block: use blkdev_issue_discard in blk_ioctl_discard

blk_ioctl_discard duplicates large amounts of code from blkdev_issue_discard,
the only difference between the two is that blkdev_issue_discard needs to
send a barrier discard request and blk_ioctl_discard a non-barrier one,
and blk_ioctl_discard needs to wait on the request.  To facilitates this
add a flags argument to blkdev_issue_discard to control both aspects of the
behaviour.  This will be very useful later on for using the waiting
funcitonality for other callers.

Based on an earlier patch from Matthew Wilcox <matthew@wil.cx>.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

fs/btrfs/extent-tree.c

@@ -1511,7 +1511,8 @@ static int remove_extent_backref(struct btrfs_trans_handle *trans,
 static void btrfs_issue_discard(struct block_device *bdev,
 				u64 start, u64 len)
 {
-	blkdev_issue_discard(bdev, start >> 9, len >> 9, GFP_KERNEL);
+	blkdev_issue_discard(bdev, start >> 9, len >> 9, GFP_KERNEL,
+			     DISCARD_FL_BARRIER);
 }
 #endif
 

fs/gfs2/rgrp.c

@@ -857,7 +857,8 @@ static void gfs2_rgrp_send_discards(struct gfs2_sbd *sdp, u64 offset,
 					goto start_new_extent;
 				if ((start + nr_sects) != blk) {
 					rv = blkdev_issue_discard(bdev, start,
-							    nr_sects, GFP_NOFS);
+							    nr_sects, GFP_NOFS,
+							    DISCARD_FL_BARRIER);
 					if (rv)
 						goto fail;
 					nr_sects = 0;
@@ -871,7 +872,8 @@ start_new_extent:
 		}
 	}
 	if (nr_sects) {
-		rv = blkdev_issue_discard(bdev, start, nr_sects, GFP_NOFS);
+		rv = blkdev_issue_discard(bdev, start, nr_sects, GFP_NOFS,
+					 DISCARD_FL_BARRIER);
 		if (rv)
 			goto fail;
 	}