Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752070Ab2FMHk6 (ORCPT ); Wed, 13 Jun 2012 03:40:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43225 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751702Ab2FMHk4 (ORCPT ); Wed, 13 Jun 2012 03:40:56 -0400 From: Asias He To: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org Cc: Asias He , Jens Axboe , Tejun Heo , Shaohua Li , Christoph Hellwig , Minchan Kim Subject: [PATCH RFC 1/2] block: Add blk_bio_map_sg() helper Date: Wed, 13 Jun 2012 15:41:46 +0800 Message-Id: <1339573307-11537-2-git-send-email-asias@redhat.com> In-Reply-To: <1339573307-11537-1-git-send-email-asias@redhat.com> References: <1339573307-11537-1-git-send-email-asias@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3383 Lines: 113 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_fn method. Cc: Jens Axboe Cc: Tejun Heo Cc: Shaohua Li Cc: linux-kernel@vger.kernel.org Signed-off-by: Christoph Hellwig Signed-off-by: Minchan Kim Signed-off-by: Asias He --- block/blk-merge.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++ include/linux/blkdev.h | 2 ++ 2 files changed, 65 insertions(+) diff --git a/block/blk-merge.c b/block/blk-merge.c index 160035f..27ba264 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -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 blk_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(blk_bio_map_sg); + static inline int ll_new_hw_segment(struct request_queue *q, struct request *req, struct bio *bio) diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index ba43f40..46916af 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -884,6 +884,8 @@ extern void blk_queue_flush_queueable(struct request_queue *q, bool queueable); 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 blk_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); -- 1.7.10.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/