2 files changed, 84 insertions, 0 deletions

diff --git a/include/linux/reboot.h b/include/linux/reboot.h
index 48bf152761c7..67fc8fcdc4b0 100644
--- a/include/linux/reboot.h
+++ b/include/linux/reboot.h
@@ -38,6 +38,9 @@ extern int reboot_force;
 extern int register_reboot_notifier(struct notifier_block *);
 extern int unregister_reboot_notifier(struct notifier_block *);
 
+extern int register_restart_handler(struct notifier_block *);
+extern int unregister_restart_handler(struct notifier_block *);
+extern void do_kernel_restart(char *cmd);
 
 /*
  * Architecture-specific implementations of sys_reboot commands.
diff --git a/kernel/reboot.c b/kernel/reboot.c
index a3a9e240fcdb..5925f5ae8dff 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -104,6 +104,87 @@ int unregister_reboot_notifier(struct notifier_block *nb)
 }
 EXPORT_SYMBOL(unregister_reboot_notifier);
 
+/*
+ *      Notifier list for kernel code which wants to be called
+ *      to restart the system.
+ */
+static ATOMIC_NOTIFIER_HEAD(restart_handler_list);
+
+/**
+ *      register_restart_handler - Register function to be called to reset
+ *                                 the system
+ *      @nb: Info about handler function to be called
+ *      @nb->priority:  Handler priority. Handlers should follow the
+ *                      following guidelines for setting priorities.
+ *                      0:      Restart handler of last resort,
+ *                              with limited restart capabilities
+ *                      128:    Default restart handler; use if no other
+ *                              restart handler is expected to be available,
+ *                              and/or if restart functionality is
+ *                              sufficient to restart the entire system
+ *                      255:    Highest priority restart handler, will
+ *                              preempt all other restart handlers
+ *
+ *      Registers a function with code to be called to restart the
+ *      system.
+ *
+ *      Registered functions will be called from machine_restart as last
+ *      step of the restart sequence (if the architecture specific
+ *      machine_restart function calls do_kernel_restart - see below
+ *      for details).
+ *      Registered functions are expected to restart the system immediately.
+ *      If more than one function is registered, the restart handler priority
+ *      selects which function will be called first.
+ *
+ *      Restart handlers are expected to be registered from non-architecture
+ *      code, typically from drivers. A typical use case would be a system
+ *      where restart functionality is provided through a watchdog. Multiple
+ *      restart handlers may exist; for example, one restart handler might
+ *      restart the entire system, while another only restarts the CPU.
+ *      In such cases, the restart handler which only restarts part of the
+ *      hardware is expected to register with low priority to ensure that
+ *      it only runs if no other means to restart the system is available.
+ *
+ *      Currently always returns zero, as atomic_notifier_chain_register()
+ *      always returns zero.
+ */
+int register_restart_handler(struct notifier_block *nb)
+{
+        return atomic_notifier_chain_register(&restart_handler_list, nb);
+}
+EXPORT_SYMBOL(register_restart_handler);
+
+/**
+ *      unregister_restart_handler - Unregister previously registered
+ *                                   restart handler
+ *      @nb: Hook to be unregistered
+ *
+ *      Unregisters a previously registered restart handler function.
+ *
+ *      Returns zero on success, or %-ENOENT on failure.
+ */
+int unregister_restart_handler(struct notifier_block *nb)
+{
+        return atomic_notifier_chain_unregister(&restart_handler_list, nb);
+}
+EXPORT_SYMBOL(unregister_restart_handler);
+
+/**
+ *      do_kernel_restart - Execute kernel restart handler call chain
+ *
+ *      Calls functions registered with register_restart_handler.
+ *
+ *      Expected to be called from machine_restart as last step of the restart
+ *      sequence.
+ *
+ *      Restarts the system immediately if a restart handler function has been
+ *      registered. Otherwise does nothing.
+ */
+void do_kernel_restart(char *cmd)
+{
+        atomic_notifier_call_chain(&restart_handler_list, reboot_mode, cmd);
+}
+
 void migrate_to_reboot_cpu(void)
 {
         /* The boot cpu is always logical cpu 0 */