dm: refactor request based completion functions

This patch factors out the clone completion code, dm_done(),
from dm_softirq_done() in preparation for a subsequent patch.
No functional change.

dm_done() will be used in barrier completion, which can't use and
doesn't need softirq.  The softirq_done callback needs to get a clone
from an original request but it can't in the case of barrier, where
an original request is shared by multiple clones.  On the other hand,
the completion of barrier clones doesn't involve re-submitting requests,
which was the primary reason of the need for softirq.

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm.c

@@ -846,34 +846,45 @@ static void dm_end_request(struct request *clone, int error)
 	rq_completed(md, rw, 1);
 }
 
-/*
- * Request completion handler for request-based dm
- */
-static void dm_softirq_done(struct request *rq)
+static void dm_done(struct request *clone, int error, bool mapped)
 {
-	struct request *clone = rq->completion_data;
+	int r = error;
 	struct dm_rq_target_io *tio = clone->end_io_data;
 	dm_request_endio_fn rq_end_io = tio->ti->type->rq_end_io;
-	int error = tio->error;
 
-	if (!(rq->cmd_flags & REQ_FAILED) && rq_end_io)
-		error = rq_end_io(tio->ti, clone, error, &tio->info);
+	if (mapped && rq_end_io)
+		r = rq_end_io(tio->ti, clone, error, &tio->info);
 
-	if (error <= 0)
+	if (r <= 0)
 		/* The target wants to complete the I/O */
-		dm_end_request(clone, error);
-	else if (error == DM_ENDIO_INCOMPLETE)
+		dm_end_request(clone, r);
+	else if (r == DM_ENDIO_INCOMPLETE)
 		/* The target will handle the I/O */
 		return;
-	else if (error == DM_ENDIO_REQUEUE)
+	else if (r == DM_ENDIO_REQUEUE)
 		/* The target wants to requeue the I/O */
 		dm_requeue_unmapped_request(clone);
 	else {
-		DMWARN("unimplemented target endio return value: %d", error);
+		DMWARN("unimplemented target endio return value: %d", r);
 		BUG();
 	}
 }
 
+/*
+ * Request completion handler for request-based dm
+ */
+static void dm_softirq_done(struct request *rq)
+{
+	bool mapped = true;
+	struct request *clone = rq->completion_data;
+	struct dm_rq_target_io *tio = clone->end_io_data;
+
+	if (rq->cmd_flags & REQ_FAILED)
+		mapped = false;
+
+	dm_done(clone, tio->error, mapped);
+}
+
 /*
  * Complete the clone and the original request with the error status
  * through softirq context.