doc: update for aya and drop the libbpf-skel support

Also update nix scripts.

Cargo.toml

@@ -17,13 +17,13 @@ opt-level = "z"
 strip = true
 
 [features]
-default = ["aya"]
+default = ["aya", "pkg-config"]
 # Enable IPv6 NAPT
 ipv6 = []
 # Enable Aya BPF loader, requires Rust>=1.80.0
-aya = ["dep:aya", "dep:pkg-config"]
+aya = ["dep:aya"]
 # Enable libbpf BPF loader
-libbpf = ["dep:libbpf-rs", "dep:libbpf-sys", "dep:pkg-config"]
+libbpf = ["dep:libbpf-rs", "dep:libbpf-sys"]
 # Enable libbpf skeleton-wrapped BPF loader, requires unpublish self_cell for now
 libbpf-skel = [
     "dep:libbpf-rs",

README.md

@@ -20,20 +20,24 @@ For implementation details, see documentations under [reference](./docs/referenc
 ## Requirement
 
 -   Linux kernel >= 5.15 (compiled with BPF and BTF support) on target machine
--   `clang` compiling BPF C code
--   `cargo` and `rustfmt` for building
+-   Rust toolchain (`cargo` etc.)
+-   `clang` for compiling BPF C code
+-   `libbpf` headers
+-   (optional) `pkg-config` to locate `libbpf` headers
 
-**aya** (default)
+`"aya"` loader (default)
 
--   `libbpf` headers
--   `llvm-strip`
+-   `llvm-strip` for stripping compiled BPF object
 
-**libbpf**
+`"libbpf"` loader
 
+-   `rustfmt` for formatting generated code
 -   `clang` libs for bindgen
 -   `libelf` from elfutils
 -   `zlib`
 
+The `"libbpf-skel"` loader is served as reference purpose and you should just use `aya` or `libbpf` instead.
+
 It's also required the eBPF JIT implementation for target architecture in kernel has implemented support for BPF-to-BPF calls, which is not the case for MIPS and other architectures have less interests. This application is only tested to work on x86-64 or aarch64.
 
 See also [OpenWrt guide](./docs/guide/openwrt.md) for pitfalls running this on OpenWrt.
@@ -42,6 +46,7 @@ See also [OpenWrt guide](./docs/guide/openwrt.md) for pitfalls running this on O
 
 ```shell
 cargo install --git https://github.com/EHfive/einat-ebpf.git
+cargo install --git https://github.com/EHfive/einat-ebpf.git
 ```
 
 You can also enable IPv6 NAT66 feature with `--features ipv6` flag, however it would increase load time of eBPF programs to about 4 times.
@@ -59,7 +64,20 @@ For NixOS, you can use module [`github:EHfive/einat-ebpf#nixosModules.default`](
 
 For OpenWrt, there are [openwrt-einat-ebpf](https://github.com/muink/openwrt-einat-ebpf) and [luci-app-einat](https://github.com/muink/luci-app-einat) by @muink.
 
-See also [cross-compilation guide](./docs/guide/cross.md) for cross-compilation on Debian/Debian-based distros.
+See also [cross-compilation guide](./docs/guide/cross-aya.md) for cross-compilation on Debian/Debian-based distros.
+
+### Build Environment Variables
+
+| Name                   | Example Value              | Note                                            |
+| ---------------------- | -------------------------- | ----------------------------------------------- |
+| `EINAT_BPF_CFLAGS`     | `-I/usr/include/<triplet>` | Specify extra CFLAGS for BPF object compilation |
+| `LIBBPF_NO_PKG_CONFIG` | `1`                        | Disable [pkg_config lookup] of libbpf.          |
+
+[pkg_config lookup]: (https://docs.rs/pkg-config/0.3.31/pkg_config/index.html#environment-variables)
+
+You can combine `LIBBPF_NO_PKG_CONFIG` and `EINAT_BPF_CFLAGS` to specify include flag of libbpf headers manually.
+
+See also [build.rs](./build.rs) for reference.
 
 ## Usage
 

build.rs

@@ -40,29 +40,42 @@ fn einat_obj_build() {
     // compile BPF C code
     let mut cmd = Command::new("clang");
 
+    cmd.args(c_args());
+
+    if let Some(cflags) = option_env!("EINAT_BPF_CFLAGS") {
+        cmd.arg(cflags);
+    }
+
+    // Specify environment variable LIBBPF_NO_PKG_CONFIG=1 to disable pkg-config lookup.
+    // Or just disable the "pkg-config" feature.
+    #[cfg(feature = "pkg-config")]
+    match pkg_config::probe_library("libbpf") {
+        Ok(libbpf) => {
+            let includes = libbpf
+                .include_paths
+                .into_iter()
+                .map(|i| format!("-I{}", i.to_string_lossy()));
+            cmd.args(includes);
+        }
+        Err(e) => {
+            eprintln!("Can not locate libbpf with pkg-config: {}", e)
+        }
+    }
+
     let target = if env::var("CARGO_CFG_TARGET_ENDIAN").unwrap() == "little" {
         "bpfel"
     } else {
         "bpfeb"
     };
 
-    let libbpf = pkg_config::probe_library("libbpf").unwrap();
-
-    let includes = libbpf
-        .include_paths
-        .into_iter()
-        .map(|i| format!("-I{}", i.to_string_lossy()));
-
-    cmd.args(c_args())
-        .arg("-target")
+    cmd.arg("-target")
         .arg(target)
         .arg("-g")
         .arg("-O2")
         .arg("-c")
         .arg(SRC)
         .arg("-o")
         .arg(bpf_obj)
-        .args(includes)
         .status()
         .expect("compile BPF object failed");
 

docs/guide/cross.md

@@ -2,12 +2,15 @@
 
 This guide gives example for cross-compiling for aarch64, replace "aarch64" and "arm64" with respective architecture identifier tokens for cross-compiling for other architectures.
 
-## Build Dependencies
+The "aya" loader is used by default.
+To enable only the "libbpf" loader, specify Cargo flags `--no-default-features --features aya,pkg-config`.
 
-Install `libelf` and `zlib1g` as it's required by `libbpf`. Install `gcc-aarch64-linux-gnu` for cross linking. Install `clang` for bindgen and compile eBPF C code in this project.
+### Build Dependencies
+
+Install `gcc-aarch64-linux-gnu` for cross linking. Install `clang` for bindgen and compile eBPF C code in this project.
 
 ```
-apt install libelf-dev zlib1g-dev gcc-aarch64-linux-gnu clang
+apt install gcc-aarch64-linux-gnu clang
 ```
 
 Install `rustup` to get Rust>=1.74, see https://www.rust-lang.org/tools/install. Also make sure `rustfmt` is installed as it's used by `libbpf-cargo`.
@@ -18,15 +21,20 @@ Add required target to Rust toolchain:
 rustup target add aarch64-unknown-linux-gnu
 ```
 
-## Target Dependencies
+### Target Dependencies
+
+For "libbpf" loader, you would also need to install `libelf` and `zlib1g` as it's required by `libbpf`.
 
 ```
 dpkg --add-architecture arm64
 apt update
+# We only need libbpf headers
+apt install libbpf-dev:arm64
+# For "libbpf" loader only
 apt install libelf-dev:arm64 zlib1g-dev:arm64
 ```
 
-## Environment Variables
+### Environment Variables
 
 ```
 export CARGO_TARGET_AARCH64_UNKNOWN_LINUX_GNU_LINKER="/usr/bin/aarch64-linux-gnu-gcc"
@@ -38,7 +46,12 @@ export CC_aarch64_unknown_linux_gnu="/usr/bin/aarch64-linux-gnu-gcc"
 export CFLAGS_aarch64_unknown_linux_gnu="-I /usr/include/aarch64-linux-gnu -L /usr/lib/aarch64-linux-gnu"
 ```
 
-## Build static binary
+Specify `EINAT_BPF_CFLAGS` if einat build script failed to locate libbpf headers.
+```
+export EINAT_BPF_CFLAGS="-I /usr/include/aarch64-linux-gnu"
+```
+
+### Build static binary
 
 ```
 cd einat-ebpf

docs/guide/openwrt.md

@@ -34,7 +34,6 @@ Additional kernel configs required, you might need to add these to kernel config
 ```
 CONFIG_BPF_SYSCALL=y
 CONFIG_BPF_JIT=y
-CONFIG_NET_CLS_BPF=y
 CONFIG_NET_ACT_BPF=y
 ```
 

flake.nix

@@ -34,9 +34,7 @@
       crossPackage' = import ./nix/cross-package.nix { inherit naersk; };
 
       overlay = final: prev: {
-        einat = defaultPackage' {
-          pkgs = (import nixpkgs) { inherit (prev) system; };
-        };
+        einat = defaultPackage' prev;
       };
 
       module = {
@@ -60,6 +58,11 @@
         crossPackage = { ... }@args: crossPackage' ({ inherit pkgs; } // args);
       in
       {
+        legacyPackages = (import nixpkgs) {
+          inherit system;
+          overlays = [ overlay ];
+        };
+
         packages = {
           default = defaultPackage;
           ipv6 = defaultPackage;

nix/cross-package.nix

@@ -44,34 +44,23 @@ let
         #required by libelf
         zstd
       ]
-    ) ++ [
-        pkgs.libbpf
-    ];
+    );
 
   buildInputsSearchFlags = map (dep: "-L${lib.getLib dep}/lib") buildInputs;
 in
 naersk'.buildPackage {
   src = ../.;
   gitSubmodules = true;
-  depsBuildBuild = with pkgs; [
-    # build dependencies of cargo build depenceies libbpf-cargo -> libbpf-sys
-    stdenv.cc
-  ];
   nativeBuildInputs = with pkgs; [
     pkg-config
-    # required by `libbpf_cargo::SkeletonBuilder`
-    rustfmt
-    ## build dependencies of cargo build depenceies libbpf-cargo -> libbpf-sys
-    stdenv.cc.libc
-    zlib
-    elfutils
 
-    ## build dependencies of libbpf-sys on target platform
-    # for cross linking libelf and zlib, and make libbpf
-    crossPkgs.stdenv.cc
     # compile BPF C code
     llvmPackages.clang-unwrapped
     llvmPackages.bintools-unwrapped
+
+    ## build dependencies of libbpf-sys on target platform
+    # for cross linking libelf and zlib, and make libbpf
+    crossPkgs.stdenv.cc
   ];
   inherit buildInputs;
   strictDeps = true;
@@ -99,6 +88,9 @@ naersk'.buildPackage {
     "-mno-outline-atomics"
   ];
 
+  LIBBPF_NO_PKG_CONFIG = 1;
+  EINAT_BPF_CFLAGS = "-I${pkgs.libbpf}/include";
+
   "CC_${targetUnderscore}" = crossCC;
   "CARGO_TARGET_${targetUnderscoreUpper}_LINKER" = crossCC;
 
@@ -115,6 +107,7 @@ naersk'.buildPackage {
 
   preBuild = ''
     export BINDGEN_EXTRA_CLANG_ARGS_${targetUnderscore}="''${NIX_CFLAGS_COMPILE}";
+
     # Avoid adding host dependencies to CFLAGS and LDFLAGS for build platform
     if [[ ${pkgs.stdenv.cc.suffixSalt} != ${crossPkgs.stdenv.cc.suffixSalt} ]]; then
       export NIX_CC_WRAPPER_TARGET_HOST_${pkgs.stdenv.cc.suffixSalt}="";

nix/package.nix

@@ -3,7 +3,6 @@
   lib,
   rustPlatform,
   pkg-config,
-  rustfmt,
   llvmPackages,
   libbpf,
   elfutils,
@@ -15,12 +14,9 @@ naersk.buildPackage {
 
   nativeBuildInputs = [
     pkg-config
-    rustfmt
     llvmPackages.clang-unwrapped
     llvmPackages.bintools-unwrapped
     rustPlatform.bindgenHook
-    elfutils
-    zlib
   ];
 
   buildInputs = [