[Drbd-dev] [PATCH 22/27] block: stop using discards for zeroing

Christoph Hellwig hch at lst.de
Wed Apr 5 19:21:20 CEST 2017

Now that we have REQ_OP_WRITE_ZEROES implemented for all devices that
support efficient zeroing, we can remove the call to blkdev_issue_discard.
This means we only have two ways of zeroing left and can simplify the

Signed-off-by: Christoph Hellwig <hch at lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen at oracle.com>
Reviewed-by: Hannes Reinecke <hare at suse.com>
 block/blk-lib.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/block/blk-lib.c b/block/blk-lib.c
index 2f882e22890b..b0c6c4bcf441 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -279,6 +279,12 @@ static int __blkdev_issue_write_zeroes(struct block_device *bdev,
  *  Zero-fill a block range, either using hardware offload or by explicitly
  *  writing zeroes to the device.
+ *  Note that this function may fail with -EOPNOTSUPP if the driver signals
+ *  zeroing offload support, but the device fails to process the command (for
+ *  some devices there is no non-destructive way to verify whether this
+ *  operation is actually supported).  In this case the caller should call
+ *  retry the call to blkdev_issue_zeroout() and the fallback path will be used.
+ *
  *  If a device is using logical block provisioning, the underlying space will
  *  not be released if %flags contains BLKDEV_ZERO_NOUNMAP.
@@ -349,12 +355,6 @@ int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
 	struct bio *bio = NULL;
 	struct blk_plug plug;
-	if (!(flags & BLKDEV_ZERO_NOUNMAP)) {
-		if (!blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask,
-			return 0;
-	}
 	ret = __blkdev_issue_zeroout(bdev, sector, nr_sects, gfp_mask,
 			&bio, flags);

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