[linux-2.6-block.git] / fs / splice.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * "splice": joining two ropes together by interweaving their strands.
 *
 * This is the "extended pipe" functionality, where a pipe is used as
 * an arbitrary in-memory buffer. Think of a pipe as a small kernel
 * buffer that you can use to transfer data from one end to the other.
 *
 * The traditional unix read/write is extended with a "splice()" operation
 * that transfers data buffers to or from a pipe buffer.
 *
 * Named by Larry McVoy, original implementation from Linus, extended by
 * Jens to support splicing to files, network, direct splicing, etc and
 * fixing lots of bugs.
 *
 * Copyright (C) 2005-2006 Jens Axboe <axboe@kernel.dk>
 * Copyright (C) 2005-2006 Linus Torvalds <torvalds@osdl.org>
 * Copyright (C) 2006 Ingo Molnar <mingo@elte.hu>
 *
 */
#include <linux/bvec.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/pagemap.h>
#include <linux/splice.h>
#include <linux/memcontrol.h>
#include <linux/mm_inline.h>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/export.h>
#include <linux/syscalls.h>
#include <linux/uio.h>
#include <linux/fsnotify.h>
#include <linux/security.h>
#include <linux/gfp.h>
#include <linux/net.h>
#include <linux/socket.h>
#include <linux/sched/signal.h>

#include "internal.h"

/*
 * Splice doesn't support FMODE_NOWAIT. Since pipes may set this flag to
 * indicate they support non-blocking reads or writes, we must clear it
 * here if set to avoid blocking other users of this pipe if splice is
 * being done on it.
 */
static noinline void pipe_clear_nowait(struct file *file)
{
        fmode_t fmode = READ_ONCE(file->f_mode);

        do {
                if (!(fmode & FMODE_NOWAIT))
                        break;
        } while (!try_cmpxchg(&file->f_mode, &fmode, fmode & ~FMODE_NOWAIT));
}

/*
 * Attempt to steal a page from a pipe buffer. This should perhaps go into
 * a vm helper function, it's already simplified quite a bit by the
 * addition of remove_mapping(). If success is returned, the caller may
 * attempt to reuse this page for another destination.
 */
static bool page_cache_pipe_buf_try_steal(struct pipe_inode_info *pipe,
                struct pipe_buffer *buf)
{
        struct folio *folio = page_folio(buf->page);
        struct address_space *mapping;

        folio_lock(folio);

        mapping = folio_mapping(folio);
        if (mapping) {
                WARN_ON(!folio_test_uptodate(folio));

                /*
                 * At least for ext2 with nobh option, we need to wait on
                 * writeback completing on this folio, since we'll remove it
                 * from the pagecache.  Otherwise truncate wont wait on the
                 * folio, allowing the disk blocks to be reused by someone else
                 * before we actually wrote our data to them. fs corruption
                 * ensues.
                 */
                folio_wait_writeback(folio);

                if (!filemap_release_folio(folio, GFP_KERNEL))
                        goto out_unlock;

                /*
                 * If we succeeded in removing the mapping, set LRU flag
                 * and return good.
                 */
                if (remove_mapping(mapping, folio)) {
                        buf->flags |= PIPE_BUF_FLAG_LRU;
                        return true;
                }
        }

        /*
         * Raced with truncate or failed to remove folio from current
         * address space, unlock and return failure.
         */
out_unlock:
        folio_unlock(folio);
        return false;
}

static void page_cache_pipe_buf_release(struct pipe_inode_info *pipe,
                                        struct pipe_buffer *buf)
{
        put_page(buf->page);
        buf->flags &= ~PIPE_BUF_FLAG_LRU;
}

/*
 * Check whether the contents of buf is OK to access. Since the content
 * is a page cache page, IO may be in flight.
 */
static int page_cache_pipe_buf_confirm(struct pipe_inode_info *pipe,
                                       struct pipe_buffer *buf)
{
        struct folio *folio = page_folio(buf->page);
        int err;

        if (!folio_test_uptodate(folio)) {
                folio_lock(folio);

                /*
                 * Folio got truncated/unhashed. This will cause a 0-byte
                 * splice, if this is the first page.
                 */
                if (!folio->mapping) {
                        err = -ENODATA;
                        goto error;
                }

                /*
                 * Uh oh, read-error from disk.
                 */
                if (!folio_test_uptodate(folio)) {
                        err = -EIO;
                        goto error;
                }

                /* Folio is ok after all, we are done */
                folio_unlock(folio);
        }

        return 0;
error:
        folio_unlock(folio);
        return err;
}

const struct pipe_buf_operations page_cache_pipe_buf_ops = {
        .confirm        = page_cache_pipe_buf_confirm,
        .release        = page_cache_pipe_buf_release,
        .try_steal      = page_cache_pipe_buf_try_steal,
        .get            = generic_pipe_buf_get,
};

static bool user_page_pipe_buf_try_steal(struct pipe_inode_info *pipe,
                struct pipe_buffer *buf)
{
        if (!(buf->flags & PIPE_BUF_FLAG_GIFT))
                return false;

        buf->flags |= PIPE_BUF_FLAG_LRU;
        return generic_pipe_buf_try_steal(pipe, buf);
}

static const struct pipe_buf_operations user_page_pipe_buf_ops = {
        .release        = page_cache_pipe_buf_release,
        .try_steal      = user_page_pipe_buf_try_steal,
        .get            = generic_pipe_buf_get,
};

static void wakeup_pipe_readers(struct pipe_inode_info *pipe)
{
        smp_mb();
        if (waitqueue_active(&pipe->rd_wait))
                wake_up_interruptible(&pipe->rd_wait);
        kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
}

/**
 * splice_to_pipe - fill passed data into a pipe
 * @pipe:       pipe to fill
 * @spd:        data to fill
 *
 * Description:
 *    @spd contains a map of pages and len/offset tuples, along with
 *    the struct pipe_buf_operations associated with these pages. This
 *    function will link that data to the pipe.
 *
 */
ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
                       struct splice_pipe_desc *spd)
{
        unsigned int spd_pages = spd->nr_pages;
        unsigned int tail = pipe->tail;
        unsigned int head = pipe->head;
        ssize_t ret = 0;
        int page_nr = 0;

        if (!spd_pages)
                return 0;

        if (unlikely(!pipe->readers)) {
                send_sig(SIGPIPE, current, 0);
                ret = -EPIPE;
                goto out;
        }

        while (!pipe_full(head, tail, pipe->max_usage)) {
                struct pipe_buffer *buf = pipe_buf(pipe, head);

                buf->page = spd->pages[page_nr];
                buf->offset = spd->partial[page_nr].offset;
                buf->len = spd->partial[page_nr].len;
                buf->private = spd->partial[page_nr].private;
                buf->ops = spd->ops;
                buf->flags = 0;

                head++;
                pipe->head = head;
                page_nr++;
                ret += buf->len;

                if (!--spd->nr_pages)
                        break;
        }

        if (!ret)
                ret = -EAGAIN;

out:
        while (page_nr < spd_pages)
                spd->spd_release(spd, page_nr++);

        return ret;
}
EXPORT_SYMBOL_GPL(splice_to_pipe);

ssize_t add_to_pipe(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
{
        unsigned int head = pipe->head;
        unsigned int tail = pipe->tail;
        int ret;

        if (unlikely(!pipe->readers)) {
                send_sig(SIGPIPE, current, 0);
                ret = -EPIPE;
        } else if (pipe_full(head, tail, pipe->max_usage)) {
                ret = -EAGAIN;
        } else {
                *pipe_buf(pipe, head) = *buf;
                pipe->head = head + 1;
                return buf->len;
        }
        pipe_buf_release(pipe, buf);
        return ret;
}
EXPORT_SYMBOL(add_to_pipe);

/*
 * Check if we need to grow the arrays holding pages and partial page
 * descriptions.
 */
int splice_grow_spd(const struct pipe_inode_info *pipe, struct splice_pipe_desc *spd)
{
        unsigned int max_usage = READ_ONCE(pipe->max_usage);

        spd->nr_pages_max = max_usage;
        if (max_usage <= PIPE_DEF_BUFFERS)
                return 0;

        spd->pages = kmalloc_array(max_usage, sizeof(struct page *), GFP_KERNEL);
        spd->partial = kmalloc_array(max_usage, sizeof(struct partial_page),
                                     GFP_KERNEL);

        if (spd->pages && spd->partial)
                return 0;

        kfree(spd->pages);
        kfree(spd->partial);
        return -ENOMEM;
}

void splice_shrink_spd(struct splice_pipe_desc *spd)
{
        if (spd->nr_pages_max <= PIPE_DEF_BUFFERS)
                return;

        kfree(spd->pages);
        kfree(spd->partial);
}

/**
 * copy_splice_read -  Copy data from a file and splice the copy into a pipe
 * @in: The file to read from
 * @ppos: Pointer to the file position to read from
 * @pipe: The pipe to splice into
 * @len: The amount to splice
 * @flags: The SPLICE_F_* flags
 *
 * This function allocates a bunch of pages sufficient to hold the requested
 * amount of data (but limited by the remaining pipe capacity), passes it to
 * the file's ->read_iter() to read into and then splices the used pages into
 * the pipe.
 *
 * Return: On success, the number of bytes read will be returned and *@ppos
 * will be updated if appropriate; 0 will be returned if there is no more data
 * to be read; -EAGAIN will be returned if the pipe had no space, and some
 * other negative error code will be returned on error.  A short read may occur
 * if the pipe has insufficient space, we reach the end of the data or we hit a
 * hole.
 */
ssize_t copy_splice_read(struct file *in, loff_t *ppos,
                         struct pipe_inode_info *pipe,
                         size_t len, unsigned int flags)
{
        struct iov_iter to;
        struct bio_vec *bv;
        struct kiocb kiocb;
        struct page **pages;
        ssize_t ret;
        size_t used, npages, chunk, remain, keep = 0;
        int i;

        /* Work out how much data we can actually add into the pipe */
        used = pipe_buf_usage(pipe);
        npages = max_t(ssize_t, pipe->max_usage - used, 0);
        len = min_t(size_t, len, npages * PAGE_SIZE);
        npages = DIV_ROUND_UP(len, PAGE_SIZE);

        bv = kzalloc(array_size(npages, sizeof(bv[0])) +
                     array_size(npages, sizeof(struct page *)), GFP_KERNEL);
        if (!bv)
                return -ENOMEM;

        pages = (struct page **)(bv + npages);
        npages = alloc_pages_bulk(GFP_USER, npages, pages);
        if (!npages) {
                kfree(bv);
                return -ENOMEM;
        }

        remain = len = min_t(size_t, len, npages * PAGE_SIZE);

        for (i = 0; i < npages; i++) {
                chunk = min_t(size_t, PAGE_SIZE, remain);
                bv[i].bv_page = pages[i];
                bv[i].bv_offset = 0;
                bv[i].bv_len = chunk;
                remain -= chunk;
        }

        /* Do the I/O */
        iov_iter_bvec(&to, ITER_DEST, bv, npages, len);
        init_sync_kiocb(&kiocb, in);
        kiocb.ki_pos = *ppos;
        ret = in->f_op->read_iter(&kiocb, &to);

        if (ret > 0) {
                keep = DIV_ROUND_UP(ret, PAGE_SIZE);
                *ppos = kiocb.ki_pos;
        }

        /*
         * Callers of ->splice_read() expect -EAGAIN on "can't put anything in
         * there", rather than -EFAULT.
         */
        if (ret == -EFAULT)
                ret = -EAGAIN;

        /* Free any pages that didn't get touched at all. */
        if (keep < npages)
                release_pages(pages + keep, npages - keep);

        /* Push the remaining pages into the pipe. */
        remain = ret;
        for (i = 0; i < keep; i++) {
                struct pipe_buffer *buf = pipe_head_buf(pipe);

                chunk = min_t(size_t, remain, PAGE_SIZE);
                *buf = (struct pipe_buffer) {
                        .ops    = &default_pipe_buf_ops,
                        .page   = bv[i].bv_page,
                        .offset = 0,
                        .len    = chunk,
                };
                pipe->head++;
                remain -= chunk;
        }

        kfree(bv);
        return ret;
}
EXPORT_SYMBOL(copy_splice_read);

const struct pipe_buf_operations default_pipe_buf_ops = {
        .release        = generic_pipe_buf_release,
        .try_steal      = generic_pipe_buf_try_steal,
        .get            = generic_pipe_buf_get,
};

/* Pipe buffer operations for a socket and similar. */
const struct pipe_buf_operations nosteal_pipe_buf_ops = {
        .release        = generic_pipe_buf_release,
        .get            = generic_pipe_buf_get,
};
EXPORT_SYMBOL(nosteal_pipe_buf_ops);

static void wakeup_pipe_writers(struct pipe_inode_info *pipe)
{
        smp_mb();
        if (waitqueue_active(&pipe->wr_wait))
                wake_up_interruptible(&pipe->wr_wait);
        kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
}

/**
 * splice_from_pipe_feed - feed available data from a pipe to a file
 * @pipe:       pipe to splice from
 * @sd:         information to @actor
 * @actor:      handler that splices the data
 *
 * Description:
 *    This function loops over the pipe and calls @actor to do the
 *    actual moving of a single struct pipe_buffer to the desired
 *    destination.  It returns when there's no more buffers left in
 *    the pipe or if the requested number of bytes (@sd->total_len)
 *    have been copied.  It returns a positive number (one) if the
 *    pipe needs to be filled with more data, zero if the required
 *    number of bytes have been copied and -errno on error.
 *
 *    This, together with splice_from_pipe_{begin,end,next}, may be
 *    used to implement the functionality of __splice_from_pipe() when
 *    locking is required around copying the pipe buffers to the
 *    destination.
 */
static int splice_from_pipe_feed(struct pipe_inode_info *pipe, struct splice_desc *sd,
                          splice_actor *actor)
{
        unsigned int head = pipe->head;
        unsigned int tail = pipe->tail;
        int ret;

        while (!pipe_empty(head, tail)) {
                struct pipe_buffer *buf = pipe_buf(pipe, tail);

                sd->len = buf->len;
                if (sd->len > sd->total_len)
                        sd->len = sd->total_len;

                ret = pipe_buf_confirm(pipe, buf);
                if (unlikely(ret)) {
                        if (ret == -ENODATA)
                                ret = 0;
                        return ret;
                }

                ret = actor(pipe, buf, sd);
                if (ret <= 0)
                        return ret;

                buf->offset += ret;
                buf->len -= ret;

                sd->num_spliced += ret;
                sd->len -= ret;
                sd->pos += ret;
                sd->total_len -= ret;

                if (!buf->len) {
                        pipe_buf_release(pipe, buf);
                        tail++;
                        pipe->tail = tail;
                        if (pipe->files)
                                sd->need_wakeup = true;
                }

                if (!sd->total_len)
                        return 0;
        }

        return 1;
}

/* We know we have a pipe buffer, but maybe it's empty? */
static inline bool eat_empty_buffer(struct pipe_inode_info *pipe)
{
        unsigned int tail = pipe->tail;
        struct pipe_buffer *buf = pipe_buf(pipe, tail);

        if (unlikely(!buf->len)) {
                pipe_buf_release(pipe, buf);
                pipe->tail = tail+1;
                return true;
        }

        return false;
}

/**
 * splice_from_pipe_next - wait for some data to splice from
 * @pipe:       pipe to splice from
 * @sd:         information about the splice operation
 *
 * Description:
 *    This function will wait for some data and return a positive
 *    value (one) if pipe buffers are available.  It will return zero
 *    or -errno if no more data needs to be spliced.
 */
static int splice_from_pipe_next(struct pipe_inode_info *pipe, struct splice_desc *sd)
{
        /*
         * Check for signal early to make process killable when there are
         * always buffers available
         */
        if (signal_pending(current))
                return -ERESTARTSYS;

repeat:
        while (pipe_is_empty(pipe)) {
                if (!pipe->writers)
                        return 0;

                if (sd->num_spliced)
                        return 0;

                if (sd->flags & SPLICE_F_NONBLOCK)
                        return -EAGAIN;

                if (signal_pending(current))
                        return -ERESTARTSYS;

                if (sd->need_wakeup) {
                        wakeup_pipe_writers(pipe);
                        sd->need_wakeup = false;
                }

                pipe_wait_readable(pipe);
        }

        if (eat_empty_buffer(pipe))
                goto repeat;

        return 1;
}

/**
 * splice_from_pipe_begin - start splicing from pipe
 * @sd:         information about the splice operation
 *
 * Description:
 *    This function should be called before a loop containing
 *    splice_from_pipe_next() and splice_from_pipe_feed() to
 *    initialize the necessary fields of @sd.
 */
static void splice_from_pipe_begin(struct splice_desc *sd)
{
        sd->num_spliced = 0;
        sd->need_wakeup = false;
}

/**
 * splice_from_pipe_end - finish splicing from pipe
 * @pipe:       pipe to splice from
 * @sd:         information about the splice operation
 *
 * Description:
 *    This function will wake up pipe writers if necessary.  It should
 *    be called after a loop containing splice_from_pipe_next() and
 *    splice_from_pipe_feed().
 */
static void splice_from_pipe_end(struct pipe_inode_info *pipe, struct splice_desc *sd)
{
        if (sd->need_wakeup)
                wakeup_pipe_writers(pipe);
}

/**
 * __splice_from_pipe - splice data from a pipe to given actor
 * @pipe:       pipe to splice from
 * @sd:         information to @actor
 * @actor:      handler that splices the data
 *
 * Description:
 *    This function does little more than loop over the pipe and call
 *    @actor to do the actual moving of a single struct pipe_buffer to
 *    the desired destination. See pipe_to_file, pipe_to_sendmsg, or
 *    pipe_to_user.
 *
 */
ssize_t __splice_from_pipe(struct pipe_inode_info *pipe, struct splice_desc *sd,
                           splice_actor *actor)
{
        int ret;

        splice_from_pipe_begin(sd);
        do {
                cond_resched();
                ret = splice_from_pipe_next(pipe, sd);
                if (ret > 0)
                        ret = splice_from_pipe_feed(pipe, sd, actor);
        } while (ret > 0);
        splice_from_pipe_end(pipe, sd);

        return sd->num_spliced ? sd->num_spliced : ret;
}
EXPORT_SYMBOL(__splice_from_pipe);

/**
 * splice_from_pipe - splice data from a pipe to a file
 * @pipe:       pipe to splice from
 * @out:        file to splice to
 * @ppos:       position in @out
 * @len:        how many bytes to splice
 * @flags:      splice modifier flags
 * @actor:      handler that splices the data
 *
 * Description:
 *    See __splice_from_pipe. This function locks the pipe inode,
 *    otherwise it's identical to __splice_from_pipe().
 *
 */
ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
                         loff_t *ppos, size_t len, unsigned int flags,
                         splice_actor *actor)
{
        ssize_t ret;
        struct splice_desc sd = {
                .total_len = len,
                .flags = flags,
                .pos = *ppos,
                .u.file = out,
        };

        pipe_lock(pipe);
        ret = __splice_from_pipe(pipe, &sd, actor);
        pipe_unlock(pipe);

        return ret;
}

/**
 * iter_file_splice_write - splice data from a pipe to a file
 * @pipe:       pipe info
 * @out:        file to write to
 * @ppos:       position in @out
 * @len:        number of bytes to splice
 * @flags:      splice modifier flags
 *
 * Description:
 *    Will either move or copy pages (determined by @flags options) from
 *    the given pipe inode to the given file.
 *    This one is ->write_iter-based.
 *
 */
ssize_t
iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
                          loff_t *ppos, size_t len, unsigned int flags)
{
        struct splice_desc sd = {
                .total_len = len,
                .flags = flags,
                .pos = *ppos,
                .u.file = out,
        };
        int nbufs = pipe->max_usage;
        struct bio_vec *array;
        ssize_t ret;

        if (!out->f_op->write_iter)
                return -EINVAL;

        array = kcalloc(nbufs, sizeof(struct bio_vec), GFP_KERNEL);
        if (unlikely(!array))
                return -ENOMEM;

        pipe_lock(pipe);

        splice_from_pipe_begin(&sd);
        while (sd.total_len) {
                struct kiocb kiocb;
                struct iov_iter from;
                unsigned int head, tail;
                size_t left;
                int n;

                ret = splice_from_pipe_next(pipe, &sd);
                if (ret <= 0)
                        break;

                if (unlikely(nbufs < pipe->max_usage)) {
                        kfree(array);
                        nbufs = pipe->max_usage;
                        array = kcalloc(nbufs, sizeof(struct bio_vec),
                                        GFP_KERNEL);
                        if (!array) {
                                ret = -ENOMEM;
                                break;
                        }
                }

                head = pipe->head;
                tail = pipe->tail;

                /* build the vector */
                left = sd.total_len;
                for (n = 0; !pipe_empty(head, tail) && left && n < nbufs; tail++) {
                        struct pipe_buffer *buf = pipe_buf(pipe, tail);
                        size_t this_len = buf->len;

                        /* zero-length bvecs are not supported, skip them */
                        if (!this_len)
                                continue;
                        this_len = min(this_len, left);

                        ret = pipe_buf_confirm(pipe, buf);
                        if (unlikely(ret)) {
                                if (ret == -ENODATA)
                                        ret = 0;
                                goto done;
                        }

                        bvec_set_page(&array[n], buf->page, this_len,
                                      buf->offset);
                        left -= this_len;
                        n++;
                }

                iov_iter_bvec(&from, ITER_SOURCE, array, n, sd.total_len - left);
                init_sync_kiocb(&kiocb, out);
                kiocb.ki_pos = sd.pos;
                ret = out->f_op->write_iter(&kiocb, &from);
                sd.pos = kiocb.ki_pos;
                if (ret <= 0)
                        break;

                sd.num_spliced += ret;
                sd.total_len -= ret;
                *ppos = sd.pos;

                /* dismiss the fully eaten buffers, adjust the partial one */
                tail = pipe->tail;
                while (ret) {
                        struct pipe_buffer *buf = pipe_buf(pipe, tail);
                        if (ret >= buf->len) {
                                ret -= buf->len;
                                buf->len = 0;
                                pipe_buf_release(pipe, buf);
                                tail++;
                                pipe->tail = tail;
                                if (pipe->files)
                                        sd.need_wakeup = true;
                        } else {
                                buf->offset += ret;
                                buf->len -= ret;
                                ret = 0;
                        }
                }
        }
done:
        kfree(array);
        splice_from_pipe_end(pipe, &sd);

        pipe_unlock(pipe);

        if (sd.num_spliced)
                ret = sd.num_spliced;

        return ret;
}

EXPORT_SYMBOL(iter_file_splice_write);

#ifdef CONFIG_NET
/**
 * splice_to_socket - splice data from a pipe to a socket
 * @pipe:       pipe to splice from
 * @out:        socket to write to
 * @ppos:       position in @out
 * @len:        number of bytes to splice
 * @flags:      splice modifier flags
 *
 * Description:
 *    Will send @len bytes from the pipe to a network socket. No data copying
 *    is involved.
 *
 */
ssize_t splice_to_socket(struct pipe_inode_info *pipe, struct file *out,
                         loff_t *ppos, size_t len, unsigned int flags)
{
        struct socket *sock = sock_from_file(out);
        struct bio_vec bvec[16];
        struct msghdr msg = {};
        ssize_t ret = 0;
        size_t spliced = 0;
        bool need_wakeup = false;

        pipe_lock(pipe);

        while (len > 0) {
                unsigned int head, tail, bc = 0;
                size_t remain = len;

                /*
                 * Check for signal early to make process killable when there
                 * are always buffers available
                 */
                ret = -ERESTARTSYS;
                if (signal_pending(current))
                        break;

                while (pipe_is_empty(pipe)) {
                        ret = 0;
                        if (!pipe->writers)
                                goto out;

                        if (spliced)
                                goto out;

                        ret = -EAGAIN;
                        if (flags & SPLICE_F_NONBLOCK)
                                goto out;

                        ret = -ERESTARTSYS;
                        if (signal_pending(current))
                                goto out;

                        if (need_wakeup) {
                                wakeup_pipe_writers(pipe);
                                need_wakeup = false;
                        }

                        pipe_wait_readable(pipe);
                }

                head = pipe->head;
                tail = pipe->tail;

                while (!pipe_empty(head, tail)) {
                        struct pipe_buffer *buf = pipe_buf(pipe, tail);
                        size_t seg;

                        if (!buf->len) {
                                tail++;
                                continue;
                        }

                        seg = min_t(size_t, remain, buf->len);

                        ret = pipe_buf_confirm(pipe, buf);
                        if (unlikely(ret)) {
                                if (ret == -ENODATA)
                                        ret = 0;
                                break;
                        }

                        bvec_set_page(&bvec[bc++], buf->page, seg, buf->offset);
                        remain -= seg;
                        if (remain == 0 || bc >= ARRAY_SIZE(bvec))
                                break;
                        tail++;
                }

                if (!bc)
                        break;

                msg.msg_flags = MSG_SPLICE_PAGES;
                if (flags & SPLICE_F_MORE)
                        msg.msg_flags |= MSG_MORE;
                if (remain && pipe_occupancy(pipe->head, tail) > 0)
                        msg.msg_flags |= MSG_MORE;
                if (out->f_flags & O_NONBLOCK)
                        msg.msg_flags |= MSG_DONTWAIT;

                iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, bvec, bc,
                              len - remain);
                ret = sock_sendmsg(sock, &msg);
                if (ret <= 0)
                        break;

                spliced += ret;
                len -= ret;
                tail = pipe->tail;
                while (ret > 0) {
                        struct pipe_buffer *buf = pipe_buf(pipe, tail);
                        size_t seg = min_t(size_t, ret, buf->len);

                        buf->offset += seg;
                        buf->len -= seg;
                        ret -= seg;

                        if (!buf->len) {
                                pipe_buf_release(pipe, buf);
                                tail++;
                        }
                }

                if (tail != pipe->tail) {
                        pipe->tail = tail;
                        if (pipe->files)
                                need_wakeup = true;
                }
        }

out:
        pipe_unlock(pipe);
        if (need_wakeup)
                wakeup_pipe_writers(pipe);
        return spliced ?: ret;
}
#endif

static int warn_unsupported(struct file *file, const char *op)
{
        pr_debug_ratelimited(
                "splice %s not supported for file %pD4 (pid: %d comm: %.20s)\n",
                op, file, current->pid, current->comm);
        return -EINVAL;
}

/*
 * Attempt to initiate a splice from pipe to file.
 */
static ssize_t do_splice_from(struct pipe_inode_info *pipe, struct file *out,
                              loff_t *ppos, size_t len, unsigned int flags)
{
        if (unlikely(!out->f_op->splice_write))
                return warn_unsupported(out, "write");
        return out->f_op->splice_write(pipe, out, ppos, len, flags);
}

/*
 * Indicate to the caller that there was a premature EOF when reading from the
 * source and the caller didn't indicate they would be sending more data after
 * this.
 */
static void do_splice_eof(struct splice_desc *sd)
{
        if (sd->splice_eof)
                sd->splice_eof(sd);
}

/*
 * Callers already called rw_verify_area() on the entire range.
 * No need to call it for sub ranges.
 */
static ssize_t do_splice_read(struct file *in, loff_t *ppos,
                              struct pipe_inode_info *pipe, size_t len,
                              unsigned int flags)
{
        unsigned int p_space;

        if (unlikely(!(in->f_mode & FMODE_READ)))
                return -EBADF;
        if (!len)
                return 0;

        /* Don't try to read more the pipe has space for. */
        p_space = pipe->max_usage - pipe_buf_usage(pipe);
        len = min_t(size_t, len, p_space << PAGE_SHIFT);

        if (unlikely(len > MAX_RW_COUNT))
                len = MAX_RW_COUNT;

        if (unlikely(!in->f_op->splice_read))
                return warn_unsupported(in, "read");
        /*
         * O_DIRECT and DAX don't deal with the pagecache, so we allocate a
         * buffer, copy into it and splice that into the pipe.
         */
        if ((in->f_flags & O_DIRECT) || IS_DAX(in->f_mapping->host))
                return copy_splice_read(in, ppos, pipe, len, flags);
        return in->f_op->splice_read(in, ppos, pipe, len, flags);
}

/**
 * vfs_splice_read - Read data from a file and splice it into a pipe
 * @in:         File to splice from
 * @ppos:       Input file offset
 * @pipe:       Pipe to splice to
 * @len:        Number of bytes to splice
 * @flags:      Splice modifier flags (SPLICE_F_*)
 *
 * Splice the requested amount of data from the input file to the pipe.  This
 * is synchronous as the caller must hold the pipe lock across the entire
 * operation.
 *
 * If successful, it returns the amount of data spliced, 0 if it hit the EOF or
 * a hole and a negative error code otherwise.
 */
ssize_t vfs_splice_read(struct file *in, loff_t *ppos,
                        struct pipe_inode_info *pipe, size_t len,
                        unsigned int flags)
{
        ssize_t ret;

        ret = rw_verify_area(READ, in, ppos, len);
        if (unlikely(ret < 0))
                return ret;

        return do_splice_read(in, ppos, pipe, len, flags);
}
EXPORT_SYMBOL_GPL(vfs_splice_read);

/**
 * splice_direct_to_actor - splices data directly between two non-pipes
 * @in:         file to splice from
 * @sd:         actor information on where to splice to
 * @actor:      handles the data splicing
 *
 * Description:
 *    This is a special case helper to splice directly between two
 *    points, without requiring an explicit pipe. Internally an allocated
 *    pipe is cached in the process, and reused during the lifetime of
 *    that process.
 *
 */
ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
                               splice_direct_actor *actor)
{
        struct pipe_inode_info *pipe;
        ssize_t ret, bytes;
        size_t len;
        int i, flags, more;

        /*
         * We require the input to be seekable, as we don't want to randomly
         * drop data for eg socket -> socket splicing. Use the piped splicing
         * for that!
         */
        if (unlikely(!(in->f_mode & FMODE_LSEEK)))
                return -EINVAL;

        /*
         * neither in nor out is a pipe, setup an internal pipe attached to
         * 'out' and transfer the wanted data from 'in' to 'out' through that
         */
        pipe = current->splice_pipe;
        if (unlikely(!pipe)) {
                pipe = alloc_pipe_info();
                if (!pipe)
                        return -ENOMEM;

                /*
                 * We don't have an immediate reader, but we'll read the stuff
                 * out of the pipe right after the splice_to_pipe(). So set
                 * PIPE_READERS appropriately.
                 */
                pipe->readers = 1;

                current->splice_pipe = pipe;
        }

        /*
         * Do the splice.
         */
        bytes = 0;
        len = sd->total_len;

        /* Don't block on output, we have to drain the direct pipe. */
        flags = sd->flags;
        sd->flags &= ~SPLICE_F_NONBLOCK;

        /*
         * We signal MORE until we've read sufficient data to fulfill the
         * request and we keep signalling it if the caller set it.
         */
        more = sd->flags & SPLICE_F_MORE;
        sd->flags |= SPLICE_F_MORE;

        WARN_ON_ONCE(!pipe_is_empty(pipe));

        while (len) {
                size_t read_len;
                loff_t pos = sd->pos, prev_pos = pos;

                ret = do_splice_read(in, &pos, pipe, len, flags);
                if (unlikely(ret <= 0))
                        goto read_failure;

                read_len = ret;
                sd->total_len = read_len;

                /*
                 * If we now have sufficient data to fulfill the request then
                 * we clear SPLICE_F_MORE if it was not set initially.
                 */
                if (read_len >= len && !more)
                        sd->flags &= ~SPLICE_F_MORE;

                /*
                 * NOTE: nonblocking mode only applies to the input. We
                 * must not do the output in nonblocking mode as then we
                 * could get stuck data in the internal pipe:
                 */
                ret = actor(pipe, sd);
                if (unlikely(ret <= 0)) {
                        sd->pos = prev_pos;
                        goto out_release;
                }

                bytes += ret;
                len -= ret;
                sd->pos = pos;

                if (ret < read_len) {
                        sd->pos = prev_pos + ret;
                        goto out_release;
                }
        }

done:
        pipe->tail = pipe->head = 0;
        file_accessed(in);
        return bytes;

read_failure:
        /*
         * If the user did *not* set SPLICE_F_MORE *and* we didn't hit that
         * "use all of len" case that cleared SPLICE_F_MORE, *and* we did a
         * "->splice_in()" that returned EOF (ie zero) *and* we have sent at
         * least 1 byte *then* we will also do the ->splice_eof() call.
         */
        if (ret == 0 && !more && len > 0 && bytes)
                do_splice_eof(sd);
out_release:
        /*
         * If we did an incomplete transfer we must release
         * the pipe buffers in question:
         */
        for (i = 0; i < pipe->ring_size; i++) {
                struct pipe_buffer *buf = &pipe->bufs[i];

                if (buf->ops)
                        pipe_buf_release(pipe, buf);
        }

        if (!bytes)
                bytes = ret;

        goto done;
}
EXPORT_SYMBOL(splice_direct_to_actor);

static int direct_splice_actor(struct pipe_inode_info *pipe,
                               struct splice_desc *sd)
{
        struct file *file = sd->u.file;
        long ret;

        file_start_write(file);
        ret = do_splice_from(pipe, file, sd->opos, sd->total_len, sd->flags);
        file_end_write(file);
        return ret;
}

static int splice_file_range_actor(struct pipe_inode_info *pipe,
                                        struct splice_desc *sd)
{
        struct file *file = sd->u.file;

        return do_splice_from(pipe, file, sd->opos, sd->total_len, sd->flags);
}

static void direct_file_splice_eof(struct splice_desc *sd)
{
        struct file *file = sd->u.file;

        if (file->f_op->splice_eof)
                file->f_op->splice_eof(file);
}

static ssize_t do_splice_direct_actor(struct file *in, loff_t *ppos,
                                      struct file *out, loff_t *opos,
                                      size_t len, unsigned int flags,
                                      splice_direct_actor *actor)
{
        struct splice_desc sd = {
                .len            = len,
                .total_len      = len,
                .flags          = flags,
                .pos            = *ppos,
                .u.file         = out,
                .splice_eof     = direct_file_splice_eof,
                .opos           = opos,
        };
        ssize_t ret;

        if (unlikely(!(out->f_mode & FMODE_WRITE)))
                return -EBADF;

        if (unlikely(out->f_flags & O_APPEND))
                return -EINVAL;

        ret = splice_direct_to_actor(in, &sd, actor);
        if (ret > 0)
                *ppos = sd.pos;

        return ret;
}
/**
 * do_splice_direct - splices data directly between two files
 * @in:         file to splice from
 * @ppos:       input file offset
 * @out:        file to splice to
 * @opos:       output file offset
 * @len:        number of bytes to splice
 * @flags:      splice modifier flags
 *
 * Description:
 *    For use by do_sendfile(). splice can easily emulate sendfile, but
 *    doing it in the application would incur an extra system call
 *    (splice in + splice out, as compared to just sendfile()). So this helper
 *    can splice directly through a process-private pipe.
 *
 * Callers already called rw_verify_area() on the entire range.
 */
ssize_t do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
                         loff_t *opos, size_t len, unsigned int flags)
{
        return do_splice_direct_actor(in, ppos, out, opos, len, flags,
                                      direct_splice_actor);
}
EXPORT_SYMBOL(do_splice_direct);

/**
 * splice_file_range - splices data between two files for copy_file_range()
 * @in:         file to splice from
 * @ppos:       input file offset
 * @out:        file to splice to
 * @opos:       output file offset
 * @len:        number of bytes to splice
 *
 * Description:
 *    For use by ->copy_file_range() methods.
 *    Like do_splice_direct(), but vfs_copy_file_range() already holds
 *    start_file_write() on @out file.
 *
 * Callers already called rw_verify_area() on the entire range.
 */
ssize_t splice_file_range(struct file *in, loff_t *ppos, struct file *out,
                          loff_t *opos, size_t len)
{
        lockdep_assert(file_write_started(out));

        return do_splice_direct_actor(in, ppos, out, opos,
                                      min_t(size_t, len, MAX_RW_COUNT),
                                      0, splice_file_range_actor);
}
EXPORT_SYMBOL(splice_file_range);

static int wait_for_space(struct pipe_inode_info *pipe, unsigned flags)
{
        for (;;) {
                if (unlikely(!pipe->readers)) {
                        send_sig(SIGPIPE, current, 0);
                        return -EPIPE;
                }
                if (!pipe_is_full(pipe))
                        return 0;
                if (flags & SPLICE_F_NONBLOCK)
                        return -EAGAIN;
                if (signal_pending(current))
                        return -ERESTARTSYS;
                pipe_wait_writable(pipe);
        }
}

static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
                               struct pipe_inode_info *opipe,
                               size_t len, unsigned int flags);

ssize_t splice_file_to_pipe(struct file *in,
                            struct pipe_inode_info *opipe,
                            loff_t *offset,
                            size_t len, unsigned int flags)
{
        ssize_t ret;

        pipe_lock(opipe);
        ret = wait_for_space(opipe, flags);
        if (!ret)
                ret = do_splice_read(in, offset, opipe, len, flags);
        pipe_unlock(opipe);
        if (ret > 0)
                wakeup_pipe_readers(opipe);
        return ret;
}

/*
 * Determine where to splice to/from.
 */
ssize_t do_splice(struct file *in, loff_t *off_in, struct file *out,
                  loff_t *off_out, size_t len, unsigned int flags)
{
        struct pipe_inode_info *ipipe;
        struct pipe_inode_info *opipe;
        loff_t offset;
        ssize_t ret;

        if (unlikely(!(in->f_mode & FMODE_READ) ||
                     !(out->f_mode & FMODE_WRITE)))
                return -EBADF;

        ipipe = get_pipe_info(in, true);
        opipe = get_pipe_info(out, true);

        if (ipipe && opipe) {
                if (off_in || off_out)
                        return -ESPIPE;

                /* Splicing to self would be fun, but... */
                if (ipipe == opipe)
                        return -EINVAL;

                if ((in->f_flags | out->f_flags) & O_NONBLOCK)
                        flags |= SPLICE_F_NONBLOCK;

                ret = splice_pipe_to_pipe(ipipe, opipe, len, flags);
        } else if (ipipe) {
                if (off_in)
                        return -ESPIPE;
                if (off_out) {
                        if (!(out->f_mode & FMODE_PWRITE))
                                return -EINVAL;
                        offset = *off_out;
                } else {
                        offset = out->f_pos;
                }

                if (unlikely(out->f_flags & O_APPEND))
                        return -EINVAL;

                ret = rw_verify_area(WRITE, out, &offset, len);
                if (unlikely(ret < 0))
                        return ret;

                if (in->f_flags & O_NONBLOCK)
                        flags |= SPLICE_F_NONBLOCK;

                file_start_write(out);
                ret = do_splice_from(ipipe, out, &offset, len, flags);
                file_end_write(out);

                if (!off_out)
                        out->f_pos = offset;
                else
                        *off_out = offset;
        } else if (opipe) {
                if (off_out)
                        return -ESPIPE;
                if (off_in) {
                        if (!(in->f_mode & FMODE_PREAD))
                                return -EINVAL;
                        offset = *off_in;
                } else {
                        offset = in->f_pos;
                }

                ret = rw_verify_area(READ, in, &offset, len);
                if (unlikely(ret < 0))
                        return ret;

                if (out->f_flags & O_NONBLOCK)
                        flags |= SPLICE_F_NONBLOCK;

                ret = splice_file_to_pipe(in, opipe, &offset, len, flags);

                if (!off_in)
                        in->f_pos = offset;
                else
                        *off_in = offset;
        } else {
                ret = -EINVAL;
        }

        if (ret > 0) {
                /*
                 * Generate modify out before access in:
                 * do_splice_from() may've already sent modify out,
                 * and this ensures the events get merged.
                 */
                fsnotify_modify(out);
                fsnotify_access(in);
        }

        return ret;
}

static ssize_t __do_splice(struct file *in, loff_t __user *off_in,
                           struct file *out, loff_t __user *off_out,
                           size_t len, unsigned int flags)
{
        struct pipe_inode_info *ipipe;
        struct pipe_inode_info *opipe;
        loff_t offset, *__off_in = NULL, *__off_out = NULL;
        ssize_t ret;

        ipipe = get_pipe_info(in, true);
        opipe = get_pipe_info(out, true);

        if (ipipe) {
                if (off_in)
                        return -ESPIPE;
                pipe_clear_nowait(in);
        }
        if (opipe) {
                if (off_out)
                        return -ESPIPE;
                pipe_clear_nowait(out);
        }

        if (off_out) {
                if (copy_from_user(&offset, off_out, sizeof(loff_t)))
                        return -EFAULT;
                __off_out = &offset;
        }
        if (off_in) {
                if (copy_from_user(&offset, off_in, sizeof(loff_t)))
                        return -EFAULT;
                __off_in = &offset;
        }

        ret = do_splice(in, __off_in, out, __off_out, len, flags);
        if (ret < 0)
                return ret;

        if (__off_out && copy_to_user(off_out, __off_out, sizeof(loff_t)))
                return -EFAULT;
        if (__off_in && copy_to_user(off_in, __off_in, sizeof(loff_t)))
                return -EFAULT;

        return ret;
}

static ssize_t iter_to_pipe(struct iov_iter *from,
                            struct pipe_inode_info *pipe,
                            unsigned int flags)
{
        struct pipe_buffer buf = {
                .ops = &user_page_pipe_buf_ops,
                .flags = flags
        };
        size_t total = 0;
        ssize_t ret = 0;

        while (iov_iter_count(from)) {
                struct page *pages[16];
                ssize_t left;
                size_t start;
                int i, n;

                left = iov_iter_get_pages2(from, pages, ~0UL, 16, &start);
                if (left <= 0) {
                        ret = left;
                        break;
                }

                n = DIV_ROUND_UP(left + start, PAGE_SIZE);
                for (i = 0; i < n; i++) {
                        int size = min_t(int, left, PAGE_SIZE - start);

                        buf.page = pages[i];
                        buf.offset = start;
                        buf.len = size;
                        ret = add_to_pipe(pipe, &buf);
                        if (unlikely(ret < 0)) {
                                iov_iter_revert(from, left);
                                // this one got dropped by add_to_pipe()
                                while (++i < n)
                                        put_page(pages[i]);
                                goto out;
                        }
                        total += ret;
                        left -= size;
                        start = 0;
                }
        }
out:
        return total ? total : ret;
}

static int pipe_to_user(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
                        struct splice_desc *sd)
{
        int n = copy_page_to_iter(buf->page, buf->offset, sd->len, sd->u.data);
        return n == sd->len ? n : -EFAULT;
}

/*
 * For lack of a better implementation, implement vmsplice() to userspace
 * as a simple copy of the pipes pages to the user iov.
 */
static ssize_t vmsplice_to_user(struct file *file, struct iov_iter *iter,
                                unsigned int flags)
{
        struct pipe_inode_info *pipe = get_pipe_info(file, true);
        struct splice_desc sd = {
                .total_len = iov_iter_count(iter),
                .flags = flags,
                .u.data = iter
        };
        ssize_t ret = 0;

        if (!pipe)
                return -EBADF;

        pipe_clear_nowait(file);

        if (sd.total_len) {
                pipe_lock(pipe);
                ret = __splice_from_pipe(pipe, &sd, pipe_to_user);
                pipe_unlock(pipe);
        }

        if (ret > 0)
                fsnotify_access(file);

        return ret;
}

/*
 * vmsplice splices a user address range into a pipe. It can be thought of
 * as splice-from-memory, where the regular splice is splice-from-file (or
 * to file). In both cases the output is a pipe, naturally.
 */
static ssize_t vmsplice_to_pipe(struct file *file, struct iov_iter *iter,
                                unsigned int flags)
{
        struct pipe_inode_info *pipe;
        ssize_t ret = 0;
        unsigned buf_flag = 0;

        if (flags & SPLICE_F_GIFT)
                buf_flag = PIPE_BUF_FLAG_GIFT;

        pipe = get_pipe_info(file, true);
        if (!pipe)
                return -EBADF;

        pipe_clear_nowait(file);

        pipe_lock(pipe);
        ret = wait_for_space(pipe, flags);
        if (!ret)
                ret = iter_to_pipe(iter, pipe, buf_flag);
        pipe_unlock(pipe);
        if (ret > 0) {
                wakeup_pipe_readers(pipe);
                fsnotify_modify(file);
        }
        return ret;
}

/*
 * Note that vmsplice only really supports true splicing _from_ user memory
 * to a pipe, not the other way around. Splicing from user memory is a simple
 * operation that can be supported without any funky alignment restrictions
 * or nasty vm tricks. We simply map in the user memory and fill them into
 * a pipe. The reverse isn't quite as easy, though. There are two possible
 * solutions for that:
 *
 *      - memcpy() the data internally, at which point we might as well just
 *        do a regular read() on the buffer anyway.
 *      - Lots of nasty vm tricks, that are neither fast nor flexible (it
 *        has restriction limitations on both ends of the pipe).
 *
 * Currently we punt and implement it as a normal copy, see pipe_to_user().
 *
 */
SYSCALL_DEFINE4(vmsplice, int, fd, const struct iovec __user *, uiov,
                unsigned long, nr_segs, unsigned int, flags)
{
        struct iovec iovstack[UIO_FASTIOV];
        struct iovec *iov = iovstack;
        struct iov_iter iter;
        ssize_t error;
        int type;

        if (unlikely(flags & ~SPLICE_F_ALL))
                return -EINVAL;

        CLASS(fd, f)(fd);
        if (fd_empty(f))
                return -EBADF;
        if (fd_file(f)->f_mode & FMODE_WRITE)
                type = ITER_SOURCE;
        else if (fd_file(f)->f_mode & FMODE_READ)
                type = ITER_DEST;
        else
                return -EBADF;

        error = import_iovec(type, uiov, nr_segs,
                             ARRAY_SIZE(iovstack), &iov, &iter);
        if (error < 0)
                return error;

        if (!iov_iter_count(&iter))
                error = 0;
        else if (type == ITER_SOURCE)
                error = vmsplice_to_pipe(fd_file(f), &iter, flags);
        else
                error = vmsplice_to_user(fd_file(f), &iter, flags);

        kfree(iov);
        return error;
}

SYSCALL_DEFINE6(splice, int, fd_in, loff_t __user *, off_in,
                int, fd_out, loff_t __user *, off_out,
                size_t, len, unsigned int, flags)
{
        if (unlikely(!len))
                return 0;

        if (unlikely(flags & ~SPLICE_F_ALL))
                return -EINVAL;

        CLASS(fd, in)(fd_in);
        if (fd_empty(in))
                return -EBADF;

        CLASS(fd, out)(fd_out);
        if (fd_empty(out))
                return -EBADF;

        return __do_splice(fd_file(in), off_in, fd_file(out), off_out,
                                            len, flags);
}

/*
 * Make sure there's data to read. Wait for input if we can, otherwise
 * return an appropriate error.
 */
static int ipipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
{
        int ret;

        /*
         * Check the pipe occupancy without the inode lock first. This function
         * is speculative anyways, so missing one is ok.
         */
        if (!pipe_is_empty(pipe))
                return 0;

        ret = 0;
        pipe_lock(pipe);

        while (pipe_is_empty(pipe)) {
                if (signal_pending(current)) {
                        ret = -ERESTARTSYS;
                        break;
                }
                if (!pipe->writers)
                        break;
                if (flags & SPLICE_F_NONBLOCK) {
                        ret = -EAGAIN;
                        break;
                }
                pipe_wait_readable(pipe);
        }

        pipe_unlock(pipe);
        return ret;
}

/*
 * Make sure there's writeable room. Wait for room if we can, otherwise
 * return an appropriate error.
 */
static int opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
{
        int ret;

        /*
         * Check pipe occupancy without the inode lock first. This function
         * is speculative anyways, so missing one is ok.
         */
        if (!pipe_is_full(pipe))
                return 0;

        ret = 0;
        pipe_lock(pipe);

        while (pipe_is_full(pipe)) {
                if (!pipe->readers) {
                        send_sig(SIGPIPE, current, 0);
                        ret = -EPIPE;
                        break;
                }
                if (flags & SPLICE_F_NONBLOCK) {
                        ret = -EAGAIN;
                        break;
                }
                if (signal_pending(current)) {
                        ret = -ERESTARTSYS;
                        break;
                }
                pipe_wait_writable(pipe);
        }

        pipe_unlock(pipe);
        return ret;
}

/*
 * Splice contents of ipipe to opipe.
 */
static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
                               struct pipe_inode_info *opipe,
                               size_t len, unsigned int flags)
{
        struct pipe_buffer *ibuf, *obuf;
        unsigned int i_head, o_head;
        unsigned int i_tail, o_tail;
        int ret = 0;
        bool input_wakeup = false;


retry:
        ret = ipipe_prep(ipipe, flags);
        if (ret)
                return ret;

        ret = opipe_prep(opipe, flags);
        if (ret)
                return ret;

        /*
         * Potential ABBA deadlock, work around it by ordering lock
         * grabbing by pipe info address. Otherwise two different processes
         * could deadlock (one doing tee from A -> B, the other from B -> A).
         */
        pipe_double_lock(ipipe, opipe);

        i_tail = ipipe->tail;
        o_head = opipe->head;

        do {
                size_t o_len;

                if (!opipe->readers) {
                        send_sig(SIGPIPE, current, 0);
                        if (!ret)
                                ret = -EPIPE;
                        break;
                }

                i_head = ipipe->head;
                o_tail = opipe->tail;

                if (pipe_empty(i_head, i_tail) && !ipipe->writers)
                        break;

                /*
                 * Cannot make any progress, because either the input
                 * pipe is empty or the output pipe is full.
                 */
                if (pipe_empty(i_head, i_tail) ||
                    pipe_full(o_head, o_tail, opipe->max_usage)) {
                        /* Already processed some buffers, break */
                        if (ret)
                                break;

                        if (flags & SPLICE_F_NONBLOCK) {
                                ret = -EAGAIN;
                                break;
                        }

                        /*
                         * We raced with another reader/writer and haven't
                         * managed to process any buffers.  A zero return
                         * value means EOF, so retry instead.
                         */
                        pipe_unlock(ipipe);
                        pipe_unlock(opipe);
                        goto retry;
                }

                ibuf = pipe_buf(ipipe, i_tail);
                obuf = pipe_buf(opipe, o_head);

                if (len >= ibuf->len) {
                        /*
                         * Simply move the whole buffer from ipipe to opipe
                         */
                        *obuf = *ibuf;
                        ibuf->ops = NULL;
                        i_tail++;
                        ipipe->tail = i_tail;
                        input_wakeup = true;
                        o_len = obuf->len;
                        o_head++;
                        opipe->head = o_head;
                } else {
                        /*
                         * Get a reference to this pipe buffer,
                         * so we can copy the contents over.
                         */
                        if (!pipe_buf_get(ipipe, ibuf)) {
                                if (ret == 0)
                                        ret = -EFAULT;
                                break;
                        }
                        *obuf = *ibuf;

                        /*
                         * Don't inherit the gift and merge flags, we need to
                         * prevent multiple steals of this page.
                         */
                        obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
                        obuf->flags &= ~PIPE_BUF_FLAG_CAN_MERGE;

                        obuf->len = len;
                        ibuf->offset += len;
                        ibuf->len -= len;
                        o_len = len;
                        o_head++;
                        opipe->head = o_head;
                }
                ret += o_len;
                len -= o_len;
        } while (len);

        pipe_unlock(ipipe);
        pipe_unlock(opipe);

        /*
         * If we put data in the output pipe, wakeup any potential readers.
         */
        if (ret > 0)
                wakeup_pipe_readers(opipe);

        if (input_wakeup)
                wakeup_pipe_writers(ipipe);

        return ret;
}

/*
 * Link contents of ipipe to opipe.
 */
static ssize_t link_pipe(struct pipe_inode_info *ipipe,
                         struct pipe_inode_info *opipe,
                         size_t len, unsigned int flags)
{
        struct pipe_buffer *ibuf, *obuf;
        unsigned int i_head, o_head;
        unsigned int i_tail, o_tail;
        ssize_t ret = 0;

        /*
         * Potential ABBA deadlock, work around it by ordering lock
         * grabbing by pipe info address. Otherwise two different processes
         * could deadlock (one doing tee from A -> B, the other from B -> A).
         */
        pipe_double_lock(ipipe, opipe);

        i_tail = ipipe->tail;
        o_head = opipe->head;

        do {
                if (!opipe->readers) {
                        send_sig(SIGPIPE, current, 0);
                        if (!ret)
                                ret = -EPIPE;
                        break;
                }

                i_head = ipipe->head;
                o_tail = opipe->tail;

                /*
                 * If we have iterated all input buffers or run out of
                 * output room, break.
                 */
                if (pipe_empty(i_head, i_tail) ||
                    pipe_full(o_head, o_tail, opipe->max_usage))
                        break;

                ibuf = pipe_buf(ipipe, i_tail);
                obuf = pipe_buf(opipe, o_head);

                /*
                 * Get a reference to this pipe buffer,
                 * so we can copy the contents over.
                 */
                if (!pipe_buf_get(ipipe, ibuf)) {
                        if (ret == 0)
                                ret = -EFAULT;
                        break;
                }

                *obuf = *ibuf;

                /*
                 * Don't inherit the gift and merge flag, we need to prevent
                 * multiple steals of this page.
                 */
                obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
                obuf->flags &= ~PIPE_BUF_FLAG_CAN_MERGE;

                if (obuf->len > len)
                        obuf->len = len;
                ret += obuf->len;
                len -= obuf->len;

                o_head++;
                opipe->head = o_head;
                i_tail++;
        } while (len);

        pipe_unlock(ipipe);
        pipe_unlock(opipe);

        /*
         * If we put data in the output pipe, wakeup any potential readers.
         */
        if (ret > 0)
                wakeup_pipe_readers(opipe);

        return ret;
}

/*
 * This is a tee(1) implementation that works on pipes. It doesn't copy
 * any data, it simply references the 'in' pages on the 'out' pipe.
 * The 'flags' used are the SPLICE_F_* variants, currently the only
 * applicable one is SPLICE_F_NONBLOCK.
 */
ssize_t do_tee(struct file *in, struct file *out, size_t len,
               unsigned int flags)
{
        struct pipe_inode_info *ipipe = get_pipe_info(in, true);
        struct pipe_inode_info *opipe = get_pipe_info(out, true);
        ssize_t ret = -EINVAL;

        if (unlikely(!(in->f_mode & FMODE_READ) ||
                     !(out->f_mode & FMODE_WRITE)))
                return -EBADF;

        /*
         * Duplicate the contents of ipipe to opipe without actually
         * copying the data.
         */
        if (ipipe && opipe && ipipe != opipe) {
                if ((in->f_flags | out->f_flags) & O_NONBLOCK)
                        flags |= SPLICE_F_NONBLOCK;

                /*
                 * Keep going, unless we encounter an error. The ipipe/opipe
                 * ordering doesn't really matter.
                 */
                ret = ipipe_prep(ipipe, flags);
                if (!ret) {
                        ret = opipe_prep(opipe, flags);
                        if (!ret)
                                ret = link_pipe(ipipe, opipe, len, flags);
                }
        }

        if (ret > 0) {
                fsnotify_access(in);
                fsnotify_modify(out);
        }

        return ret;
}

SYSCALL_DEFINE4(tee, int, fdin, int, fdout, size_t, len, unsigned int, flags)
{
        if (unlikely(flags & ~SPLICE_F_ALL))
                return -EINVAL;

        if (unlikely(!len))
                return 0;

        CLASS(fd, in)(fdin);
        if (fd_empty(in))
                return -EBADF;

        CLASS(fd, out)(fdout);
        if (fd_empty(out))
                return -EBADF;

        return do_tee(fd_file(in), fd_file(out), len, flags);
}