my $iov = pack('P'.TMPL_size_t, $_[1], $len);
my $mh = pack('PL' . # msg_name, msg_namelen (socklen_t (U32))
BYTES_4_hole . # 4-byte padding on 64-bit
my $iov = pack('P'.TMPL_size_t, $_[1], $len);
my $mh = pack('PL' . # msg_name, msg_namelen (socklen_t (U32))
BYTES_4_hole . # 4-byte padding on 64-bit