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@xxxxxxxxx>
Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
---
block/blk-map.c | 17 +++++++++++++++++
1 files changed, 17 insertions(+), 0 deletions(-)
diff --git a/block/blk-map.c b/block/blk-map.c
index 955d75c..103b1df 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:
--
1.5.2.4
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