The two sides of reflink()

Yeah, I did miss that. I'm going to have to imagine that a reflink-supporting ext3 filesystem would have a new feature bit set in the superblock. And hopefully would not be mountable on a non-reflink-supporting kernel. Two inodes sharing the same data blocks isn't something that any traditional UNIXy filesystem is going to understand. MS-DOS type filesystems surely don't support it either (cross linked files should sound familiar to anyone who used a DOS system in the 1980s or early 1990s.)