Commit 40b01b9b authored Feb 19, 2008 by Tejun Heo Committed by Jens Axboe Feb 19, 2008

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 <htejun@gmail.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

parent 56c819df

block/blk-map.c

+17 −0

Original line number	Diff line number	Diff line
		@@ -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: