inet_drv.c

#if  defined(IP_TOS) && defined(SOL_IP) && defined(SO_PRIORITY)
static int setopt_prio_tos_trick
        (int fd, int proto, int type, char* arg_ptr, int arg_sz, int propagate)
{
    /* The relations between SO_PRIORITY, TOS and other options
       is not what you (or at least I) would expect...:
       If TOS is set after priority, priority is zeroed.
       If any other option is set after tos, tos might be zeroed.
       Therefore, save tos and priority. If something else is set, 
       restore both after setting, if  tos is set, restore only 
       prio and if prio is set restore none... All to keep the
       user feeling socket options are independent. /PaN */