Add blk_rq_map_sg_one_by_one function to ll_rw_blk.c in order to allow a low
level driver to map scatter gather elements from the block subsystem one
at a time into device specific data structures instead of having to take
a copy of all of them all at once and then afterwards copy them into a device
specific format.
To follow, a patch to the cciss driver using this interface which
allows up to 256 scatter gather elements (current limit is 31).
-- steve
drivers/block/ll_rw_blk.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++
include/linux/blkdev.h | 4 +++
2 files changed, 63 insertions
--- lx2544ac3/drivers/block/ll_rw_blk.c~blkdev_sg Fri Oct 25 13:46:08 2002
+++ lx2544ac3-scameron/drivers/block/ll_rw_blk.c Fri Oct 25 13:46:08 2002
@@ -766,6 +766,64 @@ inline int blk_hw_contig_segment(request
}
/*
+ * Map a request to a single scatterlist, one by one. As each scatterlist is
+ * constructed consume_sg is called so the scattlerlist may be used. The idea
+ * is the caller won't have to allocate all the space needed for a potentially
+ * large number of sg elements, instead the consume_sg callback function
+ * consumes each element as it's made. sg_state is a pointer meant to be
+ * used by consume_sg to remember its state between calls.
+ */
+int blk_rq_map_sg_one_by_one(request_queue_t *q, struct request *rq,
+ consume_sg_callback consume_sg, void *sg_state)
+{
+ struct scatterlist sg;
+ struct bio_vec *bvec, *bvprv;
+ struct bio *bio;
+ int nsegs, i, cluster;
+
+ nsegs = 0;
+ cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
+
+ /*
+ * for each bio in rq
+ */
+ bvprv = NULL;
+ rq_for_each_bio(bio, rq) {
+ /*
+ * for each segment in bio
+ */
+ bio_for_each_segment(bvec, bio, i) {
+ int nbytes = bvec->bv_len;
+
+ if (bvprv && cluster) {
+ if (sg.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;
+
+ sg.length += nbytes;
+ } else {
+new_segment:
+ if (bvprv) consume_sg(&sg, sg_state);
+ memset(&sg,0,sizeof(struct scatterlist));
+ sg.page = bvec->bv_page;
+ sg.length = nbytes;
+ sg.offset = bvec->bv_offset;
+ nsegs++;
+ }
+ bvprv = bvec;
+ } /* segments in bio */
+ } /* bios in rq */
+
+ if (bvprv) consume_sg(&sg, sg_state);
+
+ return nsegs;
+}
+
+/*
* map a request to scatterlist, return number of sg entries setup. Caller
* must make sure sg can hold rq->nr_phys_segments entries
*/
@@ -2112,6 +2170,7 @@ EXPORT_SYMBOL(blk_queue_max_hw_segments)
EXPORT_SYMBOL(blk_queue_max_segment_size);
EXPORT_SYMBOL(blk_queue_hardsect_size);
EXPORT_SYMBOL(blk_queue_segment_boundary);
+EXPORT_SYMBOL(blk_rq_map_sg_one_by_one);
EXPORT_SYMBOL(blk_rq_map_sg);
EXPORT_SYMBOL(blk_nohighio);
EXPORT_SYMBOL(blk_dump_rq_flags);
--- lx2544ac3/include/linux/blkdev.h~blkdev_sg Fri Oct 25 13:46:08 2002
+++ lx2544ac3-scameron/include/linux/blkdev.h Fri Oct 25 13:46:08 2002
@@ -341,6 +341,10 @@ extern void blk_queue_prep_rq(request_qu
extern void blk_queue_merge_bvec(request_queue_t *, merge_bvec_fn *);
extern struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev);
+typedef void (*consume_sg_callback)(struct scatterlist *, void *);
+extern int blk_rq_map_sg_one_by_one(request_queue_t *, struct request *,
+ consume_sg_callback consume_sg, void * sg_state);
+
extern int blk_rq_map_sg(request_queue_t *, struct request *, struct scatterlist *);
extern void blk_dump_rq_flags(struct request *, char *);
extern void generic_unplug_device(void *);
.
-
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This archive was generated by hypermail 2b29 : Thu Oct 31 2002 - 22:00:28 EST