From: Goldwyn Rodrigues <[email protected]> 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 <[email protected]> --- 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
