Re: [PATCH v6 1/4] tools: add xdp-forwarder

[Alyssa Ross <hi@alyssa.is>]

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Yureka Lilian <yureka@cyberchaos.dev> writes:

> The xdp-forwarder's purpose is implementing the functionality needed
> within the net-vm (a VM running the Linux drivers for any physical
> interfaces on the spectrum system).
>
> In the future, the net-vm will load the included XDP programs on the
> passed-through physical interfaces as well as the downstream virtio
> interface going into the router (recognized by its special MAC address).
>
> The net-vm needs to multiplex between the physical interfaces, as there
> might be several interfaces in the same IOMMU-group.
>
> For this, the XDP program loaded on the physical interfaces
> (`prog_physical.o`) applies a VLAN tag corresponding to the interface id
> and redirects the packets to the router interface (identified by the
> `router_iface` bpf map). In the other direction the XDP program loaded on
> the router interface (`prog_router.o`) removes one layer of VLAN tagging
> and redirects the packets to the interface read from the VLAN tag.
>
> The helper program `set_router_iface` is used to update the `router_iface`
> bpf map to point to the interface passed as argument to the program.
>
> Co-authored-by: Demi Marie Obenour <demiobenour@gmail.com>
> Signed-off-by: Yureka Lilian <yureka@cyberchaos.dev>
> Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
> ---
>  pkgs/default.nix                       |   4 +
>  release/checks/pkg-tests.nix           |   1 +
>  tools/default.nix                      |  21 +-
>  tools/meson.build                      |   4 +
>  tools/meson_options.txt                |   3 +
>  tools/xdp-forwarder/meson.build        |  48 +++++
>  tools/xdp-forwarder/parsing_helpers.h  | 274 +++++++++++++++++++++++++
>  tools/xdp-forwarder/prog_physical.c    |  39 ++++
>  tools/xdp-forwarder/prog_router.c      |  42 ++++
>  tools/xdp-forwarder/rewrite_helpers.h  | 146 +++++++++++++
>  tools/xdp-forwarder/set_router_iface.c |  30 +++
>  11 files changed, 608 insertions(+), 4 deletions(-)
>  create mode 100644 tools/xdp-forwarder/meson.build
>  create mode 100644 tools/xdp-forwarder/parsing_helpers.h
>  create mode 100644 tools/xdp-forwarder/prog_physical.c
>  create mode 100644 tools/xdp-forwarder/prog_router.c
>  create mode 100644 tools/xdp-forwarder/rewrite_helpers.h
>  create mode 100644 tools/xdp-forwarder/set_router_iface.c
>
> diff --git a/pkgs/default.nix b/pkgs/default.nix
> index 2472218..df3cfdc 100644
> --- a/pkgs/default.nix
> +++ b/pkgs/default.nix
> @@ -42,6 +42,10 @@ let
>        appSupport = false;
>        hostSupport = true;
>      };
> +    spectrum-driver-tools = self.callSpectrumPackage ../tools {
> +      appSupport = false;
> +      driverSupport = true;
> +    };
>      xdg-desktop-portal-spectrum-host =
>        self.callSpectrumPackage ../tools/xdg-desktop-portal-spectrum-host {};
>  
> diff --git a/release/checks/pkg-tests.nix b/release/checks/pkg-tests.nix
> index d7be42b..b1a048f 100644
> --- a/release/checks/pkg-tests.nix
> +++ b/release/checks/pkg-tests.nix
> @@ -14,5 +14,6 @@ import ../../lib/call-package.nix (
>    tools = lib.recurseIntoAttrs (callSpectrumPackage ../../tools {
>      appSupport = true;
>      hostSupport = true;
> +    driverSupport = true;
>    }).tests;
>  }) (_: {})
> diff --git a/tools/default.nix b/tools/default.nix
> index 201afae..0e43997 100644
> --- a/tools/default.nix
> +++ b/tools/default.nix
> @@ -1,13 +1,17 @@
>  # SPDX-License-Identifier: MIT
>  # SPDX-FileCopyrightText: 2022-2025 Alyssa Ross <hi@alyssa.is>
> +# SPDX-FileCopyrightText: 2025 Yureka Lilian <yureka@cyberchaos.dev>
>  
>  import ../lib/call-package.nix (
>  { src, lib, stdenv, fetchCrate, fetchurl, runCommand, buildPackages
>  , meson, ninja, pkg-config, rustc
>  , clang-tools, clippy
>  , dbus
> +# clang 19 (current nixpkgs default) is too old to support -fwrapv-pointer
> +, clang_21, libbpf
>  , appSupport ? true
>  , hostSupport ? false
> +, driverSupport ? false
>  }:
>  
>  let
> @@ -70,15 +74,18 @@ stdenv.mkDerivation (finalAttrs: {
>        ./lsvm
>        ./start-vmm
>        ./subprojects
> +    ] ++ lib.optionals driverSupport [
> +      ./xdp-forwarder
>      ]));
>    };
>    sourceRoot = "source/tools";
>  
>    depsBuildBuild = lib.optionals hostSupport [ buildPackages.stdenv.cc ];
>    nativeBuildInputs = [ meson ninja ]
> -    ++ lib.optionals appSupport [ pkg-config ]
> -    ++ lib.optionals hostSupport [ rustc ];
> -  buildInputs = lib.optionals appSupport [ dbus ];
> +    ++ lib.optionals (appSupport || driverSupport) [ pkg-config ]
> +    ++ lib.optionals hostSupport [ rustc ]
> +    ++ lib.optionals driverSupport [ clang_21 ];
> +  buildInputs = lib.optionals appSupport [ dbus ] ++ lib.optionals driverSupport [ libbpf ];
>  
>    postPatch = lib.optionals hostSupport (lib.concatMapStringsSep "\n" (crate: ''
>      mkdir -p subprojects/packagecache
> @@ -88,12 +95,16 @@ stdenv.mkDerivation (finalAttrs: {
>    mesonFlags = [
>      (lib.mesonBool "app" appSupport)
>      (lib.mesonBool "host" hostSupport)
> +    (lib.mesonBool "driver" driverSupport)
>      "-Dhostfsrootdir=/run/virtiofs/virtiofs0"
>      "-Dtests=false"
>      "-Dunwind=false"
>      "-Dwerror=true"
>    ];
>  
> +  # Not supported for target bpf
> +  hardeningDisable = lib.optionals driverSupport [ "zerocallusedregs" ];
> +
>    passthru.tests = {
>      clang-tidy = finalAttrs.finalPackage.overrideAttrs (
>        { name, src, nativeBuildInputs ? [], ... }:
> @@ -105,7 +116,9 @@ stdenv.mkDerivation (finalAttrs: {
>            fileset = lib.fileset.union (lib.fileset.fromSource src) ../.clang-tidy;
>          };
>  
> -        nativeBuildInputs = nativeBuildInputs ++ [ clang-tools ];
> +        # clang-tools needs to be before clang, otherwise it will not use
> +        # the Nix include path correctly and fail to find headers
> +        nativeBuildInputs = [ clang-tools ] ++ nativeBuildInputs;
>  
>          buildPhase = ''
>            clang-tidy --warnings-as-errors='*' ../**/*.c
> diff --git a/tools/meson.build b/tools/meson.build
> index e8b0cf2..059baeb 100644
> --- a/tools/meson.build
> +++ b/tools/meson.build
> @@ -26,3 +26,7 @@ endif
>  if get_option('app')
>    subdir('xdg-desktop-portal-spectrum')
>  endif
> +
> +if get_option('driver')
> +  subdir('xdp-forwarder')
> +endif
> diff --git a/tools/meson_options.txt b/tools/meson_options.txt
> index fb520ae..7b46739 100644
> --- a/tools/meson_options.txt
> +++ b/tools/meson_options.txt
> @@ -7,6 +7,9 @@ option('host', type : 'boolean', value : false,
>  option('app', type : 'boolean',
>    description : 'Build tools for Spectrum app VMs')
>  
> +option('driver', type : 'boolean', value : false,
> +  description : 'Build tools for Spectrum driver VMs')
> +
>  option('hostfsrootdir', type : 'string', value : '/run/host',
>    description : 'Path where the virtio-fs provided by the host will be mounted')
>  
> diff --git a/tools/xdp-forwarder/meson.build b/tools/xdp-forwarder/meson.build
> new file mode 100644
> index 0000000..9b70ce3
> --- /dev/null
> +++ b/tools/xdp-forwarder/meson.build
> @@ -0,0 +1,48 @@
> +# SPDX-License-Identifier: EUPL-1.2+
> +# SPDX-FileCopyrightText: 2025 Yureka Lilian <yureka@cyberchaos.dev>
> +# SPDX-FileCopyrightText: 2025 Demi Marie Obenour <demiobenour@gmail.com>
> +
> +libbpf = dependency('libbpf', version : '1.6.2')
> +
> +executable('set-router-iface', 'set_router_iface.c',
> +  dependencies : libbpf,
> +  install : true)
> +
> +clang = find_program('clang', native: true)
> +
> +bpf_o_cmd = [
> +  clang.full_path(),
> +  '-fno-stack-protector',
> +  '-fno-strict-aliasing',
> +  '-fwrapv', '-fwrapv-pointer',
> +  '-Wall',
> +  '-Wextra',
> +  '-O2',
> +  '-target', 'bpf',
> +  '-I', meson.current_source_dir() + '/include',
> +  '-g',
> +  '-c',
> +  '-o', '@OUTPUT@',
> +  '-MD',
> +  '-MP',
> +  '-MF', '@DEPFILE@',

Demi: you suggested these arguments, but the Meson default is
-MD -MQ $out -MF $DEPFILE, as far as I can tell.

Why the difference?

> +  '--',
> +  '@INPUT@',
> +]
> +
> +prog_router_o = custom_target(
> +  input : 'prog_router.c',
> +  output : 'prog_router.o',
> +  depfile : 'prog_router.o.dep',
> +  command : bpf_o_cmd,
> +  install: true,
> +  install_dir: 'lib/xdp')
> +
> +prog_physical_o = custom_target(
> +  input : 'prog_physical.c',
> +  output : 'prog_physical.o',
> +  depfile : 'prog_physical.o.dep',
> +  command : bpf_o_cmd,
> +  install: true,
> +  install_dir: 'lib/xdp')
> +

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