Zero-Copy Send with Single Message and Buffer

Figure 1. Zero-Copy with Single Message and Buffer Example

struct onload_zc_iovec iovec;
struct onload_zc_mmsg mmsg;
rc = onload_zc_alloc_buffers(fd, &iovec, 1,
                             ONLOAD_ZC_BUFFER_HDR_TCP);
assert(rc == O);
assert(my_data_len <= iovec.iov_len);
memcpy(iovec.iov_base, my_data, my_data_len);
iovec.iov_len = my_data_len;
mmsg.fd = fd;
mmsg.msg.iov = &iovec;
mmsg.msg.msghdr.msg_iovlen = 1;
rc = onload_zc_send(&mmsg, 1, 0);
if( rc <= 0) {
  /* Probably application bug */
  return rc;
} else {
  /* Only one message, so rc should be 1 */
  assert(rc == 1);
  /* rc == 1 so we can look at the first (only) mmsg.rc */
  if( mmsg.rc < 0 )
    /* Error sending message */
    onload_zc_release_buffers(fd, &iovec.buf, 1);
  else
    /* Message sent, single msg, single iovec so
     * shouldn't worry about partial sends */
    assert(mmsg.rc == my_data_len);
}