The only reason to use an IPC or go through the kernel is to expose the fs to the rest of the OS. If an app doesn't intend to expose the fs, the entirety of the fs can exist within the app process.
Quoting:
> "Unlike many other operating systems, the notion of “mounted filesystems” does not live in a globally accessible table. Instead, the question “what mountpoints exist?” can only be answered on a filesystem-specific basis -- an arbitrary filesystem may not have access to the information about what mountpoints exist elsewhere."
Quoting: > "Unlike many other operating systems, the notion of “mounted filesystems” does not live in a globally accessible table. Instead, the question “what mountpoints exist?” can only be answered on a filesystem-specific basis -- an arbitrary filesystem may not have access to the information about what mountpoints exist elsewhere."