On 08/08/2017 03:32 PM, Shaohua Li wrote: > On Wed, Jul 26, 2017 at 06:57:58PM -0500, Goldwyn Rodrigues wrote: >> From: Goldwyn Rodrigues <rgold...@suse.com> >> >> 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. > > probably you should route this patch to Jens first, DM/MD are different trees.
Yes, I have sent it to linux-block as well, and he has commented as well. > >> Signed-off-by: Goldwyn Rodrigues <rgold...@suse.com> >> --- >> block/blk-core.c | 3 ++- >> include/linux/blkdev.h | 2 ++ >> 2 files changed, 4 insertions(+), 1 deletion(-) >> >> diff --git a/block/blk-core.c b/block/blk-core.c >> index 970b9c9638c5..1c9a981d88e5 100644 >> --- a/block/blk-core.c >> +++ b/block/blk-core.c >> @@ -2025,7 +2025,8 @@ generic_make_request_checks(struct bio *bio) >> * if queue is not a request based queue. >> */ >> >> - if ((bio->bi_opf & REQ_NOWAIT) && !queue_is_rq_based(q)) >> + if ((bio->bi_opf & REQ_NOWAIT) && !queue_is_rq_based(q) && >> + !blk_queue_supports_nowait(q)) >> goto not_supported; >> >> part = bio->bi_bdev->bd_part; >> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h >> index 25f6a0cb27d3..fae021ebec1b 100644 >> --- a/include/linux/blkdev.h >> +++ b/include/linux/blkdev.h >> @@ -633,6 +633,7 @@ struct request_queue { >> #define QUEUE_FLAG_REGISTERED 29 /* queue has been registered to a disk >> */ >> #define QUEUE_FLAG_SCSI_PASSTHROUGH 30 /* queue supports SCSI commands >> */ >> #define QUEUE_FLAG_QUIESCED 31 /* queue has been quiesced */ >> +#define QUEUE_FLAG_NOWAIT 32 /* stack device driver supports >> REQ_NOWAIT */ >> >> #define QUEUE_FLAG_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \ >> (1 << QUEUE_FLAG_STACKABLE) | \ >> @@ -732,6 +733,7 @@ static inline void queue_flag_clear(unsigned int flag, >> struct request_queue *q) >> #define blk_queue_dax(q) test_bit(QUEUE_FLAG_DAX, &(q)->queue_flags) >> #define blk_queue_scsi_passthrough(q) \ >> test_bit(QUEUE_FLAG_SCSI_PASSTHROUGH, &(q)->queue_flags) >> +#define blk_queue_supports_nowait(q) test_bit(QUEUE_FLAG_NOWAIT, >> &(q)->queue_flags) > > Should this bit consider under layer disks? For example, one raid array disk > doesn't support NOWAIT, shouldn't we disable NOWAIT for the array? Yes, it should. I will add a check before setting the flag. Thanks. Request-based devices don't wait. So, they would not have this flag set. It is only the bio-based, with the make_request_fn hook which need this. > > I have another generic question. If a bio is splitted into 2 bios, one bio > doesn't need to wait but the other need to wait. We will return -EAGAIN for > the > second bio, so the whole bio will return -EAGAIN, but the first bio is already > dispatched to disk. Is this correct behavior? > No, from a multi-device point of view, this is inconsistent. I have tried the request bio returns -EAGAIN before the split, but I shall check again. Where do you see this happening? -- Goldwyn -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel