On Mon, May 27, 2024 at 03:47:33PM +0000, Trond Myklebust wrote: > On Mon, 2024-05-27 at 15:17 +0200, Christian Brauner wrote: > > > > Returning the 64bit mount id makes this race-free because we now have > > statmount(): > > > > u64 mnt_id = 0; > > name_to_handle_at(AT_FDCWD, "/path/to/file", &handle, &mnt_id, 0); > > statmount(mnt_id); > > > > Which gets you the device number which one can use to figure out the > > uuid without ever having to open a single file (We could even expose > > the > > UUID of the filesystem through statmount() if we wanted to.). > > > > It is not race free. statmount() depends on the filesystem still being > mounted somewhere in your namespace, which is not guaranteed above. The unsigned 64bit mount is not recyclable. It is a unique identifier for a mount for the lifetime of the system. Even if bumped on every cycle it will still take hundreds of years to overflow.
