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 <[email protected]>
Signed-off-by: Dmitry Osipenko <[email protected]>
---
Changelog:
v9: - Extended commit message with a usage example.
- Corrected doc-comment with s/blocking/atomic/.
include/linux/notifier.h | 2 ++
kernel/notifier.c | 13 +++++++++++++
2 files changed, 15 insertions(+)
diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index 87069b8459af..95e2440037de 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -173,6 +173,8 @@ extern int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh
extern int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,
unsigned long val_up, unsigned long val_down, void *v);
+extern bool atomic_notifier_call_chain_is_empty(struct atomic_notifier_head *nh);
+
#define NOTIFY_DONE 0x0000 /* Don't care */
#define NOTIFY_OK 0x0001 /* Suits me */
#define NOTIFY_STOP_MASK 0x8000 /* Don't call further */
diff --git a/kernel/notifier.c b/kernel/notifier.c
index ba005ebf4730..ea7524522de4 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -204,6 +204,19 @@ int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
EXPORT_SYMBOL_GPL(atomic_notifier_call_chain);
NOKPROBE_SYMBOL(atomic_notifier_call_chain);
+/**
+ * atomicnotifier_call_chain_is_empty - Check whether notifier chain is empty
+ * @nh: Pointer to head of the atomic notifier chain
+ *
+ * Checks whether notifier chain is empty.
+ *
+ * Returns true is notifier chain is empty, false otherwise.
+ */
+bool atomic_notifier_call_chain_is_empty(struct atomic_notifier_head *nh)
+{
+ return !rcu_access_pointer(nh->head);
+}
+
/*
* Blocking notifier chain routines. All access to the chain is
* synchronized by an rwsem.
--
2.35.3