kernels/pr_673/en/builder/design-overview.md

Architecture overview

The Kernel Builder is a Nix flake that combines two components:

• kernel-builder/: a Rust-based CLI that parses and validates build.toml, scaffolds new kernel projects, and drives the build. It does not compile kernels itself: every build subcommand executes nix build/nix run/nix develop against the kernel project's flake.nix.
• nix-builder: the Nix builder drives the build itself. It generates a build matrix using the supported build configurations (see nix-builder/versions.nix) and the kernel's build.toml. The build matrix is the cartesian product of the backend (one or more of CPU/CUDA/Metal/ROCm/XPU), backend versions, and framework versions. Nix builder uses kernel-builder to generate the CMake files that drive the build. To do so, kernel-builder itself is packaged in nix-builder/pkgs.

A kernel author uses the Nix builder through the lib.genKernelFlakeOutputs that is exposed through the top-level flake.nix. This generates the Nix flake outputs for building and developing kernels, such as bundle for bundle builds and devShells for development shells.

For a deeper look at the design of the Nix builder, see Nix Builder design.