It's in the portfns on sources: x40=; 9fs sources x40=; 9p read sources/plan9/sys/src/9/port/portfns.h | grep addclock0 Timer* addclock0link(void (*)(void), int); x40=;
and it's been that way as far back as the sources dump goes (2002). Note that this is only a (relatively) recent addition to Plan 9; in Inferno there was no extra parameter. Russ
