[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>

drivers/md/md.c

@@ -645,7 +645,7 @@ static int super_90_validate(mddev_t *mddev, mdk_rdev_t *rdev)
 
 		if (sb->state & (1<<MD_SB_BITMAP_PRESENT) &&
 		    mddev->bitmap_file == NULL) {
-			if (mddev->level != 1) {
+			if (mddev->level != 1 && mddev->level != 5) {
 				/* FIXME use a better test */
 				printk(KERN_WARNING "md: bitmaps only support for raid1\n");
 				return -EINVAL;
@@ -3517,7 +3517,6 @@ void md_done_sync(mddev_t *mddev, int blocks, int ok)
  */
 void md_write_start(mddev_t *mddev, struct bio *bi)
 {
-	DEFINE_WAIT(w);
 	if (bio_data_dir(bi) != WRITE)
 		return;
 

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
 	 */