bitmap.c

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/*
 * bitmap.c two-level bitmap (C) Peter T. Breuer ([email protected]) 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
 */

/*
 * Still to do:
 *
 * flush after percent set rather than just time based. (maybe both).
 */

#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/init.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/seq_file.h>
#include "md.h"
#include "bitmap.h"

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

/*
 * 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_counts *bitmap,
                unsigned long page, int create)
__releases(bitmap->lock)
__acquires(bitmap->lock)
{
    unsigned char *mappage;

    if (page >= bitmap->pages) {
        /* This can happen if bitmap_start_sync goes beyond
         * End-of-device while looking for a whole page.
         * It is harmless.
         */
        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;

    /* this page has not been allocated yet */

    spin_unlock_irq(&bitmap->lock);
    mappage = kzalloc(PAGE_SIZE, GFP_NOIO);
    spin_lock_irq(&bitmap->lock);

    if (mappage == NULL) {
        pr_debug("md/bitmap: map page allocation failed, hijacking\n");
        /* failed - set the hijacked flag so that we can use the
         * pointer as a counter */
        if (!bitmap->bp[page].map)
            bitmap->bp[page].hijacked = 1;
    } else if (bitmap->bp[page].map ||
           bitmap->bp[page].hijacked) {
        /* somebody beat us to getting the page */
        kfree(mappage);
        return 0;
    } else {

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

        bitmap->bp[page].map = mappage;
        bitmap->missing_pages--;
    }
    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 void bitmap_checkfree(struct bitmap_counts *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;
    } else {
        /* normal case, free the page */
        ptr = bitmap->bp[page].map;
        bitmap->bp[page].map = NULL;
        bitmap->missing_pages++;
        kfree(ptr);
    }
}

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

/*
 * basic page I/O operations
 */

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

    struct md_rdev *rdev;
    sector_t target;

    rdev_for_each(rdev, mddev) {
        if (! test_bit(In_sync, &rdev->flags)
            || test_bit(Faulty, &rdev->flags))
            continue;

        target = offset + index * (PAGE_SIZE/512);

        if (sync_page_io(rdev, target,
                 roundup(size, bdev_logical_block_size(rdev->bdev)),
                 page, READ, true)) {
            page->index = index;
            return 0;
        }
    }
    return -EIO;
}

static struct md_rdev *next_active_rdev(struct md_rdev *rdev, struct mddev *mddev)
{
    /* Iterate the disks of an mddev, using rcu to protect access to the
     * linked list, and raising the refcount of devices we return to ensure
     * they don't disappear while in use.
     * As devices are only added or removed when raid_disk is < 0 and
     * nr_pending is 0 and In_sync is clear, the entries we return will
     * still be in the same position on the list when we re-enter
     * list_for_each_entry_continue_rcu.
     */
    rcu_read_lock();
    if (rdev == NULL)
        /* start at the beginning */
        rdev = list_entry_rcu(&mddev->disks, struct md_rdev, same_set);
    else {
        /* release the previous rdev and start from there. */
        rdev_dec_pending(rdev, mddev);
    }
    list_for_each_entry_continue_rcu(rdev, &mddev->disks, same_set) {
        if (rdev->raid_disk >= 0 &&
            !test_bit(Faulty, &rdev->flags)) {
            /* this is a usable devices */
            atomic_inc(&rdev->nr_pending);
            rcu_read_unlock();
            return rdev;
        }
    }
    rcu_read_unlock();
    return NULL;
}

static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
{
    struct md_rdev *rdev = NULL;
    struct block_device *bdev;
    struct mddev *mddev = bitmap->mddev;
    struct bitmap_storage *store = &bitmap->storage;

    while ((rdev = next_active_rdev(rdev, mddev)) != NULL) {
        int size = PAGE_SIZE;
        loff_t offset = mddev->bitmap_info.offset;

        bdev = (rdev->meta_bdev) ? rdev->meta_bdev : rdev->bdev;

        if (page->index == store->file_pages-1) {
            int last_page_size = store->bytes & (PAGE_SIZE-1);
            if (last_page_size == 0)
                last_page_size = PAGE_SIZE;
            size = roundup(last_page_size,
                       bdev_logical_block_size(bdev));
        }
        /* Just make sure we aren't corrupting data or
         * metadata
         */
        if (mddev->external) {
            /* Bitmap could be anywhere. */
            if (rdev->sb_start + offset + (page->index
                               * (PAGE_SIZE/512))
                > rdev->data_offset
                &&
                rdev->sb_start + offset
                < (rdev->data_offset + mddev->dev_sectors
                 + (PAGE_SIZE/512)))
                goto bad_alignment;
        } else if (offset < 0) {
            /* DATA  BITMAP METADATA  */
            if (offset
                + (long)(page->index * (PAGE_SIZE/512))
                + size/512 > 0)
                /* bitmap runs in to metadata */
                goto bad_alignment;
            if (rdev->data_offset + mddev->dev_sectors
                > rdev->sb_start + offset)
                /* data runs in to bitmap */
                goto bad_alignment;
        } else if (rdev->sb_start < rdev->data_offset) {
            /* METADATA BITMAP DATA */
            if (rdev->sb_start
                + offset
                + page->index*(PAGE_SIZE/512) + size/512
                > rdev->data_offset)
                /* bitmap runs in to data */
                goto bad_alignment;
        } else {
            /* DATA METADATA BITMAP - no problems */
        }
        md_super_write(mddev, rdev,
                   rdev->sb_start + offset
                   + page->index * (PAGE_SIZE/512),
                   size,
                   page);
    }

    if (wait)
        md_super_wait(mddev);
    return 0;

 bad_alignment:
    return -EINVAL;
}

static void bitmap_file_kick(struct bitmap *bitmap);
/*
 * write out a page to a file
 */
static void write_page(struct bitmap *bitmap, struct page *page, int wait)
{
    struct buffer_head *bh;

    if (bitmap->storage.file == NULL) {
        switch (write_sb_page(bitmap, page, wait)) {
        case -EINVAL:
            set_bit(BITMAP_WRITE_ERROR, &bitmap->flags);
        }
    } else {

        bh = page_buffers(page);

        while (bh && bh->b_blocknr) {
            atomic_inc(&bitmap->pending_writes);
            set_buffer_locked(bh);
            set_buffer_mapped(bh);
            submit_bh(WRITE | REQ_SYNC, bh);
            bh = bh->b_this_page;
        }

        if (wait)
            wait_event(bitmap->write_wait,
                   atomic_read(&bitmap->pending_writes)==0);
    }
    if (test_bit(BITMAP_WRITE_ERROR, &bitmap->flags))
        bitmap_file_kick(bitmap);
}

static void end_bitmap_write(struct buffer_head *bh, int uptodate)
{
    struct bitmap *bitmap = bh->b_private;

    if (!uptodate)
        set_bit(BITMAP_WRITE_ERROR, &bitmap->flags);
    if (atomic_dec_and_test(&bitmap->pending_writes))
        wake_up(&bitmap->write_wait);
}

/* copied from buffer.c */
static void
__clear_page_buffers(struct page *page)
{
    ClearPagePrivate(page);
    set_page_private(page, 0);
    page_cache_release(page);
}
static void free_buffers(struct page *page)
{
    struct buffer_head *bh;

    if (!PagePrivate(page))
        return;

    bh = page_buffers(page);
    while (bh) {
        struct buffer_head *next = bh->b_this_page;
        free_buffer_head(bh);
        bh = next;
    }
    __clear_page_buffers(page);
    put_page(page);
}

/* read a page from a file.
 * We both read the page, and attach buffers to the page to record the
 * address of each block (using bmap).  These addresses will be used
 * to write the block later, completely bypassing the filesystem.
 * This usage is similar to how swap files are handled, and allows us
 * to write to a file with no concerns of memory allocation failing.
 */
static int read_page(struct file *file, unsigned long index,
             struct bitmap *bitmap,
             unsigned long count,
             struct page *page)
{
    int ret = 0;
    struct inode *inode = file->f_path.dentry->d_inode;
    struct buffer_head *bh;
    sector_t block;

    pr_debug("read bitmap file (%dB @ %llu)\n", (int)PAGE_SIZE,
         (unsigned long long)index << PAGE_SHIFT);

    bh = alloc_page_buffers(page, 1<<inode->i_blkbits, 0);
    if (!bh) {
        ret = -ENOMEM;
        goto out;
    }
    attach_page_buffers(page, bh);
    block = index << (PAGE_SHIFT - inode->i_blkbits);
    while (bh) {
        if (count == 0)
            bh->b_blocknr = 0;
        else {
            bh->b_blocknr = bmap(inode, block);
            if (bh->b_blocknr == 0) {
                /* Cannot use this file! */
                ret = -EINVAL;
                goto out;
            }
            bh->b_bdev = inode->i_sb->s_bdev;
            if (count < (1<<inode->i_blkbits))
                count = 0;
            else
                count -= (1<<inode->i_blkbits);

            bh->b_end_io = end_bitmap_write;
            bh->b_private = bitmap;
            atomic_inc(&bitmap->pending_writes);
            set_buffer_locked(bh);
            set_buffer_mapped(bh);
            submit_bh(READ, bh);
        }
        block++;
        bh = bh->b_this_page;
    }
    page->index = index;

    wait_event(bitmap->write_wait,
           atomic_read(&bitmap->pending_writes)==0);
    if (test_bit(BITMAP_WRITE_ERROR, &bitmap->flags))
        ret = -EIO;
out:
    if (ret)
        printk(KERN_ALERT "md: bitmap read error: (%dB @ %llu): %d\n",
            (int)PAGE_SIZE,
            (unsigned long long)index << PAGE_SHIFT,
            ret);
    return ret;
}

/*
 * bitmap file superblock operations
 */

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

    if (!bitmap || !bitmap->mddev) /* no bitmap for this array */
        return;
    if (bitmap->mddev->bitmap_info.external)
        return;
    if (!bitmap->storage.sb_page) /* no superblock */
        return;
    sb = kmap_atomic(bitmap->storage.sb_page);
    sb->events = cpu_to_le64(bitmap->mddev->events);
    if (bitmap->mddev->events < bitmap->events_cleared)
        /* rocking back to read-only */
        bitmap->events_cleared = bitmap->mddev->events;
    sb->events_cleared = cpu_to_le64(bitmap->events_cleared);
    sb->state = cpu_to_le32(bitmap->flags);
    /* Just in case these have been changed via sysfs: */
    sb->daemon_sleep = cpu_to_le32(bitmap->mddev->bitmap_info.daemon_sleep/HZ);
    sb->write_behind = cpu_to_le32(bitmap->mddev->bitmap_info.max_write_behind);
    /* This might have been changed by a reshape */
    sb->sync_size = cpu_to_le64(bitmap->mddev->resync_max_sectors);
    sb->chunksize = cpu_to_le32(bitmap->mddev->bitmap_info.chunksize);
    sb->sectors_reserved = cpu_to_le32(bitmap->mddev->
                       bitmap_info.space);
    kunmap_atomic(sb);
    write_page(bitmap, bitmap->storage.sb_page, 1);
}

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

    if (!bitmap || !bitmap->storage.sb_page)
        return;
    sb = kmap_atomic(bitmap->storage.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);
    printk(KERN_DEBUG "max write behind: %d\n", le32_to_cpu(sb->write_behind));
    kunmap_atomic(sb);
}

/*
 * bitmap_new_disk_sb
 * @bitmap
 *
 * This function is somewhat the reverse of bitmap_read_sb.  bitmap_read_sb
 * reads and verifies the on-disk bitmap superblock and populates bitmap_info.
 * This function verifies 'bitmap_info' and populates the on-disk bitmap
 * structure, which is to be written to disk.
 *
 * Returns: 0 on success, -Exxx on error
 */
static int bitmap_new_disk_sb(struct bitmap *bitmap)
{
    bitmap_super_t *sb;
    unsigned long chunksize, daemon_sleep, write_behind;

    bitmap->storage.sb_page = alloc_page(GFP_KERNEL);
    if (bitmap->storage.sb_page == NULL)
        return -ENOMEM;
    bitmap->storage.sb_page->index = 0;

    sb = kmap_atomic(bitmap->storage.sb_page);

    sb->magic = cpu_to_le32(BITMAP_MAGIC);
    sb->version = cpu_to_le32(BITMAP_MAJOR_HI);

    chunksize = bitmap->mddev->bitmap_info.chunksize;
    BUG_ON(!chunksize);
    if (!is_power_of_2(chunksize)) {
        kunmap_atomic(sb);
        printk(KERN_ERR "bitmap chunksize not a power of 2\n");
        return -EINVAL;
    }
    sb->chunksize = cpu_to_le32(chunksize);

    daemon_sleep = bitmap->mddev->bitmap_info.daemon_sleep;
    if (!daemon_sleep ||
        (daemon_sleep < 1) || (daemon_sleep > MAX_SCHEDULE_TIMEOUT)) {
        printk(KERN_INFO "Choosing daemon_sleep default (5 sec)\n");
        daemon_sleep = 5 * HZ;
    }
    sb->daemon_sleep = cpu_to_le32(daemon_sleep);
    bitmap->mddev->bitmap_info.daemon_sleep = daemon_sleep;

    /*
     * FIXME: write_behind for RAID1.  If not specified, what
     * is a good choice?  We choose COUNTER_MAX / 2 arbitrarily.
     */
    write_behind = bitmap->mddev->bitmap_info.max_write_behind;
    if (write_behind > COUNTER_MAX)
        write_behind = COUNTER_MAX / 2;
    sb->write_behind = cpu_to_le32(write_behind);
    bitmap->mddev->bitmap_info.max_write_behind = write_behind;

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

    memcpy(sb->uuid, bitmap->mddev->uuid, 16);

    set_bit(BITMAP_STALE, &bitmap->flags);
    sb->state = cpu_to_le32(bitmap->flags);
    bitmap->events_cleared = bitmap->mddev->events;
    sb->events_cleared = cpu_to_le64(bitmap->mddev->events);

    kunmap_atomic(sb);

    return 0;
}

/* 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, write_behind;
    unsigned long long events;
    unsigned long sectors_reserved = 0;
    int err = -EINVAL;
    struct page *sb_page;

    if (!bitmap->storage.file && !bitmap->mddev->bitmap_info.offset) {
        chunksize = 128 * 1024 * 1024;
        daemon_sleep = 5 * HZ;
        write_behind = 0;
        set_bit(BITMAP_STALE, &bitmap->flags);
        err = 0;
        goto out_no_sb;
    }
    /* page 0 is the superblock, read it... */
    sb_page = alloc_page(GFP_KERNEL);
    if (!sb_page)
        return -ENOMEM;
    bitmap->storage.sb_page = sb_page;

    if (bitmap->storage.file) {
        loff_t isize = i_size_read(bitmap->storage.file->f_mapping->host);
        int bytes = isize > PAGE_SIZE ? PAGE_SIZE : isize;

        err = read_page(bitmap->storage.file, 0,
                bitmap, bytes, sb_page);
    } else {
        err = read_sb_page(bitmap->mddev,
                   bitmap->mddev->bitmap_info.offset,
                   sb_page,
                   0, sizeof(bitmap_super_t));
    }
    if (err)
        return err;

    sb = kmap_atomic(sb_page);

    chunksize = le32_to_cpu(sb->chunksize);
    daemon_sleep = le32_to_cpu(sb->daemon_sleep) * HZ;
    write_behind = le32_to_cpu(sb->write_behind);
    sectors_reserved = le32_to_cpu(sb->sectors_reserved);

    /* verify that the bitmap-specific fields are valid */
    if (sb->magic != cpu_to_le32(BITMAP_MAGIC))
        reason = "bad magic";
    else if (le32_to_cpu(sb->version) < BITMAP_MAJOR_LO ||
         le32_to_cpu(sb->version) > BITMAP_MAJOR_HI)
        reason = "unrecognized superblock version";
    else if (chunksize < 512)
        reason = "bitmap chunksize too small";
    else if (!is_power_of_2(chunksize))
        reason = "bitmap chunksize not a power of 2";
    else if (daemon_sleep < 1 || daemon_sleep > MAX_SCHEDULE_TIMEOUT)
        reason = "daemon sleep period out of range";
    else if (write_behind > COUNTER_MAX)
        reason = "write-behind limit out of range (0 - 16383)";
    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) {
        /*
         * We have a persistent array superblock, so 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);
            set_bit(BITMAP_STALE, &bitmap->flags);
        }
    }

    /* assign fields using values from superblock */
    bitmap->flags |= le32_to_cpu(sb->state);
    if (le32_to_cpu(sb->version) == BITMAP_MAJOR_HOSTENDIAN)
        set_bit(BITMAP_HOSTENDIAN, &bitmap->flags);
    bitmap->events_cleared = le64_to_cpu(sb->events_cleared);
    err = 0;
out:
    kunmap_atomic(sb);
out_no_sb:
    if (test_bit(BITMAP_STALE, &bitmap->flags))
        bitmap->events_cleared = bitmap->mddev->events;
    bitmap->mddev->bitmap_info.chunksize = chunksize;
    bitmap->mddev->bitmap_info.daemon_sleep = daemon_sleep;
    bitmap->mddev->bitmap_info.max_write_behind = write_behind;
    if (bitmap->mddev->bitmap_info.space == 0 ||
        bitmap->mddev->bitmap_info.space > sectors_reserved)
        bitmap->mddev->bitmap_info.space = sectors_reserved;
    if (err)
        bitmap_print_sb(bitmap);
    return err;
}

/*
 * general bitmap file operations
 */

/*
 * on-disk bitmap:
 *
 * Use one bit per "chunk" (block set). We do the disk I/O on the bitmap
 * file a page at a time. There's a superblock at the start of the file.
 */
/* calculate the index of the page that contains this bit */
static inline unsigned long file_page_index(struct bitmap_storage *store,
                        unsigned long chunk)
{
    if (store->sb_page)
        chunk += sizeof(bitmap_super_t) << 3;
    return chunk >> PAGE_BIT_SHIFT;
}

/* calculate the (bit) offset of this bit within a page */
static inline unsigned long file_page_offset(struct bitmap_storage *store,
                         unsigned long chunk)
{
    if (store->sb_page)
        chunk += sizeof(bitmap_super_t) << 3;
    return 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_storage *store,
                        unsigned long chunk)
{
    if (file_page_index(store, chunk) >= store->file_pages)
        return NULL;
    return store->filemap[file_page_index(store, chunk)
                  - file_page_index(store, 0)];
}

static int bitmap_storage_alloc(struct bitmap_storage *store,
                unsigned long chunks, int with_super)
{
    int pnum;
    unsigned long num_pages;
    unsigned long bytes;

    bytes = DIV_ROUND_UP(chunks, 8);
    if (with_super)
        bytes += sizeof(bitmap_super_t);

    num_pages = DIV_ROUND_UP(bytes, PAGE_SIZE);

    store->filemap = kmalloc(sizeof(struct page *)
                 * num_pages, GFP_KERNEL);
    if (!store->filemap)
        return -ENOMEM;

    if (with_super && !store->sb_page) {
        store->sb_page = alloc_page(GFP_KERNEL|__GFP_ZERO);
        if (store->sb_page == NULL)
            return -ENOMEM;
        store->sb_page->index = 0;
    }
    pnum = 0;
    if (store->sb_page) {
        store->filemap[0] = store->sb_page;
        pnum = 1;
    }
    for ( ; pnum < num_pages; pnum++) {
        store->filemap[pnum] = alloc_page(GFP_KERNEL|__GFP_ZERO);
        if (!store->filemap[pnum]) {
            store->file_pages = pnum;
            return -ENOMEM;
        }
        store->filemap[pnum]->index = pnum;
    }
    store->file_pages = pnum;

    /* We need 4 bits per page, rounded up to a multiple
     * of sizeof(unsigned long) */
    store->filemap_attr = kzalloc(
        roundup(DIV_ROUND_UP(num_pages*4, 8), sizeof(unsigned long)),
        GFP_KERNEL);
    if (!store->filemap_attr)
        return -ENOMEM;

    store->bytes = bytes;

    return 0;
}

static void bitmap_file_unmap(struct bitmap_storage *store)
{
    struct page **map, *sb_page;
    int pages;
    struct file *file;

    file = store->file;
    map = store->filemap;
    pages = store->file_pages;
    sb_page = store->sb_page;

    while (pages--)
        if (map[pages] != sb_page) /* 0 is sb_page, release it below */
            free_buffers(map[pages]);
    kfree(map);
    kfree(store->filemap_attr);

    if (sb_page)
        free_buffers(sb_page);

    if (file) {
        struct inode *inode = file->f_path.dentry->d_inode;
        invalidate_mapping_pages(inode->i_mapping, 0, -1);
        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;

    if (!test_and_set_bit(BITMAP_STALE, &bitmap->flags)) {
        bitmap_update_sb(bitmap);

        if (bitmap->storage.file) {
            path = kmalloc(PAGE_SIZE, GFP_KERNEL);
            if (path)
                ptr = d_path(&bitmap->storage.file->f_path,
                         path, PAGE_SIZE);

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

            kfree(path);
        } else
            printk(KERN_ALERT
                   "%s: disabling internal bitmap due to errors\n",
                   bmname(bitmap));
    }
}

enum bitmap_page_attr {
    BITMAP_PAGE_DIRTY = 0,     /* there are set bits that need to be synced */
    BITMAP_PAGE_PENDING = 1,   /* there are bits that are being cleaned.
                    * i.e. counter is 1 or 2. */
    BITMAP_PAGE_NEEDWRITE = 2, /* there are cleared bits that need to be synced */
};

static inline void set_page_attr(struct bitmap *bitmap, int pnum,
                 enum bitmap_page_attr attr)
{
    set_bit((pnum<<2) + attr, bitmap->storage.filemap_attr);
}

static inline void clear_page_attr(struct bitmap *bitmap, int pnum,
                   enum bitmap_page_attr attr)
{
    clear_bit((pnum<<2) + attr, bitmap->storage.filemap_attr);
}

static inline int test_page_attr(struct bitmap *bitmap, int pnum,
                 enum bitmap_page_attr attr)
{
    return test_bit((pnum<<2) + attr, bitmap->storage.filemap_attr);
}

static inline int test_and_clear_page_attr(struct bitmap *bitmap, int pnum,
                       enum bitmap_page_attr attr)
{
    return test_and_clear_bit((pnum<<2) + attr,
                  bitmap->storage.filemap_attr);
}
/*
 * 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 >> bitmap->counts.chunkshift;

    page = filemap_get_page(&bitmap->storage, chunk);
    if (!page)
        return;
    bit = file_page_offset(&bitmap->storage, chunk);

    /* set the bit */
    kaddr = kmap_atomic(page);
    if (test_bit(BITMAP_HOSTENDIAN, &bitmap->flags))
        set_bit(bit, kaddr);
    else
        test_and_set_bit_le(bit, kaddr);
    kunmap_atomic(kaddr);
    pr_debug("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->index, BITMAP_PAGE_DIRTY);
}

static void bitmap_file_clear_bit(struct bitmap *bitmap, sector_t block)
{
    unsigned long bit;
    struct page *page;
    void *paddr;
    unsigned long chunk = block >> bitmap->counts.chunkshift;

    page = filemap_get_page(&bitmap->storage, chunk);
    if (!page)
        return;
    bit = file_page_offset(&bitmap->storage, chunk);
    paddr = kmap_atomic(page);
    if (test_bit(BITMAP_HOSTENDIAN, &bitmap->flags))
        clear_bit(bit, paddr);
    else
        test_and_clear_bit_le(bit, paddr);
    kunmap_atomic(paddr);
    if (!test_page_attr(bitmap, page->index, BITMAP_PAGE_NEEDWRITE)) {
        set_page_attr(bitmap, page->index, BITMAP_PAGE_PENDING);
        bitmap->allclean = 0;
    }
}

/* 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 */
void bitmap_unplug(struct bitmap *bitmap)
{
    unsigned long i;
    int dirty, need_write;
    int wait = 0;

    if (!bitmap || !bitmap->storage.filemap ||
        test_bit(BITMAP_STALE, &bitmap->flags))
        return;

    /* 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->storage.file_pages; i++) {
        if (!bitmap->storage.filemap)
            return;
        dirty = test_and_clear_page_attr(bitmap, i, BITMAP_PAGE_DIRTY);
        need_write = test_and_clear_page_attr(bitmap, i,
                              BITMAP_PAGE_NEEDWRITE);
        if (dirty || need_write) {
            clear_page_attr(bitmap, i, BITMAP_PAGE_PENDING);
            write_page(bitmap, bitmap->storage.filemap[i], 0);
        }
        if (dirty)
            wait = 1;
    }
    if (wait) { /* if any writes were performed, we need to wait on them */
        if (bitmap->storage.file)
            wait_event(bitmap->write_wait,
                   atomic_read(&bitmap->pending_writes)==0);
        else
            md_super_wait(bitmap->mddev);
    }
    if (test_bit(BITMAP_WRITE_ERROR, &bitmap->flags))
        bitmap_file_kick(bitmap);
}
EXPORT_SYMBOL(bitmap_unplug);

static void bitmap_set_memory_bits(struct bitmap *bitmap, sector_t offset, int needed);
/* * 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.
 *
 * We ignore all bits for sectors that end earlier than 'start'.
 * This is used when reading an out-of-date bitmap...
 */
static int bitmap_init_from_disk(struct bitmap *bitmap, sector_t start)
{
    unsigned long i, chunks, index, oldindex, bit;
    struct page *page = NULL;
    unsigned long bit_cnt = 0;
    struct file *file;
    unsigned long offset;
    int outofdate;
    int ret = -ENOSPC;
    void *paddr;
    struct bitmap_storage *store = &bitmap->storage;

    chunks = bitmap->counts.chunks;
    file = store->file;

    if (!file && !bitmap->mddev->bitmap_info.offset) {
        /* No permanent bitmap - fill with '1s'. */
        store->filemap = NULL;
        store->file_pages = 0;
        for (i = 0; i < chunks ; i++) {
            /* if the disk bit is set, set the memory bit */
            int needed = ((sector_t)(i+1) << (bitmap->counts.chunkshift)
                      >= start);
            bitmap_set_memory_bits(bitmap,
                           (sector_t)i << bitmap->counts.chunkshift,
                           needed);
        }
        return 0;
    }

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

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

    oldindex = ~0L;
    offset = 0;
    if (!bitmap->mddev->bitmap_info.external)
        offset = sizeof(bitmap_super_t);

    for (i = 0; i < chunks; i++) {
        int b;
        index = file_page_index(&bitmap->storage, i);
        bit = file_page_offset(&bitmap->storage, i);
        if (index != oldindex) { /* this is a new page, read it in */
            int count;
            /* unmap the old page, we're done with it */
            if (index == store->file_pages-1)
                count = store->bytes - index * PAGE_SIZE;
            else
                count = PAGE_SIZE;
            page = store->filemap[index];
            if (file)
                ret = read_page(file, index, bitmap,
                        count, page);
            else
                ret = read_sb_page(
                    bitmap->mddev,
                    bitmap->mddev->bitmap_info.offset,
                    page,
                    index, count);

            if (ret)
                goto err;

            oldindex = index;

            if (outofdate) {
                /*
                 * if bitmap is out of date, dirty the
                 * whole page and write it out
                 */
                paddr = kmap_atomic(page);
                memset(paddr + offset, 0xff,
                       PAGE_SIZE - offset);
                kunmap_atomic(paddr);
                write_page(bitmap, page, 1);

                ret = -EIO;
                if (test_bit(BITMAP_WRITE_ERROR,
                         &bitmap->flags))
                    goto err;
            }
        }
        paddr = kmap_atomic(page);
        if (test_bit(BITMAP_HOSTENDIAN, &bitmap->flags))
            b = test_bit(bit, paddr);
        else
            b = test_bit_le(bit, paddr);
        kunmap_atomic(paddr);
        if (b) {
            /* if the disk bit is set, set the memory bit */
            int needed = ((sector_t)(i+1) << bitmap->counts.chunkshift
                      >= start);
            bitmap_set_memory_bits(bitmap,
                           (sector_t)i << bitmap->counts.chunkshift,
                           needed);
            bit_cnt++;
        }
        offset = 0;
    }

    printk(KERN_INFO "%s: bitmap initialized from disk: "
           "read %lu pages, set %lu of %lu bits\n",
           bmname(bitmap), store->file_pages,
           bit_cnt, chunks);

    return 0;

 err:
    printk(KERN_INFO "%s: bitmap initialisation failed: %d\n",
           bmname(bitmap), 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
     */
    int i;

    if (!bitmap || !bitmap->storage.filemap)
        return;
    if (bitmap->storage.file)
        /* Only one copy, so nothing needed */
        return;

    for (i = 0; i < bitmap->storage.file_pages; i++)
        set_page_attr(bitmap, i,
                  BITMAP_PAGE_NEEDWRITE);
    bitmap->allclean = 0;
}

static void bitmap_count_page(struct bitmap_counts *bitmap,
                  sector_t offset, int inc)
{
    sector_t chunk = offset >> bitmap->chunkshift;
    unsigned long page = chunk >> PAGE_COUNTER_SHIFT;
    bitmap->bp[page].count += inc;
    bitmap_checkfree(bitmap, page);
}

static void bitmap_set_pending(struct bitmap_counts *bitmap, sector_t offset)
{
    sector_t chunk = offset >> bitmap->chunkshift;
    unsigned long page = chunk >> PAGE_COUNTER_SHIFT;
    struct bitmap_page *bp = &bitmap->bp[page];

    if (!bp->pending)
        bp->pending = 1;
}

static bitmap_counter_t *bitmap_get_counter(struct bitmap_counts *bitmap,
                        sector_t offset, sector_t *blocks,
                        int create);

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

void bitmap_daemon_work(struct mddev *mddev)
{
    struct bitmap *bitmap;
    unsigned long j;
    unsigned long nextpage;
    sector_t blocks;
    struct bitmap_counts *counts;

    /* Use a mutex to guard daemon_work against
     * bitmap_destroy.
     */
    mutex_lock(&mddev->bitmap_info.mutex);
    bitmap = mddev->bitmap;
    if (bitmap == NULL) {
        mutex_unlock(&mddev->bitmap_info.mutex);
        return;
    }
    if (time_before(jiffies, bitmap->daemon_lastrun
            + mddev->bitmap_info.daemon_sleep))
        goto done;

    bitmap->daemon_lastrun = jiffies;
    if (bitmap->allclean) {
        mddev->thread->timeout = MAX_SCHEDULE_TIMEOUT;
        goto done;
    }
    bitmap->allclean = 1;

    /* Any file-page which is PENDING now needs to be written.
     * So set NEEDWRITE now, then after we make any last-minute changes
     * we will write it.
     */
    for (j = 0; j < bitmap->storage.file_pages; j++)
        if (test_and_clear_page_attr(bitmap, j,
                         BITMAP_PAGE_PENDING))
            set_page_attr(bitmap, j,
                      BITMAP_PAGE_NEEDWRITE);

    if (bitmap->need_sync &&
        mddev->bitmap_info.external == 0) {
        /* Arrange for superblock update as well as
         * other changes */
        bitmap_super_t *sb;
        bitmap->need_sync = 0;
        if (bitmap->storage.filemap) {
            sb = kmap_atomic(bitmap->storage.sb_page);
            sb->events_cleared =
                cpu_to_le64(bitmap->events_cleared);
            kunmap_atomic(sb);
            set_page_attr(bitmap, 0,
                      BITMAP_PAGE_NEEDWRITE);
        }
    }
    /* Now look at the bitmap counters and if any are '2' or '1',
     * decrement and handle accordingly.
     */
    counts = &bitmap->counts;
    spin_lock_irq(&counts->lock);
    nextpage = 0;
    for (j = 0; j < counts->chunks; j++) {
        bitmap_counter_t *bmc;
        sector_t  block = (sector_t)j << counts->chunkshift;

        if (j == nextpage) {
            nextpage += PAGE_COUNTER_RATIO;
            if (!counts->bp[j >> PAGE_COUNTER_SHIFT].pending) {
                j |= PAGE_COUNTER_MASK;
                continue;
            }
            counts->bp[j >> PAGE_COUNTER_SHIFT].pending = 0;
        }
        bmc = bitmap_get_counter(counts,
                     block,
                     &blocks, 0);

        if (!bmc) {
            j |= PAGE_COUNTER_MASK;
            continue;
        }
        if (*bmc == 1 && !bitmap->need_sync) {
            /* We can clear the bit */
            *bmc = 0;
            bitmap_count_page(counts, block, -1);
            bitmap_file_clear_bit(bitmap, block);
        } else if (*bmc && *bmc <= 2) {
            *bmc = 1;
            bitmap_set_pending(counts, block);
            bitmap->allclean = 0;
        }
    }
    spin_unlock_irq(&counts->lock);

    /* Now start writeout on any page in NEEDWRITE that isn't DIRTY.
     * DIRTY pages need to be written by bitmap_unplug so it can wait
     * for them.
     * If we find any DIRTY page we stop there and let bitmap_unplug
     * handle all the rest.  This is important in the case where
     * the first blocking holds the superblock and it has been updated.
     * We mustn't write any other blocks before the superblock.
     */
    for (j = 0;
         j < bitmap->storage.file_pages
             && !test_bit(BITMAP_STALE, &bitmap->flags);
         j++) {

        if (test_page_attr(bitmap, j,
                   BITMAP_PAGE_DIRTY))
            /* bitmap_unplug will handle the rest */
            break;
        if (test_and_clear_page_attr(bitmap, j,
                         BITMAP_PAGE_NEEDWRITE)) {
            write_page(bitmap, bitmap->storage.filemap[j], 0);
        }
    }

 done:
    if (bitmap->allclean == 0)
        mddev->thread->timeout =
            mddev->bitmap_info.daemon_sleep;
    mutex_unlock(&mddev->bitmap_info.mutex);
}

static bitmap_counter_t *bitmap_get_counter(struct bitmap_counts *bitmap,
                        sector_t offset, sector_t *blocks,
                        int create)
__releases(bitmap->lock)
__acquires(bitmap->lock)
{
    /* 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 >> bitmap->chunkshift;
    unsigned long page = chunk >> PAGE_COUNTER_SHIFT;
    unsigned long pageoff = (chunk & PAGE_COUNTER_MASK) << COUNTER_BYTE_SHIFT;
    sector_t csize;
    int err;

    err = bitmap_checkpage(bitmap, page, create);

    if (bitmap->bp[page].hijacked ||
        bitmap->bp[page].map == NULL)
        csize = ((sector_t)1) << (bitmap->chunkshift +
                      PAGE_COUNTER_SHIFT - 1);
    else
        csize = ((sector_t)1) << bitmap->chunkshift;
    *blocks = csize - (offset & (csize - 1));

    if (err < 0)
        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);
        return  &((bitmap_counter_t *)
              &bitmap->bp[page].map)[hi];
    } else /* page is allocated */
        return (bitmap_counter_t *)
            &(bitmap->bp[page].map[pageoff]);
}

int bitmap_startwrite(struct bitmap *bitmap, sector_t offset, unsigned long sectors, int behind)
{
    if (!bitmap)
        return 0;

    if (behind) {
        int bw;
        atomic_inc(&bitmap->behind_writes);
        bw = atomic_read(&bitmap->behind_writes);
        if (bw > bitmap->behind_writes_used)
            bitmap->behind_writes_used = bw;

        pr_debug("inc write-behind count %d/%lu\n",
             bw, bitmap->mddev->bitmap_info.max_write_behind);
    }

    while (sectors) {
        sector_t blocks;
        bitmap_counter_t *bmc;

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

        if (unlikely(COUNTER(*bmc) == COUNTER_MAX)) {
            DEFINE_WAIT(__wait);
            /* note that it is safe to do the prepare_to_wait
             * after the test as long as we do it before dropping
             * the spinlock.
             */
            prepare_to_wait(&bitmap->overflow_wait, &__wait,
                    TASK_UNINTERRUPTIBLE);
            spin_unlock_irq(&bitmap->counts.lock);
            schedule();
            finish_wait(&bitmap->overflow_wait, &__wait);
            continue;
        }

        switch (*bmc) {
        case 0:
            bitmap_file_set_bit(bitmap, offset);
            bitmap_count_page(&bitmap->counts, offset, 1);
            /* fall through */
        case 1:
            *bmc = 2;
        }

        (*bmc)++;

        spin_unlock_irq(&bitmap->counts.lock);

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

void bitmap_endwrite(struct bitmap *bitmap, sector_t offset, unsigned long sectors,
             int success, int behind)
{
    if (!bitmap)
        return;
    if (behind) {
        if (atomic_dec_and_test(&bitmap->behind_writes))
            wake_up(&bitmap->behind_wait);
        pr_debug("dec write-behind count %d/%lu\n",
             atomic_read(&bitmap->behind_writes),
             bitmap->mddev->bitmap_info.max_write_behind);
    }

    while (sectors) {
        sector_t blocks;
        unsigned long flags;
        bitmap_counter_t *bmc;

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

        if (success && !bitmap->mddev->degraded &&
            bitmap->events_cleared < bitmap->mddev->events) {
            bitmap->events_cleared = bitmap->mddev->events;
            bitmap->need_sync = 1;
            sysfs_notify_dirent_safe(bitmap->sysfs_can_clear);
        }

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

        if (COUNTER(*bmc) == COUNTER_MAX)
            wake_up(&bitmap->overflow_wait);

        (*bmc)--;
        if (*bmc <= 2) {
            bitmap_set_pending(&bitmap->counts, offset);
            bitmap->allclean = 0;
        }
        spin_unlock_irqrestore(&bitmap->counts.lock, flags);
        offset += blocks;
        if (sectors > blocks)
            sectors -= blocks;
        else
            sectors = 0;
    }
}
EXPORT_SYMBOL(bitmap_endwrite);

static int __bitmap_start_sync(struct bitmap *bitmap, sector_t offset, sector_t *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->counts.lock);
    bmc = bitmap_get_counter(&bitmap->counts, 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->counts.lock);
    return rv;
}

int bitmap_start_sync(struct bitmap *bitmap, sector_t offset, sector_t *blocks,
              int degraded)
{
    /* bitmap_start_sync must always report on multiples of whole
     * pages, otherwise resync (which is very PAGE_SIZE based) will
     * get confused.
     * So call __bitmap_start_sync repeatedly (if needed) until
     * At least PAGE_SIZE>>9 blocks are covered.
     * Return the 'or' of the result.
     */
    int rv = 0;
    sector_t blocks1;

    *blocks = 0;
    while (*blocks < (PAGE_SIZE>>9)) {
        rv |= __bitmap_start_sync(bitmap, offset,
                      &blocks1, degraded);
        offset += blocks1;
        *blocks += blocks1;
    }
    return rv;
}
EXPORT_SYMBOL(bitmap_start_sync);

void bitmap_end_sync(struct bitmap *bitmap, sector_t offset, sector_t *blocks, int aborted)
{
    bitmap_counter_t *bmc;
    unsigned long flags;

    if (bitmap == NULL) {
        *blocks = 1024;
        return;
    }
    spin_lock_irqsave(&bitmap->counts.lock, flags);
    bmc = bitmap_get_counter(&bitmap->counts, offset, blocks, 0);
    if (bmc == NULL)
        goto unlock;
    /* locked */
    if (RESYNC(*bmc)) {
        *bmc &= ~RESYNC_MASK;

        if (!NEEDED(*bmc) && aborted)
            *bmc |= NEEDED_MASK;
        else {
            if (*bmc <= 2) {
                bitmap_set_pending(&bitmap->counts, offset);
                bitmap->allclean = 0;
            }
        }
    }
 unlock:
    spin_unlock_irqrestore(&bitmap->counts.lock, flags);
}
EXPORT_SYMBOL(bitmap_end_sync);

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;
    sector_t blocks;
    if (!bitmap)
        return;
    while (sector < bitmap->mddev->resync_max_sectors) {
        bitmap_end_sync(bitmap, sector, &blocks, 0);
        sector += blocks;
    }
}
EXPORT_SYMBOL(bitmap_close_sync);

void bitmap_cond_end_sync(struct bitmap *bitmap, sector_t sector)
{
    sector_t s = 0;
    sector_t blocks;

    if (!bitmap)
        return;
    if (sector == 0) {
        bitmap->last_end_sync = jiffies;
        return;
    }
    if (time_before(jiffies, (bitmap->last_end_sync
                  + bitmap->mddev->bitmap_info.daemon_sleep)))
        return;
    wait_event(bitmap->mddev->recovery_wait,
           atomic_read(&bitmap->mddev->recovery_active) == 0);

    bitmap->mddev->curr_resync_completed = sector;
    set_bit(MD_CHANGE_CLEAN, &bitmap->mddev->flags);
    sector &= ~((1ULL << bitmap->counts.chunkshift) - 1);
    s = 0;
    while (s < sector && s < bitmap->mddev->resync_max_sectors) {
        bitmap_end_sync(bitmap, s, &blocks, 0);
        s += blocks;
    }
    bitmap->last_end_sync = jiffies;
    sysfs_notify(&bitmap->mddev->kobj, NULL, "sync_completed");
}
EXPORT_SYMBOL(bitmap_cond_end_sync);

static void bitmap_set_memory_bits(struct bitmap *bitmap, sector_t offset, int needed)
{
    /* For each chunk covered by any of these sectors, set the
     * counter to 2 and possibly set resync_needed.  They should all
     * be 0 at this point
     */

    sector_t secs;
    bitmap_counter_t *bmc;
    spin_lock_irq(&bitmap->counts.lock);
    bmc = bitmap_get_counter(&bitmap->counts, offset, &secs, 1);
    if (!bmc) {
        spin_unlock_irq(&bitmap->counts.lock);
        return;
    }
    if (!*bmc) {
        *bmc = 2 | (needed ? NEEDED_MASK : 0);
        bitmap_count_page(&bitmap->counts, offset, 1);
        bitmap_set_pending(&bitmap->counts, offset);
        bitmap->allclean = 0;
    }
    spin_unlock_irq(&bitmap->counts.lock);
}

/* dirty the memory and file bits for bitmap chunks "s" to "e" */
void bitmap_dirty_bits(struct bitmap *bitmap, unsigned long s, unsigned long e)
{
    unsigned long chunk;

    for (chunk = s; chunk <= e; chunk++) {
        sector_t sec = (sector_t)chunk << bitmap->counts.chunkshift;
        bitmap_set_memory_bits(bitmap, sec, 1);
        bitmap_file_set_bit(bitmap, sec);
        if (sec < bitmap->mddev->recovery_cp)
            /* We are asserting that the array is dirty,
             * so move the recovery_cp address back so
             * that it is obvious that it is dirty
             */
            bitmap->mddev->recovery_cp = sec;
    }
}

/*
 * flush out any pending updates
 */
void bitmap_flush(struct mddev *mddev)
{
    struct bitmap *bitmap = mddev->bitmap;
    long sleep;

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

    /* run the daemon_work three time to ensure everything is flushed
     * that can be
     */
    sleep = mddev->bitmap_info.daemon_sleep * 2;
    bitmap->daemon_lastrun -= sleep;
    bitmap_daemon_work(mddev);
    bitmap->daemon_lastrun -= sleep;
    bitmap_daemon_work(mddev);
    bitmap->daemon_lastrun -= sleep;
    bitmap_daemon_work(mddev);
    bitmap_update_sb(bitmap);
}

/*
 * free memory that was allocated
 */
static void bitmap_free(struct bitmap *bitmap)
{
    unsigned long k, pages;
    struct bitmap_page *bp;

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

    /* Shouldn't be needed - but just in case.... */
    wait_event(bitmap->write_wait,
           atomic_read(&bitmap->pending_writes) == 0);

    /* release the bitmap file  */
    bitmap_file_unmap(&bitmap->storage);

    bp = bitmap->counts.bp;
    pages = bitmap->counts.pages;

    /* free all allocated memory */

    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);
}

void bitmap_destroy(struct mddev *mddev)
{
    struct bitmap *bitmap = mddev->bitmap;

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

    mutex_lock(&mddev->bitmap_info.mutex);
    mddev->bitmap = NULL; /* disconnect from the md device */
    mutex_unlock(&mddev->bitmap_info.mutex);
    if (mddev->thread)
        mddev->thread->timeout = MAX_SCHEDULE_TIMEOUT;

    if (bitmap->sysfs_can_clear)
        sysfs_put(bitmap->sysfs_can_clear);

    bitmap_free(bitmap);
}

/*
 * initialize the bitmap structure
 * if this returns an error, bitmap_destroy must be called to do clean up
 */
int bitmap_create(struct mddev *mddev)
{
    struct bitmap *bitmap;
    sector_t blocks = mddev->resync_max_sectors;
    struct file *file = mddev->bitmap_info.file;
    int err;
    struct sysfs_dirent *bm = NULL;

    BUILD_BUG_ON(sizeof(bitmap_super_t) != 256);

    BUG_ON(file && mddev->bitmap_info.offset);

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

    spin_lock_init(&bitmap->counts.lock);
    atomic_set(&bitmap->pending_writes, 0);
    init_waitqueue_head(&bitmap->write_wait);
    init_waitqueue_head(&bitmap->overflow_wait);
    init_waitqueue_head(&bitmap->behind_wait);

    bitmap->mddev = mddev;

    if (mddev->kobj.sd)
        bm = sysfs_get_dirent(mddev->kobj.sd, NULL, "bitmap");
    if (bm) {
        bitmap->sysfs_can_clear = sysfs_get_dirent(bm, NULL, "can_clear");
        sysfs_put(bm);
    } else
        bitmap->sysfs_can_clear = NULL;

    bitmap->storage.file = file;
    if (file) {
        get_file(file);
        /* As future accesses to this file will use bmap,
         * and bypass the page cache, we must sync the file
         * first.
         */
        vfs_fsync(file, 1);
    }
    /* read superblock from bitmap file (this sets mddev->bitmap_info.chunksize) */
    if (!mddev->bitmap_info.external) {
        /*
         * If 'MD_ARRAY_FIRST_USE' is set, then device-mapper is
         * instructing us to create a new on-disk bitmap instance.
         */
        if (test_and_clear_bit(MD_ARRAY_FIRST_USE, &mddev->flags))
            err = bitmap_new_disk_sb(bitmap);
        else
            err = bitmap_read_sb(bitmap);
    } else {
        err = 0;
        if (mddev->bitmap_info.chunksize == 0 ||
            mddev->bitmap_info.daemon_sleep == 0)
            /* chunksize and time_base need to be
             * set first. */
            err = -EINVAL;
    }
    if (err)
        goto error;

    bitmap->daemon_lastrun = jiffies;
    err = bitmap_resize(bitmap, blocks, mddev->bitmap_info.chunksize, 1);
    if (err)
        goto error;

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

    mddev->bitmap = bitmap;
    return test_bit(BITMAP_WRITE_ERROR, &bitmap->flags) ? -EIO : 0;

 error:
    bitmap_free(bitmap);
    return err;
}

int bitmap_load(struct mddev *mddev)
{
    int err = 0;
    sector_t start = 0;
    sector_t sector = 0;
    struct bitmap *bitmap = mddev->bitmap;

    if (!bitmap)
        goto out;

    /* Clear out old bitmap info first:  Either there is none, or we
     * are resuming after someone else has possibly changed things,
     * so we should forget old cached info.
     * All chunks should be clean, but some might need_sync.
     */
    while (sector < mddev->resync_max_sectors) {
        sector_t blocks;
        bitmap_start_sync(bitmap, sector, &blocks, 0);
        sector += blocks;
    }
    bitmap_close_sync(bitmap);

    if (mddev->degraded == 0
        || bitmap->events_cleared == mddev->events)
        /* no need to keep dirty bits to optimise a
         * re-add of a missing device */
        start = mddev->recovery_cp;

    mutex_lock(&mddev->bitmap_info.mutex);
    err = bitmap_init_from_disk(bitmap, start);
    mutex_unlock(&mddev->bitmap_info.mutex);

    if (err)
        goto out;
    clear_bit(BITMAP_STALE, &bitmap->flags);

    /* Kick recovery in case any bits were set */
    set_bit(MD_RECOVERY_NEEDED, &bitmap->mddev->recovery);

    mddev->thread->timeout = mddev->bitmap_info.daemon_sleep;
    md_wakeup_thread(mddev->thread);

    bitmap_update_sb(bitmap);

    if (test_bit(BITMAP_WRITE_ERROR, &bitmap->flags))
        err = -EIO;
out:
    return err;
}
EXPORT_SYMBOL_GPL(bitmap_load);

void bitmap_status(struct seq_file *seq, struct bitmap *bitmap)
{
    unsigned long chunk_kb;
    struct bitmap_counts *counts;

    if (!bitmap)
        return;

    counts = &bitmap->counts;

    chunk_kb = bitmap->mddev->bitmap_info.chunksize >> 10;
    seq_printf(seq, "bitmap: %lu/%lu pages [%luKB], "
           "%lu%s chunk",
           counts->pages - counts->missing_pages,
           counts->pages,
           (counts->pages - counts->missing_pages)
           << (PAGE_SHIFT - 10),
           chunk_kb ? chunk_kb : bitmap->mddev->bitmap_info.chunksize,
           chunk_kb ? "KB" : "B");
    if (bitmap->storage.file) {
        seq_printf(seq, ", file: ");
        seq_path(seq, &bitmap->storage.file->f_path, " \t\n");
    }

    seq_printf(seq, "\n");
}

int bitmap_resize(struct bitmap *bitmap, sector_t blocks,
          int chunksize, int init)
{
    /* If chunk_size is 0, choose an appropriate chunk size.
     * Then possibly allocate new storage space.
     * Then quiesce, copy bits, replace bitmap, and re-start
     *
     * This function is called both to set up the initial bitmap
     * and to resize the bitmap while the array is active.
     * If this happens as a result of the array being resized,
     * chunksize will be zero, and we need to choose a suitable
     * chunksize, otherwise we use what we are given.
     */
    struct bitmap_storage store;
    struct bitmap_counts old_counts;
    unsigned long chunks;
    sector_t block;
    sector_t old_blocks, new_blocks;
    int chunkshift;
    int ret = 0;
    long pages;
    struct bitmap_page *new_bp;

    if (chunksize == 0) {
        /* If there is enough space, leave the chunk size unchanged,
         * else increase by factor of two until there is enough space.
         */
        long bytes;
        long space = bitmap->mddev->bitmap_info.space;

        if (space == 0) {
            /* We don't know how much space there is, so limit
             * to current size - in sectors.
             */
            bytes = DIV_ROUND_UP(bitmap->counts.chunks, 8);
            if (!bitmap->mddev->bitmap_info.external)
                bytes += sizeof(bitmap_super_t);
            space = DIV_ROUND_UP(bytes, 512);
            bitmap->mddev->bitmap_info.space = space;
        }
        chunkshift = bitmap->counts.chunkshift;
        chunkshift--;
        do {
            /* 'chunkshift' is shift from block size to chunk size */
            chunkshift++;
            chunks = DIV_ROUND_UP_SECTOR_T(blocks, 1 << chunkshift);
            bytes = DIV_ROUND_UP(chunks, 8);
            if (!bitmap->mddev->bitmap_info.external)
                bytes += sizeof(bitmap_super_t);
        } while (bytes > (space << 9));
    } else
        chunkshift = ffz(~chunksize) - BITMAP_BLOCK_SHIFT;

    chunks = DIV_ROUND_UP_SECTOR_T(blocks, 1 << chunkshift);
    memset(&store, 0, sizeof(store));
    if (bitmap->mddev->bitmap_info.offset || bitmap->mddev->bitmap_info.file)
        ret = bitmap_storage_alloc(&store, chunks,
                       !bitmap->mddev->bitmap_info.external);
    if (ret)
        goto err;

    pages = DIV_ROUND_UP(chunks, PAGE_COUNTER_RATIO);

    new_bp = kzalloc(pages * sizeof(*new_bp), GFP_KERNEL);
    ret = -ENOMEM;
    if (!new_bp) {
        bitmap_file_unmap(&store);
        goto err;
    }

    if (!init)
        bitmap->mddev->pers->quiesce(bitmap->mddev, 1);

    store.file = bitmap->storage.file;
    bitmap->storage.file = NULL;

    if (store.sb_page && bitmap->storage.sb_page)
        memcpy(page_address(store.sb_page),
               page_address(bitmap->storage.sb_page),
               sizeof(bitmap_super_t));
    bitmap_file_unmap(&bitmap->storage);
    bitmap->storage = store;

    old_counts = bitmap->counts;
    bitmap->counts.bp = new_bp;
    bitmap->counts.pages = pages;
    bitmap->counts.missing_pages = pages;
    bitmap->counts.chunkshift = chunkshift;
    bitmap->counts.chunks = chunks;
    bitmap->mddev->bitmap_info.chunksize = 1 << (chunkshift +
                             BITMAP_BLOCK_SHIFT);

    blocks = min(old_counts.chunks << old_counts.chunkshift,
             chunks << chunkshift);

    spin_lock_irq(&bitmap->counts.lock);
    for (block = 0; block < blocks; ) {
        bitmap_counter_t *bmc_old, *bmc_new;
        int set;

        bmc_old = bitmap_get_counter(&old_counts, block,
                         &old_blocks, 0);
        set = bmc_old && NEEDED(*bmc_old);

        if (set) {
            bmc_new = bitmap_get_counter(&bitmap->counts, block,
                             &new_blocks, 1);
            if (*bmc_new == 0) {
                /* need to set on-disk bits too. */
                sector_t end = block + new_blocks;
                sector_t start = block >> chunkshift;
                start <<= chunkshift;
                while (start < end) {
                    bitmap_file_set_bit(bitmap, block);
                    start += 1 << chunkshift;
                }
                *bmc_new = 2;
                bitmap_count_page(&bitmap->counts,
                          block, 1);
                bitmap_set_pending(&bitmap->counts,
                           block);
            }
            *bmc_new |= NEEDED_MASK;
            if (new_blocks < old_blocks)
                old_blocks = new_blocks;
        }
        block += old_blocks;
    }

    if (!init) {
        int i;
        while (block < (chunks << chunkshift)) {
            bitmap_counter_t *bmc;
            bmc = bitmap_get_counter(&bitmap->counts, block,
                         &new_blocks, 1);
            if (bmc) {
                /* new space.  It needs to be resynced, so
                 * we set NEEDED_MASK.
                 */
                if (*bmc == 0) {
                    *bmc = NEEDED_MASK | 2;
                    bitmap_count_page(&bitmap->counts,
                              block, 1);
                    bitmap_set_pending(&bitmap->counts,
                               block);
                }
            }
            block += new_blocks;
        }
        for (i = 0; i < bitmap->storage.file_pages; i++)
            set_page_attr(bitmap, i, BITMAP_PAGE_DIRTY);
    }
    spin_unlock_irq(&bitmap->counts.lock);

    if (!init) {
        bitmap_unplug(bitmap);
        bitmap->mddev->pers->quiesce(bitmap->mddev, 0);
    }
    ret = 0;
err:
    return ret;
}
EXPORT_SYMBOL_GPL(bitmap_resize);

static ssize_t
location_show(struct mddev *mddev, char *page)
{
    ssize_t len;
    if (mddev->bitmap_info.file)
        len = sprintf(page, "file");
    else if (mddev->bitmap_info.offset)
        len = sprintf(page, "%+lld", (long long)mddev->bitmap_info.offset);
    else
        len = sprintf(page, "none");
    len += sprintf(page+len, "\n");
    return len;
}

static ssize_t
location_store(struct mddev *mddev, const char *buf, size_t len)
{

    if (mddev->pers) {
        if (!mddev->pers->quiesce)
            return -EBUSY;
        if (mddev->recovery || mddev->sync_thread)
            return -EBUSY;
    }

    if (mddev->bitmap || mddev->bitmap_info.file ||
        mddev->bitmap_info.offset) {
        /* bitmap already configured.  Only option is to clear it */
        if (strncmp(buf, "none", 4) != 0)
            return -EBUSY;
        if (mddev->pers) {
            mddev->pers->quiesce(mddev, 1);
            bitmap_destroy(mddev);
            mddev->pers->quiesce(mddev, 0);
        }
        mddev->bitmap_info.offset = 0;
        if (mddev->bitmap_info.file) {
            struct file *f = mddev->bitmap_info.file;
            mddev->bitmap_info.file = NULL;
            restore_bitmap_write_access(f);
            fput(f);
        }
    } else {
        /* No bitmap, OK to set a location */
        long long offset;
        if (strncmp(buf, "none", 4) == 0)
            /* nothing to be done */;
        else if (strncmp(buf, "file:", 5) == 0) {
            /* Not supported yet */
            return -EINVAL;
        } else {
            int rv;
            if (buf[0] == '+')
                rv = strict_strtoll(buf+1, 10, &offset);
            else
                rv = strict_strtoll(buf, 10, &offset);
            if (rv)
                return rv;
            if (offset == 0)
                return -EINVAL;
            if (mddev->bitmap_info.external == 0 &&
                mddev->major_version == 0 &&
                offset != mddev->bitmap_info.default_offset)
                return -EINVAL;
            mddev->bitmap_info.offset = offset;
            if (mddev->pers) {
                mddev->pers->quiesce(mddev, 1);
                rv = bitmap_create(mddev);
                if (!rv)
                    rv = bitmap_load(mddev);
                if (rv) {
                    bitmap_destroy(mddev);
                    mddev->bitmap_info.offset = 0;
                }
                mddev->pers->quiesce(mddev, 0);
                if (rv)
                    return rv;
            }
        }
    }
    if (!mddev->external) {
        /* Ensure new bitmap info is stored in
         * metadata promptly.
         */
        set_bit(MD_CHANGE_DEVS, &mddev->flags);
        md_wakeup_thread(mddev->thread);
    }
    return len;
}

static struct md_sysfs_entry bitmap_location =
__ATTR(location, S_IRUGO|S_IWUSR, location_show, location_store);

/* 'bitmap/space' is the space available at 'location' for the
 * bitmap.  This allows the kernel to know when it is safe to
 * resize the bitmap to match a resized array.
 */
static ssize_t
space_show(struct mddev *mddev, char *page)
{
    return sprintf(page, "%lu\n", mddev->bitmap_info.space);
}

static ssize_t
space_store(struct mddev *mddev, const char *buf, size_t len)
{
    unsigned long sectors;
    int rv;

    rv = kstrtoul(buf, 10, &sectors);
    if (rv)
        return rv;

    if (sectors == 0)
        return -EINVAL;

    if (mddev->bitmap &&
        sectors < (mddev->bitmap->storage.bytes + 511) >> 9)
        return -EFBIG; /* Bitmap is too big for this small space */

    /* could make sure it isn't too big, but that isn't really
     * needed - user-space should be careful.
     */
    mddev->bitmap_info.space = sectors;
    return len;
}

static struct md_sysfs_entry bitmap_space =
__ATTR(space, S_IRUGO|S_IWUSR, space_show, space_store);

static ssize_t
timeout_show(struct mddev *mddev, char *page)
{
    ssize_t len;
    unsigned long secs = mddev->bitmap_info.daemon_sleep / HZ;
    unsigned long jifs = mddev->bitmap_info.daemon_sleep % HZ;

    len = sprintf(page, "%lu", secs);
    if (jifs)
        len += sprintf(page+len, ".%03u", jiffies_to_msecs(jifs));
    len += sprintf(page+len, "\n");
    return len;
}

static ssize_t
timeout_store(struct mddev *mddev, const char *buf, size_t len)
{
    /* timeout can be set at any time */
    unsigned long timeout;
    int rv = strict_strtoul_scaled(buf, &timeout, 4);
    if (rv)
        return rv;

    /* just to make sure we don't overflow... */
    if (timeout >= LONG_MAX / HZ)
        return -EINVAL;

    timeout = timeout * HZ / 10000;

    if (timeout >= MAX_SCHEDULE_TIMEOUT)
        timeout = MAX_SCHEDULE_TIMEOUT-1;
    if (timeout < 1)
        timeout = 1;
    mddev->bitmap_info.daemon_sleep = timeout;
    if (mddev->thread) {
        /* if thread->timeout is MAX_SCHEDULE_TIMEOUT, then
         * the bitmap is all clean and we don't need to
         * adjust the timeout right now
         */
        if (mddev->thread->timeout < MAX_SCHEDULE_TIMEOUT) {
            mddev->thread->timeout = timeout;
            md_wakeup_thread(mddev->thread);
        }
    }
    return len;
}

static struct md_sysfs_entry bitmap_timeout =
__ATTR(time_base, S_IRUGO|S_IWUSR, timeout_show, timeout_store);

static ssize_t
backlog_show(struct mddev *mddev, char *page)
{
    return sprintf(page, "%lu\n", mddev->bitmap_info.max_write_behind);
}

static ssize_t
backlog_store(struct mddev *mddev, const char *buf, size_t len)
{
    unsigned long backlog;
    int rv = strict_strtoul(buf, 10, &backlog);
    if (rv)
        return rv;
    if (backlog > COUNTER_MAX)
        return -EINVAL;
    mddev->bitmap_info.max_write_behind = backlog;
    return len;
}

static struct md_sysfs_entry bitmap_backlog =
__ATTR(backlog, S_IRUGO|S_IWUSR, backlog_show, backlog_store);

static ssize_t
chunksize_show(struct mddev *mddev, char *page)
{
    return sprintf(page, "%lu\n", mddev->bitmap_info.chunksize);
}

static ssize_t
chunksize_store(struct mddev *mddev, const char *buf, size_t len)
{
    /* Can only be changed when no bitmap is active */
    int rv;
    unsigned long csize;
    if (mddev->bitmap)
        return -EBUSY;
    rv = strict_strtoul(buf, 10, &csize);
    if (rv)
        return rv;
    if (csize < 512 ||
        !is_power_of_2(csize))
        return -EINVAL;
    mddev->bitmap_info.chunksize = csize;
    return len;
}

static struct md_sysfs_entry bitmap_chunksize =
__ATTR(chunksize, S_IRUGO|S_IWUSR, chunksize_show, chunksize_store);

static ssize_t metadata_show(struct mddev *mddev, char *page)
{
    return sprintf(page, "%s\n", (mddev->bitmap_info.external
                      ? "external" : "internal"));
}

static ssize_t metadata_store(struct mddev *mddev, const char *buf, size_t len)
{
    if (mddev->bitmap ||
        mddev->bitmap_info.file ||
        mddev->bitmap_info.offset)
        return -EBUSY;
    if (strncmp(buf, "external", 8) == 0)
        mddev->bitmap_info.external = 1;
    else if (strncmp(buf, "internal", 8) == 0)
        mddev->bitmap_info.external = 0;
    else
        return -EINVAL;
    return len;
}

static struct md_sysfs_entry bitmap_metadata =
__ATTR(metadata, S_IRUGO|S_IWUSR, metadata_show, metadata_store);

static ssize_t can_clear_show(struct mddev *mddev, char *page)
{
    int len;
    if (mddev->bitmap)
        len = sprintf(page, "%s\n", (mddev->bitmap->need_sync ?
                         "false" : "true"));
    else
        len = sprintf(page, "\n");
    return len;
}

static ssize_t can_clear_store(struct mddev *mddev, const char *buf, size_t len)
{
    if (mddev->bitmap == NULL)
        return -ENOENT;
    if (strncmp(buf, "false", 5) == 0)
        mddev->bitmap->need_sync = 1;
    else if (strncmp(buf, "true", 4) == 0) {
        if (mddev->degraded)
            return -EBUSY;
        mddev->bitmap->need_sync = 0;
    } else
        return -EINVAL;
    return len;
}

static struct md_sysfs_entry bitmap_can_clear =
__ATTR(can_clear, S_IRUGO|S_IWUSR, can_clear_show, can_clear_store);

static ssize_t
behind_writes_used_show(struct mddev *mddev, char *page)
{
    if (mddev->bitmap == NULL)
        return sprintf(page, "0\n");
    return sprintf(page, "%lu\n",
               mddev->bitmap->behind_writes_used);
}

static ssize_t
behind_writes_used_reset(struct mddev *mddev, const char *buf, size_t len)
{
    if (mddev->bitmap)
        mddev->bitmap->behind_writes_used = 0;
    return len;
}

static struct md_sysfs_entry max_backlog_used =
__ATTR(max_backlog_used, S_IRUGO | S_IWUSR,
       behind_writes_used_show, behind_writes_used_reset);

static struct attribute *md_bitmap_attrs[] = {
    &bitmap_location.attr,
    &bitmap_space.attr,
    &bitmap_timeout.attr,
    &bitmap_backlog.attr,
    &bitmap_chunksize.attr,
    &bitmap_metadata.attr,
    &bitmap_can_clear.attr,
    &max_backlog_used.attr,
    NULL
};
struct attribute_group md_bitmap_group = {
    .name = "bitmap",
    .attrs = md_bitmap_attrs,
};