linux-kernel - [PATCH v6 01/21] notifier: Add blocking_notifier_call_chain_is

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Date:   Mon, 31 Jan 2022 02:36:58 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Guo Ren <guoren@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Joshua Thompson <funaho@...ai.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Sebastian Reichel <sre@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Helge Deller <deller@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
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        Andrew Morton <akpm@...ux-foundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Ulf Hansson <ulf.hansson@...aro.org>, alankao@...estech.com,
        "K . C . Kuen-Chern Lin" <kclin@...estech.com>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:     linux-kernel@...r.kernel.org, linux-csky@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
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Subject: [PATCH v6 01/21] notifier: Add blocking_notifier_call_chain_is_empty()

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

Signed-off-by: Dmitry Osipenko <digetx@...il.com>
---
 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