On Thu, 28 Sept 2023 at 15:03, Miklos Szeredi [off-list ref] wrote:

If a mount is released then its mnt_id can immediately be reused.  This is
bad news for user interfaces that want to uniquely identify a mount.

Implementing a unique mount ID is trivial (use a 64bit counter).
Unfortunately userspace assumes 32bit size and would overflow after the
counter reaches 2^32.

Introduce a new 64bit ID alongside the old one.  Initialize the counter to
2^32, this guarantees that the old and new IDs are never mixed up.

It occurred to me that it might make sense to make this counter
per-namespace.  That would allow more separation between namespaces,
like preventing the observation of mount creations in other
namespaces.

Does a global number make any sense?

Thanks,
Miklos