[pkg/binfmt] Possible feature requests

[umarcor]

Please, tell whether it is worth creating a separate issue for any of the following feature requests:

• Add missing target architectures (arm32v6, mips and mips64el).
• Provide images for i386, arm64v8, arm32v7, arm32v6, s390x and ppc64le hosts, and a multi-arch manifest (linuxkit/binfmt).
• Add CLI options to the golang application to:
  • Select/limit the list of target architectures to be registered.
  • Clean a list of registered architectures

Coming from docker/binfmt#17:

[@justincormack]

1. there is no point in providing mips or mips64el as there are no Docker base images for those architectures. There might be some reason to provide arm32v6 but there have been no asks for it that I am aware of, all the binaries will generally run on arm32v7

The use case is development of apps for devices such as RPi2. Although both arm32v6 and arm32v7 can run on armv7 (or armv8, i.e. aarch32) devices, the opposite will not work. Thus, images for arm32v6 hosts are required in order to build multiarch images that can run on RPi2.

Overall, providing targets such as armv6 or mips is meant for testing cross-compiled binaries (e.g. ASMImproved/qemu-mips-docker). Moreover, supporting armv6 as a host allows to avoid cross-compilation (just as it is now supported for aarch64).

[@justincormack]

1. Changing the target set is not a request we have had; users can re-register handlers if they know what they are doing.

The point is that I find it great for docker/binfmt to be written in golang, since it allows to distribute it as a static executable. I think that other users/projects could greatly benefit from it. Precisely, I think it might be interesting to enhance it with spf13/cobra and upstream it as an (optional) replacement for qemu-binfmt-conf.sh .