[PATCH] md: allow md intent bitmap to be stored near the superblock.

This provides an alternate to storing the bitmap in a separate file.  The
bitmap can be stored at a given offset from the superblock.  Obviously the
creator of the array must make sure this doesn't intersect with data....
After is good for version-0.90 superblocks.

Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/include/linux/raid/md_p.h b/include/linux/raid/md_p.h
index 8ba95d67329f..8e592a25a8b5 100644
--- a/include/linux/raid/md_p.h
+++ b/include/linux/raid/md_p.h
@@ -96,6 +96,7 @@ typedef struct mdp_device_descriptor_s {
 #define MD_SB_CLEAN             0
 #define MD_SB_ERRORS            1
 
+#define MD_SB_BITMAP_PRESENT    8 /* bitmap may be present nearby */
 typedef struct mdp_superblock_s {
         /*
          * Constant generic information
@@ -184,7 +185,7 @@ struct mdp_superblock_1 {
         /* constant array information - 128 bytes */
         __u32   magic;          /* MD_SB_MAGIC: 0xa92b4efc - little endian */
         __u32   major_version;  /* 1 */
-        __u32   feature_map;    /* 0 for now */
+        __u32   feature_map;    /* bit 0 set if 'bitmap_offset' is meaningful */
         __u32   pad0;           /* always set to 0 when writing */
 
         __u8    set_uuid[16];   /* user-space generated. */
@@ -197,6 +198,10 @@ struct mdp_superblock_1 {
 
         __u32   chunksize;      /* in 512byte sectors */
         __u32   raid_disks;
+        __u32   bitmap_offset;  /* sectors after start of superblock that bitmap starts
+                                 * NOTE: signed, so bitmap can be before superblock
+                                 * only meaningful of feature_map[0] is set.
+                                 */
         __u8    pad1[128-96];   /* set to 0 when written */
 
         /* constant this-device information - 64 bytes */