io_uring is a

Linux kernel The Linux kernel is a Free and open-source software, free and open source Unix-like kernel (operating system), kernel that is used in many computer systems worldwide. The kernel was created by Linus Torvalds in 1991 and was soon adopted as the k ...

system call In computing, a system call (syscall) is the programmatic way in which a computer program requests a service from the operating system on which it is executed. This may include hardware-related services (for example, accessing a hard disk drive ...

interface for storage device

asynchronous I/O In computer science, asynchronous I/O (also non-sequential I/O) is a form of input/output processing that permits other processing to continue before the I/O operation has finished. A name used for asynchronous I/O in the Windows API is '' over ...

operations addressing performance issues with similar interfaces provided by functions like / or / etc. for operations on data accessed by

file descriptor In Unix and Unix-like computer operating systems, a file descriptor (FD, less frequently fildes) is a process-unique identifier (handle) for a file or other input/output resource, such as a pipe or network socket. File descriptors typically h ...

s. Development is ongoing, worked on primarily by Jens Axboe at

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Interface

It works by creating two

circular buffer In computer science, a circular buffer, circular queue, cyclic buffer or ring buffer is a data structure that uses a single, fixed-size buffer as if it were connected end-to-end. This structure lends itself easily to buffering data streams. The ...

s, 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). 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. 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.

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can be combined with io_uring.

History

The Linux kernel has supported

since version 2.5, but it was seen as difficult to use and inefficient. This older API only supported certain niche

use cases In both software and systems engineering, a use case is a structured description of a system’s behavior as it responds to requests from external actors, aiming to achieve a specific goal. It is used to define and validate functional requireme ...

, notably it only enables asynchronous operation when using the O_DIRECT flag and while accessing already allocated files. This prevents utilizing the

page cache In computing, a page cache, sometimes also called disk cache, is a transparent cache for the pages originating from a secondary storage device such as a hard disk drive (HDD) or a solid-state drive (SSD). The operating system keeps a page ca ...

, 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. The io_uring kernel interface was adopted in Linux kernel version 5.1 to resolve the deficiencies of Linux AIO. The liburing library provides an

API An application programming interface (API) is a connection between computers or between computer programs. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how to build ...

to interact with the kernel interface easily from

userspace A modern computer operating system usually uses virtual memory to provide separate address spaces or regions of a single address space, called user space and kernel space. This separation primarily provides memory protection and hardware prote ...

Security

io_uring has been noted for exposing a significant attack surface and structural difficulties integrating it with the Linux security subsystem. In June 2023, Google's security team reported that 60% of the exploits submitted to their

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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

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as well as Google servers. Docker also consequently disabled io_uring from their default seccomp profile.

Notes

References

External links

Efficient I/O with io_uring
in-depth description of motivation behind io_uring, interface (data structures etc.), and performance assessment
source repository

source directory in the Linux kernel repository
{{Linux kernel Interfaces of the Linux kernel Linux kernel features Articles with underscores in the title