When run in an initrd and no root= argument is set (or is set to
root=gpt-auto) we will automatically look for the root partition on the
same disk the EFI ESP is located on.
Since we look for swap, /home and /srv on the disk the root partition is
located on, we hence have a fully discoverable chain:
Firmware discovers the EFI ESP partition → the initrd discovers the
root partition → the host OS discovers swap, /home, and /srv.
Note that this requires an EFI boot loader that sets the
LoaderDevicePartUUID EFI variable, such as Gummiboot.
