When exec bio_alloc, the bi_rw is zero.But after calling bio_add_page,
it will use bi_rw.
Fox example, in functiion __bio_add_page,it will call merge_bvec_fn().
The merge_bvec_fn of raid456 will use the bi_rw to judge the merge.

quoted

if ((bvm->bi_rw & 1) == WRITE)
	return biovec->bv_len; /* always allow writes to be mergeable */

Signed-off-by: Jianpeng Ma <redacted>

There are many place like this in kernel.If you think this patch ok, i will correct those.
---
 fs/direct-io.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 1faf4cb..77f0bbf 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c

@@ -349,6 +349,7 @@ dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
 
 	bio->bi_bdev = bdev;
 	bio->bi_sector = first_sector;
+	bio->bi_rw = dio->rw;
 	if (dio->is_async)
 		bio->bi_end_io = dio_bio_end_aio;
 	else

-- 
1.7.5.4