Entry Point halt()

Entry Point halt()

The kernel calls the pfxhalt() entry point, if one exists, while performing an orderly system shutdown (see the halt(1) reference page). No other driver entry points are called after this one. The prototype is simply

void pfxhalt(void);

Since the system is shutting down, there is no point in returning allocated memory. The only purpose this entry point can serve is to leave the device in a safe and stable condition. For example, this is the place at which a disk driver could command the heads of the drive to move to a safe zone for power off.

The driver cannot assume that interrupts are disabled or enabled. The driver cannot block waiting for device actions, so whatever commands it issues to the device must take effect immediately.