On 26/04/17 01:37 AM, Roger Pau Monné wrote:

On Tue, Apr 25, 2017 at 12:21:02PM -0600, Logan Gunthorpe wrote:

quoted

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-OTvnGxWRz7hWk0Htik3J/w@public.gmane.org>
Cc: Boris Ostrovsky <redacted>
Cc: Juergen Gross <jgross-IBi9RG/b67k@public.gmane.org>
Cc: Konrad Rzeszutek Wilk <redacted>
Cc: "Roger Pau Monné" <redacted>
---
 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