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

[Pavel Emelyanov]

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
> 
> 
> 
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