Zero-Copy Send with Multiple Messages and Buffers

Figure 1. Zero-Copy with Multiple Messages and Buffers Example

#define N_BUFFERS 2
#define N_MSGS 2
struct onload_zc_iovec iovec[N_MSGS][N_BUFFERS];
struct onload_zc_mmsg mmsg[N_MSGS];
for( i = 0; i < N_MSGS; ++i ) {
  rc = onload_zc_alloc_buffers(fd, iovec[i], N_BUFFERS,
                               ONLOAD_ZC_BUFFER_HDR_TCP);
  assert(rc == 0);
  /* TODO store data in iovec[i][j].iov_base,
   * set iovec[i][j]iov_len */
  mmsg[i]fd = fd; /* Could be different for each message */
  mmsg[i].iov = iovec[i];
  mmsg[i].msg.msghdr.msg_iovlen = N_BUFFERS;
}
rc = onload_zc_send(mmsg, N_MSGS, 0);
if( rc <= 0 ) {
  /* Probably application bug */
  return rc;
} else {
  for( i = 0; i < N_MSGS; ++i ) {
    if( i < rc ) {
      /* mmsg[i] is set and we can use it */
      if( mmsg[i] < 0) {
        /* error sending this message - release buffers */
        for( j = 0; j < N_BUFFERS; ++j )
          onload_zc_release_buffers(fd, &iovec[i][j].buf, 1);
      } else if( mmsg(i] < sum_over_j(iovec[i][j].iov_len) ) {
        /* partial success */
        /* TODO use mmsg[i] to determine which buffers in
         * iovec[i] array are sent and which are still
         * owned by application */
      } else {
        /* Whole message sent, buffers now owned by Onload */
      }
    } else {
      /* mmsg[i] is not set, this message was not sent */
      for( j = 0; j < N_BUFFERS; ++j )
        onload_zc_release_buffers(fd, &iovec[i][j].buf, 1);
    }
  }
}