linux-kernel - Re: [PATCH 2/8] block: fix SG_IO vector request data length handling

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Date:	Wed, 1 Apr 2009 20:47:31 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	tj@...nel.org
Cc:	axboe@...nel.dk, bharrosh@...asas.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/8] block: fix SG_IO vector request data length
 handling

On Wed,  1 Apr 2009 20:04:38 +0900
Tejun Heo <tj@...nel.org> wrote:

> Impact: fix SG_IO behavior such that it matches the documentation
> 
> SG_IO howto says that if ->dxfer_len and sum of iovec disagress, the
> shorter one wins.  However, the current implementation returns -EINVAL
> for such cases.  Trim iovc if it's longer than ->dxfer_len.

Is that description about sg's SG_IO?


> This patch uses iov_*() helpers which take struct iovec * by casting
> struct sg_iovec * to it.  sg_iovec is always identical to iovec and
> this will be further cleaned up with later patches.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> ---
>  block/scsi_ioctl.c |   13 ++++++++++++-
>  1 files changed, 12 insertions(+), 1 deletions(-)
> 
> diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
> index 626ee27..c8e8868 100644
> --- a/block/scsi_ioctl.c
> +++ b/block/scsi_ioctl.c
> @@ -288,6 +288,7 @@ static int sg_io(struct request_queue *q, struct gendisk *bd_disk,
>  
>  	if (hdr->iovec_count) {
>  		const int size = sizeof(struct sg_iovec) * hdr->iovec_count;
> +		size_t iov_data_len;
>  		struct sg_iovec *iov;
>  
>  		iov = kmalloc(size, GFP_KERNEL);
> @@ -302,8 +303,18 @@ static int sg_io(struct request_queue *q, struct gendisk *bd_disk,
>  			goto out;
>  		}
>  
> +		/* SG_IO howto says that the shorter of the two wins */
> +		iov_data_len = iov_length((struct iovec *)iov,
> +					  hdr->iovec_count);
> +		if (hdr->dxfer_len < iov_data_len) {
> +			hdr->iovec_count = iov_shorten((struct iovec *)iov,
> +						       hdr->iovec_count,
> +						       hdr->dxfer_len);
> +			iov_data_len = hdr->dxfer_len;
> +		}
> +
>  		ret = blk_rq_map_user_iov(q, rq, NULL, iov, hdr->iovec_count,
> -					  hdr->dxfer_len, GFP_KERNEL);
> +					  iov_data_len, GFP_KERNEL);
>  		kfree(iov);
>  	} else if (hdr->dxfer_len)
>  		ret = blk_rq_map_user(q, rq, NULL, hdr->dxferp, hdr->dxfer_len,
> -- 
> 1.6.0.2
> 
> --
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