block: Introduce __blk_segment_map_sg() helper

Split the mapping code in blk_rq_map_sg() to a helper
__blk_segment_map_sg(), so that other mapping function, e.g.
blk_bio_map_sg(), can share the code.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Tejun Heo <tj@kernel.org>
Cc: Shaohua Li <shli@kernel.org>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: virtualization@lists.linux-foundation.org
Suggested-by: Jens Axboe <axboe@kernel.dk>
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Asias He <asias@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 45 insertions, 35 deletions

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 160035f54882..576b68e79248 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -110,6 +110,49 @@ static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
         return 0;
 }
 
+static void
+__blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
+                     struct scatterlist *sglist, struct bio_vec **bvprv,
+                     struct scatterlist **sg, int *nsegs, int *cluster)
+{
+
+        int nbytes = bvec->bv_len;
+
+        if (*bvprv && *cluster) {
+                if ((*sg)->length + nbytes > queue_max_segment_size(q))
+                        goto new_segment;
+
+                if (!BIOVEC_PHYS_MERGEABLE(*bvprv, bvec))
+                        goto new_segment;
+                if (!BIOVEC_SEG_BOUNDARY(q, *bvprv, bvec))
+                        goto new_segment;
+
+                (*sg)->length += nbytes;
+        } else {
+new_segment:
+                if (!*sg)
+                        *sg = sglist;
+                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, nbytes, bvec->bv_offset);
+                (*nsegs)++;
+        }
+        *bvprv = bvec;
+}
+
 /*
  * map a request to scatterlist, return number of sg entries setup. Caller
  * must make sure sg can hold rq->nr_phys_segments entries
@@ -131,41 +174,8 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
         bvprv = NULL;
         sg = NULL;
         rq_for_each_segment(bvec, rq, iter) {
-                int nbytes = bvec->bv_len;
-
-                if (bvprv && cluster) {
-                        if (sg->length + nbytes > queue_max_segment_size(q))
-                                goto new_segment;
-
-                        if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
-                                goto new_segment;
-                        if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
-                                goto new_segment;
-
-                        sg->length += nbytes;
-                } else {
-new_segment:
-                        if (!sg)
-                                sg = sglist;
-                        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, nbytes, bvec->bv_offset);
-                        nsegs++;
-                }
-                bvprv = bvec;
+                __blk_segment_map_sg(q, bvec, sglist, &bvprv, &sg,
+                                     &nsegs, &cluster);
         } /* segments in rq */