Bug 128036

System with serial console.

If the system is shutdown by "shutdown -h ..." the following prompt is displayed on the console:

"The operating system has halted.
Please press any key to reboot."

Often a single keypress is not recognised; multiple keypresses are often required for the system to reboot.

Fix: 

In sys/dev/sio.c, function siocnclose() change

    outb(iobase + com_mcr, sp->mcr | MCR_DTR | MCR_RTS);
    outb(iobase + com_ier, sp->ier);
to
    outb(iobase + com_mcr, sp->mcr | MCR_DTR | MCR_RTS);
    if (rebooting == 0) {
        /*
         * Only restore the interrupt enables if not rebooting. If 
	 * rebooting leave interrupts disabled, else a key press might be 
	 * swallowed by the interrupt handler and not seen by the shutdown code.
	 */
        outb(iobase + com_ier, sp->ier);
    }

The problem is that the shutdown code looking for a keypress on the console (loop in sys/kern/kern_shutdown.c function shutdown_halt) runs with console interrupts enabled. If the keypress generates a console interrupt then the keypress is swallowed by the console interrupt handler and not seen by the code polling for a keypress.
How-To-Repeat: On system with serial console, issue 

# shutdown -h now 

command