/*
 * 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
 */

/*
 * 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.
 */

#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/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";
}


/*
 * 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 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_path.dentry;
        v = file->f_path.mnt;

        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);

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

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

                if (sync_page_io(rdev->bdev, target, PAGE_SIZE, page, READ)) {
                        page->index = index;
                        attach_page_buffers(page, NULL); /* so that free_buffer will
                                                          * quietly no-op */
                        return page;
                }
        }
        return ERR_PTR(-EIO);

}

static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
{
        mdk_rdev_t *rdev;
        struct list_head *tmp;
        mddev_t *mddev = bitmap->mddev;

        ITERATE_RDEV(mddev, rdev, tmp)
                if (test_bit(In_sync, &rdev->flags)
                    && !test_bit(Faulty, &rdev->flags)) {
                        int size = PAGE_SIZE;
                        if (page->index == bitmap->file_pages-1)
                                size = roundup(bitmap->last_page_size,
                                               bdev_hardsect_size(rdev->bdev));
                        /* Just make sure we aren't corrupting data or
                         * metadata
                         */
                        if (bitmap->offset < 0) {
                                /* DATA  BITMAP METADATA  */
                                if (bitmap->offset
                                    + (long)(page->index * (PAGE_SIZE/512))
                                    + size/512 > 0)
                                        /* bitmap runs in to metadata */
                                        return -EINVAL;
                                if (rdev->data_offset + mddev->size*2
                                    > rdev->sb_offset*2 + bitmap->offset)
                                        /* data runs in to bitmap */
                                        return -EINVAL;
                        } else if (rdev->sb_offset*2 < rdev->data_offset) {
                                /* METADATA BITMAP DATA */
                                if (rdev->sb_offset*2
                                    + bitmap->offset
                                    + page->index*(PAGE_SIZE/512) + size/512
                                    > rdev->data_offset)
                                        /* bitmap runs in to data */
                                        return -EINVAL;
                        } else {
                                /* DATA METADATA BITMAP - no problems */
                        }
                        md_super_write(mddev, rdev,
                                       (rdev->sb_offset<<1) + bitmap->offset
                                       + page->index * (PAGE_SIZE/512),
                                       size,
                                       page);
                }

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

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->file == NULL) {
                switch (write_sb_page(bitmap, page, wait)) {
                case -EINVAL:
                        bitmap->flags |= BITMAP_WRITE_ERROR;
                }
        } 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, bh);
                        bh = bh->b_this_page;
                }

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

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

        if (!uptodate) {
                spin_lock_irqsave(&bitmap->lock, flags);
                bitmap->flags |= BITMAP_WRITE_ERROR;
                spin_unlock_irqrestore(&bitmap->lock, 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 = 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 struct page *read_page(struct file *file, unsigned long index,
                              struct bitmap *bitmap,
                              unsigned long count)
{
        struct page *page = NULL;
        struct inode *inode = file->f_path.dentry->d_inode;
        struct buffer_head *bh;
        sector_t block;

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

        page = alloc_page(GFP_KERNEL);
        if (!page)
                page = ERR_PTR(-ENOMEM);
        if (IS_ERR(page))
                goto out;

        bh = alloc_page_buffers(page, 1<<inode->i_blkbits, 0);
        if (!bh) {
                put_page(page);
                page = ERR_PTR(-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! */
                                free_buffers(page);
                                page = ERR_PTR(-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 (bitmap->flags & BITMAP_WRITE_ERROR) {
                free_buffers(page);
                page = ERR_PTR(-EIO);
        }
out:
        if (IS_ERR(page))
                printk(KERN_ALERT "md: bitmap read error: (%dB @ %Lu): %ld\n",
                        (int)PAGE_SIZE,
                        (unsigned long long)index << PAGE_SHIFT,
                        PTR_ERR(page));
        return page;
}

/*
 * 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;
        unsigned long flags;

        if (!bitmap || !bitmap->mddev) /* no bitmap for this array */
                return;
        spin_lock_irqsave(&bitmap->lock, flags);
        if (!bitmap->sb_page) { /* no superblock */
                spin_unlock_irqrestore(&bitmap->lock, flags);
                return;
        }
        spin_unlock_irqrestore(&bitmap->lock, flags);
        sb = (bitmap_super_t *)kmap_atomic(bitmap->sb_page, KM_USER0);
        sb->events = cpu_to_le64(bitmap->mddev->events);
        if (!bitmap->mddev->degraded)
                sb->events_cleared = cpu_to_le64(bitmap->mddev->events);
        kunmap_atomic(sb, KM_USER0);
        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_atomic(bitmap->sb_page, KM_USER0);
        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, KM_USER0);
}

/* 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;
        int err = -EINVAL;

        /* page 0 is the superblock, read it... */
        if (bitmap->file) {
                loff_t isize = i_size_read(bitmap->file->f_mapping->host);
                int bytes = isize > PAGE_SIZE ? PAGE_SIZE : isize;

                bitmap->sb_page = read_page(bitmap->file, 0, bitmap, bytes);
        } else {
                bitmap->sb_page = read_sb_page(bitmap->mddev, bitmap->offset, 0);
        }
        if (IS_ERR(bitmap->sb_page)) {
                err = PTR_ERR(bitmap->sb_page);
                bitmap->sb_page = NULL;
                return err;
        }

        sb = (bitmap_super_t *)kmap_atomic(bitmap->sb_page, KM_USER0);

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

        /* 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 < PAGE_SIZE)
                reason = "bitmap chunksize too small";
        else if ((1 << ffz(~chunksize)) != chunksize)
                reason = "bitmap chunksize not a power of 2";
        else if (daemon_sleep < 1 || daemon_sleep > MAX_SCHEDULE_TIMEOUT / HZ)
                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)
                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 |= cpu_to_le32(BITMAP_STALE);
        }
success:
        /* assign fields using values from superblock */
        bitmap->chunksize = chunksize;
        bitmap->daemon_sleep = daemon_sleep;
        bitmap->daemon_lastrun = jiffies;
        bitmap->max_write_behind = write_behind;
        bitmap->flags |= le32_to_cpu(sb->state);
        if (le32_to_cpu(sb->version) == BITMAP_MAJOR_HOSTENDIAN)
                bitmap->flags |= BITMAP_HOSTENDIAN;
        bitmap->events_cleared = le64_to_cpu(sb->events_cleared);
        if (sb->state & cpu_to_le32(BITMAP_STALE))
                bitmap->events_cleared = bitmap->mddev->events;
        err = 0;
out:
        kunmap_atomic(sb, KM_USER0);
        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.  Return the old value */
static int bitmap_mask_state(struct bitmap *bitmap, enum bitmap_state bits,
                             enum bitmap_mask_op op)
{
        bitmap_super_t *sb;
        unsigned long flags;
        int old;

        spin_lock_irqsave(&bitmap->lock, flags);
        if (!bitmap->sb_page) { /* can't set the state */
                spin_unlock_irqrestore(&bitmap->lock, flags);
                return 0;
        }
        spin_unlock_irqrestore(&bitmap->lock, flags);
        sb = (bitmap_super_t *)kmap_atomic(bitmap->sb_page, KM_USER0);
        old = le32_to_cpu(sb->state) & bits;
        switch (op) {
                case MASK_SET: sb->state |= cpu_to_le32(bits);
                                break;
                case MASK_UNSET: sb->state &= cpu_to_le32(~bits);
                                break;
                default: BUG();
        }
        kunmap_atomic(sb, KM_USER0);
        return old;
}

/*
 * 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)
{
        if (file_page_index(chunk) >= bitmap->file_pages) return NULL;
        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 */
                        free_buffers(map[pages]);
        kfree(map);
        kfree(attr);

        if (sb_page)
                free_buffers(sb_page);
}

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

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

        if (file)
                wait_event(bitmap->write_wait,
                           atomic_read(&bitmap->pending_writes)==0);
        bitmap_file_unmap(bitmap);

        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 (bitmap_mask_state(bitmap, BITMAP_STALE, MASK_SET) == 0) {
                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);
                } else
                        printk(KERN_ALERT
                               "%s: disabling internal bitmap due to errors\n",
                               bmname(bitmap));
        }

        bitmap_file_put(bitmap);

        return;
}

enum bitmap_page_attr {
        BITMAP_PAGE_DIRTY = 0, // there are set bits that need to be synced
        BITMAP_PAGE_CLEAN = 1, // there are bits that might need to be cleared
        BITMAP_PAGE_NEEDWRITE=2, // 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)
{
        __set_bit((page->index<<2) + attr, bitmap->filemap_attr);
}

static inline void clear_page_attr(struct bitmap *bitmap, struct page *page,
                                enum bitmap_page_attr attr)
{
        __clear_bit((page->index<<2) + attr, bitmap->filemap_attr);
}

static inline unsigned long test_page_attr(struct bitmap *bitmap, struct page *page,
                                           enum bitmap_page_attr attr)
{
        return test_bit((page->index<<2) + attr, bitmap->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 >> CHUNK_BLOCK_SHIFT(bitmap);

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

        page = filemap_get_page(bitmap, chunk);
        if (!page) return;
        bit = file_page_offset(chunk);

        /* set the bit */
        kaddr = kmap_atomic(page, KM_USER0);
        if (bitmap->flags & BITMAP_HOSTENDIAN)
                set_bit(bit, kaddr);
        else
                ext2_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 */
void bitmap_unplug(struct bitmap *bitmap)
{
        unsigned long i, flags;
        int dirty, need_write;
        struct page *page;
        int wait = 0;

        if (!bitmap)
                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->file_pages; i++) {
                spin_lock_irqsave(&bitmap->lock, flags);
                if (!bitmap->filemap) {
                        spin_unlock_irqrestore(&bitmap->lock, flags);
                        return;
                }
                page = bitmap->filemap[i];
                dirty = test_page_attr(bitmap, page, BITMAP_PAGE_DIRTY);
                need_write = test_page_attr(bitmap, page, BITMAP_PAGE_NEEDWRITE);
                clear_page_attr(bitmap, page, BITMAP_PAGE_DIRTY);
                clear_page_attr(bitmap, page, BITMAP_PAGE_NEEDWRITE);
                if (dirty)
                        wait = 1;
                spin_unlock_irqrestore(&bitmap->lock, flags);

                if (dirty | need_write)
                        write_page(bitmap, page, 0);
        }
        if (wait) { /* if any writes were performed, we need to wait on them */
                if (bitmap->file)
                        wait_event(bitmap->write_wait,
                                   atomic_read(&bitmap->pending_writes)==0);
                else
                        md_super_wait(bitmap->mddev);
        }
        if (bitmap->flags & BITMAP_WRITE_ERROR)
                bitmap_file_kick(bitmap);
}

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, *oldpage = NULL;
        unsigned long num_pages, bit_cnt = 0;
        struct file *file;
        unsigned long bytes, offset;
        int outofdate;
        int ret = -ENOSPC;
        void *paddr;

        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 err;
        }

        ret = -ENOMEM;

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

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

        oldindex = ~0L;

        for (i = 0; i < chunks; i++) {
                int b;
                index = file_page_index(i);
                bit = file_page_offset(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 == num_pages-1)
                                count = bytes + sizeof(bitmap_super_t)
                                        - index * PAGE_SIZE;
                        else
                                count = PAGE_SIZE;
                        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, bitmap, count);
                                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 err;
                        }

                        oldindex = index;
                        oldpage = page;

                        if (outofdate) {
                                /*
                                 * if bitmap is out of date, dirty the
                                 * whole page and write it out
                                 */
                                paddr = kmap_atomic(page, KM_USER0);
                                memset(paddr + offset, 0xff,
                                       PAGE_SIZE - offset);
                                kunmap_atomic(paddr, KM_USER0);
                                write_page(bitmap, page, 1);

                                ret = -EIO;
                                if (bitmap->flags & BITMAP_WRITE_ERROR) {
                                        /* release, page not in filemap yet */
                                        put_page(page);
                                        goto err;
                                }
                        }

                        bitmap->filemap[bitmap->file_pages++] = page;
                        bitmap->last_page_size = count;
                }
                paddr = kmap_atomic(page, KM_USER0);
                if (bitmap->flags & BITMAP_HOSTENDIAN)
                        b = test_bit(bit, paddr);
                else
                        b = ext2_test_bit(bit, paddr);
                kunmap_atomic(paddr, KM_USER0);
                if (b) {
                        /* if the disk bit is set, set the memory bit */
                        bitmap_set_memory_bits(bitmap, i << CHUNK_BLOCK_SHIFT(bitmap),
                                               ((i+1) << (CHUNK_BLOCK_SHIFT(bitmap)) >= start)
                                );
                        bit_cnt++;
                        set_page_attr(bitmap, page, BITMAP_PAGE_CLEAN);
                }
        }

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

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

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

        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;

        for (i=0; i < bitmap->file_pages; i++)
                set_page_attr(bitmap, bitmap->filemap[i],
                              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
 */

void bitmap_daemon_work(struct bitmap *bitmap)
{
        unsigned long j;
        unsigned long flags;
        struct page *page = NULL, *lastpage = NULL;
        int blocks;
        void *paddr;

        if (bitmap == NULL)
                return;
        if (time_before(jiffies, bitmap->daemon_lastrun + bitmap->daemon_sleep*HZ))
                return;
        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 (!test_page_attr(bitmap, page, BITMAP_PAGE_CLEAN)) {
                                int need_write = test_page_attr(bitmap, page,
                                                                BITMAP_PAGE_NEEDWRITE);
                                if (need_write)
                                        clear_page_attr(bitmap, page, BITMAP_PAGE_NEEDWRITE);

                                spin_unlock_irqrestore(&bitmap->lock, flags);
                                if (need_write)
                                        write_page(bitmap, page, 0);
                                continue;
                        }

                        /* grab the new page, sync and release the old */
                        if (lastpage != NULL) {
                                if (test_page_attr(bitmap, lastpage, BITMAP_PAGE_NEEDWRITE)) {
                                        clear_page_attr(bitmap, lastpage, BITMAP_PAGE_NEEDWRITE);
                                        spin_unlock_irqrestore(&bitmap->lock, flags);
                                        write_page(bitmap, lastpage, 0);
                                } else {
                                        set_page_attr(bitmap, lastpage, BITMAP_PAGE_NEEDWRITE);
                                        spin_unlock_irqrestore(&bitmap->lock, flags);
                                }
                        } else
                                spin_unlock_irqrestore(&bitmap->lock, flags);
                        lastpage = 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 */
                                paddr = kmap_atomic(page, KM_USER0);
                                if (bitmap->flags & BITMAP_HOSTENDIAN)
                                        clear_bit(file_page_offset(j), paddr);
                                else
                                        ext2_clear_bit(file_page_offset(j), paddr);
                                kunmap_atomic(paddr, KM_USER0);
                        }
                }
                spin_unlock_irqrestore(&bitmap->lock, flags);
        }

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

}

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, int behind)
{
        if (!bitmap) return 0;

        if (behind) {
                atomic_inc(&bitmap->behind_writes);
                PRINTK(KERN_DEBUG "inc write-behind count %d/%d\n",
                  atomic_read(&bitmap->behind_writes), bitmap->max_write_behind);
        }

        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;
                }

                if (unlikely((*bmc & COUNTER_MAX) == 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->lock);
                        blk_unplug(bitmap->mddev->queue);
                        schedule();
                        finish_wait(&bitmap->overflow_wait, &__wait);
                        continue;
                }

                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;
                }

                (*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, int behind)
{
        if (!bitmap) return;
        if (behind) {
                atomic_dec(&bitmap->behind_writes);
                PRINTK(KERN_DEBUG "dec write-behind count %d/%d\n",
                  atomic_read(&bitmap->behind_writes), bitmap->max_write_behind);
        }

        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;

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

                (*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, int needed)
{
        /* 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?NEEDED_MASK:0);
                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);

}

/* 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 = chunk << CHUNK_BLOCK_SHIFT(bitmap);
                bitmap_set_memory_bits(bitmap, sec, 1);
                bitmap_file_set_bit(bitmap, sec);
        }
}

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

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

        /* run the daemon_work three time to ensure everything is flushed
         * that can be
         */
        sleep = bitmap->daemon_sleep;
        bitmap->daemon_sleep = 0;
        bitmap_daemon_work(bitmap);
        bitmap_daemon_work(bitmap);
        bitmap_daemon_work(bitmap);
        bitmap->daemon_sleep = sleep;
        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;

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

        bp = bitmap->bp;
        pages = bitmap->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(mddev_t *mddev)
{
        struct bitmap *bitmap = mddev->bitmap;

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

        mddev->bitmap = NULL; /* disconnect from the md device */
        if (mddev->thread)
                mddev->thread->timeout = MAX_SCHEDULE_TIMEOUT;

        bitmap_free(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;
        sector_t start;

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

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

        bitmap->mddev = mddev;

        bitmap->file = file;
        bitmap->offset = mddev->bitmap_offset;
        if (file) {
                get_file(file);
                do_sync_mapping_range(file->f_mapping, 0, LLONG_MAX,
                                      SYNC_FILE_RANGE_WAIT_BEFORE |
                                      SYNC_FILE_RANGE_WRITE |
                                      SYNC_FILE_RANGE_WAIT_AFTER);
        }
        /* read superblock from bitmap file (this sets bitmap->chunksize) */
        err = bitmap_read_sb(bitmap);
        if (err)
                goto error;

        bitmap->chunkshift = ffz(~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 = kzalloc(pages * sizeof(*bitmap->bp), GFP_KERNEL);
#endif
        err = -ENOMEM;
        if (!bitmap->bp)
                goto error;

        /* now that we have some pages available, initialize the in-memory
         * bitmap from the on-disk bitmap */
        start = 0;
        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;
        err = bitmap_init_from_disk(bitmap, start);

        if (err)
                goto error;

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

        mddev->bitmap = bitmap;

        mddev->thread->timeout = bitmap->daemon_sleep * HZ;

        bitmap_update_sb(bitmap);

        return (bitmap->flags & BITMAP_WRITE_ERROR) ? -EIO : 0;

 error:
        bitmap_free(bitmap);
        return err;
}

/* 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);