Nullfs has been merged for Linux 7.0

> nullfs has extensions beyond this in the future. It will serve as a concept to support the creation of completely empty mount namespaces - which is work coming up in the next cycle."

So there might finally be "a mechanism for kernel threads to explicitly relinquish any access to the file system" that the old manual page for pivot_root promised: https://linux.die.net/man/2/pivot_root

This may sound silly, but this makes a real difference. Until this, it was not possible to run standard containers like Docker or Podman in an initramfs without ugly tricks (like using chroot instead of pivot_root, or mounting the root over itself before starting init).

This makes the initramfs rootfs un-special. Aside from being volatile, but this is a design decision.