From 40b01b9bbdf51ae543a04744283bf2d56c4a6afa Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 19 Feb 2008 11:35:38 +0100 Subject: [PATCH] block: update bio according to DMA alignment padding DMA start address and transfer size alignment for PC requests are achieved using bio_copy_user() instead of bio_map_user(). This works because bio_copy_user() always uses full pages and block DMA alignment isn't allowed to go over PAGE_SIZE. However, the implementation didn't update the last bio of the request to make this padding visible to lower layers. This patch makes blk_rq_map_user() extend the last bio such that it includes the padding area and the size of area pointed to by the request is properly aligned. Signed-off-by: Tejun Heo Cc: James Bottomley Signed-off-by: Jens Axboe --- block/blk-map.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/block/blk-map.c b/block/blk-map.c index bc5ce60691c3..a7cf63ccb5cf 100644 --- a/block/blk-map.c +++ b/block/blk-map.c @@ -139,6 +139,23 @@ int blk_rq_map_user(struct request_queue *q, struct request *rq, ubuf += ret; } + /* + * __blk_rq_map_user() copies the buffers if starting address + * or length isn't aligned. As the copied buffer is always + * page aligned, we know that there's enough room for padding. + * Extend the last bio and update rq->data_len accordingly. + * + * On unmap, bio_uncopy_user() will use unmodified + * bio_map_data pointed to by bio->bi_private. + */ + if (len & queue_dma_alignment(q)) { + unsigned int pad_len = (queue_dma_alignment(q) & ~len) + 1; + struct bio *bio = rq->biotail; + + bio->bi_io_vec[bio->bi_vcnt - 1].bv_len += pad_len; + bio->bi_size += pad_len; + } + rq->buffer = rq->data = NULL; return 0; unmap_rq: