/*
 * raid5.c : Multiple Devices driver for Linux
 *         Copyright (C) 1996, 1997 Ingo Molnar, Miguel de Icaza, Gadi Oxman
 *         Copyright (C) 1999, 2000 Ingo Molnar
 *         Copyright (C) 2002, 2003 H. Peter Anvin
 *
 * RAID-4/5/6 management functions.
 * Thanks to Penguin Computing for making the RAID-6 development possible
 * by donating a test server!
 *
 * 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.
 */

/*
 * BITMAP UNPLUGGING:
 *
 * The sequencing for updating the bitmap reliably is a little
 * subtle (and I got it wrong the first time) so it deserves some
 * explanation.
 *
 * We group bitmap updates into batches.  Each batch has a number.
 * We may write out several batches at once, but that isn't very important.
 * conf->bm_write is the number of the last batch successfully written.
 * conf->bm_flush is the number of the last batch that was closed to
 *    new additions.
 * When we discover that we will need to write to any block in a stripe
 * (in add_stripe_bio) we update the in-memory bitmap and record in sh->bm_seq
 * the number of the batch it will be in. This is bm_flush+1.
 * When we are ready to do a write, if that batch hasn't been written yet,
 *   we plug the array and queue the stripe for later.
 * When an unplug happens, we increment bm_flush, thus closing the current
 *   batch.
 * When we notice that bm_flush > bm_write, we write out all pending updates
 * to the bitmap, and advance bm_write to where bm_flush was.
 * This may occasionally write a bit out twice, but is sure never to
 * miss any bits.
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/highmem.h>
#include <linux/bitops.h>
#include <linux/kthread.h>
#include <asm/atomic.h>
#include "raid6.h"

#include <linux/raid/bitmap.h>
#include <linux/async_tx.h>

/*
 * Stripe cache
 */

#define NR_STRIPES              256
#define STRIPE_SIZE             PAGE_SIZE
#define STRIPE_SHIFT            (PAGE_SHIFT - 9)
#define STRIPE_SECTORS          (STRIPE_SIZE>>9)
#define IO_THRESHOLD            1
#define BYPASS_THRESHOLD        1
#define NR_HASH                 (PAGE_SIZE / sizeof(struct hlist_head))
#define HASH_MASK               (NR_HASH - 1)

#define stripe_hash(conf, sect) (&((conf)->stripe_hashtbl[((sect) >> STRIPE_SHIFT) & HASH_MASK]))

/* bio's attached to a stripe+device for I/O are linked together in bi_sector
 * order without overlap.  There may be several bio's per stripe+device, and
 * a bio could span several devices.
 * When walking this list for a particular stripe+device, we must never proceed
 * beyond a bio that extends past this device, as the next bio might no longer
 * be valid.
 * This macro is used to determine the 'next' bio in the list, given the sector
 * of the current stripe+device
 */
#define r5_next_bio(bio, sect) ( ( (bio)->bi_sector + ((bio)->bi_size>>9) < sect + STRIPE_SECTORS) ? (bio)->bi_next : NULL)
/*
 * The following can be used to debug the driver
 */
#define RAID5_PARANOIA  1
#if RAID5_PARANOIA && defined(CONFIG_SMP)
# define CHECK_DEVLOCK() assert_spin_locked(&conf->device_lock)
#else
# define CHECK_DEVLOCK()
#endif

#ifdef DEBUG
#define inline
#define __inline__
#endif

#define printk_rl(args...) ((void) (printk_ratelimit() && printk(args)))

#if !RAID6_USE_EMPTY_ZERO_PAGE
/* In .bss so it's zeroed */
const char raid6_empty_zero_page[PAGE_SIZE] __attribute__((aligned(256)));
#endif

static inline int raid6_next_disk(int disk, int raid_disks)
{
        disk++;
        return (disk < raid_disks) ? disk : 0;
}

static void return_io(struct bio *return_bi)
{
        struct bio *bi = return_bi;
        while (bi) {

                return_bi = bi->bi_next;
                bi->bi_next = NULL;
                bi->bi_size = 0;
                bi->bi_end_io(bi,
                              test_bit(BIO_UPTODATE, &bi->bi_flags)
                                ? 0 : -EIO);
                bi = return_bi;
        }
}

static void print_raid5_conf (raid5_conf_t *conf);

static void __release_stripe(raid5_conf_t *conf, struct stripe_head *sh)
{
        if (atomic_dec_and_test(&sh->count)) {
                BUG_ON(!list_empty(&sh->lru));
                BUG_ON(atomic_read(&conf->active_stripes)==0);
                if (test_bit(STRIPE_HANDLE, &sh->state)) {
                        if (test_bit(STRIPE_DELAYED, &sh->state)) {
                                list_add_tail(&sh->lru, &conf->delayed_list);
                                blk_plug_device(conf->mddev->queue);
                        } else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
                                   sh->bm_seq - conf->seq_write > 0) {
                                list_add_tail(&sh->lru, &conf->bitmap_list);
                                blk_plug_device(conf->mddev->queue);
                        } else {
                                clear_bit(STRIPE_BIT_DELAY, &sh->state);
                                list_add_tail(&sh->lru, &conf->handle_list);
                        }
                        md_wakeup_thread(conf->mddev->thread);
                } else {
                        BUG_ON(sh->ops.pending);
                        if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                                atomic_dec(&conf->preread_active_stripes);
                                if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD)
                                        md_wakeup_thread(conf->mddev->thread);
                        }
                        atomic_dec(&conf->active_stripes);
                        if (!test_bit(STRIPE_EXPANDING, &sh->state)) {
                                list_add_tail(&sh->lru, &conf->inactive_list);
                                wake_up(&conf->wait_for_stripe);
                                if (conf->retry_read_aligned)
                                        md_wakeup_thread(conf->mddev->thread);
                        }
                }
        }
}
static void release_stripe(struct stripe_head *sh)
{
        raid5_conf_t *conf = sh->raid_conf;
        unsigned long flags;

        spin_lock_irqsave(&conf->device_lock, flags);
        __release_stripe(conf, sh);
        spin_unlock_irqrestore(&conf->device_lock, flags);
}

static inline void remove_hash(struct stripe_head *sh)
{
        pr_debug("remove_hash(), stripe %llu\n",
                (unsigned long long)sh->sector);

        hlist_del_init(&sh->hash);
}

static inline void insert_hash(raid5_conf_t *conf, struct stripe_head *sh)
{
        struct hlist_head *hp = stripe_hash(conf, sh->sector);

        pr_debug("insert_hash(), stripe %llu\n",
                (unsigned long long)sh->sector);

        CHECK_DEVLOCK();
        hlist_add_head(&sh->hash, hp);
}


/* find an idle stripe, make sure it is unhashed, and return it. */
static struct stripe_head *get_free_stripe(raid5_conf_t *conf)
{
        struct stripe_head *sh = NULL;
        struct list_head *first;

        CHECK_DEVLOCK();
        if (list_empty(&conf->inactive_list))
                goto out;
        first = conf->inactive_list.next;
        sh = list_entry(first, struct stripe_head, lru);
        list_del_init(first);
        remove_hash(sh);
        atomic_inc(&conf->active_stripes);
out:
        return sh;
}

static void shrink_buffers(struct stripe_head *sh, int num)
{
        struct page *p;
        int i;

        for (i=0; i<num ; i++) {
                p = sh->dev[i].page;
                if (!p)
                        continue;
                sh->dev[i].page = NULL;
                put_page(p);
        }
}

static int grow_buffers(struct stripe_head *sh, int num)
{
        int i;

        for (i=0; i<num; i++) {
                struct page *page;

                if (!(page = alloc_page(GFP_KERNEL))) {
                        return 1;
                }
                sh->dev[i].page = page;
        }
        return 0;
}

static void raid5_build_block (struct stripe_head *sh, int i);

static void init_stripe(struct stripe_head *sh, sector_t sector, int pd_idx, int disks)
{
        raid5_conf_t *conf = sh->raid_conf;
        int i;

        BUG_ON(atomic_read(&sh->count) != 0);
        BUG_ON(test_bit(STRIPE_HANDLE, &sh->state));
        BUG_ON(sh->ops.pending || sh->ops.ack || sh->ops.complete);

        CHECK_DEVLOCK();
        pr_debug("init_stripe called, stripe %llu\n",
                (unsigned long long)sh->sector);

        remove_hash(sh);

        sh->sector = sector;
        sh->pd_idx = pd_idx;
        sh->state = 0;

        sh->disks = disks;

        for (i = sh->disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];

                if (dev->toread || dev->read || dev->towrite || dev->written ||
                    test_bit(R5_LOCKED, &dev->flags)) {
                        printk(KERN_ERR "sector=%llx i=%d %p %p %p %p %d\n",
                               (unsigned long long)sh->sector, i, dev->toread,
                               dev->read, dev->towrite, dev->written,
                               test_bit(R5_LOCKED, &dev->flags));
                        BUG();
                }
                dev->flags = 0;
                raid5_build_block(sh, i);
        }
        insert_hash(conf, sh);
}

static struct stripe_head *__find_stripe(raid5_conf_t *conf, sector_t sector, int disks)
{
        struct stripe_head *sh;
        struct hlist_node *hn;

        CHECK_DEVLOCK();
        pr_debug("__find_stripe, sector %llu\n", (unsigned long long)sector);
        hlist_for_each_entry(sh, hn, stripe_hash(conf, sector), hash)
                if (sh->sector == sector && sh->disks == disks)
                        return sh;
        pr_debug("__stripe %llu not in cache\n", (unsigned long long)sector);
        return NULL;
}

static void unplug_slaves(mddev_t *mddev);
static void raid5_unplug_device(struct request_queue *q);

static struct stripe_head *get_active_stripe(raid5_conf_t *conf, sector_t sector, int disks,
                                             int pd_idx, int noblock)
{
        struct stripe_head *sh;

        pr_debug("get_stripe, sector %llu\n", (unsigned long long)sector);

        spin_lock_irq(&conf->device_lock);

        do {
                wait_event_lock_irq(conf->wait_for_stripe,
                                    conf->quiesce == 0,
                                    conf->device_lock, /* nothing */);
                sh = __find_stripe(conf, sector, disks);
                if (!sh) {
                        if (!conf->inactive_blocked)
                                sh = get_free_stripe(conf);
                        if (noblock && sh == NULL)
                                break;
                        if (!sh) {
                                conf->inactive_blocked = 1;
                                wait_event_lock_irq(conf->wait_for_stripe,
                                                    !list_empty(&conf->inactive_list) &&
                                                    (atomic_read(&conf->active_stripes)
                                                     < (conf->max_nr_stripes *3/4)
                                                     || !conf->inactive_blocked),
                                                    conf->device_lock,
                                                    raid5_unplug_device(conf->mddev->queue)
                                        );
                                conf->inactive_blocked = 0;
                        } else
                                init_stripe(sh, sector, pd_idx, disks);
                } else {
                        if (atomic_read(&sh->count)) {
                          BUG_ON(!list_empty(&sh->lru));
                        } else {
                                if (!test_bit(STRIPE_HANDLE, &sh->state))
                                        atomic_inc(&conf->active_stripes);
                                if (list_empty(&sh->lru) &&
                                    !test_bit(STRIPE_EXPANDING, &sh->state))
                                        BUG();
                                list_del_init(&sh->lru);
                        }
                }
        } while (sh == NULL);

        if (sh)
                atomic_inc(&sh->count);

        spin_unlock_irq(&conf->device_lock);
        return sh;
}

/* test_and_ack_op() ensures that we only dequeue an operation once */
#define test_and_ack_op(op, pend) \
do {                                                    \
        if (test_bit(op, &sh->ops.pending) &&           \
                !test_bit(op, &sh->ops.complete)) {     \
                if (test_and_set_bit(op, &sh->ops.ack)) \
                        clear_bit(op, &pend);           \
                else                                    \
                        ack++;                          \
        } else                                          \
                clear_bit(op, &pend);                   \
} while (0)

/* find new work to run, do not resubmit work that is already
 * in flight
 */
static unsigned long get_stripe_work(struct stripe_head *sh)
{
        unsigned long pending;
        int ack = 0;

        pending = sh->ops.pending;

        test_and_ack_op(STRIPE_OP_BIOFILL, pending);
        test_and_ack_op(STRIPE_OP_COMPUTE_BLK, pending);
        test_and_ack_op(STRIPE_OP_PREXOR, pending);
        test_and_ack_op(STRIPE_OP_BIODRAIN, pending);
        test_and_ack_op(STRIPE_OP_POSTXOR, pending);
        test_and_ack_op(STRIPE_OP_CHECK, pending);
        if (test_and_clear_bit(STRIPE_OP_IO, &sh->ops.pending))
                ack++;

        sh->ops.count -= ack;
        if (unlikely(sh->ops.count < 0)) {
                printk(KERN_ERR "pending: %#lx ops.pending: %#lx ops.ack: %#lx "
                        "ops.complete: %#lx\n", pending, sh->ops.pending,
                        sh->ops.ack, sh->ops.complete);
                BUG();
        }

        return pending;
}

static void
raid5_end_read_request(struct bio *bi, int error);
static void
raid5_end_write_request(struct bio *bi, int error);

static void ops_run_io(struct stripe_head *sh)
{
        raid5_conf_t *conf = sh->raid_conf;
        int i, disks = sh->disks;

        might_sleep();

        set_bit(STRIPE_IO_STARTED, &sh->state);
        for (i = disks; i--; ) {
                int rw;
                struct bio *bi;
                mdk_rdev_t *rdev;
                if (test_and_clear_bit(R5_Wantwrite, &sh->dev[i].flags))
                        rw = WRITE;
                else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
                        rw = READ;
                else
                        continue;

                bi = &sh->dev[i].req;

                bi->bi_rw = rw;
                if (rw == WRITE)
                        bi->bi_end_io = raid5_end_write_request;
                else
                        bi->bi_end_io = raid5_end_read_request;

                rcu_read_lock();
                rdev = rcu_dereference(conf->disks[i].rdev);
                if (rdev && test_bit(Faulty, &rdev->flags))
                        rdev = NULL;
                if (rdev)
                        atomic_inc(&rdev->nr_pending);
                rcu_read_unlock();

                if (rdev) {
                        if (test_bit(STRIPE_SYNCING, &sh->state) ||
                                test_bit(STRIPE_EXPAND_SOURCE, &sh->state) ||
                                test_bit(STRIPE_EXPAND_READY, &sh->state))
                                md_sync_acct(rdev->bdev, STRIPE_SECTORS);

                        bi->bi_bdev = rdev->bdev;
                        pr_debug("%s: for %llu schedule op %ld on disc %d\n",
                                __func__, (unsigned long long)sh->sector,
                                bi->bi_rw, i);
                        atomic_inc(&sh->count);
                        bi->bi_sector = sh->sector + rdev->data_offset;
                        bi->bi_flags = 1 << BIO_UPTODATE;
                        bi->bi_vcnt = 1;
                        bi->bi_max_vecs = 1;
                        bi->bi_idx = 0;
                        bi->bi_io_vec = &sh->dev[i].vec;
                        bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
                        bi->bi_io_vec[0].bv_offset = 0;
                        bi->bi_size = STRIPE_SIZE;
                        bi->bi_next = NULL;
                        if (rw == WRITE &&
                            test_bit(R5_ReWrite, &sh->dev[i].flags))
                                atomic_add(STRIPE_SECTORS,
                                        &rdev->corrected_errors);
                        generic_make_request(bi);
                } else {
                        if (rw == WRITE)
                                set_bit(STRIPE_DEGRADED, &sh->state);
                        pr_debug("skip op %ld on disc %d for sector %llu\n",
                                bi->bi_rw, i, (unsigned long long)sh->sector);
                        clear_bit(R5_LOCKED, &sh->dev[i].flags);
                        set_bit(STRIPE_HANDLE, &sh->state);
                }
        }
}

static struct dma_async_tx_descriptor *
async_copy_data(int frombio, struct bio *bio, struct page *page,
        sector_t sector, struct dma_async_tx_descriptor *tx)
{
        struct bio_vec *bvl;
        struct page *bio_page;
        int i;
        int page_offset;

        if (bio->bi_sector >= sector)
                page_offset = (signed)(bio->bi_sector - sector) * 512;
        else
                page_offset = (signed)(sector - bio->bi_sector) * -512;
        bio_for_each_segment(bvl, bio, i) {
                int len = bio_iovec_idx(bio, i)->bv_len;
                int clen;
                int b_offset = 0;

                if (page_offset < 0) {
                        b_offset = -page_offset;
                        page_offset += b_offset;
                        len -= b_offset;
                }

                if (len > 0 && page_offset + len > STRIPE_SIZE)
                        clen = STRIPE_SIZE - page_offset;
                else
                        clen = len;

                if (clen > 0) {
                        b_offset += bio_iovec_idx(bio, i)->bv_offset;
                        bio_page = bio_iovec_idx(bio, i)->bv_page;
                        if (frombio)
                                tx = async_memcpy(page, bio_page, page_offset,
                                        b_offset, clen,
                                        ASYNC_TX_DEP_ACK,
                                        tx, NULL, NULL);
                        else
                                tx = async_memcpy(bio_page, page, b_offset,
                                        page_offset, clen,
                                        ASYNC_TX_DEP_ACK,
                                        tx, NULL, NULL);
                }
                if (clen < len) /* hit end of page */
                        break;
                page_offset +=  len;
        }

        return tx;
}

static void ops_complete_biofill(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;
        struct bio *return_bi = NULL;
        raid5_conf_t *conf = sh->raid_conf;
        int i;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        /* clear completed biofills */
        for (i = sh->disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];

                /* acknowledge completion of a biofill operation */
                /* and check if we need to reply to a read request,
                 * new R5_Wantfill requests are held off until
                 * !test_bit(STRIPE_OP_BIOFILL, &sh->ops.pending)
                 */
                if (test_and_clear_bit(R5_Wantfill, &dev->flags)) {
                        struct bio *rbi, *rbi2;

                        /* The access to dev->read is outside of the
                         * spin_lock_irq(&conf->device_lock), but is protected
                         * by the STRIPE_OP_BIOFILL pending bit
                         */
                        BUG_ON(!dev->read);
                        rbi = dev->read;
                        dev->read = NULL;
                        while (rbi && rbi->bi_sector <
                                dev->sector + STRIPE_SECTORS) {
                                rbi2 = r5_next_bio(rbi, dev->sector);
                                spin_lock_irq(&conf->device_lock);
                                if (--rbi->bi_phys_segments == 0) {
                                        rbi->bi_next = return_bi;
                                        return_bi = rbi;
                                }
                                spin_unlock_irq(&conf->device_lock);
                                rbi = rbi2;
                        }
                }
        }
        set_bit(STRIPE_OP_BIOFILL, &sh->ops.complete);

        return_io(return_bi);

        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}

static void ops_run_biofill(struct stripe_head *sh)
{
        struct dma_async_tx_descriptor *tx = NULL;
        raid5_conf_t *conf = sh->raid_conf;
        int i;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = sh->disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                if (test_bit(R5_Wantfill, &dev->flags)) {
                        struct bio *rbi;
                        spin_lock_irq(&conf->device_lock);
                        dev->read = rbi = dev->toread;
                        dev->toread = NULL;
                        spin_unlock_irq(&conf->device_lock);
                        while (rbi && rbi->bi_sector <
                                dev->sector + STRIPE_SECTORS) {
                                tx = async_copy_data(0, rbi, dev->page,
                                        dev->sector, tx);
                                rbi = r5_next_bio(rbi, dev->sector);
                        }
                }
        }

        atomic_inc(&sh->count);
        async_trigger_callback(ASYNC_TX_DEP_ACK | ASYNC_TX_ACK, tx,
                ops_complete_biofill, sh);
}

static void ops_complete_compute5(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;
        int target = sh->ops.target;
        struct r5dev *tgt = &sh->dev[target];

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        set_bit(R5_UPTODATE, &tgt->flags);
        BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));
        clear_bit(R5_Wantcompute, &tgt->flags);
        set_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.complete);
        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}

static struct dma_async_tx_descriptor *
ops_run_compute5(struct stripe_head *sh, unsigned long pending)
{
        /* kernel stack size limits the total number of disks */
        int disks = sh->disks;
        struct page *xor_srcs[disks];
        int target = sh->ops.target;
        struct r5dev *tgt = &sh->dev[target];
        struct page *xor_dest = tgt->page;
        int count = 0;
        struct dma_async_tx_descriptor *tx;
        int i;

        pr_debug("%s: stripe %llu block: %d\n",
                __func__, (unsigned long long)sh->sector, target);
        BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));

        for (i = disks; i--; )
                if (i != target)
                        xor_srcs[count++] = sh->dev[i].page;

        atomic_inc(&sh->count);

        if (unlikely(count == 1))
                tx = async_memcpy(xor_dest, xor_srcs[0], 0, 0, STRIPE_SIZE,
                        0, NULL, ops_complete_compute5, sh);
        else
                tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
                        ASYNC_TX_XOR_ZERO_DST, NULL,
                        ops_complete_compute5, sh);

        /* ack now if postxor is not set to be run */
        if (tx && !test_bit(STRIPE_OP_POSTXOR, &pending))
                async_tx_ack(tx);

        return tx;
}

static void ops_complete_prexor(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        set_bit(STRIPE_OP_PREXOR, &sh->ops.complete);
}

static struct dma_async_tx_descriptor *
ops_run_prexor(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
{
        /* kernel stack size limits the total number of disks */
        int disks = sh->disks;
        struct page *xor_srcs[disks];
        int count = 0, pd_idx = sh->pd_idx, i;

        /* existing parity data subtracted */
        struct page *xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                /* Only process blocks that are known to be uptodate */
                if (dev->towrite && test_bit(R5_Wantprexor, &dev->flags))
                        xor_srcs[count++] = dev->page;
        }

        tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
                ASYNC_TX_DEP_ACK | ASYNC_TX_XOR_DROP_DST, tx,
                ops_complete_prexor, sh);

        return tx;
}

static struct dma_async_tx_descriptor *
ops_run_biodrain(struct stripe_head *sh, struct dma_async_tx_descriptor *tx,
                 unsigned long pending)
{
        int disks = sh->disks;
        int pd_idx = sh->pd_idx, i;

        /* check if prexor is active which means only process blocks
         * that are part of a read-modify-write (Wantprexor)
         */
        int prexor = test_bit(STRIPE_OP_PREXOR, &pending);

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                struct bio *chosen;
                int towrite;

                towrite = 0;
                if (prexor) { /* rmw */
                        if (dev->towrite &&
                            test_bit(R5_Wantprexor, &dev->flags))
                                towrite = 1;
                } else { /* rcw */
                        if (i != pd_idx && dev->towrite &&
                                test_bit(R5_LOCKED, &dev->flags))
                                towrite = 1;
                }

                if (towrite) {
                        struct bio *wbi;

                        spin_lock(&sh->lock);
                        chosen = dev->towrite;
                        dev->towrite = NULL;
                        BUG_ON(dev->written);
                        wbi = dev->written = chosen;
                        spin_unlock(&sh->lock);

                        while (wbi && wbi->bi_sector <
                                dev->sector + STRIPE_SECTORS) {
                                tx = async_copy_data(1, wbi, dev->page,
                                        dev->sector, tx);
                                wbi = r5_next_bio(wbi, dev->sector);
                        }
                }
        }

        return tx;
}

static void ops_complete_postxor(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        set_bit(STRIPE_OP_POSTXOR, &sh->ops.complete);
        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}

static void ops_complete_write(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;
        int disks = sh->disks, i, pd_idx = sh->pd_idx;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                if (dev->written || i == pd_idx)
                        set_bit(R5_UPTODATE, &dev->flags);
        }

        set_bit(STRIPE_OP_BIODRAIN, &sh->ops.complete);
        set_bit(STRIPE_OP_POSTXOR, &sh->ops.complete);

        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}

static void
ops_run_postxor(struct stripe_head *sh, struct dma_async_tx_descriptor *tx,
                unsigned long pending)
{
        /* kernel stack size limits the total number of disks */
        int disks = sh->disks;
        struct page *xor_srcs[disks];

        int count = 0, pd_idx = sh->pd_idx, i;
        struct page *xor_dest;
        int prexor = test_bit(STRIPE_OP_PREXOR, &pending);
        unsigned long flags;
        dma_async_tx_callback callback;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        /* check if prexor is active which means only process blocks
         * that are part of a read-modify-write (written)
         */
        if (prexor) {
                xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (dev->written)
                                xor_srcs[count++] = dev->page;
                }
        } else {
                xor_dest = sh->dev[pd_idx].page;
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (i != pd_idx)
                                xor_srcs[count++] = dev->page;
                }
        }

        /* check whether this postxor is part of a write */
        callback = test_bit(STRIPE_OP_BIODRAIN, &pending) ?
                ops_complete_write : ops_complete_postxor;

        /* 1/ if we prexor'd then the dest is reused as a source
         * 2/ if we did not prexor then we are redoing the parity
         * set ASYNC_TX_XOR_DROP_DST and ASYNC_TX_XOR_ZERO_DST
         * for the synchronous xor case
         */
        flags = ASYNC_TX_DEP_ACK | ASYNC_TX_ACK |
                (prexor ? ASYNC_TX_XOR_DROP_DST : ASYNC_TX_XOR_ZERO_DST);

        atomic_inc(&sh->count);

        if (unlikely(count == 1)) {
                flags &= ~(ASYNC_TX_XOR_DROP_DST | ASYNC_TX_XOR_ZERO_DST);
                tx = async_memcpy(xor_dest, xor_srcs[0], 0, 0, STRIPE_SIZE,
                        flags, tx, callback, sh);
        } else
                tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
                        flags, tx, callback, sh);
}

static void ops_complete_check(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;
        int pd_idx = sh->pd_idx;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        if (test_and_clear_bit(STRIPE_OP_MOD_DMA_CHECK, &sh->ops.pending) &&
                sh->ops.zero_sum_result == 0)
                set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);

        set_bit(STRIPE_OP_CHECK, &sh->ops.complete);
        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}

static void ops_run_check(struct stripe_head *sh)
{
        /* kernel stack size limits the total number of disks */
        int disks = sh->disks;
        struct page *xor_srcs[disks];
        struct dma_async_tx_descriptor *tx;

        int count = 0, pd_idx = sh->pd_idx, i;
        struct page *xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                if (i != pd_idx)
                        xor_srcs[count++] = dev->page;
        }

        tx = async_xor_zero_sum(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
                &sh->ops.zero_sum_result, 0, NULL, NULL, NULL);

        if (tx)
                set_bit(STRIPE_OP_MOD_DMA_CHECK, &sh->ops.pending);
        else
                clear_bit(STRIPE_OP_MOD_DMA_CHECK, &sh->ops.pending);

        atomic_inc(&sh->count);
        tx = async_trigger_callback(ASYNC_TX_DEP_ACK | ASYNC_TX_ACK, tx,
                ops_complete_check, sh);
}

static void raid5_run_ops(struct stripe_head *sh, unsigned long pending)
{
        int overlap_clear = 0, i, disks = sh->disks;
        struct dma_async_tx_descriptor *tx = NULL;

        if (test_bit(STRIPE_OP_BIOFILL, &pending)) {
                ops_run_biofill(sh);
                overlap_clear++;
        }

        if (test_bit(STRIPE_OP_COMPUTE_BLK, &pending))
                tx = ops_run_compute5(sh, pending);

        if (test_bit(STRIPE_OP_PREXOR, &pending))
                tx = ops_run_prexor(sh, tx);

        if (test_bit(STRIPE_OP_BIODRAIN, &pending)) {
                tx = ops_run_biodrain(sh, tx, pending);
                overlap_clear++;
        }

        if (test_bit(STRIPE_OP_POSTXOR, &pending))
                ops_run_postxor(sh, tx, pending);

        if (test_bit(STRIPE_OP_CHECK, &pending))
                ops_run_check(sh);

        if (test_bit(STRIPE_OP_IO, &pending))
                ops_run_io(sh);

        if (overlap_clear)
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (test_and_clear_bit(R5_Overlap, &dev->flags))
                                wake_up(&sh->raid_conf->wait_for_overlap);
                }
}

static int grow_one_stripe(raid5_conf_t *conf)
{
        struct stripe_head *sh;
        sh = kmem_cache_alloc(conf->slab_cache, GFP_KERNEL);
        if (!sh)
                return 0;
        memset(sh, 0, sizeof(*sh) + (conf->raid_disks-1)*sizeof(struct r5dev));
        sh->raid_conf = conf;
        spin_lock_init(&sh->lock);

        if (grow_buffers(sh, conf->raid_disks)) {
                shrink_buffers(sh, conf->raid_disks);
                kmem_cache_free(conf->slab_cache, sh);
                return 0;
        }
        sh->disks = conf->raid_disks;
        /* we just created an active stripe so... */
        atomic_set(&sh->count, 1);
        atomic_inc(&conf->active_stripes);
        INIT_LIST_HEAD(&sh->lru);
        release_stripe(sh);
        return 1;
}

static int grow_stripes(raid5_conf_t *conf, int num)
{
        struct kmem_cache *sc;
        int devs = conf->raid_disks;

        sprintf(conf->cache_name[0], "raid5-%s", mdname(conf->mddev));
        sprintf(conf->cache_name[1], "raid5-%s-alt", mdname(conf->mddev));
        conf->active_name = 0;
        sc = kmem_cache_create(conf->cache_name[conf->active_name],
                               sizeof(struct stripe_head)+(devs-1)*sizeof(struct r5dev),
                               0, 0, NULL);
        if (!sc)
                return 1;
        conf->slab_cache = sc;
        conf->pool_size = devs;
        while (num--)
                if (!grow_one_stripe(conf))
                        return 1;
        return 0;
}

#ifdef CONFIG_MD_RAID5_RESHAPE
static int resize_stripes(raid5_conf_t *conf, int newsize)
{
        /* Make all the stripes able to hold 'newsize' devices.
         * New slots in each stripe get 'page' set to a new page.
         *
         * This happens in stages:
         * 1/ create a new kmem_cache and allocate the required number of
         *    stripe_heads.
         * 2/ gather all the old stripe_heads and tranfer the pages across
         *    to the new stripe_heads.  This will have the side effect of
         *    freezing the array as once all stripe_heads have been collected,
         *    no IO will be possible.  Old stripe heads are freed once their
         *    pages have been transferred over, and the old kmem_cache is
         *    freed when all stripes are done.
         * 3/ reallocate conf->disks to be suitable bigger.  If this fails,
         *    we simple return a failre status - no need to clean anything up.
         * 4/ allocate new pages for the new slots in the new stripe_heads.
         *    If this fails, we don't bother trying the shrink the
         *    stripe_heads down again, we just leave them as they are.
         *    As each stripe_head is processed the new one is released into
         *    active service.
         *
         * Once step2 is started, we cannot afford to wait for a write,
         * so we use GFP_NOIO allocations.
         */
        struct stripe_head *osh, *nsh;
        LIST_HEAD(newstripes);
        struct disk_info *ndisks;
        int err = 0;

        struct kmem_cache *sc;
        int i;

        if (newsize <= conf->pool_size)
                return 0; /* never bother to shrink */

        md_allow_write(conf->mddev);

        /* Step 1 */
        sc = kmem_cache_create(conf->cache_name[1-conf->active_name],
                               sizeof(struct stripe_head)+(newsize-1)*sizeof(struct r5dev),
                               0, 0, NULL);
        if (!sc)
                return -ENOMEM;

        for (i = conf->max_nr_stripes; i; i--) {
                nsh = kmem_cache_alloc(sc, GFP_KERNEL);
                if (!nsh)
                        break;

                memset(nsh, 0, sizeof(*nsh) + (newsize-1)*sizeof(struct r5dev));

                nsh->raid_conf = conf;
                spin_lock_init(&nsh->lock);

                list_add(&nsh->lru, &newstripes);
        }
        if (i) {
                /* didn't get enough, give up */
                while (!list_empty(&newstripes)) {
                        nsh = list_entry(newstripes.next, struct stripe_head, lru);
                        list_del(&nsh->lru);
                        kmem_cache_free(sc, nsh);
                }
                kmem_cache_destroy(sc);
                return -ENOMEM;
        }
        /* Step 2 - Must use GFP_NOIO now.
         * OK, we have enough stripes, start collecting inactive
         * stripes and copying them over
         */
        list_for_each_entry(nsh, &newstripes, lru) {
                spin_lock_irq(&conf->device_lock);
                wait_event_lock_irq(conf->wait_for_stripe,
                                    !list_empty(&conf->inactive_list),
                                    conf->device_lock,
                                    unplug_slaves(conf->mddev)
                        );
                osh = get_free_stripe(conf);
                spin_unlock_irq(&conf->device_lock);
                atomic_set(&nsh->count, 1);
                for(i=0; i<conf->pool_size; i++)
                        nsh->dev[i].page = osh->dev[i].page;
                for( ; i<newsize; i++)
                        nsh->dev[i].page = NULL;
                kmem_cache_free(conf->slab_cache, osh);
        }
        kmem_cache_destroy(conf->slab_cache);

        /* Step 3.
         * At this point, we are holding all the stripes so the array
         * is completely stalled, so now is a good time to resize
         * conf->disks.
         */
        ndisks = kzalloc(newsize * sizeof(struct disk_info), GFP_NOIO);
        if (ndisks) {
                for (i=0; i<conf->raid_disks; i++)
                        ndisks[i] = conf->disks[i];
                kfree(conf->disks);
                conf->disks = ndisks;
        } else
                err = -ENOMEM;

        /* Step 4, return new stripes to service */
        while(!list_empty(&newstripes)) {
                nsh = list_entry(newstripes.next, struct stripe_head, lru);
                list_del_init(&nsh->lru);
                for (i=conf->raid_disks; i < newsize; i++)
                        if (nsh->dev[i].page == NULL) {
                                struct page *p = alloc_page(GFP_NOIO);
                                nsh->dev[i].page = p;
                                if (!p)
                                        err = -ENOMEM;
                        }
                release_stripe(nsh);
        }
        /* critical section pass, GFP_NOIO no longer needed */

        conf->slab_cache = sc;
        conf->active_name = 1-conf->active_name;
        conf->pool_size = newsize;
        return err;
}
#endif

static int drop_one_stripe(raid5_conf_t *conf)
{
        struct stripe_head *sh;

        spin_lock_irq(&conf->device_lock);
        sh = get_free_stripe(conf);
        spin_unlock_irq(&conf->device_lock);
        if (!sh)
                return 0;
        BUG_ON(atomic_read(&sh->count));
        shrink_buffers(sh, conf->pool_size);
        kmem_cache_free(conf->slab_cache, sh);
        atomic_dec(&conf->active_stripes);
        return 1;
}

static void shrink_stripes(raid5_conf_t *conf)
{
        while (drop_one_stripe(conf))
                ;

        if (conf->slab_cache)
                kmem_cache_destroy(conf->slab_cache);
        conf->slab_cache = NULL;
}

static void raid5_end_read_request(struct bio * bi, int error)
{
        struct stripe_head *sh = bi->bi_private;
        raid5_conf_t *conf = sh->raid_conf;
        int disks = sh->disks, i;
        int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
        char b[BDEVNAME_SIZE];
        mdk_rdev_t *rdev;


        for (i=0 ; i<disks; i++)
                if (bi == &sh->dev[i].req)
                        break;

        pr_debug("end_read_request %llu/%d, count: %d, uptodate %d.\n",
                (unsigned long long)sh->sector, i, atomic_read(&sh->count),
                uptodate);
        if (i == disks) {
                BUG();
                return;
        }

        if (uptodate) {
                set_bit(R5_UPTODATE, &sh->dev[i].flags);
                if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
                        rdev = conf->disks[i].rdev;
                        printk_rl(KERN_INFO "raid5:%s: read error corrected"
                                  " (%lu sectors at %llu on %s)\n",
                                  mdname(conf->mddev), STRIPE_SECTORS,
                                  (unsigned long long)(sh->sector
                                                       + rdev->data_offset),
                                  bdevname(rdev->bdev, b));
                        clear_bit(R5_ReadError, &sh->dev[i].flags);
                        clear_bit(R5_ReWrite, &sh->dev[i].flags);
                }
                if (atomic_read(&conf->disks[i].rdev->read_errors))
                        atomic_set(&conf->disks[i].rdev->read_errors, 0);
        } else {
                const char *bdn = bdevname(conf->disks[i].rdev->bdev, b);
                int retry = 0;
                rdev = conf->disks[i].rdev;

                clear_bit(R5_UPTODATE, &sh->dev[i].flags);
                atomic_inc(&rdev->read_errors);
                if (conf->mddev->degraded)
                        printk_rl(KERN_WARNING
                                  "raid5:%s: read error not correctable "
                                  "(sector %llu on %s).\n",
                                  mdname(conf->mddev),
                                  (unsigned long long)(sh->sector
                                                       + rdev->data_offset),
                                  bdn);
                else if (test_bit(R5_ReWrite, &sh->dev[i].flags))
                        /* Oh, no!!! */
                        printk_rl(KERN_WARNING
                                  "raid5:%s: read error NOT corrected!! "
                                  "(sector %llu on %s).\n",
                                  mdname(conf->mddev),
                                  (unsigned long long)(sh->sector
                                                       + rdev->data_offset),
                                  bdn);
                else if (atomic_read(&rdev->read_errors)
                         > conf->max_nr_stripes)
                        printk(KERN_WARNING
                               "raid5:%s: Too many read errors, failing device %s.\n",
                               mdname(conf->mddev), bdn);
                else
                        retry = 1;
                if (retry)
                        set_bit(R5_ReadError, &sh->dev[i].flags);
                else {
                        clear_bit(R5_ReadError, &sh->dev[i].flags);
                        clear_bit(R5_ReWrite, &sh->dev[i].flags);
                        md_error(conf->mddev, rdev);
                }
        }
        rdev_dec_pending(conf->disks[i].rdev, conf->mddev);
        clear_bit(R5_LOCKED, &sh->dev[i].flags);
        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}

static void raid5_end_write_request (struct bio *bi, int error)
{
        struct stripe_head *sh = bi->bi_private;
        raid5_conf_t *conf = sh->raid_conf;
        int disks = sh->disks, i;
        int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);

        for (i=0 ; i<disks; i++)
                if (bi == &sh->dev[i].req)
                        break;

        pr_debug("end_write_request %llu/%d, count %d, uptodate: %d.\n",
                (unsigned long long)sh->sector, i, atomic_read(&sh->count),
                uptodate);
        if (i == disks) {
                BUG();
                return;
        }

        if (!uptodate)
                md_error(conf->mddev, conf->disks[i].rdev);

        rdev_dec_pending(conf->disks[i].rdev, conf->mddev);
        
        clear_bit(R5_LOCKED, &sh->dev[i].flags);
        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}


static sector_t compute_blocknr(struct stripe_head *sh, int i);
        
static void raid5_build_block (struct stripe_head *sh, int i)
{
        struct r5dev *dev = &sh->dev[i];

        bio_init(&dev->req);
        dev->req.bi_io_vec = &dev->vec;
        dev->req.bi_vcnt++;
        dev->req.bi_max_vecs++;
        dev->vec.bv_page = dev->page;
        dev->vec.bv_len = STRIPE_SIZE;
        dev->vec.bv_offset = 0;

        dev->req.bi_sector = sh->sector;
        dev->req.bi_private = sh;

        dev->flags = 0;
        dev->sector = compute_blocknr(sh, i);
}

static void error(mddev_t *mddev, mdk_rdev_t *rdev)
{
        char b[BDEVNAME_SIZE];
        raid5_conf_t *conf = (raid5_conf_t *) mddev->private;
        pr_debug("raid5: error called\n");

        if (!test_bit(Faulty, &rdev->flags)) {
                set_bit(MD_CHANGE_DEVS, &mddev->flags);
                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 was running, make sure it aborts.
                         */
                        set_bit(MD_RECOVERY_INTR, &mddev->recovery);
                }
                set_bit(Faulty, &rdev->flags);
                printk (KERN_ALERT
                        "raid5: Disk failure on %s, disabling device.\n"
                        "raid5: Operation continuing on %d devices.\n",
                        bdevname(rdev->bdev,b), conf->raid_disks - mddev->degraded);
        }
}

/*
 * Input: a 'big' sector number,
 * Output: index of the data and parity disk, and the sector # in them.
 */
static sector_t raid5_compute_sector(sector_t r_sector, unsigned int raid_disks,
                        unsigned int data_disks, unsigned int * dd_idx,
                        unsigned int * pd_idx, raid5_conf_t *conf)
{
        long stripe;
        unsigned long chunk_number;
        unsigned int chunk_offset;
        sector_t new_sector;
        int sectors_per_chunk = conf->chunk_size >> 9;

        /* First compute the information on this sector */

        /*
         * Compute the chunk number and the sector offset inside the chunk
         */
        chunk_offset = sector_div(r_sector, sectors_per_chunk);
        chunk_number = r_sector;
        BUG_ON(r_sector != chunk_number);

        /*
         * Compute the stripe number
         */
        stripe = chunk_number / data_disks;

        /*
         * Compute the data disk and parity disk indexes inside the stripe
         */
        *dd_idx = chunk_number % data_disks;

        /*
         * Select the parity disk based on the user selected algorithm.
         */
        switch(conf->level) {
        case 4:
                *pd_idx = data_disks;
                break;
        case 5:
                switch (conf->algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                        *pd_idx = data_disks - stripe % raid_disks;
                        if (*dd_idx >= *pd_idx)
                                (*dd_idx)++;
                        break;
                case ALGORITHM_RIGHT_ASYMMETRIC:
                        *pd_idx = stripe % raid_disks;
                        if (*dd_idx >= *pd_idx)
                                (*dd_idx)++;
                        break;
                case ALGORITHM_LEFT_SYMMETRIC:
                        *pd_idx = data_disks - stripe % raid_disks;
                        *dd_idx = (*pd_idx + 1 + *dd_idx) % raid_disks;
                        break;
                case ALGORITHM_RIGHT_SYMMETRIC:
                        *pd_idx = stripe % raid_disks;
                        *dd_idx = (*pd_idx + 1 + *dd_idx) % raid_disks;
                        break;
                default:
                        printk(KERN_ERR "raid5: unsupported algorithm %d\n",
                                conf->algorithm);
                }
                break;
        case 6:

                /**** FIX THIS ****/
                switch (conf->algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                        *pd_idx = raid_disks - 1 - (stripe % raid_disks);
                        if (*pd_idx == raid_disks-1)
                                (*dd_idx)++;    /* Q D D D P */
                        else if (*dd_idx >= *pd_idx)
                                (*dd_idx) += 2; /* D D P Q D */
                        break;
                case ALGORITHM_RIGHT_ASYMMETRIC:
                        *pd_idx = stripe % raid_disks;
                        if (*pd_idx == raid_disks-1)
                                (*dd_idx)++;    /* Q D D D P */
                        else if (*dd_idx >= *pd_idx)
                                (*dd_idx) += 2; /* D D P Q D */
                        break;
                case ALGORITHM_LEFT_SYMMETRIC:
                        *pd_idx = raid_disks - 1 - (stripe % raid_disks);
                        *dd_idx = (*pd_idx + 2 + *dd_idx) % raid_disks;
                        break;
                case ALGORITHM_RIGHT_SYMMETRIC:
                        *pd_idx = stripe % raid_disks;
                        *dd_idx = (*pd_idx + 2 + *dd_idx) % raid_disks;
                        break;
                default:
                        printk (KERN_CRIT "raid6: unsupported algorithm %d\n",
                                conf->algorithm);
                }
                break;
        }

        /*
         * Finally, compute the new sector number
         */
        new_sector = (sector_t)stripe * sectors_per_chunk + chunk_offset;
        return new_sector;
}


static sector_t compute_blocknr(struct stripe_head *sh, int i)
{
        raid5_conf_t *conf = sh->raid_conf;
        int raid_disks = sh->disks;
        int data_disks = raid_disks - conf->max_degraded;
        sector_t new_sector = sh->sector, check;
        int sectors_per_chunk = conf->chunk_size >> 9;
        sector_t stripe;
        int chunk_offset;
        int chunk_number, dummy1, dummy2, dd_idx = i;
        sector_t r_sector;


        chunk_offset = sector_div(new_sector, sectors_per_chunk);
        stripe = new_sector;
        BUG_ON(new_sector != stripe);

        if (i == sh->pd_idx)
                return 0;
        switch(conf->level) {
        case 4: break;
        case 5:
                switch (conf->algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                case ALGORITHM_RIGHT_ASYMMETRIC:
                        if (i > sh->pd_idx)
                                i--;
                        break;
                case ALGORITHM_LEFT_SYMMETRIC:
                case ALGORITHM_RIGHT_SYMMETRIC:
                        if (i < sh->pd_idx)
                                i += raid_disks;
                        i -= (sh->pd_idx + 1);
                        break;
                default:
                        printk(KERN_ERR "raid5: unsupported algorithm %d\n",
                               conf->algorithm);
                }
                break;
        case 6:
                if (i == raid6_next_disk(sh->pd_idx, raid_disks))
                        return 0; /* It is the Q disk */
                switch (conf->algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                case ALGORITHM_RIGHT_ASYMMETRIC:
                        if (sh->pd_idx == raid_disks-1)
                                i--;    /* Q D D D P */
                        else if (i > sh->pd_idx)
                                i -= 2; /* D D P Q D */
                        break;
                case ALGORITHM_LEFT_SYMMETRIC:
                case ALGORITHM_RIGHT_SYMMETRIC:
                        if (sh->pd_idx == raid_disks-1)
                                i--; /* Q D D D P */
                        else {
                                /* D D P Q D */
                                if (i < sh->pd_idx)
                                        i += raid_disks;
                                i -= (sh->pd_idx + 2);
                        }
                        break;
                default:
                        printk (KERN_CRIT "raid6: unsupported algorithm %d\n",
                                conf->algorithm);
                }
                break;
        }

        chunk_number = stripe * data_disks + i;
        r_sector = (sector_t)chunk_number * sectors_per_chunk + chunk_offset;

        check = raid5_compute_sector (r_sector, raid_disks, data_disks, &dummy1, &dummy2, conf);
        if (check != sh->sector || dummy1 != dd_idx || dummy2 != sh->pd_idx) {
                printk(KERN_ERR "compute_blocknr: map not correct\n");
                return 0;
        }
        return r_sector;
}



/*
 * Copy data between a page in the stripe cache, and one or more bion
 * The page could align with the middle of the bio, or there could be
 * several bion, each with several bio_vecs, which cover part of the page
 * Multiple bion are linked together on bi_next.  There may be extras
 * at the end of this list.  We ignore them.
 */
static void copy_data(int frombio, struct bio *bio,
                     struct page *page,
                     sector_t sector)
{
        char *pa = page_address(page);
        struct bio_vec *bvl;
        int i;
        int page_offset;

        if (bio->bi_sector >= sector)
                page_offset = (signed)(bio->bi_sector - sector) * 512;
        else
                page_offset = (signed)(sector - bio->bi_sector) * -512;
        bio_for_each_segment(bvl, bio, i) {
                int len = bio_iovec_idx(bio,i)->bv_len;
                int clen;
                int b_offset = 0;

                if (page_offset < 0) {
                        b_offset = -page_offset;
                        page_offset += b_offset;
                        len -= b_offset;
                }

                if (len > 0 && page_offset + len > STRIPE_SIZE)
                        clen = STRIPE_SIZE - page_offset;
                else clen = len;

                if (clen > 0) {
                        char *ba = __bio_kmap_atomic(bio, i, KM_USER0);
                        if (frombio)
                                memcpy(pa+page_offset, ba+b_offset, clen);
                        else
                                memcpy(ba+b_offset, pa+page_offset, clen);
                        __bio_kunmap_atomic(ba, KM_USER0);
                }
                if (clen < len) /* hit end of page */
                        break;
                page_offset +=  len;
        }
}

#define check_xor()     do {                                              \
                                if (count == MAX_XOR_BLOCKS) {            \
                                xor_blocks(count, STRIPE_SIZE, dest, ptr);\
                                count = 0;                                \
                           }                                              \
                        } while(0)

static void compute_parity6(struct stripe_head *sh, int method)
{
        raid6_conf_t *conf = sh->raid_conf;
        int i, pd_idx = sh->pd_idx, qd_idx, d0_idx, disks = sh->disks, count;
        struct bio *chosen;
        /**** FIX THIS: This could be very bad if disks is close to 256 ****/
        void *ptrs[disks];

        qd_idx = raid6_next_disk(pd_idx, disks);
        d0_idx = raid6_next_disk(qd_idx, disks);

        pr_debug("compute_parity, stripe %llu, method %d\n",
                (unsigned long long)sh->sector, method);

        switch(method) {
        case READ_MODIFY_WRITE:
                BUG();          /* READ_MODIFY_WRITE N/A for RAID-6 */
        case RECONSTRUCT_WRITE:
                for (i= disks; i-- ;)
                        if ( i != pd_idx && i != qd_idx && sh->dev[i].towrite ) {
                                chosen = sh->dev[i].towrite;
                                sh->dev[i].towrite = NULL;

                                if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
                                        wake_up(&conf->wait_for_overlap);

                                BUG_ON(sh->dev[i].written);
                                sh->dev[i].written = chosen;
                        }
                break;
        case CHECK_PARITY:
                BUG();          /* Not implemented yet */
        }

        for (i = disks; i--;)
                if (sh->dev[i].written) {
                        sector_t sector = sh->dev[i].sector;
                        struct bio *wbi = sh->dev[i].written;
                        while (wbi && wbi->bi_sector < sector + STRIPE_SECTORS) {
                                copy_data(1, wbi, sh->dev[i].page, sector);
                                wbi = r5_next_bio(wbi, sector);
                        }

                        set_bit(R5_LOCKED, &sh->dev[i].flags);
                        set_bit(R5_UPTODATE, &sh->dev[i].flags);
                }

//      switch(method) {
//      case RECONSTRUCT_WRITE:
//      case CHECK_PARITY:
//      case UPDATE_PARITY:
                /* Note that unlike RAID-5, the ordering of the disks matters greatly. */
                /* FIX: Is this ordering of drives even remotely optimal? */
                count = 0;
                i = d0_idx;
                do {
                        ptrs[count++] = page_address(sh->dev[i].page);
                        if (count <= disks-2 && !test_bit(R5_UPTODATE, &sh->dev[i].flags))
                                printk("block %d/%d not uptodate on parity calc\n", i,count);
                        i = raid6_next_disk(i, disks);
                } while ( i != d0_idx );
//              break;
//      }

        raid6_call.gen_syndrome(disks, STRIPE_SIZE, ptrs);

        switch(method) {
        case RECONSTRUCT_WRITE:
                set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
                set_bit(R5_UPTODATE, &sh->dev[qd_idx].flags);
                set_bit(R5_LOCKED,   &sh->dev[pd_idx].flags);
                set_bit(R5_LOCKED,   &sh->dev[qd_idx].flags);
                break;
        case UPDATE_PARITY:
                set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
                set_bit(R5_UPTODATE, &sh->dev[qd_idx].flags);
                break;
        }
}


/* Compute one missing block */
static void compute_block_1(struct stripe_head *sh, int dd_idx, int nozero)
{
        int i, count, disks = sh->disks;
        void *ptr[MAX_XOR_BLOCKS], *dest, *p;
        int pd_idx = sh->pd_idx;
        int qd_idx = raid6_next_disk(pd_idx, disks);

        pr_debug("compute_block_1, stripe %llu, idx %d\n",
                (unsigned long long)sh->sector, dd_idx);

        if ( dd_idx == qd_idx ) {
                /* We're actually computing the Q drive */
                compute_parity6(sh, UPDATE_PARITY);
        } else {
                dest = page_address(sh->dev[dd_idx].page);
                if (!nozero) memset(dest, 0, STRIPE_SIZE);
                count = 0;
                for (i = disks ; i--; ) {
                        if (i == dd_idx || i == qd_idx)
                                continue;
                        p = page_address(sh->dev[i].page);
                        if (test_bit(R5_UPTODATE, &sh->dev[i].flags))
                                ptr[count++] = p;
                        else
                                printk("compute_block() %d, stripe %llu, %d"
                                       " not present\n", dd_idx,
                                       (unsigned long long)sh->sector, i);

                        check_xor();
                }
                if (count)
                        xor_blocks(count, STRIPE_SIZE, dest, ptr);
                if (!nozero) set_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
                else clear_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
        }
}

/* Compute two missing blocks */
static void compute_block_2(struct stripe_head *sh, int dd_idx1, int dd_idx2)
{
        int i, count, disks = sh->disks;
        int pd_idx = sh->pd_idx;
        int qd_idx = raid6_next_disk(pd_idx, disks);
        int d0_idx = raid6_next_disk(qd_idx, disks);
        int faila, failb;

        /* faila and failb are disk numbers relative to d0_idx */
        /* pd_idx become disks-2 and qd_idx become disks-1 */
        faila = (dd_idx1 < d0_idx) ? dd_idx1+(disks-d0_idx) : dd_idx1-d0_idx;
        failb = (dd_idx2 < d0_idx) ? dd_idx2+(disks-d0_idx) : dd_idx2-d0_idx;

        BUG_ON(faila == failb);
        if ( failb < faila ) { int tmp = faila; faila = failb; failb = tmp; }

        pr_debug("compute_block_2, stripe %llu, idx %d,%d (%d,%d)\n",
               (unsigned long long)sh->sector, dd_idx1, dd_idx2, faila, failb);

        if ( failb == disks-1 ) {
                /* Q disk is one of the missing disks */
                if ( faila == disks-2 ) {
                        /* Missing P+Q, just recompute */
                        compute_parity6(sh, UPDATE_PARITY);
                        return;
                } else {
                        /* We're missing D+Q; recompute D from P */
                        compute_block_1(sh, (dd_idx1 == qd_idx) ? dd_idx2 : dd_idx1, 0);
                        compute_parity6(sh, UPDATE_PARITY); /* Is this necessary? */
                        return;
                }
        }

        /* We're missing D+P or D+D; build pointer table */
        {
                /**** FIX THIS: This could be very bad if disks is close to 256 ****/
                void *ptrs[disks];

                count = 0;
                i = d0_idx;
                do {
                        ptrs[count++] = page_address(sh->dev[i].page);
                        i = raid6_next_disk(i, disks);
                        if (i != dd_idx1 && i != dd_idx2 &&
                            !test_bit(R5_UPTODATE, &sh->dev[i].flags))
                                printk("compute_2 with missing block %d/%d\n", count, i);
                } while ( i != d0_idx );

                if ( failb == disks-2 ) {
                        /* We're missing D+P. */
                        raid6_datap_recov(disks, STRIPE_SIZE, faila, ptrs);
                } else {
                        /* We're missing D+D. */
                        raid6_2data_recov(disks, STRIPE_SIZE, faila, failb, ptrs);
                }

                /* Both the above update both missing blocks */
                set_bit(R5_UPTODATE, &sh->dev[dd_idx1].flags);
                set_bit(R5_UPTODATE, &sh->dev[dd_idx2].flags);
        }
}

static int
handle_write_operations5(struct stripe_head *sh, int rcw, int expand)
{
        int i, pd_idx = sh->pd_idx, disks = sh->disks;
        int locked = 0;

        if (rcw) {
                /* if we are not expanding this is a proper write request, and
                 * there will be bios with new data to be drained into the
                 * stripe cache
                 */
                if (!expand) {
                        set_bit(STRIPE_OP_BIODRAIN, &sh->ops.pending);
                        sh->ops.count++;
                }

                set_bit(STRIPE_OP_POSTXOR, &sh->ops.pending);
                sh->ops.count++;

                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];

                        if (dev->towrite) {
                                set_bit(R5_LOCKED, &dev->flags);
                                if (!expand)
                                        clear_bit(R5_UPTODATE, &dev->flags);
                                locked++;
                        }
                }
                if (locked + 1 == disks)
                        if (!test_and_set_bit(STRIPE_FULL_WRITE, &sh->state))
                                atomic_inc(&sh->raid_conf->pending_full_writes);
        } else {
                BUG_ON(!(test_bit(R5_UPTODATE, &sh->dev[pd_idx].flags) ||
                        test_bit(R5_Wantcompute, &sh->dev[pd_idx].flags)));

                set_bit(STRIPE_OP_PREXOR, &sh->ops.pending);
                set_bit(STRIPE_OP_BIODRAIN, &sh->ops.pending);
                set_bit(STRIPE_OP_POSTXOR, &sh->ops.pending);

                sh->ops.count += 3;

                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (i == pd_idx)
                                continue;

                        /* For a read-modify write there may be blocks that are
                         * locked for reading while others are ready to be
                         * written so we distinguish these blocks by the
                         * R5_Wantprexor bit
                         */
                        if (dev->towrite &&
                            (test_bit(R5_UPTODATE, &dev->flags) ||
                            test_bit(R5_Wantcompute, &dev->flags))) {
                                set_bit(R5_Wantprexor, &dev->flags);
                                set_bit(R5_LOCKED, &dev->flags);
                                clear_bit(R5_UPTODATE, &dev->flags);
                                locked++;
                        }
                }
        }

        /* keep the parity disk locked while asynchronous operations
         * are in flight
         */
        set_bit(R5_LOCKED, &sh->dev[pd_idx].flags);
        clear_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
        locked++;

        pr_debug("%s: stripe %llu locked: %d pending: %lx\n",
                __func__, (unsigned long long)sh->sector,
                locked, sh->ops.pending);

        return locked;
}

/*
 * Each stripe/dev can have one or more bion attached.
 * toread/towrite point to the first in a chain.
 * The bi_next chain must be in order.
 */
static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, int forwrite)
{
        struct bio **bip;
        raid5_conf_t *conf = sh->raid_conf;
        int firstwrite=0;

        pr_debug("adding bh b#%llu to stripe s#%llu\n",
                (unsigned long long)bi->bi_sector,
                (unsigned long long)sh->sector);


        spin_lock(&sh->lock);
        spin_lock_irq(&conf->device_lock);
        if (forwrite) {
                bip = &sh->dev[dd_idx].towrite;
                if (*bip == NULL && sh->dev[dd_idx].written == NULL)
                        firstwrite = 1;
        } else
                bip = &sh->dev[dd_idx].toread;
        while (*bip && (*bip)->bi_sector < bi->bi_sector) {
                if ((*bip)->bi_sector + ((*bip)->bi_size >> 9) > bi->bi_sector)
                        goto overlap;
                bip = & (*bip)->bi_next;
        }
        if (*bip && (*bip)->bi_sector < bi->bi_sector + ((bi->bi_size)>>9))
                goto overlap;

        BUG_ON(*bip && bi->bi_next && (*bip) != bi->bi_next);
        if (*bip)
                bi->bi_next = *bip;
        *bip = bi;
        bi->bi_phys_segments ++;
        spin_unlock_irq(&conf->device_lock);
        spin_unlock(&sh->lock);

        pr_debug("added bi b#%llu to stripe s#%llu, disk %d.\n",
                (unsigned long long)bi->bi_sector,
                (unsigned long long)sh->sector, dd_idx);

        if (conf->mddev->bitmap && firstwrite) {
                bitmap_startwrite(conf->mddev->bitmap, sh->sector,
                                  STRIPE_SECTORS, 0);
                sh->bm_seq = conf->seq_flush+1;
                set_bit(STRIPE_BIT_DELAY, &sh->state);
        }

        if (forwrite) {
                /* check if page is covered */
                sector_t sector = sh->dev[dd_idx].sector;
                for (bi=sh->dev[dd_idx].towrite;
                     sector < sh->dev[dd_idx].sector + STRIPE_SECTORS &&
                             bi && bi->bi_sector <= sector;
                     bi = r5_next_bio(bi, sh->dev[dd_idx].sector)) {
                        if (bi->bi_sector + (bi->bi_size>>9) >= sector)
                                sector = bi->bi_sector + (bi->bi_size>>9);
                }
                if (sector >= sh->dev[dd_idx].sector + STRIPE_SECTORS)
                        set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);
        }
        return 1;

 overlap:
        set_bit(R5_Overlap, &sh->dev[dd_idx].flags);
        spin_unlock_irq(&conf->device_lock);
        spin_unlock(&sh->lock);
        return 0;
}

static void end_reshape(raid5_conf_t *conf);

static int page_is_zero(struct page *p)
{
        char *a = page_address(p);
        return ((*(u32*)a) == 0 &&
                memcmp(a, a+4, STRIPE_SIZE-4)==0);
}

static int stripe_to_pdidx(sector_t stripe, raid5_conf_t *conf, int disks)
{
        int sectors_per_chunk = conf->chunk_size >> 9;
        int pd_idx, dd_idx;
        int chunk_offset = sector_div(stripe, sectors_per_chunk);

        raid5_compute_sector(stripe * (disks - conf->max_degraded)
                             *sectors_per_chunk + chunk_offset,
                             disks, disks - conf->max_degraded,
                             &dd_idx, &pd_idx, conf);
        return pd_idx;
}

static void
handle_requests_to_failed_array(raid5_conf_t *conf, struct stripe_head *sh,
                                struct stripe_head_state *s, int disks,
                                struct bio **return_bi)
{
        int i;
        for (i = disks; i--; ) {
                struct bio *bi;
                int bitmap_end = 0;

                if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
                        mdk_rdev_t *rdev;
                        rcu_read_lock();
                        rdev = rcu_dereference(conf->disks[i].rdev);
                        if (rdev && test_bit(In_sync, &rdev->flags))
                                /* multiple read failures in one stripe */
                                md_error(conf->mddev, rdev);
                        rcu_read_unlock();
                }
                spin_lock_irq(&conf->device_lock);
                /* fail all writes first */
                bi = sh->dev[i].towrite;
                sh->dev[i].towrite = NULL;
                if (bi) {
                        s->to_write--;
                        bitmap_end = 1;
                }

                if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
                        wake_up(&conf->wait_for_overlap);

                while (bi && bi->bi_sector <
                        sh->dev[i].sector + STRIPE_SECTORS) {
                        struct bio *nextbi = r5_next_bio(bi, sh->dev[i].sector);
                        clear_bit(BIO_UPTODATE, &bi->bi_flags);
                        if (--bi->bi_phys_segments == 0) {
                                md_write_end(conf->mddev);
                                bi->bi_next = *return_bi;
                                *return_bi = bi;
                        }
                        bi = nextbi;
                }
                /* and fail all 'written' */
                bi = sh->dev[i].written;
                sh->dev[i].written = NULL;
                if (bi) bitmap_end = 1;
                while (bi && bi->bi_sector <
                       sh->dev[i].sector + STRIPE_SECTORS) {
                        struct bio *bi2 = r5_next_bio(bi, sh->dev[i].sector);
                        clear_bit(BIO_UPTODATE, &bi->bi_flags);
                        if (--bi->bi_phys_segments == 0) {
                                md_write_end(conf->mddev);
                                bi->bi_next = *return_bi;
                                *return_bi = bi;
                        }
                        bi = bi2;
                }

                /* fail any reads if this device is non-operational and
                 * the data has not reached the cache yet.
                 */
                if (!test_bit(R5_Wantfill, &sh->dev[i].flags) &&
                    (!test_bit(R5_Insync, &sh->dev[i].flags) ||
                      test_bit(R5_ReadError, &sh->dev[i].flags))) {
                        bi = sh->dev[i].toread;
                        sh->dev[i].toread = NULL;
                        if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
                                wake_up(&conf->wait_for_overlap);
                        if (bi) s->to_read--;
                        while (bi && bi->bi_sector <
                               sh->dev[i].sector + STRIPE_SECTORS) {
                                struct bio *nextbi =
                                        r5_next_bio(bi, sh->dev[i].sector);
                                clear_bit(BIO_UPTODATE, &bi->bi_flags);
                                if (--bi->bi_phys_segments == 0) {
                                        bi->bi_next = *return_bi;
                                        *return_bi = bi;
                                }
                                bi = nextbi;
                        }
                }
                spin_unlock_irq(&conf->device_lock);
                if (bitmap_end)
                        bitmap_endwrite(conf->mddev->bitmap, sh->sector,
                                        STRIPE_SECTORS, 0, 0);
        }

        if (test_and_clear_bit(STRIPE_FULL_WRITE, &sh->state))
                if (atomic_dec_and_test(&conf->pending_full_writes))
                        md_wakeup_thread(conf->mddev->thread);
}

/* __handle_issuing_new_read_requests5 - returns 0 if there are no more disks
 * to process
 */
static int __handle_issuing_new_read_requests5(struct stripe_head *sh,
                        struct stripe_head_state *s, int disk_idx, int disks)
{
        struct r5dev *dev = &sh->dev[disk_idx];
        struct r5dev *failed_dev = &sh->dev[s->failed_num];

        /* don't schedule compute operations or reads on the parity block while
         * a check is in flight
         */
        if ((disk_idx == sh->pd_idx) &&
             test_bit(STRIPE_OP_CHECK, &sh->ops.pending))
                return ~0;

        /* is the data in this block needed, and can we get it? */
        if (!test_bit(R5_LOCKED, &dev->flags) &&
            !test_bit(R5_UPTODATE, &dev->flags) && (dev->toread ||
            (dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags)) ||
             s->syncing || s->expanding || (s->failed &&
             (failed_dev->toread || (failed_dev->towrite &&
             !test_bit(R5_OVERWRITE, &failed_dev->flags)
             ))))) {
                /* 1/ We would like to get this block, possibly by computing it,
                 * but we might not be able to.
                 *
                 * 2/ Since parity check operations potentially make the parity
                 * block !uptodate it will need to be refreshed before any
                 * compute operations on data disks are scheduled.
                 *

                 * 3/ We hold off parity block re-reads until check operations
                 * have quiesced.
                 */
                if ((s->uptodate == disks - 1) &&
                    (s->failed && disk_idx == s->failed_num) &&
                    !test_bit(STRIPE_OP_CHECK, &sh->ops.pending)) {
                        set_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending);
                        set_bit(R5_Wantcompute, &dev->flags);
                        sh->ops.target = disk_idx;
                        s->req_compute = 1;
                        sh->ops.count++;
                        /* Careful: from this point on 'uptodate' is in the eye
                         * of raid5_run_ops which services 'compute' operations
                         * before writes. R5_Wantcompute flags a block that will
                         * be R5_UPTODATE by the time it is needed for a
                         * subsequent operation.
                         */
                        s->uptodate++;
                        return 0; /* uptodate + compute == disks */
                } else if (test_bit(R5_Insync, &dev->flags)) {
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantread, &dev->flags);
                        if (!test_and_set_bit(STRIPE_OP_IO, &sh->ops.pending))
                                sh->ops.count++;
                        s->locked++;
                        pr_debug("Reading block %d (sync=%d)\n", disk_idx,
                                s->syncing);
                }
        }

        return ~0;
}

static void handle_issuing_new_read_requests5(struct stripe_head *sh,
                        struct stripe_head_state *s, int disks)
{
        int i;

        /* Clear completed compute operations.  Parity recovery
         * (STRIPE_OP_MOD_REPAIR_PD) implies a write-back which is handled
         * later on in this routine
         */
        if (test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.complete) &&
                !test_bit(STRIPE_OP_MOD_REPAIR_PD, &sh->ops.pending)) {
                clear_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.complete);
                clear_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.ack);
                clear_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending);
        }

        /* look for blocks to read/compute, skip this if a compute
         * is already in flight, or if the stripe contents are in the
         * midst of changing due to a write
         */
        if (!test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending) &&
                !test_bit(STRIPE_OP_PREXOR, &sh->ops.pending) &&
                !test_bit(STRIPE_OP_POSTXOR, &sh->ops.pending)) {
                for (i = disks; i--; )
                        if (__handle_issuing_new_read_requests5(
                                sh, s, i, disks) == 0)
                                break;
        }
        set_bit(STRIPE_HANDLE, &sh->state);
}

static void handle_issuing_new_read_requests6(struct stripe_head *sh,
                        struct stripe_head_state *s, struct r6_state *r6s,
                        int disks)
{
        int i;
        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                if (!test_bit(R5_LOCKED, &dev->flags) &&
                    !test_bit(R5_UPTODATE, &dev->flags) &&
                    (dev->toread || (dev->towrite &&
                     !test_bit(R5_OVERWRITE, &dev->flags)) ||
                     s->syncing || s->expanding ||
                     (s->failed >= 1 &&
                      (sh->dev[r6s->failed_num[0]].toread ||
                       s->to_write)) ||
                     (s->failed >= 2 &&
                      (sh->dev[r6s->failed_num[1]].toread ||
                       s->to_write)))) {
                        /* we would like to get this block, possibly
                         * by computing it, but we might not be able to
                         */
                        if ((s->uptodate == disks - 1) &&
                            (s->failed && (i == r6s->failed_num[0] ||
                                           i == r6s->failed_num[1]))) {
                                pr_debug("Computing stripe %llu block %d\n",
                                       (unsigned long long)sh->sector, i);
                                compute_block_1(sh, i, 0);
                                s->uptodate++;
                        } else if ( s->uptodate == disks-2 && s->failed >= 2 ) {
                                /* Computing 2-failure is *very* expensive; only
                                 * do it if failed >= 2
                                 */
                                int other;
                                for (other = disks; other--; ) {
                                        if (other == i)
                                                continue;
                                        if (!test_bit(R5_UPTODATE,
                                              &sh->dev[other].flags))
                                                break;
                                }
                                BUG_ON(other < 0);
                                pr_debug("Computing stripe %llu blocks %d,%d\n",
                                       (unsigned long long)sh->sector,
                                       i, other);
                                compute_block_2(sh, i, other);
                                s->uptodate += 2;
                        } else if (test_bit(R5_Insync, &dev->flags)) {
                                set_bit(R5_LOCKED, &dev->flags);
                                set_bit(R5_Wantread, &dev->flags);
                                s->locked++;
                                pr_debug("Reading block %d (sync=%d)\n",
                                        i, s->syncing);
                        }
                }
        }
        set_bit(STRIPE_HANDLE, &sh->state);
}


/* handle_completed_write_requests
 * any written block on an uptodate or failed drive can be returned.
 * Note that if we 'wrote' to a failed drive, it will be UPTODATE, but
 * never LOCKED, so we don't need to test 'failed' directly.
 */
static void handle_completed_write_requests(raid5_conf_t *conf,
        struct stripe_head *sh, int disks, struct bio **return_bi)
{
        int i;
        struct r5dev *dev;

        for (i = disks; i--; )
                if (sh->dev[i].written) {
                        dev = &sh->dev[i];
                        if (!test_bit(R5_LOCKED, &dev->flags) &&
                                test_bit(R5_UPTODATE, &dev->flags)) {
                                /* We can return any write requests */
                                struct bio *wbi, *wbi2;
                                int bitmap_end = 0;
                                pr_debug("Return write for disc %d\n", i);
                                spin_lock_irq(&conf->device_lock);
                                wbi = dev->written;
                                dev->written = NULL;
                                while (wbi && wbi->bi_sector <
                                        dev->sector + STRIPE_SECTORS) {
                                        wbi2 = r5_next_bio(wbi, dev->sector);
                                        if (--wbi->bi_phys_segments == 0) {
                                                md_write_end(conf->mddev);
                                                wbi->bi_next = *return_bi;
                                                *return_bi = wbi;
                                        }
                                        wbi = wbi2;
                                }
                                if (dev->towrite == NULL)
                                        bitmap_end = 1;
                                spin_unlock_irq(&conf->device_lock);
                                if (bitmap_end)
                                        bitmap_endwrite(conf->mddev->bitmap,
                                                        sh->sector,
                                                        STRIPE_SECTORS,
                                         !test_bit(STRIPE_DEGRADED, &sh->state),
                                                        0);
                        }
                }

        if (test_and_clear_bit(STRIPE_FULL_WRITE, &sh->state))
                if (atomic_dec_and_test(&conf->pending_full_writes))
                        md_wakeup_thread(conf->mddev->thread);
}

static void handle_issuing_new_write_requests5(raid5_conf_t *conf,
                struct stripe_head *sh, struct stripe_head_state *s, int disks)
{
        int rmw = 0, rcw = 0, i;
        for (i = disks; i--; ) {
                /* would I have to read this buffer for read_modify_write */
                struct r5dev *dev = &sh->dev[i];
                if ((dev->towrite || i == sh->pd_idx) &&
                    !test_bit(R5_LOCKED, &dev->flags) &&
                    !(test_bit(R5_UPTODATE, &dev->flags) ||
                      test_bit(R5_Wantcompute, &dev->flags))) {
                        if (test_bit(R5_Insync, &dev->flags))
                                rmw++;
                        else
                                rmw += 2*disks;  /* cannot read it */
                }
                /* Would I have to read this buffer for reconstruct_write */
                if (!test_bit(R5_OVERWRITE, &dev->flags) && i != sh->pd_idx &&
                    !test_bit(R5_LOCKED, &dev->flags) &&
                    !(test_bit(R5_UPTODATE, &dev->flags) ||
                    test_bit(R5_Wantcompute, &dev->flags))) {
                        if (test_bit(R5_Insync, &dev->flags)) rcw++;
                        else
                                rcw += 2*disks;
                }
        }
        pr_debug("for sector %llu, rmw=%d rcw=%d\n",
                (unsigned long long)sh->sector, rmw, rcw);
        set_bit(STRIPE_HANDLE, &sh->state);
        if (rmw < rcw && rmw > 0)
                /* prefer read-modify-write, but need to get some data */
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if ((dev->towrite || i == sh->pd_idx) &&
                            !test_bit(R5_LOCKED, &dev->flags) &&
                            !(test_bit(R5_UPTODATE, &dev->flags) ||
                            test_bit(R5_Wantcompute, &dev->flags)) &&
                            test_bit(R5_Insync, &dev->flags)) {
                                if (
                                  test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                                        pr_debug("Read_old block "
                                                "%d for r-m-w\n", i);
                                        set_bit(R5_LOCKED, &dev->flags);
                                        set_bit(R5_Wantread, &dev->flags);
                                        if (!test_and_set_bit(
                                                STRIPE_OP_IO, &sh->ops.pending))
                                                sh->ops.count++;
                                        s->locked++;
                                } else {
                                        set_bit(STRIPE_DELAYED, &sh->state);
                                        set_bit(STRIPE_HANDLE, &sh->state);
                                }
                        }
                }
        if (rcw <= rmw && rcw > 0)
                /* want reconstruct write, but need to get some data */
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (!test_bit(R5_OVERWRITE, &dev->flags) &&
                            i != sh->pd_idx &&
                            !test_bit(R5_LOCKED, &dev->flags) &&
                            !(test_bit(R5_UPTODATE, &dev->flags) ||
                            test_bit(R5_Wantcompute, &dev->flags)) &&
                            test_bit(R5_Insync, &dev->flags)) {
                                if (
                                  test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                                        pr_debug("Read_old block "
                                                "%d for Reconstruct\n", i);
                                        set_bit(R5_LOCKED, &dev->flags);
                                        set_bit(R5_Wantread, &dev->flags);
                                        if (!test_and_set_bit(
                                                STRIPE_OP_IO, &sh->ops.pending))
                                                sh->ops.count++;
                                        s->locked++;
                                } else {
                                        set_bit(STRIPE_DELAYED, &sh->state);
                                        set_bit(STRIPE_HANDLE, &sh->state);
                                }
                        }
                }
        /* now if nothing is locked, and if we have enough data,
         * we can start a write request
         */
        /* since handle_stripe can be called at any time we need to handle the
         * case where a compute block operation has been submitted and then a
         * subsequent call wants to start a write request.  raid5_run_ops only
         * handles the case where compute block and postxor are requested
         * simultaneously.  If this is not the case then new writes need to be
         * held off until the compute completes.
         */
        if ((s->req_compute ||
            !test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending)) &&
                (s->locked == 0 && (rcw == 0 || rmw == 0) &&
                !test_bit(STRIPE_BIT_DELAY, &sh->state)))
                s->locked += handle_write_operations5(sh, rcw == 0, 0);
}

static void handle_issuing_new_write_requests6(raid5_conf_t *conf,
                struct stripe_head *sh, struct stripe_head_state *s,
                struct r6_state *r6s, int disks)
{
        int rcw = 0, must_compute = 0, pd_idx = sh->pd_idx, i;
        int qd_idx = r6s->qd_idx;
        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                /* Would I have to read this buffer for reconstruct_write */
                if (!test_bit(R5_OVERWRITE, &dev->flags)
                    && i != pd_idx && i != qd_idx
                    && (!test_bit(R5_LOCKED, &dev->flags)
                            ) &&
                    !test_bit(R5_UPTODATE, &dev->flags)) {
                        if (test_bit(R5_Insync, &dev->flags)) rcw++;
                        else {
                                pr_debug("raid6: must_compute: "
                                        "disk %d flags=%#lx\n", i, dev->flags);
                                must_compute++;
                        }
                }
        }
        pr_debug("for sector %llu, rcw=%d, must_compute=%d\n",
               (unsigned long long)sh->sector, rcw, must_compute);
        set_bit(STRIPE_HANDLE, &sh->state);

        if (rcw > 0)
                /* want reconstruct write, but need to get some data */
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (!test_bit(R5_OVERWRITE, &dev->flags)
                            && !(s->failed == 0 && (i == pd_idx || i == qd_idx))
                            && !test_bit(R5_LOCKED, &dev->flags) &&
                            !test_bit(R5_UPTODATE, &dev->flags) &&
                            test_bit(R5_Insync, &dev->flags)) {
                                if (
                                  test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                                        pr_debug("Read_old stripe %llu "
                                                "block %d for Reconstruct\n",
                                             (unsigned long long)sh->sector, i);
                                        set_bit(R5_LOCKED, &dev->flags);
                                        set_bit(R5_Wantread, &dev->flags);
                                        s->locked++;
                                } else {
                                        pr_debug("Request delayed stripe %llu "
                                                "block %d for Reconstruct\n",
                                             (unsigned long long)sh->sector, i);
                                        set_bit(STRIPE_DELAYED, &sh->state);
                                        set_bit(STRIPE_HANDLE, &sh->state);
                                }
                        }
                }
        /* now if nothing is locked, and if we have enough data, we can start a
         * write request
         */
        if (s->locked == 0 && rcw == 0 &&
            !test_bit(STRIPE_BIT_DELAY, &sh->state)) {
                if (must_compute > 0) {
                        /* We have failed blocks and need to compute them */
                        switch (s->failed) {
                        case 0:
                                BUG();
                        case 1:
                                compute_block_1(sh, r6s->failed_num[0], 0);
                                break;
                        case 2:
                                compute_block_2(sh, r6s->failed_num[0],
                                                r6s->failed_num[1]);
                                break;
                        default: /* This request should have been failed? */
                                BUG();
                        }
                }

                pr_debug("Computing parity for stripe %llu\n",
                        (unsigned long long)sh->sector);
                compute_parity6(sh, RECONSTRUCT_WRITE);
                /* now every locked buffer is ready to be written */
                for (i = disks; i--; )
                        if (test_bit(R5_LOCKED, &sh->dev[i].flags)) {
                                pr_debug("Writing stripe %llu block %d\n",
                                       (unsigned long long)sh->sector, i);
                                s->locked++;
                                set_bit(R5_Wantwrite, &sh->dev[i].flags);
                        }
                if (s->locked == disks)
                        if (!test_and_set_bit(STRIPE_FULL_WRITE, &sh->state))
                                atomic_inc(&conf->pending_full_writes);
                /* after a RECONSTRUCT_WRITE, the stripe MUST be in-sync */
                set_bit(STRIPE_INSYNC, &sh->state);

                if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                        atomic_dec(&conf->preread_active_stripes);
                        if (atomic_read(&conf->preread_active_stripes) <
                            IO_THRESHOLD)
                                md_wakeup_thread(conf->mddev->thread);
                }
        }
}

static void handle_parity_checks5(raid5_conf_t *conf, struct stripe_head *sh,
                                struct stripe_head_state *s, int disks)
{
        int canceled_check = 0;

        set_bit(STRIPE_HANDLE, &sh->state);

        /* complete a check operation */
        if (test_and_clear_bit(STRIPE_OP_CHECK, &sh->ops.complete)) {
                clear_bit(STRIPE_OP_CHECK, &sh->ops.ack);
                clear_bit(STRIPE_OP_CHECK, &sh->ops.pending);
                if (s->failed == 0) {
                        if (sh->ops.zero_sum_result == 0)
                                /* parity is correct (on disc,
                                 * not in buffer any more)
                                 */
                                set_bit(STRIPE_INSYNC, &sh->state);
                        else {
                                conf->mddev->resync_mismatches +=
                                        STRIPE_SECTORS;
                                if (test_bit(
                                     MD_RECOVERY_CHECK, &conf->mddev->recovery))
                                        /* don't try to repair!! */
                                        set_bit(STRIPE_INSYNC, &sh->state);
                                else {
                                        set_bit(STRIPE_OP_COMPUTE_BLK,
                                                &sh->ops.pending);
                                        set_bit(STRIPE_OP_MOD_REPAIR_PD,
                                                &sh->ops.pending);
                                        set_bit(R5_Wantcompute,
                                                &sh->dev[sh->pd_idx].flags);
                                        sh->ops.target = sh->pd_idx;
                                        sh->ops.count++;
                                        s->uptodate++;
                                }
                        }
                } else
                        canceled_check = 1; /* STRIPE_INSYNC is not set */
        }

        /* start a new check operation if there are no failures, the stripe is
         * not insync, and a repair is not in flight
         */
        if (s->failed == 0 &&
            !test_bit(STRIPE_INSYNC, &sh->state) &&
            !test_bit(STRIPE_OP_MOD_REPAIR_PD, &sh->ops.pending)) {
                if (!test_and_set_bit(STRIPE_OP_CHECK, &sh->ops.pending)) {
                        BUG_ON(s->uptodate != disks);
                        clear_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags);
                        sh->ops.count++;
                        s->uptodate--;
                }
        }

        /* check if we can clear a parity disk reconstruct */
        if (test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.complete) &&
            test_bit(STRIPE_OP_MOD_REPAIR_PD, &sh->ops.pending)) {

                clear_bit(STRIPE_OP_MOD_REPAIR_PD, &sh->ops.pending);
                clear_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.complete);
                clear_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.ack);
                clear_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending);
        }


        /* Wait for check parity and compute block operations to complete
         * before write-back.  If a failure occurred while the check operation
         * was in flight we need to cycle this stripe through handle_stripe
         * since the parity block may not be uptodate
         */
        if (!canceled_check && !test_bit(STRIPE_INSYNC, &sh->state) &&
            !test_bit(STRIPE_OP_CHECK, &sh->ops.pending) &&
            !test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending)) {
                struct r5dev *dev;
                /* either failed parity check, or recovery is happening */
                if (s->failed == 0)
                        s->failed_num = sh->pd_idx;
                dev = &sh->dev[s->failed_num];
                BUG_ON(!test_bit(R5_UPTODATE, &dev->flags));
                BUG_ON(s->uptodate != disks);

                set_bit(R5_LOCKED, &dev->flags);
                set_bit(R5_Wantwrite, &dev->flags);
                if (!test_and_set_bit(STRIPE_OP_IO, &sh->ops.pending))
                        sh->ops.count++;

                clear_bit(STRIPE_DEGRADED, &sh->state);
                s->locked++;
                set_bit(STRIPE_INSYNC, &sh->state);
        }
}


static void handle_parity_checks6(raid5_conf_t *conf, struct stripe_head *sh,
                                struct stripe_head_state *s,
                                struct r6_state *r6s, struct page *tmp_page,
                                int disks)
{
        int update_p = 0, update_q = 0;
        struct r5dev *dev;
        int pd_idx = sh->pd_idx;
        int qd_idx = r6s->qd_idx;

        set_bit(STRIPE_HANDLE, &sh->state);

        BUG_ON(s->failed > 2);
        BUG_ON(s->uptodate < disks);
        /* Want to check and possibly repair P and Q.
         * However there could be one 'failed' device, in which
         * case we can only check one of them, possibly using the
         * other to generate missing data
         */

        /* If !tmp_page, we cannot do the calculations,
         * but as we have set STRIPE_HANDLE, we will soon be called
         * by stripe_handle with a tmp_page - just wait until then.
         */
        if (tmp_page) {
                if (s->failed == r6s->q_failed) {
                        /* The only possible failed device holds 'Q', so it
                         * makes sense to check P (If anything else were failed,
                         * we would have used P to recreate it).
                         */
                        compute_block_1(sh, pd_idx, 1);
                        if (!page_is_zero(sh->dev[pd_idx].page)) {
                                compute_block_1(sh, pd_idx, 0);
                                update_p = 1;
                        }
                }
                if (!r6s->q_failed && s->failed < 2) {
                        /* q is not failed, and we didn't use it to generate
                         * anything, so it makes sense to check it
                         */
                        memcpy(page_address(tmp_page),
                               page_address(sh->dev[qd_idx].page),
                               STRIPE_SIZE);
                        compute_parity6(sh, UPDATE_PARITY);
                        if (memcmp(page_address(tmp_page),
                                   page_address(sh->dev[qd_idx].page),
                                   STRIPE_SIZE) != 0) {
                                clear_bit(STRIPE_INSYNC, &sh->state);
                                update_q = 1;
                        }
                }
                if (update_p || update_q) {
                        conf->mddev->resync_mismatches += STRIPE_SECTORS;
                        if (test_bit(MD_RECOVERY_CHECK, &conf->mddev->recovery))
                                /* don't try to repair!! */
                                update_p = update_q = 0;
                }

                /* now write out any block on a failed drive,
                 * or P or Q if they need it
                 */

                if (s->failed == 2) {
                        dev = &sh->dev[r6s->failed_num[1]];
                        s->locked++;
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantwrite, &dev->flags);
                }
                if (s->failed >= 1) {
                        dev = &sh->dev[r6s->failed_num[0]];
                        s->locked++;
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantwrite, &dev->flags);
                }

                if (update_p) {
                        dev = &sh->dev[pd_idx];
                        s->locked++;
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantwrite, &dev->flags);
                }
                if (update_q) {
                        dev = &sh->dev[qd_idx];
                        s->locked++;
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantwrite, &dev->flags);
                }
                clear_bit(STRIPE_DEGRADED, &sh->state);

                set_bit(STRIPE_INSYNC, &sh->state);
        }
}

static void handle_stripe_expansion(raid5_conf_t *conf, struct stripe_head *sh,
                                struct r6_state *r6s)
{
        int i;

        /* We have read all the blocks in this stripe and now we need to
         * copy some of them into a target stripe for expand.
         */
        struct dma_async_tx_descriptor *tx = NULL;
        clear_bit(STRIPE_EXPAND_SOURCE, &sh->state);
        for (i = 0; i < sh->disks; i++)
                if (i != sh->pd_idx && (!r6s || i != r6s->qd_idx)) {
                        int dd_idx, pd_idx, j;
                        struct stripe_head *sh2;

                        sector_t bn = compute_blocknr(sh, i);
                        sector_t s = raid5_compute_sector(bn, conf->raid_disks,
                                                conf->raid_disks -
                                                conf->max_degraded, &dd_idx,
                                                &pd_idx, conf);
                        sh2 = get_active_stripe(conf, s, conf->raid_disks,
                                                pd_idx, 1);
                        if (sh2 == NULL)
                                /* so far only the early blocks of this stripe
                                 * have been requested.  When later blocks
                                 * get requested, we will try again
                                 */
                                continue;
                        if (!test_bit(STRIPE_EXPANDING, &sh2->state) ||
                           test_bit(R5_Expanded, &sh2->dev[dd_idx].flags)) {
                                /* must have already done this block */
                                release_stripe(sh2);
                                continue;
                        }

                        /* place all the copies on one channel */
                        tx = async_memcpy(sh2->dev[dd_idx].page,
                                sh->dev[i].page, 0, 0, STRIPE_SIZE,
                                ASYNC_TX_DEP_ACK, tx, NULL, NULL);

                        set_bit(R5_Expanded, &sh2->dev[dd_idx].flags);
                        set_bit(R5_UPTODATE, &sh2->dev[dd_idx].flags);
                        for (j = 0; j < conf->raid_disks; j++)
                                if (j != sh2->pd_idx &&
                                    (!r6s || j != raid6_next_disk(sh2->pd_idx,
                                                                 sh2->disks)) &&
                                    !test_bit(R5_Expanded, &sh2->dev[j].flags))
                                        break;
                        if (j == conf->raid_disks) {
                                set_bit(STRIPE_EXPAND_READY, &sh2->state);
                                set_bit(STRIPE_HANDLE, &sh2->state);
                        }
                        release_stripe(sh2);

                }
        /* done submitting copies, wait for them to complete */
        if (tx) {
                async_tx_ack(tx);
                dma_wait_for_async_tx(tx);
        }
}


/*
 * handle_stripe - do things to a stripe.
 *
 * We lock the stripe and then examine the state of various bits
 * to see what needs to be done.
 * Possible results:
 *    return some read request which now have data
 *    return some write requests which are safely on disc
 *    schedule a read on some buffers
 *    schedule a write of some buffers
 *    return confirmation of parity correctness
 *
 * buffers are taken off read_list or write_list, and bh_cache buffers
 * get BH_Lock set before the stripe lock is released.
 *
 */

static void handle_stripe5(struct stripe_head *sh)
{
        raid5_conf_t *conf = sh->raid_conf;
        int disks = sh->disks, i;
        struct bio *return_bi = NULL;
        struct stripe_head_state s;
        struct r5dev *dev;
        unsigned long pending = 0;
        mdk_rdev_t *blocked_rdev = NULL;
        int prexor;

        memset(&s, 0, sizeof(s));
        pr_debug("handling stripe %llu, state=%#lx cnt=%d, pd_idx=%d "
                "ops=%lx:%lx:%lx\n", (unsigned long long)sh->sector, sh->state,
                atomic_read(&sh->count), sh->pd_idx,
                sh->ops.pending, sh->ops.ack, sh->ops.complete);

        spin_lock(&sh->lock);
        clear_bit(STRIPE_HANDLE, &sh->state);
        clear_bit(STRIPE_DELAYED, &sh->state);

        s.syncing = test_bit(STRIPE_SYNCING, &sh->state);
        s.expanding = test_bit(STRIPE_EXPAND_SOURCE, &sh->state);
        s.expanded = test_bit(STRIPE_EXPAND_READY, &sh->state);
        /* Now to look around and see what can be done */

        /* clean-up completed biofill operations */
        if (test_bit(STRIPE_OP_BIOFILL, &sh->ops.complete)) {
                clear_bit(STRIPE_OP_BIOFILL, &sh->ops.pending);
                clear_bit(STRIPE_OP_BIOFILL, &sh->ops.ack);
                clear_bit(STRIPE_OP_BIOFILL, &sh->ops.complete);
        }

        rcu_read_lock();
        for (i=disks; i--; ) {
                mdk_rdev_t *rdev;
                struct r5dev *dev = &sh->dev[i];
                clear_bit(R5_Insync, &dev->flags);

                pr_debug("check %d: state 0x%lx toread %p read %p write %p "
                        "written %p\n", i, dev->flags, dev->toread, dev->read,
                        dev->towrite, dev->written);

                /* maybe we can request a biofill operation
                 *
                 * new wantfill requests are only permitted while
                 * STRIPE_OP_BIOFILL is clear
                 */
                if (test_bit(R5_UPTODATE, &dev->flags) && dev->toread &&
                        !test_bit(STRIPE_OP_BIOFILL, &sh->ops.pending))
                        set_bit(R5_Wantfill, &dev->flags);

                /* now count some things */
                if (test_bit(R5_LOCKED, &dev->flags)) s.locked++;
                if (test_bit(R5_UPTODATE, &dev->flags)) s.uptodate++;
                if (test_bit(R5_Wantcompute, &dev->flags)) s.compute++;

                if (test_bit(R5_Wantfill, &dev->flags))
                        s.to_fill++;
                else if (dev->toread)
                        s.to_read++;
                if (dev->towrite) {
                        s.to_write++;
                        if (!test_bit(R5_OVERWRITE, &dev->flags))
                                s.non_overwrite++;
                }
                if (dev->written)
                        s.written++;
                rdev = rcu_dereference(conf->disks[i].rdev);
                if (rdev && unlikely(test_bit(Blocked, &rdev->flags))) {
                        blocked_rdev = rdev;
                        atomic_inc(&rdev->nr_pending);
                        break;
                }
                if (!rdev || !test_bit(In_sync, &rdev->flags)) {
                        /* The ReadError flag will just be confusing now */
                        clear_bit(R5_ReadError, &dev->flags);
                        clear_bit(R5_ReWrite, &dev->flags);
                }
                if (!rdev || !test_bit(In_sync, &rdev->flags)
                    || test_bit(R5_ReadError, &dev->flags)) {
                        s.failed++;
                        s.failed_num = i;
                } else
                        set_bit(R5_Insync, &dev->flags);
        }
        rcu_read_unlock();

        if (unlikely(blocked_rdev)) {
                set_bit(STRIPE_HANDLE, &sh->state);
                goto unlock;
        }

        if (s.to_fill && !test_and_set_bit(STRIPE_OP_BIOFILL, &sh->ops.pending))
                sh->ops.count++;

        pr_debug("locked=%d uptodate=%d to_read=%d"
                " to_write=%d failed=%d failed_num=%d\n",
                s.locked, s.uptodate, s.to_read, s.to_write,
                s.failed, s.failed_num);
        /* check if the array has lost two devices and, if so, some requests might
         * need to be failed
         */
        if (s.failed > 1 && s.to_read+s.to_write+s.written)
                handle_requests_to_failed_array(conf, sh, &s, disks,
                                                &return_bi);
        if (s.failed > 1 && s.syncing) {
                md_done_sync(conf->mddev, STRIPE_SECTORS,0);
                clear_bit(STRIPE_SYNCING, &sh->state);
                s.syncing = 0;
        }

        /* might be able to return some write requests if the parity block
         * is safe, or on a failed drive
         */
        dev = &sh->dev[sh->pd_idx];
        if ( s.written &&
             ((test_bit(R5_Insync, &dev->flags) &&
               !test_bit(R5_LOCKED, &dev->flags) &&
               test_bit(R5_UPTODATE, &dev->flags)) ||
               (s.failed == 1 && s.failed_num == sh->pd_idx)))
                handle_completed_write_requests(conf, sh, disks, &return_bi);

        /* Now we might consider reading some blocks, either to check/generate
         * parity, or to satisfy requests
         * or to load a block that is being partially written.
         */
        if (s.to_read || s.non_overwrite ||
            (s.syncing && (s.uptodate + s.compute < disks)) || s.expanding ||
            test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending))
                handle_issuing_new_read_requests5(sh, &s, disks);

        /* Now we check to see if any write operations have recently
         * completed
         */

        /* leave prexor set until postxor is done, allows us to distinguish
         * a rmw from a rcw during biodrain
         */
        prexor = 0;
        if (test_bit(STRIPE_OP_PREXOR, &sh->ops.complete) &&
                test_bit(STRIPE_OP_POSTXOR, &sh->ops.complete)) {

                prexor = 1;
                clear_bit(STRIPE_OP_PREXOR, &sh->ops.complete);
                clear_bit(STRIPE_OP_PREXOR, &sh->ops.ack);
                clear_bit(STRIPE_OP_PREXOR, &sh->ops.pending);

                for (i = disks; i--; )
                        clear_bit(R5_Wantprexor, &sh->dev[i].flags);
        }

        /* if only POSTXOR is set then this is an 'expand' postxor */
        if (test_bit(STRIPE_OP_BIODRAIN, &sh->ops.complete) &&
                test_bit(STRIPE_OP_POSTXOR, &sh->ops.complete)) {

                clear_bit(STRIPE_OP_BIODRAIN, &sh->ops.complete);
                clear_bit(STRIPE_OP_BIODRAIN, &sh->ops.ack);
                clear_bit(STRIPE_OP_BIODRAIN, &sh->ops.pending);

                clear_bit(STRIPE_OP_POSTXOR, &sh->ops.complete);
                clear_bit(STRIPE_OP_POSTXOR, &sh->ops.ack);
                clear_bit(STRIPE_OP_POSTXOR, &sh->ops.pending);

                /* All the 'written' buffers and the parity block are ready to
                 * be written back to disk
                 */
                BUG_ON(!test_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags));
                for (i = disks; i--; ) {
                        dev = &sh->dev[i];
                        if (test_bit(R5_LOCKED, &dev->flags) &&
                                (i == sh->pd_idx || dev->written)) {
                                pr_debug("Writing block %d\n", i);
                                set_bit(R5_Wantwrite, &dev->flags);
                                if (!test_and_set_bit(
                                    STRIPE_OP_IO, &sh->ops.pending))
                                        sh->ops.count++;
                                if (prexor)
                                        continue;
                                if (!test_bit(R5_Insync, &dev->flags) ||
                                    (i == sh->pd_idx && s.failed == 0))
                                        set_bit(STRIPE_INSYNC, &sh->state);
                        }
                }
                if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                        atomic_dec(&conf->preread_active_stripes);
                        if (atomic_read(&conf->preread_active_stripes) <
                                IO_THRESHOLD)
                                md_wakeup_thread(conf->mddev->thread);
                }
        }

        /* Now to consider new write requests and what else, if anything
         * should be read.  We do not handle new writes when:
         * 1/ A 'write' operation (copy+xor) is already in flight.
         * 2/ A 'check' operation is in flight, as it may clobber the parity
         *    block.
         */
        if (s.to_write && !test_bit(STRIPE_OP_POSTXOR, &sh->ops.pending) &&
                          !test_bit(STRIPE_OP_CHECK, &sh->ops.pending))
                handle_issuing_new_write_requests5(conf, sh, &s, disks);

        /* maybe we need to check and possibly fix the parity for this stripe
         * Any reads will already have been scheduled, so we just see if enough
         * data is available.  The parity check is held off while parity
         * dependent operations are in flight.
         */
        if ((s.syncing && s.locked == 0 &&
             !test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending) &&
             !test_bit(STRIPE_INSYNC, &sh->state)) ||
              test_bit(STRIPE_OP_CHECK, &sh->ops.pending) ||
              test_bit(STRIPE_OP_MOD_REPAIR_PD, &sh->ops.pending))
                handle_parity_checks5(conf, sh, &s, disks);

        if (s.syncing && s.locked == 0 && test_bit(STRIPE_INSYNC, &sh->state)) {
                md_done_sync(conf->mddev, STRIPE_SECTORS,1);
                clear_bit(STRIPE_SYNCING, &sh->state);
        }

        /* If the failed drive is just a ReadError, then we might need to progress
         * the repair/check process
         */
        if (s.failed == 1 && !conf->mddev->ro &&
            test_bit(R5_ReadError, &sh->dev[s.failed_num].flags)
            && !test_bit(R5_LOCKED, &sh->dev[s.failed_num].flags)
            && test_bit(R5_UPTODATE, &sh->dev[s.failed_num].flags)
                ) {
                dev = &sh->dev[s.failed_num];
                if (!test_bit(R5_ReWrite, &dev->flags)) {
                        set_bit(R5_Wantwrite, &dev->flags);
                        if (!test_and_set_bit(STRIPE_OP_IO, &sh->ops.pending))
                                sh->ops.count++;
                        set_bit(R5_ReWrite, &dev->flags);
                        set_bit(R5_LOCKED, &dev->flags);
                        s.locked++;
                } else {
                        /* let's read it back */
                        set_bit(R5_Wantread, &dev->flags);
                        if (!test_and_set_bit(STRIPE_OP_IO, &sh->ops.pending))
                                sh->ops.count++;
                        set_bit(R5_LOCKED, &dev->flags);
                        s.locked++;
                }
        }

        /* Finish postxor operations initiated by the expansion
         * process
         */
        if (test_bit(STRIPE_OP_POSTXOR, &sh->ops.complete) &&
                !test_bit(STRIPE_OP_BIODRAIN, &sh->ops.pending)) {

                clear_bit(STRIPE_EXPANDING, &sh->state);

                clear_bit(STRIPE_OP_POSTXOR, &sh->ops.pending);
                clear_bit(STRIPE_OP_POSTXOR, &sh->ops.ack);
                clear_bit(STRIPE_OP_POSTXOR, &sh->ops.complete);

                for (i = conf->raid_disks; i--; ) {
                        set_bit(R5_Wantwrite, &sh->dev[i].flags);
                        set_bit(R5_LOCKED, &dev->flags);
                        s.locked++;
                        if (!test_and_set_bit(STRIPE_OP_IO, &sh->ops.pending))
                                sh->ops.count++;
                }
        }

        if (s.expanded && test_bit(STRIPE_EXPANDING, &sh->state) &&
                !test_bit(STRIPE_OP_POSTXOR, &sh->ops.pending)) {
                /* Need to write out all blocks after computing parity */
                sh->disks = conf->raid_disks;
                sh->pd_idx = stripe_to_pdidx(sh->sector, conf,
                        conf->raid_disks);
                s.locked += handle_write_operations5(sh, 1, 1);
        } else if (s.expanded &&
                   s.locked == 0 &&
                !test_bit(STRIPE_OP_POSTXOR, &sh->ops.pending)) {
                clear_bit(STRIPE_EXPAND_READY, &sh->state);
                atomic_dec(&conf->reshape_stripes);
                wake_up(&conf->wait_for_overlap);
                md_done_sync(conf->mddev, STRIPE_SECTORS, 1);
        }

        if (s.expanding && s.locked == 0 &&
            !test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending))
                handle_stripe_expansion(conf, sh, NULL);

        if (sh->ops.count)
                pending = get_stripe_work(sh);

 unlock:
        spin_unlock(&sh->lock);

        /* wait for this device to become unblocked */
        if (unlikely(blocked_rdev))
                md_wait_for_blocked_rdev(blocked_rdev, conf->mddev);

        if (pending)
                raid5_run_ops(sh, pending);

        return_io(return_bi);

}

static void handle_stripe6(struct stripe_head *sh, struct page *tmp_page)
{
        raid6_conf_t *conf = sh->raid_conf;
        int disks = sh->disks;
        struct bio *return_bi = NULL;
        int i, pd_idx = sh->pd_idx;
        struct stripe_head_state s;
        struct r6_state r6s;
        struct r5dev *dev, *pdev, *qdev;
        mdk_rdev_t *blocked_rdev = NULL;

        r6s.qd_idx = raid6_next_disk(pd_idx, disks);
        pr_debug("handling stripe %llu, state=%#lx cnt=%d, "
                "pd_idx=%d, qd_idx=%d\n",
               (unsigned long long)sh->sector, sh->state,
               atomic_read(&sh->count), pd_idx, r6s.qd_idx);
        memset(&s, 0, sizeof(s));

        spin_lock(&sh->lock);
        clear_bit(STRIPE_HANDLE, &sh->state);
        clear_bit(STRIPE_DELAYED, &sh->state);

        s.syncing = test_bit(STRIPE_SYNCING, &sh->state);
        s.expanding = test_bit(STRIPE_EXPAND_SOURCE, &sh->state);
        s.expanded = test_bit(STRIPE_EXPAND_READY, &sh->state);
        /* Now to look around and see what can be done */

        rcu_read_lock();
        for (i=disks; i--; ) {
                mdk_rdev_t *rdev;
                dev = &sh->dev[i];
                clear_bit(R5_Insync, &dev->flags);

                pr_debug("check %d: state 0x%lx read %p write %p written %p\n",
                        i, dev->flags, dev->toread, dev->towrite, dev->written);
                /* maybe we can reply to a read */
                if (test_bit(R5_UPTODATE, &dev->flags) && dev->toread) {
                        struct bio *rbi, *rbi2;
                        pr_debug("Return read for disc %d\n", i);
                        spin_lock_irq(&conf->device_lock);
                        rbi = dev->toread;
                        dev->toread = NULL;
                        if (test_and_clear_bit(R5_Overlap, &dev->flags))
                                wake_up(&conf->wait_for_overlap);
                        spin_unlock_irq(&conf->device_lock);
                        while (rbi && rbi->bi_sector < dev->sector + STRIPE_SECTORS) {
                                copy_data(0, rbi, dev->page, dev->sector);
                                rbi2 = r5_next_bio(rbi, dev->sector);
                                spin_lock_irq(&conf->device_lock);
                                if (--rbi->bi_phys_segments == 0) {
                                        rbi->bi_next = return_bi;
                                        return_bi = rbi;
                                }
                                spin_unlock_irq(&conf->device_lock);
                                rbi = rbi2;
                        }
                }

                /* now count some things */
                if (test_bit(R5_LOCKED, &dev->flags)) s.locked++;
                if (test_bit(R5_UPTODATE, &dev->flags)) s.uptodate++;