[PATCH] md: Infrastructure to allow normal IO to continue while array is expanding

We need to allow that different stripes are of different effective sizes, and
use the appropriate size.  Also, when a stripe is being expanded, we must
block any IO attempts until the stripe is stable again.

Key elements in this change are:
 - each stripe_head gets a 'disk' field which is part of the key,
   thus there can sometimes be two stripe heads of the same area of
   the array, but covering different numbers of devices.  One of these
   will be marked STRIPE_EXPANDING and so won't accept new requests.
 - conf->expand_progress tracks how the expansion is progressing and
   is used to determine whether the target part of the array has been
   expanded yet or not.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/linux/raid/raid5.h b/include/linux/raid/raid5.h
index b7b2653af7bb..6fa274aea2a0 100644
--- a/include/linux/raid/raid5.h
+++ b/include/linux/raid/raid5.h
@@ -135,6 +135,7 @@ struct stripe_head {
         atomic_t                count;                  /* nr of active thread/requests */
         spinlock_t              lock;
         int                     bm_seq; /* sequence number for bitmap flushes */
+        int                     disks;                  /* disks in stripe */
         struct r5dev {
                 struct bio      req;
                 struct bio_vec  vec;
@@ -174,6 +175,7 @@ struct stripe_head {
 #define STRIPE_DELAYED          6
 #define STRIPE_DEGRADED         7
 #define STRIPE_BIT_DELAY        8
+#define STRIPE_EXPANDING        9
 
 /*
  * Plugging:
@@ -211,6 +213,10 @@ struct raid5_private_data {
         int                     raid_disks, working_disks, failed_disks;
         int                     max_nr_stripes;
 
+        /* used during an expand */
+        sector_t                expand_progress;        /* MaxSector when no expand happening */
+        int                     previous_raid_disks;
+
         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 */