[PATCH 3/5] blk_rq_map_sg_ring as a counterpart to blk_rq_map_sg.

Rusty Russell
2007-12-20T05:51:00Z

Obvious counterpart to blk_rq_map_sg.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -31,6 +31,7 @@
#include <linux/blktrace_api.h>
#include <linux/fault-inject.h>
#include <linux/scatterlist.h>
+#include <linux/sg_ring.h>

/*
* for max sense size
@@ -1364,6 +1365,68 @@ new_segment:

EXPORT_SYMBOL(blk_rq_map_sg);

+/**
+ * blk_rq_map_sg_ring - map a request to a scatterlist ring.
+ * @q: the request queue this request applies to.
+ * @rq: the request to map
+ * @sg: the sg_ring to populate.
+ *
+ * There must be enough elements in the sg_ring(s) to map the request.
+ */
+void blk_rq_map_sg_ring(struct request_queue *q, struct request *rq,
+ struct sg_ring *sg)
+{
+ struct bio_vec *bvec, *bvprv;
+ struct req_iterator iter;
+ int i, cluster;
+ struct sg_ring *head = sg;
+ struct scatterlist *sgprv;
+
+ i = 0;
+ cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
+
+ /*
+ * for each bio in rq
+ */
+ bvprv = NULL;
+ sgprv = NULL;
+ rq_for_each_segment(bvec, rq, iter) {
+ int nbytes = bvec->bv_len;
+
+ if (bvprv && cluster) {
+ if (sgprv->length + nbytes > q->max_segment_size)
+ goto new_segment;
+
+ if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
+ goto new_segment;
+ if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
+ goto new_segment;
+
+ sgprv->length += nbytes;
+ } else {
+new_segment:
+ sg_set_page(sg->sg + i, bvec->bv_page, nbytes,
+ bvec->bv_offset);
+ sgprv = sg->sg + i;
+ if (++i == sg->max) {
+ sg->num = i;
+ sg = sg_ring_next(sg, head);
+ i = 0;
+ }
+ }
+ bvprv = bvec;
+ } /* segments in rq */
+
+ /* If we were still working on an sg_ring, set the number and
+ * clear any following sg_rings. */
+ if (sg) {
+ sg->num = i;
+ for (sg = sg_ring_next(sg,head); sg; sg = sg_ring_next(sg,head))
+ sg->num = 0;
+ }
+}
+EXPORT_SYMBOL(blk_rq_map_sg_ring);
+
/*
* the standard queue merge functions, can be overridden with device
* specific ones if so desired
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -777,6 +777,8 @@ extern void blk_ordered_complete_seq(str
extern void blk_ordered_complete_seq(struct request_queue *, unsigned, int);

extern int blk_rq_map_sg(struct request_queue *, struct request *, struct scatterlist *);
+struct sg_ring;
+extern void blk_rq_map_sg_ring(struct request_queue *, struct request *, struct sg_ring *);
extern void blk_dump_rq_flags(struct request *, char *);
extern void generic_unplug_device(struct request_queue *);
extern void __generic_unplug_device(struct request_queue *);