Re: [PATCH V2] block: correctly fallback for zeroout

Shaohua Li
2016-06-10T02:55:30Z

On Thu, Jun 09, 2016 at 10:04:08PM -0400, Martin K. Petersen wrote:
> >>>>> "Shaohua" == Shaohua Li <shli@fb.com> writes:
>
> Shaohua,
>
> 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;
> +}
> +
>
> What does the extra io_err buy us? Just have this function return an
> error. And then in blkdev_issue_discard if you get -EOPNOTSUPP you
> special case it there.

The __blkdev_issue_discard returns -EOPNOTSUPP if disk doesn't support discard.
in that case, blkdev_issue_discard doesn't return 0. blkdev_issue_discard only
returns 0 if IO error is -EOPNOTSUPP. Please see bbd848e0fade51ae51da.

Thanks,
Shaohua