[PATCH] md: optimised resync using Bitmap based intent logging

With this patch, the intent to write to some block in the array can be logged
to a bitmap file.  Each bit represents some number of sectors and is set
before any update happens, and only cleared when all writes relating to all
sectors are complete.

After an unclean shutdown, information in this bitmap can be used to optimise
resync - only sectors which could be out-of-sync need to be updated.

Also if a drive is removed and then added back into an array, the recovery can
make use of the bitmap to optimise reconstruction.  This is not implemented in
this patch.

Currently the bitmap is stored in a file which must (obviously) be stored on a
separate device.

The patch only provided infrastructure.  It does not update any personalities
to bitmap intent logging.

Md arrays can still be used with no bitmap file.  This patch has minimal
impact on such arrays.

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, 7 insertions, 0 deletions

diff --git a/include/linux/raid/md_u.h b/include/linux/raid/md_u.h
index a2df5c2a42af..81da20ccec4d 100644
--- a/include/linux/raid/md_u.h
+++ b/include/linux/raid/md_u.h
@@ -23,6 +23,7 @@
 #define GET_DISK_INFO           _IOR (MD_MAJOR, 0x12, mdu_disk_info_t)
 #define PRINT_RAID_DEBUG        _IO (MD_MAJOR, 0x13)
 #define RAID_AUTORUN            _IO (MD_MAJOR, 0x14)
+#define GET_BITMAP_FILE         _IOR (MD_MAJOR, 0x15, mdu_bitmap_file_t)
 
 /* configuration */
 #define CLEAR_ARRAY             _IO (MD_MAJOR, 0x20)
@@ -36,6 +37,7 @@
 #define HOT_ADD_DISK            _IO (MD_MAJOR, 0x28)
 #define SET_DISK_FAULTY         _IO (MD_MAJOR, 0x29)
 #define HOT_GENERATE_ERROR      _IO (MD_MAJOR, 0x2a)
+#define SET_BITMAP_FILE         _IOW (MD_MAJOR, 0x2b, int)
 
 /* usage */
 #define RUN_ARRAY               _IOW (MD_MAJOR, 0x30, mdu_param_t)
@@ -106,6 +108,11 @@ typedef struct mdu_start_info_s {
 
 } mdu_start_info_t;
 
+typedef struct mdu_bitmap_file_s
+{
+        char pathname[4096];
+} mdu_bitmap_file_t;
+
 typedef struct mdu_param_s
 {
         int                     personality;    /* 1,2,3,4 */