md/bitmap: record the space available for the bitmap in the superblock.

Now that bitmaps can grow and shrink it is best if we record
how much space is available.  This means that when
we reduce the size of the bitmap we won't "lose" the space
for late when we might want to increase the size of the bitmap
again.

Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 8f681da00277aa262322f8a31f62186efcae58d7..15dbe03117e473da9ce6166b6978b7f496b7bc2a 100644 (file)
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -423,6 +423,8 @@ void bitmap_update_sb(struct bitmap *bitmap)
        /* 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);
 }
@@ -536,6 +538,7 @@ static int bitmap_read_sb(struct bitmap *bitmap)
        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;
 
@@ -573,6 +576,7 @@ static int bitmap_read_sb(struct bitmap *bitmap)
        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))
@@ -633,6 +637,9 @@ out_no_sb:
        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;

diff --git a/drivers/md/bitmap.h b/drivers/md/bitmap.h
index 04dcde3871be59cfa442880705346567b4c5b1cd..df4aeb6ac6f04ea0c30b9e28812fc64c8c3646a0 100644 (file)
--- a/drivers/md/bitmap.h
+++ b/drivers/md/bitmap.h
@@ -128,8 +128,10 @@ typedef struct bitmap_super_s {
        __le32 chunksize;    /* 52  the bitmap chunk size in bytes */
        __le32 daemon_sleep; /* 56  seconds between disk flushes */
        __le32 write_behind; /* 60  number of outstanding write-behind writes */
+       __le32 sectors_reserved; /* 64 number of 512-byte sectors that are
+                                 * reserved for the bitmap. */
 
-       __u8  pad[256 - 64]; /* set to zero */
+       __u8  pad[256 - 68]; /* set to zero */
 } bitmap_super_t;
 
 /* notes: