liburing

This is the io_uring library, liburing. liburing provides helpers to setup and teardown io_uring instances, and also a simplified interface for applications that don't need (or want) to deal with the full kernel side implementation.

For more info on io_uring, please see:

https://kernel.dk/io_uring.pdf

Subscribe to io-uring@vger.kernel.org for io_uring related discussions and development for both kernel and userspace. The list is archived here:

https://lore.kernel.org/io-uring/

kernel version dependency

liburing itself is not tied to any specific kernel release, and hence it's possible to use the newest liburing release even on older kernels (and vice versa). Newer features may only be available on more recent kernels, obviously.

ulimit settings

io_uring accounts memory it needs under the rlimit memlocked option, which can be quite low on some setups (64K). The default is usually enough for most use cases, but bigger rings or things like registered buffers deplete it quickly. root isn't under this restriction, but regular users are. Going into detail on how to bump the limit on various systems is beyond the scope of this little blurb, but check /etc/security/limits.conf for user specific settings, or /etc/systemd/user.conf and /etc/systemd/system.conf for systemd setups. This affects 5.11 and earlier, new kernels are less dependent on RLIMIT_MEMLOCK as it is only used for registering buffers.

Regressions tests

The bulk of liburing is actually regression/unit tests for both liburing and the kernel io_uring support. Please note that this suite isn't expected to pass on older kernels, and may even crash or hang older kernels!

Building liburing

#
# Prepare build config (optional).
#
#  --cc  specifies the C   compiler.
#  --cxx specifies the C++ compiler.
#
./configure --cc=gcc --cxx=g++;

#
# Build liburing.
#
make -j$(nproc);

#
# Install liburing (headers, shared/static libs, and manpage).
#
sudo make install;

See './configure --help' for more information about build config options.

FFI support

By default, the build results in 4 lib files:

2 shared libs:

    liburing.so
    liburing-ffi.so

2 static libs:

    liburing.a
    liburing-ffi.a

Languages and applications that can't use 'static inline' functions in liburing.h should use the FFI variants.

liburing's main public interface lives in liburing.h as 'static inline' functions. Users wishing to consume liburing purely as a binary dependency should link against liburing-ffi. It contains definitions for every 'static inline' function.

License

All software contained within this repo is dual licensed LGPL and MIT, see COPYING and LICENSE, except for a header coming from the kernel which is dual licensed GPL with a Linux-syscall-note exception and MIT, see COPYING.GPL and https://spdx.org/licenses/Linux-syscall-note.html.

Jens Axboe 2022-05-19