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

[Demi Marie Obenour <demiobenour@gmail.com>]

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On 9/25/25 05:55, Alyssa Ross wrote:
> 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?

I didn't know of -MQ.  -MP is almost certainly
redundant.  Go with what Meson recommended.

>> +  '--',
>> +  '@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')
>> +


-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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