From 7aeacf982203fb4dea2f3434eefdc268cfd5d6d9 Mon Sep 17 00:00:00 2001
From: Jens Axboe <jens.axboe@oracle.com>
Date: Tue, 23 Oct 2007 09:49:25 +0200
Subject: [PATCH] [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>
---
block/ll_rw_blk.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
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;
--
2.20.1