null_blk: create a helper for mem-backed ops

This patch creates a helper for handling requests when null_blk is
memory backed in the null_handle_cmd(). Although the helper is very
simple right now, it makes the code flow consistent with the rest of
code in the null_handle_cmd() and provides a uniform code structure
for future code.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/null_blk_main.c

@@ -1168,13 +1168,26 @@ static inline blk_status_t null_handle_badblocks(struct nullb_cmd *cmd,
 	return BLK_STS_OK;
 }
 
+static inline blk_status_t null_handle_memory_backed(struct nullb_cmd *cmd,
+						     enum req_opf op)
+{
+	struct nullb_device *dev = cmd->nq->dev;
+	int err;
+
+	if (dev->queue_mode == NULL_Q_BIO)
+		err = null_handle_bio(cmd);
+	else
+		err = null_handle_rq(cmd);
+
+	return errno_to_blk_status(err);
+}
+
 static blk_status_t null_handle_cmd(struct nullb_cmd *cmd, sector_t sector,
 				    sector_t nr_sectors, enum req_opf op)
 {
 	struct nullb_device *dev = cmd->nq->dev;
 	struct nullb *nullb = dev->nullb;
 	blk_status_t sts;
-	int err = 0;
 
 	if (test_bit(NULLB_DEV_FL_THROTTLED, &dev->flags)) {
 		sts = null_handle_throttled(cmd);
@@ -1193,14 +1206,8 @@ static blk_status_t null_handle_cmd(struct nullb_cmd *cmd, sector_t sector,
 			goto out;
 	}
 
-	if (dev->memory_backed) {
-		if (dev->queue_mode == NULL_Q_BIO)
-			err = null_handle_bio(cmd);
-		else
-			err = null_handle_rq(cmd);
-	}
-
-	cmd->error = errno_to_blk_status(err);
+	if (dev->memory_backed)
+		cmd->error = null_handle_memory_backed(cmd, op);
 
 	if (!cmd->error && dev->zoned) {
 		if (op == REQ_OP_WRITE)