block: opencode devcgroup_inode_permission

Just call devcgroup_check_permission to avoid various superflous checks
and a double conversion of the access flags.

Signed-off-by: Christoph Hellwig <[e-mail]>
Acked-by: Tejun Heo <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>
Reviewed-by: Hannes Reinecke <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

fs/block_dev.c

···
 	struct block_device *claiming;
 	bool unblock_events = true;
 	struct gendisk *disk;
-	int perm = 0;
 	int partno;
 	int ret;
 
-	if (mode & FMODE_READ)
-		perm |= MAY_READ;
-	if (mode & FMODE_WRITE)
-		perm |= MAY_WRITE;
-	ret = devcgroup_inode_permission(bdev->bd_inode, perm);
+	ret = devcgroup_check_permission(DEVCG_DEV_BLOCK,
+			imajor(bdev->bd_inode), iminor(bdev->bd_inode),
+			((mode & FMODE_READ) ? DEVCG_ACC_READ : 0) |
+			((mode & FMODE_WRITE) ? DEVCG_ACC_WRITE : 0));
 	if (ret)
 		goto bdput;