while ( 1 )
{
      bzero(&clientaddr, sizeof(struct sockaddr_un));
      slen = 0;
      rn = recvfrom(fd,buf, sizeof(buf), 0 ,(struct sockaddr *)&clientaddr, slen);
      if ( rn == -1)
      {
                perror("recvfrom");
      } 
      buf[n] = 0;   
}

　　ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags, struct sockaddr *src_addr, socklen_t *addrlen);

=====================================================================================================================
　　　　If  src_addr  is  not  NULL,  and  the underlying protocol provides the
       source address, this source address is filled  in.   When  src_addr  is
       NULL,  nothing  is  filled  in;  in this case, addrlen is not used, and
       should also be NULL.  The argument addrlen is a value-result  argument,
       which  the  caller should initialize before the call to the size of the
       buffer associated with src_addr, and modified on return to indicate the
       actual  size  of the source address.  The returned address is truncated
       if the buffer provided is too small; in this case, addrlen will  return
       a value greater than was supplied to the call.