Using Rust to make a small user namespaces test binary

This repo contains source code to a program that, in less than 200 bytes of compiled binary, figures out if your system supports Linux's user namespaces feature. I created it for the Sandstorm installer so that I can embed a compiled binary in the install shell script (which is admittedly a strange thing to do) because I could find no better way to check for that kernel feature.

This repo contains the Rust source code for that binary, as well as a hand-written assembly version.

At the time of writing, this compiles down to a program 157 bytes long. That number might be out of date, so feel free to re-compile it yourself.

To build the Rust version, we use a custom toolchain. Keegan McAllister developed that toolchain for https://github.com/kmcallister/tiny-rust-demo ; this project merely re-uses it.

Massive thanks to @kmc and @bstrie for helping me create this silly thing.

The code in the Sandstorm install script

To rebuild it, run:

./build.sh

The source code is in:

tinyrust.rs

Alternate implementation in assembly

See

tinyasm.s

and

./build-asm.sh

The assembly strategy shaves 4 bytes off the result, but the installer still uses the Rust version for now.