io_uring_register_ring_fd(3)    liburing Manual   io_uring_register_ring_fd(3)

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) registers the file descriptor of the ring.

       Whenever 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) 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.


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_register_files(3)

liburing-2.2                    March 11, 2022    io_uring_register_ring_fd(3)