add unique mount ID
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.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Link: https://lore.kernel.org/r/20231025140205.3586473-2-mszeredi@redhat.com
Reviewed-by: Ian Kent <raven@themaw.net>
Signed-off-by: Christian Brauner <brauner@kernel.org>