Fun little thing I have been working on: teach systemd to boot directly into a disk image downloaded via HTTP within the initrd.
In v257 systemd learnt the ability to download disk images at boot via systemd-import-generator, both DDIs and tarballs, and place them in /var/lib/machines/, /var/lib/portables/, /var/lib/confexts, /var/lib/extensions/. The goal was to provide a way to provision any of these resources automatically at boot. But now that we have this, we can take it a step further:
download the root disk image itself with this. There were a bunch of missing bits to make this nice though:
First of all, for raw disk images we need to attach them to a loopback block device, to make them mountable. Easy-peasy, systemd-dissect --attach already delivers that.
Then, for tar disk images we need to bind mount the downloaded and unpacked image to /sysroot/ (which is where the rootfs goes before we transition into it).
Net result of this: I can now point my UEFI to a single URL where it will load the UKI from. A few seconds later the initrd will pick up the rootfs from the same source, and boot it up. Magic!
Why all this though?
@highvoltage well, you probably need it once to create that HTTP boot URL BootXXX efi variable so that the target system just goes to your development device asking for the UKI.
(you could of course also use DHCP/pxe stuff instead, but uh, that's pain, you'd have to use a separate network for that, and run your own DHCP server, much more painful)
Lennart Poettering
highvoltage