io_uring_register_ring_fd(3)

💖 io_uring_register_ring_fd — register a ring file descriptor 💖

okay bestie, gather round, because this one is a little function with big main character energy ✨ it lives in liburing, and it's basically "hey kernel, remember my ring fd so you stop doing extra paperwork every single time" 🎀

✨ SYNOPSIS ✨

#include <liburing.h>

int io_uring_register_ring_fd(struct io_uring *ring);

🌸 DESCRIPTION 🌸

So io_uring_register_ring_fd(3) registers the file descriptor of the ring. That's it. That's the whole vibe. 💅

Here's the tea though: every time io_uring_enter(2) gets called — whether you're submitting a request or waiting on completions — the kernel has to grab a reference to the file descriptor. And if the app using io_uring is threaded, the file table gets marked as shared, and suddenly that reference grab-and-put on the file descriptor count costs way more than it does for a non-threaded app. it's giving unnecessary overhead, fr fr 😭

So, kind of like how io_uring already lets you register files, this lil function lets you register the ring file descriptor itself. Which means the overhead of the io_uring_enter(2) system call goes down. slay. 🔥

And like — if your app using liburing is threaded, you should call this function to register the ring descriptor when the ring gets set up. Just do it, bestie 🫶

heads up tho: check out NOTES for the restrictions that apply when a ring is shared 👀

Available since kernel 5.18. ⭐

🦋 NOTES 🦋

When the ring descriptor is registered, it gets stored internally in the struct io_uring structure. periodt.

But here's where it gets spicy 🌶️ — for applications that share a ring between threads, like one thread doing the submits and another reaping events, this optimization cannot be used, because each thread may have a different index for the registered ring fd. so yeah, that one's off the table. sorry bestie 😭💀

👑 RETURN VALUE 👑

Returns 1 on success — indicating that one file descriptor was registered — or -errno on error. that's the whole return journey, no cap 🌈

🌟 SEE ALSO 🌟

• io_uring_unregister_ring_fd(3)
• io_uring_register_files(3)

and that's the page, bestie!! 💜 this lil baddie comes to you courtesy of liburing-2.2, dated March 11, 2022 — go forth and register that ring fd, you absolute icon 🎀✨🦋💖