codegen: tidy up

- Document the need for external rustfmt invocation.
- Remove reexports.
- Remove `write_to_file`.
- Avoid allocating strings when using bindgen to write bindings.

.github/workflows/gen.yml

@@ -31,8 +31,9 @@ jobs:
           sudo apt -y install libelf-dev libc6-dev libc6-dev-{arm64,armel,loong64,riscv64,ppc64el,s390x,mips}-cross
 
       - run: cargo xtask codegen
-      - run: cargo xtask public-api --bless
+      # aya-ebpf-bindings aren't emitted directly from bindgen and so aren't formatted.
       - run: cargo fmt --all
+      - run: cargo xtask public-api --bless
 
       - id: libbpf
         working-directory: xtask/libbpf

aya-tool/src/generate.rs

@@ -9,8 +9,6 @@ use std::{
 use tempfile::tempdir;
 use thiserror::Error;
 
-use crate::bindgen;
-
 #[derive(Error, Debug)]
 pub enum Error {
     #[error("error executing bpftool")]
@@ -44,7 +42,7 @@ pub fn generate<T: AsRef<str>>(
         .map(|s| s.as_ref().into())
         .collect::<Vec<_>>();
 
-    let mut bindgen = bindgen::bpf_builder();
+    let mut bindgen = crate::bindgen::bpf_builder();
     let (additional_flags, ctypes_prefix) = extract_ctypes_prefix(&additional_flags);
 
     if let Some(prefix) = ctypes_prefix {

aya-tool/src/lib.rs

@@ -1,22 +1,2 @@
-use std::{
-    fs::{File, create_dir_all},
-    io::{self, Write},
-    path::Path,
-};
-
 pub mod bindgen;
 pub mod generate;
-
-pub use generate::{InputFile, generate};
-
-pub fn write_to_file<T: AsRef<Path>>(path: T, code: &str) -> Result<(), io::Error> {
-    // Create parent directories if they don't exist already
-    if let Some(parent) = path.as_ref().parent() {
-        if !parent.exists() {
-            create_dir_all(parent)?;
-        }
-    }
-
-    let mut file = File::create(path)?;
-    file.write_all(code.as_bytes())
-}

xtask/src/codegen/aya.rs

@@ -1,7 +1,10 @@
-use std::path::{Path, PathBuf};
+use std::{
+    fs::create_dir_all,
+    path::{Path, PathBuf},
+};
 
 use anyhow::{Context as _, Result};
-use aya_tool::{bindgen, write_to_file};
+use aya_tool::bindgen;
 
 use crate::codegen::{Architecture, SysrootOptions};
 
@@ -26,10 +29,10 @@ fn codegen_internal_btf_bindings(libbpf_dir: &Path) -> Result<()> {
         bindgen = bindgen.allowlist_type(x);
     }
 
-    let bindings = bindgen.generate().context("bindgen failed")?.to_string();
+    let bindings = bindgen.generate().context("bindgen failed")?;
 
     // write the bindings, with the original helpers removed
-    write_to_file(generated.join("btf_internal_bindings.rs"), &bindings)?;
+    bindings.write_to_file(generated.join("btf_internal_bindings.rs"))?;
 
     Ok(())
 }
@@ -47,6 +50,7 @@ fn codegen_bindings(opts: &SysrootOptions, libbpf_dir: &Path) -> Result<()> {
     } = opts;
     let dir = PathBuf::from("aya-obj");
     let generated = dir.join("src/generated");
+    create_dir_all(&generated)?;
 
     let builder = || {
         let mut bindgen = bindgen::user_builder()
@@ -223,13 +227,10 @@ fn codegen_bindings(opts: &SysrootOptions, libbpf_dir: &Path) -> Result<()> {
         };
         bindgen = bindgen.clang_args(["-I", sysroot.to_str().unwrap()]);
 
-        let bindings = bindgen.generate().context("bindgen failed")?.to_string();
+        let bindings = bindgen.generate().context("bindgen failed")?;
 
         // write the bindings, with the original helpers removed
-        write_to_file(
-            generated.join(format!("linux_bindings_{arch}.rs")),
-            &bindings.to_string(),
-        )?;
+        bindings.write_to_file(generated.join(format!("linux_bindings_{arch}.rs")))?;
     }
 
     Ok(())

xtask/src/codegen/aya_ebpf_bindings.rs

@@ -1,12 +1,12 @@
 use std::{
     ffi::OsString,
-    fs::create_dir_all,
+    fs::{File, create_dir_all},
     path::{Path, PathBuf},
     process::Command,
 };
 
 use anyhow::{Context as _, Result};
-use aya_tool::{bindgen, write_to_file};
+use aya_tool::bindgen;
 use proc_macro2::TokenStream;
 use quote::ToTokens;
 use syn::{Item, parse_str};
@@ -132,7 +132,8 @@ pub fn codegen(opts: &SysrootOptions, libbpf_dir: &Path) -> Result<()> {
         };
         bindgen = bindgen.clang_args(["-I", sysroot.to_str().unwrap()]);
 
-        let bindings = bindgen.generate().context("bindgen failed")?.to_string();
+        let bindings = bindgen.generate().context("bindgen failed")?;
+        let bindings = bindings.to_string();
 
         let mut tree = parse_str::<syn::File>(&bindings).unwrap();
 
@@ -143,21 +144,26 @@ pub fn codegen(opts: &SysrootOptions, libbpf_dir: &Path) -> Result<()> {
         }
 
         let generated = dir.join("src").join(arch.to_string());
-        if !generated.exists() {
         create_dir_all(&generated)?;
-        }
 
         // write the bindings, with the original helpers removed
-        write_to_file(
+        //
+        // write the new helpers as expanded by expand_helpers()
+        for (path, code) in [
+            (
                 generated.join("bindings.rs"),
                 &tree.to_token_stream().to_string(),
-        )?;
-
-        // write the new helpers as expanded by expand_helpers()
-        write_to_file(
+            ),
+            (
                 generated.join("helpers.rs"),
                 &format!("use super::bindings::*; {helpers}"),
-        )?;
+            ),
+        ] {
+            use std::io::Write as _;
+
+            let mut file = File::create(path)?;
+            file.write_all(code.as_bytes())?;
+        }
     }
 
     Ok(())