[PATCH] md: add write-behind support for md/raid1

If a device is flagged 'WriteMostly' and the array has a bitmap, and the
bitmap superblock indicates that write_behind is allowed, then write_behind is
enabled for WriteMostly devices.

Write requests will be acknowledges as complete to the caller (via b_end_io)
when all non-WriteMostly devices have completed the write, but will not be
cleared from the bitmap until all devices complete.

This requires memory allocation to make a local copy of the data being
written.  If there is insufficient memory, then we fall-back on normal write
semantics.

Signed-Off-By: Paul Clements <paul.clements@steeleye.com>
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, 13 insertions, 0 deletions

diff --git a/include/linux/raid/raid1.h b/include/linux/raid/raid1.h
index 9d93cf12e890..60e19b667548 100644
--- a/include/linux/raid/raid1.h
+++ b/include/linux/raid/raid1.h
@@ -80,6 +80,9 @@ struct r1bio_s {
         atomic_t                remaining; /* 'have we finished' count,
                                             * used from IRQ handlers
                                             */
+        atomic_t                behind_remaining; /* number of write-behind ios remaining
+                                                 * in this BehindIO request
+                                                 */
         sector_t                sector;
         int                     sectors;
         unsigned long           state;
@@ -107,4 +110,14 @@ struct r1bio_s {
 #define R1BIO_Uptodate  0
 #define R1BIO_IsSync    1
 #define R1BIO_Degraded  2
+#define R1BIO_BehindIO   3
+/* For write-behind requests, we call bi_end_io when
+ * the last non-write-behind device completes, providing
+ * any write was successful.  Otherwise we call when
+ * any write-behind write succeeds, otherwise we call
+ * with failure when last write completes (and all failed).
+ * Record that bi_end_io was called with this flag...
+ */
+#define R1BIO_Returned 4
+
 #endif