[CRIU] [PATCH] criu: Add exec-cmd option (v2)

[Andrew Vagin]

On Fri, Mar 21, 2014 at 08:40:41AM +0400, Pavel Emelyanov wrote:
> On 03/20/2014 08:40 PM, Christopher Covington wrote:
> > Hi Deyan,
> > 
> > On 03/20/2014 12:24 PM, Deyan Doychev wrote:
> >> From: Deyan Doychev <deyandoichev at gmail.com>
> >>
> >> The --exec-cmd option specifies a command that will be execvp()-ed on successful
> >> restore. This way the command specified here will become the parent process of
> >> the restored process tree.
> >>
> >> When this option is specified criu will fork to become a daemon before it starts
> >> restoring the processes. It also implies the -d option so waiting for the
> >> restored processes to finish is responsibility of the command specified here.
> >>
> >> This option will be used when restoring LinuX Containers and it seems helpful
> >> for perf or other use cases when restored processes must be supervised by a
> >> parent.
> >>
> >> Two directions were researched in order to integrate CRIU and LXC:
> >>
> >> 1. We tell to CRIU, that after restoring container is should execve()
> >>    lxc properly explaining to it that there's a new container hanging
> >>    around.
> >>
> >> 2. We make LXC set himself as child subreaper, then fork() criu and ask
> >>    it to detach (-d) from restore container afterwards. Being a subreaper,
> >>    it should get the container's init into his child list after it.
> >>
> >> The main reason for choosing the first option is that the second one can't work
> >> with the RPC service. If we call restore via the service then criu service will
> >> be the top-most task in the hierarchy and will not be able to reparent the
> >> restore trees to any other task in the system. Calling execve from service
> >> worker sub-task (and daemonizing it) should solve this.
> > 
> > Looks good overall. On the subject of file descriptor sharing, I wonder if all
> > of the CRIU open, dup, etc. calls should also be changed to use the O_CLOEXEC
> > flag?
> 
> Presumably they should. There're quite a few of them, I'm pretty sure
> that the main criu task only uses some service fds. By the way, what do
> you think about redirecting the logfd into 1 and 2 before exec()-ing?

We can do this if a criu is executed as a sevice. If we execute
'criu restore' directly, we need to leave original descriptors.

> 
> 
> Thanks,
> Pavel