Rust bindings to *nix APIs

Nix seeks to provide friendly bindings to various *nix platform APIs (Linux, Darwin,
...). The goal is to not provide a 100% unified interface, but to unify
what can be while still providing platform specific APIs.

For many system APIs, Nix provides a safe alternative to the unsafe APIs
exposed by the libc crate. This is done by
wrapping the libc functionality with types/abstractions that enforce legal/safe
usage.

As an example of what Nix provides, examine the differences between what is
exposed by libc and nix for the
gethostname system
call:

rust
// libc api (unsafe, requires handling return code/errno)
pub unsafe extern fn gethostname(name: *mut c_char, len: size_t) -> c_int;

// nix api (returns a nix::Result<OsString>)
pub fn gethostname() -> Result<OsString>;

Supported Platforms

nix target support consists of three tiers. While nix attempts to support all
platforms supported by libc, only some
platforms are actively supported due to either technical or manpower
limitations. Support for platforms is split into three tiers:

Tier 1 - Builds and tests for this target are run in CI. Failures of either
block the inclusion of new code.
Tier 2 - Builds for this target are run in CI. Failures during the build
blocks the inclusion of new code. Tests may be run, but failures
in tests don't block the inclusion of new code.
Tier 3 - Builds for this target are run in CI. Failures during the build
do not necessarily block the inclusion of new code. That is, at
our discretion a Tier 3 target may be dropped at any time, if it
would otherwise block development.

Platforms not listed are supported on a best-effort basis, relying on our users
to report any problems.

The following targets are supported by nix:

<table> <tr> <th>Tier 1</th> <th>Tier 2</th> <th>Tier 3</th> </tr> <tr> <td> <ul> <li>aarch64-apple-darwin</li> <li>aarch64-unknown-linux-gnu</li> <li>arm-unknown-linux-gnueabi</li> <li>armv7-unknown-linux-gnueabihf</li> <li>i686-unknown-freebsd</li> <li>i686-unknown-linux-gnu</li> <li>i686-unknown-linux-musl</li> <li>mips-unknown-linux-gnu</li> <li>mips64-unknown-linux-gnuabi64</li> <li>mips64el-unknown-linux-gnuabi64</li> <li>mipsel-unknown-linux-gnu</li> <li>powerpc64le-unknown-linux-gnu</li> <li>x86_64-unknown-freebsd</li> <li>x86_64-unknown-linux-gnu</li> <li>x86_64-unknown-linux-musl</li> </ul> </td> <td> <ul> <li>aarch64-apple-ios</li> <li>aarch64-linux-android</li> <li>aarch64-unknown-linux-ohos</li> <li>arm-linux-androideabi</li> <li>arm-unknown-linux-musleabi</li> <li>armv7-linux-androideabi</li> <li>armv7-unknown-linux-ohos</li> <li>i686-linux-android</li> <li>loongarch64-unknown-linux-gnu</li> <li>s390x-unknown-linux-gnu</li> <li>x86_64-linux-android</li> <li>x86_64-unknown-illumos</li> <li>x86_64-unknown-linux-ohos</li> <li>x86_64-unknown-netbsd</li> </td> <td> <li>armv7-unknown-linux-uclibceabihf</li> <li>powerpc64-unknown-linux-gnu</li> <li>x86_64-unknown-fuchsia</li> <li>x86_64-unknown-dragonfly</li> <li>x86_64-unknown-haiku</li> <li>x86_64-unknown-linux-gnux32</li> <li>x86_64-unknown-openbsd</li> <li>x86_64-unknown-redox</li> <li>i686-unknown-hurd-gnu</li> </td> </tr> </table>