Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 2136 insertions, 0 deletions

diff --git a/drivers/md/raid6main.c b/drivers/md/raid6main.c
new file mode 100644
index 000000000000..7e30ab29691a
--- /dev/null
+++ b/drivers/md/raid6main.c
@@ -0,0 +1,2136 @@
+/*
+ * raid6main.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-6 management functions.  This code is derived from raid5.c.
+ * Last merge from raid5.c bkcvs version 1.79 (kernel 2.6.1).
+ *
+ * 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.
+ */
+
+
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/highmem.h>
+#include <linux/bitops.h>
+#include <asm/atomic.h>
+#include "raid6.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 HASH_PAGES              1
+#define HASH_PAGES_ORDER        0
+#define NR_HASH                 (HASH_PAGES * PAGE_SIZE / sizeof(struct stripe_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 RAID6_DEBUG     0       /* Extremely verbose printk */
+#define RAID6_PARANOIA  1       /* Check spinlocks */
+#define RAID6_DUMPSTATE 0       /* Include stripe cache state in /proc/mdstat */
+#if RAID6_PARANOIA && defined(CONFIG_SMP)
+# define CHECK_DEVLOCK() assert_spin_locked(&conf->device_lock)
+#else
+# define CHECK_DEVLOCK()
+#endif
+
+#define PRINTK(x...) ((void)(RAID6_DEBUG && printk(KERN_DEBUG x)))
+#if RAID6_DEBUG
+#undef inline
+#undef __inline__
+#define inline
+#define __inline__
+#endif
+
+#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 print_raid6_conf (raid6_conf_t *conf);
+
+static inline void __release_stripe(raid6_conf_t *conf, struct stripe_head *sh)
+{
+        if (atomic_dec_and_test(&sh->count)) {
+                if (!list_empty(&sh->lru))
+                        BUG();
+                if (atomic_read(&conf->active_stripes)==0)
+                        BUG();
+                if (test_bit(STRIPE_HANDLE, &sh->state)) {
+                        if (test_bit(STRIPE_DELAYED, &sh->state))
+                                list_add_tail(&sh->lru, &conf->delayed_list);
+                        else
+                                list_add_tail(&sh->lru, &conf->handle_list);
+                        md_wakeup_thread(conf->mddev->thread);
+                } else {
+                        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);
+                        }
+                        list_add_tail(&sh->lru, &conf->inactive_list);
+                        atomic_dec(&conf->active_stripes);
+                        if (!conf->inactive_blocked ||
+                            atomic_read(&conf->active_stripes) < (NR_STRIPES*3/4))
+                                wake_up(&conf->wait_for_stripe);
+                }
+        }
+}
+static void release_stripe(struct stripe_head *sh)
+{
+        raid6_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 void remove_hash(struct stripe_head *sh)
+{
+        PRINTK("remove_hash(), stripe %llu\n", (unsigned long long)sh->sector);
+
+        if (sh->hash_pprev) {
+                if (sh->hash_next)
+                        sh->hash_next->hash_pprev = sh->hash_pprev;
+                *sh->hash_pprev = sh->hash_next;
+                sh->hash_pprev = NULL;
+        }
+}
+
+static __inline__ void insert_hash(raid6_conf_t *conf, struct stripe_head *sh)
+{
+        struct stripe_head **shp = &stripe_hash(conf, sh->sector);
+
+        PRINTK("insert_hash(), stripe %llu\n", (unsigned long long)sh->sector);
+
+        CHECK_DEVLOCK();
+        if ((sh->hash_next = *shp) != NULL)
+                (*shp)->hash_pprev = &sh->hash_next;
+        *shp = sh;
+        sh->hash_pprev = shp;
+}
+
+
+/* find an idle stripe, make sure it is unhashed, and return it. */
+static struct stripe_head *get_free_stripe(raid6_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;
+                page_cache_release(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 raid6_build_block (struct stripe_head *sh, int i);
+
+static inline void init_stripe(struct stripe_head *sh, sector_t sector, int pd_idx)
+{
+        raid6_conf_t *conf = sh->raid_conf;
+        int disks = conf->raid_disks, i;
+
+        if (atomic_read(&sh->count) != 0)
+                BUG();
+        if (test_bit(STRIPE_HANDLE, &sh->state))
+                BUG();
+
+        CHECK_DEVLOCK();
+        PRINTK("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;
+
+        for (i=disks; i--; ) {
+                struct r5dev *dev = &sh->dev[i];
+
+                if (dev->toread || dev->towrite || dev->written ||
+                    test_bit(R5_LOCKED, &dev->flags)) {
+                        PRINTK("sector=%llx i=%d %p %p %p %d\n",
+                               (unsigned long long)sh->sector, i, dev->toread,
+                               dev->towrite, dev->written,
+                               test_bit(R5_LOCKED, &dev->flags));
+                        BUG();
+                }
+                dev->flags = 0;
+                raid6_build_block(sh, i);
+        }
+        insert_hash(conf, sh);
+}
+
+static struct stripe_head *__find_stripe(raid6_conf_t *conf, sector_t sector)
+{
+        struct stripe_head *sh;
+
+        CHECK_DEVLOCK();
+        PRINTK("__find_stripe, sector %llu\n", (unsigned long long)sector);
+        for (sh = stripe_hash(conf, sector); sh; sh = sh->hash_next)
+                if (sh->sector == sector)
+                        return sh;
+        PRINTK("__stripe %llu not in cache\n", (unsigned long long)sector);
+        return NULL;
+}
+
+static void unplug_slaves(mddev_t *mddev);
+
+static struct stripe_head *get_active_stripe(raid6_conf_t *conf, sector_t sector,
+                                             int pd_idx, int noblock)
+{
+        struct stripe_head *sh;
+
+        PRINTK("get_stripe, sector %llu\n", (unsigned long long)sector);
+
+        spin_lock_irq(&conf->device_lock);
+
+        do {
+                sh = __find_stripe(conf, sector);
+                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) < (NR_STRIPES *3/4)
+                                                     || !conf->inactive_blocked),
+                                                    conf->device_lock,
+                                                    unplug_slaves(conf->mddev);
+                                        );
+                                conf->inactive_blocked = 0;
+                        } else
+                                init_stripe(sh, sector, pd_idx);
+                } else {
+                        if (atomic_read(&sh->count)) {
+                                if (!list_empty(&sh->lru))
+                                        BUG();
+                        } else {
+                                if (!test_bit(STRIPE_HANDLE, &sh->state))
+                                        atomic_inc(&conf->active_stripes);
+                                if (list_empty(&sh->lru))
+                                        BUG();
+                                list_del_init(&sh->lru);
+                        }
+                }
+        } while (sh == NULL);
+
+        if (sh)
+                atomic_inc(&sh->count);
+
+        spin_unlock_irq(&conf->device_lock);
+        return sh;
+}
+
+static int grow_stripes(raid6_conf_t *conf, int num)
+{
+        struct stripe_head *sh;
+        kmem_cache_t *sc;
+        int devs = conf->raid_disks;
+
+        sprintf(conf->cache_name, "raid6/%s", mdname(conf->mddev));
+
+        sc = kmem_cache_create(conf->cache_name,
+                               sizeof(struct stripe_head)+(devs-1)*sizeof(struct r5dev),
+                               0, 0, NULL, NULL);
+        if (!sc)
+                return 1;
+        conf->slab_cache = sc;
+        while (num--) {
+                sh = kmem_cache_alloc(sc, GFP_KERNEL);
+                if (!sh)
+                        return 1;
+                memset(sh, 0, sizeof(*sh) + (devs-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(sc, sh);
+                        return 1;
+                }
+                /* 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 0;
+}
+
+static void shrink_stripes(raid6_conf_t *conf)
+{
+        struct stripe_head *sh;
+
+        while (1) {
+                spin_lock_irq(&conf->device_lock);
+                sh = get_free_stripe(conf);
+                spin_unlock_irq(&conf->device_lock);
+                if (!sh)
+                        break;
+                if (atomic_read(&sh->count))
+                        BUG();
+                shrink_buffers(sh, conf->raid_disks);
+                kmem_cache_free(conf->slab_cache, sh);
+                atomic_dec(&conf->active_stripes);
+        }
+        kmem_cache_destroy(conf->slab_cache);
+        conf->slab_cache = NULL;
+}
+
+static int raid6_end_read_request (struct bio * bi, unsigned int bytes_done,
+                                   int error)
+{
+        struct stripe_head *sh = bi->bi_private;
+        raid6_conf_t *conf = sh->raid_conf;
+        int disks = conf->raid_disks, i;
+        int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
+
+        if (bi->bi_size)
+                return 1;
+
+        for (i=0 ; i<disks; i++)
+                if (bi == &sh->dev[i].req)
+                        break;
+
+        PRINTK("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 0;
+        }
+
+        if (uptodate) {
+#if 0
+                struct bio *bio;
+                unsigned long flags;
+                spin_lock_irqsave(&conf->device_lock, flags);
+                /* we can return a buffer if we bypassed the cache or
+                 * if the top buffer is not in highmem.  If there are
+                 * multiple buffers, leave the extra work to
+                 * handle_stripe
+                 */
+                buffer = sh->bh_read[i];
+                if (buffer &&
+                    (!PageHighMem(buffer->b_page)
+                     || buffer->b_page == bh->b_page )
+                        ) {
+                        sh->bh_read[i] = buffer->b_reqnext;
+                        buffer->b_reqnext = NULL;
+                } else
+                        buffer = NULL;
+                spin_unlock_irqrestore(&conf->device_lock, flags);
+                if (sh->bh_page[i]==bh->b_page)
+                        set_buffer_uptodate(bh);
+                if (buffer) {
+                        if (buffer->b_page != bh->b_page)
+                                memcpy(buffer->b_data, bh->b_data, bh->b_size);
+                        buffer->b_end_io(buffer, 1);
+                }
+#else
+                set_bit(R5_UPTODATE, &sh->dev[i].flags);
+#endif
+        } else {
+                md_error(conf->mddev, conf->disks[i].rdev);
+                clear_bit(R5_UPTODATE, &sh->dev[i].flags);
+        }
+        rdev_dec_pending(conf->disks[i].rdev, conf->mddev);
+#if 0
+        /* must restore b_page before unlocking buffer... */
+        if (sh->bh_page[i] != bh->b_page) {
+                bh->b_page = sh->bh_page[i];
+                bh->b_data = page_address(bh->b_page);
+                clear_buffer_uptodate(bh);
+        }
+#endif
+        clear_bit(R5_LOCKED, &sh->dev[i].flags);
+        set_bit(STRIPE_HANDLE, &sh->state);
+        release_stripe(sh);
+        return 0;
+}
+
+static int raid6_end_write_request (struct bio *bi, unsigned int bytes_done,
+                                    int error)
+{
+        struct stripe_head *sh = bi->bi_private;
+        raid6_conf_t *conf = sh->raid_conf;
+        int disks = conf->raid_disks, i;
+        unsigned long flags;
+        int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
+
+        if (bi->bi_size)
+                return 1;
+
+        for (i=0 ; i<disks; i++)
+                if (bi == &sh->dev[i].req)
+                        break;
+
+        PRINTK("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 0;
+        }
+
+        spin_lock_irqsave(&conf->device_lock, flags);
+        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(conf, sh);
+        spin_unlock_irqrestore(&conf->device_lock, flags);
+        return 0;
+}
+
+
+static sector_t compute_blocknr(struct stripe_head *sh, int i);
+
+static void raid6_build_block (struct stripe_head *sh, int i)
+{
+        struct r5dev *dev = &sh->dev[i];
+        int pd_idx = sh->pd_idx;
+        int qd_idx = raid6_next_disk(pd_idx, sh->raid_conf->raid_disks);
+
+        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;
+        if (i != pd_idx && i != qd_idx)
+                dev->sector = compute_blocknr(sh, i);
+}
+
+static void error(mddev_t *mddev, mdk_rdev_t *rdev)
+{
+        char b[BDEVNAME_SIZE];
+        raid6_conf_t *conf = (raid6_conf_t *) mddev->private;
+        PRINTK("raid6: error called\n");
+
+        if (!rdev->faulty) {
+                mddev->sb_dirty = 1;
+                if (rdev->in_sync) {
+                        conf->working_disks--;
+                        mddev->degraded++;
+                        conf->failed_disks++;
+                        rdev->in_sync = 0;
+                        /*
+                         * if recovery was running, make sure it aborts.
+                         */
+                        set_bit(MD_RECOVERY_ERR, &mddev->recovery);
+                }
+                rdev->faulty = 1;
+                printk (KERN_ALERT
+                        "raid6: Disk failure on %s, disabling device."
+                        " Operation continuing on %d devices\n",
+                        bdevname(rdev->bdev,b), conf->working_disks);
+        }
+}
+
+/*
+ * Input: a 'big' sector number,
+ * Output: index of the data and parity disk, and the sector # in them.
+ */
+static sector_t raid6_compute_sector(sector_t r_sector, unsigned int raid_disks,
+                        unsigned int data_disks, unsigned int * dd_idx,
+                        unsigned int * pd_idx, raid6_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;
+        if ( r_sector != chunk_number ) {
+                printk(KERN_CRIT "raid6: ERROR: r_sector = %llu, chunk_number = %lu\n",
+                       (unsigned long long)r_sector, (unsigned long)chunk_number);
+                BUG();
+        }
+
+        /*
+         * 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.
+         */
+
+        /**** 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);
+        }
+
+        PRINTK("raid6: chunk_number = %lu, pd_idx = %u, dd_idx = %u\n",
+               chunk_number, *pd_idx, *dd_idx);
+
+        /*
+         * 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)
+{
+        raid6_conf_t *conf = sh->raid_conf;
+        int raid_disks = conf->raid_disks, data_disks = raid_disks - 2;
+        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;
+        int i0 = i;
+
+        chunk_offset = sector_div(new_sector, sectors_per_chunk);
+        stripe = new_sector;
+        if ( new_sector != stripe ) {
+                printk(KERN_CRIT "raid6: ERROR: new_sector = %llu, stripe = %lu\n",
+                       (unsigned long long)new_sector, (unsigned long)stripe);
+                BUG();
+        }
+
+        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);
+        }
+
+        PRINTK("raid6: compute_blocknr: pd_idx = %u, i0 = %u, i = %u\n", sh->pd_idx, i0, i);
+
+        chunk_number = stripe * data_disks + i;
+        r_sector = (sector_t)chunk_number * sectors_per_chunk + chunk_offset;
+
+        check = raid6_compute_sector (r_sector, raid_disks, data_disks, &dummy1, &dummy2, conf);
+        if (check != sh->sector || dummy1 != dd_idx || dummy2 != sh->pd_idx) {
+                printk(KERN_CRIT "raid6: 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_block(count, STRIPE_SIZE, ptr);     \
+                                count = 1;                              \
+                           }                                            \
+                        } while(0)
+
+/* Compute P and Q syndromes */
+static void compute_parity(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 = conf->raid_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);
+
+        PRINTK("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);
+
+                                if (sh->dev[i].written) BUG();
+                                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)
+{
+        raid6_conf_t *conf = sh->raid_conf;
+        int i, count, disks = conf->raid_disks;
+        void *ptr[MAX_XOR_BLOCKS], *p;
+        int pd_idx = sh->pd_idx;
+        int qd_idx = raid6_next_disk(pd_idx, disks);
+
+        PRINTK("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_parity(sh, UPDATE_PARITY);
+        } else {
+                ptr[0] = page_address(sh->dev[dd_idx].page);
+                memset(ptr[0], 0, STRIPE_SIZE);
+                count = 1;
+                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 != 1)
+                        xor_block(count, STRIPE_SIZE, ptr);
+                set_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)
+{
+        raid6_conf_t *conf = sh->raid_conf;
+        int i, count, disks = conf->raid_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; }
+
+        PRINTK("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_parity(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);
+                        compute_parity(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);
+        }
+}
+
+
+/*
+ * 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;
+        raid6_conf_t *conf = sh->raid_conf;
+
+        PRINTK("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;
+        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;
+
+        if (*bip && bi->bi_next && (*bip) != bi->bi_next)
+                BUG();
+        if (*bip)
+                bi->bi_next = *bip;
+        *bip = bi;
+        bi->bi_phys_segments ++;
+        spin_unlock_irq(&conf->device_lock);
+        spin_unlock(&sh->lock);
+
+        PRINTK("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 (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;
+}
+
+
+/*
+ * 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
+ *
+ * Parity calculations are done inside the stripe lock
+ * 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_stripe(struct stripe_head *sh)
+{
+        raid6_conf_t *conf = sh->raid_conf;
+        int disks = conf->raid_disks;
+        struct bio *return_bi= NULL;
+        struct bio *bi;
+        int i;
+        int syncing;
+        int locked=0, uptodate=0, to_read=0, to_write=0, failed=0, written=0;
+        int non_overwrite = 0;
+        int failed_num[2] = {0, 0};
+        struct r5dev *dev, *pdev, *qdev;
+        int pd_idx = sh->pd_idx;
+        int qd_idx = raid6_next_disk(pd_idx, disks);
+        int p_failed, q_failed;
+
+        PRINTK("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, qd_idx);
+
+        spin_lock(&sh->lock);
+        clear_bit(STRIPE_HANDLE, &sh->state);
+        clear_bit(STRIPE_DELAYED, &sh->state);
+
+        syncing = test_bit(STRIPE_SYNCING, &sh->state);
+        /* Now to look around and see what can be done */
+
+        for (i=disks; i--; ) {
+                mdk_rdev_t *rdev;
+                dev = &sh->dev[i];
+                clear_bit(R5_Insync, &dev->flags);
+                clear_bit(R5_Syncio, &dev->flags);
+
+                PRINTK("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;
+                        PRINTK("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)) locked++;
+                if (test_bit(R5_UPTODATE, &dev->flags)) uptodate++;
+
+
+                if (dev->toread) to_read++;
+                if (dev->towrite) {
+                        to_write++;
+                        if (!test_bit(R5_OVERWRITE, &dev->flags))
+                                non_overwrite++;
+                }
+                if (dev->written) written++;
+                rdev = conf->disks[i].rdev; /* FIXME, should I be looking rdev */
+                if (!rdev || !rdev->in_sync) {
+                        if ( failed < 2 )
+                                failed_num[failed] = i;
+                        failed++;
+                } else
+                        set_bit(R5_Insync, &dev->flags);
+        }
+        PRINTK("locked=%d uptodate=%d to_read=%d"
+               " to_write=%d failed=%d failed_num=%d,%d\n",
+               locked, uptodate, to_read, to_write, failed,
+               failed_num[0], failed_num[1]);
+        /* check if the array has lost >2 devices and, if so, some requests might
+         * need to be failed
+         */
+        if (failed > 2 && to_read+to_write+written) {
+                spin_lock_irq(&conf->device_lock);
+                for (i=disks; i--; ) {
+                        /* fail all writes first */
+                        bi = sh->dev[i].towrite;
+                        sh->dev[i].towrite = NULL;
+                        if (bi) to_write--;
+
+                        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;
+                        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 */
+                        if (!test_bit(R5_Insync, &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) 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 (failed > 2 && syncing) {
+                md_done_sync(conf->mddev, STRIPE_SECTORS,0);
+                clear_bit(STRIPE_SYNCING, &sh->state);
+                syncing = 0;
+        }
+
+        /*
+         * might be able to return some write requests if the parity blocks
+         * are safe, or on a failed drive
+         */
+        pdev = &sh->dev[pd_idx];
+        p_failed = (failed >= 1 && failed_num[0] == pd_idx)
+                || (failed >= 2 && failed_num[1] == pd_idx);
+        qdev = &sh->dev[qd_idx];
+        q_failed = (failed >= 1 && failed_num[0] == qd_idx)
+                || (failed >= 2 && failed_num[1] == qd_idx);
+
+        if ( written &&
+             ( p_failed || ((test_bit(R5_Insync, &pdev->flags)
+                             && !test_bit(R5_LOCKED, &pdev->flags)
+                             && test_bit(R5_UPTODATE, &pdev->flags))) ) &&
+             ( q_failed || ((test_bit(R5_Insync, &qdev->flags)
+                             && !test_bit(R5_LOCKED, &qdev->flags)
+                             && test_bit(R5_UPTODATE, &qdev->flags))) ) ) {
+                /* 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.
+                 */
+                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;
+                                        PRINTK("Return write for stripe %llu disc %d\n",
+                                               (unsigned long long)sh->sector, 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;
+                                        }
+                                        spin_unlock_irq(&conf->device_lock);
+                                }
+                        }
+        }
+
+        /* 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 (to_read || non_overwrite || (to_write && failed) || (syncing && (uptodate < disks))) {
+                for (i=disks; i--;) {
+                        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)) ||
+                             syncing ||
+                             (failed >= 1 && (sh->dev[failed_num[0]].toread || to_write)) ||
+                             (failed >= 2 && (sh->dev[failed_num[1]].toread || to_write))
+                                    )
+                                ) {
+                                /* we would like to get this block, possibly
+                                 * by computing it, but we might not be able to
+                                 */
+                                if (uptodate == disks-1) {
+                                        PRINTK("Computing stripe %llu block %d\n",
+                                               (unsigned long long)sh->sector, i);
+                                        compute_block_1(sh, i);
+                                        uptodate++;
+                                } else if ( uptodate == disks-2 && 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);
+                                        PRINTK("Computing stripe %llu blocks %d,%d\n",
+                                               (unsigned long long)sh->sector, i, other);
+                                        compute_block_2(sh, i, other);
+                                        uptodate += 2;
+                                } else if (test_bit(R5_Insync, &dev->flags)) {
+                                        set_bit(R5_LOCKED, &dev->flags);
+                                        set_bit(R5_Wantread, &dev->flags);
+#if 0
+                                        /* if I am just reading this block and we don't have
+                                           a failed drive, or any pending writes then sidestep the cache */
+                                        if (sh->bh_read[i] && !sh->bh_read[i]->b_reqnext &&
+                                            ! syncing && !failed && !to_write) {
+                                                sh->bh_cache[i]->b_page =  sh->bh_read[i]->b_page;
+                                                sh->bh_cache[i]->b_data =  sh->bh_read[i]->b_data;
+                                        }
+#endif
+                                        locked++;
+                                        PRINTK("Reading block %d (sync=%d)\n",
+                                                i, syncing);
+                                        if (syncing)
+                                                md_sync_acct(conf->disks[i].rdev->bdev,
+                                                             STRIPE_SECTORS);
+                                }
+                        }
+                }
+                set_bit(STRIPE_HANDLE, &sh->state);
+        }
+
+        /* now to consider writing and what else, if anything should be read */
+        if (to_write) {
+                int rcw=0, must_compute=0;
+                for (i=disks ; i--;) {
+                        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)
+#if 0
+                                || sh->bh_page[i] != bh->b_page
+#endif
+                                    ) &&
+                            !test_bit(R5_UPTODATE, &dev->flags)) {
+                                if (test_bit(R5_Insync, &dev->flags)) rcw++;
+                                else {
+                                        PRINTK("raid6: must_compute: disk %d flags=%#lx\n", i, dev->flags);
+                                        must_compute++;
+                                }
+                        }
+                }
+                PRINTK("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--;) {
+                                dev = &sh->dev[i];
+                                if (!test_bit(R5_OVERWRITE, &dev->flags)
+                                    && !(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))
+                                        {
+                                                PRINTK("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);
+                                                locked++;
+                                        } else {
+                                                PRINTK("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 (locked == 0 && rcw == 0) {
+                        if ( must_compute > 0 ) {
+                                /* We have failed blocks and need to compute them */
+                                switch ( failed ) {
+                                case 0: BUG();
+                                case 1: compute_block_1(sh, failed_num[0]); break;
+                                case 2: compute_block_2(sh, failed_num[0], failed_num[1]); break;
+                                default: BUG(); /* This request should have been failed? */
+                                }
+                        }
+
+                        PRINTK("Computing parity for stripe %llu\n", (unsigned long long)sh->sector);
+                        compute_parity(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)) {
+                                        PRINTK("Writing stripe %llu block %d\n",
+                                               (unsigned long long)sh->sector, i);
+                                        locked++;
+                                        set_bit(R5_Wantwrite, &sh->dev[i].flags);
+#if 0 /**** FIX: I don't understand the logic here... ****/
+                                        if (!test_bit(R5_Insync, &sh->dev[i].flags)
+                                            || ((i==pd_idx || i==qd_idx) && failed == 0)) /* FIX? */
+                                                set_bit(STRIPE_INSYNC, &sh->state);
+#endif
+                                }
+                        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);
+                        }
+                }
+        }
+
+        /* 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
+         */
+        if (syncing && locked == 0 &&
+            !test_bit(STRIPE_INSYNC, &sh->state) && failed <= 2) {
+                set_bit(STRIPE_HANDLE, &sh->state);
+#if 0 /* RAID-6: Don't support CHECK PARITY yet */
+                if (failed == 0) {
+                        char *pagea;
+                        if (uptodate != disks)
+                                BUG();
+                        compute_parity(sh, CHECK_PARITY);
+                        uptodate--;
+                        pagea = page_address(sh->dev[pd_idx].page);
+                        if ((*(u32*)pagea) == 0 &&
+                            !memcmp(pagea, pagea+4, STRIPE_SIZE-4)) {
+                                /* parity is correct (on disc, not in buffer any more) */
+                                set_bit(STRIPE_INSYNC, &sh->state);
+                        }
+                }
+#endif
+                if (!test_bit(STRIPE_INSYNC, &sh->state)) {
+                        int failed_needupdate[2];
+                        struct r5dev *adev, *bdev;
+
+                        if ( failed < 1 )
+                                failed_num[0] = pd_idx;
+                        if ( failed < 2 )
+                                failed_num[1] = (failed_num[0] == qd_idx) ? pd_idx : qd_idx;
+
+                        failed_needupdate[0] = !test_bit(R5_UPTODATE, &sh->dev[failed_num[0]].flags);
+                        failed_needupdate[1] = !test_bit(R5_UPTODATE, &sh->dev[failed_num[1]].flags);
+
+                        PRINTK("sync: failed=%d num=%d,%d fnu=%u%u\n",
+                               failed, failed_num[0], failed_num[1], failed_needupdate[0], failed_needupdate[1]);
+
+#if 0  /* RAID-6: This code seems to require that CHECK_PARITY destroys the uptodateness of the parity */
+                        /* should be able to compute the missing block(s) and write to spare */
+                        if ( failed_needupdate[0] ^ failed_needupdate[1] ) {
+                                if (uptodate+1 != disks)
+                                        BUG();
+                                compute_block_1(sh, failed_needupdate[0] ? failed_num[0] : failed_num[1]);
+                                uptodate++;
+                        } else if ( failed_needupdate[0] & failed_needupdate[1] ) {
+                                if (uptodate+2 != disks)
+                                        BUG();
+                                compute_block_2(sh, failed_num[0], failed_num[1]);
+                                uptodate += 2;
+                        }
+#else
+                        compute_block_2(sh, failed_num[0], failed_num[1]);
+                        uptodate += failed_needupdate[0] + failed_needupdate[1];
+#endif
+
+                        if (uptodate != disks)
+                                BUG();
+
+                        PRINTK("Marking for sync stripe %llu blocks %d,%d\n",
+                               (unsigned long long)sh->sector, failed_num[0], failed_num[1]);
+
+                        /**** FIX: Should we really do both of these unconditionally? ****/
+                        adev = &sh->dev[failed_num[0]];
+                        locked += !test_bit(R5_LOCKED, &adev->flags);
+                        set_bit(R5_LOCKED, &adev->flags);
+                        set_bit(R5_Wantwrite, &adev->flags);
+                        bdev = &sh->dev[failed_num[1]];
+                        locked += !test_bit(R5_LOCKED, &bdev->flags);
+                        set_bit(R5_LOCKED, &bdev->flags);
+                        set_bit(R5_Wantwrite, &bdev->flags);
+
+                        set_bit(STRIPE_INSYNC, &sh->state);
+                        set_bit(R5_Syncio, &adev->flags);
+                        set_bit(R5_Syncio, &bdev->flags);
+                }
+        }
+        if (syncing && locked == 0 && test_bit(STRIPE_INSYNC, &sh->state)) {
+                md_done_sync(conf->mddev, STRIPE_SECTORS,1);
+                clear_bit(STRIPE_SYNCING, &sh->state);
+        }
+
+        spin_unlock(&sh->lock);
+
+        while ((bi=return_bi)) {
+                int bytes = bi->bi_size;
+
+                return_bi = bi->bi_next;
+                bi->bi_next = NULL;
+                bi->bi_size = 0;
+                bi->bi_end_io(bi, bytes, 0);
+        }
+        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 = 1;
+                else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
+                        rw = 0;
+                else
+                        continue;
+
+                bi = &sh->dev[i].req;
+
+                bi->bi_rw = rw;
+                if (rw)
+                        bi->bi_end_io = raid6_end_write_request;
+                else
+                        bi->bi_end_io = raid6_end_read_request;
+
+                rcu_read_lock();
+                rdev = conf->disks[i].rdev;
+                if (rdev && rdev->faulty)
+                        rdev = NULL;
+                if (rdev)
+                        atomic_inc(&rdev->nr_pending);
+                rcu_read_unlock();
+
+                if (rdev) {
+                        if (test_bit(R5_Syncio, &sh->dev[i].flags))
+                                md_sync_acct(rdev->bdev, STRIPE_SECTORS);
+
+                        bi->bi_bdev = rdev->bdev;
+                        PRINTK("for %llu schedule op %ld on disc %d\n",
+                                (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;
+                        generic_make_request(bi);
+                } else {
+                        PRINTK("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 inline void raid6_activate_delayed(raid6_conf_t *conf)
+{
+        if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD) {
+                while (!list_empty(&conf->delayed_list)) {
+                        struct list_head *l = conf->delayed_list.next;
+                        struct stripe_head *sh;
+                        sh = list_entry(l, struct stripe_head, lru);
+                        list_del_init(l);
+                        clear_bit(STRIPE_DELAYED, &sh->state);
+                        if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
+                                atomic_inc(&conf->preread_active_stripes);
+                        list_add_tail(&sh->lru, &conf->handle_list);
+                }
+        }
+}
+
+static void unplug_slaves(mddev_t *mddev)
+{
+        raid6_conf_t *conf = mddev_to_conf(mddev);
+        int i;
+
+        rcu_read_lock();
+        for (i=0; i<mddev->raid_disks; i++) {
+                mdk_rdev_t *rdev = conf->disks[i].rdev;
+                if (rdev && !rdev->faulty && atomic_read(&rdev->nr_pending)) {
+                        request_queue_t *r_queue = bdev_get_queue(rdev->bdev);
+
+                        atomic_inc(&rdev->nr_pending);
+                        rcu_read_unlock();
+
+                        if (r_queue->unplug_fn)
+                                r_queue->unplug_fn(r_queue);
+
+                        rdev_dec_pending(rdev, mddev);
+                        rcu_read_lock();
+                }
+        }
+        rcu_read_unlock();
+}
+
+static void raid6_unplug_device(request_queue_t *q)
+{
+        mddev_t *mddev = q->queuedata;
+        raid6_conf_t *conf = mddev_to_conf(mddev);
+        unsigned long flags;
+
+        spin_lock_irqsave(&conf->device_lock, flags);
+
+        if (blk_remove_plug(q))
+                raid6_activate_delayed(conf);
+        md_wakeup_thread(mddev->thread);
+
+        spin_unlock_irqrestore(&conf->device_lock, flags);
+
+        unplug_slaves(mddev);
+}
+
+static int raid6_issue_flush(request_queue_t *q, struct gendisk *disk,
+                             sector_t *error_sector)
+{
+        mddev_t *mddev = q->queuedata;
+        raid6_conf_t *conf = mddev_to_conf(mddev);
+        int i, ret = 0;
+
+        rcu_read_lock();
+        for (i=0; i<mddev->raid_disks && ret == 0; i++) {
+                mdk_rdev_t *rdev = conf->disks[i].rdev;
+                if (rdev && !rdev->faulty) {
+                        struct block_device *bdev = rdev->bdev;
+                        request_queue_t *r_queue = bdev_get_queue(bdev);
+
+                        if (!r_queue->issue_flush_fn)
+                                ret = -EOPNOTSUPP;
+                        else {
+                                atomic_inc(&rdev->nr_pending);
+                                rcu_read_unlock();
+                                ret = r_queue->issue_flush_fn(r_queue, bdev->bd_disk,
+                                                              error_sector);
+                                rdev_dec_pending(rdev, mddev);
+                                rcu_read_lock();
+                        }
+                }
+        }
+        rcu_read_unlock();
+        return ret;
+}
+
+static inline void raid6_plug_device(raid6_conf_t *conf)
+{
+        spin_lock_irq(&conf->device_lock);
+        blk_plug_device(conf->mddev->queue);
+        spin_unlock_irq(&conf->device_lock);
+}
+
+static int make_request (request_queue_t *q, struct bio * bi)
+{
+        mddev_t *mddev = q->queuedata;
+        raid6_conf_t *conf = mddev_to_conf(mddev);
+        const unsigned int raid_disks = conf->raid_disks;
+        const unsigned int data_disks = raid_disks - 2;
+        unsigned int dd_idx, pd_idx;
+        sector_t new_sector;
+        sector_t logical_sector, last_sector;
+        struct stripe_head *sh;
+
+        if (bio_data_dir(bi)==WRITE) {
+                disk_stat_inc(mddev->gendisk, writes);
+                disk_stat_add(mddev->gendisk, write_sectors, bio_sectors(bi));
+        } else {
+                disk_stat_inc(mddev->gendisk, reads);
+                disk_stat_add(mddev->gendisk, read_sectors, bio_sectors(bi));
+        }
+
+        logical_sector = bi->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
+        last_sector = bi->bi_sector + (bi->bi_size>>9);
+
+        bi->bi_next = NULL;
+        bi->bi_phys_segments = 1;       /* over-loaded to count active stripes */
+        if ( bio_data_dir(bi) == WRITE )
+                md_write_start(mddev);
+        for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
+                DEFINE_WAIT(w);
+
+                new_sector = raid6_compute_sector(logical_sector,
+                                                  raid_disks, data_disks, &dd_idx, &pd_idx, conf);
+
+                PRINTK("raid6: make_request, sector %llu logical %llu\n",
+                       (unsigned long long)new_sector,
+                       (unsigned long long)logical_sector);
+
+        retry:
+                prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
+                sh = get_active_stripe(conf, new_sector, pd_idx, (bi->bi_rw&RWA_MASK));
+                if (sh) {
+                        if (!add_stripe_bio(sh, bi, dd_idx, (bi->bi_rw&RW_MASK))) {
+                                /* Add failed due to overlap.  Flush everything
+                                 * and wait a while
+                                 */
+                                raid6_unplug_device(mddev->queue);
+                                release_stripe(sh);
+                                schedule();
+                                goto retry;
+                        }
+                        finish_wait(&conf->wait_for_overlap, &w);
+                        raid6_plug_device(conf);
+                        handle_stripe(sh);
+                        release_stripe(sh);
+                } else {
+                        /* cannot get stripe for read-ahead, just give-up */
+                        clear_bit(BIO_UPTODATE, &bi->bi_flags);
+                        finish_wait(&conf->wait_for_overlap, &w);
+                        break;
+                }
+
+        }
+        spin_lock_irq(&conf->device_lock);
+        if (--bi->bi_phys_segments == 0) {
+                int bytes = bi->bi_size;
+
+                if ( bio_data_dir(bi) == WRITE )
+                        md_write_end(mddev);
+                bi->bi_size = 0;
+                bi->bi_end_io(bi, bytes, 0);
+        }
+        spin_unlock_irq(&conf->device_lock);
+        return 0;
+}
+
+/* FIXME go_faster isn't used */
+static int sync_request (mddev_t *mddev, sector_t sector_nr, int go_faster)
+{
+        raid6_conf_t *conf = (raid6_conf_t *) mddev->private;
+        struct stripe_head *sh;
+        int sectors_per_chunk = conf->chunk_size >> 9;
+        sector_t x;
+        unsigned long stripe;
+        int chunk_offset;
+        int dd_idx, pd_idx;
+        sector_t first_sector;
+        int raid_disks = conf->raid_disks;
+        int data_disks = raid_disks - 2;
+
+        if (sector_nr >= mddev->size <<1) {
+                /* just being told to finish up .. nothing much to do */
+                unplug_slaves(mddev);
+                return 0;
+        }
+        /* if there are 2 or more failed drives and we are trying
+         * to resync, then assert that we are finished, because there is
+         * nothing we can do.
+         */
+        if (mddev->degraded >= 2 && test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
+                int rv = (mddev->size << 1) - sector_nr;
+                md_done_sync(mddev, rv, 1);
+                return rv;
+        }
+
+        x = sector_nr;
+        chunk_offset = sector_div(x, sectors_per_chunk);
+        stripe = x;
+        BUG_ON(x != stripe);
+
+        first_sector = raid6_compute_sector((sector_t)stripe*data_disks*sectors_per_chunk
+                + chunk_offset, raid_disks, data_disks, &dd_idx, &pd_idx, conf);
+        sh = get_active_stripe(conf, sector_nr, pd_idx, 1);
+        if (sh == NULL) {
+                sh = get_active_stripe(conf, sector_nr, pd_idx, 0);
+                /* make sure we don't swamp the stripe cache if someone else
+                 * is trying to get access
+                 */
+                set_current_state(TASK_UNINTERRUPTIBLE);
+                schedule_timeout(1);
+        }
+        spin_lock(&sh->lock);
+        set_bit(STRIPE_SYNCING, &sh->state);
+        clear_bit(STRIPE_INSYNC, &sh->state);
+        spin_unlock(&sh->lock);
+
+        handle_stripe(sh);
+        release_stripe(sh);
+
+        return STRIPE_SECTORS;
+}
+
+/*
+ * This is our raid6 kernel thread.
+ *
+ * We scan the hash table for stripes which can be handled now.
+ * During the scan, completed stripes are saved for us by the interrupt
+ * handler, so that they will not have to wait for our next wakeup.
+ */
+static void raid6d (mddev_t *mddev)
+{
+        struct stripe_head *sh;
+        raid6_conf_t *conf = mddev_to_conf(mddev);
+        int handled;
+
+        PRINTK("+++ raid6d active\n");
+
+        md_check_recovery(mddev);
+        md_handle_safemode(mddev);
+
+        handled = 0;
+        spin_lock_irq(&conf->device_lock);
+        while (1) {
+                struct list_head *first;
+
+                if (list_empty(&conf->handle_list) &&
+                    atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD &&
+                    !blk_queue_plugged(mddev->queue) &&
+                    !list_empty(&conf->delayed_list))
+                        raid6_activate_delayed(conf);
+
+                if (list_empty(&conf->handle_list))
+                        break;
+
+                first = conf->handle_list.next;
+                sh = list_entry(first, struct stripe_head, lru);
+
+                list_del_init(first);
+                atomic_inc(&sh->count);
+                if (atomic_read(&sh->count)!= 1)
+                        BUG();
+                spin_unlock_irq(&conf->device_lock);
+
+                handled++;
+                handle_stripe(sh);
+                release_stripe(sh);
+
+                spin_lock_irq(&conf->device_lock);
+        }
+        PRINTK("%d stripes handled\n", handled);
+
+        spin_unlock_irq(&conf->device_lock);
+
+        unplug_slaves(mddev);
+
+        PRINTK("--- raid6d inactive\n");
+}
+
+static int run (mddev_t *mddev)
+{
+        raid6_conf_t *conf;
+        int raid_disk, memory;
+        mdk_rdev_t *rdev;
+        struct disk_info *disk;
+        struct list_head *tmp;
+
+        if (mddev->level != 6) {
+                PRINTK("raid6: %s: raid level not set to 6 (%d)\n", mdname(mddev), mddev->level);
+                return -EIO;
+        }
+
+        mddev->private = kmalloc (sizeof (raid6_conf_t)
+                                  + mddev->raid_disks * sizeof(struct disk_info),
+                                  GFP_KERNEL);
+        if ((conf = mddev->private) == NULL)
+                goto abort;
+        memset (conf, 0, sizeof (*conf) + mddev->raid_disks * sizeof(struct disk_info) );
+        conf->mddev = mddev;
+
+        if ((conf->stripe_hashtbl = (struct stripe_head **) __get_free_pages(GFP_ATOMIC, HASH_PAGES_ORDER)) == NULL)
+                goto abort;
+        memset(conf->stripe_hashtbl, 0, HASH_PAGES * PAGE_SIZE);
+
+        spin_lock_init(&conf->device_lock);
+        init_waitqueue_head(&conf->wait_for_stripe);
+        init_waitqueue_head(&conf->wait_for_overlap);
+        INIT_LIST_HEAD(&conf->handle_list);
+        INIT_LIST_HEAD(&conf->delayed_list);
+        INIT_LIST_HEAD(&conf->inactive_list);
+        atomic_set(&conf->active_stripes, 0);
+        atomic_set(&conf->preread_active_stripes, 0);
+
+        mddev->queue->unplug_fn = raid6_unplug_device;
+        mddev->queue->issue_flush_fn = raid6_issue_flush;
+
+        PRINTK("raid6: run(%s) called.\n", mdname(mddev));
+
+        ITERATE_RDEV(mddev,rdev,tmp) {
+                raid_disk = rdev->raid_disk;
+                if (raid_disk >= mddev->raid_disks
+                    || raid_disk < 0)
+                        continue;
+                disk = conf->disks + raid_disk;
+
+                disk->rdev = rdev;
+
+                if (rdev->in_sync) {
+                        char b[BDEVNAME_SIZE];
+                        printk(KERN_INFO "raid6: device %s operational as raid"
+                               " disk %d\n", bdevname(rdev->bdev,b),
+                               raid_disk);
+                        conf->working_disks++;
+                }
+        }
+
+        conf->raid_disks = mddev->raid_disks;
+
+        /*
+         * 0 for a fully functional array, 1 or 2 for a degraded array.
+         */
+        mddev->degraded = conf->failed_disks = conf->raid_disks - conf->working_disks;
+        conf->mddev = mddev;
+        conf->chunk_size = mddev->chunk_size;
+        conf->level = mddev->level;
+        conf->algorithm = mddev->layout;
+        conf->max_nr_stripes = NR_STRIPES;
+
+        /* device size must be a multiple of chunk size */
+        mddev->size &= ~(mddev->chunk_size/1024 -1);
+
+        if (conf->raid_disks < 4) {
+                printk(KERN_ERR "raid6: not enough configured devices for %s (%d, minimum 4)\n",
+                       mdname(mddev), conf->raid_disks);
+                goto abort;
+        }
+        if (!conf->chunk_size || conf->chunk_size % 4) {
+                printk(KERN_ERR "raid6: invalid chunk size %d for %s\n",
+                       conf->chunk_size, mdname(mddev));
+                goto abort;
+        }
+        if (conf->algorithm > ALGORITHM_RIGHT_SYMMETRIC) {
+                printk(KERN_ERR
+                       "raid6: unsupported parity algorithm %d for %s\n",
+                       conf->algorithm, mdname(mddev));
+                goto abort;
+        }
+        if (mddev->degraded > 2) {
+                printk(KERN_ERR "raid6: not enough operational devices for %s"
+                       " (%d/%d failed)\n",
+                       mdname(mddev), conf->failed_disks, conf->raid_disks);
+                goto abort;
+        }
+
+#if 0                           /* FIX: For now */
+        if (mddev->degraded > 0 &&
+            mddev->recovery_cp != MaxSector) {
+                printk(KERN_ERR "raid6: cannot start dirty degraded array for %s\n", mdname(mddev));
+                goto abort;
+        }
+#endif
+
+        {
+                mddev->thread = md_register_thread(raid6d, mddev, "%s_raid6");
+                if (!mddev->thread) {
+                        printk(KERN_ERR
+                               "raid6: couldn't allocate thread for %s\n",
+                               mdname(mddev));
+                        goto abort;
+                }
+        }
+
+        memory = conf->max_nr_stripes * (sizeof(struct stripe_head) +
+                 conf->raid_disks * ((sizeof(struct bio) + PAGE_SIZE))) / 1024;
+        if (grow_stripes(conf, conf->max_nr_stripes)) {
+                printk(KERN_ERR
+                       "raid6: couldn't allocate %dkB for buffers\n", memory);
+                shrink_stripes(conf);
+                md_unregister_thread(mddev->thread);
+                goto abort;
+        } else
+                printk(KERN_INFO "raid6: allocated %dkB for %s\n",
+                       memory, mdname(mddev));
+
+        if (mddev->degraded == 0)
+                printk(KERN_INFO "raid6: raid level %d set %s active with %d out of %d"
+                       " devices, algorithm %d\n", conf->level, mdname(mddev),
+                       mddev->raid_disks-mddev->degraded, mddev->raid_disks,
+                       conf->algorithm);
+        else
+                printk(KERN_ALERT "raid6: raid level %d set %s active with %d"
+                       " out of %d devices, algorithm %d\n", conf->level,
+                       mdname(mddev), mddev->raid_disks - mddev->degraded,
+                       mddev->raid_disks, conf->algorithm);
+
+        print_raid6_conf(conf);
+
+        /* read-ahead size must cover two whole stripes, which is
+         * 2 * (n-2) * chunksize where 'n' is the number of raid devices
+         */
+        {
+                int stripe = (mddev->raid_disks-2) * mddev->chunk_size
+                        / PAGE_CACHE_SIZE;
+                if (mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
+                        mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
+        }
+
+        /* Ok, everything is just fine now */
+        mddev->array_size =  mddev->size * (mddev->raid_disks - 2);
+        return 0;
+abort:
+        if (conf) {
+                print_raid6_conf(conf);
+                if (conf->stripe_hashtbl)
+                        free_pages((unsigned long) conf->stripe_hashtbl,
+                                                        HASH_PAGES_ORDER);
+                kfree(conf);
+        }
+        mddev->private = NULL;
+        printk(KERN_ALERT "raid6: failed to run raid set %s\n", mdname(mddev));
+        return -EIO;
+}
+
+
+
+static int stop (mddev_t *mddev)
+{
+        raid6_conf_t *conf = (raid6_conf_t *) mddev->private;
+
+        md_unregister_thread(mddev->thread);
+        mddev->thread = NULL;
+        shrink_stripes(conf);
+        free_pages((unsigned long) conf->stripe_hashtbl, HASH_PAGES_ORDER);
+        blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
+        kfree(conf);
+        mddev->private = NULL;
+        return 0;
+}
+
+#if RAID6_DUMPSTATE
+static void print_sh (struct seq_file *seq, struct stripe_head *sh)
+{
+        int i;
+
+        seq_printf(seq, "sh %llu, pd_idx %d, state %ld.\n",
+                   (unsigned long long)sh->sector, sh->pd_idx, sh->state);
+        seq_printf(seq, "sh %llu,  count %d.\n",
+                   (unsigned long long)sh->sector, atomic_read(&sh->count));
+        seq_printf(seq, "sh %llu, ", (unsigned long long)sh->sector);
+        for (i = 0; i < sh->raid_conf->raid_disks; i++) {
+                seq_printf(seq, "(cache%d: %p %ld) ",
+                           i, sh->dev[i].page, sh->dev[i].flags);
+        }
+        seq_printf(seq, "\n");
+}
+
+static void printall (struct seq_file *seq, raid6_conf_t *conf)
+{
+        struct stripe_head *sh;
+        int i;
+
+        spin_lock_irq(&conf->device_lock);
+        for (i = 0; i < NR_HASH; i++) {
+                sh = conf->stripe_hashtbl[i];
+                for (; sh; sh = sh->hash_next) {
+                        if (sh->raid_conf != conf)
+                                continue;
+                        print_sh(seq, sh);
+                }
+        }
+        spin_unlock_irq(&conf->device_lock);
+}
+#endif
+
+static void status (struct seq_file *seq, mddev_t *mddev)
+{
+        raid6_conf_t *conf = (raid6_conf_t *) mddev->private;
+        int i;
+
+        seq_printf (seq, " level %d, %dk chunk, algorithm %d", mddev->level, mddev->chunk_size >> 10, mddev->layout);
+        seq_printf (seq, " [%d/%d] [", conf->raid_disks, conf->working_disks);
+        for (i = 0; i < conf->raid_disks; i++)
+                seq_printf (seq, "%s",
+                            conf->disks[i].rdev &&
+                            conf->disks[i].rdev->in_sync ? "U" : "_");
+        seq_printf (seq, "]");
+#if RAID6_DUMPSTATE
+        seq_printf (seq, "\n");
+        printall(seq, conf);
+#endif
+}
+
+static void print_raid6_conf (raid6_conf_t *conf)
+{
+        int i;
+        struct disk_info *tmp;
+
+        printk("RAID6 conf printout:\n");
+        if (!conf) {
+                printk("(conf==NULL)\n");
+                return;
+        }
+        printk(" --- rd:%d wd:%d fd:%d\n", conf->raid_disks,
+                 conf->working_disks, conf->failed_disks);
+
+        for (i = 0; i < conf->raid_disks; i++) {
+                char b[BDEVNAME_SIZE];
+                tmp = conf->disks + i;
+                if (tmp->rdev)
+                printk(" disk %d, o:%d, dev:%s\n",
+                        i, !tmp->rdev->faulty,
+                        bdevname(tmp->rdev->bdev,b));
+        }
+}
+
+static int raid6_spare_active(mddev_t *mddev)
+{
+        int i;
+        raid6_conf_t *conf = mddev->private;
+        struct disk_info *tmp;
+
+        for (i = 0; i < conf->raid_disks; i++) {
+                tmp = conf->disks + i;
+                if (tmp->rdev
+                    && !tmp->rdev->faulty
+                    && !tmp->rdev->in_sync) {
+                        mddev->degraded--;
+                        conf->failed_disks--;
+                        conf->working_disks++;
+                        tmp->rdev->in_sync = 1;
+                }
+        }
+        print_raid6_conf(conf);
+        return 0;
+}
+
+static int raid6_remove_disk(mddev_t *mddev, int number)
+{
+        raid6_conf_t *conf = mddev->private;
+        int err = 0;
+        mdk_rdev_t *rdev;
+        struct disk_info *p = conf->disks + number;
+
+        print_raid6_conf(conf);
+        rdev = p->rdev;
+        if (rdev) {
+                if (rdev->in_sync ||
+                    atomic_read(&rdev->nr_pending)) {
+                        err = -EBUSY;
+                        goto abort;
+                }
+                p->rdev = NULL;
+                synchronize_kernel();
+                if (atomic_read(&rdev->nr_pending)) {
+                        /* lost the race, try later */
+                        err = -EBUSY;
+                        p->rdev = rdev;
+                }
+        }
+
+abort:
+
+        print_raid6_conf(conf);
+        return err;
+}
+
+static int raid6_add_disk(mddev_t *mddev, mdk_rdev_t *rdev)
+{
+        raid6_conf_t *conf = mddev->private;
+        int found = 0;
+        int disk;
+        struct disk_info *p;
+
+        if (mddev->degraded > 2)
+                /* no point adding a device */
+                return 0;
+        /*
+         * find the disk ...
+         */
+        for (disk=0; disk < mddev->raid_disks; disk++)
+                if ((p=conf->disks + disk)->rdev == NULL) {
+                        rdev->in_sync = 0;
+                        rdev->raid_disk = disk;
+                        found = 1;
+                        p->rdev = rdev;
+                        break;
+                }
+        print_raid6_conf(conf);
+        return found;
+}
+
+static int raid6_resize(mddev_t *mddev, sector_t sectors)
+{
+        /* no resync is happening, and there is enough space
+         * on all devices, so we can resize.
+         * We need to make sure resync covers any new space.
+         * If the array is shrinking we should possibly wait until
+         * any io in the removed space completes, but it hardly seems
+         * worth it.
+         */
+        sectors &= ~((sector_t)mddev->chunk_size/512 - 1);
+        mddev->array_size = (sectors * (mddev->raid_disks-2))>>1;
+        set_capacity(mddev->gendisk, mddev->array_size << 1);
+        mddev->changed = 1;
+        if (sectors/2  > mddev->size && mddev->recovery_cp == MaxSector) {
+                mddev->recovery_cp = mddev->size << 1;
+                set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
+        }
+        mddev->size = sectors /2;
+        return 0;
+}
+
+static mdk_personality_t raid6_personality=
+{
+        .name           = "raid6",
+        .owner          = THIS_MODULE,
+        .make_request   = make_request,
+        .run            = run,
+        .stop           = stop,
+        .status         = status,
+        .error_handler  = error,
+        .hot_add_disk   = raid6_add_disk,
+        .hot_remove_disk= raid6_remove_disk,
+        .spare_active   = raid6_spare_active,
+        .sync_request   = sync_request,
+        .resize         = raid6_resize,
+};
+
+static int __init raid6_init (void)
+{
+        int e;
+
+        e = raid6_select_algo();
+        if ( e )
+                return e;
+
+        return register_md_personality (RAID6, &raid6_personality);
+}
+
+static void raid6_exit (void)
+{
+        unregister_md_personality (RAID6);
+}
+
+module_init(raid6_init);
+module_exit(raid6_exit);
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("md-personality-8"); /* RAID6 */