From: Jens Axboe <jens.axboe@oracle.com>
Date: Tue, 23 Oct 2007 07:49:25 +0000 (+0200)
Subject: [BLOCK] blk_rq_map_sg: force clear termination bit
X-Git-Tag: v2.6.24-rc1~34^2~14
X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=7aeacf982203fb4dea2f3434eefdc268cfd5d6d9;p=linux-2.6-omap-h63xx.git

[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>
---

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;