When doing re-attach/auto-attach of cached files for which the lock has been lost, PCC looks them up with kern_path.  However, kern_path is subject to namespaces, so if the user process is containerized, it will use the container namespace.

This means PCC must be mounted in the container namespace, which is not desirable.

Instead we can do a lookup with lookup_one_len, starting from the PCC root, which is in the true root file system and not subject to the container namespace.  It is correct to ignore the container namespace because PCC is file system caching functionality, and because the user can't control the PCC path, so it's not a potential security concern.