[PATCH v3 1/2] fs/proc: Optimize arrays defined by struct ctl_path

[Meng Tang <tangmeng@xxxxxxxxxxxxx>]

Previously, arrays defined by struct ctl_path is terminated
with an empty one. When we actually only register one ctl_path,
we've gone from 8 bytes to 16 bytes.

So, I use ARRAY_SIZE() as a boundary condition to optimize it.

Since the original __register_sysctl_paths is only used in
fs/proc/proc_sysctl.c, in order to not change the usage of
register_sysctl_paths, delete __register_sysctl_paths from
include/linux/sysctl.h, change it to __register_sysctl_paths_init
in fs/proc/proc_sysctl.c, and modify it with static.
The register_sysctl_paths becomes __register_sysctl_paths,
and the macro definition is used in include/linux/sysctl.h
to expand register_sysctl_paths(path, table) to
__register_sysctl_paths(path, ARRAY_SIZE(path), table).

Signed-off-by: Meng Tang <tangmeng@xxxxxxxxxxxxx>
---
 fs/proc/proc_sysctl.c  | 22 +++++++++++++---------
 include/linux/sysctl.h |  9 ++++-----
 2 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 9ecd5c87e8dd..721a8bec63d6 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -1589,9 +1589,10 @@ static int register_leaf_sysctl_tables(const char *path, char *pos,
 }
 
 /**
- * __register_sysctl_paths - register a sysctl table hierarchy
+ * __register_sysctl_paths_init - register a sysctl table hierarchy
  * @set: Sysctl tree to register on
  * @path: The path to the directory the sysctl table is in.
+ * @ctl_path_num: The numbers(ARRAY_SIZE(path)) of ctl_path
  * @table: the top-level table structure
  *
  * Register a sysctl table hierarchy. @table should be a filled in ctl_table
@@ -1599,22 +1600,23 @@ static int register_leaf_sysctl_tables(const char *path, char *pos,
  *
  * See __register_sysctl_table for more details.
  */
-struct ctl_table_header *__register_sysctl_paths(
+static struct ctl_table_header *__register_sysctl_paths_init(
 	struct ctl_table_set *set,
-	const struct ctl_path *path, struct ctl_table *table)
+	const struct ctl_path *path, int ctl_path_num, struct ctl_table *table)
 {
 	struct ctl_table *ctl_table_arg = table;
 	int nr_subheaders = count_subheaders(table);
 	struct ctl_table_header *header = NULL, **subheaders, **subheader;
 	const struct ctl_path *component;
 	char *new_path, *pos;
+	int i;
 
 	pos = new_path = kmalloc(PATH_MAX, GFP_KERNEL);
 	if (!new_path)
 		return NULL;
 
 	pos[0] = '\0';
-	for (component = path; component->procname; component++) {
+	for (component = path, i = 0; component->procname && i < ctl_path_num; component++, i++) {
 		pos = append_path(new_path, pos, component->procname);
 		if (!pos)
 			goto out;
@@ -1663,20 +1665,22 @@ struct ctl_table_header *__register_sysctl_paths(
 /**
  * register_sysctl_paths - register a sysctl table hierarchy
  * @path: The path to the directory the sysctl table is in.
+ * @ctl_path_num: The numbers(ARRAY_SIZE(path)) of ctl_path
  * @table: the top-level table structure
  *
  * Register a sysctl table hierarchy. @table should be a filled in ctl_table
  * array. A completely 0 filled entry terminates the table.
  *
- * See __register_sysctl_paths for more details.
+ * See __register_sysctl_paths_init for more details.
  */
-struct ctl_table_header *register_sysctl_paths(const struct ctl_path *path,
+struct ctl_table_header *__register_sysctl_paths(const struct ctl_path *path,
+						int ctl_path_num,
 						struct ctl_table *table)
 {
-	return __register_sysctl_paths(&sysctl_table_root.default_set,
-					path, table);
+	return __register_sysctl_paths_init(&sysctl_table_root.default_set,
+					path, ctl_path_num, table);
 }
-EXPORT_SYMBOL(register_sysctl_paths);
+EXPORT_SYMBOL(__register_sysctl_paths);
 
 /**
  * register_sysctl_table - register a sysctl table hierarchy
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 889c995d8a08..37958aeecfb5 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -219,13 +219,12 @@ extern void retire_sysctl_set(struct ctl_table_set *set);
 struct ctl_table_header *__register_sysctl_table(
 	struct ctl_table_set *set,
 	const char *path, struct ctl_table *table);
-struct ctl_table_header *__register_sysctl_paths(
-	struct ctl_table_set *set,
-	const struct ctl_path *path, struct ctl_table *table);
 struct ctl_table_header *register_sysctl(const char *path, struct ctl_table *table);
 struct ctl_table_header *register_sysctl_table(struct ctl_table * table);
-struct ctl_table_header *register_sysctl_paths(const struct ctl_path *path,
-						struct ctl_table *table);
+#define register_sysctl_paths(path, table) \
+	__register_sysctl_paths(path, ARRAY_SIZE(path), table)
+extern struct ctl_table_header *__register_sysctl_paths(const struct ctl_path *path,
+						int ctl_path_num, struct ctl_table *table);
 
 void unregister_sysctl_table(struct ctl_table_header * table);
 
-- 
2.20.1