block: Abstract out bvec iterator

[linux-2.6-block.git] / drivers / md / raid10.c

/*
 * raid10.c : Multiple Devices driver for Linux
 *
 * Copyright (C) 2000-2004 Neil Brown
 *
 * RAID-10 support for md.
 *
 * Base on code in raid1.c.  See raid1.c for further copyright information.
 *
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * You should have received a copy of the GNU General Public License
 * (for example /usr/src/linux/COPYING); if not, write to the Free
 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <linux/slab.h>
#include <linux/delay.h>
#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/seq_file.h>
#include <linux/ratelimit.h>
#include <linux/kthread.h>
#include "md.h"
#include "raid10.h"
#include "raid0.h"
#include "bitmap.h"

/*
 * RAID10 provides a combination of RAID0 and RAID1 functionality.
 * The layout of data is defined by
 *    chunk_size
 *    raid_disks
 *    near_copies (stored in low byte of layout)
 *    far_copies (stored in second byte of layout)
 *    far_offset (stored in bit 16 of layout )
 *    use_far_sets (stored in bit 17 of layout )
 *
 * The data to be stored is divided into chunks using chunksize.  Each device
 * is divided into far_copies sections.   In each section, chunks are laid out
 * in a style similar to raid0, but near_copies copies of each chunk is stored
 * (each on a different drive).  The starting device for each section is offset
 * near_copies from the starting device of the previous section.  Thus there
 * are (near_copies * far_copies) of each chunk, and each is on a different
 * drive.  near_copies and far_copies must be at least one, and their product
 * is at most raid_disks.
 *
 * If far_offset is true, then the far_copies are handled a bit differently.
 * The copies are still in different stripes, but instead of being very far
 * apart on disk, there are adjacent stripes.
 *
 * The far and offset algorithms are handled slightly differently if
 * 'use_far_sets' is true.  In this case, the array's devices are grouped into
 * sets that are (near_copies * far_copies) in size.  The far copied stripes
 * are still shifted by 'near_copies' devices, but this shifting stays confined
 * to the set rather than the entire array.  This is done to improve the number
 * of device combinations that can fail without causing the array to fail.
 * Example 'far' algorithm w/o 'use_far_sets' (each letter represents a chunk
 * on a device):
 *    A B C D    A B C D E
 *      ...         ...
 *    D A B C    E A B C D
 * Example 'far' algorithm w/ 'use_far_sets' enabled (sets illustrated w/ []'s):
 *    [A B] [C D]    [A B] [C D E]
 *    |...| |...|    |...| | ... |
 *    [B A] [D C]    [B A] [E C D]
 */

/*
 * Number of guaranteed r10bios in case of extreme VM load:
 */
#define NR_RAID10_BIOS 256

/* when we get a read error on a read-only array, we redirect to another
 * device without failing the first device, or trying to over-write to
 * correct the read error.  To keep track of bad blocks on a per-bio
 * level, we store IO_BLOCKED in the appropriate 'bios' pointer
 */
#define IO_BLOCKED ((struct bio *)1)
/* When we successfully write to a known bad-block, we need to remove the
 * bad-block marking which must be done from process context.  So we record
 * the success by setting devs[n].bio to IO_MADE_GOOD
 */
#define IO_MADE_GOOD ((struct bio *)2)

#define BIO_SPECIAL(bio) ((unsigned long)bio <= 2)

/* When there are this many requests queued to be written by
 * the raid10 thread, we become 'congested' to provide back-pressure
 * for writeback.
 */
static int max_queued_requests = 1024;

static void allow_barrier(struct r10conf *conf);
static void lower_barrier(struct r10conf *conf);
static int _enough(struct r10conf *conf, int previous, int ignore);
static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr,
                                int *skipped);
static void reshape_request_write(struct mddev *mddev, struct r10bio *r10_bio);
static void end_reshape_write(struct bio *bio, int error);
static void end_reshape(struct r10conf *conf);

static void * r10bio_pool_alloc(gfp_t gfp_flags, void *data)
{
        struct r10conf *conf = data;
        int size = offsetof(struct r10bio, devs[conf->copies]);

        /* allocate a r10bio with room for raid_disks entries in the
         * bios array */
        return kzalloc(size, gfp_flags);
}

static void r10bio_pool_free(void *r10_bio, void *data)
{
        kfree(r10_bio);
}

/* Maximum size of each resync request */
#define RESYNC_BLOCK_SIZE (64*1024)
#define RESYNC_PAGES ((RESYNC_BLOCK_SIZE + PAGE_SIZE-1) / PAGE_SIZE)
/* amount of memory to reserve for resync requests */
#define RESYNC_WINDOW (1024*1024)
/* maximum number of concurrent requests, memory permitting */
#define RESYNC_DEPTH (32*1024*1024/RESYNC_BLOCK_SIZE)

/*
 * When performing a resync, we need to read and compare, so
 * we need as many pages are there are copies.
 * When performing a recovery, we need 2 bios, one for read,
 * one for write (we recover only one drive per r10buf)
 *
 */
static void * r10buf_pool_alloc(gfp_t gfp_flags, void *data)
{
        struct r10conf *conf = data;
        struct page *page;
        struct r10bio *r10_bio;
        struct bio *bio;
        int i, j;
        int nalloc;

        r10_bio = r10bio_pool_alloc(gfp_flags, conf);
        if (!r10_bio)
                return NULL;

        if (test_bit(MD_RECOVERY_SYNC, &conf->mddev->recovery) ||
            test_bit(MD_RECOVERY_RESHAPE, &conf->mddev->recovery))
                nalloc = conf->copies; /* resync */
        else
                nalloc = 2; /* recovery */

        /*
         * Allocate bios.
         */
        for (j = nalloc ; j-- ; ) {
                bio = bio_kmalloc(gfp_flags, RESYNC_PAGES);
                if (!bio)
                        goto out_free_bio;
                r10_bio->devs[j].bio = bio;
                if (!conf->have_replacement)
                        continue;
                bio = bio_kmalloc(gfp_flags, RESYNC_PAGES);
                if (!bio)
                        goto out_free_bio;
                r10_bio->devs[j].repl_bio = bio;
        }
        /*
         * Allocate RESYNC_PAGES data pages and attach them
         * where needed.
         */
        for (j = 0 ; j < nalloc; j++) {
                struct bio *rbio = r10_bio->devs[j].repl_bio;
                bio = r10_bio->devs[j].bio;
                for (i = 0; i < RESYNC_PAGES; i++) {
                        if (j > 0 && !test_bit(MD_RECOVERY_SYNC,
                                               &conf->mddev->recovery)) {
                                /* we can share bv_page's during recovery
                                 * and reshape */
                                struct bio *rbio = r10_bio->devs[0].bio;
                                page = rbio->bi_io_vec[i].bv_page;
                                get_page(page);
                        } else
                                page = alloc_page(gfp_flags);
                        if (unlikely(!page))
                                goto out_free_pages;

                        bio->bi_io_vec[i].bv_page = page;
                        if (rbio)
                                rbio->bi_io_vec[i].bv_page = page;
                }
        }

        return r10_bio;

out_free_pages:
        for ( ; i > 0 ; i--)
                safe_put_page(bio->bi_io_vec[i-1].bv_page);
        while (j--)
                for (i = 0; i < RESYNC_PAGES ; i++)
                        safe_put_page(r10_bio->devs[j].bio->bi_io_vec[i].bv_page);
        j = 0;
out_free_bio:
        for ( ; j < nalloc; j++) {
                if (r10_bio->devs[j].bio)
                        bio_put(r10_bio->devs[j].bio);
                if (r10_bio->devs[j].repl_bio)
                        bio_put(r10_bio->devs[j].repl_bio);
        }
        r10bio_pool_free(r10_bio, conf);
        return NULL;
}

static void r10buf_pool_free(void *__r10_bio, void *data)
{
        int i;
        struct r10conf *conf = data;
        struct r10bio *r10bio = __r10_bio;
        int j;

        for (j=0; j < conf->copies; j++) {
                struct bio *bio = r10bio->devs[j].bio;
                if (bio) {
                        for (i = 0; i < RESYNC_PAGES; i++) {
                                safe_put_page(bio->bi_io_vec[i].bv_page);
                                bio->bi_io_vec[i].bv_page = NULL;
                        }
                        bio_put(bio);
                }
                bio = r10bio->devs[j].repl_bio;
                if (bio)
                        bio_put(bio);
        }
        r10bio_pool_free(r10bio, conf);
}

static void put_all_bios(struct r10conf *conf, struct r10bio *r10_bio)
{
        int i;

        for (i = 0; i < conf->copies; i++) {
                struct bio **bio = & r10_bio->devs[i].bio;
                if (!BIO_SPECIAL(*bio))
                        bio_put(*bio);
                *bio = NULL;
                bio = &r10_bio->devs[i].repl_bio;
                if (r10_bio->read_slot < 0 && !BIO_SPECIAL(*bio))
                        bio_put(*bio);
                *bio = NULL;
        }
}

static void free_r10bio(struct r10bio *r10_bio)
{
        struct r10conf *conf = r10_bio->mddev->private;

        put_all_bios(conf, r10_bio);
        mempool_free(r10_bio, conf->r10bio_pool);
}

static void put_buf(struct r10bio *r10_bio)
{
        struct r10conf *conf = r10_bio->mddev->private;

        mempool_free(r10_bio, conf->r10buf_pool);

        lower_barrier(conf);
}

static void reschedule_retry(struct r10bio *r10_bio)
{
        unsigned long flags;
        struct mddev *mddev = r10_bio->mddev;
        struct r10conf *conf = mddev->private;

        spin_lock_irqsave(&conf->device_lock, flags);
        list_add(&r10_bio->retry_list, &conf->retry_list);
        conf->nr_queued ++;
        spin_unlock_irqrestore(&conf->device_lock, flags);

        /* wake up frozen array... */
        wake_up(&conf->wait_barrier);

        md_wakeup_thread(mddev->thread);
}

/*
 * raid_end_bio_io() is called when we have finished servicing a mirrored
 * operation and are ready to return a success/failure code to the buffer
 * cache layer.
 */
static void raid_end_bio_io(struct r10bio *r10_bio)
{
        struct bio *bio = r10_bio->master_bio;
        int done;
        struct r10conf *conf = r10_bio->mddev->private;

        if (bio->bi_phys_segments) {
                unsigned long flags;
                spin_lock_irqsave(&conf->device_lock, flags);
                bio->bi_phys_segments--;
                done = (bio->bi_phys_segments == 0);
                spin_unlock_irqrestore(&conf->device_lock, flags);
        } else
                done = 1;
        if (!test_bit(R10BIO_Uptodate, &r10_bio->state))
                clear_bit(BIO_UPTODATE, &bio->bi_flags);
        if (done) {
                bio_endio(bio, 0);
                /*
                 * Wake up any possible resync thread that waits for the device
                 * to go idle.
                 */
                allow_barrier(conf);
        }
        free_r10bio(r10_bio);
}

/*
 * Update disk head position estimator based on IRQ completion info.
 */
static inline void update_head_pos(int slot, struct r10bio *r10_bio)
{
        struct r10conf *conf = r10_bio->mddev->private;

        conf->mirrors[r10_bio->devs[slot].devnum].head_position =
                r10_bio->devs[slot].addr + (r10_bio->sectors);
}

/*
 * Find the disk number which triggered given bio
 */
static int find_bio_disk(struct r10conf *conf, struct r10bio *r10_bio,
                         struct bio *bio, int *slotp, int *replp)
{
        int slot;
        int repl = 0;

        for (slot = 0; slot < conf->copies; slot++) {
                if (r10_bio->devs[slot].bio == bio)
                        break;
                if (r10_bio->devs[slot].repl_bio == bio) {
                        repl = 1;
                        break;
                }
        }

        BUG_ON(slot == conf->copies);
        update_head_pos(slot, r10_bio);

        if (slotp)
                *slotp = slot;
        if (replp)
                *replp = repl;
        return r10_bio->devs[slot].devnum;
}

static void raid10_end_read_request(struct bio *bio, int error)
{
        int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
        struct r10bio *r10_bio = bio->bi_private;
        int slot, dev;
        struct md_rdev *rdev;
        struct r10conf *conf = r10_bio->mddev->private;


        slot = r10_bio->read_slot;
        dev = r10_bio->devs[slot].devnum;
        rdev = r10_bio->devs[slot].rdev;
        /*
         * this branch is our 'one mirror IO has finished' event handler:
         */
        update_head_pos(slot, r10_bio);

        if (uptodate) {
                /*
                 * Set R10BIO_Uptodate in our master bio, so that
                 * we will return a good error code to the higher
                 * levels even if IO on some other mirrored buffer fails.
                 *
                 * The 'master' represents the composite IO operation to
                 * user-side. So if something waits for IO, then it will
                 * wait for the 'master' bio.
                 */
                set_bit(R10BIO_Uptodate, &r10_bio->state);
        } else {
                /* If all other devices that store this block have
                 * failed, we want to return the error upwards rather
                 * than fail the last device.  Here we redefine
                 * "uptodate" to mean "Don't want to retry"
                 */
                if (!_enough(conf, test_bit(R10BIO_Previous, &r10_bio->state),
                             rdev->raid_disk))
                        uptodate = 1;
        }
        if (uptodate) {
                raid_end_bio_io(r10_bio);
                rdev_dec_pending(rdev, conf->mddev);
        } else {
                /*
                 * oops, read error - keep the refcount on the rdev
                 */
                char b[BDEVNAME_SIZE];
                printk_ratelimited(KERN_ERR
                                   "md/raid10:%s: %s: rescheduling sector %llu\n",
                                   mdname(conf->mddev),
                                   bdevname(rdev->bdev, b),
                                   (unsigned long long)r10_bio->sector);
                set_bit(R10BIO_ReadError, &r10_bio->state);
                reschedule_retry(r10_bio);
        }
}

static void close_write(struct r10bio *r10_bio)
{
        /* clear the bitmap if all writes complete successfully */
        bitmap_endwrite(r10_bio->mddev->bitmap, r10_bio->sector,
                        r10_bio->sectors,
                        !test_bit(R10BIO_Degraded, &r10_bio->state),
                        0);
        md_write_end(r10_bio->mddev);
}

static void one_write_done(struct r10bio *r10_bio)
{
        if (atomic_dec_and_test(&r10_bio->remaining)) {
                if (test_bit(R10BIO_WriteError, &r10_bio->state))
                        reschedule_retry(r10_bio);
                else {
                        close_write(r10_bio);
                        if (test_bit(R10BIO_MadeGood, &r10_bio->state))
                                reschedule_retry(r10_bio);
                        else
                                raid_end_bio_io(r10_bio);
                }
        }
}

static void raid10_end_write_request(struct bio *bio, int error)
{
        int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
        struct r10bio *r10_bio = bio->bi_private;
        int dev;
        int dec_rdev = 1;
        struct r10conf *conf = r10_bio->mddev->private;
        int slot, repl;
        struct md_rdev *rdev = NULL;

        dev = find_bio_disk(conf, r10_bio, bio, &slot, &repl);

        if (repl)
                rdev = conf->mirrors[dev].replacement;
        if (!rdev) {
                smp_rmb();
                repl = 0;
                rdev = conf->mirrors[dev].rdev;
        }
        /*
         * this branch is our 'one mirror IO has finished' event handler:
         */
        if (!uptodate) {
                if (repl)
                        /* Never record new bad blocks to replacement,
                         * just fail it.
                         */
                        md_error(rdev->mddev, rdev);
                else {
                        set_bit(WriteErrorSeen, &rdev->flags);
                        if (!test_and_set_bit(WantReplacement, &rdev->flags))
                                set_bit(MD_RECOVERY_NEEDED,
                                        &rdev->mddev->recovery);
                        set_bit(R10BIO_WriteError, &r10_bio->state);
                        dec_rdev = 0;
                }
        } else {
                /*
                 * Set R10BIO_Uptodate in our master bio, so that
                 * we will return a good error code for to the higher
                 * levels even if IO on some other mirrored buffer fails.
                 *
                 * The 'master' represents the composite IO operation to
                 * user-side. So if something waits for IO, then it will
                 * wait for the 'master' bio.
                 */
                sector_t first_bad;
                int bad_sectors;

                /*
                 * Do not set R10BIO_Uptodate if the current device is
                 * rebuilding or Faulty. This is because we cannot use
                 * such device for properly reading the data back (we could
                 * potentially use it, if the current write would have felt
                 * before rdev->recovery_offset, but for simplicity we don't
                 * check this here.
                 */
                if (test_bit(In_sync, &rdev->flags) &&
                    !test_bit(Faulty, &rdev->flags))
                        set_bit(R10BIO_Uptodate, &r10_bio->state);

                /* Maybe we can clear some bad blocks. */
                if (is_badblock(rdev,
                                r10_bio->devs[slot].addr,
                                r10_bio->sectors,
                                &first_bad, &bad_sectors)) {
                        bio_put(bio);
                        if (repl)
                                r10_bio->devs[slot].repl_bio = IO_MADE_GOOD;
                        else
                                r10_bio->devs[slot].bio = IO_MADE_GOOD;
                        dec_rdev = 0;
                        set_bit(R10BIO_MadeGood, &r10_bio->state);
                }
        }

        /*
         *
         * Let's see if all mirrored write operations have finished
         * already.
         */
        one_write_done(r10_bio);
        if (dec_rdev)
                rdev_dec_pending(rdev, conf->mddev);
}

/*
 * RAID10 layout manager
 * As well as the chunksize and raid_disks count, there are two
 * parameters: near_copies and far_copies.
 * near_copies * far_copies must be <= raid_disks.
 * Normally one of these will be 1.
 * If both are 1, we get raid0.
 * If near_copies == raid_disks, we get raid1.
 *
 * Chunks are laid out in raid0 style with near_copies copies of the
 * first chunk, followed by near_copies copies of the next chunk and
 * so on.
 * If far_copies > 1, then after 1/far_copies of the array has been assigned
 * as described above, we start again with a device offset of near_copies.
 * So we effectively have another copy of the whole array further down all
 * the drives, but with blocks on different drives.
 * With this layout, and block is never stored twice on the one device.
 *
 * raid10_find_phys finds the sector offset of a given virtual sector
 * on each device that it is on.
 *
 * raid10_find_virt does the reverse mapping, from a device and a
 * sector offset to a virtual address
 */

static void __raid10_find_phys(struct geom *geo, struct r10bio *r10bio)
{
        int n,f;
        sector_t sector;
        sector_t chunk;
        sector_t stripe;
        int dev;
        int slot = 0;
        int last_far_set_start, last_far_set_size;

        last_far_set_start = (geo->raid_disks / geo->far_set_size) - 1;
        last_far_set_start *= geo->far_set_size;

        last_far_set_size = geo->far_set_size;
        last_far_set_size += (geo->raid_disks % geo->far_set_size);

        /* now calculate first sector/dev */
        chunk = r10bio->sector >> geo->chunk_shift;
        sector = r10bio->sector & geo->chunk_mask;

        chunk *= geo->near_copies;
        stripe = chunk;
        dev = sector_div(stripe, geo->raid_disks);
        if (geo->far_offset)
                stripe *= geo->far_copies;

        sector += stripe << geo->chunk_shift;

        /* and calculate all the others */
        for (n = 0; n < geo->near_copies; n++) {
                int d = dev;
                int set;
                sector_t s = sector;
                r10bio->devs[slot].devnum = d;
                r10bio->devs[slot].addr = s;
                slot++;

                for (f = 1; f < geo->far_copies; f++) {
                        set = d / geo->far_set_size;
                        d += geo->near_copies;

                        if ((geo->raid_disks % geo->far_set_size) &&
                            (d > last_far_set_start)) {
                                d -= last_far_set_start;
                                d %= last_far_set_size;
                                d += last_far_set_start;
                        } else {
                                d %= geo->far_set_size;
                                d += geo->far_set_size * set;
                        }
                        s += geo->stride;
                        r10bio->devs[slot].devnum = d;
                        r10bio->devs[slot].addr = s;
                        slot++;
                }
                dev++;
                if (dev >= geo->raid_disks) {
                        dev = 0;
                        sector += (geo->chunk_mask + 1);
                }
        }
}

static void raid10_find_phys(struct r10conf *conf, struct r10bio *r10bio)
{
        struct geom *geo = &conf->geo;

        if (conf->reshape_progress != MaxSector &&
            ((r10bio->sector >= conf->reshape_progress) !=
             conf->mddev->reshape_backwards)) {
                set_bit(R10BIO_Previous, &r10bio->state);
                geo = &conf->prev;
        } else
                clear_bit(R10BIO_Previous, &r10bio->state);

        __raid10_find_phys(geo, r10bio);
}

static sector_t raid10_find_virt(struct r10conf *conf, sector_t sector, int dev)
{
        sector_t offset, chunk, vchunk;
        /* Never use conf->prev as this is only called during resync
         * or recovery, so reshape isn't happening
         */
        struct geom *geo = &conf->geo;
        int far_set_start = (dev / geo->far_set_size) * geo->far_set_size;
        int far_set_size = geo->far_set_size;
        int last_far_set_start;

        if (geo->raid_disks % geo->far_set_size) {
                last_far_set_start = (geo->raid_disks / geo->far_set_size) - 1;
                last_far_set_start *= geo->far_set_size;

                if (dev >= last_far_set_start) {
                        far_set_size = geo->far_set_size;
                        far_set_size += (geo->raid_disks % geo->far_set_size);
                        far_set_start = last_far_set_start;
                }
        }

        offset = sector & geo->chunk_mask;
        if (geo->far_offset) {
                int fc;
                chunk = sector >> geo->chunk_shift;
                fc = sector_div(chunk, geo->far_copies);
                dev -= fc * geo->near_copies;
                if (dev < far_set_start)
                        dev += far_set_size;
        } else {
                while (sector >= geo->stride) {
                        sector -= geo->stride;
                        if (dev < (geo->near_copies + far_set_start))
                                dev += far_set_size - geo->near_copies;
                        else
                                dev -= geo->near_copies;
                }
                chunk = sector >> geo->chunk_shift;
        }
        vchunk = chunk * geo->raid_disks + dev;
        sector_div(vchunk, geo->near_copies);
        return (vchunk << geo->chunk_shift) + offset;
}

/**
 *      raid10_mergeable_bvec -- tell bio layer if a two requests can be merged
 *      @q: request queue
 *      @bvm: properties of new bio
 *      @biovec: the request that could be merged to it.
 *
 *      Return amount of bytes we can accept at this offset
 *      This requires checking for end-of-chunk if near_copies != raid_disks,
 *      and for subordinate merge_bvec_fns if merge_check_needed.
 */
static int raid10_mergeable_bvec(struct request_queue *q,
                                 struct bvec_merge_data *bvm,
                                 struct bio_vec *biovec)
{
        struct mddev *mddev = q->queuedata;
        struct r10conf *conf = mddev->private;
        sector_t sector = bvm->bi_sector + get_start_sect(bvm->bi_bdev);
        int max;
        unsigned int chunk_sectors;
        unsigned int bio_sectors = bvm->bi_size >> 9;
        struct geom *geo = &conf->geo;

        chunk_sectors = (conf->geo.chunk_mask & conf->prev.chunk_mask) + 1;
        if (conf->reshape_progress != MaxSector &&
            ((sector >= conf->reshape_progress) !=
             conf->mddev->reshape_backwards))
                geo = &conf->prev;

        if (geo->near_copies < geo->raid_disks) {
                max = (chunk_sectors - ((sector & (chunk_sectors - 1))
                                        + bio_sectors)) << 9;
                if (max < 0)
                        /* bio_add cannot handle a negative return */
                        max = 0;
                if (max <= biovec->bv_len && bio_sectors == 0)
                        return biovec->bv_len;
        } else
                max = biovec->bv_len;

        if (mddev->merge_check_needed) {
                struct {
                        struct r10bio r10_bio;
                        struct r10dev devs[conf->copies];
                } on_stack;
                struct r10bio *r10_bio = &on_stack.r10_bio;
                int s;
                if (conf->reshape_progress != MaxSector) {
                        /* Cannot give any guidance during reshape */
                        if (max <= biovec->bv_len && bio_sectors == 0)
                                return biovec->bv_len;
                        return 0;
                }
                r10_bio->sector = sector;
                raid10_find_phys(conf, r10_bio);
                rcu_read_lock();
                for (s = 0; s < conf->copies; s++) {
                        int disk = r10_bio->devs[s].devnum;
                        struct md_rdev *rdev = rcu_dereference(
                                conf->mirrors[disk].rdev);
                        if (rdev && !test_bit(Faulty, &rdev->flags)) {
                                struct request_queue *q =
                                        bdev_get_queue(rdev->bdev);
                                if (q->merge_bvec_fn) {
                                        bvm->bi_sector = r10_bio->devs[s].addr
                                                + rdev->data_offset;
                                        bvm->bi_bdev = rdev->bdev;
                                        max = min(max, q->merge_bvec_fn(
                                                          q, bvm, biovec));
                                }
                        }
                        rdev = rcu_dereference(conf->mirrors[disk].replacement);
                        if (rdev && !test_bit(Faulty, &rdev->flags)) {
                                struct request_queue *q =
                                        bdev_get_queue(rdev->bdev);
                                if (q->merge_bvec_fn) {
                                        bvm->bi_sector = r10_bio->devs[s].addr
                                                + rdev->data_offset;
                                        bvm->bi_bdev = rdev->bdev;
                                        max = min(max, q->merge_bvec_fn(
                                                          q, bvm, biovec));
                                }
                        }
                }
                rcu_read_unlock();
        }
        return max;
}

/*
 * This routine returns the disk from which the requested read should
 * be done. There is a per-array 'next expected sequential IO' sector
 * number - if this matches on the next IO then we use the last disk.
 * There is also a per-disk 'last know head position' sector that is
 * maintained from IRQ contexts, both the normal and the resync IO
 * completion handlers update this position correctly. If there is no
 * perfect sequential match then we pick the disk whose head is closest.
 *
 * If there are 2 mirrors in the same 2 devices, performance degrades
 * because position is mirror, not device based.
 *
 * The rdev for the device selected will have nr_pending incremented.
 */

/*
 * FIXME: possibly should rethink readbalancing and do it differently
 * depending on near_copies / far_copies geometry.
 */
static struct md_rdev *read_balance(struct r10conf *conf,
                                    struct r10bio *r10_bio,
                                    int *max_sectors)
{
        const sector_t this_sector = r10_bio->sector;
        int disk, slot;
        int sectors = r10_bio->sectors;
        int best_good_sectors;
        sector_t new_distance, best_dist;
        struct md_rdev *best_rdev, *rdev = NULL;
        int do_balance;
        int best_slot;
        struct geom *geo = &conf->geo;

        raid10_find_phys(conf, r10_bio);
        rcu_read_lock();
retry:
        sectors = r10_bio->sectors;
        best_slot = -1;
        best_rdev = NULL;
        best_dist = MaxSector;
        best_good_sectors = 0;
        do_balance = 1;
        /*
         * Check if we can balance. We can balance on the whole
         * device if no resync is going on (recovery is ok), or below
         * the resync window. We take the first readable disk when
         * above the resync window.
         */
        if (conf->mddev->recovery_cp < MaxSector
            && (this_sector + sectors >= conf->next_resync))
                do_balance = 0;

        for (slot = 0; slot < conf->copies ; slot++) {
                sector_t first_bad;
                int bad_sectors;
                sector_t dev_sector;

                if (r10_bio->devs[slot].bio == IO_BLOCKED)
                        continue;
                disk = r10_bio->devs[slot].devnum;
                rdev = rcu_dereference(conf->mirrors[disk].replacement);
                if (rdev == NULL || test_bit(Faulty, &rdev->flags) ||
                    test_bit(Unmerged, &rdev->flags) ||
                    r10_bio->devs[slot].addr + sectors > rdev->recovery_offset)
                        rdev = rcu_dereference(conf->mirrors[disk].rdev);
                if (rdev == NULL ||
                    test_bit(Faulty, &rdev->flags) ||
                    test_bit(Unmerged, &rdev->flags))
                        continue;
                if (!test_bit(In_sync, &rdev->flags) &&
                    r10_bio->devs[slot].addr + sectors > rdev->recovery_offset)
                        continue;

                dev_sector = r10_bio->devs[slot].addr;
                if (is_badblock(rdev, dev_sector, sectors,
                                &first_bad, &bad_sectors)) {
                        if (best_dist < MaxSector)
                                /* Already have a better slot */
                                continue;
                        if (first_bad <= dev_sector) {
                                /* Cannot read here.  If this is the
                                 * 'primary' device, then we must not read
                                 * beyond 'bad_sectors' from another device.
                                 */
                                bad_sectors -= (dev_sector - first_bad);
                                if (!do_balance && sectors > bad_sectors)
                                        sectors = bad_sectors;
                                if (best_good_sectors > sectors)
                                        best_good_sectors = sectors;
                        } else {
                                sector_t good_sectors =
                                        first_bad - dev_sector;
                                if (good_sectors > best_good_sectors) {
                                        best_good_sectors = good_sectors;
                                        best_slot = slot;
                                        best_rdev = rdev;
                                }
                                if (!do_balance)
                                        /* Must read from here */
                                        break;
                        }
                        continue;
                } else
                        best_good_sectors = sectors;

                if (!do_balance)
                        break;

                /* This optimisation is debatable, and completely destroys
                 * sequential read speed for 'far copies' arrays.  So only
                 * keep it for 'near' arrays, and review those later.
                 */
                if (geo->near_copies > 1 && !atomic_read(&rdev->nr_pending))
                        break;

                /* for far > 1 always use the lowest address */
                if (geo->far_copies > 1)
                        new_distance = r10_bio->devs[slot].addr;
                else
                        new_distance = abs(r10_bio->devs[slot].addr -
                                           conf->mirrors[disk].head_position);
                if (new_distance < best_dist) {
                        best_dist = new_distance;
                        best_slot = slot;
                        best_rdev = rdev;
                }
        }
        if (slot >= conf->copies) {
                slot = best_slot;
                rdev = best_rdev;
        }

        if (slot >= 0) {
                atomic_inc(&rdev->nr_pending);
                if (test_bit(Faulty, &rdev->flags)) {
                        /* Cannot risk returning a device that failed
                         * before we inc'ed nr_pending
                         */
                        rdev_dec_pending(rdev, conf->mddev);
                        goto retry;
                }
                r10_bio->read_slot = slot;
        } else
                rdev = NULL;
        rcu_read_unlock();
        *max_sectors = best_good_sectors;

        return rdev;
}

int md_raid10_congested(struct mddev *mddev, int bits)
{
        struct r10conf *conf = mddev->private;
        int i, ret = 0;

        if ((bits & (1 << BDI_async_congested)) &&
            conf->pending_count >= max_queued_requests)
                return 1;

        rcu_read_lock();
        for (i = 0;
             (i < conf->geo.raid_disks || i < conf->prev.raid_disks)
                     && ret == 0;
             i++) {
                struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
                if (rdev && !test_bit(Faulty, &rdev->flags)) {
                        struct request_queue *q = bdev_get_queue(rdev->bdev);

                        ret |= bdi_congested(&q->backing_dev_info, bits);
                }
        }
        rcu_read_unlock();
        return ret;
}
EXPORT_SYMBOL_GPL(md_raid10_congested);

static int raid10_congested(void *data, int bits)
{
        struct mddev *mddev = data;

        return mddev_congested(mddev, bits) ||
                md_raid10_congested(mddev, bits);
}

static void flush_pending_writes(struct r10conf *conf)
{
        /* Any writes that have been queued but are awaiting
         * bitmap updates get flushed here.
         */
        spin_lock_irq(&conf->device_lock);

        if (conf->pending_bio_list.head) {
                struct bio *bio;
                bio = bio_list_get(&conf->pending_bio_list);
                conf->pending_count = 0;
                spin_unlock_irq(&conf->device_lock);
                /* flush any pending bitmap writes to disk
                 * before proceeding w/ I/O */
                bitmap_unplug(conf->mddev->bitmap);
                wake_up(&conf->wait_barrier);

                while (bio) { /* submit pending writes */
                        struct bio *next = bio->bi_next;
                        bio->bi_next = NULL;
                        if (unlikely((bio->bi_rw & REQ_DISCARD) &&
                            !blk_queue_discard(bdev_get_queue(bio->bi_bdev))))
                                /* Just ignore it */
                                bio_endio(bio, 0);
                        else
                                generic_make_request(bio);
                        bio = next;
                }
        } else
                spin_unlock_irq(&conf->device_lock);
}

/* Barriers....
 * Sometimes we need to suspend IO while we do something else,
 * either some resync/recovery, or reconfigure the array.
 * To do this we raise a 'barrier'.
 * The 'barrier' is a counter that can be raised multiple times
 * to count how many activities are happening which preclude
 * normal IO.
 * We can only raise the barrier if there is no pending IO.
 * i.e. if nr_pending == 0.
 * We choose only to raise the barrier if no-one is waiting for the
 * barrier to go down.  This means that as soon as an IO request
 * is ready, no other operations which require a barrier will start
 * until the IO request has had a chance.
 *
 * So: regular IO calls 'wait_barrier'.  When that returns there
 *    is no backgroup IO happening,  It must arrange to call
 *    allow_barrier when it has finished its IO.
 * backgroup IO calls must call raise_barrier.  Once that returns
 *    there is no normal IO happeing.  It must arrange to call
 *    lower_barrier when the particular background IO completes.
 */

static void raise_barrier(struct r10conf *conf, int force)
{
        BUG_ON(force && !conf->barrier);
        spin_lock_irq(&conf->resync_lock);

        /* Wait until no block IO is waiting (unless 'force') */
        wait_event_lock_irq(conf->wait_barrier, force || !conf->nr_waiting,
                            conf->resync_lock);

        /* block any new IO from starting */
        conf->barrier++;

        /* Now wait for all pending IO to complete */
        wait_event_lock_irq(conf->wait_barrier,
                            !conf->nr_pending && conf->barrier < RESYNC_DEPTH,
                            conf->resync_lock);

        spin_unlock_irq(&conf->resync_lock);
}

static void lower_barrier(struct r10conf *conf)
{
        unsigned long flags;
        spin_lock_irqsave(&conf->resync_lock, flags);
        conf->barrier--;
        spin_unlock_irqrestore(&conf->resync_lock, flags);
        wake_up(&conf->wait_barrier);
}

static void wait_barrier(struct r10conf *conf)
{
        spin_lock_irq(&conf->resync_lock);
        if (conf->barrier) {
                conf->nr_waiting++;
                /* Wait for the barrier to drop.
                 * However if there are already pending
                 * requests (preventing the barrier from
                 * rising completely), and the
                 * pre-process bio queue isn't empty,
                 * then don't wait, as we need to empty
                 * that queue to get the nr_pending
                 * count down.
                 */
                wait_event_lock_irq(conf->wait_barrier,
                                    !conf->barrier ||
                                    (conf->nr_pending &&
                                     current->bio_list &&
                                     !bio_list_empty(current->bio_list)),
                                    conf->resync_lock);
                conf->nr_waiting--;
        }
        conf->nr_pending++;
        spin_unlock_irq(&conf->resync_lock);
}

static void allow_barrier(struct r10conf *conf)
{
        unsigned long flags;
        spin_lock_irqsave(&conf->resync_lock, flags);
        conf->nr_pending--;
        spin_unlock_irqrestore(&conf->resync_lock, flags);
        wake_up(&conf->wait_barrier);
}

static void freeze_array(struct r10conf *conf, int extra)
{
        /* stop syncio and normal IO and wait for everything to
         * go quiet.
         * We increment barrier and nr_waiting, and then
         * wait until nr_pending match nr_queued+extra
         * This is called in the context of one normal IO request
         * that has failed. Thus any sync request that might be pending
         * will be blocked by nr_pending, and we need to wait for
         * pending IO requests to complete or be queued for re-try.
         * Thus the number queued (nr_queued) plus this request (extra)
         * must match the number of pending IOs (nr_pending) before
         * we continue.
         */
        spin_lock_irq(&conf->resync_lock);
        conf->barrier++;
        conf->nr_waiting++;
        wait_event_lock_irq_cmd(conf->wait_barrier,
                                conf->nr_pending == conf->nr_queued+extra,
                                conf->resync_lock,
                                flush_pending_writes(conf));

        spin_unlock_irq(&conf->resync_lock);
}

static void unfreeze_array(struct r10conf *conf)
{
        /* reverse the effect of the freeze */
        spin_lock_irq(&conf->resync_lock);
        conf->barrier--;
        conf->nr_waiting--;
        wake_up(&conf->wait_barrier);
        spin_unlock_irq(&conf->resync_lock);
}

static sector_t choose_data_offset(struct r10bio *r10_bio,
                                   struct md_rdev *rdev)
{
        if (!test_bit(MD_RECOVERY_RESHAPE, &rdev->mddev->recovery) ||
            test_bit(R10BIO_Previous, &r10_bio->state))
                return rdev->data_offset;
        else
                return rdev->new_data_offset;
}

struct raid10_plug_cb {
        struct blk_plug_cb      cb;
        struct bio_list         pending;
        int                     pending_cnt;
};

static void raid10_unplug(struct blk_plug_cb *cb, bool from_schedule)
{
        struct raid10_plug_cb *plug = container_of(cb, struct raid10_plug_cb,
                                                   cb);
        struct mddev *mddev = plug->cb.data;
        struct r10conf *conf = mddev->private;
        struct bio *bio;

        if (from_schedule || current->bio_list) {
                spin_lock_irq(&conf->device_lock);
                bio_list_merge(&conf->pending_bio_list, &plug->pending);
                conf->pending_count += plug->pending_cnt;
                spin_unlock_irq(&conf->device_lock);
                wake_up(&conf->wait_barrier);
                md_wakeup_thread(mddev->thread);
                kfree(plug);
                return;
        }

        /* we aren't scheduling, so we can do the write-out directly. */
        bio = bio_list_get(&plug->pending);
        bitmap_unplug(mddev->bitmap);
        wake_up(&conf->wait_barrier);

        while (bio) { /* submit pending writes */
                struct bio *next = bio->bi_next;
                bio->bi_next = NULL;
                if (unlikely((bio->bi_rw & REQ_DISCARD) &&
                    !blk_queue_discard(bdev_get_queue(bio->bi_bdev))))
                        /* Just ignore it */
                        bio_endio(bio, 0);
                else
                        generic_make_request(bio);
                bio = next;
        }
        kfree(plug);
}

static void make_request(struct mddev *mddev, struct bio * bio)
{
        struct r10conf *conf = mddev->private;
        struct r10bio *r10_bio;
        struct bio *read_bio;
        int i;
        sector_t chunk_mask = (conf->geo.chunk_mask & conf->prev.chunk_mask);
        int chunk_sects = chunk_mask + 1;
        const int rw = bio_data_dir(bio);
        const unsigned long do_sync = (bio->bi_rw & REQ_SYNC);
        const unsigned long do_fua = (bio->bi_rw & REQ_FUA);
        const unsigned long do_discard = (bio->bi_rw
                                          & (REQ_DISCARD | REQ_SECURE));
        const unsigned long do_same = (bio->bi_rw & REQ_WRITE_SAME);
        unsigned long flags;
        struct md_rdev *blocked_rdev;
        struct blk_plug_cb *cb;
        struct raid10_plug_cb *plug = NULL;
        int sectors_handled;
        int max_sectors;
        int sectors;

        if (unlikely(bio->bi_rw & REQ_FLUSH)) {
                md_flush_request(mddev, bio);
                return;
        }

        /* If this request crosses a chunk boundary, we need to
         * split it.  This will only happen for 1 PAGE (or less) requests.
         */
        if (unlikely((bio->bi_iter.bi_sector & chunk_mask) + bio_sectors(bio)
                     > chunk_sects
                     && (conf->geo.near_copies < conf->geo.raid_disks
                         || conf->prev.near_copies < conf->prev.raid_disks))) {
                struct bio_pair *bp;
                /* Sanity check -- queue functions should prevent this happening */
                if (bio_segments(bio) > 1)
                        goto bad_map;
                /* This is a one page bio that upper layers
                 * refuse to split for us, so we need to split it.
                 */
                bp = bio_split(bio, chunk_sects -
                               (bio->bi_iter.bi_sector & (chunk_sects - 1)));

                /* Each of these 'make_request' calls will call 'wait_barrier'.
                 * If the first succeeds but the second blocks due to the resync
                 * thread raising the barrier, we will deadlock because the
                 * IO to the underlying device will be queued in generic_make_request
                 * and will never complete, so will never reduce nr_pending.
                 * So increment nr_waiting here so no new raise_barriers will
                 * succeed, and so the second wait_barrier cannot block.
                 */
                spin_lock_irq(&conf->resync_lock);
                conf->nr_waiting++;
                spin_unlock_irq(&conf->resync_lock);

                make_request(mddev, &bp->bio1);
                make_request(mddev, &bp->bio2);

                spin_lock_irq(&conf->resync_lock);
                conf->nr_waiting--;
                wake_up(&conf->wait_barrier);
                spin_unlock_irq(&conf->resync_lock);

                bio_pair_release(bp);
                return;
        bad_map:
                printk("md/raid10:%s: make_request bug: can't convert block across chunks"
                       " or bigger than %dk %llu %d\n", mdname(mddev), chunk_sects/2,
                       (unsigned long long)bio->bi_iter.bi_sector,
                       bio_sectors(bio) / 2);

                bio_io_error(bio);
                return;
        }

        md_write_start(mddev, bio);

        /*
         * Register the new request and wait if the reconstruction
         * thread has put up a bar for new requests.
         * Continue immediately if no resync is active currently.
         */
        wait_barrier(conf);

        sectors = bio_sectors(bio);
        while (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
            bio->bi_iter.bi_sector < conf->reshape_progress &&
            bio->bi_iter.bi_sector + sectors > conf->reshape_progress) {
                /* IO spans the reshape position.  Need to wait for
                 * reshape to pass
                 */
                allow_barrier(conf);
                wait_event(conf->wait_barrier,
                           conf->reshape_progress <= bio->bi_iter.bi_sector ||
                           conf->reshape_progress >= bio->bi_iter.bi_sector +
                           sectors);
                wait_barrier(conf);
        }
        if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
            bio_data_dir(bio) == WRITE &&
            (mddev->reshape_backwards
             ? (bio->bi_iter.bi_sector < conf->reshape_safe &&
                bio->bi_iter.bi_sector + sectors > conf->reshape_progress)
             : (bio->bi_iter.bi_sector + sectors > conf->reshape_safe &&
                bio->bi_iter.bi_sector < conf->reshape_progress))) {
                /* Need to update reshape_position in metadata */
                mddev->reshape_position = conf->reshape_progress;
                set_bit(MD_CHANGE_DEVS, &mddev->flags);
                set_bit(MD_CHANGE_PENDING, &mddev->flags);
                md_wakeup_thread(mddev->thread);
                wait_event(mddev->sb_wait,
                           !test_bit(MD_CHANGE_PENDING, &mddev->flags));

                conf->reshape_safe = mddev->reshape_position;
        }

        r10_bio = mempool_alloc(conf->r10bio_pool, GFP_NOIO);

        r10_bio->master_bio = bio;
        r10_bio->sectors = sectors;

        r10_bio->mddev = mddev;
        r10_bio->sector = bio->bi_iter.bi_sector;
        r10_bio->state = 0;

        /* We might need to issue multiple reads to different
         * devices if there are bad blocks around, so we keep
         * track of the number of reads in bio->bi_phys_segments.
         * If this is 0, there is only one r10_bio and no locking
         * will be needed when the request completes.  If it is
         * non-zero, then it is the number of not-completed requests.
         */
        bio->bi_phys_segments = 0;
        clear_bit(BIO_SEG_VALID, &bio->bi_flags);

        if (rw == READ) {
                /*
                 * read balancing logic:
                 */
                struct md_rdev *rdev;
                int slot;

read_again:
                rdev = read_balance(conf, r10_bio, &max_sectors);
                if (!rdev) {
                        raid_end_bio_io(r10_bio);
                        return;
                }
                slot = r10_bio->read_slot;

                read_bio = bio_clone_mddev(bio, GFP_NOIO, mddev);
                bio_trim(read_bio, r10_bio->sector - bio->bi_iter.bi_sector,
                         max_sectors);

                r10_bio->devs[slot].bio = read_bio;
                r10_bio->devs[slot].rdev = rdev;

                read_bio->bi_iter.bi_sector = r10_bio->devs[slot].addr +
                        choose_data_offset(r10_bio, rdev);
                read_bio->bi_bdev = rdev->bdev;
                read_bio->bi_end_io = raid10_end_read_request;
                read_bio->bi_rw = READ | do_sync;
                read_bio->bi_private = r10_bio;

                if (max_sectors < r10_bio->sectors) {
                        /* Could not read all from this device, so we will
                         * need another r10_bio.
                         */
                        sectors_handled = (r10_bio->sectors + max_sectors
                                           - bio->bi_iter.bi_sector);
                        r10_bio->sectors = max_sectors;
                        spin_lock_irq(&conf->device_lock);
                        if (bio->bi_phys_segments == 0)
                                bio->bi_phys_segments = 2;
                        else
                                bio->bi_phys_segments++;
                        spin_unlock(&conf->device_lock);
                        /* Cannot call generic_make_request directly
                         * as that will be queued in __generic_make_request
                         * and subsequent mempool_alloc might block
                         * waiting for it.  so hand bio over to raid10d.
                         */
                        reschedule_retry(r10_bio);

                        r10_bio = mempool_alloc(conf->r10bio_pool, GFP_NOIO);

                        r10_bio->master_bio = bio;
                        r10_bio->sectors = bio_sectors(bio) - sectors_handled;
                        r10_bio->state = 0;
                        r10_bio->mddev = mddev;
                        r10_bio->sector = bio->bi_iter.bi_sector +
                                sectors_handled;
                        goto read_again;
                } else
                        generic_make_request(read_bio);
                return;
        }

        /*
         * WRITE:
         */
        if (conf->pending_count >= max_queued_requests) {
                md_wakeup_thread(mddev->thread);
                wait_event(conf->wait_barrier,
                           conf->pending_count < max_queued_requests);
        }
        /* first select target devices under rcu_lock and
         * inc refcount on their rdev.  Record them by setting
         * bios[x] to bio
         * If there are known/acknowledged bad blocks on any device
         * on which we have seen a write error, we want to avoid
         * writing to those blocks.  This potentially requires several
         * writes to write around the bad blocks.  Each set of writes
         * gets its own r10_bio with a set of bios attached.  The number
         * of r10_bios is recored in bio->bi_phys_segments just as with
         * the read case.
         */

        r10_bio->read_slot = -1; /* make sure repl_bio gets freed */
        raid10_find_phys(conf, r10_bio);
retry_write:
        blocked_rdev = NULL;
        rcu_read_lock();
        max_sectors = r10_bio->sectors;

        for (i = 0;  i < conf->copies; i++) {
                int d = r10_bio->devs[i].devnum;
                struct md_rdev *rdev = rcu_dereference(conf->mirrors[d].rdev);
                struct md_rdev *rrdev = rcu_dereference(
                        conf->mirrors[d].replacement);
                if (rdev == rrdev)
                        rrdev = NULL;
                if (rdev && unlikely(test_bit(Blocked, &rdev->flags))) {
                        atomic_inc(&rdev->nr_pending);
                        blocked_rdev = rdev;
                        break;
                }
                if (rrdev && unlikely(test_bit(Blocked, &rrdev->flags))) {
                        atomic_inc(&rrdev->nr_pending);
                        blocked_rdev = rrdev;
                        break;
                }
                if (rdev && (test_bit(Faulty, &rdev->flags)
                             || test_bit(Unmerged, &rdev->flags)))
                        rdev = NULL;
                if (rrdev && (test_bit(Faulty, &rrdev->flags)
                              || test_bit(Unmerged, &rrdev->flags)))
                        rrdev = NULL;

                r10_bio->devs[i].bio = NULL;
                r10_bio->devs[i].repl_bio = NULL;

                if (!rdev && !rrdev) {
                        set_bit(R10BIO_Degraded, &r10_bio->state);
                        continue;
                }
                if (rdev && test_bit(WriteErrorSeen, &rdev->flags)) {
                        sector_t first_bad;
                        sector_t dev_sector = r10_bio->devs[i].addr;
                        int bad_sectors;
                        int is_bad;

                        is_bad = is_badblock(rdev, dev_sector,
                                             max_sectors,
                                             &first_bad, &bad_sectors);
                        if (is_bad < 0) {
                                /* Mustn't write here until the bad block
                                 * is acknowledged
                                 */
                                atomic_inc(&rdev->nr_pending);
                                set_bit(BlockedBadBlocks, &rdev->flags);
                                blocked_rdev = rdev;
                                break;
                        }
                        if (is_bad && first_bad <= dev_sector) {
                                /* Cannot write here at all */
                                bad_sectors -= (dev_sector - first_bad);
                                if (bad_sectors < max_sectors)
                                        /* Mustn't write more than bad_sectors
                                         * to other devices yet
                                         */
                                        max_sectors = bad_sectors;
                                /* We don't set R10BIO_Degraded as that
                                 * only applies if the disk is missing,
                                 * so it might be re-added, and we want to
                                 * know to recover this chunk.
                                 * In this case the device is here, and the
                                 * fact that this chunk is not in-sync is
                                 * recorded in the bad block log.
                                 */
                                continue;
                        }
                        if (is_bad) {
                                int good_sectors = first_bad - dev_sector;
                                if (good_sectors < max_sectors)
                                        max_sectors = good_sectors;
                        }
                }
                if (rdev) {
                        r10_bio->devs[i].bio = bio;
                        atomic_inc(&rdev->nr_pending);
                }
                if (rrdev) {
                        r10_bio->devs[i].repl_bio = bio;
                        atomic_inc(&rrdev->nr_pending);
                }
        }
        rcu_read_unlock();

        if (unlikely(blocked_rdev)) {
                /* Have to wait for this device to get unblocked, then retry */
                int j;
                int d;

                for (j = 0; j < i; j++) {
                        if (r10_bio->devs[j].bio) {
                                d = r10_bio->devs[j].devnum;
                                rdev_dec_pending(conf->mirrors[d].rdev, mddev);
                        }
                        if (r10_bio->devs[j].repl_bio) {
                                struct md_rdev *rdev;
                                d = r10_bio->devs[j].devnum;
                                rdev = conf->mirrors[d].replacement;
                                if (!rdev) {
                                        /* Race with remove_disk */
                                        smp_mb();
                                        rdev = conf->mirrors[d].rdev;
                                }
                                rdev_dec_pending(rdev, mddev);
                        }
                }
                allow_barrier(conf);
                md_wait_for_blocked_rdev(blocked_rdev, mddev);
                wait_barrier(conf);
                goto retry_write;
        }

        if (max_sectors < r10_bio->sectors) {
                /* We are splitting this into multiple parts, so
                 * we need to prepare for allocating another r10_bio.
                 */
                r10_bio->sectors = max_sectors;
                spin_lock_irq(&conf->device_lock);
                if (bio->bi_phys_segments == 0)
                        bio->bi_phys_segments = 2;
                else
                        bio->bi_phys_segments++;
                spin_unlock_irq(&conf->device_lock);
        }
        sectors_handled = r10_bio->sector + max_sectors -
                bio->bi_iter.bi_sector;

        atomic_set(&r10_bio->remaining, 1);
        bitmap_startwrite(mddev->bitmap, r10_bio->sector, r10_bio->sectors, 0);

        for (i = 0; i < conf->copies; i++) {
                struct bio *mbio;
                int d = r10_bio->devs[i].devnum;
                if (r10_bio->devs[i].bio) {
                        struct md_rdev *rdev = conf->mirrors[d].rdev;
                        mbio = bio_clone_mddev(bio, GFP_NOIO, mddev);
                        bio_trim(mbio, r10_bio->sector - bio->bi_iter.bi_sector,
                                 max_sectors);
                        r10_bio->devs[i].bio = mbio;

                        mbio->bi_iter.bi_sector = (r10_bio->devs[i].addr+
                                           choose_data_offset(r10_bio,
                                                              rdev));
                        mbio->bi_bdev = rdev->bdev;
                        mbio->bi_end_io = raid10_end_write_request;
                        mbio->bi_rw =
                                WRITE | do_sync | do_fua | do_discard | do_same;
                        mbio->bi_private = r10_bio;

                        atomic_inc(&r10_bio->remaining);

                        cb = blk_check_plugged(raid10_unplug, mddev,
                                               sizeof(*plug));
                        if (cb)
                                plug = container_of(cb, struct raid10_plug_cb,
                                                    cb);
                        else
                                plug = NULL;
                        spin_lock_irqsave(&conf->device_lock, flags);
                        if (plug) {
                                bio_list_add(&plug->pending, mbio);
                                plug->pending_cnt++;
                        } else {
                                bio_list_add(&conf->pending_bio_list, mbio);
                                conf->pending_count++;
                        }
                        spin_unlock_irqrestore(&conf->device_lock, flags);
                        if (!plug)
                                md_wakeup_thread(mddev->thread);
                }

                if (r10_bio->devs[i].repl_bio) {
                        struct md_rdev *rdev = conf->mirrors[d].replacement;
                        if (rdev == NULL) {
                                /* Replacement just got moved to main 'rdev' */
                                smp_mb();
                                rdev = conf->mirrors[d].rdev;
                        }
                        mbio = bio_clone_mddev(bio, GFP_NOIO, mddev);
                        bio_trim(mbio, r10_bio->sector - bio->bi_iter.bi_sector,
                                 max_sectors);
                        r10_bio->devs[i].repl_bio = mbio;

                        mbio->bi_iter.bi_sector = (r10_bio->devs[i].addr +
                                           choose_data_offset(
                                                   r10_bio, rdev));
                        mbio->bi_bdev = rdev->bdev;
                        mbio->bi_end_io = raid10_end_write_request;
                        mbio->bi_rw =
                                WRITE | do_sync | do_fua | do_discard | do_same;
                        mbio->bi_private = r10_bio;

                        atomic_inc(&r10_bio->remaining);
                        spin_lock_irqsave(&conf->device_lock, flags);
                        bio_list_add(&conf->pending_bio_list, mbio);
                        conf->pending_count++;
                        spin_unlock_irqrestore(&conf->device_lock, flags);
                        if (!mddev_check_plugged(mddev))
                                md_wakeup_thread(mddev->thread);
                }
        }

        /* Don't remove the bias on 'remaining' (one_write_done) until
         * after checking if we need to go around again.
         */

        if (sectors_handled < bio_sectors(bio)) {
                one_write_done(r10_bio);
                /* We need another r10_bio.  It has already been counted
                 * in bio->bi_phys_segments.
                 */
                r10_bio = mempool_alloc(conf->r10bio_pool, GFP_NOIO);

                r10_bio->master_bio = bio;
                r10_bio->sectors = bio_sectors(bio) - sectors_handled;

                r10_bio->mddev = mddev;
                r10_bio->sector = bio->bi_iter.bi_sector + sectors_handled;
                r10_bio->state = 0;
                goto retry_write;
        }
        one_write_done(r10_bio);

        /* In case raid10d snuck in to freeze_array */
        wake_up(&conf->wait_barrier);
}

static void status(struct seq_file *seq, struct mddev *mddev)
{
        struct r10conf *conf = mddev->private;
        int i;

        if (conf->geo.near_copies < conf->geo.raid_disks)
                seq_printf(seq, " %dK chunks", mddev->chunk_sectors / 2);
        if (conf->geo.near_copies > 1)
                seq_printf(seq, " %d near-copies", conf->geo.near_copies);
        if (conf->geo.far_copies > 1) {
                if (conf->geo.far_offset)
                        seq_printf(seq, " %d offset-copies", conf->geo.far_copies);
                else
                        seq_printf(seq, " %d far-copies", conf->geo.far_copies);
        }
        seq_printf(seq, " [%d/%d] [", conf->geo.raid_disks,
                                        conf->geo.raid_disks - mddev->degraded);
        for (i = 0; i < conf->geo.raid_disks; i++)
                seq_printf(seq, "%s",
                              conf->mirrors[i].rdev &&
                              test_bit(In_sync, &conf->mirrors[i].rdev->flags) ? "U" : "_");
        seq_printf(seq, "]");
}

/* check if there are enough drives for
 * every block to appear on atleast one.
 * Don't consider the device numbered 'ignore'
 * as we might be about to remove it.
 */
static int _enough(struct r10conf *conf, int previous, int ignore)
{
        int first = 0;
        int has_enough = 0;
        int disks, ncopies;
        if (previous) {
                disks = conf->prev.raid_disks;
                ncopies = conf->prev.near_copies;
        } else {
                disks = conf->geo.raid_disks;
                ncopies = conf->geo.near_copies;
        }

        rcu_read_lock();
        do {
                int n = conf->copies;
                int cnt = 0;
                int this = first;
                while (n--) {
                        struct md_rdev *rdev;
                        if (this != ignore &&
                            (rdev = rcu_dereference(conf->mirrors[this].rdev)) &&
                            test_bit(In_sync, &rdev->flags))
                                cnt++;
                        this = (this+1) % disks;
                }
                if (cnt == 0)
                        goto out;
                first = (first + ncopies) % disks;
        } while (first != 0);
        has_enough = 1;
out:
        rcu_read_unlock();
        return has_enough;
}

static int enough(struct r10conf *conf, int ignore)
{
        /* when calling 'enough', both 'prev' and 'geo' must
         * be stable.
         * This is ensured if ->reconfig_mutex or ->device_lock
         * is held.
         */
        return _enough(conf, 0, ignore) &&
                _enough(conf, 1, ignore);
}

static void error(struct mddev *mddev, struct md_rdev *rdev)
{
        char b[BDEVNAME_SIZE];
        struct r10conf *conf = mddev->private;
        unsigned long flags;

        /*
         * If it is not operational, then we have already marked it as dead
         * else if it is the last working disks, ignore the error, let the
         * next level up know.
         * else mark the drive as failed
         */
        spin_lock_irqsave(&conf->device_lock, flags);
        if (test_bit(In_sync, &rdev->flags)
            && !enough(conf, rdev->raid_disk)) {
                /*
                 * Don't fail the drive, just return an IO error.
                 */
                spin_unlock_irqrestore(&conf->device_lock, flags);
                return;
        }
        if (test_and_clear_bit(In_sync, &rdev->flags)) {
                mddev->degraded++;
                        /*
                 * if recovery is running, make sure it aborts.
                 */
                set_bit(MD_RECOVERY_INTR, &mddev->recovery);
        }
        set_bit(Blocked, &rdev->flags);
        set_bit(Faulty, &rdev->flags);
        set_bit(MD_CHANGE_DEVS, &mddev->flags);
        spin_unlock_irqrestore(&conf->device_lock, flags);
        printk(KERN_ALERT
               "md/raid10:%s: Disk failure on %s, disabling device.\n"
               "md/raid10:%s: Operation continuing on %d devices.\n",
               mdname(mddev), bdevname(rdev->bdev, b),
               mdname(mddev), conf->geo.raid_disks - mddev->degraded);
}

static void print_conf(struct r10conf *conf)
{
        int i;
        struct raid10_info *tmp;

        printk(KERN_DEBUG "RAID10 conf printout:\n");
        if (!conf) {
                printk(KERN_DEBUG "(!conf)\n");
                return;
        }
        printk(KERN_DEBUG " --- wd:%d rd:%d\n", conf->geo.raid_disks - conf->mddev->degraded,
                conf->geo.raid_disks);

        for (i = 0; i < conf->geo.raid_disks; i++) {
                char b[BDEVNAME_SIZE];
                tmp = conf->mirrors + i;
                if (tmp->rdev)
                        printk(KERN_DEBUG " disk %d, wo:%d, o:%d, dev:%s\n",
                                i, !test_bit(In_sync, &tmp->rdev->flags),
                                !test_bit(Faulty, &tmp->rdev->flags),
                                bdevname(tmp->rdev->bdev,b));
        }
}

static void close_sync(struct r10conf *conf)
{
        wait_barrier(conf);
        allow_barrier(conf);

        mempool_destroy(conf->r10buf_pool);
        conf->r10buf_pool = NULL;
}

static int raid10_spare_active(struct mddev *mddev)
{
        int i;
        struct r10conf *conf = mddev->private;
        struct raid10_info *tmp;
        int count = 0;
        unsigned long flags;

        /*
         * Find all non-in_sync disks within the RAID10 configuration
         * and mark them in_sync
         */
        for (i = 0; i < conf->geo.raid_disks; i++) {
                tmp = conf->mirrors + i;
                if (tmp->replacement
                    && tmp->replacement->recovery_offset == MaxSector
                    && !test_bit(Faulty, &tmp->replacement->flags)
                    && !test_and_set_bit(In_sync, &tmp->replacement->flags)) {
                        /* Replacement has just become active */
                        if (!tmp->rdev
                            || !test_and_clear_bit(In_sync, &tmp->rdev->flags))
                                count++;
                        if (tmp->rdev) {
                                /* Replaced device not technically faulty,
                                 * but we need to be sure it gets removed
                                 * and never re-added.
                                 */
                                set_bit(Faulty, &tmp->rdev->flags);
                                sysfs_notify_dirent_safe(
                                        tmp->rdev->sysfs_state);
                        }
                        sysfs_notify_dirent_safe(tmp->replacement->sysfs_state);
                } else if (tmp->rdev
                           && tmp->rdev->recovery_offset == MaxSector
                           && !test_bit(Faulty, &tmp->rdev->flags)
                           && !test_and_set_bit(In_sync, &tmp->rdev->flags)) {
                        count++;
                        sysfs_notify_dirent_safe(tmp->rdev->sysfs_state);
                }
        }
        spin_lock_irqsave(&conf->device_lock, flags);
        mddev->degraded -= count;
        spin_unlock_irqrestore(&conf->device_lock, flags);

        print_conf(conf);
        return count;
}


static int raid10_add_disk(struct mddev *mddev, struct md_rdev *rdev)
{
        struct r10conf *conf = mddev->private;
        int err = -EEXIST;
        int mirror;
        int first = 0;
        int last = conf->geo.raid_disks - 1;
        struct request_queue *q = bdev_get_queue(rdev->bdev);

        if (mddev->recovery_cp < MaxSector)
                /* only hot-add to in-sync arrays, as recovery is
                 * very different from resync
                 */
                return -EBUSY;
        if (rdev->saved_raid_disk < 0 && !_enough(conf, 1, -1))
                return -EINVAL;

        if (rdev->raid_disk >= 0)
                first = last = rdev->raid_disk;

        if (q->merge_bvec_fn) {
                set_bit(Unmerged, &rdev->flags);
                mddev->merge_check_needed = 1;
        }

        if (rdev->saved_raid_disk >= first &&
            conf->mirrors[rdev->saved_raid_disk].rdev == NULL)
                mirror = rdev->saved_raid_disk;
        else
                mirror = first;
        for ( ; mirror <= last ; mirror++) {
                struct raid10_info *p = &conf->mirrors[mirror];
                if (p->recovery_disabled == mddev->recovery_disabled)
                        continue;
                if (p->rdev) {
                        if (!test_bit(WantReplacement, &p->rdev->flags) ||
                            p->replacement != NULL)
                                continue;
                        clear_bit(In_sync, &rdev->flags);
                        set_bit(Replacement, &rdev->flags);
                        rdev->raid_disk = mirror;
                        err = 0;
                        if (mddev->gendisk)
                                disk_stack_limits(mddev->gendisk, rdev->bdev,
                                                  rdev->data_offset << 9);
                        conf->fullsync = 1;
                        rcu_assign_pointer(p->replacement, rdev);
                        break;
                }

                if (mddev->gendisk)
                        disk_stack_limits(mddev->gendisk, rdev->bdev,
                                          rdev->data_offset << 9);

                p->head_position = 0;
                p->recovery_disabled = mddev->recovery_disabled - 1;
                rdev->raid_disk = mirror;
                err = 0;
                if (rdev->saved_raid_disk != mirror)
                        conf->fullsync = 1;
                rcu_assign_pointer(p->rdev, rdev);
                break;
        }
        if (err == 0 && test_bit(Unmerged, &rdev->flags)) {
                /* Some requests might not have seen this new
                 * merge_bvec_fn.  We must wait for them to complete
                 * before merging the device fully.
                 * First we make sure any code which has tested
                 * our function has submitted the request, then
                 * we wait for all outstanding requests to complete.
                 */
                synchronize_sched();
                freeze_array(conf, 0);
                unfreeze_array(conf);
                clear_bit(Unmerged, &rdev->flags);
        }
        md_integrity_add_rdev(rdev, mddev);
        if (mddev->queue && blk_queue_discard(bdev_get_queue(rdev->bdev)))
                queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, mddev->queue);

        print_conf(conf);
        return err;
}

static int raid10_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
{
        struct r10conf *conf = mddev->private;
        int err = 0;
        int number = rdev->raid_disk;
        struct md_rdev **rdevp;
        struct raid10_info *p = conf->mirrors + number;

        print_conf(conf);
        if (rdev == p->rdev)
                rdevp = &p->rdev;
        else if (rdev == p->replacement)
                rdevp = &p->replacement;
        else
                return 0;

        if (test_bit(In_sync, &rdev->flags) ||
            atomic_read(&rdev->nr_pending)) {
                err = -EBUSY;
                goto abort;
        }
        /* Only remove faulty devices if recovery
         * is not possible.
         */
        if (!test_bit(Faulty, &rdev->flags) &&
            mddev->recovery_disabled != p->recovery_disabled &&
            (!p->replacement || p->replacement == rdev) &&
            number < conf->geo.raid_disks &&
            enough(conf, -1)) {
                err = -EBUSY;
                goto abort;
        }
        *rdevp = NULL;
        synchronize_rcu();
        if (atomic_read(&rdev->nr_pending)) {
                /* lost the race, try later */
                err = -EBUSY;
                *rdevp = rdev;
                goto abort;
        } else if (p->replacement) {
                /* We must have just cleared 'rdev' */
                p->rdev = p->replacement;
                clear_bit(Replacement, &p->replacement->flags);
                smp_mb(); /* Make sure other CPUs may see both as identical
                           * but will never see neither -- if they are careful.
                           */
                p->replacement = NULL;
                clear_bit(WantReplacement, &rdev->flags);
        } else
                /* We might have just remove the Replacement as faulty
                 * Clear the flag just in case
                 */
                clear_bit(WantReplacement, &rdev->flags);

        err = md_integrity_register(mddev);

abort:

        print_conf(conf);
        return err;
}


static void end_sync_read(struct bio *bio, int error)
{
        struct r10bio *r10_bio = bio->bi_private;
        struct r10conf *conf = r10_bio->mddev->private;
        int d;

        if (bio == r10_bio->master_bio) {
                /* this is a reshape read */
                d = r10_bio->read_slot; /* really the read dev */
        } else
                d = find_bio_disk(conf, r10_bio, bio, NULL, NULL);

        if (test_bit(BIO_UPTODATE, &bio->bi_flags))
                set_bit(R10BIO_Uptodate, &r10_bio->state);
        else
                /* The write handler will notice the lack of
                 * R10BIO_Uptodate and record any errors etc
                 */
                atomic_add(r10_bio->sectors,
                           &conf->mirrors[d].rdev->corrected_errors);

        /* for reconstruct, we always reschedule after a read.
         * for resync, only after all reads
         */
        rdev_dec_pending(conf->mirrors[d].rdev, conf->mddev);
        if (test_bit(R10BIO_IsRecover, &r10_bio->state) ||
            atomic_dec_and_test(&r10_bio->remaining)) {
                /* we have read all the blocks,
                 * do the comparison in process context in raid10d
                 */
                reschedule_retry(r10_bio);
        }
}

static void end_sync_request(struct r10bio *r10_bio)
{
        struct mddev *mddev = r10_bio->mddev;

        while (atomic_dec_and_test(&r10_bio->remaining)) {
                if (r10_bio->master_bio == NULL) {
                        /* the primary of several recovery bios */
                        sector_t s = r10_bio->sectors;
                        if (test_bit(R10BIO_MadeGood, &r10_bio->state) ||
                            test_bit(R10BIO_WriteError, &r10_bio->state))
                                reschedule_retry(r10_bio);
                        else
                                put_buf(r10_bio);
                        md_done_sync(mddev, s, 1);
                        break;
                } else {
                        struct r10bio *r10_bio2 = (struct r10bio *)r10_bio->master_bio;
                        if (test_bit(R10BIO_MadeGood, &r10_bio->state) ||
                            test_bit(R10BIO_WriteError, &r10_bio->state))
                                reschedule_retry(r10_bio);
                        else
                                put_buf(r10_bio);
                        r10_bio = r10_bio2;
                }
        }
}

static void end_sync_write(struct bio *bio, int error)
{
        int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
        struct r10bio *r10_bio = bio->bi_private;
        struct mddev *mddev = r10_bio->mddev;
        struct r10conf *conf = mddev->private;
        int d;
        sector_t first_bad;
        int bad_sectors;
        int slot;
        int repl;
        struct md_rdev *rdev = NULL;

        d = find_bio_disk(conf, r10_bio, bio, &slot, &repl);
        if (repl)
                rdev = conf->mirrors[d].replacement;
        else
                rdev = conf->mirrors[d].rdev;

        if (!uptodate) {
                if (repl)
                        md_error(mddev, rdev);
                else {
                        set_bit(WriteErrorSeen, &rdev->flags);
                        if (!test_and_set_bit(WantReplacement, &rdev->flags))
                                set_bit(MD_RECOVERY_NEEDED,
                                        &rdev->mddev->recovery);
                        set_bit(R10BIO_WriteError, &r10_bio->state);
                }
        } else if (is_badblock(rdev,
                             r10_bio->devs[slot].addr,
                             r10_bio->sectors,
                             &first_bad, &bad_sectors))
                set_bit(R10BIO_MadeGood, &r10_bio->state);

        rdev_dec_pending(rdev, mddev);

        end_sync_request(r10_bio);
}

/*
 * Note: sync and recover and handled very differently for raid10
 * This code is for resync.
 * For resync, we read through virtual addresses and read all blocks.
 * If there is any error, we schedule a write.  The lowest numbered
 * drive is authoritative.
 * However requests come for physical address, so we need to map.
 * For every physical address there are raid_disks/copies virtual addresses,
 * which is always are least one, but is not necessarly an integer.
 * This means that a physical address can span multiple chunks, so we may
 * have to submit multiple io requests for a single sync request.
 */
/*
 * We check if all blocks are in-sync and only write to blocks that
 * aren't in sync
 */
static void sync_request_write(struct mddev *mddev, struct r10bio *r10_bio)
{
        struct r10conf *conf = mddev->private;
        int i, first;
        struct bio *tbio, *fbio;
        int vcnt;

        atomic_set(&r10_bio->remaining, 1);

        /* find the first device with a block */
        for (i=0; i<conf->copies; i++)
                if (test_bit(BIO_UPTODATE, &r10_bio->devs[i].bio->bi_flags))
                        break;

        if (i == conf->copies)
                goto done;

        first = i;
        fbio = r10_bio->devs[i].bio;

        vcnt = (r10_bio->sectors + (PAGE_SIZE >> 9) - 1) >> (PAGE_SHIFT - 9);
        /* now find blocks with errors */
        for (i=0 ; i < conf->copies ; i++) {
                int  j, d;

                tbio = r10_bio->devs[i].bio;

                if (tbio->bi_end_io != end_sync_read)
                        continue;
                if (i == first)
                        continue;
                if (test_bit(BIO_UPTODATE, &r10_bio->devs[i].bio->bi_flags)) {
                        /* We know that the bi_io_vec layout is the same for
                         * both 'first' and 'i', so we just compare them.
                         * All vec entries are PAGE_SIZE;
                         */
                        int sectors = r10_bio->sectors;
                        for (j = 0; j < vcnt; j++) {
                                int len = PAGE_SIZE;
                                if (sectors < (len / 512))
                                        len = sectors * 512;
                                if (memcmp(page_address(fbio->bi_io_vec[j].bv_page),
                                           page_address(tbio->bi_io_vec[j].bv_page),
                                           len))
                                        break;
                                sectors -= len/512;
                        }
                        if (j == vcnt)
                                continue;
                        atomic64_add(r10_bio->sectors, &mddev->resync_mismatches);
                        if (test_bit(MD_RECOVERY_CHECK, &mddev->recovery))
                                /* Don't fix anything. */
                                continue;
                }
                /* Ok, we need to write this bio, either to correct an
                 * inconsistency or to correct an unreadable block.
                 * First we need to fixup bv_offset, bv_len and
                 * bi_vecs, as the read request might have corrupted these
                 */
                bio_reset(tbio);

                tbio->bi_vcnt = vcnt;
                tbio->bi_iter.bi_size = r10_bio->sectors << 9;
                tbio->bi_rw = WRITE;
                tbio->bi_private = r10_bio;
                tbio->bi_iter.bi_sector = r10_bio->devs[i].addr;

                for (j=0; j < vcnt ; j++) {
                        tbio->bi_io_vec[j].bv_offset = 0;
                        tbio->bi_io_vec[j].bv_len = PAGE_SIZE;

                        memcpy(page_address(tbio->bi_io_vec[j].bv_page),
                               page_address(fbio->bi_io_vec[j].bv_page),
                               PAGE_SIZE);
                }
                tbio->bi_end_io = end_sync_write;

                d = r10_bio->devs[i].devnum;
                atomic_inc(&conf->mirrors[d].rdev->nr_pending);
                atomic_inc(&r10_bio->remaining);
                md_sync_acct(conf->mirrors[d].rdev->bdev, bio_sectors(tbio));

                tbio->bi_iter.bi_sector += conf->mirrors[d].rdev->data_offset;
                tbio->bi_bdev = conf->mirrors[d].rdev->bdev;
                generic_make_request(tbio);
        }

        /* Now write out to any replacement devices
         * that are active
         */
        for (i = 0; i < conf->copies; i++) {
                int j, d;

                tbio = r10_bio->devs[i].repl_bio;
                if (!tbio || !tbio->bi_end_io)
                        continue;
                if (r10_bio->devs[i].bio->bi_end_io != end_sync_write
                    && r10_bio->devs[i].bio != fbio)
                        for (j = 0; j < vcnt; j++)
                                memcpy(page_address(tbio->bi_io_vec[j].bv_page),
                                       page_address(fbio->bi_io_vec[j].bv_page),
                                       PAGE_SIZE);
                d = r10_bio->devs[i].devnum;
                atomic_inc(&r10_bio->remaining);
                md_sync_acct(conf->mirrors[d].replacement->bdev,
                             bio_sectors(tbio));
                generic_make_request(tbio);
        }

done:
        if (atomic_dec_and_test(&r10_bio->remaining)) {
                md_done_sync(mddev, r10_bio->sectors, 1);
                put_buf(r10_bio);
        }
}

/*
 * Now for the recovery code.
 * Recovery happens across physical sectors.
 * We recover all non-is_sync drives by finding the virtual address of
 * each, and then choose a working drive that also has that virt address.
 * There is a separate r10_bio for each non-in_sync drive.
 * Only the first two slots are in use. The first for reading,
 * The second for writing.
 *
 */
static void fix_recovery_read_error(struct r10bio *r10_bio)
{
        /* We got a read error during recovery.
         * We repeat the read in smaller page-sized sections.
         * If a read succeeds, write it to the new device or record
         * a bad block if we cannot.
         * If a read fails, record a bad block on both old and
         * new devices.
         */
        struct mddev *mddev = r10_bio->mddev;
        struct r10conf *conf = mddev->private;
        struct bio *bio = r10_bio->devs[0].bio;
        sector_t sect = 0;
        int sectors = r10_bio->sectors;
        int idx = 0;
        int dr = r10_bio->devs[0].devnum;
        int dw = r10_bio->devs[1].devnum;

        while (sectors) {
                int s = sectors;
                struct md_rdev *rdev;
                sector_t addr;
                int ok;

                if (s > (PAGE_SIZE>>9))
                        s = PAGE_SIZE >> 9;

                rdev = conf->mirrors[dr].rdev;
                addr = r10_bio->devs[0].addr + sect,
                ok = sync_page_io(rdev,
                                  addr,
                                  s << 9,
                                  bio->bi_io_vec[idx].bv_page,
                                  READ, false);
                if (ok) {
                        rdev = conf->mirrors[dw].rdev;
                        addr = r10_bio->devs[1].addr + sect;
                        ok = sync_page_io(rdev,
                                          addr,
                                          s << 9,
                                          bio->bi_io_vec[idx].bv_page,
                                          WRITE, false);
                        if (!ok) {
                                set_bit(WriteErrorSeen, &rdev->flags);
                                if (!test_and_set_bit(WantReplacement,
                                                      &rdev->flags))
                                        set_bit(MD_RECOVERY_NEEDED,
                                                &rdev->mddev->recovery);
                        }
                }
                if (!ok) {
                        /* We don't worry if we cannot set a bad block -
                         * it really is bad so there is no loss in not
                         * recording it yet
                         */
                        rdev_set_badblocks(rdev, addr, s, 0);

                        if (rdev != conf->mirrors[dw].rdev) {
                                /* need bad block on destination too */
                                struct md_rdev *rdev2 = conf->mirrors[dw].rdev;
                                addr = r10_bio->devs[1].addr + sect;
                                ok = rdev_set_badblocks(rdev2, addr, s, 0);
                                if (!ok) {
                                        /* just abort the recovery */
                                        printk(KERN_NOTICE
                                               "md/raid10:%s: recovery aborted"
                                               " due to read error\n",
                                               mdname(mddev));

                                        conf->mirrors[dw].recovery_disabled
                                                = mddev->recovery_disabled;
                                        set_bit(MD_RECOVERY_INTR,
                                                &mddev->recovery);
                                        break;
                                }
                        }
                }

                sectors -= s;
                sect += s;
                idx++;
        }
}

static void recovery_request_write(struct mddev *mddev, struct r10bio *r10_bio)
{
        struct r10conf *conf = mddev->private;
        int d;
        struct bio *wbio, *wbio2;

        if (!test_bit(R10BIO_Uptodate, &r10_bio->state)) {
                fix_recovery_read_error(r10_bio);
                end_sync_request(r10_bio);
                return;
        }

        /*
         * share the pages with the first bio
         * and submit the write request
         */
        d = r10_bio->devs[1].devnum;
        wbio = r10_bio->devs[1].bio;
        wbio2 = r10_bio->devs[1].repl_bio;
        /* Need to test wbio2->bi_end_io before we call
         * generic_make_request as if the former is NULL,
         * the latter is free to free wbio2.
         */
        if (wbio2 && !wbio2->bi_end_io)
                wbio2 = NULL;
        if (wbio->bi_end_io) {
                atomic_inc(&conf->mirrors[d].rdev->nr_pending);
                md_sync_acct(conf->mirrors[d].rdev->bdev, bio_sectors(wbio));
                generic_make_request(wbio);
        }
        if (wbio2) {
                atomic_inc(&conf->mirrors[d].replacement->nr_pending);
                md_sync_acct(conf->mirrors[d].replacement->bdev,
                             bio_sectors(wbio2));
                generic_make_request(wbio2);
        }
}


/*
 * Used by fix_read_error() to decay the per rdev read_errors.
 * We halve the read error count for every hour that has elapsed
 * since the last recorded read error.
 *
 */
static void check_decay_read_errors(struct mddev *mddev, struct md_rdev *rdev)
{
        struct timespec cur_time_mon;
        unsigned long hours_since_last;
        unsigned int read_errors = atomic_read(&rdev->read_errors);

        ktime_get_ts(&cur_time_mon);

        if (rdev->last_read_error.tv_sec == 0 &&
            rdev->last_read_error.tv_nsec == 0) {
                /* first time we've seen a read error */
                rdev->last_read_error = cur_time_mon;
                return;
        }

        hours_since_last = (cur_time_mon.tv_sec -
                            rdev->last_read_error.tv_sec) / 3600;

        rdev->last_read_error = cur_time_mon;

        /*
         * if hours_since_last is > the number of bits in read_errors
         * just set read errors to 0. We do this to avoid
         * overflowing the shift of read_errors by hours_since_last.
         */
        if (hours_since_last >= 8 * sizeof(read_errors))
                atomic_set(&rdev->read_errors, 0);
        else
                atomic_set(&rdev->read_errors, read_errors >> hours_since_last);
}

static int r10_sync_page_io(struct md_rdev *rdev, sector_t sector,
                            int sectors, struct page *page, int rw)
{
        sector_t first_bad;
        int bad_sectors;

        if (is_badblock(rdev, sector, sectors, &first_bad, &bad_sectors)
            && (rw == READ || test_bit(WriteErrorSeen, &rdev->flags)))
                return -1;
        if (sync_page_io(rdev, sector, sectors << 9, page, rw, false))
                /* success */
                return 1;
        if (rw == WRITE) {
                set_bit(WriteErrorSeen, &rdev->flags);
                if (!test_and_set_bit(WantReplacement, &rdev->flags))
                        set_bit(MD_RECOVERY_NEEDED,
                                &rdev->mddev->recovery);
        }
        /* need to record an error - either for the block or the device */
        if (!rdev_set_badblocks(rdev, sector, sectors, 0))
                md_error(rdev->mddev, rdev);
        return 0;
}

/*
 * This is a kernel thread which:
 *
 *      1.      Retries failed read operations on working mirrors.
 *      2.      Updates the raid superblock when problems encounter.
 *      3.      Performs writes following reads for array synchronising.
 */

static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10bio *r10_bio)
{
        int sect = 0; /* Offset from r10_bio->sector */
        int sectors = r10_bio->sectors;
        struct md_rdev*rdev;
        int max_read_errors = atomic_read(&mddev->max_corr_read_errors);
        int d = r10_bio->devs[r10_bio->read_slot].devnum;

        /* still own a reference to this rdev, so it cannot
         * have been cleared recently.
         */
        rdev = conf->mirrors[d].rdev;

        if (test_bit(Faulty, &rdev->flags))
                /* drive has already been failed, just ignore any
                   more fix_read_error() attempts */
                return;

        check_decay_read_errors(mddev, rdev);
        atomic_inc(&rdev->read_errors);
        if (atomic_read(&rdev->read_errors) > max_read_errors) {
                char b[BDEVNAME_SIZE];
                bdevname(rdev->bdev, b);

                printk(KERN_NOTICE
                       "md/raid10:%s: %s: Raid device exceeded "
                       "read_error threshold [cur %d:max %d]\n",
                       mdname(mddev), b,
                       atomic_read(&rdev->read_errors), max_read_errors);
                printk(KERN_NOTICE
                       "md/raid10:%s: %s: Failing raid device\n",
                       mdname(mddev), b);
                md_error(mddev, conf->mirrors[d].rdev);
                r10_bio->devs[r10_bio->read_slot].bio = IO_BLOCKED;
                return;
        }

        while(sectors) {
                int s = sectors;
                int sl = r10_bio->read_slot;
                int success = 0;
                int start;

                if (s > (PAGE_SIZE>>9))
                        s = PAGE_SIZE >> 9;

                rcu_read_lock();
                do {
                        sector_t first_bad;
                        int bad_sectors;

                        d = r10_bio->devs[sl].devnum;
                        rdev = rcu_dereference(conf->mirrors[d].rdev);
                        if (rdev &&
                            !test_bit(Unmerged, &rdev->flags) &&
                            test_bit(In_sync, &rdev->flags) &&
                            is_badblock(rdev, r10_bio->devs[sl].addr + sect, s,
                                        &first_bad, &bad_sectors) == 0) {
                                atomic_inc(&rdev->nr_pending);
                                rcu_read_unlock();
                                success = sync_page_io(rdev,
                                                       r10_bio->devs[sl].addr +
                                                       sect,
                                                       s<<9,
                                                       conf->tmppage, READ, false);
                                rdev_dec_pending(rdev, mddev);
                                rcu_read_lock();
                                if (success)
                                        break;
                        }
                        sl++;
                        if (sl == conf->copies)
                                sl = 0;
                } while (!success && sl != r10_bio->read_slot);
                rcu_read_unlock();

                if (!success) {
                        /* Cannot read from anywhere, just mark the block
                         * as bad on the first device to discourage future
                         * reads.
                         */
                        int dn = r10_bio->devs[r10_bio->read_slot].devnum;
                        rdev = conf->mirrors[dn].rdev;

                        if (!rdev_set_badblocks(
                                    rdev,
                                    r10_bio->devs[r10_bio->read_slot].addr
                                    + sect,
                                    s, 0)) {
                                md_error(mddev, rdev);
                                r10_bio->devs[r10_bio->read_slot].bio
                                        = IO_BLOCKED;
                        }
                        break;
                }

                start = sl;
                /* write it back and re-read */
                rcu_read_lock();
                while (sl != r10_bio->read_slot) {
                        char b[BDEVNAME_SIZE];

                        if (sl==0)
                                sl = conf->copies;
                        sl--;
                        d = r10_bio->devs[sl].devnum;
                        rdev = rcu_dereference(conf->mirrors[d].rdev);
                        if (!rdev ||
                            test_bit(Unmerged, &rdev->flags) ||
                            !test_bit(In_sync, &rdev->flags))
                                continue;

                        atomic_inc(&rdev->nr_pending);
                        rcu_read_unlock();
                        if (r10_sync_page_io(rdev,
                                             r10_bio->devs[sl].addr +
                                             sect,
                                             s, conf->tmppage, WRITE)
                            == 0) {
                                /* Well, this device is dead */
                                printk(KERN_NOTICE
                                       "md/raid10:%s: read correction "
                                       "write failed"
                                       " (%d sectors at %llu on %s)\n",
                                       mdname(mddev), s,
                                       (unsigned long long)(
                                               sect +
                                               choose_data_offset(r10_bio,
                                                                  rdev)),
                                       bdevname(rdev->bdev, b));
                                printk(KERN_NOTICE "md/raid10:%s: %s: failing "
                                       "drive\n",
                                       mdname(mddev),
                                       bdevname(rdev->bdev, b));
                        }
                        rdev_dec_pending(rdev, mddev);
                        rcu_read_lock();
                }
                sl = start;
                while (sl != r10_bio->read_slot) {
                        char b[BDEVNAME_SIZE];

                        if (sl==0)
                                sl = conf->copies;
                        sl--;
                        d = r10_bio->devs[sl].devnum;
                        rdev = rcu_dereference(conf->mirrors[d].rdev);
                        if (!rdev ||
                            !test_bit(In_sync, &rdev->flags))
                                continue;

                        atomic_inc(&rdev->nr_pending);
                        rcu_read_unlock();
                        switch (r10_sync_page_io(rdev,
                                             r10_bio->devs[sl].addr +
                                             sect,
                                             s, conf->tmppage,
                                                 READ)) {
                        case 0:
                                /* Well, this device is dead */
                                printk(KERN_NOTICE
                                       "md/raid10:%s: unable to read back "
                                       "corrected sectors"
                                       " (%d sectors at %llu on %s)\n",
                                       mdname(mddev), s,
                                       (unsigned long long)(
                                               sect +
                                               choose_data_offset(r10_bio, rdev)),
                                       bdevname(rdev->bdev, b));
                                printk(KERN_NOTICE "md/raid10:%s: %s: failing "
                                       "drive\n",
                                       mdname(mddev),
                                       bdevname(rdev->bdev, b));
                                break;
                        case 1:
                                printk(KERN_INFO
                                       "md/raid10:%s: read error corrected"
                                       " (%d sectors at %llu on %s)\n",
                                       mdname(mddev), s,
                                       (unsigned long long)(
                                               sect +
                                               choose_data_offset(r10_bio, rdev)),
                                       bdevname(rdev->bdev, b));
                                atomic_add(s, &rdev->corrected_errors);
                        }

                        rdev_dec_pending(rdev, mddev);
                        rcu_read_lock();
                }
                rcu_read_unlock();

                sectors -= s;
                sect += s;
        }
}

static int narrow_write_error(struct r10bio *r10_bio, int i)
{
        struct bio *bio = r10_bio->master_bio;
        struct mddev *mddev = r10_bio->mddev;
        struct r10conf *conf = mddev->private;
        struct md_rdev *rdev = conf->mirrors[r10_bio->devs[i].devnum].rdev;
        /* bio has the data to be written to slot 'i' where
         * we just recently had a write error.
         * We repeatedly clone the bio and trim down to one block,
         * then try the write.  Where the write fails we record
         * a bad block.
         * It is conceivable that the bio doesn't exactly align with
         * blocks.  We must handle this.
         *
         * We currently own a reference to the rdev.
         */

        int block_sectors;
        sector_t sector;
        int sectors;
        int sect_to_write = r10_bio->sectors;
        int ok = 1;

        if (rdev->badblocks.shift < 0)
                return 0;

        block_sectors = 1 << rdev->badblocks.shift;
        sector = r10_bio->sector;
        sectors = ((r10_bio->sector + block_sectors)
                   & ~(sector_t)(block_sectors - 1))
                - sector;

        while (sect_to_write) {
                struct bio *wbio;
                if (sectors > sect_to_write)
                        sectors = sect_to_write;
                /* Write at 'sector' for 'sectors' */
                wbio = bio_clone_mddev(bio, GFP_NOIO, mddev);
                bio_trim(wbio, sector - bio->bi_iter.bi_sector, sectors);
                wbio->bi_iter.bi_sector = (r10_bio->devs[i].addr+
                                   choose_data_offset(r10_bio, rdev) +
                                   (sector - r10_bio->sector));
                wbio->bi_bdev = rdev->bdev;
                if (submit_bio_wait(WRITE, wbio) == 0)
                        /* Failure! */
                        ok = rdev_set_badblocks(rdev, sector,
                                                sectors, 0)
                                && ok;

                bio_put(wbio);
                sect_to_write -= sectors;
                sector += sectors;
                sectors = block_sectors;
        }
        return ok;
}

static void handle_read_error(struct mddev *mddev, struct r10bio *r10_bio)
{
        int slot = r10_bio->read_slot;
        struct bio *bio;
        struct r10conf *conf = mddev->private;
        struct md_rdev *rdev = r10_bio->devs[slot].rdev;
        char b[BDEVNAME_SIZE];
        unsigned long do_sync;
        int max_sectors;

        /* we got a read error. Maybe the drive is bad.  Maybe just
         * the block and we can fix it.
         * We freeze all other IO, and try reading the block from
         * other devices.  When we find one, we re-write
         * and check it that fixes the read error.
         * This is all done synchronously while the array is
         * frozen.
         */
        bio = r10_bio->devs[slot].bio;
        bdevname(bio->bi_bdev, b);
        bio_put(bio);
        r10_bio->devs[slot].bio = NULL;

        if (mddev->ro == 0) {
                freeze_array(conf, 1);
                fix_read_error(conf, mddev, r10_bio);
                unfreeze_array(conf);
        } else
                r10_bio->devs[slot].bio = IO_BLOCKED;

        rdev_dec_pending(rdev, mddev);

read_more:
        rdev = read_balance(conf, r10_bio, &max_sectors);
        if (rdev == NULL) {
                printk(KERN_ALERT "md/raid10:%s: %s: unrecoverable I/O"
                       " read error for block %llu\n",
                       mdname(mddev), b,
                       (unsigned long long)r10_bio->sector);
                raid_end_bio_io(r10_bio);
                return;
        }

        do_sync = (r10_bio->master_bio->bi_rw & REQ_SYNC);
        slot = r10_bio->read_slot;
        printk_ratelimited(
                KERN_ERR
                "md/raid10:%s: %s: redirecting "
                "sector %llu to another mirror\n",
                mdname(mddev),
                bdevname(rdev->bdev, b),
                (unsigned long long)r10_bio->sector);
        bio = bio_clone_mddev(r10_bio->master_bio,
                              GFP_NOIO, mddev);
        bio_trim(bio, r10_bio->sector - bio->bi_iter.bi_sector, max_sectors);
        r10_bio->devs[slot].bio = bio;
        r10_bio->devs[slot].rdev = rdev;
        bio->bi_iter.bi_sector = r10_bio->devs[slot].addr
                + choose_data_offset(r10_bio, rdev);
        bio->bi_bdev = rdev->bdev;
        bio->bi_rw = READ | do_sync;
        bio->bi_private = r10_bio;
        bio->bi_end_io = raid10_end_read_request;
        if (max_sectors < r10_bio->sectors) {
                /* Drat - have to split this up more */
                struct bio *mbio = r10_bio->master_bio;
                int sectors_handled =
                        r10_bio->sector + max_sectors
                        - mbio->bi_iter.bi_sector;
                r10_bio->sectors = max_sectors;
                spin_lock_irq(&conf->device_lock);
                if (mbio->bi_phys_segments == 0)
                        mbio->bi_phys_segments = 2;
                else
                        mbio->bi_phys_segments++;
                spin_unlock_irq(&conf->device_lock);
                generic_make_request(bio);

                r10_bio = mempool_alloc(conf->r10bio_pool,
                                        GFP_NOIO);
                r10_bio->master_bio = mbio;
                r10_bio->sectors = bio_sectors(mbio) - sectors_handled;
                r10_bio->state = 0;
                set_bit(R10BIO_ReadError,
                        &r10_bio->state);
                r10_bio->mddev = mddev;
                r10_bio->sector = mbio->bi_iter.bi_sector
                        + sectors_handled;

                goto read_more;
        } else
                generic_make_request(bio);
}

static void handle_write_completed(struct r10conf *conf, struct r10bio *r10_bio)
{
        /* Some sort of write request has finished and it
         * succeeded in writing where we thought there was a
         * bad block.  So forget the bad block.
         * Or possibly if failed and we need to record
         * a bad block.
         */
        int m;
        struct md_rdev *rdev;

        if (test_bit(R10BIO_IsSync, &r10_bio->state) ||
            test_bit(R10BIO_IsRecover, &r10_bio->state)) {
                for (m = 0; m < conf->copies; m++) {
                        int dev = r10_bio->devs[m].devnum;
                        rdev = conf->mirrors[dev].rdev;
                        if (r10_bio->devs[m].bio == NULL)
                                continue;
                        if (test_bit(BIO_UPTODATE,
                                     &r10_bio->devs[m].bio->bi_flags)) {
                                rdev_clear_badblocks(
                                        rdev,
                                        r10_bio->devs[m].addr,
                                        r10_bio->sectors, 0);
                        } else {
                                if (!rdev_set_badblocks(
                                            rdev,
                                            r10_bio->devs[m].addr,
                                            r10_bio->sectors, 0))
                                        md_error(conf->mddev, rdev);
                        }
                        rdev = conf->mirrors[dev].replacement;
                        if (r10_bio->devs[m].repl_bio == NULL)
                                continue;
                        if (test_bit(BIO_UPTODATE,
                                     &r10_bio->devs[m].repl_bio->bi_flags)) {
                                rdev_clear_badblocks(
                                        rdev,
                                        r10_bio->devs[m].addr,
                                        r10_bio->sectors, 0);
                        } else {
                                if (!rdev_set_badblocks(
                                            rdev,
                                            r10_bio->devs[m].addr,
                                            r10_bio->sectors, 0))
                                        md_error(conf->mddev, rdev);
                        }
                }
                put_buf(r10_bio);
        } else {
                for (m = 0; m < conf->copies; m++) {
                        int dev = r10_bio->devs[m].devnum;
                        struct bio *bio = r10_bio->devs[m].bio;
                        rdev = conf->mirrors[dev].rdev;
                        if (bio == IO_MADE_GOOD) {
                                rdev_clear_badblocks(
                                        rdev,
                                        r10_bio->devs[m].addr,
                                        r10_bio->sectors, 0);
                                rdev_dec_pending(rdev, conf->mddev);
                        } else if (bio != NULL &&
                                   !test_bit(BIO_UPTODATE, &bio->bi_flags)) {
                                if (!narrow_write_error(r10_bio, m)) {
                                        md_error(conf->mddev, rdev);
                                        set_bit(R10BIO_Degraded,
                                                &r10_bio->state);
                                }
                                rdev_dec_pending(rdev, conf->mddev);
                        }
                        bio = r10_bio->devs[m].repl_bio;
                        rdev = conf->mirrors[dev].replacement;
                        if (rdev && bio == IO_MADE_GOOD) {
                                rdev_clear_badblocks(
                                        rdev,
                                        r10_bio->devs[m].addr,
                                        r10_bio->sectors, 0);
                                rdev_dec_pending(rdev, conf->mddev);
                        }
                }
                if (test_bit(R10BIO_WriteError,
                             &r10_bio->state))
                        close_write(r10_bio);
                raid_end_bio_io(r10_bio);
        }
}

static void raid10d(struct md_thread *thread)
{
        struct mddev *mddev = thread->mddev;
        struct r10bio *r10_bio;
        unsigned long flags;
        struct r10conf *conf = mddev->private;
        struct list_head *head = &conf->retry_list;
        struct blk_plug plug;

        md_check_recovery(mddev);

        blk_start_plug(&plug);
        for (;;) {

                flush_pending_writes(conf);

                spin_lock_irqsave(&conf->device_lock, flags);
                if (list_empty(head)) {
                        spin_unlock_irqrestore(&conf->device_lock, flags);
                        break;
                }
                r10_bio = list_entry(head->prev, struct r10bio, retry_list);
                list_del(head->prev);
                conf->nr_queued--;
                spin_unlock_irqrestore(&conf->device_lock, flags);

                mddev = r10_bio->mddev;
                conf = mddev->private;
                if (test_bit(R10BIO_MadeGood, &r10_bio->state) ||
                    test_bit(R10BIO_WriteError, &r10_bio->state))
                        handle_write_completed(conf, r10_bio);
                else if (test_bit(R10BIO_IsReshape, &r10_bio->state))
                        reshape_request_write(mddev, r10_bio);
                else if (test_bit(R10BIO_IsSync, &r10_bio->state))
                        sync_request_write(mddev, r10_bio);
                else if (test_bit(R10BIO_IsRecover, &r10_bio->state))
                        recovery_request_write(mddev, r10_bio);
                else if (test_bit(R10BIO_ReadError, &r10_bio->state))
                        handle_read_error(mddev, r10_bio);
                else {
                        /* just a partial read to be scheduled from a
                         * separate context
                         */
                        int slot = r10_bio->read_slot;
                        generic_make_request(r10_bio->devs[slot].bio);
                }

                cond_resched();
                if (mddev->flags & ~(1<<MD_CHANGE_PENDING))
                        md_check_recovery(mddev);
        }
        blk_finish_plug(&plug);
}


static int init_resync(struct r10conf *conf)
{
        int buffs;
        int i;

        buffs = RESYNC_WINDOW / RESYNC_BLOCK_SIZE;
        BUG_ON(conf->r10buf_pool);
        conf->have_replacement = 0;
        for (i = 0; i < conf->geo.raid_disks; i++)
                if (conf->mirrors[i].replacement)
                        conf->have_replacement = 1;
        conf->r10buf_pool = mempool_create(buffs, r10buf_pool_alloc, r10buf_pool_free, conf);
        if (!conf->r10buf_pool)
                return -ENOMEM;
        conf->next_resync = 0;
        return 0;
}

/*
 * perform a "sync" on one "block"
 *
 * We need to make sure that no normal I/O request - particularly write
 * requests - conflict with active sync requests.
 *
 * This is achieved by tracking pending requests and a 'barrier' concept
 * that can be installed to exclude normal IO requests.
 *
 * Resync and recovery are handled very differently.
 * We differentiate by looking at MD_RECOVERY_SYNC in mddev->recovery.
 *
 * For resync, we iterate over virtual addresses, read all copies,
 * and update if there are differences.  If only one copy is live,
 * skip it.
 * For recovery, we iterate over physical addresses, read a good
 * value for each non-in_sync drive, and over-write.
 *
 * So, for recovery we may have several outstanding complex requests for a
 * given address, one for each out-of-sync device.  We model this by allocating
 * a number of r10_bio structures, one for each out-of-sync device.
 * As we setup these structures, we collect all bio's together into a list
 * which we then process collectively to add pages, and then process again
 * to pass to generic_make_request.
 *
 * The r10_bio structures are linked using a borrowed master_bio pointer.
 * This link is counted in ->remaining.  When the r10_bio that points to NULL
 * has its remaining count decremented to 0, the whole complex operation
 * is complete.
 *
 */

static sector_t sync_request(struct mddev *mddev, sector_t sector_nr,
                             int *skipped, int go_faster)
{
        struct r10conf *conf = mddev->private;
        struct r10bio *r10_bio;
        struct bio *biolist = NULL, *bio;
        sector_t max_sector, nr_sectors;
        int i;
        int max_sync;
        sector_t sync_blocks;
        sector_t sectors_skipped = 0;
        int chunks_skipped = 0;
        sector_t chunk_mask = conf->geo.chunk_mask;

        if (!conf->r10buf_pool)
                if (init_resync(conf))
                        return 0;

        /*
         * Allow skipping a full rebuild for incremental assembly
         * of a clean array, like RAID1 does.
         */
        if (mddev->bitmap == NULL &&
            mddev->recovery_cp == MaxSector &&
            mddev->reshape_position == MaxSector &&
            !test_bit(MD_RECOVERY_SYNC, &mddev->recovery) &&
            !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) &&
            !test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
            conf->fullsync == 0) {
                *skipped = 1;
                return mddev->dev_sectors - sector_nr;
        }

 skipped:
        max_sector = mddev->dev_sectors;
        if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery) ||
            test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
                max_sector = mddev->resync_max_sectors;
        if (sector_nr >= max_sector) {
                /* If we aborted, we need to abort the
                 * sync on the 'current' bitmap chucks (there can
                 * be several when recovering multiple devices).
                 * as we may have started syncing it but not finished.
                 * We can find the current address in
                 * mddev->curr_resync, but for recovery,
                 * we need to convert that to several
                 * virtual addresses.
                 */
                if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery)) {
                        end_reshape(conf);
                        return 0;
                }

                if (mddev->curr_resync < max_sector) { /* aborted */
                        if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery))
                                bitmap_end_sync(mddev->bitmap, mddev->curr_resync,
                                                &sync_blocks, 1);
                        else for (i = 0; i < conf->geo.raid_disks; i++) {
                                sector_t sect =
                                        raid10_find_virt(conf, mddev->curr_resync, i);
                                bitmap_end_sync(mddev->bitmap, sect,
                                                &sync_blocks, 1);
                        }
                } else {
                        /* completed sync */
                        if ((!mddev->bitmap || conf->fullsync)
                            && conf->have_replacement
                            && test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
                                /* Completed a full sync so the replacements
                                 * are now fully recovered.
                                 */
                                for (i = 0; i < conf->geo.raid_disks; i++)
                                        if (conf->mirrors[i].replacement)
                                                conf->mirrors[i].replacement
                                                        ->recovery_offset
                                                        = MaxSector;
                        }
                        conf->fullsync = 0;
                }
                bitmap_close_sync(mddev->bitmap);
                close_sync(conf);
                *skipped = 1;
                return sectors_skipped;
        }

        if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
                return reshape_request(mddev, sector_nr, skipped);

        if (chunks_skipped >= conf->geo.raid_disks) {
                /* if there has been nothing to do on any drive,
                 * then there is nothing to do at all..
                 */
                *skipped = 1;
                return (max_sector - sector_nr) + sectors_skipped;
        }

        if (max_sector > mddev->resync_max)
                max_sector = mddev->resync_max; /* Don't do IO beyond here */

        /* make sure whole request will fit in a chunk - if chunks
         * are meaningful
         */
        if (conf->geo.near_copies < conf->geo.raid_disks &&
            max_sector > (sector_nr | chunk_mask))
                max_sector = (sector_nr | chunk_mask) + 1;
        /*
         * If there is non-resync activity waiting for us then
         * put in a delay to throttle resync.
         */
        if (!go_faster && conf->nr_waiting)
                msleep_interruptible(1000);

        /* Again, very different code for resync and recovery.
         * Both must result in an r10bio with a list of bios that
         * have bi_end_io, bi_sector, bi_bdev set,
         * and bi_private set to the r10bio.
         * For recovery, we may actually create several r10bios
         * with 2 bios in each, that correspond to the bios in the main one.
         * In this case, the subordinate r10bios link back through a
         * borrowed master_bio pointer, and the counter in the master
         * includes a ref from each subordinate.
         */
        /* First, we decide what to do and set ->bi_end_io
         * To end_sync_read if we want to read, and
         * end_sync_write if we will want to write.
         */

        max_sync = RESYNC_PAGES << (PAGE_SHIFT-9);
        if (!test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
                /* recovery... the complicated one */
                int j;
                r10_bio = NULL;

                for (i = 0 ; i < conf->geo.raid_disks; i++) {
                        int still_degraded;
                        struct r10bio *rb2;
                        sector_t sect;
                        int must_sync;
                        int any_working;
                        struct raid10_info *mirror = &conf->mirrors[i];

                        if ((mirror->rdev == NULL ||
                             test_bit(In_sync, &mirror->rdev->flags))
                            &&
                            (mirror->replacement == NULL ||
                             test_bit(Faulty,
                                      &mirror->replacement->flags)))
                                continue;

                        still_degraded = 0;
                        /* want to reconstruct this device */
                        rb2 = r10_bio;
                        sect = raid10_find_virt(conf, sector_nr, i);
                        if (sect >= mddev->resync_max_sectors) {
                                /* last stripe is not complete - don't
                                 * try to recover this sector.
                                 */
                                continue;
                        }
                        /* Unless we are doing a full sync, or a replacement
                         * we only need to recover the block if it is set in
                         * the bitmap
                         */
                        must_sync = bitmap_start_sync(mddev->bitmap, sect,
                                                      &sync_blocks, 1);
                        if (sync_blocks < max_sync)
                                max_sync = sync_blocks;
                        if (!must_sync &&
                            mirror->replacement == NULL &&
                            !conf->fullsync) {
                                /* yep, skip the sync_blocks here, but don't assume
                                 * that there will never be anything to do here
                                 */
                                chunks_skipped = -1;
                                continue;
                        }

                        r10_bio = mempool_alloc(conf->r10buf_pool, GFP_NOIO);
                        raise_barrier(conf, rb2 != NULL);
                        atomic_set(&r10_bio->remaining, 0);

                        r10_bio->master_bio = (struct bio*)rb2;
                        if (rb2)
                                atomic_inc(&rb2->remaining);
                        r10_bio->mddev = mddev;
                        set_bit(R10BIO_IsRecover, &r10_bio->state);
                        r10_bio->sector = sect;

                        raid10_find_phys(conf, r10_bio);

                        /* Need to check if the array will still be
                         * degraded
                         */
                        for (j = 0; j < conf->geo.raid_disks; j++)
                                if (conf->mirrors[j].rdev == NULL ||
                                    test_bit(Faulty, &conf->mirrors[j].rdev->flags)) {
                                        still_degraded = 1;
                                        break;
                                }

                        must_sync = bitmap_start_sync(mddev->bitmap, sect,
                                                      &sync_blocks, still_degraded);

                        any_working = 0;
                        for (j=0; j<conf->copies;j++) {
                                int k;
                                int d = r10_bio->devs[j].devnum;
                                sector_t from_addr, to_addr;
                                struct md_rdev *rdev;
                                sector_t sector, first_bad;
                                int bad_sectors;
                                if (!conf->mirrors[d].rdev ||
                                    !test_bit(In_sync, &conf->mirrors[d].rdev->flags))
                                        continue;
                                /* This is where we read from */
                                any_working = 1;
                                rdev = conf->mirrors[d].rdev;
                                sector = r10_bio->devs[j].addr;

                                if (is_badblock(rdev, sector, max_sync,
                                                &first_bad, &bad_sectors)) {
                                        if (first_bad > sector)
                                                max_sync = first_bad - sector;
                                        else {
                                                bad_sectors -= (sector
                                                                - first_bad);
                                                if (max_sync > bad_sectors)
                                                        max_sync = bad_sectors;
                                                continue;
                                        }
                                }
                                bio = r10_bio->devs[0].bio;
                                bio_reset(bio);
                                bio->bi_next = biolist;
                                biolist = bio;
                                bio->bi_private = r10_bio;
                                bio->bi_end_io = end_sync_read;
                                bio->bi_rw = READ;
                                from_addr = r10_bio->devs[j].addr;
                                bio->bi_iter.bi_sector = from_addr +
                                        rdev->data_offset;
                                bio->bi_bdev = rdev->bdev;
                                atomic_inc(&rdev->nr_pending);
                                /* and we write to 'i' (if not in_sync) */

                                for (k=0; k<conf->copies; k++)
                                        if (r10_bio->devs[k].devnum == i)
                                                break;
                                BUG_ON(k == conf->copies);
                                to_addr = r10_bio->devs[k].addr;
                                r10_bio->devs[0].devnum = d;
                                r10_bio->devs[0].addr = from_addr;
                                r10_bio->devs[1].devnum = i;
                                r10_bio->devs[1].addr = to_addr;

                                rdev = mirror->rdev;
                                if (!test_bit(In_sync, &rdev->flags)) {
                                        bio = r10_bio->devs[1].bio;
                                        bio_reset(bio);
                                        bio->bi_next = biolist;
                                        biolist = bio;
                                        bio->bi_private = r10_bio;
                                        bio->bi_end_io = end_sync_write;
                                        bio->bi_rw = WRITE;
                                        bio->bi_iter.bi_sector = to_addr
                                                + rdev->data_offset;
                                        bio->bi_bdev = rdev->bdev;
                                        atomic_inc(&r10_bio->remaining);
                                } else
                                        r10_bio->devs[1].bio->bi_end_io = NULL;

                                /* and maybe write to replacement */
                                bio = r10_bio->devs[1].repl_bio;
                                if (bio)
                                        bio->bi_end_io = NULL;
                                rdev = mirror->replacement;
                                /* Note: if rdev != NULL, then bio
                                 * cannot be NULL as r10buf_pool_alloc will
                                 * have allocated it.
                                 * So the second test here is pointless.
                                 * But it keeps semantic-checkers happy, and
                                 * this comment keeps human reviewers
                                 * happy.
                                 */
                                if (rdev == NULL || bio == NULL ||
                                    test_bit(Faulty, &rdev->flags))
                                        break;
                                bio_reset(bio);
                                bio->bi_next = biolist;
                                biolist = bio;
                                bio->bi_private = r10_bio;
                                bio->bi_end_io = end_sync_write;
                                bio->bi_rw = WRITE;
                                bio->bi_iter.bi_sector = to_addr +
                                        rdev->data_offset;
                                bio->bi_bdev = rdev->bdev;
                                atomic_inc(&r10_bio->remaining);
                                break;
                        }
                        if (j == conf->copies) {
                                /* Cannot recover, so abort the recovery or
                                 * record a bad block */
                                put_buf(r10_bio);
                                if (rb2)
                                        atomic_dec(&rb2->remaining);
                                r10_bio = rb2;
                                if (any_working) {
                                        /* problem is that there are bad blocks
                                         * on other device(s)
                                         */
                                        int k;
                                        for (k = 0; k < conf->copies; k++)
                                                if (r10_bio->devs[k].devnum == i)
                                                        break;
                                        if (!test_bit(In_sync,
                                                      &mirror->rdev->flags)
                                            && !rdev_set_badblocks(
                                                    mirror->rdev,
                                                    r10_bio->devs[k].addr,
                                                    max_sync, 0))
                                                any_working = 0;
                                        if (mirror->replacement &&
                                            !rdev_set_badblocks(
                                                    mirror->replacement,
                                                    r10_bio->devs[k].addr,
                                                    max_sync, 0))
                                                any_working = 0;
                                }
                                if (!any_working)  {
                                        if (!test_and_set_bit(MD_RECOVERY_INTR,
                                                              &mddev->recovery))
                                                printk(KERN_INFO "md/raid10:%s: insufficient "
                                                       "working devices for recovery.\n",
                                                       mdname(mddev));
                                        mirror->recovery_disabled
                                                = mddev->recovery_disabled;
                                }
                                break;
                        }
                }
                if (biolist == NULL) {
                        while (r10_bio) {
                                struct r10bio *rb2 = r10_bio;
                                r10_bio = (struct r10bio*) rb2->master_bio;
                                rb2->master_bio = NULL;
                                put_buf(rb2);
                        }
                        goto giveup;
                }
        } else {
                /* resync. Schedule a read for every block at this virt offset */
                int count = 0;

                bitmap_cond_end_sync(mddev->bitmap, sector_nr);

                if (!bitmap_start_sync(mddev->bitmap, sector_nr,
                                       &sync_blocks, mddev->degraded) &&
                    !conf->fullsync && !test_bit(MD_RECOVERY_REQUESTED,
                                                 &mddev->recovery)) {
                        /* We can skip this block */
                        *skipped = 1;
                        return sync_blocks + sectors_skipped;
                }
                if (sync_blocks < max_sync)
                        max_sync = sync_blocks;
                r10_bio = mempool_alloc(conf->r10buf_pool, GFP_NOIO);

                r10_bio->mddev = mddev;
                atomic_set(&r10_bio->remaining, 0);
                raise_barrier(conf, 0);
                conf->next_resync = sector_nr;

                r10_bio->master_bio = NULL;
                r10_bio->sector = sector_nr;
                set_bit(R10BIO_IsSync, &r10_bio->state);
                raid10_find_phys(conf, r10_bio);
                r10_bio->sectors = (sector_nr | chunk_mask) - sector_nr + 1;

                for (i = 0; i < conf->copies; i++) {
                        int d = r10_bio->devs[i].devnum;
                        sector_t first_bad, sector;
                        int bad_sectors;

                        if (r10_bio->devs[i].repl_bio)
                                r10_bio->devs[i].repl_bio->bi_end_io = NULL;

                        bio = r10_bio->devs[i].bio;
                        bio_reset(bio);
                        clear_bit(BIO_UPTODATE, &bio->bi_flags);
                        if (conf->mirrors[d].rdev == NULL ||
                            test_bit(Faulty, &conf->mirrors[d].rdev->flags))
                                continue;
                        sector = r10_bio->devs[i].addr;
                        if (is_badblock(conf->mirrors[d].rdev,
                                        sector, max_sync,
                                        &first_bad, &bad_sectors)) {
                                if (first_bad > sector)
                                        max_sync = first_bad - sector;
                                else {
                                        bad_sectors -= (sector - first_bad);
                                        if (max_sync > bad_sectors)
                                                max_sync = bad_sectors;
                                        continue;
                                }
                        }
                        atomic_inc(&conf->mirrors[d].rdev->nr_pending);
                        atomic_inc(&r10_bio->remaining);
                        bio->bi_next = biolist;
                        biolist = bio;
                        bio->bi_private = r10_bio;
                        bio->bi_end_io = end_sync_read;
                        bio->bi_rw = READ;
                        bio->bi_iter.bi_sector = sector +
                                conf->mirrors[d].rdev->data_offset;
                        bio->bi_bdev = conf->mirrors[d].rdev->bdev;
                        count++;

                        if (conf->mirrors[d].replacement == NULL ||
                            test_bit(Faulty,
                                     &conf->mirrors[d].replacement->flags))
                                continue;

                        /* Need to set up for writing to the replacement */
                        bio = r10_bio->devs[i].repl_bio;
                        bio_reset(bio);
                        clear_bit(BIO_UPTODATE, &bio->bi_flags);

                        sector = r10_bio->devs[i].addr;
                        atomic_inc(&conf->mirrors[d].rdev->nr_pending);
                        bio->bi_next = biolist;
                        biolist = bio;
                        bio->bi_private = r10_bio;
                        bio->bi_end_io = end_sync_write;
                        bio->bi_rw = WRITE;
                        bio->bi_iter.bi_sector = sector +
                                conf->mirrors[d].replacement->data_offset;
                        bio->bi_bdev = conf->mirrors[d].replacement->bdev;
                        count++;
                }

                if (count < 2) {
                        for (i=0; i<conf->copies; i++) {
                                int d = r10_bio->devs[i].devnum;
                                if (r10_bio->devs[i].bio->bi_end_io)
                                        rdev_dec_pending(conf->mirrors[d].rdev,
                                                         mddev);
                                if (r10_bio->devs[i].repl_bio &&
                                    r10_bio->devs[i].repl_bio->bi_end_io)
                                        rdev_dec_pending(
                                                conf->mirrors[d].replacement,
                                                mddev);
                        }
                        put_buf(r10_bio);
                        biolist = NULL;
                        goto giveup;
                }
        }

        nr_sectors = 0;
        if (sector_nr + max_sync < max_sector)
                max_sector = sector_nr + max_sync;
        do {
                struct page *page;
                int len = PAGE_SIZE;
                if (sector_nr + (len>>9) > max_sector)
                        len = (max_sector - sector_nr) << 9;
                if (len == 0)
                        break;
                for (bio= biolist ; bio ; bio=bio->bi_next) {
                        struct bio *bio2;
                        page = bio->bi_io_vec[bio->bi_vcnt].bv_page;
                        if (bio_add_page(bio, page, len, 0))
                                continue;

                        /* stop here */
                        bio->bi_io_vec[bio->bi_vcnt].bv_page = page;
                        for (bio2 = biolist;
                             bio2 && bio2 != bio;
                             bio2 = bio2->bi_next) {
                                /* remove last page from this bio */
                                bio2->bi_vcnt--;
                                bio2->bi_iter.bi_size -= len;
                                bio2->bi_flags &= ~(1<< BIO_SEG_VALID);
                        }
                        goto bio_full;
                }
                nr_sectors += len>>9;
                sector_nr += len>>9;
        } while (biolist->bi_vcnt < RESYNC_PAGES);
 bio_full:
        r10_bio->sectors = nr_sectors;

        while (biolist) {
                bio = biolist;
                biolist = biolist->bi_next;

                bio->bi_next = NULL;
                r10_bio = bio->bi_private;
                r10_bio->sectors = nr_sectors;

                if (bio->bi_end_io == end_sync_read) {
                        md_sync_acct(bio->bi_bdev, nr_sectors);
                        set_bit(BIO_UPTODATE, &bio->bi_flags);
                        generic_make_request(bio);
                }
        }

        if (sectors_skipped)
                /* pretend they weren't skipped, it makes
                 * no important difference in this case
                 */
                md_done_sync(mddev, sectors_skipped, 1);

        return sectors_skipped + nr_sectors;
 giveup:
        /* There is nowhere to write, so all non-sync
         * drives must be failed or in resync, all drives
         * have a bad block, so try the next chunk...
         */
        if (sector_nr + max_sync < max_sector)
                max_sector = sector_nr + max_sync;

        sectors_skipped += (max_sector - sector_nr);
        chunks_skipped ++;
        sector_nr = max_sector;
        goto skipped;
}

static sector_t
raid10_size(struct mddev *mddev, sector_t sectors, int raid_disks)
{
        sector_t size;
        struct r10conf *conf = mddev->private;

        if (!raid_disks)
                raid_disks = min(conf->geo.raid_disks,
                                 conf->prev.raid_disks);
        if (!sectors)
                sectors = conf->dev_sectors;

        size = sectors >> conf->geo.chunk_shift;
        sector_div(size, conf->geo.far_copies);
        size = size * raid_disks;
        sector_div(size, conf->geo.near_copies);

        return size << conf->geo.chunk_shift;
}

static void calc_sectors(struct r10conf *conf, sector_t size)
{
        /* Calculate the number of sectors-per-device that will
         * actually be used, and set conf->dev_sectors and
         * conf->stride
         */

        size = size >> conf->geo.chunk_shift;
        sector_div(size, conf->geo.far_copies);
        size = size * conf->geo.raid_disks;
        sector_div(size, conf->geo.near_copies);
        /* 'size' is now the number of chunks in the array */
        /* calculate "used chunks per device" */
        size = size * conf->copies;

        /* We need to round up when dividing by raid_disks to
         * get the stride size.
         */
        size = DIV_ROUND_UP_SECTOR_T(size, conf->geo.raid_disks);

        conf->dev_sectors = size << conf->geo.chunk_shift;

        if (conf->geo.far_offset)
                conf->geo.stride = 1 << conf->geo.chunk_shift;
        else {
                sector_div(size, conf->geo.far_copies);
                conf->geo.stride = size << conf->geo.chunk_shift;
        }
}

enum geo_type {geo_new, geo_old, geo_start};
static int setup_geo(struct geom *geo, struct mddev *mddev, enum geo_type new)
{
        int nc, fc, fo;
        int layout, chunk, disks;
        switch (new) {
        case geo_old:
                layout = mddev->layout;
                chunk = mddev->chunk_sectors;
                disks = mddev->raid_disks - mddev->delta_disks;
                break;
        case geo_new:
                layout = mddev->new_layout;
                chunk = mddev->new_chunk_sectors;
                disks = mddev->raid_disks;
                break;
        default: /* avoid 'may be unused' warnings */
        case geo_start: /* new when starting reshape - raid_disks not
                         * updated yet. */
                layout = mddev->new_layout;
                chunk = mddev->new_chunk_sectors;
                disks = mddev->raid_disks + mddev->delta_disks;
                break;
        }
        if (layout >> 18)
                return -1;
        if (chunk < (PAGE_SIZE >> 9) ||
            !is_power_of_2(chunk))
                return -2;
        nc = layout & 255;
        fc = (layout >> 8) & 255;
        fo = layout & (1<<16);
        geo->raid_disks = disks;
        geo->near_copies = nc;
        geo->far_copies = fc;
        geo->far_offset = fo;
        geo->far_set_size = (layout & (1<<17)) ? disks / fc : disks;
        geo->chunk_mask = chunk - 1;
        geo->chunk_shift = ffz(~chunk);
        return nc*fc;
}

static struct r10conf *setup_conf(struct mddev *mddev)
{
        struct r10conf *conf = NULL;
        int err = -EINVAL;
        struct geom geo;
        int copies;

        copies = setup_geo(&geo, mddev, geo_new);

        if (copies == -2) {
                printk(KERN_ERR "md/raid10:%s: chunk size must be "
                       "at least PAGE_SIZE(%ld) and be a power of 2.\n",
                       mdname(mddev), PAGE_SIZE);
                goto out;
        }

        if (copies < 2 || copies > mddev->raid_disks) {
                printk(KERN_ERR "md/raid10:%s: unsupported raid10 layout: 0x%8x\n",
                       mdname(mddev), mddev->new_layout);
                goto out;
        }

        err = -ENOMEM;
        conf = kzalloc(sizeof(struct r10conf), GFP_KERNEL);
        if (!conf)
                goto out;

        /* FIXME calc properly */
        conf->mirrors = kzalloc(sizeof(struct raid10_info)*(mddev->raid_disks +
                                                            max(0,-mddev->delta_disks)),
                                GFP_KERNEL);
        if (!conf->mirrors)
                goto out;

        conf->tmppage = alloc_page(GFP_KERNEL);
        if (!conf->tmppage)
                goto out;

        conf->geo = geo;
        conf->copies = copies;
        conf->r10bio_pool = mempool_create(NR_RAID10_BIOS, r10bio_pool_alloc,
                                           r10bio_pool_free, conf);
        if (!conf->r10bio_pool)
                goto out;

        calc_sectors(conf, mddev->dev_sectors);
        if (mddev->reshape_position == MaxSector) {
                conf->prev = conf->geo;
                conf->reshape_progress = MaxSector;
        } else {
                if (setup_geo(&conf->prev, mddev, geo_old) != conf->copies) {
                        err = -EINVAL;
                        goto out;
                }
                conf->reshape_progress = mddev->reshape_position;
                if (conf->prev.far_offset)
                        conf->prev.stride = 1 << conf->prev.chunk_shift;
                else
                        /* far_copies must be 1 */
                        conf->prev.stride = conf->dev_sectors;
        }
        spin_lock_init(&conf->device_lock);
        INIT_LIST_HEAD(&conf->retry_list);

        spin_lock_init(&conf->resync_lock);
        init_waitqueue_head(&conf->wait_barrier);

        conf->thread = md_register_thread(raid10d, mddev, "raid10");
        if (!conf->thread)
                goto out;

        conf->mddev = mddev;
        return conf;

 out:
        if (err == -ENOMEM)
                printk(KERN_ERR "md/raid10:%s: couldn't allocate memory.\n",
                       mdname(mddev));
        if (conf) {
                if (conf->r10bio_pool)
                        mempool_destroy(conf->r10bio_pool);
                kfree(conf->mirrors);
                safe_put_page(conf->tmppage);
                kfree(conf);
        }
        return ERR_PTR(err);
}

static int run(struct mddev *mddev)
{
        struct r10conf *conf;
        int i, disk_idx, chunk_size;
        struct raid10_info *disk;
        struct md_rdev *rdev;
        sector_t size;
        sector_t min_offset_diff = 0;
        int first = 1;
        bool discard_supported = false;

        if (mddev->private == NULL) {
                conf = setup_conf(mddev);
                if (IS_ERR(conf))
                        return PTR_ERR(conf);
                mddev->private = conf;
        }
        conf = mddev->private;
        if (!conf)
                goto out;

        mddev->thread = conf->thread;
        conf->thread = NULL;

        chunk_size = mddev->chunk_sectors << 9;
        if (mddev->queue) {
                blk_queue_max_discard_sectors(mddev->queue,
                                              mddev->chunk_sectors);
                blk_queue_max_write_same_sectors(mddev->queue, 0);
                blk_queue_io_min(mddev->queue, chunk_size);
                if (conf->geo.raid_disks % conf->geo.near_copies)
                        blk_queue_io_opt(mddev->queue, chunk_size * conf->geo.raid_disks);
                else
                        blk_queue_io_opt(mddev->queue, chunk_size *
                                         (conf->geo.raid_disks / conf->geo.near_copies));
        }

        rdev_for_each(rdev, mddev) {
                long long diff;
                struct request_queue *q;

                disk_idx = rdev->raid_disk;
                if (disk_idx < 0)
                        continue;
                if (disk_idx >= conf->geo.raid_disks &&
                    disk_idx >= conf->prev.raid_disks)
                        continue;
                disk = conf->mirrors + disk_idx;

                if (test_bit(Replacement, &rdev->flags)) {
                        if (disk->replacement)
                                goto out_free_conf;
                        disk->replacement = rdev;
                } else {
                        if (disk->rdev)
                                goto out_free_conf;
                        disk->rdev = rdev;
                }
                q = bdev_get_queue(rdev->bdev);
                if (q->merge_bvec_fn)
                        mddev->merge_check_needed = 1;
                diff = (rdev->new_data_offset - rdev->data_offset);
                if (!mddev->reshape_backwards)
                        diff = -diff;
                if (diff < 0)
                        diff = 0;
                if (first || diff < min_offset_diff)
                        min_offset_diff = diff;

                if (mddev->gendisk)
                        disk_stack_limits(mddev->gendisk, rdev->bdev,
                                          rdev->data_offset << 9);

                disk->head_position = 0;

                if (blk_queue_discard(bdev_get_queue(rdev->bdev)))
                        discard_supported = true;
        }

        if (mddev->queue) {
                if (discard_supported)
                        queue_flag_set_unlocked(QUEUE_FLAG_DISCARD,
                                                mddev->queue);
                else
                        queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD,
                                                  mddev->queue);
        }
        /* need to check that every block has at least one working mirror */
        if (!enough(conf, -1)) {
                printk(KERN_ERR "md/raid10:%s: not enough operational mirrors.\n",
                       mdname(mddev));
                goto out_free_conf;
        }

        if (conf->reshape_progress != MaxSector) {
                /* must ensure that shape change is supported */
                if (conf->geo.far_copies != 1 &&
                    conf->geo.far_offset == 0)
                        goto out_free_conf;
                if (conf->prev.far_copies != 1 &&
                    conf->prev.far_offset == 0)
                        goto out_free_conf;
        }

        mddev->degraded = 0;
        for (i = 0;
             i < conf->geo.raid_disks
                     || i < conf->prev.raid_disks;
             i++) {

                disk = conf->mirrors + i;

                if (!disk->rdev && disk->replacement) {
                        /* The replacement is all we have - use it */
                        disk->rdev = disk->replacement;
                        disk->replacement = NULL;
                        clear_bit(Replacement, &disk->rdev->flags);
                }

                if (!disk->rdev ||
                    !test_bit(In_sync, &disk->rdev->flags)) {
                        disk->head_position = 0;
                        mddev->degraded++;
                        if (disk->rdev)
                                conf->fullsync = 1;
                }
                disk->recovery_disabled = mddev->recovery_disabled - 1;
        }

        if (mddev->recovery_cp != MaxSector)
                printk(KERN_NOTICE "md/raid10:%s: not clean"
                       " -- starting background reconstruction\n",
                       mdname(mddev));
        printk(KERN_INFO
                "md/raid10:%s: active with %d out of %d devices\n",
                mdname(mddev), conf->geo.raid_disks - mddev->degraded,
                conf->geo.raid_disks);
        /*
         * Ok, everything is just fine now
         */
        mddev->dev_sectors = conf->dev_sectors;
        size = raid10_size(mddev, 0, 0);
        md_set_array_sectors(mddev, size);
        mddev->resync_max_sectors = size;

        if (mddev->queue) {
                int stripe = conf->geo.raid_disks *
                        ((mddev->chunk_sectors << 9) / PAGE_SIZE);
                mddev->queue->backing_dev_info.congested_fn = raid10_congested;
                mddev->queue->backing_dev_info.congested_data = mddev;

                /* Calculate max read-ahead size.
                 * We need to readahead at least twice a whole stripe....
                 * maybe...
                 */
                stripe /= conf->geo.near_copies;
                if (mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
                        mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
                blk_queue_merge_bvec(mddev->queue, raid10_mergeable_bvec);
        }


        if (md_integrity_register(mddev))
                goto out_free_conf;

        if (conf->reshape_progress != MaxSector) {
                unsigned long before_length, after_length;

                before_length = ((1 << conf->prev.chunk_shift) *
                                 conf->prev.far_copies);
                after_length = ((1 << conf->geo.chunk_shift) *
                                conf->geo.far_copies);

                if (max(before_length, after_length) > min_offset_diff) {
                        /* This cannot work */
                        printk("md/raid10: offset difference not enough to continue reshape\n");
                        goto out_free_conf;
                }
                conf->offset_diff = min_offset_diff;

                conf->reshape_safe = conf->reshape_progress;
                clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
                clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
                set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
                set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
                mddev->sync_thread = md_register_thread(md_do_sync, mddev,
                                                        "reshape");
        }

        return 0;

out_free_conf:
        md_unregister_thread(&mddev->thread);
        if (conf->r10bio_pool)
                mempool_destroy(conf->r10bio_pool);
        safe_put_page(conf->tmppage);
        kfree(conf->mirrors);
        kfree(conf);
        mddev->private = NULL;
out:
        return -EIO;
}

static int stop(struct mddev *mddev)
{
        struct r10conf *conf = mddev->private;

        raise_barrier(conf, 0);
        lower_barrier(conf);

        md_unregister_thread(&mddev->thread);
        if (mddev->queue)
                /* the unplug fn references 'conf'*/
                blk_sync_queue(mddev->queue);

        if (conf->r10bio_pool)
                mempool_destroy(conf->r10bio_pool);
        safe_put_page(conf->tmppage);
        kfree(conf->mirrors);
        kfree(conf);
        mddev->private = NULL;
        return 0;
}

static void raid10_quiesce(struct mddev *mddev, int state)
{
        struct r10conf *conf = mddev->private;

        switch(state) {
        case 1:
                raise_barrier(conf, 0);
                break;
        case 0:
                lower_barrier(conf);
                break;
        }
}

static int raid10_resize(struct mddev *mddev, sector_t sectors)
{
        /* Resize of 'far' arrays is not supported.
         * For 'near' and 'offset' arrays we can set the
         * number of sectors used to be an appropriate multiple
         * of the chunk size.
         * For 'offset', this is far_copies*chunksize.
         * For 'near' the multiplier is the LCM of
         * near_copies and raid_disks.
         * So if far_copies > 1 && !far_offset, fail.
         * Else find LCM(raid_disks, near_copy)*far_copies and
         * multiply by chunk_size.  Then round to this number.
         * This is mostly done by raid10_size()
         */
        struct r10conf *conf = mddev->private;
        sector_t oldsize, size;

        if (mddev->reshape_position != MaxSector)
                return -EBUSY;

        if (conf->geo.far_copies > 1 && !conf->geo.far_offset)
                return -EINVAL;

        oldsize = raid10_size(mddev, 0, 0);
        size = raid10_size(mddev, sectors, 0);
        if (mddev->external_size &&
            mddev->array_sectors > size)
                return -EINVAL;
        if (mddev->bitmap) {
                int ret = bitmap_resize(mddev->bitmap, size, 0, 0);
                if (ret)
                        return ret;
        }
        md_set_array_sectors(mddev, size);
        set_capacity(mddev->gendisk, mddev->array_sectors);
        revalidate_disk(mddev->gendisk);
        if (sectors > mddev->dev_sectors &&
            mddev->recovery_cp > oldsize) {
                mddev->recovery_cp = oldsize;
                set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
        }
        calc_sectors(conf, sectors);
        mddev->dev_sectors = conf->dev_sectors;
        mddev->resync_max_sectors = size;
        return 0;
}

static void *raid10_takeover_raid0(struct mddev *mddev)
{
        struct md_rdev *rdev;
        struct r10conf *conf;

        if (mddev->degraded > 0) {
                printk(KERN_ERR "md/raid10:%s: Error: degraded raid0!\n",
                       mdname(mddev));
                return ERR_PTR(-EINVAL);
        }

        /* Set new parameters */
        mddev->new_level = 10;
        /* new layout: far_copies = 1, near_copies = 2 */
        mddev->new_layout = (1<<8) + 2;
        mddev->new_chunk_sectors = mddev->chunk_sectors;
        mddev->delta_disks = mddev->raid_disks;
        mddev->raid_disks *= 2;
        /* make sure it will be not marked as dirty */
        mddev->recovery_cp = MaxSector;

        conf = setup_conf(mddev);
        if (!IS_ERR(conf)) {
                rdev_for_each(rdev, mddev)
                        if (rdev->raid_disk >= 0)
                                rdev->new_raid_disk = rdev->raid_disk * 2;
                conf->barrier = 1;
        }

        return conf;
}

static void *raid10_takeover(struct mddev *mddev)
{
        struct r0conf *raid0_conf;

        /* raid10 can take over:
         *  raid0 - providing it has only two drives
         */
        if (mddev->level == 0) {
                /* for raid0 takeover only one zone is supported */
                raid0_conf = mddev->private;
                if (raid0_conf->nr_strip_zones > 1) {
                        printk(KERN_ERR "md/raid10:%s: cannot takeover raid 0"
                               " with more than one zone.\n",
                               mdname(mddev));
                        return ERR_PTR(-EINVAL);
                }
                return raid10_takeover_raid0(mddev);
        }
        return ERR_PTR(-EINVAL);
}

static int raid10_check_reshape(struct mddev *mddev)
{
        /* Called when there is a request to change
         * - layout (to ->new_layout)
         * - chunk size (to ->new_chunk_sectors)
         * - raid_disks (by delta_disks)
         * or when trying to restart a reshape that was ongoing.
         *
         * We need to validate the request and possibly allocate
         * space if that might be an issue later.
         *
         * Currently we reject any reshape of a 'far' mode array,
         * allow chunk size to change if new is generally acceptable,
         * allow raid_disks to increase, and allow
         * a switch between 'near' mode and 'offset' mode.
         */
        struct r10conf *conf = mddev->private;
        struct geom geo;

        if (conf->geo.far_copies != 1 && !conf->geo.far_offset)
                return -EINVAL;

        if (setup_geo(&geo, mddev, geo_start) != conf->copies)
                /* mustn't change number of copies */
                return -EINVAL;
        if (geo.far_copies > 1 && !geo.far_offset)
                /* Cannot switch to 'far' mode */
                return -EINVAL;

        if (mddev->array_sectors & geo.chunk_mask)
                        /* not factor of array size */
                        return -EINVAL;

        if (!enough(conf, -1))
                return -EINVAL;

        kfree(conf->mirrors_new);
        conf->mirrors_new = NULL;
        if (mddev->delta_disks > 0) {
                /* allocate new 'mirrors' list */
                conf->mirrors_new = kzalloc(
                        sizeof(struct raid10_info)
                        *(mddev->raid_disks +
                          mddev->delta_disks),
                        GFP_KERNEL);
                if (!conf->mirrors_new)
                        return -ENOMEM;
        }
        return 0;
}

/*
 * Need to check if array has failed when deciding whether to:
 *  - start an array
 *  - remove non-faulty devices
 *  - add a spare
 *  - allow a reshape
 * This determination is simple when no reshape is happening.
 * However if there is a reshape, we need to carefully check
 * both the before and after sections.
 * This is because some failed devices may only affect one
 * of the two sections, and some non-in_sync devices may
 * be insync in the section most affected by failed devices.
 */
static int calc_degraded(struct r10conf *conf)
{
        int degraded, degraded2;
        int i;

        rcu_read_lock();
        degraded = 0;
        /* 'prev' section first */
        for (i = 0; i < conf->prev.raid_disks; i++) {
                struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
                if (!rdev || test_bit(Faulty, &rdev->flags))
                        degraded++;
                else if (!test_bit(In_sync, &rdev->flags))
                        /* When we can reduce the number of devices in
                         * an array, this might not contribute to
                         * 'degraded'.  It does now.
                         */
                        degraded++;
        }
        rcu_read_unlock();
        if (conf->geo.raid_disks == conf->prev.raid_disks)
                return degraded;
        rcu_read_lock();
        degraded2 = 0;
        for (i = 0; i < conf->geo.raid_disks; i++) {
                struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
                if (!rdev || test_bit(Faulty, &rdev->flags))
                        degraded2++;
                else if (!test_bit(In_sync, &rdev->flags)) {
                        /* If reshape is increasing the number of devices,
                         * this section has already been recovered, so
                         * it doesn't contribute to degraded.
                         * else it does.
                         */
                        if (conf->geo.raid_disks <= conf->prev.raid_disks)
                                degraded2++;
                }
        }
        rcu_read_unlock();
        if (degraded2 > degraded)
                return degraded2;
        return degraded;
}

static int raid10_start_reshape(struct mddev *mddev)
{
        /* A 'reshape' has been requested. This commits
         * the various 'new' fields and sets MD_RECOVER_RESHAPE
         * This also checks if there are enough spares and adds them
         * to the array.
         * We currently require enough spares to make the final
         * array non-degraded.  We also require that the difference
         * between old and new data_offset - on each device - is
         * enough that we never risk over-writing.
         */

        unsigned long before_length, after_length;
        sector_t min_offset_diff = 0;
        int first = 1;
        struct geom new;
        struct r10conf *conf = mddev->private;
        struct md_rdev *rdev;
        int spares = 0;
        int ret;

        if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
                return -EBUSY;

        if (setup_geo(&new, mddev, geo_start) != conf->copies)
                return -EINVAL;

        before_length = ((1 << conf->prev.chunk_shift) *
                         conf->prev.far_copies);
        after_length = ((1 << conf->geo.chunk_shift) *
                        conf->geo.far_copies);

        rdev_for_each(rdev, mddev) {
                if (!test_bit(In_sync, &rdev->flags)
                    && !test_bit(Faulty, &rdev->flags))
                        spares++;
                if (rdev->raid_disk >= 0) {
                        long long diff = (rdev->new_data_offset
                                          - rdev->data_offset);
                        if (!mddev->reshape_backwards)
                                diff = -diff;
                        if (diff < 0)
                                diff = 0;
                        if (first || diff < min_offset_diff)
                                min_offset_diff = diff;
                }
        }

        if (max(before_length, after_length) > min_offset_diff)
                return -EINVAL;

        if (spares < mddev->delta_disks)
                return -EINVAL;

        conf->offset_diff = min_offset_diff;
        spin_lock_irq(&conf->device_lock);
        if (conf->mirrors_new) {
                memcpy(conf->mirrors_new, conf->mirrors,
                       sizeof(struct raid10_info)*conf->prev.raid_disks);
                smp_mb();
                kfree(conf->mirrors_old); /* FIXME and elsewhere */
                conf->mirrors_old = conf->mirrors;
                conf->mirrors = conf->mirrors_new;
                conf->mirrors_new = NULL;
        }
        setup_geo(&conf->geo, mddev, geo_start);
        smp_mb();
        if (mddev->reshape_backwards) {
                sector_t size = raid10_size(mddev, 0, 0);
                if (size < mddev->array_sectors) {
                        spin_unlock_irq(&conf->device_lock);
                        printk(KERN_ERR "md/raid10:%s: array size must be reduce before number of disks\n",
                               mdname(mddev));
                        return -EINVAL;
                }
                mddev->resync_max_sectors = size;
                conf->reshape_progress = size;
        } else
                conf->reshape_progress = 0;
        spin_unlock_irq(&conf->device_lock);

        if (mddev->delta_disks && mddev->bitmap) {
                ret = bitmap_resize(mddev->bitmap,
                                    raid10_size(mddev, 0,
                                                conf->geo.raid_disks),
                                    0, 0);
                if (ret)
                        goto abort;
        }
        if (mddev->delta_disks > 0) {
                rdev_for_each(rdev, mddev)
                        if (rdev->raid_disk < 0 &&
                            !test_bit(Faulty, &rdev->flags)) {
                                if (raid10_add_disk(mddev, rdev) == 0) {
                                        if (rdev->raid_disk >=
                                            conf->prev.raid_disks)
                                                set_bit(In_sync, &rdev->flags);
                                        else
                                                rdev->recovery_offset = 0;

                                        if (sysfs_link_rdev(mddev, rdev))
                                                /* Failure here  is OK */;
                                }
                        } else if (rdev->raid_disk >= conf->prev.raid_disks
                                   && !test_bit(Faulty, &rdev->flags)) {
                                /* This is a spare that was manually added */
                                set_bit(In_sync, &rdev->flags);
                        }
        }
        /* When a reshape changes the number of devices,
         * ->degraded is measured against the larger of the
         * pre and  post numbers.
         */
        spin_lock_irq(&conf->device_lock);
        mddev->degraded = calc_degraded(conf);
        spin_unlock_irq(&conf->device_lock);
        mddev->raid_disks = conf->geo.raid_disks;
        mddev->reshape_position = conf->reshape_progress;
        set_bit(MD_CHANGE_DEVS, &mddev->flags);

        clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
        clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
        set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
        set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);

        mddev->sync_thread = md_register_thread(md_do_sync, mddev,
                                                "reshape");
        if (!mddev->sync_thread) {
                ret = -EAGAIN;
                goto abort;
        }
        conf->reshape_checkpoint = jiffies;
        md_wakeup_thread(mddev->sync_thread);
        md_new_event(mddev);
        return 0;

abort:
        mddev->recovery = 0;
        spin_lock_irq(&conf->device_lock);
        conf->geo = conf->prev;
        mddev->raid_disks = conf->geo.raid_disks;
        rdev_for_each(rdev, mddev)
                rdev->new_data_offset = rdev->data_offset;
        smp_wmb();
        conf->reshape_progress = MaxSector;
        mddev->reshape_position = MaxSector;
        spin_unlock_irq(&conf->device_lock);
        return ret;
}

/* Calculate the last device-address that could contain
 * any block from the chunk that includes the array-address 's'
 * and report the next address.
 * i.e. the address returned will be chunk-aligned and after
 * any data that is in the chunk containing 's'.
 */
static sector_t last_dev_address(sector_t s, struct geom *geo)
{
        s = (s | geo->chunk_mask) + 1;
        s >>= geo->chunk_shift;
        s *= geo->near_copies;
        s = DIV_ROUND_UP_SECTOR_T(s, geo->raid_disks);
        s *= geo->far_copies;
        s <<= geo->chunk_shift;
        return s;
}

/* Calculate the first device-address that could contain
 * any block from the chunk that includes the array-address 's'.
 * This too will be the start of a chunk
 */
static sector_t first_dev_address(sector_t s, struct geom *geo)
{
        s >>= geo->chunk_shift;
        s *= geo->near_copies;
        sector_div(s, geo->raid_disks);
        s *= geo->far_copies;
        s <<= geo->chunk_shift;
        return s;
}

static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr,
                                int *skipped)
{
        /* We simply copy at most one chunk (smallest of old and new)
         * at a time, possibly less if that exceeds RESYNC_PAGES,
         * or we hit a bad block or something.
         * This might mean we pause for normal IO in the middle of
         * a chunk, but that is not a problem was mddev->reshape_position
         * can record any location.
         *
         * If we will want to write to a location that isn't
         * yet recorded as 'safe' (i.e. in metadata on disk) then
         * we need to flush all reshape requests and update the metadata.
         *
         * When reshaping forwards (e.g. to more devices), we interpret
         * 'safe' as the earliest block which might not have been copied
         * down yet.  We divide this by previous stripe size and multiply
         * by previous stripe length to get lowest device offset that we
         * cannot write to yet.
         * We interpret 'sector_nr' as an address that we want to write to.
         * From this we use last_device_address() to find where we might
         * write to, and first_device_address on the  'safe' position.
         * If this 'next' write position is after the 'safe' position,
         * we must update the metadata to increase the 'safe' position.
         *
         * When reshaping backwards, we round in the opposite direction
         * and perform the reverse test:  next write position must not be
         * less than current safe position.
         *
         * In all this the minimum difference in data offsets
         * (conf->offset_diff - always positive) allows a bit of slack,
         * so next can be after 'safe', but not by more than offset_disk
         *
         * We need to prepare all the bios here before we start any IO
         * to ensure the size we choose is acceptable to all devices.
         * The means one for each copy for write-out and an extra one for
         * read-in.
         * We store the read-in bio in ->master_bio and the others in
         * ->devs[x].bio and ->devs[x].repl_bio.
         */
        struct r10conf *conf = mddev->private;
        struct r10bio *r10_bio;
        sector_t next, safe, last;
        int max_sectors;
        int nr_sectors;
        int s;
        struct md_rdev *rdev;
        int need_flush = 0;
        struct bio *blist;
        struct bio *bio, *read_bio;
        int sectors_done = 0;

        if (sector_nr == 0) {
                /* If restarting in the middle, skip the initial sectors */
                if (mddev->reshape_backwards &&
                    conf->reshape_progress < raid10_size(mddev, 0, 0)) {
                        sector_nr = (raid10_size(mddev, 0, 0)
                                     - conf->reshape_progress);
                } else if (!mddev->reshape_backwards &&
                           conf->reshape_progress > 0)
                        sector_nr = conf->reshape_progress;
                if (sector_nr) {
                        mddev->curr_resync_completed = sector_nr;
                        sysfs_notify(&mddev->kobj, NULL, "sync_completed");
                        *skipped = 1;
                        return sector_nr;
                }
        }

        /* We don't use sector_nr to track where we are up to
         * as that doesn't work well for ->reshape_backwards.
         * So just use ->reshape_progress.
         */
        if (mddev->reshape_backwards) {
                /* 'next' is the earliest device address that we might
                 * write to for this chunk in the new layout
                 */
                next = first_dev_address(conf->reshape_progress - 1,
                                         &conf->geo);

                /* 'safe' is the last device address that we might read from
                 * in the old layout after a restart
                 */
                safe = last_dev_address(conf->reshape_safe - 1,
                                        &conf->prev);

                if (next + conf->offset_diff < safe)
                        need_flush = 1;

                last = conf->reshape_progress - 1;
                sector_nr = last & ~(sector_t)(conf->geo.chunk_mask
                                               & conf->prev.chunk_mask);
                if (sector_nr + RESYNC_BLOCK_SIZE/512 < last)
                        sector_nr = last + 1 - RESYNC_BLOCK_SIZE/512;
        } else {
                /* 'next' is after the last device address that we
                 * might write to for this chunk in the new layout
                 */
                next = last_dev_address(conf->reshape_progress, &conf->geo);

                /* 'safe' is the earliest device address that we might
                 * read from in the old layout after a restart
                 */
                safe = first_dev_address(conf->reshape_safe, &conf->prev);

                /* Need to update metadata if 'next' might be beyond 'safe'
                 * as that would possibly corrupt data
                 */
                if (next > safe + conf->offset_diff)
                        need_flush = 1;

                sector_nr = conf->reshape_progress;
                last  = sector_nr | (conf->geo.chunk_mask
                                     & conf->prev.chunk_mask);

                if (sector_nr + RESYNC_BLOCK_SIZE/512 <= last)
                        last = sector_nr + RESYNC_BLOCK_SIZE/512 - 1;
        }

        if (need_flush ||
            time_after(jiffies, conf->reshape_checkpoint + 10*HZ)) {
                /* Need to update reshape_position in metadata */
                wait_barrier(conf);
                mddev->reshape_position = conf->reshape_progress;
                if (mddev->reshape_backwards)
                        mddev->curr_resync_completed = raid10_size(mddev, 0, 0)
                                - conf->reshape_progress;
                else
                        mddev->curr_resync_completed = conf->reshape_progress;
                conf->reshape_checkpoint = jiffies;
                set_bit(MD_CHANGE_DEVS, &mddev->flags);
                md_wakeup_thread(mddev->thread);
                wait_event(mddev->sb_wait, mddev->flags == 0 ||
                           test_bit(MD_RECOVERY_INTR, &mddev->recovery));
                if (test_bit(MD_RECOVERY_INTR, &mddev->recovery)) {
                        allow_barrier(conf);
                        return sectors_done;
                }
                conf->reshape_safe = mddev->reshape_position;
                allow_barrier(conf);
        }

read_more:
        /* Now schedule reads for blocks from sector_nr to last */
        r10_bio = mempool_alloc(conf->r10buf_pool, GFP_NOIO);
        raise_barrier(conf, sectors_done != 0);
        atomic_set(&r10_bio->remaining, 0);
        r10_bio->mddev = mddev;
        r10_bio->sector = sector_nr;
        set_bit(R10BIO_IsReshape, &r10_bio->state);
        r10_bio->sectors = last - sector_nr + 1;
        rdev = read_balance(conf, r10_bio, &max_sectors);
        BUG_ON(!test_bit(R10BIO_Previous, &r10_bio->state));

        if (!rdev) {
                /* Cannot read from here, so need to record bad blocks
                 * on all the target devices.
                 */
                // FIXME
                set_bit(MD_RECOVERY_INTR, &mddev->recovery);
                return sectors_done;
        }

        read_bio = bio_alloc_mddev(GFP_KERNEL, RESYNC_PAGES, mddev);

        read_bio->bi_bdev = rdev->bdev;
        read_bio->bi_iter.bi_sector = (r10_bio->devs[r10_bio->read_slot].addr
                               + rdev->data_offset);
        read_bio->bi_private = r10_bio;
        read_bio->bi_end_io = end_sync_read;
        read_bio->bi_rw = READ;
        read_bio->bi_flags &= ~(BIO_POOL_MASK - 1);
        read_bio->bi_flags |= 1 << BIO_UPTODATE;
        read_bio->bi_vcnt = 0;
        read_bio->bi_iter.bi_size = 0;
        r10_bio->master_bio = read_bio;
        r10_bio->read_slot = r10_bio->devs[r10_bio->read_slot].devnum;

        /* Now find the locations in the new layout */
        __raid10_find_phys(&conf->geo, r10_bio);

        blist = read_bio;
        read_bio->bi_next = NULL;

        for (s = 0; s < conf->copies*2; s++) {
                struct bio *b;
                int d = r10_bio->devs[s/2].devnum;
                struct md_rdev *rdev2;
                if (s&1) {
                        rdev2 = conf->mirrors[d].replacement;
                        b = r10_bio->devs[s/2].repl_bio;
                } else {
                        rdev2 = conf->mirrors[d].rdev;
                        b = r10_bio->devs[s/2].bio;
                }
                if (!rdev2 || test_bit(Faulty, &rdev2->flags))
                        continue;

                bio_reset(b);
                b->bi_bdev = rdev2->bdev;
                b->bi_iter.bi_sector = r10_bio->devs[s/2].addr +
                        rdev2->new_data_offset;
                b->bi_private = r10_bio;
                b->bi_end_io = end_reshape_write;
                b->bi_rw = WRITE;
                b->bi_next = blist;
                blist = b;
        }

        /* Now add as many pages as possible to all of these bios. */

        nr_sectors = 0;
        for (s = 0 ; s < max_sectors; s += PAGE_SIZE >> 9) {
                struct page *page = r10_bio->devs[0].bio->bi_io_vec[s/(PAGE_SIZE>>9)].bv_page;
                int len = (max_sectors - s) << 9;
                if (len > PAGE_SIZE)
                        len = PAGE_SIZE;
                for (bio = blist; bio ; bio = bio->bi_next) {
                        struct bio *bio2;
                        if (bio_add_page(bio, page, len, 0))
                                continue;

                        /* Didn't fit, must stop */
                        for (bio2 = blist;
                             bio2 && bio2 != bio;
                             bio2 = bio2->bi_next) {
                                /* Remove last page from this bio */
                                bio2->bi_vcnt--;
                                bio2->bi_iter.bi_size -= len;
                                bio2->bi_flags &= ~(1<<BIO_SEG_VALID);
                        }
                        goto bio_full;
                }
                sector_nr += len >> 9;
                nr_sectors += len >> 9;
        }
bio_full:
        r10_bio->sectors = nr_sectors;

        /* Now submit the read */
        md_sync_acct(read_bio->bi_bdev, r10_bio->sectors);
        atomic_inc(&r10_bio->remaining);
        read_bio->bi_next = NULL;
        generic_make_request(read_bio);
        sector_nr += nr_sectors;
        sectors_done += nr_sectors;
        if (sector_nr <= last)
                goto read_more;

        /* Now that we have done the whole section we can
         * update reshape_progress
         */
        if (mddev->reshape_backwards)
                conf->reshape_progress -= sectors_done;
        else
                conf->reshape_progress += sectors_done;

        return sectors_done;
}

static void end_reshape_request(struct r10bio *r10_bio);
static int handle_reshape_read_error(struct mddev *mddev,
                                     struct r10bio *r10_bio);
static void reshape_request_write(struct mddev *mddev, struct r10bio *r10_bio)
{
        /* Reshape read completed.  Hopefully we have a block
         * to write out.
         * If we got a read error then we do sync 1-page reads from
         * elsewhere until we find the data - or give up.
         */
        struct r10conf *conf = mddev->private;
        int s;

        if (!test_bit(R10BIO_Uptodate, &r10_bio->state))
                if (handle_reshape_read_error(mddev, r10_bio) < 0) {
                        /* Reshape has been aborted */
                        md_done_sync(mddev, r10_bio->sectors, 0);
                        return;
                }

        /* We definitely have the data in the pages, schedule the
         * writes.
         */
        atomic_set(&r10_bio->remaining, 1);
        for (s = 0; s < conf->copies*2; s++) {
                struct bio *b;
                int d = r10_bio->devs[s/2].devnum;
                struct md_rdev *rdev;
                if (s&1) {
                        rdev = conf->mirrors[d].replacement;
                        b = r10_bio->devs[s/2].repl_bio;
                } else {
                        rdev = conf->mirrors[d].rdev;
                        b = r10_bio->devs[s/2].bio;
                }
                if (!rdev || test_bit(Faulty, &rdev->flags))
                        continue;
                atomic_inc(&rdev->nr_pending);
                md_sync_acct(b->bi_bdev, r10_bio->sectors);
                atomic_inc(&r10_bio->remaining);
                b->bi_next = NULL;
                generic_make_request(b);
        }
        end_reshape_request(r10_bio);
}

static void end_reshape(struct r10conf *conf)
{
        if (test_bit(MD_RECOVERY_INTR, &conf->mddev->recovery))
                return;

        spin_lock_irq(&conf->device_lock);
        conf->prev = conf->geo;
        md_finish_reshape(conf->mddev);
        smp_wmb();
        conf->reshape_progress = MaxSector;
        spin_unlock_irq(&conf->device_lock);

        /* read-ahead size must cover two whole stripes, which is
         * 2 * (datadisks) * chunksize where 'n' is the number of raid devices
         */
        if (conf->mddev->queue) {
                int stripe = conf->geo.raid_disks *
                        ((conf->mddev->chunk_sectors << 9) / PAGE_SIZE);
                stripe /= conf->geo.near_copies;
                if (conf->mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
                        conf->mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
        }
        conf->fullsync = 0;
}


static int handle_reshape_read_error(struct mddev *mddev,
                                     struct r10bio *r10_bio)
{
        /* Use sync reads to get the blocks from somewhere else */
        int sectors = r10_bio->sectors;
        struct r10conf *conf = mddev->private;
        struct {
                struct r10bio r10_bio;
                struct r10dev devs[conf->copies];
        } on_stack;
        struct r10bio *r10b = &on_stack.r10_bio;
        int slot = 0;
        int idx = 0;
        struct bio_vec *bvec = r10_bio->master_bio->bi_io_vec;

        r10b->sector = r10_bio->sector;
        __raid10_find_phys(&conf->prev, r10b);

        while (sectors) {
                int s = sectors;
                int success = 0;
                int first_slot = slot;

                if (s > (PAGE_SIZE >> 9))
                        s = PAGE_SIZE >> 9;

                while (!success) {
                        int d = r10b->devs[slot].devnum;
                        struct md_rdev *rdev = conf->mirrors[d].rdev;
                        sector_t addr;
                        if (rdev == NULL ||
                            test_bit(Faulty, &rdev->flags) ||
                            !test_bit(In_sync, &rdev->flags))
                                goto failed;

                        addr = r10b->devs[slot].addr + idx * PAGE_SIZE;
                        success = sync_page_io(rdev,
                                               addr,
                                               s << 9,
                                               bvec[idx].bv_page,
                                               READ, false);
                        if (success)
                                break;
                failed:
                        slot++;
                        if (slot >= conf->copies)
                                slot = 0;
                        if (slot == first_slot)
                                break;
                }
                if (!success) {
                        /* couldn't read this block, must give up */
                        set_bit(MD_RECOVERY_INTR,
                                &mddev->recovery);
                        return -EIO;
                }
                sectors -= s;
                idx++;
        }
        return 0;
}

static void end_reshape_write(struct bio *bio, int error)
{
        int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
        struct r10bio *r10_bio = bio->bi_private;
        struct mddev *mddev = r10_bio->mddev;
        struct r10conf *conf = mddev->private;
        int d;
        int slot;
        int repl;
        struct md_rdev *rdev = NULL;

        d = find_bio_disk(conf, r10_bio, bio, &slot, &repl);
        if (repl)
                rdev = conf->mirrors[d].replacement;
        if (!rdev) {
                smp_mb();
                rdev = conf->mirrors[d].rdev;
        }

        if (!uptodate) {
                /* FIXME should record badblock */
                md_error(mddev, rdev);
        }

        rdev_dec_pending(rdev, mddev);
        end_reshape_request(r10_bio);
}

static void end_reshape_request(struct r10bio *r10_bio)
{
        if (!atomic_dec_and_test(&r10_bio->remaining))
                return;
        md_done_sync(r10_bio->mddev, r10_bio->sectors, 1);
        bio_put(r10_bio->master_bio);
        put_buf(r10_bio);
}

static void raid10_finish_reshape(struct mddev *mddev)
{
        struct r10conf *conf = mddev->private;

        if (test_bit(MD_RECOVERY_INTR, &mddev->recovery))
                return;

        if (mddev->delta_disks > 0) {
                sector_t size = raid10_size(mddev, 0, 0);
                md_set_array_sectors(mddev, size);
                if (mddev->recovery_cp > mddev->resync_max_sectors) {
                        mddev->recovery_cp = mddev->resync_max_sectors;
                        set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
                }
                mddev->resync_max_sectors = size;
                set_capacity(mddev->gendisk, mddev->array_sectors);
                revalidate_disk(mddev->gendisk);
        } else {
                int d;
                for (d = conf->geo.raid_disks ;
                     d < conf->geo.raid_disks - mddev->delta_disks;
                     d++) {
                        struct md_rdev *rdev = conf->mirrors[d].rdev;
                        if (rdev)
                                clear_bit(In_sync, &rdev->flags);
                        rdev = conf->mirrors[d].replacement;
                        if (rdev)
                                clear_bit(In_sync, &rdev->flags);
                }
        }
        mddev->layout = mddev->new_layout;
        mddev->chunk_sectors = 1 << conf->geo.chunk_shift;
        mddev->reshape_position = MaxSector;
        mddev->delta_disks = 0;
        mddev->reshape_backwards = 0;
}

static struct md_personality raid10_personality =
{
        .name           = "raid10",
        .level          = 10,
        .owner          = THIS_MODULE,
        .make_request   = make_request,
        .run            = run,
        .stop           = stop,
        .status         = status,
        .error_handler  = error,
        .hot_add_disk   = raid10_add_disk,
        .hot_remove_disk= raid10_remove_disk,
        .spare_active   = raid10_spare_active,
        .sync_request   = sync_request,
        .quiesce        = raid10_quiesce,
        .size           = raid10_size,
        .resize         = raid10_resize,
        .takeover       = raid10_takeover,
        .check_reshape  = raid10_check_reshape,
        .start_reshape  = raid10_start_reshape,
        .finish_reshape = raid10_finish_reshape,
};

static int __init raid_init(void)
{
        return register_md_personality(&raid10_personality);
}

static void raid_exit(void)
{
        unregister_md_personality(&raid10_personality);
}

module_init(raid_init);
module_exit(raid_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("RAID10 (striped mirror) personality for MD");
MODULE_ALIAS("md-personality-9"); /* RAID10 */
MODULE_ALIAS("md-raid10");
MODULE_ALIAS("md-level-10");

module_param(max_queued_requests, int, S_IRUGO|S_IWUSR);