Developer Manual ################ As a developer working on Liminix, or implementing a service or module, you probably want to test your changes more conveniently than by building and flashing a new image every time. This manual documents various affordances for iteration and experiments. In general, packages and tools that run on the "build" machine are available in the ``buildEnv`` derivation and can most easily be added to your environment by running :command:`nix-shell` Emulated devices **************** Liminix has a ``qemu`` device, which generates images suitable for running on your build machine using the free `QEMU machine emulator `_. This is useful for developing userland without needing to keep flashing or messing with U-Boot: it also enables testing against emulated network peers using `QEMU socket networking `_, which may be preferable to letting Liminix loose on your actual LAN. To build it, .. code-block:: console nix-build -I liminix-config=path/to/your/configuration.nix --arg device "import ./devices/qemu" -A outputs.default In a ``buildEnv`` nix-shell, you can use the :command:`mips-vm` command to run Qemu with appropriate options. It connects the Liminix serial console and the `QEMU monitor `_ to stdin/stdout. Use ^P (not ^A) to switch to the monitor. .. code-block:: console nix-shell --run "mips-vm result/vmlinux result/squashfs" If you run with ``--background /path/to/some/directory`` as the first parameter, it will fork into the background and open Unix sockets in that directory for console and monitor. Use :command:`connect-vm` (also in the ``buildEnv`` environment) to connect to either of these sockets, and ^O to disconnect. Networking ========== VMs can network with each other using QEMU socket networking. We observe these conventions, so that we can run multiple emulated instances and have them wired up to each other in the right way: * multicast 230.0.0.1:1234 : access (interconnect between router and "isp") * multicast 230.0.0.1:1235 : lan * multicast 230.0.0.1:1236 : world (the internet) A VM started with :command:`mips-vm` is connected to "lan" and "access", and the emulated border network gateway (see below) runs PPPoE and is connected to "access" and "world". Border Network Gateway ---------------------- In pkgs/routeros there is a derivation to install and configure `Mikrotik RouterOS `_ as a PPPoE access concentrator connected to the ``access`` and ``world`` networks, so that Liminix PPPoE client support can be tested without actual hardware. This is made available as the :command:`routeros` command in ``buildEnv``, so you can do something like:: mkdir ros-sockets nix-shell nix-shell$ routeros ros-sockets nix-shell$ connect-vm ./ros-sockets/console to start it and connect to it. Note that by default it runs in the background. It is connected to "access" and "world" virtual networks and runs a PPPoE service on "access" - so a Liminix VM with a PPPOE client can connect to it and thus reach the virtual internet. [ check, but pretty sure this is not the actual internet ] `Liminix does not provide RouterOS licences and it is your own responsibility if you use this to ensure you're compliant with the terms of Mikrotik's licencing. It may be supplemented or replaced in time with configurations for RP-PPPoE and/or Accel PPP.` Hardware devices **************** How you get your image onto hardware will vary according to the device, but is likely to involve taking it apart to add wires to serial console pads/headers, then using U-Boot to fetch images over TFTP. There is a rudimentary TFTP server bundled with the system which runs from the command line, has an allowlist for client connections, and follows symlinks, so you can have your device download images direct from the :file:`./result` directory without exposing :file:`/nix/store/` to the internet or mucking about copying files to :file:`/tftproot`. If the permitted device is to be given the IP address 192.168.8.251 you might do something like this: .. code-block:: console nix-shell --run "tufted -a 192.168.8.251 result" and then issue appropriate U-boot commands to download and flash the image. For a faster edit-compile-test cycle, you can build a TFTP-bootable image instead of flashing. In your device configuration add .. code-block:: nix imports = [ ./modules/phram.nix ]; boot.tftp = { serverip = "192.168.200.148"; ipaddr = "192.168.200.251"; }; and then build ``outputs.tftproot``. This creates a file in ``result/`` called ``boot.scr``, which you can copy and paste into U-Boot to transfer the kernel and filesystem over TFTP and boot the kernel from RAM. Networking ========== You probably don't want to be testing a device that might serve DHCP, DNS and routing protocols on the same LAN as you (or your colleagues, employees, or family) are using for anything else, because it will interfere. You also might want to test the device against an "upstream" connection without having to unplug your regular home router from the internet so you can borrow the cable/fibre/DSL. ``bordervm`` is included for this purpose. You will need * a Linux machine with a spare PCI ethernet card which you can dedicate to Liminix * an L2TP service such as https://www.aa.net.uk/broadband/l2tp-service/ You need to configure the Ethernet card for VFIO passthru, then you can execute :command:`run-border-vm` in a ``buildEnv`` shell, which starts up QEMU using the NixOS configuration in :file:`bordervm-configuration.nix`. In this VM * your Liminix checkout is mounted under :file:`/home/liminix/liminix` * TFTP is listening on the ethernet device and serving :file:`/home/liminix/liminix`. The server IP address is 10.0.0.1 * a PPPOE-L2TP relay is running on the same ethernet card, which spawns L2TPv2 Access Concentrator sessions to your specified L2TP LNS when the connected Liminix device makes PPPoE requests. Note that authentication is expected at the PPP layer not the L2TP layer, so the same PAP/CHAP credentials provided by your L2TP service can be configured into your test device - bordervm doesn't need to know about them. To configure bordervm, you need a file called :file:`bordervm.conf.nix` which you can create by copying and appropriately editing :file:`bordervm.conf-example.nix` .. note:: If you make changes to the bordervm configuration after executing :command:`run-border-vm`, you need to remove the :file:`border.qcow2` disk image file otherwise the changes won't get picked up. Running tests ************* You can run all of the tests by evaluating :file:`ci.nix`, which is the input I use in Hydra. Note that it expects Nixpkgs stable `and` unstable as inputs, because it builds the qemu device against both. .. code-block:: console nix-build --argstr liminix `pwd` --arg nixpkgs "" \ --argstr unstable `pwd`/../unstable-nixpkgs/ ci.nix or to run a named test, use the ``-A`` flag. For example, ``-A pppoe`` Troubleshooting *************** Diagnosing unexpectedly large images ==================================== Sometimes you can add a package and it causes the image size to balloon because it has dependencies on other things you didn't know about. Build the ``outputs.manifest`` attribute, which is a JSON representation of the filesystem, and you can run :command:`nix-store --query` on it. .. code-block:: console nix-build -I liminix-config=path/to/your/configuration.nix \ --arg device "import ./devices/qemu" -A outputs.manifest \ -o manifest nix-store -q --tree manifest Contributing ************ Contributions are welcome, though in these early days there may be a bit of back and forth involved before patches are merged: Please get in touch somehow `before` you invest a lot of time into a code contribution I haven't asked for. Just so I know it's expected and you're not wasting time doing something I won't accept or have already started on. Nix language style ================== This section describes some Nix language style points that we attempt to adhere to in this repo. * favour ``callPackage`` over raw ``import`` for calling derivations or any function that may generate one - any code that might need ``pkgs`` or parts of it. * prefer ``let inherit (quark) up down strange charm`` over ``with quark``, in any context where the scope is more than a single expression or there is more than one reference to ``up``, ``down`` etc. ``with pkgs; [ foo bar baz]`` is OK, ``with lib; stdenv.mkDerivation { ... }`` is usually not. * ```` is defined only when running tests, so don't refer to it in "application" code * the parameters to a derivation are sorted alphabetically, except for ``lib``, ``stdenv`` and maybe other non-package "special cases" * indentation is whatever emacs nix-mode says it is. * where a ``let`` form defines multiple names, put a newline after the token ``let``, and indent each name two characters * to decide whether some code should be a package or a module? Packages are self-contained - they live in ``/nix/store/eeeeeee-name`` and don't directly change system behaviour by their presence or absense. modules can add to ``/etc`` or ``/bin`` or other global state, create services, all that side-effecty stuff. Generally it should be a package unless it can't be. Copyright ========= The Nix code in Liminix is MIT-licenced (same as Nixpkgs), but the code it combines from other places (e.g. Linux, OpenWrt) may have a variety of licences. I have no intention of asking for copyright assignment: just like when submitting to the Linux kernel you retain the copyright on the code you contribute. Code of Conduct =============== Please govern yourself in Liminix project venues according to the guidance in the `geekfeminism "Community Anti-harassment Policy" `_. Where to send patches ===================== Liminix' primary repo is https://gti.telent.net/dan/liminix but you can't send code there directly because it doesn't have open registrations. * There's a `mirror on Github `_ for convenience and visibility: you can open PRs against that * or, you can send me your patch by email using `git send-email `_ * or in the future, some day, we will have federated Gitea using ActivityPub.