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Subject[PATCH v1 1/6] notifier: Add blocking_notifier_call_chain_empty()
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Add blocking_notifier_call_chain_empty() that returns true if call chain
is empty and false otherwise.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
include/linux/notifier.h | 2 ++
kernel/notifier.c | 14 ++++++++++++++
2 files changed, 16 insertions(+)

diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index 87069b8459af..f0b1d600d9f6 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_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 b8251dc0bc0f..1f7ba8988b90 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -322,6 +322,20 @@ int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
}
EXPORT_SYMBOL_GPL(blocking_notifier_call_chain);

+/**
+ * blocking_notifier_call_chain_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_empty(struct blocking_notifier_head *nh)
+{
+ return !rcu_access_pointer(nh->head);
+}
+EXPORT_SYMBOL_GPL(blocking_notifier_call_chain_empty);
+
/*
* Raw notifier chain routines. There is no protection;
* the caller must provide it. Use at your own risk!
--
2.32.0
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