Function io_uring_prep_msg_ring_fd 

pub unsafe fn io_uring_prep_msg_ring_fd(
    sqe: *mut io_uring_sqe,
    fd: c_int,
    source_fd: c_int,
    target_fd: c_int,
    data: u64,
    flags: c_uint,
)

Send a direct descriptor to another ring

DESCRIPTION

io_uring_prep_msg_ring_fd prepares an SQE to send a direct file descriptor to another ring. The submission queue entry sqe is setup to use the file descriptor fd, which must identify a target io_uring context, to send the locally registered file descriptor with value source_fd to the destination ring into index target_fd and passing data as the user data in the target CQE with the request modifier flags set by flags. Currently there are no valid flag modifiers, this field must contain 0.

io_uring_prep_msg_ring_fd_alloc is similar to io_uring_prep_msg_ring_fd, but doesn’t specify a target index for the direct descriptor. Instead, this index is allocated in the target ring and returned in the CQE res 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.

-EINVAL
Target ring is identical to the source ring.

-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.

-ENFILE
The direct descriptor table in the target ring was full, no new descriptors could be successfully allocated.