On Wed, Oct 04, 2017 at 05:03:16PM +0200, Ilya Dryomov wrote:
> sd_config_write_same() ignores ->max_ws_blocks == 0 and resets it to
> permit trying WRITE SAME on older SCSI devices, unless ->no_write_same
> is set. Because REQ_OP_WRITE_ZEROES is implemented in terms of WRITE
> SAME, blkdev_issue_zeroout() may fail with -EREMOTEIO:
>
> $ fallocate -zn -l 1k /dev/sdg
> fallocate: fallocate failed: Remote I/O error
> $ fallocate -zn -l 1k /dev/sdg # OK
> $ fallocate -zn -l 1k /dev/sdg # OK
Can we wire this up for blktests somehow?
>
> The following calls succeed because sd_done() sets ->no_write_same in
> response to a sense that would become BLK_STS_TARGET/-EREMOTEIO, causing
> __blkdev_issue_zeroout() to fall back to generating ZERO_PAGE bios.
>
> This means blkdev_issue_zeroout() must cope with WRITE ZEROES failing
> and fall back to manually zeroing, unless BLKDEV_ZERO_NOFALLBACK is
> specified. For BLKDEV_ZERO_NOFALLBACK case, return -EOPNOTSUPP if
> sd_done() has just set ->no_write_same thus indicating lack of offload
> support.
>
> Fixes: c20cfc27a473 ("block: stop using blkdev_issue_write_same for zeroing")
> Cc: Christoph Hellwig <[email protected]>
> Cc: "Martin K. Petersen" <[email protected]>
> Cc: Hannes Reinecke <[email protected]>
> Signed-off-by: Ilya Dryomov <[email protected]>
> ---
> block/blk-lib.c | 41 +++++++++++++++++++++++++++++++----------
> 1 file changed, 31 insertions(+), 10 deletions(-)
>
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index 9d2ab8bba52a..17494275673e 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -321,12 +321,6 @@ static int __blkdev_issue_zero_pages(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.
> *
> @@ -370,18 +364,45 @@ EXPORT_SYMBOL(__blkdev_issue_zeroout);
> int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
> sector_t nr_sects, gfp_t gfp_mask, unsigned flags)
> {
> - int ret;
> - struct bio *bio = NULL;
> + int ret = 0;
> + sector_t bs_mask;
> + struct bio *bio;
> struct blk_plug plug;
> + bool try_write_zeroes = !!bdev_write_zeroes_sectors(bdev);
> +
> + bs_mask = (bdev_logical_block_size(bdev) >> 9) - 1;
> + if ((sector | nr_sects) & bs_mask)
> + return -EINVAL;
>
> +retry:
> + bio = NULL;
> blk_start_plug(&plug);
> - ret = __blkdev_issue_zeroout(bdev, sector, nr_sects, gfp_mask,
> - &bio, flags);
> + if (try_write_zeroes) {
> + ret = __blkdev_issue_write_zeroes(bdev, sector, nr_sects,
> + gfp_mask, &bio, flags);
> + } else if (!(flags & BLKDEV_ZERO_NOFALLBACK)) {
> + ret = __blkdev_issue_zero_pages(bdev, sector, nr_sects,
> + gfp_mask, &bio);
> + } else if (!bdev_write_zeroes_sectors(bdev)) {
> + /*
> + * Manual zeroout is not allowed and either:
> + * - no zeroing offload support
> + * - zeroing offload support was indicated, but the device
> + * reported ILLEGAL REQUEST (for some devices there is no
> + * non-destructive way to verify whether WRITE ZEROES is
> + * actually supported)
> + */
> + ret = -EOPNOTSUPP;
I don't understand the conditional above this error return - if
we can't zero using either method we should always return an error.
Except for that the patch looks fine.
