                return;

        spin_lock(&eb->refs_lock);
        set_bit(EXTENT_BUFFER_STALE, &eb->bflags);

        if (atomic_read(&eb->refs) == 2 && !extent_buffer_under_io(eb) &&
            test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
                atomic_dec(&eb->refs);
        release_extent_buffer(eb);
}

static void btree_clear_page_dirty(struct page *page)
{
        ASSERT(PageDirty(page));
        ASSERT(PageLocked(page));
        clear_page_dirty_for_io(page);
        xa_lock_irq(&page->mapping->i_pages);
        if (!PageDirty(page))
                __xa_clear_mark(&page->mapping->i_pages,
                                page_index(page), PAGECACHE_TAG_DIRTY);
        xa_unlock_irq(&page->mapping->i_pages);
}

static void clear_subpage_extent_buffer_dirty(const struct extent_buffer *eb)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        struct page *page = eb->pages[0];
        bool last;

        /* btree_clear_page_dirty() needs page locked */
        lock_page(page);
        last = btrfs_subpage_clear_and_test_dirty(fs_info, page, eb->start,
                                                  eb->len);
        if (last)
                btree_clear_page_dirty(page);
        unlock_page(page);
        WARN_ON(atomic_read(&eb->refs) == 0);
}

void btrfs_clear_buffer_dirty(struct btrfs_trans_handle *trans,
                              struct extent_buffer *eb)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        int i;
        int num_pages;
        struct page *page;

        btrfs_assert_tree_write_locked(eb);

        if (trans && btrfs_header_generation(eb) != trans->transid)
                return;

        if (!test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags))
                return;

        percpu_counter_add_batch(&fs_info->dirty_metadata_bytes, -eb->len,
                                 fs_info->dirty_metadata_batch);

        if (eb->fs_info->nodesize < PAGE_SIZE)
                return clear_subpage_extent_buffer_dirty(eb);

        num_pages = num_extent_pages(eb);

        for (i = 0; i < num_pages; i++) {
                page = eb->pages[i];
                if (!PageDirty(page))
                        continue;
                lock_page(page);
                btree_clear_page_dirty(page);
                ClearPageError(page);
                unlock_page(page);
        }
        WARN_ON(atomic_read(&eb->refs) == 0);
}

bool set_extent_buffer_dirty(struct extent_buffer *eb)
{
        int i;
        int num_pages;
        bool was_dirty;

        check_buffer_tree_ref(eb);

        was_dirty = test_and_set_bit(EXTENT_BUFFER_DIRTY, &eb->bflags);

        num_pages = num_extent_pages(eb);
        WARN_ON(atomic_read(&eb->refs) == 0);
        WARN_ON(!test_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags));

        if (!was_dirty) {
                bool subpage = eb->fs_info->nodesize < PAGE_SIZE;

                /*
                 * For subpage case, we can have other extent buffers in the
                 * same page, and in clear_subpage_extent_buffer_dirty() we
                 * have to clear page dirty without subpage lock held.
                 * This can cause race where our page gets dirty cleared after
                 * we just set it.
                 *
                 * Thankfully, clear_subpage_extent_buffer_dirty() has locked
                 * its page for other reasons, we can use page lock to prevent
                 * the above race.
                 */
                if (subpage)
                        lock_page(eb->pages[0]);
                for (i = 0; i < num_pages; i++)
                        btrfs_page_set_dirty(eb->fs_info, eb->pages[i],
                                             eb->start, eb->len);
                if (subpage)
                        unlock_page(eb->pages[0]);
        }
#ifdef CONFIG_BTRFS_DEBUG
        for (i = 0; i < num_pages; i++)
                ASSERT(PageDirty(eb->pages[i]));
#endif

        return was_dirty;
}

void clear_extent_buffer_uptodate(struct extent_buffer *eb)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        struct page *page;
        int num_pages;
        int i;

        clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
        num_pages = num_extent_pages(eb);
        for (i = 0; i < num_pages; i++) {
                page = eb->pages[i];
                if (!page)
                        continue;

                /*
                 * This is special handling for metadata subpage, as regular
                 * btrfs_is_subpage() can not handle cloned/dummy metadata.
                 */
                if (fs_info->nodesize >= PAGE_SIZE)
                        ClearPageUptodate(page);
                else
                        btrfs_subpage_clear_uptodate(fs_info, page, eb->start,
                                                     eb->len);
        }
}

void set_extent_buffer_uptodate(struct extent_buffer *eb)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        struct page *page;
        int num_pages;
        int i;

        set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
        num_pages = num_extent_pages(eb);
        for (i = 0; i < num_pages; i++) {
                page = eb->pages[i];

                /*
                 * This is special handling for metadata subpage, as regular
                 * btrfs_is_subpage() can not handle cloned/dummy metadata.
                 */
                if (fs_info->nodesize >= PAGE_SIZE)
                        SetPageUptodate(page);
                else
                        btrfs_subpage_set_uptodate(fs_info, page, eb->start,
                                                   eb->len);
        }
}

static int read_extent_buffer_subpage(struct extent_buffer *eb, int wait,
                                      int mirror_num,
                                      struct btrfs_tree_parent_check *check)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;
        struct extent_io_tree *io_tree;
        struct page *page = eb->pages[0];
        struct extent_state *cached_state = NULL;
        struct btrfs_bio_ctrl bio_ctrl = {
                .mirror_num = mirror_num,
                .parent_check = check,
        };
        int ret = 0;

        ASSERT(!test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags));
        ASSERT(PagePrivate(page));
        ASSERT(check);
        io_tree = &BTRFS_I(fs_info->btree_inode)->io_tree;

        if (wait == WAIT_NONE) {
                if (!try_lock_extent(io_tree, eb->start, eb->start + eb->len - 1,
                                     &cached_state))
                        return -EAGAIN;
        } else {
                ret = lock_extent(io_tree, eb->start, eb->start + eb->len - 1,
                                  &cached_state);
                if (ret < 0)
                        return ret;
        }

        ret = 0;
        if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags) ||
            PageUptodate(page) ||
            btrfs_subpage_test_uptodate(fs_info, page, eb->start, eb->len)) {
                set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
                unlock_extent(io_tree, eb->start, eb->start + eb->len - 1,
                              &cached_state);
                return ret;
        }

        clear_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags);
        eb->read_mirror = 0;
        atomic_set(&eb->io_pages, 1);
        check_buffer_tree_ref(eb);
        bio_ctrl.end_io_func = end_bio_extent_readpage;

        btrfs_subpage_clear_error(fs_info, page, eb->start, eb->len);

        btrfs_subpage_start_reader(fs_info, page, eb->start, eb->len);
        ret = submit_extent_page(REQ_OP_READ, NULL, &bio_ctrl,
                                 eb->start, page, eb->len,
                                 eb->start - page_offset(page), 0, true);
        if (ret) {
                /*
                 * In the endio function, if we hit something wrong we will
                 * increase the io_pages, so here we need to decrease it for
                 * error path.
                 */
                atomic_dec(&eb->io_pages);
        }
        submit_one_bio(&bio_ctrl);
        if (ret || wait != WAIT_COMPLETE) {
                free_extent_state(cached_state);
                return ret;
        }

        wait_extent_bit(io_tree, eb->start, eb->start + eb->len - 1,
                        EXTENT_LOCKED, &cached_state);
        if (!test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
                ret = -EIO;
        return ret;
}

int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num,
                             struct btrfs_tree_parent_check *check)
{
        int i;
        struct page *page;
        int err;
        int ret = 0;
        int locked_pages = 0;
        int all_uptodate = 1;
        int num_pages;
        unsigned long num_reads = 0;
        struct btrfs_bio_ctrl bio_ctrl = {
                .mirror_num = mirror_num,
                .parent_check = check,
        };

        if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
                return 0;

        /*
         * We could have had EXTENT_BUFFER_UPTODATE cleared by the write
         * operation, which could potentially still be in flight.  In this case
         * we simply want to return an error.
         */
        if (unlikely(test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags)))
                return -EIO;

        if (eb->fs_info->nodesize < PAGE_SIZE)
                return read_extent_buffer_subpage(eb, wait, mirror_num, check);

        num_pages = num_extent_pages(eb);
        for (i = 0; i < num_pages; i++) {
                page = eb->pages[i];
                if (wait == WAIT_NONE) {
                        /*
                         * WAIT_NONE is only utilized by readahead. If we can't
                         * acquire the lock atomically it means either the eb
                         * is being read out or under modification.
                         * Either way the eb will be or has been cached,
                         * readahead can exit safely.
                         */
                        if (!trylock_page(page))
                                goto unlock_exit;
                } else {
                        lock_page(page);
                }
                locked_pages++;
        }
        /*
         * We need to firstly lock all pages to make sure that
         * the uptodate bit of our pages won't be affected by
         * clear_extent_buffer_uptodate().
         */
        for (i = 0; i < num_pages; i++) {
                page = eb->pages[i];
                if (!PageUptodate(page)) {
                        num_reads++;
                        all_uptodate = 0;
                }
        }

        if (all_uptodate) {
                set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
                goto unlock_exit;
        }

        clear_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags);
        eb->read_mirror = 0;
        atomic_set(&eb->io_pages, num_reads);
        /*
         * It is possible for release_folio to clear the TREE_REF bit before we
         * set io_pages. See check_buffer_tree_ref for a more detailed comment.
         */
        check_buffer_tree_ref(eb);
        bio_ctrl.end_io_func = end_bio_extent_readpage;
        for (i = 0; i < num_pages; i++) {
                page = eb->pages[i];

                if (!PageUptodate(page)) {
                        if (ret) {
                                atomic_dec(&eb->io_pages);
                                unlock_page(page);
                                continue;
                        }

                        ClearPageError(page);
                        err = submit_extent_page(REQ_OP_READ, NULL,
                                         &bio_ctrl, page_offset(page), page,
                                         PAGE_SIZE, 0, 0, false);
                        if (err) {
                                /*
                                 * We failed to submit the bio so it's the
                                 * caller's responsibility to perform cleanup
                                 * i.e unlock page/set error bit.
                                 */
                                ret = err;
                                SetPageError(page);
                                unlock_page(page);
                                atomic_dec(&eb->io_pages);
                        }
                } else {
                        unlock_page(page);
                }
        }

        submit_one_bio(&bio_ctrl);

        if (ret || wait != WAIT_COMPLETE)
                return ret;

        for (i = 0; i < num_pages; i++) {
                page = eb->pages[i];
                wait_on_page_locked(page);
                if (!PageUptodate(page))
                        ret = -EIO;
        }

        return ret;

unlock_exit:
        while (locked_pages > 0) {
                locked_pages--;
                page = eb->pages[locked_pages];
                unlock_page(page);
        }
        return ret;
}

static bool report_eb_range(const struct extent_buffer *eb, unsigned long start,
                            unsigned long len)
{
        btrfs_warn(eb->fs_info,
                "access to eb bytenr %llu len %lu out of range start %lu len %lu",
                eb->start, eb->len, start, len);
        WARN_ON(IS_ENABLED(CONFIG_BTRFS_DEBUG));

        return true;
}

/*
 * Check if the [start, start + len) range is valid before reading/writing
 * the eb.
 * NOTE: @start and @len are offset inside the eb, not logical address.
 *
 * Caller should not touch the dst/src memory if this function returns error.
 */
static inline int check_eb_range(const struct extent_buffer *eb,
                                 unsigned long start, unsigned long len)
{
        unsigned long offset;

        /* start, start + len should not go beyond eb->len nor overflow */
        if (unlikely(check_add_overflow(start, len, &offset) || offset > eb->len))
                return report_eb_range(eb, start, len);

        return false;
}

void read_extent_buffer(const struct extent_buffer *eb, void *dstv,
                        unsigned long start, unsigned long len)
{
        size_t cur;
        size_t offset;
        struct page *page;
        char *kaddr;
        char *dst = (char *)dstv;
        unsigned long i = get_eb_page_index(start);

        if (check_eb_range(eb, start, len))
                return;

        offset = get_eb_offset_in_page(eb, start);

        while (len > 0) {
                page = eb->pages[i];

                cur = min(len, (PAGE_SIZE - offset));
                kaddr = page_address(page);
                memcpy(dst, kaddr + offset, cur);

                dst += cur;
                len -= cur;
                offset = 0;
                i++;
        }
}

int read_extent_buffer_to_user_nofault(const struct extent_buffer *eb,
                                       void __user *dstv,
                                       unsigned long start, unsigned long len)
{
        size_t cur;
        size_t offset;
        struct page *page;
        char *kaddr;
        char __user *dst = (char __user *)dstv;
        unsigned long i = get_eb_page_index(start);
        int ret = 0;

        WARN_ON(start > eb->len);
        WARN_ON(start + len > eb->start + eb->len);

        offset = get_eb_offset_in_page(eb, start);

        while (len > 0) {
                page = eb->pages[i];

                cur = min(len, (PAGE_SIZE - offset));
                kaddr = page_address(page);
                if (copy_to_user_nofault(dst, kaddr + offset, cur)) {
                        ret = -EFAULT;
                        break;
                }

                dst += cur;
                len -= cur;
                offset = 0;
                i++;
        }

        return ret;
}

int memcmp_extent_buffer(const struct extent_buffer *eb, const void *ptrv,
                         unsigned long start, unsigned long len)
{
        size_t cur;
        size_t offset;
        struct page *page;
        char *kaddr;
        char *ptr = (char *)ptrv;
        unsigned long i = get_eb_page_index(start);
        int ret = 0;

        if (check_eb_range(eb, start, len))
                return -EINVAL;

        offset = get_eb_offset_in_page(eb, start);

        while (len > 0) {
                page = eb->pages[i];

                cur = min(len, (PAGE_SIZE - offset));

                kaddr = page_address(page);
                ret = memcmp(ptr, kaddr + offset, cur);
                if (ret)
                        break;

                ptr += cur;
                len -= cur;
                offset = 0;
                i++;
        }
        return ret;
}

/*
 * Check that the extent buffer is uptodate.
 *
 * For regular sector size == PAGE_SIZE case, check if @page is uptodate.
 * For subpage case, check if the range covered by the eb has EXTENT_UPTODATE.
 */
static void assert_eb_page_uptodate(const struct extent_buffer *eb,
                                    struct page *page)
{
        struct btrfs_fs_info *fs_info = eb->fs_info;

        /*
         * If we are using the commit root we could potentially clear a page
         * Uptodate while we're using the extent buffer that we've previously
         * looked up.  We don't want to complain in this case, as the page was
         * valid before, we just didn't write it out.  Instead we want to catch
         * the case where we didn't actually read the block properly, which
         * would have !PageUptodate && !PageError, as we clear PageError before
         * reading.
         */
        if (fs_info->nodesize < PAGE_SIZE) {
                bool uptodate, error;

                uptodate = btrfs_subpage_test_uptodate(fs_info, page,
                                                       eb->start, eb->len);
                error = btrfs_subpage_test_error(fs_info, page, eb->start, eb->len);
                WARN_ON(!uptodate && !error);
        } else {
                WARN_ON(!PageUptodate(page) && !PageError(page));
        }
}

void write_extent_buffer_chunk_tree_uuid(const struct extent_buffer *eb,
                const void *srcv)
{
        char *kaddr;

        assert_eb_page_uptodate(eb, eb->pages[0]);
        kaddr = page_address(eb->pages[0]) +
                get_eb_offset_in_page(eb, offsetof(struct btrfs_header,
                                                   chunk_tree_uuid));
        memcpy(kaddr, srcv, BTRFS_FSID_SIZE);
}

void write_extent_buffer_fsid(const struct extent_buffer *eb, const void *srcv)
{
        char *kaddr;

        assert_eb_page_uptodate(eb, eb->pages[0]);
        kaddr = page_address(eb->pages[0]) +
                get_eb_offset_in_page(eb, offsetof(struct btrfs_header, fsid));
        memcpy(kaddr, srcv, BTRFS_FSID_SIZE);
}

void write_extent_buffer(const struct extent_buffer *eb, const void *srcv,
                         unsigned long start, unsigned long len)
{
        size_t cur;
        size_t offset;
        struct page *page;
        char *kaddr;
        char *src = (char *)srcv;
        unsigned long i = get_eb_page_index(start);

        WARN_ON(test_bit(EXTENT_BUFFER_NO_CHECK, &eb->bflags));

        if (check_eb_range(eb, start, len))
                return;

        offset = get_eb_offset_in_page(eb, start);

        while (len > 0) {
                page = eb->pages[i];
                assert_eb_page_uptodate(eb, page);

                cur = min(len, PAGE_SIZE - offset);
                kaddr = page_address(page);
                memcpy(kaddr + offset, src, cur);

                src += cur;
                len -= cur;
                offset = 0;
                i++;
        }
}

void memzero_extent_buffer(const struct extent_buffer *eb, unsigned long start,
                unsigned long len)
{
        size_t cur;
        size_t offset;
        struct page *page;
        char *kaddr;
        unsigned long i = get_eb_page_index(start);

        if (check_eb_range(eb, start, len))
                return;

        offset = get_eb_offset_in_page(eb, start);

        while (len > 0) {
                page = eb->pages[i];
                assert_eb_page_uptodate(eb, page);

                cur = min(len, PAGE_SIZE - offset);
                kaddr = page_address(page);
                memset(kaddr + offset, 0, cur);

                len -= cur;
                offset = 0;
                i++;
        }
}

void copy_extent_buffer_full(const struct extent_buffer *dst,
                             const struct extent_buffer *src)
{
        int i;
        int num_pages;

        ASSERT(dst->len == src->len);

        if (dst->fs_info->nodesize >= PAGE_SIZE) {
                num_pages = num_extent_pages(dst);
                for (i = 0; i < num_pages; i++)
                        copy_page(page_address(dst->pages[i]),
                                  page_address(src->pages[i]));
        } else {
                size_t src_offset = get_eb_offset_in_page(src, 0);
                size_t dst_offset = get_eb_offset_in_page(dst, 0);

                ASSERT(src->fs_info->nodesize < PAGE_SIZE);
                memcpy(page_address(dst->pages[0]) + dst_offset,
                       page_address(src->pages[0]) + src_offset,
                       src->len);
        }
}

void copy_extent_buffer(const struct extent_buffer *dst,
                        const struct extent_buffer *src,
                        unsigned long dst_offset, unsigned long src_offset,
                        unsigned long len)
{
        u64 dst_len = dst->len;
        size_t cur;
        size_t offset;
        struct page *page;
        char *kaddr;
        unsigned long i = get_eb_page_index(dst_offset);

        if (check_eb_range(dst, dst_offset, len) ||
            check_eb_range(src, src_offset, len))
                return;

        WARN_ON(src->len != dst_len);

        offset = get_eb_offset_in_page(dst, dst_offset);

        while (len > 0) {
                page = dst->pages[i];
                assert_eb_page_uptodate(dst, page);

                cur = min(len, (unsigned long)(PAGE_SIZE - offset));

                kaddr = page_address(page);
                read_extent_buffer(src, kaddr + offset, src_offset, cur);

                src_offset += cur;
                len -= cur;
                offset = 0;
                i++;
        }
}

/*
 * eb_bitmap_offset() - calculate the page and offset of the byte containing the
 * given bit number
 * @eb: the extent buffer
 * @start: offset of the bitmap item in the extent buffer
 * @nr: bit number
 * @page_index: return index of the page in the extent buffer that contains the
 * given bit number
 * @page_offset: return offset into the page given by page_index
 *
 * This helper hides the ugliness of finding the byte in an extent buffer which
 * contains a given bit.
 */
static inline void eb_bitmap_offset(const struct extent_buffer *eb,
                                    unsigned long start, unsigned long nr,
                                    unsigned long *page_index,
                                    size_t *page_offset)
{
        size_t byte_offset = BIT_BYTE(nr);
        size_t offset;

        /*
         * The byte we want is the offset of the extent buffer + the offset of
         * the bitmap item in the extent buffer + the offset of the byte in the
         * bitmap item.
         */
        offset = start + offset_in_page(eb->start) + byte_offset;

        *page_index = offset >> PAGE_SHIFT;
        *page_offset = offset_in_page(offset);
}

/*
 * Determine whether a bit in a bitmap item is set.
 *
 * @eb:     the extent buffer
 * @start:  offset of the bitmap item in the extent buffer
 * @nr:     bit number to test
 */
int extent_buffer_test_bit(const struct extent_buffer *eb, unsigned long start,
                           unsigned long nr)
{
        u8 *kaddr;
        struct page *page;
        unsigned long i;
        size_t offset;

        eb_bitmap_offset(eb, start, nr, &i, &offset);
        page = eb->pages[i];
        assert_eb_page_uptodate(eb, page);
        kaddr = page_address(page);
        return 1U & (kaddr[offset] >> (nr & (BITS_PER_BYTE - 1)));
}

/*
 * Set an area of a bitmap to 1.
 *
 * @eb:     the extent buffer
 * @start:  offset of the bitmap item in the extent buffer
 * @pos:    bit number of the first bit
 * @len:    number of bits to set
 */
void extent_buffer_bitmap_set(const struct extent_buffer *eb, unsigned long start,
                              unsigned long pos, unsigned long len)
{
        u8 *kaddr;
        struct page *page;
        unsigned long i;
        size_t offset;
        const unsigned int size = pos + len;
        int bits_to_set = BITS_PER_BYTE - (pos % BITS_PER_BYTE);
        u8 mask_to_set = BITMAP_FIRST_BYTE_MASK(pos);

        eb_bitmap_offset(eb, start, pos, &i, &offset);
        page = eb->pages[i];
        assert_eb_page_uptodate(eb, page);
        kaddr = page_address(page);

        while (len >= bits_to_set) {
                kaddr[offset] |= mask_to_set;
                len -= bits_to_set;
                bits_to_set = BITS_PER_BYTE;
                mask_to_set = ~0;
                if (++offset >= PAGE_SIZE && len > 0) {
                        offset = 0;
                        page = eb->pages[++i];
                        assert_eb_page_uptodate(eb, page);
                        kaddr = page_address(page);
                }
        }
        if (len) {
                mask_to_set &= BITMAP_LAST_BYTE_MASK(size);
                kaddr[offset] |= mask_to_set;
        }
}


/*
 * Clear an area of a bitmap.
 *
 * @eb:     the extent buffer
 * @start:  offset of the bitmap item in the extent buffer
 * @pos:    bit number of the first bit
 * @len:    number of bits to clear
 */
void extent_buffer_bitmap_clear(const struct extent_buffer *eb,
                                unsigned long start, unsigned long pos,
                                unsigned long len)
{
        u8 *kaddr;
        struct page *page;
        unsigned long i;
        size_t offset;
        const unsigned int size = pos + len;
        int bits_to_clear = BITS_PER_BYTE - (pos % BITS_PER_BYTE);
        u8 mask_to_clear = BITMAP_FIRST_BYTE_MASK(pos);

        eb_bitmap_offset(eb, start, pos, &i, &offset);
        page = eb->pages[i];
        assert_eb_page_uptodate(eb, page);
        kaddr = page_address(page);

        while (len >= bits_to_clear) {
                kaddr[offset] &= ~mask_to_clear;
                len -= bits_to_clear;
                bits_to_clear = BITS_PER_BYTE;
                mask_to_clear = ~0;
                if (++offset >= PAGE_SIZE && len > 0) {
                        offset = 0;
                        page = eb->pages[++i];
                        assert_eb_page_uptodate(eb, page);
                        kaddr = page_address(page);
                }
        }
        if (len) {
                mask_to_clear &= BITMAP_LAST_BYTE_MASK(size);
                kaddr[offset] &= ~mask_to_clear;
        }
}

static inline bool areas_overlap(unsigned long src, unsigned long dst, unsigned long len)
{
        unsigned long distance = (src > dst) ? src - dst : dst - src;
        return distance < len;
}

static void copy_pages(struct page *dst_page, struct page *src_page,
                       unsigned long dst_off, unsigned long src_off,
                       unsigned long len)
{
        char *dst_kaddr = page_address(dst_page);
        char *src_kaddr;
        int must_memmove = 0;

        if (dst_page != src_page) {
                src_kaddr = page_address(src_page);
        } else {
                src_kaddr = dst_kaddr;
                if (areas_overlap(src_off, dst_off, len))
                        must_memmove = 1;
        }

        if (must_memmove)
                memmove(dst_kaddr + dst_off, src_kaddr + src_off, len);
        else
                memcpy(dst_kaddr + dst_off, src_kaddr + src_off, len);
}

void memcpy_extent_buffer(const struct extent_buffer *dst,
                          unsigned long dst_offset, unsigned long src_offset,
                          unsigned long len)
{
        size_t cur;
        size_t dst_off_in_page;
        size_t src_off_in_page;
        unsigned long dst_i;
        unsigned long src_i;

        if (check_eb_range(dst, dst_offset, len) ||
            check_eb_range(dst, src_offset, len))
                return;

        while (len > 0) {
                dst_off_in_page = get_eb_offset_in_page(dst, dst_offset);
                src_off_in_page = get_eb_offset_in_page(dst, src_offset);

                dst_i = get_eb_page_index(dst_offset);
                src_i = get_eb_page_index(src_offset);

                cur = min(len, (unsigned long)(PAGE_SIZE -
                                               src_off_in_page));
                cur = min_t(unsigned long, cur,
                        (unsigned long)(PAGE_SIZE - dst_off_in_page));

                copy_pages(dst->pages[dst_i], dst->pages[src_i],
                           dst_off_in_page, src_off_in_page, cur);

                src_offset += cur;
                dst_offset += cur;
                len -= cur;
        }
}

void memmove_extent_buffer(const struct extent_buffer *dst,
                           unsigned long dst_offset, unsigned long src_offset,
                           unsigned long len)
{
        size_t cur;
        size_t dst_off_in_page;
        size_t src_off_in_page;
        unsigned long dst_end = dst_offset + len - 1;
        unsigned long src_end = src_offset + len - 1;
        unsigned long dst_i;
        unsigned long src_i;

        if (check_eb_range(dst, dst_offset, len) ||
            check_eb_range(dst, src_offset, len))
                return;
        if (dst_offset < src_offset) {
                memcpy_extent_buffer(dst, dst_offset, src_offset, len);
                return;
        }
        while (len > 0) {
                dst_i = get_eb_page_index(dst_end);
                src_i = get_eb_page_index(src_end);

                dst_off_in_page = get_eb_offset_in_page(dst, dst_end);
                src_off_in_page = get_eb_offset_in_page(dst, src_end);

                cur = min_t(unsigned long, len, src_off_in_page + 1);
                cur = min(cur, dst_off_in_page + 1);
                copy_pages(dst->pages[dst_i], dst->pages[src_i],
                           dst_off_in_page - cur + 1,
                           src_off_in_page - cur + 1, cur);

                dst_end -= cur;
                src_end -= cur;
                len -= cur;
        }
}

#define GANG_LOOKUP_SIZE        16
static struct extent_buffer *get_next_extent_buffer(
                struct btrfs_fs_info *fs_info, struct page *page, u64 bytenr)
{
        struct extent_buffer *gang[GANG_LOOKUP_SIZE];
        struct extent_buffer *found = NULL;
        u64 page_start = page_offset(page);
        u64 cur = page_start;

        ASSERT(in_range(bytenr, page_start, PAGE_SIZE));
        lockdep_assert_held(&fs_info->buffer_lock);

        while (cur < page_start + PAGE_SIZE) {
                int ret;
                int i;

                ret = radix_tree_gang_lookup(&fs_info->buffer_radix,
                                (void **)gang, cur >> fs_info->sectorsize_bits,
                                min_t(unsigned int, GANG_LOOKUP_SIZE,
                                      PAGE_SIZE / fs_info->nodesize));
                if (ret == 0)
                        goto out;
                for (i = 0; i < ret; i++) {
                        /* Already beyond page end */
                        if (gang[i]->start >= page_start + PAGE_SIZE)
                                goto out;
                        /* Found one */
                        if (gang[i]->start >= bytenr) {
                                found = gang[i];
                                goto out;
                        }
                }
                cur = gang[ret - 1]->start + gang[ret - 1]->len;
        }
out:
        return found;
}

static int try_release_subpage_extent_buffer(struct page *page)
{
        struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
        u64 cur = page_offset(page);
        const u64 end = page_offset(page) + PAGE_SIZE;
        int ret;

        while (cur < end) {
                struct extent_buffer *eb = NULL;

                /*
                 * Unlike try_release_extent_buffer() which uses page->private
                 * to grab buffer, for subpage case we rely on radix tree, thus
                 * we need to ensure radix tree consistency.
                 *
                 * We also want an atomic snapshot of the radix tree, thus go
                 * with spinlock rather than RCU.
                 */
                spin_lock(&fs_info->buffer_lock);
                eb = get_next_extent_buffer(fs_info, page, cur);
                if (!eb) {
                        /* No more eb in the page range after or at cur */
                        spin_unlock(&fs_info->buffer_lock);
                        break;
                }
                cur = eb->start + eb->len;

                /*
                 * The same as try_release_extent_buffer(), to ensure the eb
                 * won't disappear out from under us.
                 */
                spin_lock(&eb->refs_lock);
                if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
                        spin_unlock(&eb->refs_lock);
                        spin_unlock(&fs_info->buffer_lock);
                        break;
                }
                spin_unlock(&fs_info->buffer_lock);

                /*
                 * If tree ref isn't set then we know the ref on this eb is a
                 * real ref, so just return, this eb will likely be freed soon
                 * anyway.
                 */
                if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
                        spin_unlock(&eb->refs_lock);
                        break;
                }

                /*
                 * Here we don't care about the return value, we will always
                 * check the page private at the end.  And
                 * release_extent_buffer() will release the refs_lock.
                 */
                release_extent_buffer(eb);
        }
        /*
         * Finally to check if we have cleared page private, as if we have
         * released all ebs in the page, the page private should be cleared now.
         */
        spin_lock(&page->mapping->private_lock);
        if (!PagePrivate(page))
                ret = 1;
        else
                ret = 0;
        spin_unlock(&page->mapping->private_lock);
        return ret;

}

int try_release_extent_buffer(struct page *page)
{
        struct extent_buffer *eb;

        if (btrfs_sb(page->mapping->host->i_sb)->nodesize < PAGE_SIZE)
                return try_release_subpage_extent_buffer(page);

        /*
         * We need to make sure nobody is changing page->private, as we rely on
         * page->private as the pointer to extent buffer.
         */
        spin_lock(&page->mapping->private_lock);
        if (!PagePrivate(page)) {
                spin_unlock(&page->mapping->private_lock);
                return 1;
        }

        eb = (struct extent_buffer *)page->private;
        BUG_ON(!eb);

        /*
         * This is a little awful but should be ok, we need to make sure that
         * the eb doesn't disappear out from under us while we're looking at
         * this page.
         */
        spin_lock(&eb->refs_lock);
        if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
                spin_unlock(&eb->refs_lock);
                spin_unlock(&page->mapping->private_lock);
                return 0;
        }
        spin_unlock(&page->mapping->private_lock);

        /*
         * If tree ref isn't set then we know the ref on this eb is a real ref,
         * so just return, this page will likely be freed soon anyway.
         */
        if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
                spin_unlock(&eb->refs_lock);
                return 0;
        }

        return release_extent_buffer(eb);
}

/*
 * btrfs_readahead_tree_block - attempt to readahead a child block
 * @fs_info:    the fs_info
 * @bytenr:     bytenr to read
 * @owner_root: objectid of the root that owns this eb
 * @gen:        generation for the uptodate check, can be 0
 * @level:      level for the eb
 *
 * Attempt to readahead a tree block at @bytenr.  If @gen is 0 then we do a
 * normal uptodate check of the eb, without checking the generation.  If we have
 * to read the block we will not block on anything.
 */
void btrfs_readahead_tree_block(struct btrfs_fs_info *fs_info,
                                u64 bytenr, u64 owner_root, u64 gen, int level)
{
        struct btrfs_tree_parent_check check = {
                .has_first_key = 0,
                .level = level,
                .transid = gen
        };
        struct extent_buffer *eb;
        int ret;

        eb = btrfs_find_create_tree_block(fs_info, bytenr, owner_root, level);
        if (IS_ERR(eb))
                return;

        if (btrfs_buffer_uptodate(eb, gen, 1)) {
                free_extent_buffer(eb);
                return;
        }

        ret = read_extent_buffer_pages(eb, WAIT_NONE, 0, &check);
        if (ret < 0)
                free_extent_buffer_stale(eb);
        else
                free_extent_buffer(eb);
}

/*
 * btrfs_readahead_node_child - readahead a node's child block
 * @node:       parent node we're reading from
 * @slot:       slot in the parent node for the child we want to read
 *
 * A helper for btrfs_readahead_tree_block, we simply read the bytenr pointed at
 * the slot in the node provided.
 */
void btrfs_readahead_node_child(struct extent_buffer *node, int slot)
{
        btrfs_readahead_tree_block(node->fs_info,
                                   btrfs_node_blockptr(node, slot),
                                   btrfs_header_owner(node),
                                   btrfs_node_ptr_generation(node, slot),
                                   btrfs_header_level(node) - 1);
}