xtask: ensure libbpf submodule is initialized

For xtask tasks which need libbpf, make sure it's initialized automatically.
This eases the user-experience so that users don't need to think about the submodule,
while retaining all the benefits of using a submodule vs forcing the user to manually
check out libbpf and stick it in some pre-defined place.

xtask/src/codegen/aya.rs

@@ -3,7 +3,10 @@ use std::path::PathBuf;
 
 use aya_tool::{bindgen, write_to_file};
 
-use crate::codegen::{Architecture, SysrootOptions};
+use crate::{
+    codegen::{Architecture, SysrootOptions},
+    libbpf,
+};
 
 pub fn codegen(opts: &SysrootOptions) -> Result<(), anyhow::Error> {
     codegen_internal_btf_bindings()?;
@@ -13,7 +16,7 @@ pub fn codegen(opts: &SysrootOptions) -> Result<(), anyhow::Error> {
 fn codegen_internal_btf_bindings() -> Result<(), anyhow::Error> {
     let dir = PathBuf::from("aya-obj");
     let generated = dir.join("src/generated");
-    let libbpf_dir = PathBuf::from("libbpf");
+    let libbpf_dir = libbpf::ensure_initialized()?;
 
     let mut bindgen = bindgen::user_builder()
         .clang_arg(format!(
@@ -162,7 +165,7 @@ fn codegen_bindings(opts: &SysrootOptions) -> Result<(), anyhow::Error> {
 
     let dir = PathBuf::from("aya-obj");
     let generated = dir.join("src/generated");
-    let libbpf_dir = PathBuf::from("libbpf");
+    let libbpf_dir = libbpf::ensure_initialized()?;
 
     let builder = || {
         bindgen::user_builder()

xtask/src/codegen/aya_bpf_bindings.rs

@@ -6,9 +6,12 @@ use std::path::PathBuf;
 use aya_tool::{bindgen, write_to_file_fmt};
 use syn::{parse_str, Item};
 
-use crate::codegen::{
-    helpers::{expand_helpers, extract_helpers},
-    Architecture, SysrootOptions,
+use crate::{
+    codegen::{
+        helpers::{expand_helpers, extract_helpers},
+        Architecture, SysrootOptions,
+    },
+    libbpf,
 };
 
 pub fn codegen(opts: &SysrootOptions) -> Result<(), anyhow::Error> {
@@ -20,7 +23,7 @@ pub fn codegen(opts: &SysrootOptions) -> Result<(), anyhow::Error> {
     } = opts;
 
     let dir = PathBuf::from("bpf/aya-bpf-bindings");
-    let libbpf_dir = PathBuf::from("libbpf");
+    let libbpf_dir = libbpf::ensure_initialized()?;
 
     let builder = || {
         let mut bindgen = bindgen::bpf_builder()

xtask/src/libbpf.rs

@@ -0,0 +1,23 @@
+/// Functionality for ensuring that the submodule is properly set up.
+use std::{path::PathBuf, process::Command};
+
+use anyhow::Context;
+
+/// Ensures that the submodule is initialized and returns the path to the submodule.
+pub(crate) fn ensure_initialized() -> Result<PathBuf, anyhow::Error> {
+    // It's okay to hard-code this path because the submodule is checked in.
+    let libbpf_dir = PathBuf::from("libbpf");
+    // Exec `git submodule update --init` to ensure that the submodule is initialized.
+    let status = Command::new("git")
+        .args(["submodule", "update", "--init", "--"])
+        .arg(&libbpf_dir)
+        .status()
+        .context("failed to initialized submodules")?;
+    if status.success() {
+        Ok(libbpf_dir)
+    } else {
+        Err(anyhow::anyhow!(
+            "failed to initialize submodules: {status:?}"
+        ))
+    }
+}

xtask/src/main.rs

@@ -1,5 +1,6 @@
 mod codegen;
 mod docs;
+mod libbpf;
 mod run;
 
 use clap::Parser;

xtask/src/run.rs

@@ -5,6 +5,7 @@ use std::{
     process::{Command, Stdio},
 };
 
+use crate::libbpf;
 use anyhow::{Context as _, Result};
 use cargo_metadata::{Artifact, CompilerMessage, Message, Target};
 use clap::Parser;
@@ -33,6 +34,7 @@ pub struct Options {
 
 /// Build the project
 pub fn build(opts: BuildOptions) -> Result<Vec<(String, PathBuf)>> {
+    let _libbpf_dir = libbpf::ensure_initialized()?;
     let BuildOptions { release, target } = opts;
     let mut cmd = Command::new("cargo");
     cmd.env("AYA_BUILD_INTEGRATION_BPF", "true").args([