RE: [PATCH 16/22] xen-blkfront: Make use of the new sg_map helper function

Sent: 13 April 2017 23:05
Straightforward conversion to the new helper, except due to
the lack of error path, we have to warn if unmapable memory
is ever present in the sgl.

Signed-off-by: Logan Gunthorpe <logang-OTvnGxWRz7hWk0Htik3J/w@public.gmane.org>
---
 drivers/block/xen-blkfront.c | 33 +++++++++++++++++++++++++++------
 1 file changed, 27 insertions(+), 6 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 5067a0a..7dcf41d 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c

@@ -807,8 +807,19 @@ 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, SG_KMAP_ATOMIC);
+			if (IS_ERR(setup.bvec_data)) {
+				/*
+				 * This should really never happen unless
+				 * the code is changed to use memory that is
+				 * not mappable in the sg. Seeing there is a
+				 * questionable error path out of here,
+				 * we WARN.
+				 */
+				WARN(1, "Non-mappable memory used in sg!");
+				return 1;
+			}