Re: How much of a mess does OpenVZ make? ;) Was: What can OpenVZdo?

[Alexey Dobriyan]

On Fri, Feb 27, 2009 at 10:19:09AM +0100, Greg Kurz wrote:
> On Fri, 2009-02-27 at 01:17 +0300, Alexey Dobriyan wrote:
> > On Thu, Feb 26, 2009 at 07:30:16PM +0100, Greg Kurz wrote:
> > > On Thu, 2009-02-26 at 18:33 +0100, Ingo Molnar wrote:
> > > > I think the main question is: will we ever find ourselves in the 
> > > > future saying that "C/R sucks, nobody but a small minority uses 
> > > > it, wish we had never merged it"? I think the likelyhood of that 
> > > > is very low. I think the current OpenVZ stuff already looks very 
> > > 
> > > We've been maintaining for some years now a C/R middleware with only a
> > > few hooks in the kernel. Our strategy is to leverage existing kernel
> > > paths as they do most of the work right.
> > > 
> > > Most of the checkpoint is performed from userspace, using regular
> > > syscalls in a signal handler or /proc parsing. Restart is a bit trickier
> > > and needs some kernel support to bypass syscall checks and enforce a
> > > specific id for a resource. At the end, we support C/R and live
> > > migration of networking apps (websphere application server for example).
> > > 
> > > >From our experience, we can tell:
> > > 
> > > Pros: mostly not-so-tricky userland code, independent from kernel
> > > internals
> > > Cons: sub-optimal for some resources
> > 
> > How do you restore struct task_struct::did_exec ?
> 
> With sys_execve().

How do you restore set of uts_namespace's? Kernel never exposes to
userspace which are the same, which are independent.
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