[lxc-devel] Variable expansions in default config.

[Michael H. Warfield]

Hey all,

I'm in the middle of some cleanup and fix-ups in the Fedora and CentOS
templates including hardening the root password and some static MAC
address code and generally reconciling the two templates into some
semblance of coherency.

I noticed this in the comments emitted from the CentOS template into the
container config:

#lxc.network.veth.pair = v-$name-e0

Hmmm...  That's interesting.  I wonder if that would work in the default
config?  That could be real handy (subject to name collisions
understood.)  Nope.  It's a literal copy from the default config over to
the initial starting point container config.  Sigh...

That's an idea, though, if variables could be expanded.  That's easy
enough to deal with in the templates.  Since I'm already recopying that
initialized config to add some hwaddr addresses (in my upcoming
patches), I can add this to those templates and do the expansions
(reading from the initial default config and copying back to the target
config)...

    # This should catch variable expansions from the default config...
    if expr "${LINE}" : '.*\$' > /dev/null 2>&1
    then
            LINE=$(eval "echo \"${LINE}\"")
    fi

I've got that working and will submit it along with my other patches
shortly...

It's a thought, though there may be other ways we could do this.  It
could be useful.  I can use it.  Does no harm if nobody puts environment
variables in the default config.  Not sure what the potential for random
acts of terrorism is if someone stuffs something STUPID in there...
Simple expansions like above are prone to abuse in unexpected ways...
Other shell meta characters could be a PITA...

Thoughts?

Regards,
Mike
-- 
Michael H. Warfield (AI4NB) | (770) 978-7061 |  mhw at WittsEnd.com
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
   NIC whois: MHW9          | An optimist believes we live in the best of all
 PGP Key: 0x674627FF        | possible worlds.  A pessimist is sure of it!

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