dm kcopyd: accept zero size jobs

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 <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/md/dm-kcopyd.c b/drivers/md/dm-kcopyd.c
index 3e3fc06cb861..addf83475040 100644
--- a/drivers/md/dm-kcopyd.c
+++ b/drivers/md/dm-kcopyd.c
@@ -450,7 +450,10 @@ static void dispatch_job(struct kcopyd_job *job)
 {
         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);
 }