From: Mikulas Patocka <[email-masked]>

dm-kcopyd: accept zero-size jobs

This patch changes dm-kcopyd so that it accepts zero-size jobs and completes
them immediatelly via its completion thread.

It is needed for multisnapshots snapshot resizing. When we are writing to
a chunk beyond origin end, no copying is done. To simplify the code, we submit
an empty request to kcopyd and let kcopyd complete it. If we didn't submit
a request to kcopyd and called the completion routine immediatelly, it would
violate the principle that completion is called only from one thread and
it would need additional locking.

Signed-off-by: Mikulas Patocka <[email-masked]>
Signed-off-by: Alasdair G Kergon <[email-masked]>

---
 drivers/md/dm-kcopyd.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Index: linux-2.6.32/drivers/md/dm-kcopyd.c
===================================================================
--- linux-2.6.32.orig/drivers/md/dm-kcopyd.c
+++ linux-2.6.32/drivers/md/dm-kcopyd.c
@@ -450,7 +450,10 @@ static void dispatch_job(struct kcopyd_j
 {
 	struct dm_kcopyd_client *kc = job->kc;
 	atomic_inc(&kc->nr_jobs);
-	push(&kc->pages_jobs, job);
+	if (unlikely(!job->source.count))
+		push(&kc->complete_jobs, job);
+	else
+		push(&kc->pages_jobs, job);
 	wake(kc);
 }