io uring

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).{{Cite web|title=Getting Hands-on with io_uring using Go|url=https://developers.mattermost.com/blog/hands-on-iouring-go/|access-date=2021-11-20|website=developers.mattermost.com|language=en-us}} 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.{{Cite web |title=Linux Kernel Getting io_uring To Deliver Fast & Efficient I/O |date=2019-02-14 |url=https://www.phoronix.com/scan.php?page=news_item&px=Linux-io_uring-Fast-Efficient |access-date=2021-03-14 |website=Phoronix}}{{Cite web|title=The rapid growth of io_uring [LWN.net]|url=https://lwn.net/Articles/810414/|access-date=2021-11-20|website=lwn.net}} 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.{{R|name=Phoronix2019|page=3}}

eBPF can be combined with io_uring.{{Cite web |title=BPF meets io_uring [LWN.net] |url=https://lwn.net/Articles/847951/ |access-date=2023-04-17 |website=LWN.net}}

The Linux kernel has supported asynchronous I/O since version 2.5, but it was seen as difficult to use and inefficient.{{Cite web|last=Corbet|first=Jonathan|title=Ringing in a new asynchronous I/O API|url=https://lwn.net/Articles/776703/|access-date=2021-03-14|website=LWN.net}} This older API only supported certain niche use cases,{{cite web | url = https://kernel.dk/axboe-kr2022.pdf | title = What's new with io_uring | access-date = 2022-06-01}} 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.{{Cite web |url=http://code.google.com/p/kernel/wiki/AIOUserGuide |title=Linux Asynchronous I/O |date=2014-04-21 |archive-url=https://web.archive.org/web/20150406015143/http://code.google.com/p/kernel/wiki/AIOUserGuide |access-date=2023-06-16 |archive-date=2015-04-06 |quote=Blocking during io_submit on ext4, on buffered operations, network access, pipes, etc. Some operations are not well-represented by the AIO interface. With completely unsupported operations like buffered reads, operations on a socket or pipes, the entire operation will be performed during the io_submit syscall, with the completion available immediately for access with io_getevents. AIO access to a file on a filesystem like ext4 is partially supported: if a metadata read is required to look up the data block (ie if the metadata is not already in memory), then the io_submit call will block on the metadata read. Certain types of file-enlarging writes are completely unsupported and block for the entire duration of the operation. }}

The io_uring kernel interface was adopted in Linux kernel version 5.1 to resolve the deficiencies of Linux AIO.{{R|name=Phoronix2019}}{{Cite web |title=Faster IO through io_uring |url=https://archives.kernel-recipes.org/document/faster-io-through-io_uring/ |url-status=live |archive-url=https://web.archive.org/web/20250424005512/https://archives.kernel-recipes.org/document/faster-io-through-io_uring/ |archive-date=2025-04-24 |access-date=2025-04-24 |website=Kernel Recipes 2019 |language=en-GB}} The liburing library provides an API to interact with the kernel interface easily from userspace.{{R|name=Phoronix2019|page=12}}

io_uring has been noted for exposing a significant attack surface and structural difficulties integrating it with the Linux security subsystem.{{Cite web |url=https://lwn.net/Articles/902466/ |title=Security requirements for new kernel features |date=2022-07-28 |access-date=2023-06-16 |website=LWN.net |last=Corbet |first=Jonathan}}

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.{{cite web |last1=Koczka |first1=Tamás |title=Learnings from kCTF VRP's 42 Linux kernel exploits submissions |url=https://security.googleblog.com/2023/06/learnings-from-kctf-vrps-42-linux.html |website=Google Online Security Blog |publisher=Google |access-date=14 June 2023 |language=en |archive-url=https://web.archive.org/web/20240922183950/https://security.googleblog.com/2023/06/learnings-from-kctf-vrps-42-linux.html |archive-date=2024-09-22 |url-status=live |quote=60% of the submissions exploited the io_uring component of the Linux kernel}} Docker also consequently disabled io_uring from their default seccomp profile.{{Cite web |title=Update RuntimeDefault seccomp profile to disallow io_uring related syscalls by vinayakankugoyal · Pull Request #9320 · containerd/containerd |url=https://github.com/containerd/containerd/pull/9320 |date=2023-11-02 |access-date=2024-10-20 |website=GitHub |language=en |archive-url=https://web.archive.org/web/20240106225425/https://github.com/containerd/containerd/pull/9320 |archive-date=2024-01-06 |url-status=live}}

{{Notelist}}

{{Reflist}}

• [https://kernel.dk/io_uring.pdf Efficient I/O with io_uring], in-depth description of motivation behind io_uring, interface (data structures etc.), and performance assessment
• [https://git.kernel.dk/cgit/liburing/tree/ {{Code|liburing}} source repository]
• [https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/io_uring {{Code|io_uring}} source directory in the Linux kernel repository]

{{Linux kernel}}

Category:Interfaces of the Linux kernel

Category:Linux kernel features

Category:Articles with underscores in the title