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Mikulas Patocka 11-02-2009 01:09 AM

dm-kcopyd: accept zero-size jobs

This is a simple patch that makes kcopyd accept zero-size jobs. It is
needed for handling snapshot resizing in shared snapshots.



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 <>

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

Index: linux-
================================================== =================
--- linux- 2009-11-02 01:21:49.000000000 +0100
+++ linux- 2009-11-02 01:22:01.000000000 +0100
@@ -450,7 +450,10 @@ static void dispatch_job(struct kcopyd_j
struct dm_kcopyd_client *kc = job->kc;
- push(&kc->pages_jobs, job);
+ if (unlikely(!job->source.count))
+ push(&kc->complete_jobs, job);
+ else
+ push(&kc->pages_jobs, job);

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