A Bytecode Alliance project
rsix (formerly known as posish) provides efficient memory-safe and
I/O-safe wrappers to POSIX-like, Unix-like, and Linux syscall APIs, with
configurable backends. It uses Rust references, slices, and return values
instead of raw pointers, and io-lifetimes instead of raw file descriptors,
providing memory safety and I/O safety. It uses Results for reporting
errors, bitflags instead of bare integer flags, an Arg trait with
optimizations to efficiently accept any Rust string type, and several other
efficient conveniences.
rsix is low-level and does not support Windows; for higher-level and more
portable APIs built on this functionality, see the system-interface,
cap-std, and fs-set-times crates, for example.
rsix currently has two backends available: linux_raw and libc.
The linux_raw backend is enabled by default on Linux on x86-64, x86, aarch64,
and riscv64gc, and uses raw Linux system calls and vDSO calls. It supports
stable as well as nightly Rust.
- By being implemented entirely in Rust, avoiding
libc,errno, and pthread cancellation, and employing some specialized optimizations, most functions compile down to very efficient code. On nightly Rust, they can often be fully inlined into user code. - Most functions in
linux_rawpreserve memory and I/O safety all the way down to the syscalls. linux_rawuses a 64-bittime_ttype on all platforms, avoiding the y2038 bug.
The libc backend is enabled by default on all other platforms, and can be
set explicitly for any target by setting RUSTFLAGS to --cfg rsix_use_libc.
It uses the libc crate which provides bindings to native libc libraries
and is portable to many OS's.
Similar crates
rsix is similar to nix, simple_libc, unix, and nc. rsix is
a relatively new project with less overall coverage, architected for
I/O safety with most APIs using OwnedFd and AsFd to manipulate file
descriptors rather than File or even c_int, and supporting multiple
backends so that it can use direct syscalls while still being usable on all
platforms libc supports. Like nix, rsix has an optimized and flexible
filename argument mechanism that allows users to use a variety of string types,
including non-UTF-8 string types.
relibc is a similar project which aims to be a full "libc", including
C-compatible interfaces and higher-level C/POSIX standard-library
functionality; rsix just aims to provide safe and idiomatic Rust interfaces
to low-level syscalls. relibc also doesn't tend to support features not
supported on Redox, such as *at functions like openat, which are
important features for rsix.
rsix has its own code for making direct syscalls, similar to the sc
and scall crates, though rsix currently only supports direct syscalls on
Linux on x86_64, x86, aarch64, and riscv64. rsix can use either the unstable
Rust asm! macro or out-of-line .s files so it supports both Stable and
Nightly Rust. rsix's syscalls report errors using an optimized Error type,
and rsix supports Linux's vDSO mechanism to optimize Linux clock_gettime on
all architectures, and all Linux system calls on x86.
rsix's *at functions are similar to the openat crate, but rsix
provides them as free functions rather than associated functions of a Dir
type. rsix's cwd() function exposes the special AT_FDCWD value in a safe
way, so users don't need to open . to get a current-directory handle.
rsix's openat2 function is similar to the openat2 crate, but uses
I/O safety types rather than RawFd. rsix does not provide dynamic feature
detection, so users must handle NOSYS themselves.