ppp_idle
((struct ppp_idle *)data)->xmit_idle = t - sc->sc_last_sent;
((struct ppp_idle *)data)->recv_idle = t - sc->sc_last_recv;
#define PPPIOCGIDLE _IOR('t', 74, struct ppp_idle) /* get idle time */
struct ppp_idle idle;
int get_idle_time(int, struct ppp_idle *);
get_idle_time(int u, struct ppp_idle *ip)