notifier: Add atomic_notifier_call_chain_is_empty()

Add atomic_notifier_call_chain_is_empty() that returns true if given atomic call chain is empty. The first user of this new notifier API function will be the kernel power-off core code that will support power-off call chains. The core code will need to check whether there is a power-off handler registered at all in order to decide whether to halt machine or power it off.

Dmitry Osipenko committed 4 years ago

Commit 13dfd971 parent 42226c92 files · +15 −0Browse files

Unified · Split

2 files

include/linux/notifier.h +2 −0
kernel/notifier.c +13 −0

include/linux/notifier.h+2−0

@@ -173,6 +173,8 @@ extern int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh · 172 unmodified lines
173	extern int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,	173	extern int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,
174	unsigned long val_up, unsigned long val_down, void *v);	174	unsigned long val_up, unsigned long val_down, void *v);
175		175
		176	extern bool atomic_notifier_call_chain_is_empty(struct atomic_notifier_head *nh);
		177
176	#define NOTIFY_DONE 0x0000 /* Don't care */	178	#define NOTIFY_DONE 0x0000 /* Don't care */
177	#define NOTIFY_OK 0x0001 /* Suits me */	179	#define NOTIFY_OK 0x0001 /* Suits me */
178	#define NOTIFY_STOP_MASK 0x8000 /* Don't call further */	180	#define NOTIFY_STOP_MASK 0x8000 /* Don't call further */

kernel/notifier.c+13−0

@@ -204,6 +204,19 @@ int atomic_notifier_call_chain(struct atomic_notifier_head *nh, · 203 unmodified lines
204	EXPORT_SYMBOL_GPL(atomic_notifier_call_chain);	204	EXPORT_SYMBOL_GPL(atomic_notifier_call_chain);
205	NOKPROBE_SYMBOL(atomic_notifier_call_chain);	205	NOKPROBE_SYMBOL(atomic_notifier_call_chain);
206		206
		207	/**
		208	* atomic_notifier_call_chain_is_empty - Check whether notifier chain is empty
		209	* @nh: Pointer to head of the atomic notifier chain
		210	*
		211	* Checks whether notifier chain is empty.
		212	*
		213	* Returns true is notifier chain is empty, false otherwise.
		214	*/
		215	bool atomic_notifier_call_chain_is_empty(struct atomic_notifier_head *nh)
		216	{
		217	return !rcu_access_pointer(nh->head);
		218	}
		219
207	/*	220	/*
208	* Blocking notifier chain routines. All access to the chain is	221	* Blocking notifier chain routines. All access to the chain is
209	* synchronized by an rwsem.	222	* synchronized by an rwsem.