[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 */