io_uring_prep_msg_ring(3) — Linux manual page


io_uring_prep_msg_ring(3)    liburing Manual   io_uring_prep_msg_ring(3)

NAME         top

       io_uring_prep_msg_ring - send a message to another ring

SYNOPSIS         top

       #include <liburing.h>

       void io_uring_prep_msg_ring(struct io_uring_sqe *sqe,
                               int fd,
                               unsigned int len,
                               __u64 data,
                               unsigned int flags);

       void io_uring_prep_msg_ring_cqe_flags(struct io_uring_sqe *sqe,
                               int fd,
                               unsigned int len,
                               __u64 data,
                               unsigned int flags,
                               unsigned int cqe_flags);

DESCRIPTION         top

       io_uring_prep_msg_ring(3) prepares to send a CQE to an io_uring
       file descriptor. The submission queue entry sqe is setup to use
       the file descriptor fd, which must identify a io_uring context,
       to post a CQE on that ring where the target CQE res field will
       contain the content of len and the user_data of data with the
       request modifier flags set by flags.  Currently there are no
       valid flag modifiers, this field must contain 0.

       The targeted ring may be any ring that the user has access to,
       even the ring itself. This request can be used for simple message
       passing to another ring, allowing 32+64 bits of data to be
       transferred through the len and data fields. The use case may be
       anything from simply waking up someone waiting on the targeted
       ring, or it can be used to pass messages between the two rings.

       io_uring_prep_msg_ring_cqe_flags(3) is similar to
       io_uring_prep_msg_ring(3).  But has an addition cqe_flags
       parameter, which is used to set flags field on CQE side. That
       way, you can set the CQE flags field cqe->flags when sending a
       message. Be aware that io_uring could potentially set additional
       bits into this field.

RETURN VALUE         top


ERRORS         top

       These are the errors that are reported in the CQE res field.

              The kernel was unable to allocate memory for the request.

              One of the fields set in the SQE was invalid.

              The descriptor passed in fd does not refer to an io_uring
              file descriptor, or the ring is in a disabled state.

              The kernel was unable to fill a CQE on the target ring.
              This can happen if the target CQ ring is in an overflow
              state and the kernel wasn't able to allocate memory for a
              new CQE entry.

COLOPHON         top

       This page is part of the liburing (A library for io_uring)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug report for
       this manual page, send it to  This page
       was obtained from the project's upstream Git repository
       ⟨⟩ on 2023-06-23.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-06-22.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

liburing-2.2                 March 10, 2022    io_uring_prep_msg_ring(3)

Pages that refer to this page: io_uring_prep_msg_ring(3)io_uring_prep_msg_ring_cqe_flags(3)