# Genodepkgs November update

A summary of changes in the past couple of months:

## Dhall interpreter

The native Dhall interpreter for Genode is close to compliance with the
language spec, but due to performance problems with the parser, this
sub-project is temporarily stalled. The library can be used to construct
and normalize expressions programatically, but parsing code is currently
too slow to comfortably generate configuration. De-emphasizing dynamically
generated configuration means more focus building on static systems
defined using the traditional NixOS method.


## Init

The Genode init system has been patched to accept a slightly different
configuration schema than the upstream init. This change removes wildcard
rules for routing RPC services between components. These rules were in
place to make init configurations more ergonomic to manually describe, but
with a sufficiently powerful DSL these are no longer needed. This change
somewhat reduces the complexity of the init schema system and makes
configurations easier to manually audit. At some point it may be practical
to replace the init component for something that accepts a more
Nix-friendly configuration schema, but not within a foreseeable future.
Note that this init cannot appropriately be compared to systemd - systemd
is +300KLOC and the Genode init is around 10KLOC, including libraries.


## Linking

The LLD linker has been patched to link libraries by absolute path, that
means that rather than use references like "libcrypto.so", ELF artifacts
will refer to full paths such as
"/nix/store/…-openssl-1.1.1g-x86_64-unknown-genode/lib/libcrypto.so". This
explicitly establishes what the runtime dependencies of a binary are and
optimizes loading times. Note Genode loads libraries externally, the
loader parses the ELF header locally then makes an RPC requests by library
name for a memory region containing the library. The libraries are then
loaded from the file-system by a dedicated component that manages a cache
of binaries and libraries. Linking libraries by absolute path as a general
policy within Nixpkgs has been proposed, but has not been implemented.
Genode makes this much easier by bypassing the libc during loading.

Link to libraries through absolute paths?
https://github.com/NixOS/nixpkgs/issues/24844


## NixOS modules

The biggest update is the transition from a custom test framework to
simply adopting the NixOS module system for building test systems. There
are now NixOS modules that define which kernel to boot from and a hardware
module that configures drivers and IP stacks to coincide with standard
NixOS parameters.

### Systemd

I am currently working on translating systemd services to Genode init
children. This is achievable in simple cases by extracting
"config.systemd.services.….service.serviceConfig.ExecStart" and requiring
a few extra parameters. In a simple example this currently looks like this:

```
{ pkgs, ... }: {
  imports = [ ../nixos-modules/systemd.nix ../nixos-modules/hardware.nix ];
  networking.interfaces.eth1.genode.stack = "lwip";
  services.foo = { };
  systemd.services.foo.genode = {
    enable = true;
    interface = "eth1";
  };
}
```

Systemd translation is still a work in progress.


### Nix store

You might wonder what form the Nix store takes in such a system. Currently
a store closure is collected from the system configuration and packaged as 
a tarball. This tarball is bundled with the initial binaries that are used
to bootstrap the system and is passed to the Genode core component from
the bootloader via the kernel. Sub-systems may access this store tarball
by a read-only file-system RPC session or using the ROM loading RPC. The
entire Nix store is available to each client component, but hosting
multiple store instances will soon become practical.

The current systems I'm able to build are similar to a Linux system that
hasn't booted beyond an initramfs. When I'm able to successfully translate
systemd services I will add block-device drivers and file-systems, as well
as a framebuffer for log output.


## Project infrastructure

### Hydra / CI

My Hydra is gone I need to arrange for a new one. If anyone can donate
some Hydra time, please let me know. Being without a Hydra unfortunately
means that the Sotest hardware tests have also stopped.

### Cachix

There is now a Cachix cache that contains the custom toolchains and many
of the packages: https://app.cachix.org/cache/genodepkgs


## Summary

I will keep working on translating existing NixOS configurations until at
least the next update. Without proper documentation it would be difficult
for additional contributors to get accustomed to working within the
repository, however, if anyone would like to get involved and has a
specific system they would like to build, I'd be happy to assist, and it
would help me streamline the development processes.

That's all for now,
Emery

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