Io uring

io_uring^[a] is a Linux kernel system call interface for storage device asynchronous I/O operations addressing performance issues with similar interfaces provided by functions like read()/write() or aio_read()/aio_write() etc. for operations on data accessed by file descriptors.^[2][3]: 2

• Computer programming portal
• Linux portal

Development is ongoing, worked on primarily by Jens Axboe at Meta.^[2]

Interface

It works by creating two circular buffers, called "queue rings", to track the submission and completion of I/O requests, respectively. For storage devices, these are called the submission queue (SQ) and completion queue (CQ).^[4] Keeping these buffers shared between the kernel and application helps to boost the I/O performance by eliminating the need to issue extra and expensive system calls to copy these buffers between the two.^[2][4][5] According to the io_uring design paper, the SQ buffer is writable only by consumer applications, and the CQ buffer is writable only by the kernel.^[2]: 3

eBPF can be combined with io_uring.^[6]

History

The Linux kernel has supported asynchronous I/O since version 2.5, but it was seen as difficult to use and inefficient.^[7] This older API only supported certain niche use cases,^[8] notably it only enables asynchronous operation when using the O_DIRECT flag and while accessing already allocated files. This prevents utilizing the page cache, while also exposing the application to complex O_DIRECT semantics. Linux AIO also does not support sockets, so it cannot be used to multiplex network and disk I/O.^[9]

The io_uring kernel interface was adopted in Linux kernel version 5.1 to resolve the deficiencies of Linux AIO.^[2][5][10] The liburing library provides an API to interact with the kernel interface easily from userspace.^[2]: 12

Security

io_uring has been noted for exposing a significant attack surface and structural difficulties integrating it with the Linux security subsystem.^[11]

In June 2023, Google's security team reported that 60% of the exploits submitted to their bug bounty program in 2022 were exploits of the Linux kernel's io_uring vulnerabilities. As a result, io_uring was disabled for apps in Android, and disabled entirely in ChromeOS as well as Google servers.^[12] Docker also consequently disabled io_uring from their default seccomp profile.^[13]

Notes

1. Input/output user ring^[1]