block: move req_gap_{back,front}_merge to blk-merge.c
Keep it close to the actual users instead of exposing the function to all
drivers.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-merge.c b/block/blk-merge.c
index aaec38c..ad8a226 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -12,6 +12,71 @@
#include "blk.h"
+/*
+ * Check if the two bvecs from two bios can be merged to one segment. If yes,
+ * no need to check gap between the two bios since the 1st bio and the 1st bvec
+ * in the 2nd bio can be handled in one segment.
+ */
+static inline bool bios_segs_mergeable(struct request_queue *q,
+ struct bio *prev, struct bio_vec *prev_last_bv,
+ struct bio_vec *next_first_bv)
+{
+ if (!BIOVEC_PHYS_MERGEABLE(prev_last_bv, next_first_bv))
+ return false;
+ if (!BIOVEC_SEG_BOUNDARY(q, prev_last_bv, next_first_bv))
+ return false;
+ if (prev->bi_seg_back_size + next_first_bv->bv_len >
+ queue_max_segment_size(q))
+ return false;
+ return true;
+}
+
+static inline bool bio_will_gap(struct request_queue *q,
+ struct request *prev_rq, struct bio *prev, struct bio *next)
+{
+ struct bio_vec pb, nb;
+
+ if (!bio_has_data(prev) || !queue_virt_boundary(q))
+ return false;
+
+ /*
+ * Don't merge if the 1st bio starts with non-zero offset, otherwise it
+ * is quite difficult to respect the sg gap limit. We work hard to
+ * merge a huge number of small single bios in case of mkfs.
+ */
+ if (prev_rq)
+ bio_get_first_bvec(prev_rq->bio, &pb);
+ else
+ bio_get_first_bvec(prev, &pb);
+ if (pb.bv_offset)
+ return true;
+
+ /*
+ * We don't need to worry about the situation that the merged segment
+ * ends in unaligned virt boundary:
+ *
+ * - if 'pb' ends aligned, the merged segment ends aligned
+ * - if 'pb' ends unaligned, the next bio must include
+ * one single bvec of 'nb', otherwise the 'nb' can't
+ * merge with 'pb'
+ */
+ bio_get_last_bvec(prev, &pb);
+ bio_get_first_bvec(next, &nb);
+ if (bios_segs_mergeable(q, prev, &pb, &nb))
+ return false;
+ return __bvec_gap_to_prev(q, &pb, nb.bv_offset);
+}
+
+static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
+{
+ return bio_will_gap(req->q, req, req->biotail, bio);
+}
+
+static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
+{
+ return bio_will_gap(req->q, NULL, bio, req->bio);
+}
+
static struct bio *blk_bio_discard_split(struct request_queue *q,
struct bio *bio,
struct bio_set *bs,
