Merge lp://staging/~gary/charms/oneiric/buildbot-master/run-as-buildbot into lp://staging/~yellow/charms/oneiric/buildbot-master/trunk

All those helpers are taken from setuplxc.py, btw.

The su contextmanager has an issue: the euid and egid are not set back properly when there is an error in the with block, for some reason. This can cause some problems: for some reason the juju log command hangs when the buildbot user tries to use it. Benji and I took a quick look at it and did not see a reason why they would do this. Perhaps it takes a moment to propagate?

I have not yet run the existing tests. I will do this before landing, resolving any issues. That said, this will bring up a master and slave for lpbuildbot, and at least check out the branch. Subsequently there's an error within Twisted/Buildbot itself, but it's on the right track.

> All those helpers are taken from setuplxc.py, btw.
>
> The su contextmanager has an issue: the euid and egid are not set back
> properly when there is an error in the with block, for some reason.

Trapping the error (re-raised inside the generator) using a try/finally statement should solve this.
E.g. http://pastebin.ubuntu.com/836410/

Hi Gary,

Nice branch; thanks for this. I'll merge it presently with the master trunk.

363 + try:
364 + return subprocess.call(['buildslave', 'start', buildbot_dir])
365 + except OSError:
366 + return subprocess.call(['buildbot', 'start', buildbot_dir])

Instead of this you could do something like this:

    def get_buildslave_command():
        if subprocess.call(['which', 'buildslave']) == 0:
            return 'buildslave'
        else:
            return 'buildbot'

and then call get_buildslave_command() where you need it.

> Nice branch; thanks for this. I'll merge it presently with the master trunk.

... and then I read your bit about the tests. How about I give that a shot first :)