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. Reviewed-by: Michał Mirosław <mirq-linux@rere.qmqm.pl> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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@ -173,6 +173,8 @@ extern int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh
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extern int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,
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unsigned long val_up, unsigned long val_down, void *v);
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extern bool atomic_notifier_call_chain_is_empty(struct atomic_notifier_head *nh);
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#define NOTIFY_DONE 0x0000 /* Don't care */
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#define NOTIFY_OK 0x0001 /* Suits me */
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#define NOTIFY_STOP_MASK 0x8000 /* Don't call further */
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@ -204,6 +204,19 @@ int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
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EXPORT_SYMBOL_GPL(atomic_notifier_call_chain);
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NOKPROBE_SYMBOL(atomic_notifier_call_chain);
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/**
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* atomic_notifier_call_chain_is_empty - Check whether notifier chain is empty
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* @nh: Pointer to head of the atomic notifier chain
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*
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* Checks whether notifier chain is empty.
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*
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* Returns true is notifier chain is empty, false otherwise.
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*/
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bool atomic_notifier_call_chain_is_empty(struct atomic_notifier_head *nh)
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{
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return !rcu_access_pointer(nh->head);
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}
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/*
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* Blocking notifier chain routines. All access to the chain is
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* synchronized by an rwsem.
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