Enable CRIU configuration files

CRIU 3.11 introduces configuration files:

https://criu.org/Configuration_files
https://lisas.de/~adrian/posts/2018-Nov-08-criu-configuration-files.html

This enables the user to influence CRIU's behaviour without code changes
if using new CRIU features or if the user wants to enable certain CRIU
behaviour without always specifying certain options.

With this it is possible to write 'tcp-established' to the configuration
file:

$ echo tcp-established > /etc/criu/runc.conf

and from now on all checkpoints will preserve the state of established
TCP connections. This removes the need to always use

$ runc checkpoint --tcp-stablished

If the goal is to always checkpoint with '--tcp-established'

It also adds the possibility for unexpected CRIU behaviour if the user
created a configuration file at some point in time and forgets about it.

Signed-off-by: Adrian Reber <[email protected]>

libcontainer/container_linux.go

@@ -925,6 +925,9 @@ func (c *linuxContainer) Checkpoint(criuOpts *CriuOpts) error {
 		OrphanPtsMaster: proto.Bool(true),
 		AutoDedup:       proto.Bool(criuOpts.AutoDedup),
 		LazyPages:       proto.Bool(criuOpts.LazyPages),
+		// CRIU will evaluate a configuration starting with release 3.11.
+		// Settings in the configuration file will overwrite RPC settings.
+		ConfigFile: proto.String("/etc/criu/runc.conf"),
 	}
 
 	// If the container is running in a network namespace and has
@@ -1174,6 +1177,7 @@ func (c *linuxContainer) Restore(process *Process, criuOpts *CriuOpts) error {
 			OrphanPtsMaster: proto.Bool(true),
 			AutoDedup:       proto.Bool(criuOpts.AutoDedup),
 			LazyPages:       proto.Bool(criuOpts.LazyPages),
+			ConfigFile:      proto.String("/etc/criu/runc.conf"),
 		},
 	}