datapath: compat: Introduce static key support

Static keys allow the inclusion of seldom used features in
performance-sensitive fast-path kernel code, via a GCC feature and a
code patching technique. For more information:
    * https://www.kernel.org/doc/Documentation/static-keys.txt

Since upstream ovs kernel module now uses some static key API that was
introduced in v4.3 kernel, we shall backport them to the compat module
for older kernel supprots.

This backport is based on upstream net-next commit 11276d5306b8
("locking/static_keys: Add a new static_key interface").

Signed-off-by: Yi-Hung Wei <yihung.wei@gmail.com>
Signed-off-by: Justin Pettit <jpettit@ovn.org>

2 files changed, 71 insertions, 0 deletions

diff --git a/datapath/linux/Modules.mk b/datapath/linux/Modules.mk
index f5c3b6580..2fec6500e 100644
--- a/datapath/linux/Modules.mk
+++ b/datapath/linux/Modules.mk
@@ -63,6 +63,7 @@ openvswitch_headers += \
 	linux/compat/include/linux/reciprocal_div.h \
 	linux/compat/include/linux/rtnetlink.h \
 	linux/compat/include/linux/skbuff.h \
+	linux/compat/include/linux/static_key.h \
 	linux/compat/include/linux/stddef.h \
 	linux/compat/include/linux/types.h \
 	linux/compat/include/linux/u64_stats_sync.h \
diff --git a/datapath/linux/compat/include/linux/static_key.h b/datapath/linux/compat/include/linux/static_key.h
new file mode 100644
index 000000000..ea59e3e28
--- /dev/null
+++ b/datapath/linux/compat/include/linux/static_key.h
@@ -0,0 +1,70 @@
+#ifndef _STATIC_KEY_WRAPPER_H
+#define _STATIC_KEY_WRAPPER_H
+
+#include_next <linux/static_key.h>
+#ifndef HAVE_UPSTREAM_STATIC_KEY
+/*
+ * This backport is based on upstream net-next commit 11276d5306b8
+ * ("locking/static_keys: Add a new static_key interface").
+ *
+ * For kernel that does not support the new static key interface,
+ * we do not backport the jump label support but the fall back version
+ * of static key that is simply a conditional branch.
+ */
+
+struct static_key_true {
+	struct static_key key;
+};
+
+struct static_key_false {
+	struct static_key key;
+};
+
+#define rpl_STATIC_KEY_INIT_TRUE	{ .enabled = ATOMIC_INIT(1) }
+#define rpl_STATIC_KEY_INIT_FALSE	{ .enabled = ATOMIC_INIT(0) }
+
+#define STATIC_KEY_TRUE_INIT	\
+	(struct static_key_true) { .key = rpl_STATIC_KEY_INIT_TRUE,  }
+#define STATIC_KEY_FALSE_INIT	\
+	(struct static_key_false){ .key = rpl_STATIC_KEY_INIT_FALSE, }
+
+#define DEFINE_STATIC_KEY_TRUE(name)	\
+	struct static_key_true name = STATIC_KEY_TRUE_INIT
+
+#define DEFINE_STATIC_KEY_FALSE(name)	\
+	struct static_key_false name = STATIC_KEY_FALSE_INIT
+
+static inline int rpl_static_key_count(struct static_key *key)
+{
+	return atomic_read(&key->enabled);
+}
+
+static inline void rpl_static_key_enable(struct static_key *key)
+{
+	int count = rpl_static_key_count(key);
+
+	WARN_ON_ONCE(count < 0 || count > 1);
+
+	if (!count)
+		static_key_slow_inc(key);
+}
+
+static inline void rpl_static_key_disable(struct static_key *key)
+{
+	int count = rpl_static_key_count(key);
+
+	WARN_ON_ONCE(count < 0 || count > 1);
+
+	if (count)
+		static_key_slow_dec(key);
+}
+
+#define static_branch_likely(x)		likely(static_key_enabled(&(x)->key))
+#define static_branch_unlikely(x)	unlikely(static_key_enabled(&(x)->key))
+
+#define static_branch_enable(x)		rpl_static_key_enable(&(x)->key)
+#define static_branch_disable(x)	rpl_static_key_disable(&(x)->key)
+
+#endif /* HAVE_UPSTREAM_STATIC_KEY */
+
+#endif /* _STATIC_KEY_WRAPPER_H */