From: Gerd Hoffmann on
gitlab.com
https://gitlab.com/cki-project/kernel-ark/-/merge_requests/2817#note_1696...
If you boot with an initrd it will be the initrd not the kernel which handles
the root= command line. So maybe mkosi has built-in support for virtiofs, or
it passes control back to the kernel for cases it can't handle. dracut
initrd's will error out without the virtiofs module.