overlay/fcos: pin legacy ifnames on existing machines

[lucab]

This introduces a coreos-keep-legacy-ifnames service to pin
network interface names to the legacy scheme on machines
where 99-default.link is missing.
This is in order to ensure that those machines do not jump
into the new scheme via auto-updates as soon as FCOS starts
shipping such unit in the OS.

Ref: coreos/fedora-coreos-tracker#484

[lucab]

@jlebon please double-check the my knowledge here: if injected this way, the net.ifnames=0 will be retained even if the next update payload does not have it in its embedded kargs. Correct?

[cgwalters]

The update payload doesn't have kargs. Supporting that is ostreedev/ostree#479

So yes it will be retained because there's nothing to override it.

[cgwalters]

The update payload doesn't have kargs. Supporting that is ostreedev/ostree#479

So yes it will be retained because there's nothing to override it.

[jlebon]

Cool, thanks! One optional tweak, but LGTM as is too.

[lucab]

Rebased. The PR to drop this logic and get back to systemd default persistent names is at #491.

[dustymabe]

LGTM

[cgwalters]

Writing an ext test for this probably wouldn't be too hard (not a blocker though)

[lucab]

@cgwalters do you mean literally on this logic, or are you maybe thinking of #491? I was planning to have it on the latter, as this one requires a reboot to be really tested and the old behavior will be gone from CI in a couple of releases.

[lucab]

Rebased to fix the typos too.

[dustymabe]

will merge this in a bit unless anyone has anything else

[cgwalters]

FTR, this service fails on the live ISO because /boot is read-only:

Jul 01 11:59:18 localhost systemd[1]: Starting CoreOS Keep Legacy Network Interface Names...
Jul 01 11:59:18 localhost coreos-keep-legacy-ifnames[956]: sed: couldn't open temporary file /boot/loader/entries/sedTIEkyv: Read-only file system
Jul 01 11:59:18 localhost systemd[1]: coreos-keep-legacy-ifnames.service: Main process exited, code=exited, status=4/NOPERMISSION
Jul 01 11:59:18 localhost systemd[1]: coreos-keep-legacy-ifnames.service: Failed with result 'exit-code'.
Jul 01 11:59:18 localhost systemd[1]: Failed to start CoreOS Keep Legacy Network Interface Names.

[jlebon]

Ahh of course. This should've had something like ConditionPathExists=!/run/ostree-live.

We should add some basic test of the live path as part of fcosKola since it's so radically different in setup from qemu. I guess coreos/coreos-assembler#1571 will make that easier too.

[tmartin-git]

(dustymabe@aaf6867#commitcomment-40293518)

(Just a quit note about this - someone may encouter the same issue I had)

I noticed that all kernel configurations are impacted by this change and as a consequence it actually kind of "corrupts" your rollback.

As an example, I had setup a /etc/systemd/network/99-default.link configuration file (not /usr/lib/systemd/network/99-default.link as expected) to avoid conflict with package systemd-dev.
When the update took place to FCOS v>=32, it also added net.ifnames="0" to my previous kernel-attached configuration deployement.

Then I did a rollback (to my previously working FCOS 31) and unfortunatly, my system was broken (i.e. I had legacy names on my network interfaces).

[cgwalters]

As an example, I had setup a /etc/systemd/network/99-default.link configuration file

In other words, you'd manually enabled the new names, and our change reverted it?

Yes...we clearly should have been checking for that. I suspect a relatively small number of people have done this, and those who have can drop this override and use the new names going forward.

If we get more reports of this we may need to try to adjust the code to detect this case. Sorry about that, and thank you for following up here!

[tmartin-git]

I was more concerned about the changes applied to all bootable kernel cmdline parameters. (by the way don't really know if this can be done a different way)
As a result, a rollback did not work - and as far as I understand, rpm-ostree rollback should always work, shouldn't it ?