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>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/md/bitmap.h b/drivers/md/bitmap.h
index 04dcde3871be..df4aeb6ac6f0 100644
--- 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: