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Date: Thu, 27 Apr 2017 14:19:24 -0600 From: Logan Gunthorpe <logang@...tatee.com> To: Roger Pau Monné <roger.pau@...rix.com> Cc: linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org, linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org, linux-raid@...r.kernel.org, linux-mmc@...r.kernel.org, linux-nvdimm@...ts.01.org, linux-scsi@...r.kernel.org, open-iscsi@...glegroups.com, megaraidlinux.pdl@...adcom.com, sparmaintainer@...sys.com, devel@...verdev.osuosl.org, target-devel@...r.kernel.org, netdev@...r.kernel.org, linux-rdma@...r.kernel.org, dm-devel@...hat.com, Christoph Hellwig <hch@....de>, "Martin K. Petersen" <martin.petersen@...cle.com>, "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>, Jens Axboe <axboe@...nel.dk>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Dan Williams <dan.j.williams@...el.com>, Ross Zwisler <ross.zwisler@...ux.intel.com>, Matthew Wilcox <mawilcox@...rosoft.com>, Sumit Semwal <sumit.semwal@...aro.org>, Stephen Bates <sbates@...thlin.com>, Boris Ostrovsky <boris.ostrovsky@...cle.com>, Juergen Gross <jgross@...e.com>, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, Julien Grall <julien.grall@....com> Subject: Re: [PATCH v2 15/21] xen-blkfront: Make use of the new sg_map helper function On 26/04/17 01:37 AM, Roger Pau Monné 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 <logang@...tatee.com> >> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com> >> Cc: Juergen Gross <jgross@...e.com> >> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> >> Cc: "Roger Pau Monné" <roger.pau@...rix.com> >> --- >> 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 >> --- a/drivers/block/xen-blkfront.c >> +++ 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 = sg->offset; >> - setup.bvec_data = kmap_atomic(sg_page(sg)); >> + setup.bvec_off = 0; >> + setup.bvec_data = 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 bvec_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. Logan
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