[PATCH 1/5] rcusync: introduce struct rcu_sync_ops

[Oleg Nesterov <oleg@redhat.com>]

Add the new struct rcu_sync_ops which holds sync/call methods, and
turn the function pointers in rcu_sync_struct into the single pointer
to struct rcu_sync_ops.

This simplifies the "init" helpers, and this way it is simpler to add
the new methods we need, especially ifdef'ed.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 include/linux/rcusync.h |   63 +++++++++++++++++++++--------------------------
 kernel/rcusync.c        |   40 ++++++++++++++---------------
 2 files changed, 47 insertions(+), 56 deletions(-)

diff --git a/include/linux/rcusync.h b/include/linux/rcusync.h
index 7858491..30c6037 100644
--- a/include/linux/rcusync.h
+++ b/include/linux/rcusync.h
@@ -4,6 +4,11 @@
 #include <linux/wait.h>
 #include <linux/rcupdate.h>
 
+struct rcu_sync_ops {
+	void (*sync)(void);
+	void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
+};
+
 struct rcu_sync_struct {
 	int			gp_state;
 	int			gp_count;
@@ -12,43 +17,9 @@ struct rcu_sync_struct {
 	int			cb_state;
 	struct rcu_head		cb_head;
 
-	void (*sync)(void);
-	void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
+	struct rcu_sync_ops	*ops;
 };
 
-#define ___RCU_SYNC_INIT(name)						\
-	.gp_state = 0,							\
-	.gp_count = 0,							\
-	.gp_wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.gp_wait),		\
-	.cb_state = 0
-
-#define __RCU_SCHED_SYNC_INIT(name) {					\
-	___RCU_SYNC_INIT(name),						\
-	.sync = synchronize_sched,					\
-	.call = call_rcu_sched,						\
-}
-
-#define __RCU_BH_SYNC_INIT(name) {					\
-	___RCU_SYNC_INIT(name),						\
-	.sync = synchronize_rcu_bh,					\
-	.call = call_rcu_bh,						\
-}
-
-#define __RCU_SYNC_INIT(name) {						\
-	___RCU_SYNC_INIT(name),						\
-	.sync = synchronize_rcu,					\
-	.call = call_rcu,						\
-}
-
-#define DEFINE_RCU_SCHED_SYNC(name)					\
-	struct rcu_sync_struct name = __RCU_SCHED_SYNC_INIT(name)
-
-#define DEFINE_RCU_BH_SYNC(name)					\
-	struct rcu_sync_struct name = __RCU_BH_SYNC_INIT(name)
-
-#define DEFINE_RCU_SYNC(name)						\
-	struct rcu_sync_struct name = __RCU_SYNC_INIT(name)
-
 static inline bool rcu_sync_is_idle(struct rcu_sync_struct *rss)
 {
 	return !rss->gp_state; /* GP_IDLE */
@@ -60,5 +31,27 @@ extern void rcu_sync_init(struct rcu_sync_struct *, enum rcu_sync_type);
 extern void rcu_sync_enter(struct rcu_sync_struct *);
 extern void rcu_sync_exit(struct rcu_sync_struct *);
 
+extern struct rcu_sync_ops rcu_sync_ops_array[];
+
+#define __RCU_SYNC_INITIALIZER(name, type) {				\
+		.gp_state = 0,						\
+		.gp_count = 0,						\
+		.gp_wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.gp_wait),	\
+		.cb_state = 0,						\
+		.ops = rcu_sync_ops_array + (type),			\
+	}
+
+#define	__DEFINE_RCU_SYNC(name, type)	\
+	struct rcu_sync_struct name = __RCU_SYNC_INITIALIZER(name, type)
+
+#define DEFINE_RCU_SYNC(name)		\
+	__DEFINE_RCU_SYNC(name, RCU_SYNC)
+
+#define DEFINE_RCU_SCHED_SYNC(name)	\
+	__DEFINE_RCU_SYNC(name, RCU_SCHED_SYNC)
+
+#define DEFINE_RCU_BH_SYNC(name)	\
+	__DEFINE_RCU_SYNC(name, RCU_BH_SYNC)
+
 #endif /* _LINUX_RCUSYNC_H_ */
 
diff --git a/kernel/rcusync.c b/kernel/rcusync.c
index f84176a..1cefb83 100644
--- a/kernel/rcusync.c
+++ b/kernel/rcusync.c
@@ -1,4 +1,3 @@
-
 #include <linux/rcusync.h>
 #include <linux/sched.h>
 
@@ -7,27 +6,26 @@ enum { CB_IDLE = 0, CB_PENDING, CB_REPLAY };
 
 #define	rss_lock	gp_wait.lock
 
+struct rcu_sync_ops rcu_sync_ops_array[] = {
+	[RCU_SYNC] = {
+		.sync = synchronize_rcu,
+		.call = call_rcu,
+	},
+	[RCU_SCHED_SYNC] = {
+		.sync = synchronize_sched,
+		.call = call_rcu_sched,
+	},
+	[RCU_BH_SYNC] = {
+		.sync = synchronize_rcu_bh,
+		.call = call_rcu_bh,
+	},
+};
+
 void rcu_sync_init(struct rcu_sync_struct *rss, enum rcu_sync_type type)
 {
 	memset(rss, 0, sizeof(*rss));
 	init_waitqueue_head(&rss->gp_wait);
-
-	switch (type) {
-	case RCU_SYNC:
-		rss->sync = synchronize_rcu;
-		rss->call = call_rcu;
-		break;
-
-	case RCU_SCHED_SYNC:
-		rss->sync = synchronize_sched;
-		rss->call = call_rcu_sched;
-		break;
-
-	case RCU_BH_SYNC:
-		rss->sync = synchronize_rcu_bh;
-		rss->call = call_rcu_bh;
-		break;
-	}
+	rss->ops = rcu_sync_ops_array + type;
 }
 
 void rcu_sync_enter(struct rcu_sync_struct *rss)
@@ -44,7 +42,7 @@ void rcu_sync_enter(struct rcu_sync_struct *rss)
 	BUG_ON(need_wait && need_sync);
 
 	if (need_sync) {
-		rss->sync();
+		rss->ops->sync();
 		rss->gp_state = GP_PASSED;
 		wake_up_all(&rss->gp_wait);
 	} else if (need_wait) {
@@ -81,7 +79,7 @@ static void rcu_sync_func(struct rcu_head *rcu)
 		 * to catch a later GP.
 		 */
 		rss->cb_state = CB_PENDING;
-		rss->call(&rss->cb_head, rcu_sync_func);
+		rss->ops->call(&rss->cb_head, rcu_sync_func);
 	} else {
 		/*
 		 * We're at least a GP after rcu_sync_exit(); eveybody will now
@@ -99,7 +97,7 @@ void rcu_sync_exit(struct rcu_sync_struct *rss)
 	if (!--rss->gp_count) {
 		if (rss->cb_state == CB_IDLE) {
 			rss->cb_state = CB_PENDING;
-			rss->call(&rss->cb_head, rcu_sync_func);
+			rss->ops->call(&rss->cb_head, rcu_sync_func);
 		} else if (rss->cb_state == CB_PENDING) {
 			rss->cb_state = CB_REPLAY;
 		}
-- 
1.5.5.1