Commits on Apr 11, 2020

1. Add support for docker in docker …

   When using docker-in-docker, for example in dev or CI containers, one
   normally gives access to the host docker environment to the docker
   container. If the container spins up another child container, and wishes
   to share a directory, one needs to compute the pass the right paths from
   view of the host system.
   
   If the environment variable CROSS_DOCKER_IN_DOCKER=true, we call `docker
   inspect $HOSTNAME`, to learn about details of the current container.
   The `Mounts` field contains information about all mounts from the host
   into the current container. The `GraphDriver` field gives us information
   about the storage driver and the location in the host system of the
   current containers root directory. Based on these information we compute
   a table of all container mounts (`source->destination`).
   
   When starting a child container we adapt all paths to be mounted having
   a prefix in the table, to start with source. For example when mounting a
   dev containers `/usr/local/cargo` directory, we will actually mount
   `/var/lib/docker/overlay2/<parent container id>/merged/usr/local/cargo`.
   
   If the project itself is mounted into the parent container, we will not
   use the overlay directory, but find the project path on the host.
   
   In order to access the parent containers rust setup, the child container
   mounts the parents overlayfs. The parent must not be stopped before the
   child container, as the overlayfs can not be unmounted correctly by
   docker if the child container still accesses it.

   

   urso authored and urso committed Apr 11, 2020
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