+ /*
+ * __blk_rq_map_user() copies the buffers if starting address
+ * or length isn't aligned to dma_pad_mask. 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 & q->dma_pad_mask) {
+ unsigned int pad_len = (q->dma_pad_mask & ~len) + 1;
+ struct bio *tail = rq->biotail;
+
+ tail->bi_io_vec[tail->bi_vcnt - 1].bv_len += pad_len;
+ tail->bi_size += pad_len;
+
+ rq->extra_len += pad_len;
+ }
+