[PATCH] md: support write-mostly device in raid1

This allows a device in a raid1 to be marked as "write mostly".  Read requests
will only be sent if there is no other option.

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>

2 files changed, 12 insertions, 2 deletions

diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index 817062bf7352..7ef78e15ce04 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -181,6 +181,9 @@ struct mdk_rdev_s
         int faulty;                     /* if faulty do not issue IO requests */
         int in_sync;                    /* device is a full member of the array */
 
+        unsigned long   flags;          /* Should include faulty and in_sync here. */
+#define WriteMostly     4               /* Avoid reading if at all possible */
+
         int desc_nr;                    /* descriptor index in the superblock */
         int raid_disk;                  /* role of device in array */
         int saved_raid_disk;            /* role that device used to have in the
diff --git a/include/linux/raid/md_p.h b/include/linux/raid/md_p.h
index dc65cd435494..4f047f84fb1f 100644
--- a/include/linux/raid/md_p.h
+++ b/include/linux/raid/md_p.h
@@ -79,6 +79,11 @@
 #define MD_DISK_SYNC            2 /* disk is in sync with the raid set */
 #define MD_DISK_REMOVED         3 /* disk is in sync with the raid set */
 
+#define MD_DISK_WRITEMOSTLY     9 /* disk is "write-mostly" is RAID1 config.
+                                   * read requests will only be sent here in
+                                   * dire need
+                                   */
+
 typedef struct mdp_device_descriptor_s {
         __u32 number;           /* 0 Device number in the entire set          */
         __u32 major;            /* 1 Device major number                      */
@@ -193,7 +198,7 @@ struct mdp_superblock_1 {
 
         __u64   ctime;          /* lo 40 bits are seconds, top 24 are microseconds or 0*/
         __u32   level;          /* -4 (multipath), -1 (linear), 0,1,4,5 */
-        __u32   layout;         /* only for raid5 currently */
+        __u32   layout;         /* only for raid5 and raid10 currently */
         __u64   size;           /* used size of component devices, in 512byte sectors */
 
         __u32   chunksize;      /* in 512byte sectors */
@@ -212,7 +217,9 @@ struct mdp_superblock_1 {
         __u32   dev_number;     /* permanent identifier of this  device - not role in raid */
         __u32   cnt_corrected_read; /* number of read errors that were corrected by re-writing */
         __u8    device_uuid[16]; /* user-space setable, ignored by kernel */
-        __u8    pad2[64-56];    /* set to 0 when writing */
+        __u8    devflags;       /* per-device flags.  Only one defined...*/
+#define WriteMostly1    1       /* mask for writemostly flag in above */
+        __u8    pad2[64-57];    /* set to 0 when writing */
 
         /* array state information - 64 bytes */
         __u64   utime;          /* 40 bits second, 24 btes microseconds */