systemd introduces optional Rust support for new components, using Meson instead of Cargo while keeping its existing C architecture intact.

EEE

The systemd project has officially introduced support for developing programs in Rust, following the merger of a pull request submitted by Linux kernel developer Christian Brauner. The change, merged into the project’s main branch, establishes a new development option for systemd while keeping its existing C-based architecture intact.

And before anyone assumes systemd is preparing a complete rewrite in Rust, that’s not the case. The maintainers agreed on a deliberately limited approach: Rust may be used only for new, standalone components that other parts of systemd do not depend on. Existing C code will remain untouched.

Another important decision concerns the build process. Rather than introducing Cargo, Rust’s standard package manager and build tool, systemd continues to use Meson for all builds. This keeps Rust development integrated into the project’s existing build infrastructure.

The implementation also places strict limits on dependencies. Rust programs use the no_std approach, meaning they do not rely on Rust’s standard library or external third-party crates. Instead, they interact with systemd’s existing C libraries through generated bindings.

For memory management, systemd provides its own Rust implementations of common container types, with allocation failures handled explicitly rather than causing the program to abort. The new infrastructure also includes wrappers for logging, command-line argument handling, event processing, and error management, allowing Rust utilities to behave consistently with their C counterparts.

Rust support is optional and automatically detected during configuration. Developers wishing to enable it need Rust 1.85 or later, bindgen 0.71.1 or later, and Meson 1.4 or later. Systems without the required toolchain can continue building systemd without Rust support.

Interestingly, initial tests show that a stripped Rust command-line utility occupies about 32 KB, compared to 20 KB for its C equivalent built with link-time optimization. This gives an early indication of the additional overhead, though the comparison involves only a small test program.

The first planned real-world application of this infrastructure is systemd-keyring-setup, a new utility intended to help manage certificates in Linux kernel keyrings. Its implementation is being developed separately, alongside additional Rust wrappers for systemd’s shared libraries.

For Linux distributions, the change introduces packaging considerations. Builds that enable all available features will need the appropriate Rust compiler and bindgen dependencies or must disable Rust support to avoid build failures.

Whether Rust becomes widely used within systemd will depend on future development, but the necessary groundwork is now in place.

  • thingsiplay@lemmy.ml
    0·
    2 days ago

    No, I am not talking about the same functionality and without using cargo. I am talking about using rustc to compile individual Rust programs.

    $ ls -1
hello.rs
main.rs

    main.rs:

    mod hello;

fn main() {
    hello::print_hello();
}

    hello.rs:

    pub fn print_hello() {
    println!("Hello World!");
}

    $ rustc --target helloworld main.rs
$ ./helloworld
Hello World!

    No Cargo, no toml, no registry.

    • Ferk@lemmy.ml
      1·
      2 days ago

      Nobody is gonna manually compile each .rs file one by one and link it… unless you really are specifically talking about 1 file simple projects like a helloworld, you’d want to use another tool (like make or cargo), to automate it.

      • thingsiplay@lemmy.ml
        1·
        2 days ago

        What does nobody mean here? We are doing this for ages in C in example. A Makefile can help automate this process. Download git project and run make without any Cargo or regristry or other requirements. Don’t talk about everyone, just because you are not doing it.

        Also the shown example is a single rustc command that will automatically compile and link all associated (with the dependency in the files) and produce a single output.

        • Ferk@lemmy.ml
          1·
          2 days ago

          If you use a Makefile, then you are not doing it manually, you are using a tool to automate it. I think that was the point.

          “nobody” means: those who have big projects with multiple .rs files but no Makefile, no cargo.toml, no build.sh, nothing, only the .rs files. Can you point to a project that does that?

          • thingsiplay@lemmy.ml
            1·
            2 days ago

            “nobody” means: those who have big projects with multiple .rs files but no Makefile, no cargo.toml, no build.sh, nothing, only the .rs files. Can you point to a project that does that?

            That’s the point. We don’t have default rustc on all machines and repositories. In example in Archlinux repositories there is not package rustc only and its standard libraries to install. That’s why most people don’t do it. You can’t fault the missing projects are missing, because the infrastructure is not there yet.

          • thingsiplay@lemmy.ml
            1·
            2 days ago

            But that was not MY point at all. My point is to avoid Cargo, the registry and external dependencies from cratesio. The makefile just uses standard Linux make command. It was just an example to automate this (it could have been a simple Bash script too), but the point is it can be done manually. In this example and even in more useful ones, it can be just a simple rustc invocation.

            • Ferk@lemmy.ml
              1·
              2 days ago

              I think one of the reasons why this is not done is because Rust deliberately works against using precompiled dependencies.

              Unlike traditional C compilers, for the Rust compiler trying to keep ABI compatibility is a non-goal… the Rust compiler retains the freedom to aggressively optimize how data is laid out in memory and how functions are called. Binaries generated by one version (or particular settings) might not work in the next… making it much harder to work the way we work with C libraries.

              This means managing dependencies between rust libraries is a lot more involved… since you are essentially recompiling the library along with your project, so you need a way to download, not just the library headers as you would with C, but its entire sourcecode.

              So your approach might work if you just want to use a little bit of Rust included in a C project… or if your Rust project is small and does not have many dependencies… but the moment you start relying in more and more components and the dependency tree grows enough, it’ll become hard to manage.

              • thingsiplay@lemmy.ml
                1·
                2 days ago

                I think one of the reasons why this is not done is because Rust deliberately pushes away from relying on precompiled binaries.

                Rust? You mean the developers of Rust? That’s not a decision to make by them. Also the Linux distributions include many precompiled binaries. So I don’t see what this point is.

                My suggestion is not to download and use the libraries from third party repositories. The idea is to have all libraries in the repository of the project itself (such as Git) or the standard library in the package manager, matching the rustc compiler that is also packaged there. In example if Debian would include such packages, then this would become quasi industry standard version everyone can target. Basically the same thing that happens with Python in example. So it stays ABI compatible.

                I am not suggesting for full cargo replacement, and suggest not to depend on the registry of those. And I actually believe we will get to that point at some point when gccrs is ready (GNU Compiler Collection including Rust).

                • Ferk@lemmy.ml
                  1·
                  2 days ago

                  Rust? You mean the developers of Rust? That’s not a decision to make by them. Also the Linux distributions include many precompiled binaries. So I don’t see what this point is.

                  I’m talking about the compiler. ABI compatibility is a non-goal in the compiler itself. You’d need to make a new version of rustc that somehow manages to handle generics/templates in an ABI-compatible way and handles optimizations with more care.

                  What distribution includes precompiled libraries (not user programs) in Rust?

                  If you install a C library like libcurl via apt install, you get a precompiled .so file. If you install a Rust library like librust-serde-dev via Debian’s package manager, you do not get a precompiled binary. If you inspect that package, it is literally just a zip file of raw .rs source code that gets dumped into /usr/share/cargo/registry/.

                  Putting all libraries into the git repo or using OS package managers to essentially maintain a registry just like cargo’s can work… but it’s duplicated effort in keeping everything well managed, updated, and free of vulnerabilities.

                  If you use your distro’s package manager, depending on which one you use, it might not offer as much flexibility (like how if you need 2 different versions of the same library in Debian, you’ll need workarounds if the maintainers have not created separate versions for it) or be as build-aware as an integrated build tool would. Some libraries might only need a particular dependency when a particular feature flag is enabled… a package manager most likely would have to download all dependencies of every library you want to use since it does not know what build options you are gonna use when you install the package.

                  • thingsiplay@lemmy.ml
                    1·
                    2 days ago

                    a package manager most likely would have to download all dependencies of every library you want to use since it does not know what build options you are gonna use when you install the package

                    That’s exactly what is to be avoided. I’m not suggesting a dependency heavy program to compile. Someone making a program without Cargo wouldn’t probably make lot of dependencies, and if any, they are all included in its own repository.

                    What distribution includes precompiled libraries (not user programs) in Rust?

                    I thought you was talking about user programs. About the libraries, that’s what I’m suggesting to include too, alongside with the correct rustc compiler. Maybe even the version which the Linux developers use, so that would be the standard one everyone can target.