---
name: "io_uring_register_ring_fd"
section: "3"
platform: "linux"
package: "liburing"
version: "2.15-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/io_uring_register_ring_fd"
---

# io\_uring\_register\_ring\_fd(3)

register a ring file descriptor

## NAME

io\_uring\_register\_ring\_fd - register a ring file descriptor

## SYNOPSIS

```
#include <liburing.h>
```

**int io\_uring\_register\_ring\_fd(struct io\_uring \****ring***);**

## DESCRIPTION

[**io\_uring\_register\_ring\_fd**(3)](/io_uring_register_ring_fd/3.md) registers the file descriptor of the ring.

Whenever [**io\_uring\_enter**(2)](/io_uring_enter/2.md) is called to submit request or wait for completions, the kernel must grab a reference to the file descriptor. If the application using io\_uring is threaded, the file table is marked as shared, and the reference grab and put of the file descriptor count is more expensive than it is for a non-threaded application.

Similarly to how io\_uring allows registration of files, this allow registration of the ring file descriptor itself. This reduces the overhead of the [**io\_uring\_enter**(2)](/io_uring_enter/2.md) system call.

If an application using liburing is threaded, then an application should call this function to register the ring descriptor when a ring is set up. See NOTES for restrictions when a ring is shared.

Available since kernel 5.18.

## NOTES

When the ring descriptor is registered, it is stored internally in the *struct io\_uring* structure. For applications that share a ring between threads, for example having one thread do submits and another reap events, then this optimization cannot be used as each thread may have a different index for the registered ring fd.

## RETURN VALUE

Returns 1 on success, indicating that one file descriptor was registered, or **-errno** on error.

## SEE ALSO

[**io\_uring\_unregister\_ring\_fd**(3)](/io_uring_unregister_ring_fd/3.md), [**io\_uring\_register\_files**(3)](/io_uring_register_files/3.md)