[CRIU] implementing some kind of --leave-frozen option for c/r in CRIU

[Tycho Andersen]

On Mon, May 16, 2016 at 04:00:41PM +0300, Batalov Eugene wrote:
> Hello.
> 
> The idea of Pavel to reuse part of "restore: restore freezer cgroup state"
> patch looks good and simple.
> 
> About networking unlock. Yes. There is a work in progress on new criu gc
> command.
> You can find patch commit here:
> https://github.com/AuthenticEshkinKot/criu/commit/2ab52fec7a05f9792c871709758d14137fe9f379
> 
> The main problem with it is the fact that network unlock and link remaps
> cleanup logic
> is coupled with logic of criu restore command. And criu restore logic is
> not trivial.
> So we're trying to carefully reduce the amount of code in CRIU gc. We need
> to reuse CRIU restore command code and need not to introduce ugly hacks and
> excessive CRIU restore code dependencies (this dependence would limit CRIU
> restore code changes at the same time).
> 
> GRIU gc both able print what's left in the system after dump (iptables,
> link remaps) and to cleanup this stuff too.

Whoops, just read the first mail in the thread and responded to that.
Anyway, this combined with --leave-frozen seems to be exactly what I'm
after. I will re-do my --leave-frozen patch and resend that. Let me
know if you guys want some help with `criu gc`, I'm very interested in
the work :)

Tycho

> 
> 2016-05-16 15:31 GMT+03:00 Pavel Emelyanov <xemul at virtuozzo.com>:
> 
> > On 05/10/2016 08:04 PM, Tycho Andersen wrote:
> > > Hi guys,
> > >
> > > I'm looking at implementing some kind of --leave-frozen option in
> > > CRIU, so that we can have a basic UX in LXD where we can wait for the
> > > restore to be successful before we kill the checkpointed container. I
> > > know p.haul does this by just using a callback, but it would be sort
> > > of painful to absorb just the callback part without doing a lot of
> > > extra engineering. We'll get LXD using p.haul someday, though :)
> > >
> > > The actual --leave-frozen patch is not so bad (see attached), but I'm
> > > not sure what to do about the network locking/unlocking bits.
> >
> > There was a patch 8b04551c (restore: restore freezer cgroup state) in 2.0
> > that turned cgroup into whatever state it was before dump. Can it be fixed
> > to make '--leave-frozen' alter the behavior of
> > add_freezer_state_for_restore()
> > and set it to 'frozen' always?
> >
> > > It seems like it is always safe to do the bits in
> > > cpt_unlock_tcp_connections() since that's just disabling tcp repair
> > > mode, but all of the iptables rules seem necessary in order to keep
> > > the network locked.
> > >
> > > So my question is: is there a nice way we can "tag" these rules so
> > > that something can come by and delete them later? I was thinking about
> > > having criu add a comment (via -m comment --comment "CRIU-LOCK-RULE")
> > > to each rule it adds, but I'm not sure if there's a better way, or if
> > > I've missed something entirely.
> >
> > Yes, there's an issue #45 -- show what's left in the system after dump.
> > Iptables
> > rules are in the list :) I know that some gentlemen (Cc) from
> > Saint-Petersburg were
> > interested in implementing it in form of 'criu gc' action, so probably
> > tuning this
> > option to support '--show-only' would help you?
> >
> > > Thanks!
> > >
> > > Tycho
> > >
> > >
> > >
> > > _______________________________________________
> > > CRIU mailing list
> > > CRIU at openvz.org
> > > https://lists.openvz.org/mailman/listinfo/criu
> > >
> >
> >
> 
> 
> -- 
> Best regards,
> Eugene Batalov.