[CRIU] Inherit FD via RPC

[Adrian Reber]

On Fri, Aug 03, 2018 at 03:28:04PM +0000, Adrian Reber wrote:
> Hello Andrei,
> 
> this is my next try to get inherit-fd support into RPC.
> 
> For each inherit-fd a new notify message ('request-inherit-fd') is sent to
> the RPC client, which then transmits the actual FD back to CRIU.
> 
> I have this working in combination with runc and I am just sending this
> out if this is how you described it.
> 
> I have not waited for the travis results but just wanted to get some
> feedback from you. Let me know if you think this is the right way to
> go.
> 
> I still would change the commit messages to have more details and
> fix errors if travis or jenkins complains.

I just saw that runc already uses the existing inherit-fd interface:

        for i := range fds {
                if s := fds[i]; strings.Contains(s, "pipe:") {
                        inheritFd := new(criurpc.InheritFd)
                        inheritFd.Key = proto.String(s)
                        inheritFd.Fd = proto.Int32(int32(i))
                        req.Opts.InheritFd = append(req.Opts.InheritFd, inheritFd)
                }
        }

The debug output of runc:

CRIU option InheritFd with value [key:\"pipe:[168249]\" fd:0 key:\"pipe:[168230]\" fd:1  key:\"pipe:[168230]\" fd:2 ]

So this probably only works because FD 0, 1, 2 are always the same.

So runc would need to change its behaviour at this point. This could be
done based on the CRIU version detected.

		Adrian