dm: refactor ioctl handling

This moves the call to blkdev_ioctl and the argument checking to DM core
code, and only leaves a callout to find the block device to operate on
in the targets.  This simplifies the code and allows us to pass through
ioctl-like command using other methods in the next patch.

Also split out a helper around calling the prepare_ioctl method that
will be reused for persistent reservation handling.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-verity.c b/drivers/md/dm-verity.c
index edc624b..ccf4188 100644
--- a/drivers/md/dm-verity.c
+++ b/drivers/md/dm-verity.c
@@ -631,18 +631,17 @@
 	}
 }
 
-static int verity_ioctl(struct dm_target *ti, unsigned cmd,
-			unsigned long arg)
+static int verity_prepare_ioctl(struct dm_target *ti,
+		struct block_device **bdev, fmode_t *mode)
 {
 	struct dm_verity *v = ti->private;
-	int r = 0;
+
+	*bdev = v->data_dev->bdev;
 
 	if (v->data_start ||
 	    ti->len != i_size_read(v->data_dev->bdev->bd_inode) >> SECTOR_SHIFT)
-		r = scsi_verify_blk_ioctl(NULL, cmd);
-
-	return r ? : __blkdev_driver_ioctl(v->data_dev->bdev, v->data_dev->mode,
-				     cmd, arg);
+		return 1;
+	return 0;
 }
 
 static int verity_iterate_devices(struct dm_target *ti,
@@ -965,7 +964,7 @@
 	.dtr		= verity_dtr,
 	.map		= verity_map,
 	.status		= verity_status,
-	.ioctl		= verity_ioctl,
+	.prepare_ioctl	= verity_prepare_ioctl,
 	.iterate_devices = verity_iterate_devices,
 	.io_hints	= verity_io_hints,
 };