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rustembedded-linuxrust-cargobuildroot

Developing Rust app in buildroot (problem with cargo build --offline --locked)

I created a new buildroot package which is a Rust application built with cargo.

I followed the buildroot manual for Cargo packages, and my .mk is quite simple:

MY_RUST_APP_VERSION = 1.1.0
MY_RUST_APP_SITE = $(BR2_EXTERNAL_PATH)/package/my-rust-app
MY_RUST_APP_SUBDIR = my-rust-app
MY_RUST_APP_SITE_METHOD = local

# Release build for smaller size and faster execution
# cargo already builds as --release by default in buildroot
#MY_RUST_APP_CARGO_BUILD_OPTS = --release

$(eval $(cargo-package))

It builds fine when Cargo.toml has no dependencies added.

However, when I add the first external dependency to Cargo.toml, buildroot fails to download and build it:

[dependencies]
tracing = "0.1.40"

buildroot output:

error: no matching package named `tracing` found
location searched: registry `crates-io`
required by package `my-rust-app v1.1.0`
As a reminder, you're using offline mode (--offline) which can sometimes cause surprising resolution failures, if this error is too confusing you may wish to retry without the offline flag.

I see that buildroot by default invokes Cargo with --offline and --locked which makes it harder to add new crates to Cargo.toml.

How to remove these default flags? Or maybe the approach to development and building a local Rust package should be different?

make my-rust-app-reconfigure
>>> my-rust-app 1.1.0 Building
[...]
__CARGO_TEST_CHANNEL_OVERRIDE_DO_NOT_USE_THIS="nightly"
CARGO_UNSTABLE_TARGET_APPLIES_TO_HOST="true" CARGO_TARGET_APPLIES_TO_HOST="false"
CARGO_BUILD_TARGET="armv7-unknown-linux-gnueabihf"
CARGO_TARGET_ARMV7_UNKNOWN_LINUX_GNUEABIHF_LINKER=arm-buildroot-linux-gnueabihf-gcc
RUSTFLAGS="-Clink-arg=-Wl,--allow-multiple-definition"  cargo build --offline --release --manifest-path Cargo.toml --locked

Before posting the question, I also tried purging the build directory in hope it will allow Cargo to build. However even make my-rust-app-dirclean && make my-rust-app-reconfigure doesn't help. I wanted to remove downloads from buildroot/dl/ but cannot locate anything related to Rust dependencies. At the same time, I can successfully build from my package source directory with cargo build.

Solution

  • I finally managed to solve the problem. Instead of building a local package, I've placed the Rust code in a repository, and used buildroot's git method of installation.

    .mk file looks like this:

    MY_RUST_APP_VERSION = f799b21347968628fff067742d3a05e4152a1ba9 # git hash
MY_RUST_APP_SITE = [email protected]:org/repo.git
MY_RUST_APP_SITE_METHOD = git
MY_RUST_APP_SUBDIR = "packages/my-rust-app"

# Install steps
define MY_RUST_APP_INSTALL_TARGET_CMDS
    $(INSTALL) -D \
        $(@D)/target/$(RUSTC_TARGET_NAME)/release/my-rust-app \
        $(TARGET_DIR)/usr/bin/
endef

$(eval $(cargo-package))

    Installing Rust/Cargo crate from git doesn't suffer from the limitations on local crate (--offline) and doesn't require additional steps like manually creating the .lock file and fetching the index.