linux-kernel - Re: [dm-devel] [PATCH] block: do not return -EOPNOTSUPP only when issue a discard request

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Date:	Wed, 3 Feb 2016 17:19:44 +0100 (CET)
From:	Lukáš Czerner <lczerner@...hat.com>
To:	jiangyiwen <jiangyiwen@...wei.com>
cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org, dm-devel@...hat.com,
	martin.petersen@...cle.com, xuejiufei@...wei.com,
	"Qijiang (Joseph, Euler)" <joseph.qi@...wei.com>
Subject: Re: [dm-devel] [PATCH] block: do not return -EOPNOTSUPP only when
 issue a discard request

On Wed, 3 Feb 2016, jiangyiwen wrote:

> Date: Wed, 3 Feb 2016 17:54:36 +0800
> From: jiangyiwen <jiangyiwen@...wei.com>
> To: axboe@...nel.dk, linux-kernel@...r.kernel.org
> Cc: dm-devel@...hat.com, martin.petersen@...cle.com,
>     Lukáš Czerner <lczerner@...hat.com>, xuejiufei@...wei.com,
>     "Qijiang (Joseph, Euler)" <joseph.qi@...wei.com>
> Subject: [dm-devel] [PATCH] block: do not return -EOPNOTSUPP only when issue a
>      discard request
> 
> commit 8af1954d172a("blkdev: Do not return -EOPNOTSUPP if discard
> is supported") only solve the situation of discard, because When
> applications issue a discard request to device, they can't expect
> deterministic behaviour. However, WRITE SAME should not ignore error
> with EOPNOTSUPP, because if applications issue WRITE SAME requests to
> device, it should return deterministic results to applications
> according to the T10 standard, or else it will cause an inconsistent
> state between upper layer and bottom layer.
> 
> So ignoring error with EOPNOTSUPP only in discard situation.
> 
> Signed-off-by: Yiwen Jiang <jiangyiwen@...wei.com>

Looks good.

Reviewed-by: Lukas Czerner <lczerner@...hat.com>

Thanks!
-Lukas

> ---
>  block/blk-lib.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index 9ebf653..e4f02f1 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -19,7 +19,9 @@ static void bio_batch_end_io(struct bio *bio)
>  {
>  	struct bio_batch *bb = bio->bi_private;
> 
> -	if (bio->bi_error && bio->bi_error != -EOPNOTSUPP)
> +	/* ignore -EOPNOTSUPP only when issue a discard request */
> +	if (bio->bi_error && (!(bio->bi_rw & REQ_DISCARD) ||
> +			(bio->bi_error != -EOPNOTSUPP)))
>  		bb->error = bio->bi_error;
>  	if (atomic_dec_and_test(&bb->done))
>  		complete(bb->wait);
>