microvm underlying VM's kernel and packages configuration

[jkuro-tii]

The microvm component is used for running virtual machines inside Ghaf environment. It builds a kernel for virtual machines and filesystems. Filesystems contains NixOS components and additional needed by microvm during runtime (startup scripts, etc.).

Microvm's feature is that it contains hard-coded kernel and package set definitions: kernel configuration and VM's NixOS packages set. There is no way to define a custom packages configuration.
It means that we are unable to define a VM with our own kernel version, configuration, and applied patches. We also cannot change the default package set. I solved this issue in the PR#94, source.

After getting more familiar with Nix/NixOS mechanisms, I have a proposal of solving the problem other way.

Solution

The microvm component is added additional options:

• microvm.vm.kernel: VM kernel package
• microvm.vm.packages: VM NixOS packages to be included in the build

Example

microvm.vm.kernel = pkgs.linuxPackages_5_4.callPackage ./memsharevm-kernel.nix {};
microvm.vm.packages = pkgs.linuxPackages_5_4.extend (_: _: {
kernel = microvm.vm.kernel;
});

Sample kernel configuration: memsharevm-kernel.nix

I think that such change should be easily accepted by microvm's author. I already contacted him regarding other change.

[vilvo]

There is related recent work in the microvm.nix upstream - see comment and context at astro/microvm.nix#82 (comment)

In general - yes, we need support for guest VMs with custom kernels and user spaces. Also, discussion with the microvm's author is very much appreciated.

[mikatammi]

astro/microvm.nix#82

This was merged some time ago and our ghaf flake.lock is already using this.

I haven't tested yet, but it should be possible to use the regular boot.kernelPackages = ...; inside the microvm now