[Buildroot] [PATCH 1/1] skeleton: add systemd network.service unit

Maxime Ripard maxime.ripard at free-electrons.com
Wed Jan 29 08:26:12 UTC 2014



On Tue, Jan 28, 2014 at 06:20:20PM +0100, Arnout Vandecappelle wrote:
> On 28/01/14 14:20, Maxime Ripard wrote:
> >On Tue, Jan 28, 2014 at 09:25:20AM +0100, Maxime Hadjinlian wrote:
> >>I would even like to go even further, as I have noticed that a lot of
> >>the defined LIBFOO_INSTALL_INIT_SYSTEMD and LIBFOO_INSTALL_INIT_SYSV
> >>almost always do the exact same stuff.
> >>I would like for the infrastructure to take care of this, if no
> >>function is defined, and a .service or S\d{0,2}*, then we should take
> >>it and install it.
> >>
> >>In that case, any particular requirements, the package define a
> >>function, other than that, it's taken care of and we avoid duplicate
> >>code in all the packages.
> >
> >Actually, there's two main issues that prevents this in the systemd
> >case, and are why we did it that way:
> >   - the multi-user-wants thing is actually comparable to the sysvinit
> >     runlevels. Some packages might want to set their units to other
> >     targets than multi-user (for example, graphical applications are
> >     likely to go in the graphical target, not the multi-user one)
> 
>  I disagree with this one. Buildroot's defaults should support only
> a single runlevel/target. That's how it's done for sysv init, and

Hmm, afaik, it's not done at all in the sysvinit case, because the
default sysvinit we use most of the time (busybox's) doesn't handle
the runlevel at all. It's not really the same story there.

> I'm very happy with it: it's dead easy to see which scripts will be
> executed at startup, you don't have to find out the runlevel etc.
> With systemd, things can become even more complex (because there can
> be several "targets" active at the same time IIRC), and I'd prefer
> to exclude this complexity by default.
> 
>  If a user requires several runlevels/targets, than most likely any
> default that buildroot provide will not fit anyway, so the user will
> have to manipulate things in their rootfs overlay or post-build
> script anyway. Therefore, I think it is better for the user if the
> defaults are simple and predictable.
> 
> 
> >   - Some units also takes "variables" from the created link names. For
> >     example, when you want to run getty, you just have a single getty
> >     unit, and the device to run getty on is set in the link name to
> >     that unit (so you'd end up with a link in multi-user.target.wants
> >     that will be getty.ttyS0.service, linking to
> >     /etc/systemd/system/getty.service).
> 
>  That is one of the special cases that would be handled in a
> post-install hook. But specifically for the getty case, it's not
> even necessary because we start only a single getty in the default
> setup, so we can directly install it to getty at ttyS0.service .

Which won't work if you don't have a different tty to export a shell
on, but yes, I get your point.

> >At the time, we thought that in the systemd case, the easiest would be
> >to simply write down the 2-3 commands we need to setup the unit,
> >instead of having to give a whole bunch of variables. And we did the
> >same for sysvinit scripts, for consistency.
> 
>  I think at the time, we mainly thought that we didn't know yet if
> the installation could be generalized. Now that we have a few
> packages that install unit files, it's more clear that they always
> to the same.

We have *three* packages with systemd units in current master. I
hardly see how you can generalize something out of 3 (similar)
samples.

>  Also, as far as I understand, the idea is not to add variables, but
> rather to check for the existence of package/foo/*.service and
> install that.

This also doesn't cover the case anymore where a package would ship
together with the source code a systemd unit file. I expect it to be
more and more common, and it's something that we will want to use most
of the time, and not duplicate the unit file in the buildroot package
itself.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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