raid10.c

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/*
 * 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 )
 *
 * 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 they 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 be very far apart
 * on disk, there are adjacent stripes.
 */

/*
 * 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 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"
         */
        unsigned long flags;
        spin_lock_irqsave(&conf->device_lock, flags);
        if (!enough(conf, rdev->raid_disk))
            uptodate = 1;
        spin_unlock_irqrestore(&conf->device_lock, flags);
    }
    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;

        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;

    /* 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;
        sector_t s = sector;
        r10bio->devs[slot].addr = sector;
        r10bio->devs[slot].devnum = d;
        slot++;

        for (f = 1; f < geo->far_copies; f++) {
            d += geo->near_copies;
            if (d >= geo->raid_disks)
                d -= geo->raid_disks;
            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;

    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 < 0)
            dev += geo->raid_disks;
    } else {
        while (sector >= geo->stride) {
            sector -= geo->stride;
            if (dev < geo->near_copies)
                dev += geo->raid_disks - 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;
}

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)
{
    /* 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+1
     * 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 (1)
     * 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(conf->wait_barrier,
                conf->nr_pending == conf->nr_queued+1,
                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);
        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;
        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));
    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_sector & chunk_mask) + (bio->bi_size >> 9)
             > 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->bi_vcnt != 1 && bio->bi_vcnt != 0) ||
            bio->bi_idx != 0)
            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_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_sector, bio->bi_size >> 10);

        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->bi_size >> 9;
    while (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
        bio->bi_sector < conf->reshape_progress &&
        bio->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_sector ||
               conf->reshape_progress >= bio->bi_sector + sectors);
        wait_barrier(conf);
    }
    if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
        bio_data_dir(bio) == WRITE &&
        (mddev->reshape_backwards
         ? (bio->bi_sector < conf->reshape_safe &&
        bio->bi_sector + sectors > conf->reshape_progress)
         : (bio->bi_sector + sectors > conf->reshape_safe &&
        bio->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_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);
        md_trim_bio(read_bio, r10_bio->sector - bio->bi_sector,
                max_sectors);

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

        read_bio->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_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->bi_size >> 9)
                        - sectors_handled);
            r10_bio->state = 0;
            r10_bio->mddev = mddev;
            r10_bio->sector = bio->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_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);
            md_trim_bio(mbio, r10_bio->sector - bio->bi_sector,
                    max_sectors);
            r10_bio->devs[i].bio = mbio;

            mbio->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;
            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);
            md_trim_bio(mbio, r10_bio->sector - bio->bi_sector,
                    max_sectors);
            r10_bio->devs[i].repl_bio = mbio;

            mbio->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;
            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->bi_size >> 9)) {
        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->bi_size >> 9) - sectors_handled;

        r10_bio->mddev = mddev;
        r10_bio->sector = bio->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, struct geom *geo, int ignore)
{
    int first = 0;

    do {
        int n = conf->copies;
        int cnt = 0;
        int this = first;
        while (n--) {
            if (conf->mirrors[this].rdev &&
                this != ignore)
                cnt++;
            this = (this+1) % geo->raid_disks;
        }
        if (cnt == 0)
            return 0;
        first = (first + geo->near_copies) % geo->raid_disks;
    } while (first != 0);
    return 1;
}

static int enough(struct r10conf *conf, int ignore)
{
    return _enough(conf, &conf->geo, ignore) &&
        _enough(conf, &conf->prev, ignore);
}

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

    /*
     * 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
     */
    if (test_bit(In_sync, &rdev->flags)
        && !enough(conf, rdev->raid_disk))
        /*
         * Don't fail the drive, just return an IO error.
         */
        return;
    if (test_and_clear_bit(In_sync, &rdev->flags)) {
        unsigned long flags;
        spin_lock_irqsave(&conf->device_lock, flags);
        mddev->degraded++;
        spin_unlock_irqrestore(&conf->device_lock, flags);
        /*
         * 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);
    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
               && !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, &conf->prev, -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;
            disk_stack_limits(mddev->gendisk, rdev->bdev,
                      rdev->data_offset << 9);
            conf->fullsync = 1;
            rcu_assign_pointer(p->replacement, rdev);
            break;
        }

        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();
        raise_barrier(conf, 0);
        lower_barrier(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;
             */
            for (j = 0; j < vcnt; j++)
                if (memcmp(page_address(fbio->bi_io_vec[j].bv_page),
                       page_address(tbio->bi_io_vec[j].bv_page),
                       fbio->bi_io_vec[j].bv_len))
                    break;
            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
         */
        tbio->bi_vcnt = vcnt;
        tbio->bi_size = r10_bio->sectors << 9;
        tbio->bi_idx = 0;
        tbio->bi_phys_segments = 0;
        tbio->bi_flags &= ~(BIO_POOL_MASK - 1);
        tbio->bi_flags |= 1 << BIO_UPTODATE;
        tbio->bi_next = NULL;
        tbio->bi_rw = WRITE;
        tbio->bi_private = r10_bio;
        tbio->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, tbio->bi_size >> 9);

        tbio->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,
                 tbio->bi_size >> 9);
        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;
    if (wbio->bi_end_io) {
        atomic_inc(&conf->mirrors[d].rdev->nr_pending);
        md_sync_acct(conf->mirrors[d].rdev->bdev, wbio->bi_size >> 9);
        generic_make_request(wbio);
    }
    if (wbio2 && wbio2->bi_end_io) {
        atomic_inc(&conf->mirrors[d].replacement->nr_pending);
        md_sync_acct(conf->mirrors[d].replacement->bdev,
                 wbio2->bi_size >> 9);
        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 void bi_complete(struct bio *bio, int error)
{
    complete((struct completion *)bio->bi_private);
}

static int submit_bio_wait(int rw, struct bio *bio)
{
    struct completion event;
    rw |= REQ_SYNC;

    init_completion(&event);
    bio->bi_private = &event;
    bio->bi_end_io = bi_complete;
    submit_bio(rw, bio);
    wait_for_completion(&event);

    return test_bit(BIO_UPTODATE, &bio->bi_flags);
}

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);
        md_trim_bio(wbio, sector - bio->bi_sector, sectors);
        wbio->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);
        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);
    md_trim_bio(bio,
            r10_bio->sector - bio->bi_sector,
            max_sectors);
    r10_bio->devs[slot].bio = bio;
    r10_bio->devs[slot].rdev = rdev;
    bio->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_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 = (mbio->bi_size >> 9)
            - sectors_handled;
        r10_bio->state = 0;
        set_bit(R10BIO_ReadError,
            &r10_bio->state);
        r10_bio->mddev = mddev;
        r10_bio->sector = mbio->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;

 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->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_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->bi_next = biolist;
                    biolist = bio;
                    bio->bi_private = r10_bio;
                    bio->bi_end_io = end_sync_write;
                    bio->bi_rw = WRITE;
                    bio->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->bi_next = biolist;
                biolist = bio;
                bio->bi_private = r10_bio;
                bio->bi_end_io = end_sync_write;
                bio->bi_rw = WRITE;
                bio->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->bi_end_io = NULL;
            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_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;
            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_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;
        }
    }

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

        bio->bi_flags &= ~(BIO_POOL_MASK - 1);
        if (bio->bi_end_io)
            bio->bi_flags |= 1 << BIO_UPTODATE;
        bio->bi_vcnt = 0;
        bio->bi_idx = 0;
        bio->bi_phys_segments = 0;
        bio->bi_size = 0;
    }

    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_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);
            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 >> 17)
        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->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_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->geo.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);
    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 ||
               kthread_should_stop());
        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_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_idx = 0;
    read_bio->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;
        b->bi_bdev = rdev2->bdev;
        b->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_flags &= ~(BIO_POOL_MASK - 1);
        b->bi_flags |= 1 << BIO_UPTODATE;
        b->bi_next = blist;
        b->bi_vcnt = 0;
        b->bi_idx = 0;
        b->bi_size = 0;
        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_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);