Add a helper to map a bio to a scatterlist, modelled after blk_rq_map_sg.
This helper is useful for any driver that wants to create a scatterlist
from its ->make_request method.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Index: linux-2.6/block/blk-merge.c
===================================================================
--- linux-2.6.orig/block/blk-merge.c 2011-10-04 11:49:32.857014742 -0400
+++ linux-2.6/block/blk-merge.c 2011-10-04 13:37:51.305630951 -0400
@@ -199,6 +199,69 @@ new_segment:
}
EXPORT_SYMBOL(blk_rq_map_sg);
+/*
+ * map a bio to a scatterlist, return number of sg entries setup. Caller
+ * must make sure sg can hold bio->bi_phys_segments entries
+ */
+int bio_map_sg(struct request_queue *q, struct bio *bio,
+ struct scatterlist *sglist)
+{
+ struct bio_vec *bvec, *bvprv;
+ struct scatterlist *sg;
+ int nsegs, cluster;
+ unsigned long i;
+
+ nsegs = 0;
+ cluster = blk_queue_cluster(q);
+
+ bvprv = NULL;
+ sg = NULL;
+ bio_for_each_segment(bvec, bio, i) {
+ 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;
+ } /* segments in bio */
+
+ if (sg)
+ sg_mark_end(sg);
+
+ BUG_ON(bio->bi_phys_segments && nsegs > bio->bi_phys_segments);
+ return nsegs;
+}
+EXPORT_SYMBOL(bio_map_sg);
+
static inline int ll_new_hw_segment(struct request_queue *q,
struct request *req,
struct bio *bio)
Index: linux-2.6/include/linux/blkdev.h
===================================================================
--- linux-2.6.orig/include/linux/blkdev.h 2011-10-04 13:37:13.216148915 -0400
+++ linux-2.6/include/linux/blkdev.h 2011-10-04 13:37:51.317613617 -0400
@@ -854,6 +854,8 @@ extern void blk_queue_flush_queueable(st
extern struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev);
extern int blk_rq_map_sg(struct request_queue *, struct request *, struct scatterlist *);
+extern int bio_map_sg(struct request_queue *q, struct bio *bio,
+ struct scatterlist *sglist);
extern void blk_dump_rq_flags(struct request *, char *);
extern long nr_blockdev_pages(void);
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