On Thu, Feb 22, 2024 at 10:14:20AM +0100, Miklos Szeredi wrote: > On Wed, 21 Feb 2024 at 22:08, Josef Bacik <josef@xxxxxxxxxxxxxx> wrote: > > > > On Wed, Feb 21, 2024 at 04:06:34PM +0100, Miklos Szeredi wrote: > > > On Wed, 21 Feb 2024 at 01:51, Kent Overstreet <kent.overstreet@xxxxxxxxx> wrote: > > > > > > > > Recently we had a pretty long discussion on statx extensions, which > > > > eventually got a bit offtopic but nevertheless hashed out all the major > > > > issues. > > > > > > > > To summarize: > > > > - guaranteeing inode number uniqueness is becoming increasingly > > > > infeasible, we need a bit to tell userspace "inode number is not > > > > unique, use filehandle instead" > > > > > > This is a tough one. POSIX says "The st_ino and st_dev fields taken > > > together uniquely identify the file within the system." > > > > > > > Which is what btrfs has done forever, and we've gotten yelled at forever for > > doing it. We have a compromise and a way forward, but it's not a widely held > > view that changing st_dev to give uniqueness is an acceptable solution. It may > > have been for overlayfs because you guys are already doing something special, > > but it's not an option that is afforded the rest of us. > > Overlayfs tries hard not to use st_dev to give uniqueness and instead > partitions the 64bit st_ino space within the same st_dev. There are > various fallback cases, some involve switching st_dev and some using > non-persistent st_ino. Yeah no, you can't crap multiple 64 bit inode number spaces into 64 bits: pigeonhole principle. We need something better than "hacks". > What overlayfs does may or may not be applicable to btrfs/bcachefs, > but that's not my point. My point is that adding a flag to statx does > not solve anything. You can't just say that from now on btrfs > doesn't have use unique st_ino/st_dev because we've just indicated > that in statx and everything is fine. That will trigger the > no-regressions rule and then it's game over. At least I would expect > that to happen. > > What we can do instead is introduce a new API that is better, This isn't a serious proposal.
