[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>
diff --git a/include/linux/raid/md_p.h b/include/linux/raid/md_p.h
index 8ba95d6..8e592a2 100644
--- a/include/linux/raid/md_p.h
+++ b/include/linux/raid/md_p.h
@@ -96,6 +96,7 @@
#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 @@
/* 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 @@
__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 */