When there is one merging snapshot and other non-merging snapshots, make
exceptions in non-merging snapshots while merging.

This is not yet complete (the exception is not made when remapping directly to
the origin), another patch fixes that.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 drivers/md/dm-snap.c |   29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

Index: linux-2.6.26-devel/drivers/md/dm-snap.c
===================================================================
--- linux-2.6.26-devel.orig/drivers/md/dm-snap.c	2008-07-14 20:23:58.000000000 +0200
+++ linux-2.6.26-devel/drivers/md/dm-snap.c	2008-07-14 20:24:03.000000000 +0200
@@ -157,6 +157,8 @@ struct origin {
 static struct list_head *_origins;
 static struct rw_semaphore _origins_lock;
 
+static DECLARE_WAIT_QUEUE_HEAD(_pending_exception_done);
+
 static int init_origin_hash(void)
 {
 	int i;
@@ -567,12 +569,17 @@ static int set_chunk_size(struct dm_snap
 static void flush_bios(struct bio *bio);
 static void error_bios(struct bio *bio);
 
+static int __origin_write(struct list_head *snapshots, sector_t sector, struct bio *bio);
+
 static void merge_callback(int read_err, unsigned long write_err, void *context);
 
 static void snapshot_merge_process(struct dm_snapshot *s)
 {
 	int r;
 	chunk_t old_chunk, new_chunk;
+	struct origin *o;
+	chunk_t min_chunksize;
+	int must_wait;
 	struct dm_io_region src, dest;
 
 	BUG_ON(!s->merge_running);
@@ -605,6 +612,26 @@ static void snapshot_merge_process(struc
 	src.sector = chunk_to_sector(s, new_chunk);
 	src.count = dest.count;
 
+	test_again:
+	/* Reallocate other snapshots */
+	down_read(&_origins_lock);
+	o = __lookup_origin(s->origin->bdev);
+	must_wait = 0;
+	min_chunksize = minimum_chunk_size(o);
+	if (min_chunksize) {
+		chunk_t n;
+		for (n = 0; n < s->chunk_size; n += min_chunksize) {
+			r = __origin_write(&o->snapshots, dest.sector + n, NULL);
+			if (r == DM_MAPIO_SUBMITTED)
+				must_wait = 1;
+		}
+	}
+	up_read(&_origins_lock);
+	if (must_wait) {
+		sleep_on_timeout(&_pending_exception_done, HZ / 100 + 1);
+		goto test_again;
+	}
+
 	down_write(&s->lock);
 	s->merge_write_interlock = old_chunk;
 	s->merge_write_interlock_n = 1;
@@ -1074,6 +1101,8 @@ static void pending_complete(struct dm_s
 	origin_bios = bio_list_get(&pe->origin_bios);
 	free_pending_exception(pe);
 
+	wake_up_all(&_pending_exception_done);
+
 	up_write(&s->lock);
 
 	/* Submit any pending write bios */