tracers - Rust instrumentation library

Summary

tracers is intended to be an easy to use and cross-platform Rust crate which makes it easy to add high-performance low-overhead probes to Rust programs. Underneath it will use each platform's native probing mechanism, like System Tap on Linux, DTrace on BSD, and ETW on Windows. Those platforms without a supported probing mechanism will fall back to a no-op implementation.

A key goal of this crate is to be able to drop it in to any Rust project, create and fire probes wherever it makes sense, and leave those probes in place all the time. When probes are disabled at compile time, there should be zero runtime impact, and when probes are compiled in but not enabled at runtime the probe impact should be no more than one or two CPU instructions.

Status

IMPORTANT: tracers is still experimental. The author is using it internally but this crate is still not yet widely used and may contain subtle and critical defects.

Quick start

In your Cargo.toml you need to add:

[dependencies]
...
tracers = "0.1.0"
tracers-macros = "0.1.0"

[build-dependencies]
...
tracers-build = "0.1.0"

It's important not to forget to add tracers-build to your build-dependencies, because you'll need that available at build time for the next step, which is to create a src/build.rs file if you don't have one already, and make sure it contains this:

use tracers_build::build;

fn main() {
build();
}

If you have an existing build.rs you'll need to make sure you add a call to tracers_build::build() somewhere in the main function, preferably early.

At this point you have all you need to define a tracer. Here's a simple example:

use tracers_macros::{probe, tracer};

#[tracer]
trait SimpleProbes {
fn hello(who: &str);
fn greeting(greeting: &str, name: &str);
fn optional_greeting(greeting: &str, name: &Option<&str>);
}

fn main() {
loop {
    probe!(SimpleProbes::hello("world"));
    probe!(SimpleProbes::greeting("hello", "world"));
    let name = Some("world");
    probe!(SimpleProbes::optional_greeting("hello", &name));
    let name: Option<&str> = None;
    probe!(SimpleProbes::optional_greeting("hello", &name));
}
}

You have have defined three probes, hello, greeting, and optional_greeting. By default, tracing is disabled at compile time, so when you run this code all of the probing infrastructure will be optimized away and you'll be left with zero runtime overhead.

To actually enable probing you need to activate one of the corresponding features in the tracers crate. For example, in your Cargo.toml:

[dependencies]
...
tracers = { version = "0.1.0", features = [ "force_static_stap"]

will enable SystemTap tracing. If you rebuild again and use a tool like tplist from BCC you should be able to see the probes in the binary.

Note also that the #[tracers] macro generates some useful documentation on your trait. Try cargo doc and find your trait in the docs for additional hints on how to use each probe.

The examples/ directory has some simple examples.

Platforms

The tracers crate and runtime components should compile and run on any supported Rust platform (although no_std is not yet supported). Adding tracers as a dependency shouldn't break your project on any platform; if it does that's a bug and you're encouraged to open a GitHub issue.

That said, the tracers crate by default doesn't actually trace anything; it compiles away to nothing. To actually enable tracing you need a supported platform. As of this writing that means:

• Linux with System Tap (the force_static_stap feature)
• Linux with LTT-ng (the force_static_lttng) feature

There is work being done to support:

• Windows (with the Event Tracing for Windows system API)
• FreeBSD and macOS (with DTrace)

License

Except where otherwise indicated, this project is licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

However, the following -sys crates have the license corresponding to the third-party code which they wrap:

• tracers-libelf-sys - Wraps elfutils libraries and thus is licensed LGPLv3
• tracers-libstapsdt-sys - Wraps libstapsdt and thus is licensed MIT

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in tracers by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

Releasing

This section applies to maintainers only.

To release a new version, dependent crates must be released first. The bin/publish.sh script helps to automate the process but it's still quite manual.

Release process:

1. Update the version property of all crates and of all crates' dependencies on other tracers crates to the new target version.

2. Ensure all dependencies have both a path dependency for local development, and a version dependency for publishing. These must be consistent with the new version being published.

3. Update the documentation link to reflect the current version.

Crates must be published in this order:

• tracers-core
• tracers-libelf-sys
• tracers-libstapsdt-sys
• tracers-codegen
• tracers-macros-hack
• tracers-macros
• tracers-dyn-stap
• tracers-dyn-noop
• tracers-build
• tracers