[BLOCK] blk_rq_map_sg: force clear termination bit

Since blk_rq_map_sg() sets the termination bit at the end of the sg
table, we could see it prematurely on the next mapping unless we
force drivers to do a full sg_init_table() prior to each mapping. So
force clear the termination bit to avoid having to put that clear in
the driver for every mapping.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 13 insertions, 1 deletions

diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index fb8fb8852c3..de5ba479c22 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -1351,8 +1351,20 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 new_segment:
                         if (!sg)
                                 sg = sglist;
-                        else
+                        else {
+                                /*
+                                 * If the driver previously mapped a shorter
+                                 * list, we could see a termination bit
+                                 * prematurely unless it fully inits the sg
+                                 * table on each mapping. We KNOW that there
+                                 * must be more entries here or the driver
+                                 * would be buggy, so force clear the
+                                 * termination bit to avoid doing a full
+                                 * sg_init_table() in drivers for each command.
+                                 */
+                                sg->page_link &= ~0x02;
                                 sg = sg_next(sg);
+                        }
 
                         sg_set_page(sg, bvec->bv_page);
                         sg->length = nbytes;