io\_uring\_register\_ring\_fd(3) liburing Manual io\_uring\_register\_ring\_fd(3)

# [NAME](#NAME)

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

# [SYNOPSIS](#SYNOPSIS)

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

```
int io_uring_register_ring_fd(struct io_uring *ring);
```

# [DESCRIPTION](#DESCRIPTION)

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

Whenever [**io\_uring\_enter**(2)](/man/os/liburing/io_uring_enter.2) 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)](/man/os/liburing/io_uring_enter.2) 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](#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](#RETURN_VALUE)

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

# [SEE ALSO](#SEE_ALSO)

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

March 11, 2022 liburing-2.2

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Document: io_uring_register_ring_fd(3) from liburing 2.15-r4 (Chainguard OS)
Source: https://github.com/axboe/liburing.git