[PATCH V3 1/5] loop: simplify do_req_filebacked()

[Ming Lei <ming.lei@redhat.com>]

lo_rw_aio() is only called for READ/WRITE operation, which can be
figured out from request directly, so remove 'rw' parameter from
lo_rw_aio(), meantime rename the local variable as 'dir' which makes
the check more readable in lo_rw_aio().

Meantime add lo_rw_simple() so that do_req_filebacked() can be
simplified in the following way:

```
	if (cmd->use_aio)
		return lo_rw_aio(lo, cmd, pos);
	else
		return lo_rw_simple(lo, rq, pos);
```

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 drivers/block/loop.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 674527d770dc..339b19671450 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -277,6 +277,13 @@ static int lo_read_simple(struct loop_device *lo, struct request *rq,
 	return 0;
 }
 
+static int lo_rw_simple(struct loop_device *lo, struct request *rq, loff_t pos)
+{
+	if (req_op(rq) == REQ_OP_READ)
+		return lo_read_simple(lo, rq, pos);
+	return lo_write_simple(lo, rq, pos);
+}
+
 static void loop_clear_limits(struct loop_device *lo, int mode)
 {
 	struct queue_limits lim = queue_limits_start_update(lo->lo_queue);
@@ -392,13 +399,13 @@ static void lo_rw_aio_complete(struct kiocb *iocb, long ret)
 	lo_rw_aio_do_completion(cmd);
 }
 
-static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
-		     loff_t pos, int rw)
+static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, loff_t pos)
 {
 	struct iov_iter iter;
 	struct req_iterator rq_iter;
 	struct bio_vec *bvec;
 	struct request *rq = blk_mq_rq_from_pdu(cmd);
+	int dir = (req_op(rq) == REQ_OP_READ) ? ITER_DEST : ITER_SOURCE;
 	struct bio *bio = rq->bio;
 	struct file *file = lo->lo_backing_file;
 	struct bio_vec tmp;
@@ -440,7 +447,7 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
 	}
 	atomic_set(&cmd->ref, 2);
 
-	iov_iter_bvec(&iter, rw, bvec, nr_bvec, blk_rq_bytes(rq));
+	iov_iter_bvec(&iter, dir, bvec, nr_bvec, blk_rq_bytes(rq));
 	iter.iov_offset = offset;
 
 	cmd->iocb.ki_pos = pos;
@@ -449,7 +456,7 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
 	cmd->iocb.ki_flags = IOCB_DIRECT;
 	cmd->iocb.ki_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, 0);
 
-	if (rw == ITER_SOURCE)
+	if (dir == ITER_SOURCE)
 		ret = file->f_op->write_iter(&cmd->iocb, &iter);
 	else
 		ret = file->f_op->read_iter(&cmd->iocb, &iter);
@@ -490,15 +497,11 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq)
 	case REQ_OP_DISCARD:
 		return lo_fallocate(lo, rq, pos, FALLOC_FL_PUNCH_HOLE);
 	case REQ_OP_WRITE:
-		if (cmd->use_aio)
-			return lo_rw_aio(lo, cmd, pos, ITER_SOURCE);
-		else
-			return lo_write_simple(lo, rq, pos);
 	case REQ_OP_READ:
 		if (cmd->use_aio)
-			return lo_rw_aio(lo, cmd, pos, ITER_DEST);
+			return lo_rw_aio(lo, cmd, pos);
 		else
-			return lo_read_simple(lo, rq, pos);
+			return lo_rw_simple(lo, rq, pos);
 	default:
 		WARN_ON_ONCE(1);
 		return -EIO;
-- 
2.47.0