[PATCH V3 2/5] loop: cleanup lo_rw_aio()

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

Cleanup lo_rw_aio() a bit by refactoring it into three parts:

- lo_cmd_nr_bvec(), for calculating how many bvecs in this request

- lo_rw_aio_prep(), for preparing loop command, which need to be called
once

- lo_submit_rw_aio(), for submitting this lo command, which can be
called multiple times

Prepare for trying to handle loop command by NOWAIT read/write IO
first.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 drivers/block/loop.c | 81 ++++++++++++++++++++++++++++++--------------
 1 file changed, 56 insertions(+), 25 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 339b19671450..419ca675342a 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -386,7 +386,6 @@ static void lo_rw_aio_do_completion(struct loop_cmd *cmd)
 	if (!atomic_dec_and_test(&cmd->ref))
 		return;
 	kfree(cmd->bvec);
-	cmd->bvec = NULL;
 	if (likely(!blk_should_fake_timeout(rq->q)))
 		blk_mq_complete_request(rq);
 }
@@ -399,24 +398,29 @@ 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)
+static inline unsigned lo_cmd_nr_bvec(struct loop_cmd *cmd)
 {
-	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;
-	unsigned int offset;
 	int nr_bvec = 0;
-	int ret;
 
 	rq_for_each_bvec(tmp, rq, rq_iter)
 		nr_bvec++;
 
+	return nr_bvec;
+}
+
+static int lo_rw_aio_prep(struct loop_device *lo, struct loop_cmd *cmd,
+			  unsigned nr_bvec)
+{
+	struct request *rq = blk_mq_rq_from_pdu(cmd);
+	loff_t pos = ((loff_t) blk_rq_pos(rq) << 9) + lo->lo_offset;
+
 	if (rq->bio != rq->biotail) {
+		struct req_iterator rq_iter;
+		struct bio_vec *bvec;
+		struct bio_vec tmp;
 
 		bvec = kmalloc_array(nr_bvec, sizeof(struct bio_vec),
 				     GFP_NOIO);
@@ -434,35 +438,62 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, loff_t pos)
 			*bvec = tmp;
 			bvec++;
 		}
-		bvec = cmd->bvec;
-		offset = 0;
 	} else {
+		cmd->bvec = NULL;
+	}
+	cmd->iocb.ki_pos = pos;
+	cmd->iocb.ki_filp = lo->lo_backing_file;
+	cmd->iocb.ki_complete = lo_rw_aio_complete;
+	cmd->iocb.ki_flags = IOCB_DIRECT;
+	cmd->iocb.ki_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, 0);
+
+	return 0;
+}
+
+static int lo_submit_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
+			    int nr_bvec)
+{
+	struct request *rq = blk_mq_rq_from_pdu(cmd);
+	int dir = (req_op(rq) == REQ_OP_READ) ? ITER_DEST : ITER_SOURCE;
+	struct file *file = lo->lo_backing_file;
+	struct iov_iter iter;
+	int ret;
+
+	if (cmd->bvec) {
+		iov_iter_bvec(&iter, dir, cmd->bvec, nr_bvec, blk_rq_bytes(rq));
+		iter.iov_offset = 0;
+	} else {
+		struct bio *bio = rq->bio;
+		struct bio_vec *bvec = __bvec_iter_bvec(bio->bi_io_vec,
+				bio->bi_iter);
+
 		/*
 		 * Same here, this bio may be started from the middle of the
 		 * 'bvec' because of bio splitting, so offset from the bvec
 		 * must be passed to iov iterator
 		 */
-		offset = bio->bi_iter.bi_bvec_done;
-		bvec = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
+		iov_iter_bvec(&iter, dir, bvec, nr_bvec, blk_rq_bytes(rq));
+		iter.iov_offset = bio->bi_iter.bi_bvec_done;
 	}
-	atomic_set(&cmd->ref, 2);
-
-	iov_iter_bvec(&iter, dir, bvec, nr_bvec, blk_rq_bytes(rq));
-	iter.iov_offset = offset;
-
-	cmd->iocb.ki_pos = pos;
-	cmd->iocb.ki_filp = file;
-	cmd->iocb.ki_complete = lo_rw_aio_complete;
-	cmd->iocb.ki_flags = IOCB_DIRECT;
-	cmd->iocb.ki_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, 0);
 
+	atomic_set(&cmd->ref, 2);
 	if (dir == ITER_SOURCE)
 		ret = file->f_op->write_iter(&cmd->iocb, &iter);
 	else
 		ret = file->f_op->read_iter(&cmd->iocb, &iter);
-
 	lo_rw_aio_do_completion(cmd);
 
+	return ret;
+}
+
+
+static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd)
+{
+	unsigned int nr_bvec = lo_cmd_nr_bvec(cmd);
+	int ret = lo_rw_aio_prep(lo, cmd, nr_bvec);
+
+	if (ret >= 0)
+		ret = lo_submit_rw_aio(lo, cmd, nr_bvec);
 	if (ret != -EIOCBQUEUED)
 		lo_rw_aio_complete(&cmd->iocb, ret);
 	return 0;
@@ -499,7 +530,7 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq)
 	case REQ_OP_WRITE:
 	case REQ_OP_READ:
 		if (cmd->use_aio)
-			return lo_rw_aio(lo, cmd, pos);
+			return lo_rw_aio(lo, cmd);
 		else
 			return lo_rw_simple(lo, rq, pos);
 	default:
-- 
2.47.0