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Subject[PATCH 004 of 5] md: Improve detection of lack of barrier support in raid1

Move the test for 'do barrier work' down a bit so that if the first
write to a raid1 is a BIO_RW_BARRIER write, the checking done by
superblock writes will cause the right thing to happen.


Signed-off-by: Neil Brown <neilb@suse.de>

### Diffstat output
./drivers/md/raid1.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)

diff ./drivers/md/raid1.c~current~ ./drivers/md/raid1.c
--- ./drivers/md/raid1.c~current~ 2006-04-28 12:17:27.000000000 +1000
+++ ./drivers/md/raid1.c 2006-04-28 12:17:40.000000000 +1000
@@ -753,18 +753,24 @@ static int make_request(request_queue_t
const int rw = bio_data_dir(bio);
int do_barriers;

- if (unlikely(!mddev->barriers_work && bio_barrier(bio))) {
- bio_endio(bio, bio->bi_size, -EOPNOTSUPP);
- return 0;
- }
-
/*
* Register the new request and wait if the reconstruction
* thread has put up a bar for new requests.
* Continue immediately if no resync is active currently.
+ * We test barriers_work *after* md_write_start as md_write_start
+ * may cause the first superblock write, and that will check out
+ * if barriers work.
*/
+
md_write_start(mddev, bio); /* wait on superblock update early */

+ if (unlikely(!mddev->barriers_work && bio_barrier(bio))) {
+ if (rw == WRITE)
+ md_write_end(mddev);
+ bio_endio(bio, bio->bi_size, -EOPNOTSUPP);
+ return 0;
+ }
+
wait_barrier(conf);

disk_stat_inc(mddev->gendisk, ios[rw]);
-
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