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.

       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_register_files(3)

liburing-2.2                                     March 11, 2022                     io_uring_register_ring_fd(3)