kernel/reboot: Add SYS_OFF_MODE_RESTART_PREPARE mode

Add SYS_OFF_MODE_RESTART_PREPARE callbacks to be invoked before
a system restart.

Suggested-by: Dmitry Osipenko <[email protected]>
Reviewed-by: Dmitry Osipenko <[email protected]>
Signed-off-by: Kai-Heng Feng <[email protected]>
[ rjw: Changelog edits ]
Signed-off-by: Rafael J. Wysocki <[email protected]>
diff --git a/include/linux/reboot.h b/include/linux/reboot.h
index e5d9ef88..2b6bb593 100644
--- a/include/linux/reboot.h
+++ b/include/linux/reboot.h
@@ -106,6 +106,14 @@ enum sys_off_mode {
 	SYS_OFF_MODE_POWER_OFF,
 
 	/**
+	 * @SYS_OFF_MODE_RESTART_PREPARE:
+	 *
+	 * Handlers prepare system to be restarted. Handlers are
+	 * allowed to sleep.
+	 */
+	SYS_OFF_MODE_RESTART_PREPARE,
+
+	/**
 	 * @SYS_OFF_MODE_RESTART:
 	 *
 	 * Handlers restart system. Handlers are disallowed to sleep.