Re: [Devel] Re: [PATCH 0/9] OpenVZ kernel based checkpointing/restart

[Oren Laadan <orenl@cs.columbia.edu>]

Andrey Mirkin wrote:
> On Monday 20 October 2008 19:55 Dave Hansen wrote:
>> On Mon, 2008-10-20 at 16:14 +0400, Andrey Mirkin wrote:
>>> Right now my patchset (v2) provides an ability to checkpoint and restart
>>> a group of processes. The process of checkpointing and restart can be
>>> initiated from external process (not from the process which should be
>>> checkpointed).
>> Absolutely.  Oren's code does it this way to make for a smaller patch at
>> first.  The syscall takes a pid argument so it is surely expected to be
>> expanded upon later.
>>
>>> Also I think that all the restart job (including process forking) should
>>> be done in kernel, as in this case we will not depend on user space and
>>> will be more secure. This is also implemented in my patchset.
>> Do you think that this is an approach that Oren's patches are married
>> to, or is this a "feature" we can add on later?
> 
> Well, AFAICS from Oren's patch set his approach is oriented on process 
> creation in user space. I think we should choose right now what approach will 
> be used for process creation.
> We have two options here: fork processes in kernel or fork them in user space.
> If process will be forked in user space, then there will be a gap when process 
> will be in user space and can be killed with received signal before entering 

> kernel. Also we will need a functionolity to create processes with predefined 
> PID. I think it is not very good to provide such ability to user space. That 

Rethinking this -- if the user wishes she can construct a suitable
checkpoint image that would do exactly that. It takes more effort than
using a system call, but the result is similar.

What I had in mind for that special clone-with-pid is to restrict when
it can be used (e.g. when the container is in a "restarting" state or
something like that.

[...]

Oren.