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README.md

dlt-sys

Crates.io Documentation License Low-level FFI bindings to the COVESA DLT (Diagnostic Log and Trace) C library (libdlt).

Overview

dlt-sys provides unsafe Rust bindings to the COVESA DLT daemon C library. This crate is intended to be used as a foundation for higher-level safe Rust abstractions (see dlt-rs). Please note that this is only implements functionality required for dlt-rs and does not cover the entire libdlt API.

Features

  • Direct FFI bindings to libdlt functions
  • Custom C wrapper for improved API ergonomics
  • Support for all DLT log levels and message types
  • Optional trace_load_ctrl feature for load control support

Prerequisites

  • libdlt and its development headers must be installed on your system.
    You can install it like so:
    • On Debian-based systems: apt install libdlt-dev
    • On macOS with Homebrew: 
      brew tap COVESA/dlt-daemon https://github.com/COVESA/dlt-daemon
brew install COVESA/dlt-daemon/dlt-daemon
  • bindgen prerequisites must be available at build time (clang and libclang). dlt-sys generates Rust bindings on the fly during cargo build, using the installed DLT headers.

Usage

This is a low-level crate with unsafe APIs. Most users should use dlt-rs instead for a safe, idiomatic Rust API.

Features

  • trace_load_ctrl - Enable DLT load control support (may be required in some environments, depending on the DLT build time daemon configuration)
  • generate-bindings - Regenerate bindings from C headers (development only)

Compatibility Across DLT Releases

  • dlt-sys is designed to work with multiple libdlt releases.
  • Bindings are generated at build time from the locally installed DLT headers, so the Rust FFI shape matches the installed release.
  • DltContextData uses zero-initialization in Rust to remain source-compatible when libdlt adds fields.
  • Optional C APIs are resolved dynamically in the wrapper at runtime. If dlt_register_log_level_changed_callback is unavailable in an older libdlt, callback registration returns a DLT error instead of failing at link time.
  • In CI, the repository setup action supports selecting a DLT daemon ref (dlt-ref) so workflows can validate multiple releases.

Selecting The Linked DLT Release

When consuming this crate from crates.io, select the installed DLT release by pointing include and library paths to that installation.

  • DLT_INCLUDE_DIR: include directory containing dlt/ headers
  • DLT_LIB_DIR: library directory containing libdlt
  • DLT_USER_INCLUDE_DIR: optional additional include directory
  • DLT_LIB_NAME: optional library name override (default: dlt)

Example:

DLT_INCLUDE_DIR=/opt/homebrew/include \
DLT_LIB_DIR=/opt/homebrew/lib \
cargo build

Safety

All functions in this crate are unsafe as they directly call C library functions. Proper usage requires understanding of:

  • DLT library initialization and cleanup
  • Memory management across FFI boundaries
  • Thread safety considerations For safe abstractions, use the dlt-rs crate.

License

Licensed under the Apache License, Version 2.0. See LICENSE for details.

Contributing

This project is part of Eclipse OpenSOVD, but can be used independently. See CONTRIBUTING.md for guidelines.

References