Re: [gentoo-dev] eselect init

[Michał Górny]

On Sat, 25 May 2013 11:54:48 +0200
Luca Barbato <lu_zero@g.o> wrote:

> - /sbin/init (or whatever linux currently calls by default with top
> priority) should be either a symlink to the actual implementation or a
> wrapper such as our gcc one. I like better the latter since it is
> overall safer. The former might or might work since linux has some
> fallback capabilities but hadn't been tested.

Increased complexity is never safer. And a wrapper means the additional
complexity gets there every boot. And considering how the discussion
goes, the wrapper will grow openrc-size in a few months...

Symlinks are simple. They're filesystem feature, they're handled
by kernel. The worst thing that could happen is symlink target
disappearing -- but then it's:

a) our responsibility to make sure to call eselect-init (if applies)
when uninstalling an init system,

b) something that would fail anyway if user did that by hand.

Linux fallback mechanism is *good enough*. You may think that fallback
to sysvinit is good but it's not. *If* I have my system set up to boot
X, at some point the config for Y will get seriously outdated.

I use systemd for a few months now, and last time I checked openrc
boots somehow. But considering the general complexity of it, I wouldn't
be much surprised if it failed in funny ways (like not being able to
handle automounts properly), caused cruft on the filesystem or even
caused *damage*.

And since you've been failing long at keeping init.d scripts simple
and reasonable, the damage potential is not something purely
theoretical.

That said, switching /sbin/init is the reasonable way. If it fails,
Linux runs /bin/sh. EOT. You broke, you fix, any way you like. Without
unexpectedly switching init system to something else just because it
was around.

> - init gets effectively switched only at boot/reboot, eselect init must
> keep track of the current active init and make sure the current init
> configuration is used till the system reboots, if we use the wrapper
> approach, it would pick up what's the new init at boot and that would be
> enough for simple cases, hooks on reboot are still needed for more
> complex ones.

Pointless and overcomplex. If an init system actually fails to work
when /sbin/init doesn't point to it, it is seriously broken by design.
And because of that breakage, we keep stuff like 'telinit' or 'reboot'
intact, and because of it systemd has 'pass-through' mode when linked
to /sbin/init.

> - we could try to not have the changes to the current init systems
> ebuild or reduce them to the bare minimum (e.g. not overwrite /sbin/init)

Which means the kernel fallback will be dangerously active
as I explained before. Just don't do it.

> # FOCUS
>
> My interest is mostly if not all on bb-init-openrc and slightly on
> runit-openrc.
>
> There are enough people involved in systemd and since I still consider
> it a dangerously frail implementation of a bad idea is better if I do
> not touch it at all.

You've been able to keep this thread on topic very long. Good job!

-- 
Best regards,
Michał Górny