find_mountpoint

The documentation is here.

This started as a simple crate to simplify getting at one field returned from statfs(2) on macOS. It takes care of all of the unsafe stuff and reflects my best understanding as a Rust newbie of how to deal with libc memory management efficiently. It has since grown a bit and should work on all platforms supported by Rust.

Its error handling is pretty conservative. It doesn't use .unwrap() and should therefore never panic unless you fail to handle the Result in your own code. I created a new find_mountpoint::Error that's a sum type over the error types returned by the calls I make, which was presented as idiomatic by the Rust book.

Although the macOS version makes unsafe calls, I've tried to keep it all in a single critical section to minimize the amount of weirdness that can happen. Because one of my goals was to minimize memory overhead, I thought about using a static variable for the buffer passed to statfs(2), but then realized that would make it unsafe for use in threaded code or with Tokio, so each call results in a new allocation for a statfs structure.

Since developing the macOS version, I've written a (slower) version that doesn't rely on libc and should work on all other variants of UNIX. There's also an even simpler version for Windows, which passes its (pretty simple) tests on AppVeyor, so maybe it will work for you, friendly Windows developer, as well. Sample code for the API I'm using on Windows is thin on the ground.

That said, It took me less than half an hour to get the project up and tests passing on AppVeyor, thanks to this configuration and rustup. It's pretty impressive how quickly everything came together. Thanks, Rust! Thust!

This is my first published Rust crate, so I'm sure even this short chunk of code has problems that I would love help in fixing. There aren't a lot of examples out there of libc::statfs in use, and pretty much everybody does some variant of what I do, but bugs and PRs are welcome.

justification

Dealing with libc calls is fiddly (&str → Path → OsStr → CStr and back again, just for strings!). nix doesn't expose the field I want in its Statfs structure. None of the filesystem crates I could find exposed this function. If somebody wants to assimilate this into their library, or work with me to get this function merged into their crate (including nix), that would be fantastic!

Until then, I needed this for my own nefarious purposes, so here it is.