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

Ming Lei
2025-03-22T01:26:47Z

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