This option was previously not available and required postprocessing of a `tar-kernel-initrd` output.
Comparison with `iso-efi`:
`iso-efi` only loads the kernel at boot, and the root filesystem is mounted from the actual boot media (eg, a CD-ROM - physical or emulated). This can often cause trouble (it has for us) for multiple reasons:
- the linuxkit kernel might not have the correct drivers built-in for the hardware (see #3154)
- especially with virtual or emulated CD-ROMs, performance can be abysmal: we saw the case where the server IPMI allowed using a ISO stored in AWS S3 over HTTP...you can imagine what happens when you start doing random I/O on the root fs in that case.
- The ISO image has the root device name baked in (ie, `/dev/sr0`) which fails if for some reason the CD-ROM we're running from doesn't end up using that device, so manual tweaking is required (see #2375)
`iso-efi-initrd`, on the other hand, packs the root filesystem as an initramfs (ie similar to what the raw output does, except that in this case we're preparing an ISO image), so both the kernel and the initramfs are loaded in memory by the boot loader and, once running, we don't need to worry about root devices or kernel drivers (and the speed is good, as everything runs in RAM).
Also, the generated ISO can be copied verbatim (eg with `dd`) onto a USB media and it still works.
Finally, the image size is much smaller compared to `iso-efi`.
IMHO, `iso-efi-initrd` could be used almost anywhere `iso-efi` would be used, or might even supersede it. I can't think of a scenario where one might explicitly want to use `iso-efi`.
Points to consider:
- Not tested under aarch64 as I don't have access to that arch. If the automated CI tests also test that, then it should be fine.
- I'm not sure what to put inside `images.yaml` for the `iso-efi-initrd` image. As it is it works of course (my personal image on docker hub), but I guess it'll have to be some more "official" image. However, that cannot be until this PR is merged, so it's kind of a chicken and egg situation. Please advise.
- I can look into adding the corresponding `iso-bios-initrd` builder if there is interest.
Signed-off-by: Davide Brini <waldner@katamail.com>
