[RFC RESEND] iomap: set REQ_NOWAIT according to IOCB_NOWAIT in Direct IO

[Hao Xu <haoxu@linux.alibaba.com>]

Currently, IOCB_NOWAIT is ignored in direct io, REQ_NOWAIT is only set
when IOCB_HIPRI is set. But REQ_NOWAIT should be set as well when
IOCB_NOWAIT is set.

Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
---

Hi all,
I tested fio io_uring direct read for a file on ext4 filesystem on a
nvme ssd. I found that IOCB_NOWAIT is ignored in iomap layer, which
means REQ_NOWAIT is not set in bio->bi_opf. This makes nowait IO a
normal IO. Since I'm new to iomap and block layer, I sincerely ask
yours opinions in case I misunderstand the code which is very likely
to happen.:)

 fs/block_dev.c       | 3 +++
 fs/iomap/direct-io.c | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 9e84b1928b94..b7db3b7e2ba1 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -424,6 +424,9 @@ static void blkdev_bio_end_io(struct bio *bio)
 		if (!nr_pages) {
 			bool polled = false;
 
+			if (iocb->ki_flags & IOCB_NOWAIT)
+				bio->bi_opf |= REQ_NOWAIT;
+
 			if (iocb->ki_flags & IOCB_HIPRI) {
 				bio_set_polled(bio, iocb);
 				polled = true;
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 933f234d5bec..22f7488bf5e5 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -64,6 +64,9 @@ static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap *iomap,
 {
 	atomic_inc(&dio->ref);
 
+	if (dio->iocb->ki_flags & IOCB_NOWAIT)
+		bio->bi_opf |= REQ_NOWAIT;
+
 	if (dio->iocb->ki_flags & IOCB_HIPRI)
 		bio_set_polled(bio, dio->iocb);
 
-- 
1.8.3.1