block: update request stacking methods to support discards

Propagate REQ_DISCARD in cmd_flags when cloning a discard request.
Skip blk_rq_check_limits's existing checks for discard requests because
discard limits will have already been checked in blkdev_issue_discard.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 5ab3ac22930c..7da630e25ae7 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1644,6 +1644,9 @@ EXPORT_SYMBOL(submit_bio);
  */
 int blk_rq_check_limits(struct request_queue *q, struct request *rq)
 {
+        if (rq->cmd_flags & REQ_DISCARD)
+                return 0;
+
         if (blk_rq_sectors(rq) > queue_max_sectors(q) ||
             blk_rq_bytes(rq) > queue_max_hw_sectors(q) << 9) {
                 printk(KERN_ERR "%s: over max size limit.\n", __func__);
@@ -2492,6 +2495,8 @@ static void __blk_rq_prep_clone(struct request *dst, struct request *src)
 {
         dst->cpu = src->cpu;
         dst->cmd_flags = (rq_data_dir(src) | REQ_NOMERGE);
+        if (src->cmd_flags & REQ_DISCARD)
+                dst->cmd_flags |= REQ_DISCARD;
         dst->cmd_type = src->cmd_type;
         dst->__sector = blk_rq_pos(src);
         dst->__data_len = blk_rq_bytes(src);