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Re: Really, about udev, not init systems

On Wed, Nov 28, 2012 at 05:04:25PM +0100, Tollef Fog Heen wrote:
> ]] Bjørn Mork 

> >   "The default 'configure' install locations have changed. Packages for
> >    systems with the historic / vs. /usr split need to be adapted,
> >    otherwise udev will be installed in /usr and not work
> >    properly. Example configuration options to install things the
> >    traditional way are in INSTALL."
> > 
> > Just stating the facts.  I see no reason to discuss these issues any
> > further.

> «default location» vs «architecture of udev».  Reality check, please?

No, this really is an architecture question.  The udev architecture, which
launches short-lived (time-limited) processes in response to kernel events,
and in some cases uses the output of those helper processes as input to its
own rules for further processing, introduces/encourages dependencies on
components that would not be considered appropriate for / per the FHS
because they aren't related to system bring-up.  Nevertheless, having them
in /usr and having /usr on a separate filesystem results in different and
possibly racy system behavior.

This certainly could have been addressed with a different udev architecture.
For instance, udev could have a policy of not allowing anything in its
database that's not directly related to device node creation (excluding,
e.g., upower), or it could have a standard mechanism for reparsing rules
(particularly PROGRAM= and RUN= rules) after /usr is mounted.  There are
various reasons why these are not considered appropriate / worth doing, and
that's fine; I've been convinced myself that it's not reasonable to have a
system with /usr on a separate partition and expect that to work without an
initramfs, and think we *should* simplify our overall architecture rather
than continuing to put effort into moving libraries around between /usr/lib
and /lib.  But we should be honest with ourselves that this is driven by
architecture decisions, not just by default locations.

Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                    http://www.debian.org/
slangasek@ubuntu.com                                     vorlon@debian.org

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