Features:
+* add small wrapper around qemu that implements sd_notify/AF_VSOCK + machined and
+ maybe some other stuff and boots it
+
+* mybe add new flags to gpt partition tables for rootfs and usrfs indicating
+ purpose, i.e. whether something is supposed to be bootable in a VM, on
+ baremetal, on an nspawn-style container, if it is a portable service image,
+ or a sysext for initrd, for host os, or for portable container. Then hook
+ portabled/… up to udev to watch block devices coming up with the flags set, and
+ use it.
+
+* portabled: read a credential "portable.extra" or so, that takes a list of
+ file system paths to enable on start.
+
* sd-boot should look for information what to boot in SMBIOS, too, so that VM
managers can tell sd-boot what to boot into and suchlike