[CRIU] unclear CRIU and docker problems

[Adrian Reber]

So I am trying Ross Boucher's docker branch to checkpoint/restore docker
containers and I can successfully checkpoint a container. If I try to
restore a container CRIU exists pretty early with following error:

(00.002935) Warn  (cr-restore.c:1029): Set CLONE_PARENT | CLONE_NEWPID but it might cause restore problem,because not all kernels support such clone flags combinations!
(00.002938) Forking task with 1 pid (flags 0x6c028000)
(00.002952) Saved netns fd for links restore
(00.002962) Error (cr-restore.c:1134): Can't fork for 1: Invalid argument

I am not sure if I read the log correctly but it sounds like it wants to
restore the process with the PID 1, which does sound wrong. Any ideas
where I should look for further errors.

This is with CRIU 1.6 on an older kernel with backports. Could also be
that some kernel changes are missing on my side.

		Adrian