[PATCH v6 01/21] notifier: Add blocking_notifier_call_chain_is_empty()

[Dmitry Osipenko <digetx@xxxxxxxxx>]

Add blocking_notifier_call_chain_is_empty() that returns true if call
chain is empty.

Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
---
 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..d4717bc0ab85 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 blocking_notifier_call_chain_is_empty(struct 
blocking_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..4ed6bda8f127 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -323,6 +323,19 @@ int blocking_notifier_call_chain(struct 
blocking_notifier_head *nh,
 }
 EXPORT_SYMBOL_GPL(blocking_notifier_call_chain);
 
+/**
+ *     blocking_notifier_call_chain_is_empty - Check whether notifier chain is 
empty
+ *     @nh: Pointer to head of the blocking notifier chain
+ *
+ *     Checks whether notifier chain is empty.
+ *
+ *     Returns true is notifier chain is empty, false otherwise.
+ */
+bool blocking_notifier_call_chain_is_empty(struct blocking_notifier_head *nh)
+{
+       return !rcu_access_pointer(nh->head);
+}
+
 /*
  *     Raw notifier chain routines.  There is no protection;
  *     the caller must provide it.  Use at your own risk!
-- 
2.34.1