process checkpoint restore facility now in DragonFly BSD

[Siddharth Aggarwal]

Thanks for your reply.

I understand the complexity of checkpointing a process and I do agree that
capturing the complete state of a system is really difficult. So my
question is that if a subset of that functinality was to be implemented
(e.g. not guaranteeing certain things to processes when they restart, and
I believe that you have already implemented this for DragonFly), why is it
more difficult to do it for a physical machine versus in a VMM like Xen?
Or do you have any arguments in the reverse direction i.e.
better/easier/efficient/reliable in a physical machine than a VMM? Or do
you now believe since this feature was implemented over a year ago, that a
VMM is the way to go?



On Wed, 12 Jan 2005, Kip Macy wrote:

> I've promised Nate to port the functionality to FreeBSD. I'm busy doing some
> things with the FreeBSD port to Xen at the moment.
>
> Checkpointing a process is intrinsically messy for reasons beyond the obvious
> statefulness of TCP connections. Process state, particularly with regard to
> devices, is often not cleanly associated with the process in the kernel. What
> happens if a file that the process had open has gone away? Other issues abound -
> checkpointing a process pipeline can be made to work, but some work would need
> to be done on pipes. The list goes on.
>
>
> 					-Kip
>
>
> On Wed, 12 Jan 2005, Siddharth Aggarwal wrote:
>
> >
> > Hi all,
> >
> > I am responding to a post back in Oct 2003 when the checkpointing feature
> > was announced for DragonFly. I have been doing some research on this, and
> > have seen some projects that use Xen VMM to achieve checkpoints of guest
> > OSes.
> >
> > So I was looking for inputs from people as to what everyone feels about
> > checkpointing, whether it should be done at the physical machine level or
> > VM level. Pros and Cons of each approach, if any further development was
> > done on DragonFly for checkpoint since then and if it was stopped, why?
> > Are there serious limitations to checkpointing a physical machine?
> >
> > Sorry for such a vague posting, but I thought this would be a good
> > platform to get some feedback.
> >
> > Thanks,
> > Sid.
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>
> --
> "Debugging is twice as hard as writing the code in the first place.
> Therefore, if you write the code as cleverly as possible, you are,
> by definition, not smart enough to debug it." - Brian W. Kernighan
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