With this patch, blk_rq_map_user_iov uses bio_copy_user_iov when a low
level driver needs padding or a buffer in sg_iovec isn't aligned. That
is, it uses temporary kernel buffers instead of mapping user pages
directly.
When a LLD needs padding, later blk_rq_map_sg needs to extend the last
entry of a scatter list. bio_copy_user_iov guarantees that there is
enough space for padding by using temporary kernel buffers instead of
user pages.
blk_rq_map_user_iov needs buffers in sg_iovec to be aligned. The
comment in blk_rq_map_user_iov indicates that drivers/scsi/sg.c also
needs buffers in sg_iovec to be aligned. Actually, drivers/scsi/sg.c
works with unaligned buffers in sg_iovec (it always uses temporary
kernel buffers).
Signed-off-by: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
Cc: Tejun Heo <htejun@xxxxxxxxx>
Cc: Mike Christie <michaelc@xxxxxxxxxxx>
Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Cc: Jens Axboe <jens.axboe@xxxxxxxxxx>
---
block/blk-map.c | 22 +++++++++++++++++-----
1 files changed, 17 insertions(+), 5 deletions(-)
diff --git a/block/blk-map.c b/block/blk-map.c
index c07d9c8..ab43533 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -5,6 +5,7 @@
#include <linux/module.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
+#include <scsi/sg.h> /* for struct sg_iovec */
#include "blk.h"
@@ -194,15 +195,26 @@ int blk_rq_map_user_iov(struct request_queue *q, struct request *rq,
struct sg_iovec *iov, int iov_count, unsigned int len)
{
struct bio *bio;
+ int i, read = rq_data_dir(rq) == READ;
+ int unaligned = 0;
if (!iov || iov_count <= 0)
return -EINVAL;
- /* we don't allow misaligned data like bio_map_user() does. If the
- * user is using sg, they're expected to know the alignment constraints
- * and respect them accordingly */
- bio = bio_map_user_iov(q, NULL, iov, iov_count,
- rq_data_dir(rq) == READ);
+ for (i = 0; i < iov_count; i++) {
+ unsigned long uaddr = (unsigned long)iov[i].iov_base;
+
+ if (uaddr & queue_dma_alignment(q)) {
+ unaligned = 1;
+ break;
+ }
+ }
+
+ if (unaligned || (q->dma_pad_mask & len))
+ bio = bio_copy_user_iov(q, iov, iov_count, read);
+ else
+ bio = bio_map_user_iov(q, NULL, iov, iov_count, read);
+
if (IS_ERR(bio))
return PTR_ERR(bio);
--
1.5.4.2
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