docker-module-builder

Build kernel modules for Docker for Mac and Docker for Windows -- now called Docker Desktop.

This repo contains a simple recipe to build kernel modules that can be loaded into the kernel of the Docker Desktop VM.

Usage

Place a Makefile and any additional sources you need into the module directory. It will be copied into a Docker build container at /usr/src/module and the default make target will be run from that directory.

Once your module is built, make sure your make target copies the output .ko binary files into /usr/src/module. Those binaries will be copied into the resulting scratch image.

Once your module/Makefile is ready, you can use the make build target in this repo to start the build!

Options

There are a few options you can specify to make build.

• BUILD_REF is the image used to perform the build. Your BUILD_REF must provide the same version of gcc used to compile the target kernel. NB: The Docker Desktop VM runs Alpine Linux, which uses musl-libc. The default value is library/alpine:3.10 which has been tested to work on Docker Desktop 2.3.0.2.

• KERNEL_REF is the image that contains kernel sources packaged as part of the Docker Desktop VM's build. Docker, Inc. currently publishes sources to Docker Hub. If this value is not set, the Makefile can fetch data about the build environment by running a privileged container. You can leave it unset if you're comfortable with the default behaviour.

• MODULE_REF is the output image ref. It is a scratch image that contains only the built .ko binaries. The default is kernel-module.

Rationale

Docker Desktop has recently (starting in 2.3.0.2) removed a number of kernel modules from the VM they provide. This change has broken a number of containers that rely on modules previously shipped with Docker Desktop. Although Docker, Inc. has never provided any explicit interface for the VM's Linux environment, this change has caught many people by surprise and broken many existing containers.

It's important to also note that Docker Desktop does not version the VM separately from the other components in the Docker Desktop product. So despite this breaking change, the only indicator in docker version that can be used to detect the missing features is the Built: date value.

See Also

There are many kernel modules missing from the latest Docker Desktop release. Here are a few GitHub issues that report missing modules. You'll note that most have been ignored by Docker, Inc.

• #4552 sctp module.
• #4560 wireguard module.
• #4581 drm support for the radeon, i915, nouveau modules.
• #4660 openvswitch module.
• #4549 device-mapper modules. This issue was immediately resolved in the next release of Docker Desktop.