From: Jason Gunthorpe Subject: Re: [PATCH v2 15/21] xen-blkfront: Make use of the new sg_map helper function Date: Thu, 27 Apr 2017 14:53:39 -0600 Message-ID: <20170427205339.GB26330@obsidianresearch.com> References: <1493144468-22493-1-git-send-email-logang@deltatee.com> <1493144468-22493-16-git-send-email-logang@deltatee.com> <20170426073720.okv33ly2ldepilti@dhcp-3-128.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Cc: Boris Ostrovsky , linux-nvdimm-y27Ovi1pjclAfugRpC6u6w@public.gmane.org, dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org, dm-devel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, target-devel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Christoph Hellwig , devel-gWbeCf7V1WCQmaza687I9mD2FQJk+8+b@public.gmane.org, "James E.J. Bottomley" , linux-scsi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Matthew Wilcox , linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Sumit Semwal , open-iscsi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org, linux-media-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Juergen Gross , Julien Grall , intel-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org, sparmaintainer-GLv8BlqOqDDQT0dZR+AlfA@public.gmane.org, linux-raid-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, megaraidlinux.pdl-dY08KVG/lbpWk0Htik3J/w@public.gmane.org, Jens Axboe , "Martin K. Petersen" , netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mmc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-crypto-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Greg Kroah-Hartman Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" List-Id: linux-crypto.vger.kernel.org On Thu, Apr 27, 2017 at 02:19:24PM -0600, Logan Gunthorpe wrote: > = > = > On 26/04/17 01:37 AM, Roger Pau Monn=E9 wrote: > > On Tue, Apr 25, 2017 at 12:21:02PM -0600, Logan Gunthorpe wrote: > >> Straightforward conversion to the new helper, except due to the lack > >> of error path, we have to use SG_MAP_MUST_NOT_FAIL which may BUG_ON in > >> certain cases in the future. > >> > >> Signed-off-by: Logan Gunthorpe > >> Cc: Boris Ostrovsky > >> Cc: Juergen Gross > >> Cc: Konrad Rzeszutek Wilk > >> Cc: "Roger Pau Monn=E9" > >> drivers/block/xen-blkfront.c | 20 +++++++++++--------- > >> 1 file changed, 11 insertions(+), 9 deletions(-) > >> > >> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront= .c > >> index 3945963..ed62175 100644 > >> +++ b/drivers/block/xen-blkfront.c > >> @@ -816,8 +816,9 @@ static int blkif_queue_rw_req(struct request *req,= struct blkfront_ring_info *ri > >> BUG_ON(sg->offset + sg->length > PAGE_SIZE); > >> = > >> if (setup.need_copy) { > >> - setup.bvec_off =3D sg->offset; > >> - setup.bvec_data =3D kmap_atomic(sg_page(sg)); > >> + setup.bvec_off =3D 0; > >> + setup.bvec_data =3D sg_map(sg, 0, SG_KMAP_ATOMIC | > >> + SG_MAP_MUST_NOT_FAIL); > > = > > I assume that sg_map already adds sg->offset to the address? > = > Correct. > = > > Also wondering whether we can get rid of bvec_off and just increment bv= ec_data, > > adding Julien who IIRC added this code. > = > bvec_off is used to keep track of the offset within the current mapping > so it's not a great idea given that you'd want to kunmap_atomic the > original address and not something with an offset. It would be nice if > this could be converted to use the sg_miter interface but that's a much > more invasive change that would require someone who knows this code and > can properly test it. I'd be very grateful if someone actually took that = on. blkfront is one of the drivers I looked at, and it appears to only be memcpying with the bvec_data pointer, so I wonder why it does not use sg_copy_X_buffer instead.. Jason