NAME

       io_uring_prep_msg_ring - send a message to another ring

SYNOPSIS

       #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

       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

       None

ERRORS

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

       -ENOMEM
              The kernel was unable to allocate memory for the request.

       -EINVAL
              One of the fields set in the SQE was invalid.

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

       -EOVERFLOW
              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.