[CRIU] SWRK mode legalization

[Saied Kazemi]

Great!  Now that Andrey has confirmed it works with libcontainer, we should
definitely publish this method and make it available.

Thanks,

--Saied


On Mon, Mar 30, 2015 at 12:58 AM, Andrew Vagin <avagin at parallels.com> wrote:

> On Thu, Mar 26, 2015 at 06:18:07PM +0300, Pavel Emelyanov wrote:
> > Hi,
> >
> > As you know there are currently 2 ways of using CRIU -- one via CLI and
> another
> > one by starting a CRIU service and talking to it using RPC commands (and
> a .so
> > which provides C function wrappers around RPC calls).
> >
> > We have yet another undocumented way to use CRIU which is called SWRK.
> In this
> > mode CRIU is fork+exec-ed as it if is about to be used as CLI tool, but
> instead
> > of passing arguments via CLI, caller gives to CRIU a socket and sends RPC
> > commands directly into it. IOW, swrk mode is a mixture of CLI and RPC --
> one
> > doesn't have to start a service, but can request CRIU with easier-to-use
> RPC
> > commands.
> >
> > The mode is not documented as the way to start one seemed not nice from
> my
> > perspective, it's like this
> >
> >    int sk[2];
> >    socketpair(PF_UNIX, SOCK_SEQPACKET, 0, sk);
> >    if (fork() == 0) {
> >          close(sk[0]);
> >          sprintf(buf, "%d", sk[1]);
> >          execl("criu", "criu", "swrk", buf, NULL);
> >    }
> >    close(sk[1]);
> >    /* start feeding RPC commands into sk[0] here */
> >
> > Originally this mode was done to make life for the P.Haul easier, but
> right now
> > it looks like integration with Docker would be much easier if done in
> swrk way.
> > LXC can probably also benefit from it.
> >
> > So I think it's a good time to stop hiding it, nail down the API and use
> in
> > Docker (and probably LXC).
>
> Hi Pavel,
>
> I have reworked libcontainer to use the swrk mode. It works and I like
> it. I have sent a patch which is added inherite_fd into rpc request.
>
> https://github.com/docker/libcontainer/pull/486
>
> I vote to open swrk.
>
> Thanks,
> Andrey
>
> >
> > Having nothing better as the above code snippet in mind, I thought to
> just add
> > a couple of argv[] sanity checks to criu and declare this as official
> swrk API.
> > If you have suggestions how to make it better -- you're warmly welcome :)
> >
> > The RPC is described here (http://criu.org/RPC) and there's a small
> section
> > about swrk in the bottom of the page.
> >
> > -- Pavel
>
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