lib/fastboot Rust FFI

Fastboot uses some functionality implemented by Rust libraries, so we need some FFI support.

Generating the FFI code

Since we‘re calling Rust APIs from a C++ program we’ll use cbindgen which takes a bit more manual effort than the other way around (bindgen). This currently does not tie into the build system, so the headers need to be re-generated manually whenever the API changes.

Prereqs

1. Install the Rust toolchain (https://www.rust-lang.org/tools/install).

2. Install cbindgen:

   cargo install cbindgen
   

Generation

1. Adjust fx set to include cargo generation. See fuchsia.dev cargo docs for the latest instructions; currently this is done by:

   fx set <product>.<board> --cargo-toml-gen <other fx args>
   

   Alternatively, you can use fx args and manually add the necessary target to the host_labels arg:

   host_labels = [
     "//build/rust:cargo_toml_gen",
   ]
   

2. Configure the Rust toolchain for per-package-target support.

   At the time of this writing, cbindgen requires cargo support for the per-package-target feature, which is not yet available on the stable releases, so we need to switch to the nightly release track:

   rustup default nightly
   

   Note: the nightly build may not always be compatible with different versions of cbindgen, so you may need to set the default to a specific version instead. These instructions were originally tested using:

   • rustc 1.73.0-nightly
   • cbindgen 0.24.5

3. Run the generation script in this directory (this requires a host Python installation):

   $ python3 cbindgen.py
   

4. Switch back the stable Rust toolchain (optional)

   If you want to return your host to the stable Rust toolchain, run:

   rustup default stable
   

   You can also just leave it on the nightly release