[PATCH V2] block: correctly fallback for zeroout

Shaohua Li
2016-06-06T22:34:52Z

blkdev_issue_zeroout try discard/writesame first, if they fail, zeroout
fallback to regular write. The problem is discard/writesame doesn't
return error for -EOPNOTSUPP, then zeroout can't do fallback and leave
disk data not changed. zeroout should have guaranteed zero-fill
behavior.

https://bugzilla.kernel.org/show_bug.cgi?id=118581

V2: move the return value policy to blkdev_issue_discard and
delete the policy for blkdev_issue_write_same (Martin)

Cc: Sitsofe Wheeler <sitsofe@yahoo.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Jens Axboe <axboe@fb.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Shaohua Li <shli@fb.com>
---
block/blk-lib.c | 49 +++++++++++++++++++++++++++++++------------------
1 file changed, 31 insertions(+), 18 deletions(-)

diff --git a/block/blk-lib.c b/block/blk-lib.c
index 23d7f30..a3a26c8 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -84,6 +84,28 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
}
EXPORT_SYMBOL(__blkdev_issue_discard);

+static int do_blkdev_issue_discard(struct block_device *bdev, sector_t sector,
+ sector_t nr_sects, gfp_t gfp_mask, unsigned long flags,
+ int *io_err)
+{
+ int type = REQ_WRITE | REQ_DISCARD;
+ struct bio *bio = NULL;
+ struct blk_plug plug;
+ int ret;
+
+ if (flags & BLKDEV_DISCARD_SECURE)
+ type |= REQ_SECURE;
+
+ blk_start_plug(&plug);
+ ret = __blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask, type,
+ &bio);
+ if (!ret && bio)
+ *io_err = submit_bio_wait(type, bio);
+ blk_finish_plug(&plug);
+
+ return ret;
+}
+
/**
* blkdev_issue_discard - queue a discard
* @bdev: blockdev to issue discard for
@@ -98,23 +120,12 @@ EXPORT_SYMBOL(__blkdev_issue_discard);
int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
sector_t nr_sects, gfp_t gfp_mask, unsigned long flags)
{
- int type = REQ_WRITE | REQ_DISCARD;
- struct bio *bio = NULL;
- struct blk_plug plug;
- int ret;
+ int ret, io_err;

- if (flags & BLKDEV_DISCARD_SECURE)
- type |= REQ_SECURE;
-
- blk_start_plug(&plug);
- ret = __blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask, type,
- &bio);
- if (!ret && bio) {
- ret = submit_bio_wait(type, bio);
- if (ret == -EOPNOTSUPP)
- ret = 0;
- }
- blk_finish_plug(&plug);
+ ret = do_blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask,
+ flags, &io_err);
+ if (!ret && io_err != -EOPNOTSUPP)
+ ret = io_err;

return ret;
}
@@ -167,7 +178,7 @@ int blkdev_issue_write_same(struct block_device *bdev, sector_t sector,

if (bio)
ret = submit_bio_wait(REQ_WRITE | REQ_WRITE_SAME, bio);
- return ret != -EOPNOTSUPP ? ret : 0;
+ return ret;
}
EXPORT_SYMBOL(blkdev_issue_write_same);

@@ -236,9 +247,11 @@ int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
sector_t nr_sects, gfp_t gfp_mask, bool discard)
{
struct request_queue *q = bdev_get_queue(bdev);
+ int io_err = 0;

if (discard && blk_queue_discard(q) && q->limits.discard_zeroes_data &&
- blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask, 0) == 0)
+ (do_blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask, 0,
+ &io_err) == 0 && io_err == 0))
return 0;

if (bdev_write_same(bdev) &&
--
2.8.0.rc2