block: fix SG_IO vector request data length handling

Impact: fix SG_IO behavior such that it matches the documentation

SG_IO howto says that if ->dxfer_len and sum of iovec disagress, the
shorter one wins.  However, the current implementation returns -EINVAL
for such cases.  Trim iovc if it's longer than ->dxfer_len.

This patch uses iov_*() helpers which take struct iovec * by casting
struct sg_iovec * to it.  sg_iovec is always identical to iovec and
this will be further cleaned up with later patches.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 12 insertions, 1 deletions

diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
index 84b7f8709f41..82a0ca2f6729 100644
--- a/block/scsi_ioctl.c
+++ b/block/scsi_ioctl.c
@@ -290,6 +290,7 @@ static int sg_io(struct request_queue *q, struct gendisk *bd_disk,
 
         if (hdr->iovec_count) {
                 const int size = sizeof(struct sg_iovec) * hdr->iovec_count;
+                size_t iov_data_len;
                 struct sg_iovec *iov;
 
                 iov = kmalloc(size, GFP_KERNEL);
@@ -304,8 +305,18 @@ static int sg_io(struct request_queue *q, struct gendisk *bd_disk,
                         goto out;
                 }
 
+                /* SG_IO howto says that the shorter of the two wins */
+                iov_data_len = iov_length((struct iovec *)iov,
+                                          hdr->iovec_count);
+                if (hdr->dxfer_len < iov_data_len) {
+                        hdr->iovec_count = iov_shorten((struct iovec *)iov,
+                                                       hdr->iovec_count,
+                                                       hdr->dxfer_len);
+                        iov_data_len = hdr->dxfer_len;
+                }
+
                 ret = blk_rq_map_user_iov(q, rq, NULL, iov, hdr->iovec_count,
-                                          hdr->dxfer_len, GFP_KERNEL);
+                                          iov_data_len, GFP_KERNEL);
                 kfree(iov);
         } else if (hdr->dxfer_len)
                 ret = blk_rq_map_user(q, rq, NULL, hdr->dxferp, hdr->dxfer_len,