[PATCH] md: always honour md bitmap being read from disk

[linux-2.6/openmoko-kernel/knife-kernel.git] / drivers / md / bitmap.c

/*
 * bitmap.c two-level bitmap (C) Peter T. Breuer (ptb@ot.uc3m.es) 2003
 *
 * bitmap_create  - sets up the bitmap structure
 * bitmap_destroy - destroys the bitmap structure
 *
 * additions, Copyright (C) 2003-2004, Paul Clements, SteelEye Technology, Inc.:
 * - added disk storage for bitmap
 * - changes to allow various bitmap chunk sizes
 * - added bitmap daemon (to asynchronously clear bitmap bits from disk)
 */

/*
 * Still to do:
 *
 * flush after percent set rather than just time based. (maybe both).
 * wait if count gets too high, wake when it drops to half.
 * allow bitmap to be mirrored with superblock (before or after...)
 * allow hot-add to re-instate a current device.
 * allow hot-add of bitmap after quiessing device
 */

#include <linux/module.h>
#include <linux/version.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/config.h>
#include <linux/timer.h>
#include <linux/sched.h>
#include <linux/list.h>
#include <linux/file.h>
#include <linux/mount.h>
#include <linux/buffer_head.h>
#include <linux/raid/md.h>
#include <linux/raid/bitmap.h>

/* debug macros */

#define DEBUG 0

#if DEBUG
/* these are for debugging purposes only! */

/* define one and only one of these */
#define INJECT_FAULTS_1 0 /* cause bitmap_alloc_page to fail always */
#define INJECT_FAULTS_2 0 /* cause bitmap file to be kicked when first bit set*/
#define INJECT_FAULTS_3 0 /* treat bitmap file as kicked at init time */
#define INJECT_FAULTS_4 0 /* undef */
#define INJECT_FAULTS_5 0 /* undef */
#define INJECT_FAULTS_6 0

/* if these are defined, the driver will fail! debug only */
#define INJECT_FATAL_FAULT_1 0 /* fail kmalloc, causing bitmap_create to fail */
#define INJECT_FATAL_FAULT_2 0 /* undef */
#define INJECT_FATAL_FAULT_3 0 /* undef */
#endif

//#define DPRINTK PRINTK /* set this NULL to avoid verbose debug output */
#define DPRINTK(x...) do { } while(0)

#ifndef PRINTK
#  if DEBUG > 0
#    define PRINTK(x...) printk(KERN_DEBUG x)
#  else
#    define PRINTK(x...)
#  endif
#endif

static inline char * bmname(struct bitmap *bitmap)
{
        return bitmap->mddev ? mdname(bitmap->mddev) : "mdX";
}


/*
 * test if the bitmap is active
 */
int bitmap_active(struct bitmap *bitmap)
{
        unsigned long flags;
        int res = 0;

        if (!bitmap)
                return res;
        spin_lock_irqsave(&bitmap->lock, flags);
        res = bitmap->flags & BITMAP_ACTIVE;
        spin_unlock_irqrestore(&bitmap->lock, flags);
        return res;
}

#define WRITE_POOL_SIZE 256
/* mempool for queueing pending writes on the bitmap file */
static void *write_pool_alloc(unsigned int gfp_flags, void *data)
{
        return kmalloc(sizeof(struct page_list), gfp_flags);
}

static void write_pool_free(void *ptr, void *data)
{
        kfree(ptr);
}

/*
 * just a placeholder - calls kmalloc for bitmap pages
 */
static unsigned char *bitmap_alloc_page(struct bitmap *bitmap)
{
        unsigned char *page;

#ifdef INJECT_FAULTS_1
        page = NULL;
#else
        page = kmalloc(PAGE_SIZE, GFP_NOIO);
#endif
        if (!page)
                printk("%s: bitmap_alloc_page FAILED\n", bmname(bitmap));
        else
                PRINTK("%s: bitmap_alloc_page: allocated page at %p\n",
                        bmname(bitmap), page);
        return page;
}

/*
 * for now just a placeholder -- just calls kfree for bitmap pages
 */
static void bitmap_free_page(struct bitmap *bitmap, unsigned char *page)
{
        PRINTK("%s: bitmap_free_page: free page %p\n", bmname(bitmap), page);
        kfree(page);
}

/*
 * check a page and, if necessary, allocate it (or hijack it if the alloc fails)
 *
 * 1) check to see if this page is allocated, if it's not then try to alloc
 * 2) if the alloc fails, set the page's hijacked flag so we'll use the
 *    page pointer directly as a counter
 *
 * if we find our page, we increment the page's refcount so that it stays
 * allocated while we're using it
 */
static int bitmap_checkpage(struct bitmap *bitmap, unsigned long page, int create)
{
        unsigned char *mappage;

        if (page >= bitmap->pages) {
                printk(KERN_ALERT
                        "%s: invalid bitmap page request: %lu (> %lu)\n",
                        bmname(bitmap), page, bitmap->pages-1);
                return -EINVAL;
        }


        if (bitmap->bp[page].hijacked) /* it's hijacked, don't try to alloc */
                return 0;

        if (bitmap->bp[page].map) /* page is already allocated, just return */
                return 0;

        if (!create)
                return -ENOENT;

        spin_unlock_irq(&bitmap->lock);

        /* this page has not been allocated yet */

        if ((mappage = bitmap_alloc_page(bitmap)) == NULL) {
                PRINTK("%s: bitmap map page allocation failed, hijacking\n",
                        bmname(bitmap));
                /* failed - set the hijacked flag so that we can use the
                 * pointer as a counter */
                spin_lock_irq(&bitmap->lock);
                if (!bitmap->bp[page].map)
                        bitmap->bp[page].hijacked = 1;
                goto out;
        }

        /* got a page */

        spin_lock_irq(&bitmap->lock);

        /* recheck the page */

        if (bitmap->bp[page].map || bitmap->bp[page].hijacked) {
                /* somebody beat us to getting the page */
                bitmap_free_page(bitmap, mappage);
                return 0;
        }

        /* no page was in place and we have one, so install it */

        memset(mappage, 0, PAGE_SIZE);
        bitmap->bp[page].map = mappage;
        bitmap->missing_pages--;
out:
        return 0;
}


/* if page is completely empty, put it back on the free list, or dealloc it */
/* if page was hijacked, unmark the flag so it might get alloced next time */
/* Note: lock should be held when calling this */
static inline void bitmap_checkfree(struct bitmap *bitmap, unsigned long page)
{
        char *ptr;

        if (bitmap->bp[page].count) /* page is still busy */
                return;

        /* page is no longer in use, it can be released */

        if (bitmap->bp[page].hijacked) { /* page was hijacked, undo this now */
                bitmap->bp[page].hijacked = 0;
                bitmap->bp[page].map = NULL;
                return;
        }

        /* normal case, free the page */

#if 0
/* actually ... let's not.  We will probably need the page again exactly when
 * memory is tight and we are flusing to disk
 */
        return;
#else
        ptr = bitmap->bp[page].map;
        bitmap->bp[page].map = NULL;
        bitmap->missing_pages++;
        bitmap_free_page(bitmap, ptr);
        return;
#endif
}


/*
 * bitmap file handling - read and write the bitmap file and its superblock
 */

/* copy the pathname of a file to a buffer */
char *file_path(struct file *file, char *buf, int count)
{
        struct dentry *d;
        struct vfsmount *v;

        if (!buf)
                return NULL;

        d = file->f_dentry;
        v = file->f_vfsmnt;

        buf = d_path(d, v, buf, count);

        return IS_ERR(buf) ? NULL : buf;
}

/*
 * basic page I/O operations
 */

/* IO operations when bitmap is stored near all superblocks */
static struct page *read_sb_page(mddev_t *mddev, long offset, unsigned long index)
{
        /* choose a good rdev and read the page from there */

        mdk_rdev_t *rdev;
        struct list_head *tmp;
        struct page *page = alloc_page(GFP_KERNEL);
        sector_t target;

        if (!page)
                return ERR_PTR(-ENOMEM);
        do {
                ITERATE_RDEV(mddev, rdev, tmp)
                        if (rdev->in_sync && !rdev->faulty)
                                goto found;
                return ERR_PTR(-EIO);

        found:
                target = (rdev->sb_offset << 1) + offset + index * (PAGE_SIZE/512);

        } while (!sync_page_io(rdev->bdev, target, PAGE_SIZE, page, READ));

        page->index = index;
        return page;
}

static int write_sb_page(mddev_t *mddev, long offset, struct page *page, int wait)
{
        mdk_rdev_t *rdev;
        struct list_head *tmp;

        ITERATE_RDEV(mddev, rdev, tmp)
                if (rdev->in_sync && !rdev->faulty)
                        md_super_write(mddev, rdev,
                                       (rdev->sb_offset<<1) + offset
                                       + page->index * (PAGE_SIZE/512),
                                       PAGE_SIZE,
                                       page);

        if (wait)
                wait_event(mddev->sb_wait, atomic_read(&mddev->pending_writes)==0);
        return 0;
}

/*
 * write out a page to a file
 */
static int write_page(struct bitmap *bitmap, struct page *page, int wait)
{
        int ret = -ENOMEM;

        if (bitmap->file == NULL)
                return write_sb_page(bitmap->mddev, bitmap->offset, page, wait);

        if (wait)
                lock_page(page);
        else {
                if (TestSetPageLocked(page))
                        return -EAGAIN; /* already locked */
                if (PageWriteback(page)) {
                        unlock_page(page);
                        return -EAGAIN;
                }
        }

        ret = page->mapping->a_ops->prepare_write(NULL, page, 0, PAGE_SIZE);
        if (!ret)
                ret = page->mapping->a_ops->commit_write(NULL, page, 0,
                        PAGE_SIZE);
        if (ret) {
                unlock_page(page);
                return ret;
        }

        set_page_dirty(page); /* force it to be written out */

        if (!wait) {
                /* add to list to be waited for by daemon */
                struct page_list *item = mempool_alloc(bitmap->write_pool, GFP_NOIO);
                item->page = page;
                page_cache_get(page);
                spin_lock(&bitmap->write_lock);
                list_add(&item->list, &bitmap->complete_pages);
                spin_unlock(&bitmap->write_lock);
                md_wakeup_thread(bitmap->writeback_daemon);
        }
        return write_one_page(page, wait);
}

/* read a page from a file, pinning it into cache, and return bytes_read */
static struct page *read_page(struct file *file, unsigned long index,
                                        unsigned long *bytes_read)
{
        struct inode *inode = file->f_mapping->host;
        struct page *page = NULL;
        loff_t isize = i_size_read(inode);
        unsigned long end_index = isize >> PAGE_CACHE_SHIFT;

        PRINTK("read bitmap file (%dB @ %Lu)\n", (int)PAGE_CACHE_SIZE,
                        (unsigned long long)index << PAGE_CACHE_SHIFT);

        page = read_cache_page(inode->i_mapping, index,
                        (filler_t *)inode->i_mapping->a_ops->readpage, file);
        if (IS_ERR(page))
                goto out;
        wait_on_page_locked(page);
        if (!PageUptodate(page) || PageError(page)) {
                page_cache_release(page);
                page = ERR_PTR(-EIO);
                goto out;
        }

        if (index > end_index) /* we have read beyond EOF */
                *bytes_read = 0;
        else if (index == end_index) /* possible short read */
                *bytes_read = isize & ~PAGE_CACHE_MASK;
        else
                *bytes_read = PAGE_CACHE_SIZE; /* got a full page */
out:
        if (IS_ERR(page))
                printk(KERN_ALERT "md: bitmap read error: (%dB @ %Lu): %ld\n",
                        (int)PAGE_CACHE_SIZE,
                        (unsigned long long)index << PAGE_CACHE_SHIFT,
                        PTR_ERR(page));
        return page;
}

/*
 * bitmap file superblock operations
 */

/* update the event counter and sync the superblock to disk */
int bitmap_update_sb(struct bitmap *bitmap)
{
        bitmap_super_t *sb;
        unsigned long flags;

        if (!bitmap || !bitmap->mddev) /* no bitmap for this array */
                return 0;
        spin_lock_irqsave(&bitmap->lock, flags);
        if (!bitmap->sb_page) { /* no superblock */
                spin_unlock_irqrestore(&bitmap->lock, flags);
                return 0;
        }
        spin_unlock_irqrestore(&bitmap->lock, flags);
        sb = (bitmap_super_t *)kmap(bitmap->sb_page);
        sb->events = cpu_to_le64(bitmap->mddev->events);
        if (!bitmap->mddev->degraded)
                sb->events_cleared = cpu_to_le64(bitmap->mddev->events);
        kunmap(bitmap->sb_page);
        return write_page(bitmap, bitmap->sb_page, 1);
}

/* print out the bitmap file superblock */
void bitmap_print_sb(struct bitmap *bitmap)
{
        bitmap_super_t *sb;

        if (!bitmap || !bitmap->sb_page)
                return;
        sb = (bitmap_super_t *)kmap(bitmap->sb_page);
        printk(KERN_DEBUG "%s: bitmap file superblock:\n", bmname(bitmap));
        printk(KERN_DEBUG "         magic: %08x\n", le32_to_cpu(sb->magic));
        printk(KERN_DEBUG "       version: %d\n", le32_to_cpu(sb->version));
        printk(KERN_DEBUG "          uuid: %08x.%08x.%08x.%08x\n",
                                        *(__u32 *)(sb->uuid+0),
                                        *(__u32 *)(sb->uuid+4),
                                        *(__u32 *)(sb->uuid+8),
                                        *(__u32 *)(sb->uuid+12));
        printk(KERN_DEBUG "        events: %llu\n",
                        (unsigned long long) le64_to_cpu(sb->events));
        printk(KERN_DEBUG "events cleared: %llu\n",
                        (unsigned long long) le64_to_cpu(sb->events_cleared));
        printk(KERN_DEBUG "         state: %08x\n", le32_to_cpu(sb->state));
        printk(KERN_DEBUG "     chunksize: %d B\n", le32_to_cpu(sb->chunksize));
        printk(KERN_DEBUG "  daemon sleep: %ds\n", le32_to_cpu(sb->daemon_sleep));
        printk(KERN_DEBUG "     sync size: %llu KB\n",
                        (unsigned long long)le64_to_cpu(sb->sync_size)/2);
        kunmap(bitmap->sb_page);
}

/* read the superblock from the bitmap file and initialize some bitmap fields */
static int bitmap_read_sb(struct bitmap *bitmap)
{
        char *reason = NULL;
        bitmap_super_t *sb;
        unsigned long chunksize, daemon_sleep;
        unsigned long bytes_read;
        unsigned long long events;
        int err = -EINVAL;

        /* page 0 is the superblock, read it... */
        if (bitmap->file)
                bitmap->sb_page = read_page(bitmap->file, 0, &bytes_read);
        else {
                bitmap->sb_page = read_sb_page(bitmap->mddev, bitmap->offset, 0);
                bytes_read = PAGE_SIZE;
        }
        if (IS_ERR(bitmap->sb_page)) {
                err = PTR_ERR(bitmap->sb_page);
                bitmap->sb_page = NULL;
                return err;
        }

        sb = (bitmap_super_t *)kmap(bitmap->sb_page);

        if (bytes_read < sizeof(*sb)) { /* short read */
                printk(KERN_INFO "%s: bitmap file superblock truncated\n",
                        bmname(bitmap));
                err = -ENOSPC;
                goto out;
        }

        chunksize = le32_to_cpu(sb->chunksize);
        daemon_sleep = le32_to_cpu(sb->daemon_sleep);

        /* verify that the bitmap-specific fields are valid */
        if (sb->magic != cpu_to_le32(BITMAP_MAGIC))
                reason = "bad magic";
        else if (sb->version != cpu_to_le32(BITMAP_MAJOR))
                reason = "unrecognized superblock version";
        else if (chunksize < 512 || chunksize > (1024 * 1024 * 4))
                reason = "bitmap chunksize out of range (512B - 4MB)";
        else if ((1 << ffz(~chunksize)) != chunksize)
                reason = "bitmap chunksize not a power of 2";
        else if (daemon_sleep < 1 || daemon_sleep > 15)
                reason = "daemon sleep period out of range";
        if (reason) {
                printk(KERN_INFO "%s: invalid bitmap file superblock: %s\n",
                        bmname(bitmap), reason);
                goto out;
        }

        /* keep the array size field of the bitmap superblock up to date */
        sb->sync_size = cpu_to_le64(bitmap->mddev->resync_max_sectors);

        if (!bitmap->mddev->persistent)
                goto success;

        /*
         * if we have a persistent array superblock, compare the
         * bitmap's UUID and event counter to the mddev's
         */
        if (memcmp(sb->uuid, bitmap->mddev->uuid, 16)) {
                printk(KERN_INFO "%s: bitmap superblock UUID mismatch\n",
                        bmname(bitmap));
                goto out;
        }
        events = le64_to_cpu(sb->events);
        if (events < bitmap->mddev->events) {
                printk(KERN_INFO "%s: bitmap file is out of date (%llu < %llu) "
                        "-- forcing full recovery\n", bmname(bitmap), events,
                        (unsigned long long) bitmap->mddev->events);
                sb->state |= BITMAP_STALE;
        }
success:
        /* assign fields using values from superblock */
        bitmap->chunksize = chunksize;
        bitmap->daemon_sleep = daemon_sleep;
        bitmap->flags |= sb->state;
        bitmap->events_cleared = le64_to_cpu(sb->events_cleared);
        err = 0;
out:
        kunmap(bitmap->sb_page);
        if (err)
                bitmap_print_sb(bitmap);
        return err;
}

enum bitmap_mask_op {
        MASK_SET,
        MASK_UNSET
};

/* record the state of the bitmap in the superblock */
static void bitmap_mask_state(struct bitmap *bitmap, enum bitmap_state bits,
                                enum bitmap_mask_op op)
{
        bitmap_super_t *sb;
        unsigned long flags;

        spin_lock_irqsave(&bitmap->lock, flags);
        if (!bitmap || !bitmap->sb_page) { /* can't set the state */
                spin_unlock_irqrestore(&bitmap->lock, flags);
                return;
        }
        page_cache_get(bitmap->sb_page);
        spin_unlock_irqrestore(&bitmap->lock, flags);
        sb = (bitmap_super_t *)kmap(bitmap->sb_page);
        switch (op) {
                case MASK_SET: sb->state |= bits;
                                break;
                case MASK_UNSET: sb->state &= ~bits;
                                break;
                default: BUG();
        }
        kunmap(bitmap->sb_page);
        page_cache_release(bitmap->sb_page);
}

/*
 * general bitmap file operations
 */

/* calculate the index of the page that contains this bit */
static inline unsigned long file_page_index(unsigned long chunk)
{
        return CHUNK_BIT_OFFSET(chunk) >> PAGE_BIT_SHIFT;
}

/* calculate the (bit) offset of this bit within a page */
static inline unsigned long file_page_offset(unsigned long chunk)
{
        return CHUNK_BIT_OFFSET(chunk) & (PAGE_BITS - 1);
}

/*
 * return a pointer to the page in the filemap that contains the given bit
 *
 * this lookup is complicated by the fact that the bitmap sb might be exactly
 * 1 page (e.g., x86) or less than 1 page -- so the bitmap might start on page
 * 0 or page 1
 */
static inline struct page *filemap_get_page(struct bitmap *bitmap,
                                        unsigned long chunk)
{
        return bitmap->filemap[file_page_index(chunk) - file_page_index(0)];
}


static void bitmap_file_unmap(struct bitmap *bitmap)
{
        struct page **map, *sb_page;
        unsigned long *attr;
        int pages;
        unsigned long flags;

        spin_lock_irqsave(&bitmap->lock, flags);
        map = bitmap->filemap;
        bitmap->filemap = NULL;
        attr = bitmap->filemap_attr;
        bitmap->filemap_attr = NULL;
        pages = bitmap->file_pages;
        bitmap->file_pages = 0;
        sb_page = bitmap->sb_page;
        bitmap->sb_page = NULL;
        spin_unlock_irqrestore(&bitmap->lock, flags);

        while (pages--)
                if (map[pages]->index != 0) /* 0 is sb_page, release it below */
                        page_cache_release(map[pages]);
        kfree(map);
        kfree(attr);

        if (sb_page)
                page_cache_release(sb_page);
}

static void bitmap_stop_daemons(struct bitmap *bitmap);

/* dequeue the next item in a page list -- don't call from irq context */
static struct page_list *dequeue_page(struct bitmap *bitmap)
{
        struct page_list *item = NULL;
        struct list_head *head = &bitmap->complete_pages;

        spin_lock(&bitmap->write_lock);
        if (list_empty(head))
                goto out;
        item = list_entry(head->prev, struct page_list, list);
        list_del(head->prev);
out:
        spin_unlock(&bitmap->write_lock);
        return item;
}

static void drain_write_queues(struct bitmap *bitmap)
{
        struct page_list *item;

        while ((item = dequeue_page(bitmap))) {
                /* don't bother to wait */
                page_cache_release(item->page);
                mempool_free(item, bitmap->write_pool);
        }

        wake_up(&bitmap->write_wait);
}

static void bitmap_file_put(struct bitmap *bitmap)
{
        struct file *file;
        struct inode *inode;
        unsigned long flags;

        spin_lock_irqsave(&bitmap->lock, flags);
        file = bitmap->file;
        bitmap->file = NULL;
        spin_unlock_irqrestore(&bitmap->lock, flags);

        bitmap_stop_daemons(bitmap);

        drain_write_queues(bitmap);

        bitmap_file_unmap(bitmap);

        if (file) {
                inode = file->f_mapping->host;
                spin_lock(&inode->i_lock);
                atomic_set(&inode->i_writecount, 1); /* allow writes again */
                spin_unlock(&inode->i_lock);
                fput(file);
        }
}


/*
 * bitmap_file_kick - if an error occurs while manipulating the bitmap file
 * then it is no longer reliable, so we stop using it and we mark the file
 * as failed in the superblock
 */
static void bitmap_file_kick(struct bitmap *bitmap)
{
        char *path, *ptr = NULL;

        bitmap_mask_state(bitmap, BITMAP_STALE, MASK_SET);
        bitmap_update_sb(bitmap);

        if (bitmap->file) {
                path = kmalloc(PAGE_SIZE, GFP_KERNEL);
                if (path)
                        ptr = file_path(bitmap->file, path, PAGE_SIZE);

                printk(KERN_ALERT "%s: kicking failed bitmap file %s from array!\n",
                       bmname(bitmap), ptr ? ptr : "");

                kfree(path);
        }

        bitmap_file_put(bitmap);

        return;
}

enum bitmap_page_attr {
        BITMAP_PAGE_DIRTY = 1, // there are set bits that need to be synced
        BITMAP_PAGE_CLEAN = 2, // there are bits that might need to be cleared
        BITMAP_PAGE_NEEDWRITE=4, // there are cleared bits that need to be synced
};

static inline void set_page_attr(struct bitmap *bitmap, struct page *page,
                                enum bitmap_page_attr attr)
{
        bitmap->filemap_attr[page->index] |= attr;
}

static inline void clear_page_attr(struct bitmap *bitmap, struct page *page,
                                enum bitmap_page_attr attr)
{
        bitmap->filemap_attr[page->index] &= ~attr;
}

static inline unsigned long get_page_attr(struct bitmap *bitmap, struct page *page)
{
        return bitmap->filemap_attr[page->index];
}

/*
 * bitmap_file_set_bit -- called before performing a write to the md device
 * to set (and eventually sync) a particular bit in the bitmap file
 *
 * we set the bit immediately, then we record the page number so that
 * when an unplug occurs, we can flush the dirty pages out to disk
 */
static void bitmap_file_set_bit(struct bitmap *bitmap, sector_t block)
{
        unsigned long bit;
        struct page *page;
        void *kaddr;
        unsigned long chunk = block >> CHUNK_BLOCK_SHIFT(bitmap);

        if (!bitmap->filemap) {
                return;
        }

        page = filemap_get_page(bitmap, chunk);
        bit = file_page_offset(chunk);


        /* make sure the page stays cached until it gets written out */
        if (! (get_page_attr(bitmap, page) & BITMAP_PAGE_DIRTY))
                page_cache_get(page);

        /* set the bit */
        kaddr = kmap_atomic(page, KM_USER0);
        set_bit(bit, kaddr);
        kunmap_atomic(kaddr, KM_USER0);
        PRINTK("set file bit %lu page %lu\n", bit, page->index);

        /* record page number so it gets flushed to disk when unplug occurs */
        set_page_attr(bitmap, page, BITMAP_PAGE_DIRTY);

}

/* this gets called when the md device is ready to unplug its underlying
 * (slave) device queues -- before we let any writes go down, we need to
 * sync the dirty pages of the bitmap file to disk */
int bitmap_unplug(struct bitmap *bitmap)
{
        unsigned long i, attr, flags;
        struct page *page;
        int wait = 0;
        int err;

        if (!bitmap)
                return 0;

        /* look at each page to see if there are any set bits that need to be
         * flushed out to disk */
        for (i = 0; i < bitmap->file_pages; i++) {
                spin_lock_irqsave(&bitmap->lock, flags);
                if (!bitmap->filemap) {
                        spin_unlock_irqrestore(&bitmap->lock, flags);
                        return 0;
                }
                page = bitmap->filemap[i];
                attr = get_page_attr(bitmap, page);
                clear_page_attr(bitmap, page, BITMAP_PAGE_DIRTY);
                clear_page_attr(bitmap, page, BITMAP_PAGE_NEEDWRITE);
                if ((attr & BITMAP_PAGE_DIRTY))
                        wait = 1;
                spin_unlock_irqrestore(&bitmap->lock, flags);

                if (attr & (BITMAP_PAGE_DIRTY | BITMAP_PAGE_NEEDWRITE)) {
                        err = write_page(bitmap, page, 0);
                        if (err == -EAGAIN) {
                                if (attr & BITMAP_PAGE_DIRTY)
                                        err = write_page(bitmap, page, 1);
                                else
                                        err = 0;
                        }
                        if (err)
                                return 1;
                }
        }
        if (wait) { /* if any writes were performed, we need to wait on them */
                if (bitmap->file) {
                        spin_lock_irq(&bitmap->write_lock);
                        wait_event_lock_irq(bitmap->write_wait,
                                            list_empty(&bitmap->complete_pages), bitmap->write_lock,
                                            wake_up_process(bitmap->writeback_daemon->tsk));
                        spin_unlock_irq(&bitmap->write_lock);
                } else
                        wait_event(bitmap->mddev->sb_wait,
                                   atomic_read(&bitmap->mddev->pending_writes)==0);
        }
        return 0;
}

static void bitmap_set_memory_bits(struct bitmap *bitmap, sector_t offset);
/* * bitmap_init_from_disk -- called at bitmap_create time to initialize
 * the in-memory bitmap from the on-disk bitmap -- also, sets up the
 * memory mapping of the bitmap file
 * Special cases:
 *   if there's no bitmap file, or if the bitmap file had been
 *   previously kicked from the array, we mark all the bits as
 *   1's in order to cause a full resync.
 */
static int bitmap_init_from_disk(struct bitmap *bitmap)
{
        unsigned long i, chunks, index, oldindex, bit;
        struct page *page = NULL, *oldpage = NULL;
        unsigned long num_pages, bit_cnt = 0;
        struct file *file;
        unsigned long bytes, offset, dummy;
        int outofdate;
        int ret = -ENOSPC;

        chunks = bitmap->chunks;
        file = bitmap->file;

        BUG_ON(!file && !bitmap->offset);

#ifdef INJECT_FAULTS_3
        outofdate = 1;
#else
        outofdate = bitmap->flags & BITMAP_STALE;
#endif
        if (outofdate)
                printk(KERN_INFO "%s: bitmap file is out of date, doing full "
                        "recovery\n", bmname(bitmap));

        bytes = (chunks + 7) / 8;

        num_pages = (bytes + sizeof(bitmap_super_t) + PAGE_SIZE - 1) / PAGE_SIZE;

        if (file && i_size_read(file->f_mapping->host) < bytes + sizeof(bitmap_super_t)) {
                printk(KERN_INFO "%s: bitmap file too short %lu < %lu\n",
                        bmname(bitmap),
                        (unsigned long) i_size_read(file->f_mapping->host),
                        bytes + sizeof(bitmap_super_t));
                goto out;
        }

        ret = -ENOMEM;

        bitmap->filemap = kmalloc(sizeof(struct page *) * num_pages, GFP_KERNEL);
        if (!bitmap->filemap)
                goto out;

        bitmap->filemap_attr = kmalloc(sizeof(long) * num_pages, GFP_KERNEL);
        if (!bitmap->filemap_attr)
                goto out;

        memset(bitmap->filemap_attr, 0, sizeof(long) * num_pages);

        oldindex = ~0L;

        for (i = 0; i < chunks; i++) {
                index = file_page_index(i);
                bit = file_page_offset(i);
                if (index != oldindex) { /* this is a new page, read it in */
                        /* unmap the old page, we're done with it */
                        if (oldpage != NULL)
                                kunmap(oldpage);
                        if (index == 0) {
                                /*
                                 * if we're here then the superblock page
                                 * contains some bits (PAGE_SIZE != sizeof sb)
                                 * we've already read it in, so just use it
                                 */
                                page = bitmap->sb_page;
                                offset = sizeof(bitmap_super_t);
                        } else if (file) {
                                page = read_page(file, index, &dummy);
                                offset = 0;
                        } else {
                                page = read_sb_page(bitmap->mddev, bitmap->offset, index);
                                offset = 0;
                        }
                        if (IS_ERR(page)) { /* read error */
                                ret = PTR_ERR(page);
                                goto out;
                        }

                        oldindex = index;
                        oldpage = page;
                        kmap(page);

                        if (outofdate) {
                                /*
                                 * if bitmap is out of date, dirty the
                                 * whole page and write it out
                                 */
                                memset(page_address(page) + offset, 0xff,
                                        PAGE_SIZE - offset);
                                ret = write_page(bitmap, page, 1);
                                if (ret) {
                                        kunmap(page);
                                        /* release, page not in filemap yet */
                                        page_cache_release(page);
                                        goto out;
                                }
                        }

                        bitmap->filemap[bitmap->file_pages++] = page;
                }
                if (test_bit(bit, page_address(page))) {
                        /* if the disk bit is set, set the memory bit */
                        bitmap_set_memory_bits(bitmap, i << CHUNK_BLOCK_SHIFT(bitmap));
                        bit_cnt++;
                }
        }

        /* everything went OK */
        ret = 0;
        bitmap_mask_state(bitmap, BITMAP_STALE, MASK_UNSET);

        if (page) /* unmap the last page */
                kunmap(page);

        if (bit_cnt) { /* Kick recovery if any bits were set */
                set_bit(MD_RECOVERY_NEEDED, &bitmap->mddev->recovery);
                md_wakeup_thread(bitmap->mddev->thread);
        }

out:
        printk(KERN_INFO "%s: bitmap initialized from disk: "
                "read %lu/%lu pages, set %lu bits, status: %d\n",
                bmname(bitmap), bitmap->file_pages, num_pages, bit_cnt, ret);

        return ret;
}

void bitmap_write_all(struct bitmap *bitmap)
{
        /* We don't actually write all bitmap blocks here,
         * just flag them as needing to be written
         */

        unsigned long chunks = bitmap->chunks;
        unsigned long bytes = (chunks+7)/8 + sizeof(bitmap_super_t);
        unsigned long num_pages = (bytes + PAGE_SIZE-1) / PAGE_SIZE;
        while (num_pages--)
                bitmap->filemap_attr[num_pages] |= BITMAP_PAGE_NEEDWRITE;
}


static void bitmap_count_page(struct bitmap *bitmap, sector_t offset, int inc)
{
        sector_t chunk = offset >> CHUNK_BLOCK_SHIFT(bitmap);
        unsigned long page = chunk >> PAGE_COUNTER_SHIFT;
        bitmap->bp[page].count += inc;
/*
        if (page == 0) printk("count page 0, offset %llu: %d gives %d\n",
                              (unsigned long long)offset, inc, bitmap->bp[page].count);
*/
        bitmap_checkfree(bitmap, page);
}
static bitmap_counter_t *bitmap_get_counter(struct bitmap *bitmap,
                                            sector_t offset, int *blocks,
                                            int create);

/*
 * bitmap daemon -- periodically wakes up to clean bits and flush pages
 *                      out to disk
 */

int bitmap_daemon_work(struct bitmap *bitmap)
{
        unsigned long j;
        unsigned long flags;
        struct page *page = NULL, *lastpage = NULL;
        int err = 0;
        int blocks;
        int attr;

        if (bitmap == NULL)
                return 0;
        if (time_before(jiffies, bitmap->daemon_lastrun + bitmap->daemon_sleep*HZ))
                return 0;
        bitmap->daemon_lastrun = jiffies;

        for (j = 0; j < bitmap->chunks; j++) {
                bitmap_counter_t *bmc;
                spin_lock_irqsave(&bitmap->lock, flags);
                if (!bitmap->filemap) {
                        /* error or shutdown */
                        spin_unlock_irqrestore(&bitmap->lock, flags);
                        break;
                }

                page = filemap_get_page(bitmap, j);

                if (page != lastpage) {
                        /* skip this page unless it's marked as needing cleaning */
                        if (!((attr=get_page_attr(bitmap, page)) & BITMAP_PAGE_CLEAN)) {
                                if (attr & BITMAP_PAGE_NEEDWRITE) {
                                        page_cache_get(page);
                                        clear_page_attr(bitmap, page, BITMAP_PAGE_NEEDWRITE);
                                }
                                spin_unlock_irqrestore(&bitmap->lock, flags);
                                if (attr & BITMAP_PAGE_NEEDWRITE) {
                                        switch (write_page(bitmap, page, 0)) {
                                        case -EAGAIN:
                                                set_page_attr(bitmap, page, BITMAP_PAGE_NEEDWRITE);
                                                break;
                                        case 0:
                                                break;
                                        default:
                                                bitmap_file_kick(bitmap);
                                        }
                                        page_cache_release(page);
                                }
                                continue;
                        }

                        /* grab the new page, sync and release the old */
                        page_cache_get(page);
                        if (lastpage != NULL) {
                                if (get_page_attr(bitmap, lastpage) & BITMAP_PAGE_NEEDWRITE) {
                                        clear_page_attr(bitmap, lastpage, BITMAP_PAGE_NEEDWRITE);
                                        spin_unlock_irqrestore(&bitmap->lock, flags);
                                        err = write_page(bitmap, lastpage, 0);
                                        if (err == -EAGAIN) {
                                                err = 0;
                                                set_page_attr(bitmap, lastpage, BITMAP_PAGE_NEEDWRITE);
                                        }
                                } else {
                                        set_page_attr(bitmap, lastpage, BITMAP_PAGE_NEEDWRITE);
                                        spin_unlock_irqrestore(&bitmap->lock, flags);
                                }
                                kunmap(lastpage);
                                page_cache_release(lastpage);
                                if (err)
                                        bitmap_file_kick(bitmap);
                        } else
                                spin_unlock_irqrestore(&bitmap->lock, flags);
                        lastpage = page;
                        kmap(page);
/*
                        printk("bitmap clean at page %lu\n", j);
*/
                        spin_lock_irqsave(&bitmap->lock, flags);
                        clear_page_attr(bitmap, page, BITMAP_PAGE_CLEAN);
                }
                bmc = bitmap_get_counter(bitmap, j << CHUNK_BLOCK_SHIFT(bitmap),
                                        &blocks, 0);
                if (bmc) {
/*
  if (j < 100) printk("bitmap: j=%lu, *bmc = 0x%x\n", j, *bmc);
*/
                        if (*bmc == 2) {
                                *bmc=1; /* maybe clear the bit next time */
                                set_page_attr(bitmap, page, BITMAP_PAGE_CLEAN);
                        } else if (*bmc == 1) {
                                /* we can clear the bit */
                                *bmc = 0;
                                bitmap_count_page(bitmap, j << CHUNK_BLOCK_SHIFT(bitmap),
                                                  -1);

                                /* clear the bit */
                                clear_bit(file_page_offset(j), page_address(page));
                        }
                }
                spin_unlock_irqrestore(&bitmap->lock, flags);
        }

        /* now sync the final page */
        if (lastpage != NULL) {
                kunmap(lastpage);
                spin_lock_irqsave(&bitmap->lock, flags);
                if (get_page_attr(bitmap, lastpage) &BITMAP_PAGE_NEEDWRITE) {
                        clear_page_attr(bitmap, lastpage, BITMAP_PAGE_NEEDWRITE);
                        spin_unlock_irqrestore(&bitmap->lock, flags);
                        err = write_page(bitmap, lastpage, 0);
                        if (err == -EAGAIN) {
                                set_page_attr(bitmap, lastpage, BITMAP_PAGE_NEEDWRITE);
                                err = 0;
                        }
                } else {
                        set_page_attr(bitmap, lastpage, BITMAP_PAGE_NEEDWRITE);
                        spin_unlock_irqrestore(&bitmap->lock, flags);
                }

                page_cache_release(lastpage);
        }

        return err;
}

static void daemon_exit(struct bitmap *bitmap, mdk_thread_t **daemon)
{
        mdk_thread_t *dmn;
        unsigned long flags;

        /* if no one is waiting on us, we'll free the md thread struct
         * and exit, otherwise we let the waiter clean things up */
        spin_lock_irqsave(&bitmap->lock, flags);
        if ((dmn = *daemon)) { /* no one is waiting, cleanup and exit */
                *daemon = NULL;
                spin_unlock_irqrestore(&bitmap->lock, flags);
                kfree(dmn);
                complete_and_exit(NULL, 0); /* do_exit not exported */
        }
        spin_unlock_irqrestore(&bitmap->lock, flags);
}

static void bitmap_writeback_daemon(mddev_t *mddev)
{
        struct bitmap *bitmap = mddev->bitmap;
        struct page *page;
        struct page_list *item;
        int err = 0;

        if (signal_pending(current)) {
                printk(KERN_INFO
                       "%s: bitmap writeback daemon got signal, exiting...\n",
                       bmname(bitmap));
                err = -EINTR;
                goto out;
        }

        PRINTK("%s: bitmap writeback daemon woke up...\n", bmname(bitmap));
        /* wait on bitmap page writebacks */
        while ((item = dequeue_page(bitmap))) {
                page = item->page;
                mempool_free(item, bitmap->write_pool);
                PRINTK("wait on page writeback: %p\n", page);
                wait_on_page_writeback(page);
                PRINTK("finished page writeback: %p\n", page);

                err = PageError(page);
                page_cache_release(page);
                if (err) {
                        printk(KERN_WARNING "%s: bitmap file writeback "
                               "failed (page %lu): %d\n",
                               bmname(bitmap), page->index, err);
                        bitmap_file_kick(bitmap);
                        goto out;
                }
        }
 out:
        wake_up(&bitmap->write_wait);
        if (err) {
                printk(KERN_INFO "%s: bitmap writeback daemon exiting (%d)\n",
                       bmname(bitmap), err);
                daemon_exit(bitmap, &bitmap->writeback_daemon);
        }
}

static int bitmap_start_daemon(struct bitmap *bitmap, mdk_thread_t **ptr,
                                void (*func)(mddev_t *), char *name)
{
        mdk_thread_t *daemon;
        unsigned long flags;
        char namebuf[32];

        spin_lock_irqsave(&bitmap->lock, flags);
        *ptr = NULL;

        if (!bitmap->file) /* no need for daemon if there's no backing file */
                goto out_unlock;

        spin_unlock_irqrestore(&bitmap->lock, flags);

#ifdef INJECT_FATAL_FAULT_2
        daemon = NULL;
#else
        sprintf(namebuf, "%%s_%s", name);
        daemon = md_register_thread(func, bitmap->mddev, namebuf);
#endif
        if (!daemon) {
                printk(KERN_ERR "%s: failed to start bitmap daemon\n",
                        bmname(bitmap));
                return -ECHILD;
        }

        spin_lock_irqsave(&bitmap->lock, flags);
        *ptr = daemon;

        md_wakeup_thread(daemon); /* start it running */

        PRINTK("%s: %s daemon (pid %d) started...\n",
                bmname(bitmap), name, daemon->tsk->pid);
out_unlock:
        spin_unlock_irqrestore(&bitmap->lock, flags);
        return 0;
}

static int bitmap_start_daemons(struct bitmap *bitmap)
{
        int err = bitmap_start_daemon(bitmap, &bitmap->writeback_daemon,
                                        bitmap_writeback_daemon, "bitmap_wb");
        return err;
}

static void bitmap_stop_daemon(struct bitmap *bitmap, mdk_thread_t **ptr)
{
        mdk_thread_t *daemon;
        unsigned long flags;

        spin_lock_irqsave(&bitmap->lock, flags);
        daemon = *ptr;
        *ptr = NULL;
        spin_unlock_irqrestore(&bitmap->lock, flags);
        if (daemon)
                md_unregister_thread(daemon); /* destroy the thread */
}

static void bitmap_stop_daemons(struct bitmap *bitmap)
{
        /* the daemons can't stop themselves... they'll just exit instead... */
        if (bitmap->writeback_daemon &&
            current->pid != bitmap->writeback_daemon->tsk->pid)
                bitmap_stop_daemon(bitmap, &bitmap->writeback_daemon);
}

static bitmap_counter_t *bitmap_get_counter(struct bitmap *bitmap,
                                            sector_t offset, int *blocks,
                                            int create)
{
        /* If 'create', we might release the lock and reclaim it.
         * The lock must have been taken with interrupts enabled.
         * If !create, we don't release the lock.
         */
        sector_t chunk = offset >> CHUNK_BLOCK_SHIFT(bitmap);
        unsigned long page = chunk >> PAGE_COUNTER_SHIFT;
        unsigned long pageoff = (chunk & PAGE_COUNTER_MASK) << COUNTER_BYTE_SHIFT;
        sector_t csize;

        if (bitmap_checkpage(bitmap, page, create) < 0) {
                csize = ((sector_t)1) << (CHUNK_BLOCK_SHIFT(bitmap));
                *blocks = csize - (offset & (csize- 1));
                return NULL;
        }
        /* now locked ... */

        if (bitmap->bp[page].hijacked) { /* hijacked pointer */
                /* should we use the first or second counter field
                 * of the hijacked pointer? */
                int hi = (pageoff > PAGE_COUNTER_MASK);
                csize = ((sector_t)1) << (CHUNK_BLOCK_SHIFT(bitmap) +
                                          PAGE_COUNTER_SHIFT - 1);
                *blocks = csize - (offset & (csize- 1));
                return  &((bitmap_counter_t *)
                          &bitmap->bp[page].map)[hi];
        } else { /* page is allocated */
                csize = ((sector_t)1) << (CHUNK_BLOCK_SHIFT(bitmap));
                *blocks = csize - (offset & (csize- 1));
                return (bitmap_counter_t *)
                        &(bitmap->bp[page].map[pageoff]);
        }
}

int bitmap_startwrite(struct bitmap *bitmap, sector_t offset, unsigned long sectors)
{
        if (!bitmap) return 0;
        while (sectors) {
                int blocks;
                bitmap_counter_t *bmc;

                spin_lock_irq(&bitmap->lock);
                bmc = bitmap_get_counter(bitmap, offset, &blocks, 1);
                if (!bmc) {
                        spin_unlock_irq(&bitmap->lock);
                        return 0;
                }

                switch(*bmc) {
                case 0:
                        bitmap_file_set_bit(bitmap, offset);
                        bitmap_count_page(bitmap,offset, 1);
                        blk_plug_device(bitmap->mddev->queue);
                        /* fall through */
                case 1:
                        *bmc = 2;
                }
                if ((*bmc & COUNTER_MAX) == COUNTER_MAX) BUG();
                (*bmc)++;

                spin_unlock_irq(&bitmap->lock);

                offset += blocks;
                if (sectors > blocks)
                        sectors -= blocks;
                else sectors = 0;
        }
        return 0;
}

void bitmap_endwrite(struct bitmap *bitmap, sector_t offset, unsigned long sectors,
                     int success)
{
        if (!bitmap) return;
        while (sectors) {
                int blocks;
                unsigned long flags;
                bitmap_counter_t *bmc;

                spin_lock_irqsave(&bitmap->lock, flags);
                bmc = bitmap_get_counter(bitmap, offset, &blocks, 0);
                if (!bmc) {
                        spin_unlock_irqrestore(&bitmap->lock, flags);
                        return;
                }

                if (!success && ! (*bmc & NEEDED_MASK))
                        *bmc |= NEEDED_MASK;

                (*bmc)--;
                if (*bmc <= 2) {
                        set_page_attr(bitmap,
                                      filemap_get_page(bitmap, offset >> CHUNK_BLOCK_SHIFT(bitmap)),
                                      BITMAP_PAGE_CLEAN);
                }
                spin_unlock_irqrestore(&bitmap->lock, flags);
                offset += blocks;
                if (sectors > blocks)
                        sectors -= blocks;
                else sectors = 0;
        }
}

int bitmap_start_sync(struct bitmap *bitmap, sector_t offset, int *blocks,
                        int degraded)
{
        bitmap_counter_t *bmc;
        int rv;
        if (bitmap == NULL) {/* FIXME or bitmap set as 'failed' */
                *blocks = 1024;
                return 1; /* always resync if no bitmap */
        }
        spin_lock_irq(&bitmap->lock);
        bmc = bitmap_get_counter(bitmap, offset, blocks, 0);
        rv = 0;
        if (bmc) {
                /* locked */
                if (RESYNC(*bmc))
                        rv = 1;
                else if (NEEDED(*bmc)) {
                        rv = 1;
                        if (!degraded) { /* don't set/clear bits if degraded */
                                *bmc |= RESYNC_MASK;
                                *bmc &= ~NEEDED_MASK;
                        }
                }
        }
        spin_unlock_irq(&bitmap->lock);
        return rv;
}

void bitmap_end_sync(struct bitmap *bitmap, sector_t offset, int *blocks, int aborted)
{
        bitmap_counter_t *bmc;
        unsigned long flags;
/*
        if (offset == 0) printk("bitmap_end_sync 0 (%d)\n", aborted);
*/      if (bitmap == NULL) {
                *blocks = 1024;
                return;
        }
        spin_lock_irqsave(&bitmap->lock, flags);
        bmc = bitmap_get_counter(bitmap, offset, blocks, 0);
        if (bmc == NULL)
                goto unlock;
        /* locked */
/*
        if (offset == 0) printk("bitmap_end sync found 0x%x, blocks %d\n", *bmc, *blocks);
*/
        if (RESYNC(*bmc)) {
                *bmc &= ~RESYNC_MASK;

                if (!NEEDED(*bmc) && aborted)
                        *bmc |= NEEDED_MASK;
                else {
                        if (*bmc <= 2) {
                                set_page_attr(bitmap,
                                              filemap_get_page(bitmap, offset >> CHUNK_BLOCK_SHIFT(bitmap)),
                                              BITMAP_PAGE_CLEAN);
                        }
                }
        }
 unlock:
        spin_unlock_irqrestore(&bitmap->lock, flags);
}

void bitmap_close_sync(struct bitmap *bitmap)
{
        /* Sync has finished, and any bitmap chunks that weren't synced
         * properly have been aborted.  It remains to us to clear the
         * RESYNC bit wherever it is still on
         */
        sector_t sector = 0;
        int blocks;
        if (!bitmap) return;
        while (sector < bitmap->mddev->resync_max_sectors) {
                bitmap_end_sync(bitmap, sector, &blocks, 0);
/*
                if (sector < 500) printk("bitmap_close_sync: sec %llu blks %d\n",
                                         (unsigned long long)sector, blocks);
*/              sector += blocks;
        }
}

static void bitmap_set_memory_bits(struct bitmap *bitmap, sector_t offset)
{
        /* For each chunk covered by any of these sectors, set the
         * counter to 1 and set resync_needed.  They should all
         * be 0 at this point
         */

        int secs;
        bitmap_counter_t *bmc;
        spin_lock_irq(&bitmap->lock);
        bmc = bitmap_get_counter(bitmap, offset, &secs, 1);
        if (!bmc) {
                spin_unlock_irq(&bitmap->lock);
                return;
        }
        if (! *bmc) {
                struct page *page;
                *bmc = 1 | NEEDED_MASK;
                bitmap_count_page(bitmap, offset, 1);
                page = filemap_get_page(bitmap, offset >> CHUNK_BLOCK_SHIFT(bitmap));
                set_page_attr(bitmap, page, BITMAP_PAGE_CLEAN);
        }
        spin_unlock_irq(&bitmap->lock);

}

/*
 * free memory that was allocated
 */
void bitmap_destroy(mddev_t *mddev)
{
        unsigned long k, pages;
        struct bitmap_page *bp;
        struct bitmap *bitmap = mddev->bitmap;

        if (!bitmap) /* there was no bitmap */
                return;

        mddev->bitmap = NULL; /* disconnect from the md device */

        /* release the bitmap file and kill the daemon */
        bitmap_file_put(bitmap);

        bp = bitmap->bp;
        pages = bitmap->pages;

        /* free all allocated memory */

        mempool_destroy(bitmap->write_pool);

        if (bp) /* deallocate the page memory */
                for (k = 0; k < pages; k++)
                        if (bp[k].map && !bp[k].hijacked)
                                kfree(bp[k].map);
        kfree(bp);
        kfree(bitmap);
}

/*
 * initialize the bitmap structure
 * if this returns an error, bitmap_destroy must be called to do clean up
 */
int bitmap_create(mddev_t *mddev)
{
        struct bitmap *bitmap;
        unsigned long blocks = mddev->resync_max_sectors;
        unsigned long chunks;
        unsigned long pages;
        struct file *file = mddev->bitmap_file;
        int err;

        BUG_ON(sizeof(bitmap_super_t) != 256);

        if (!file && !mddev->bitmap_offset) /* bitmap disabled, nothing to do */
                return 0;

        BUG_ON(file && mddev->bitmap_offset);

        bitmap = kmalloc(sizeof(*bitmap), GFP_KERNEL);
        if (!bitmap)
                return -ENOMEM;

        memset(bitmap, 0, sizeof(*bitmap));

        spin_lock_init(&bitmap->lock);
        bitmap->mddev = mddev;
        mddev->bitmap = bitmap;

        spin_lock_init(&bitmap->write_lock);
        INIT_LIST_HEAD(&bitmap->complete_pages);
        init_waitqueue_head(&bitmap->write_wait);
        bitmap->write_pool = mempool_create(WRITE_POOL_SIZE, write_pool_alloc,
                                write_pool_free, NULL);
        if (!bitmap->write_pool)
                return -ENOMEM;

        bitmap->file = file;
        bitmap->offset = mddev->bitmap_offset;
        if (file) get_file(file);
        /* read superblock from bitmap file (this sets bitmap->chunksize) */
        err = bitmap_read_sb(bitmap);
        if (err)
                return err;

        bitmap->chunkshift = find_first_bit(&bitmap->chunksize,
                                        sizeof(bitmap->chunksize));

        /* now that chunksize and chunkshift are set, we can use these macros */
        chunks = (blocks + CHUNK_BLOCK_RATIO(bitmap) - 1) /
                        CHUNK_BLOCK_RATIO(bitmap);
        pages = (chunks + PAGE_COUNTER_RATIO - 1) / PAGE_COUNTER_RATIO;

        BUG_ON(!pages);

        bitmap->chunks = chunks;
        bitmap->pages = pages;
        bitmap->missing_pages = pages;
        bitmap->counter_bits = COUNTER_BITS;

        bitmap->syncchunk = ~0UL;

#ifdef INJECT_FATAL_FAULT_1
        bitmap->bp = NULL;
#else
        bitmap->bp = kmalloc(pages * sizeof(*bitmap->bp), GFP_KERNEL);
#endif
        if (!bitmap->bp)
                return -ENOMEM;
        memset(bitmap->bp, 0, pages * sizeof(*bitmap->bp));

        bitmap->flags |= BITMAP_ACTIVE;

        /* now that we have some pages available, initialize the in-memory
         * bitmap from the on-disk bitmap */
        err = bitmap_init_from_disk(bitmap);

        if (err)
                return err;

        printk(KERN_INFO "created bitmap (%lu pages) for device %s\n",
                pages, bmname(bitmap));

        /* kick off the bitmap daemons */
        err = bitmap_start_daemons(bitmap);
        if (err)
                return err;
        return bitmap_update_sb(bitmap);
}

/* the bitmap API -- for raid personalities */
EXPORT_SYMBOL(bitmap_startwrite);
EXPORT_SYMBOL(bitmap_endwrite);
EXPORT_SYMBOL(bitmap_start_sync);
EXPORT_SYMBOL(bitmap_end_sync);
EXPORT_SYMBOL(bitmap_unplug);
EXPORT_SYMBOL(bitmap_close_sync);
EXPORT_SYMBOL(bitmap_daemon_work);