[PATCH] md: add write-intent-bitmap support to raid5

Most awkward part of this is delaying write requests until bitmap updates have
been flushed.

To achieve this, we have a sequence number (seq_flush) which is incremented
each time the raid5 is unplugged.

If the raid thread notices that this has changed, it flushes bitmap changes,
and assigned the value of seq_flush to seq_write.

When a write request arrives, it is given the number from seq_write, and that
write request may not complete until seq_flush is larger than the saved seq
number.

We have a new queue for storing stripes which are waiting for a bitmap flush
and an extra flag for stripes to record if the write was 'degraded' and so
should not clear the a bit in the bitmap.

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, 1 deletions

diff --git a/include/linux/raid/raid5.h b/include/linux/raid/raid5.h
index d63ddcb4afad..176fc653c284 100644
--- a/include/linux/raid/raid5.h
+++ b/include/linux/raid/raid5.h
@@ -134,6 +134,7 @@ struct stripe_head {
         unsigned long           state;                  /* state flags */
         atomic_t                count;                  /* nr of active thread/requests */
         spinlock_t              lock;
+        int                     bm_seq; /* sequence number for bitmap flushes */
         struct r5dev {
                 struct bio      req;
                 struct bio_vec  vec;
@@ -165,12 +166,13 @@ struct stripe_head {
 /*
  * Stripe state
  */
-#define STRIPE_ERROR            1
 #define STRIPE_HANDLE           2
 #define STRIPE_SYNCING          3
 #define STRIPE_INSYNC           4
 #define STRIPE_PREREAD_ACTIVE   5
 #define STRIPE_DELAYED          6
+#define STRIPE_DEGRADED         7
+#define STRIPE_BIT_DELAY        8
 
 /*
  * Plugging:
@@ -210,10 +212,20 @@ struct raid5_private_data {
 
         struct list_head        handle_list; /* stripes needing handling */
         struct list_head        delayed_list; /* stripes that have plugged requests */
+        struct list_head        bitmap_list; /* stripes delaying awaiting bitmap update */
         atomic_t                preread_active_stripes; /* stripes with scheduled io */
 
         char                    cache_name[20];
         kmem_cache_t            *slab_cache; /* for allocating stripes */
+
+        int                     seq_flush, seq_write;
+        int                     quiesce;
+
+        int                     fullsync;  /* set to 1 if a full sync is needed,
+                                            * (fresh device added).
+                                            * Cleared when a sync completes.
+                                            */
+
         /*
          * Free stripes pool
          */