Re: [PATCH] Allow disabling the build of all of systemd, leaving just udev

[William Hubbs <w.d.hubbs@gmail.com>]

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On Sun, Jun 03, 2012 at 07:13:03PM -0700, Bryan Kadzban wrote:
> William Hubbs wrote:
> > On Sun, Jun 03, 2012 at 03:00:27PM -0700, Bryan Kadzban wrote:
> >> I'd rather not replace "cp -a /lib/udev/devices/* /dev" in a boot
> >> script with a binary that nothing else uses, plus its configuration
> >> (which doesn't use nodes in /lib/udev/devices like what has been
> >> the udev ABI for *years*, but instead uses a list of device
> >> descriptions), plus any systemd-level libraries it may or may not
> >> need in the future.
> > 
> > Actually other things could use it because of /tmp and /run and 
> > creating/removing files/directories there on bootup.
> 
> Possibly, but the full functionality will require systemd anyway.  The
> program still has to be run by something; simply installing it won't do
> anything useful.  Plus it will have to depend on having mounted the
> various temporary filesystems that it changes.

I agree that just installing it does nothing. But, it can be run at the
appropriate time by your boot scripts, so the other concerns you mention
here would be taken care of that way.

> >> If a system is already running systemd, then systemd-tmpfiles may
> >> or may not be the best place to do this (the ABI change is a
> >> problem for those systems, unless I'm missing something in the
> >> *tmpfiles* manpages). But if systemd is not running, then sticking
> >> to the previous ABI explicitly is the right way to go I think.
> > 
> > Unless you don't have a previous abi.
> 
> Except that udev-182 and earlier *provided* an ABI.  "Put files in
> /lib/udev/devices and they'll be copied to /dev at boot time" was the
> rule, just like "put programs in /lib/udev and refer to them in rules
> you install with IMPORT{program}="" or RUN+="" without a path" was the
> rule.
>
> Now that rule has apparently been changed, so programs are going to have
> to expend effort coping.  Unless I'm missing some functionality of
> systemd-tmpfiles when I read the docs.

It has definitely been changed. See the systemd NEWS file. That is
exactly why I think we need the systemd-tmpfiles executable and man
page.

There are several tools in the systemd build that can be used on
non-systemd systems. Maybe those don't belong as part of the udev
ebuild, but as a separate --enable/--disable-tools switch or something
like that.

> > Gentoo relies on udev copying things from /lib/udev/devices, which is
> > gone with this version of udev, so we need the new abi.
> 
> I think you need something in the bootscripts somewhere that implements
> the *old* ABI.  Adding a line to the udev start script that does the
> copy will give you that.

Also it will allow users to copy any kind of file they please into /dev,
just by putting it in /usr/lib/udev/devices.

William


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