Please provide an option to make ownership of shared volumes configurable.

For example my current use case is to have logstash-forwarder running within a container, that has /var/lib/docker shared read-only as volume from the host.

Since /var/lib/docker is set to 0700 root:root on the host I can't access the volume as non root user.

What I would like to have is something like with NFS where one can map uid & gid from the host to users & groups on the client.

I.e. docker run -v /var/lib/docker:/var/lib/docker:ro:$user:$group would make the volume available in the container as read only, belonging to $user:$group.