[lxc-devel] lxc-clone rewrite

[Serge Hallyn]

Quoting Stéphane Graber (stgraber at ubuntu.com):
> On Mon, Aug 31, 2015 at 01:43:07PM +0000, Serge Hallyn wrote:
> > Quoting Christian Brauner (christianvanbrauner at gmail.com):
> > > On Fri, Aug 28, 2015 at 12:46:17AM +0200, Christian Brauner wrote:
> > > > On Thu, Aug 27, 2015 at 03:41:03PM -0400, Stéphane Graber wrote:
> > > > > On Sun, Aug 16, 2015 at 04:46:31PM +0000, Serge Hallyn wrote:
> > > > > > Quoting Christian Brauner (christianvanbrauner at gmail.com):
> > > > > > Hey,
> > > > > > 
> > > > > > I'll leave this to Stéphane, as he's pretty keen on leaving the # commands
> > > > > > low.  As you say we might eventually be able to deprecate lxc-clone, and
> > > > > > lxc-copy might eventually be a nice hook for migration.
> > > > > 
> > > > > That'd be fine with me I think, bonus point if we can somehow merge
> > > > > lxc-start-ephemeral in there and kill two birds with one stone
> > > > > (lxc-clone & lxc-start-ephemeral).
> > > > > 
> > > > > The timeline for this would be having lxc-copy in 1.2 with both
> > > > > lxc-clone and lxc-start-ephemeral doing arg swapping + re-exec tricks
> > > > > with a warning that they'll go away for good in 2.0.
> > > > > 
> > > > > How does that sound?
> > > > 
> > > > Sounds good! I'm on it!
> > > > 
> > > > Christian
> > > 
> > > In the current python implementation of lxc-start-ephemeral we generate a
> > > pre-mount and post-stop script. The post-stop script seems to be used to destroy
> > > the container. For the rewrite in C and the merge with lxc-clone I thought about
> > > using a simple snapshot-clone with c->clone() with a random name, start it
> > > c->start() and when the container is shutdown destroy it with c->destroy().
> > > This seems cleaner to me then generating scripts. Are there any reasons to not
> > > do it this way? And if so what would you prefer?
> > 
> > If you can do this robustly and cleanly then I prefer this.
> 
> The reason was that the container could be started backgrounded (-d) in
> which case lxc-start-ephemeral wasn't around anymore to clean things up
> when the container exits.
> 
> The post-stop method ensured that the container would be destroyed
> whenever it finally dies and regardless of how it was killed (either
> shutdown from inside the container or lxc-stop/lxc-destroy).

Right, so to do this without post-stop we'd probably have to hack a special
case into the reboot: loop around container-start.  Maybe even hardcode the
'transient' case into the lxc_handler struct.  Or just have a 'special'
post-stop hook (doesn't even have to be a script, just a hard-code value
checked for before we run the script) telling us 'delete this thing'.

It could end up looking nice, or could end up a mess.  I reserve final
judgement until there's code :)