block: provide a blk_rq_map_sg variant that returns the last element

To be able to move some of the special purpose hacks in blk_rq_map_sg
into the callers we need a variant that returns the last mapped
S/G list element to the caller.  Add that variant as __blk_rq_map_sg
and make blk_rq_map_sg a trivial inline wrapper around it.

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 99c9759..ee618cd 100644 (file)
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -519,24 +519,23 @@ static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
  * map a request to scatterlist, return number of sg entries setup. Caller
  * must make sure sg can hold rq->nr_phys_segments entries
  */
-int blk_rq_map_sg(struct request_queue *q, struct request *rq,
-                 struct scatterlist *sglist)
+int __blk_rq_map_sg(struct request_queue *q, struct request *rq,
+               struct scatterlist *sglist, struct scatterlist **last_sg)
 {
-       struct scatterlist *sg = NULL;
        int nsegs = 0;
 
        if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
-               nsegs = __blk_bvec_map_sg(rq->special_vec, sglist, &sg);
+               nsegs = __blk_bvec_map_sg(rq->special_vec, sglist, last_sg);
        else if (rq->bio && bio_op(rq->bio) == REQ_OP_WRITE_SAME)
-               nsegs = __blk_bvec_map_sg(bio_iovec(rq->bio), sglist, &sg);
+               nsegs = __blk_bvec_map_sg(bio_iovec(rq->bio), sglist, last_sg);
        else if (rq->bio)
-               nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
+               nsegs = __blk_bios_map_sg(q, rq->bio, sglist, last_sg);
 
        if (blk_rq_bytes(rq) && (blk_rq_bytes(rq) & q->dma_pad_mask)) {
                unsigned int pad_len =
                        (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
 
-               sg->length += pad_len;
+               (*last_sg)->length += pad_len;
                rq->extra_len += pad_len;
        }
 
@@ -544,9 +543,9 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
                if (op_is_write(req_op(rq)))
                        memset(q->dma_drain_buffer, 0, q->dma_drain_size);
 
-               sg_unmark_end(sg);
-               sg = sg_next(sg);
-               sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
+               sg_unmark_end(*last_sg);
+               *last_sg = sg_next(*last_sg);
+               sg_set_page(*last_sg, virt_to_page(q->dma_drain_buffer),
                            q->dma_drain_size,
                            ((unsigned long)q->dma_drain_buffer) &
                            (PAGE_SIZE - 1));
@@ -554,8 +553,8 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
                rq->extra_len += q->dma_drain_size;
        }
 
-       if (sg)
-               sg_mark_end(sg);
+       if (*last_sg)
+               sg_mark_end(*last_sg);
 
        /*
         * Something must have been wrong if the figured number of
@@ -565,7 +564,7 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 
        return nsegs;
 }
-EXPORT_SYMBOL(blk_rq_map_sg);
+EXPORT_SYMBOL(__blk_rq_map_sg);
 
 static inline int ll_new_hw_segment(struct request *req, struct bio *bio,
                unsigned int nr_phys_segs)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 76da162..496dc94 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1136,7 +1136,15 @@ static inline unsigned short blk_rq_nr_discard_segments(struct request *rq)
        return max_t(unsigned short, rq->nr_phys_segments, 1);
 }
 
-extern int blk_rq_map_sg(struct request_queue *, struct request *, struct scatterlist *);
+int __blk_rq_map_sg(struct request_queue *q, struct request *rq,
+               struct scatterlist *sglist, struct scatterlist **last_sg);
+static inline int blk_rq_map_sg(struct request_queue *q, struct request *rq,
+               struct scatterlist *sglist)
+{
+       struct scatterlist *last_sg = NULL;
+
+       return __blk_rq_map_sg(q, rq, sglist, &last_sg);
+}
 extern void blk_dump_rq_flags(struct request *, char *);
 extern long nr_blockdev_pages(void);