Banning checkpoint (was: Re: What can OpenVZ do?)

[Alexey Dobriyan]

On Mon, Feb 23, 2009 at 09:11:25PM -0800, Dave Hansen wrote:
> On Tue, 2009-02-24 at 07:47 +0300, Alexey Dobriyan wrote:
> > > I think what I posted is a decent compromise.  It gets you those
> > > warnings at runtime and is a one-way trip for any given process.  But,
> > > it does detect in certain cases (fork() and unshare(FILES)) when it is
> > > safe to make the trip back to the "I'm checkpointable" state again.
> > 
> > "Checkpointable" is not even per-process property.
> > 
> > Imagine, set of SAs (struct xfrm_state) and SPDs (struct xfrm_policy).
> > They are a) per-netns, b) persistent.
> > 
> > You can hook into socketcalls to mark process as uncheckpointable,
> > but since SAs and SPDs are persistent, original process already exited.
> > You're going to walk every process with same netns as SA adder and mark
> > it as uncheckpointable. Definitely doable, but ugly, isn't it?
> > 
> > Same for iptable rules.
> > 
> > "Checkpointable" is container property, OK?
> 
> Ideally, I completely agree.
> 
> But, we don't currently have a concept of a true container in the
> kernel.  Do you have any suggestions for any current objects that we
> could use in its place for a while?

After all foo_ns changes struct nsproxy is such thing.

More specific, a process with fully cloned nsproxy acting as init,
all its children. In terms of data structures, every task_struct in such
tree, every nsproxy of them, every foo_ns, and so on to lower levels.