volume: allow a prefix for all bind mounts

[giuseppe]

volume: allow a prefix for all bind mounts

Introduce a new environment variable DOCKER_BIND_MOUNT_PREFIX that is added as a prefix to the source for every bind mount. This allows Docker to run inside of a container, and be able to see the host rootfs.

Signed-off-by: Giuseppe Scrivano gscrivan@redhat.com

[rhatdan]

So if I am running docker in a container with /host mounted and a user on the host says

docker run -v /var/lib/mariadb:/var/lib/mariadb ...

You will get /host/var/lib/mariadb:/var/lib/mariadb mounted?

We would need something similar to this in CRI-o also. I think you should add the above explanation to your PR.

[giuseppe]

So if I am running docker in a container with /host mounted and a user on the host says

docker run -v /var/lib/mariadb:/var/lib/mariadb ...

You will get /host/var/lib/mariadb:/var/lib/mariadb mounted?

yes exactly. In this way we can have the same visibility as if running on the host.

I've amended the commit log message with this example.

[giuseppe]

does the new version look fine?

[giuseppe]

I've tested the PR with symlinks and they are correctly resolved with the /host prefix before the mount

[rhatdan]

LGTM Do we have a PR for this in CRI-O?

[giuseppe]

not yet, I can work on it

[rhatdan]

@runcom PTAL

[giuseppe]

The CRI-O counterpart: https://github.com/kubernetes-incubator/cri-o/pull/1485

[giuseppe]

anything blocking this PR?

[runcom]

LGTM

[runcom]

we need this in branch docker-1.13.1-rhel as well @giuseppe

[giuseppe]

@runcom backport here: https://github.com/projectatomic/docker/pull/308