On Thu, Apr 27, 2017 at 02:19:24PM -0600, Logan Gunthorpe wrote: > > > 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@xxxxxxxxxxxx> > >> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> > >> Cc: Juergen Gross <jgross@xxxxxxxx> > >> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> > >> Cc: "Roger Pau Monné" <roger.pau@xxxxxxxxxx> > >> 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 = 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. 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