Re: [dm-devel] [PATCH 10/15] sd: use bvec_virt

From: Bart Van Assche <bvanassche@acm.org>
To: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>
Cc: Jan Hoeppner <hoeppner@linux.ibm.com>,
	Mike Snitzer <snitzer@redhat.com>,
	linux-nvme@lists.infradead.org,
	virtualization@lists.linux-foundation.org,
	Song Liu <song@kernel.org>,
	dm-devel@redhat.com,
	Anton Ivanov <anton.ivanov@cambridgegreys.com>,
	linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org,
	Richard Weinberger <richard@nod.at>,
	Ilya Dryomov <idryomov@gmail.com>,
	linux-um@lists.infradead.org, Coly Li <colyli@suse.de>,
	linux-raid@vger.kernel.org, linux-bcache@vger.kernel.org,
	Stefan Haberland <sth@linux.ibm.com>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Phillip Lougher <phillip@squashfs.org.uk>,
	ceph-devel@vger.kernel.org, linux-block@vger.kernel.org,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Geoff Levand <geoff@infradead.org>,
	Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [dm-devel] [PATCH 10/15] sd: use bvec_virt
Date: Thu, 5 Aug 2021 09:31:08 -0700	[thread overview]
Message-ID: <8b487c0f-71be-19d6-249c-9cd1ba228548@acm.org> (raw)
In-Reply-To: <20210804095634.460779-11-hch@lst.de>

On 8/4/21 2:56 AM, Christoph Hellwig wrote:
> Use bvec_virt instead of open coding it.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   drivers/scsi/sd.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index b8d55af763f9..5b5b8266e142 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -886,7 +886,7 @@ static blk_status_t sd_setup_unmap_cmnd(struct scsi_cmnd *cmd)
>   	cmd->cmnd[0] = UNMAP;
>   	cmd->cmnd[8] = 24;
>   
> -	buf = page_address(rq->special_vec.bv_page);
> +	buf = bvec_virt(&rq->special_vec);
>   	put_unaligned_be16(6 + 16, &buf[0]);
>   	put_unaligned_be16(16, &buf[2]);
>   	put_unaligned_be64(lba, &buf[8]);

The patch description is not correct. The above patch involves a 
functional change while the patch description suggests that no 
functionality has been changed.

Although the above patch looks fine to me, why has page_address() been 
changed into bvec_virt() in the sd driver? My understanding is that the 
sd driver always sets bv_offset to zero.

Thanks,

Bart.

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