'Some patches for Linux 6.15-rc4 (updating the kernel driver for the Bcachefs file system) triggered some "straight-to-the-point wisdom" from Linus Torvalds about case-insensitive filesystems, reports Phoronix. Bcachefs developer Kent Overstreet started the conversation, explaining how some buggy patches for their case-insensitive file and folder support were upstreamed into the Bcachefs kernel driver nearly two years ago: When I was discussing with the developer who did the implementation, I noted that fstests should already have tests. However, it seems I neglected to tell him to make sure the tests actually run... It is _not_ enough to simply rely on the automated tests. You have to have eyes on what your code is doing. Overstreet added "There's a story behind the case insensitive directory fixes, and lessons to be learned." To which Torvalds replied.... "No." "The only lesson to be learned is that filesystem people never learn." Torvalds: Case-insensitive names are horribly wrong, and you shouldn't have done them at all. The problem wasn't the lack of testing, the problem was implementing it in the first place. The problem is then compounded by "trying to do it right", and in the process doing it horrible wrong indeed, because "right" doesn't exist, but trying to will make random bytes have very magical meaning. And btw, the tests are all completely broken anyway. Last I saw, they didn't actually test for all the really interesting cases — the ones that cause security issues in user land. Security issues like "user space checked that the filename didn't match some security-sensitive pattern". And then the shit-for-brains filesystem ends up matching that pattern *anyway*, because the people who do case insensitivity *INVARIABLY* do things like ignore non-printing characters, so now "case insensitive" also means "insensitive to other things too".... Dammit. Case sensitivity is a BUG. The fact that filesystem people *still* think it's a feature, I cannot understand. It's like they revere the old FAT filesystem _so_ much that they have to recreate it — badly. And this led to a very lively back-and-forth discussion.' -- source: https://linux.slashdot.org/story/25/04/27/0547245 Cheers, Peter