From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
Nowait is a feature of direct AIO, where users can request
to return immediately if the I/O is going to block. This translates
to REQ_NOWAIT in bio.bi_opf flags. While request based devices
don't wait, stacked devices such as md/dm will.
In order to explicitly mark stacked devices as supported, we
set the QUEUE_FLAG_NOWAIT in the queue_flags and return -EAGAIN
whenever the device would block.
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
---
block/blk-core.c | 4 ++--
include/linux/blkdev.h | 6 ++++++
2 files changed, 8 insertions(+), 2 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index 048be4aa6024..8de633f8c633 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2044,10 +2044,10 @@ generic_make_request_checks(struct bio *bio)
/*
* For a REQ_NOWAIT based request, return -EOPNOTSUPP
- * if queue is not a request based queue.
+ * if queue cannot handle nowait bio's
*/
- if ((bio->bi_opf & REQ_NOWAIT) && !queue_is_rq_based(q))
+ if ((bio->bi_opf & REQ_NOWAIT) && !blk_queue_supports_nowait(q))
goto not_supported;
if (should_fail_request(&bio->bi_disk->part0, bio->bi_iter.bi_size))
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 02fa42d24b52..1d0da2a9cf46 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -631,6 +631,7 @@ struct request_queue {
#define QUEUE_FLAG_REGISTERED 26 /* queue has been registered to a disk */
#define QUEUE_FLAG_SCSI_PASSTHROUGH 27 /* queue supports SCSI commands */
#define QUEUE_FLAG_QUIESCED 28 /* queue has been quiesced */
+#define QUEUE_FLAG_NOWAIT 29 /* stack device driver supports REQ_NOWAIT */
#define QUEUE_FLAG_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
(1 << QUEUE_FLAG_STACKABLE) | \
@@ -759,6 +760,11 @@ static inline bool queue_is_rq_based(struct request_queue *q)
return q->request_fn || q->mq_ops;
}
+static inline bool blk_queue_supports_nowait(struct request_queue *q)
+{
+ return queue_is_rq_based(q) || test_bit(QUEUE_FLAG_NOWAIT, &q->queue_flags);
+}
+
static inline unsigned int blk_queue_cluster(struct request_queue *q)
{
return q->limits.cluster;
--
2.14.2
