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

Showing the changes to kernel (1 of 2 files). Show all

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kernel/notifier.c+13−0

@@ -204,6 +204,19 @@ int atomic_notifier_call_chain(struct atomic_notifier_head *nh, · 203 unmodified lines
204	204	EXPORT_SYMBOL_GPL(atomic_notifier_call_chain);
205	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	221	* Blocking notifier chain routines. All access to the chain is
209	222	* synchronized by an rwsem.