Re: [RFC] initoverlayfs - a scalable initial filesystem

Eric Curtin
2023-12-09T14:43:38Z

On Sat, 9 Dec 2023 at 12:46, Luca Boccassi <bluca@debian.org> wrote:
>
> On Fri, 8 Dec 2023 at 19:00, Eric Curtin <ecurtin@redhat.com> wrote:
> >
> > We have been working on a new initial filesystem called initoverlayfs.
> > It is a new filesystem that provides a more scalable approach to
> > initial filesystems as opposed to just using initrds. We are writing
> > this RFC to the systemd and dracut mailing lists (feel free to forward
> > to UAPI group also) because although this solution works without
> > changing the code in these projects, it operates in the same area as
> > systemd, udev, dracut, etc. and uses these tools.
>
> It seems to me everything you described already exists? If you want to
> avoid having an initrd -> rootfs transition, you can already do that -

You need a initrd -> rootfs transition for generic linux operating
systems right? Or else you start building all sorts of things directly
into the kernel which isn't really scalable.

> the initrd code paths run because there's /etc/initrd-release, omit
> that and the transition/phase is avoided. If you want to have an
> overlay with r/o images, you can already do that with sysexts. You'll
> need to reimplement and maintain separately TPM support, LUKS support,
> fido2, etc etc

This is intended to be something you can use with or without sysexts,
not a competing alternative. There will be some reimplementations, but
our hope is to minimize that, leave as much as possible to systemd,
initoverlayfs stage, etc. where you don't pay the upfront cost for
decompressing and copying all the bytes.

We are open to executing minified systemd libraries/binaries in the
minified initramfs, we do that in the current version of storage-init
by calling systemd udev binaries.

>