ref: d95be792d6b5e4a2f9f1615a40492020c764ee30
dir: /sys/src/libc/port/hangup.c/
#include <u.h>
#include <libc.h>
#include <ctype.h>
/*
* force a connection to hangup
*/
int
hangup(int ctl)
{
static char msg[] = "hangup";
return write(ctl, msg, sizeof(msg)-1) != sizeof(msg)-1;
}