fs: fs-writeback: move sysctl to fs/fs-writeback.c

The dirtytime_expire_interval belongs to fs/fs-writeback.c, move it to
fs/fs-writeback.c from /kernel/sysctl.c. And remove the useless extern
variable declaration and the function declaration from
include/linux/writeback.h

Signed-off-by: Kaixiong Yu <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>
Reviewed-by: Jeff Layton <[e-mail]>
Signed-off-by: Joel Granados <[e-mail]>

fs/fs-writeback.c

···
  * timestamps written to disk after 12 hours, but in the worst case a
  * few inodes might not their timestamps updated for 24 hours.
  */
-unsigned int dirtytime_expire_interval = 12 * 60 * 60;
+static unsigned int dirtytime_expire_interval = 12 * 60 * 60;
 
 static inline struct inode *wb_inode(struct list_head *head)
 {
···
 	schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
 }
 
-static int __init start_dirtytime_writeback(void)
-{
-	schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
-	return 0;
-}
-__initcall(start_dirtytime_writeback);
-
-int dirtytime_interval_handler(const struct ctl_table *table, int write,
+static int dirtytime_interval_handler(const struct ctl_table *table, int write,
 			       void *buffer, size_t *lenp, loff_t *ppos)
 {
 	int ret;
···
 		mod_delayed_work(system_wq, &dirtytime_work, 0);
 	return ret;
 }
+
+static const struct ctl_table vm_fs_writeback_table[] = {
+	{
+		.procname	= "dirtytime_expire_seconds",
+		.data		= &dirtytime_expire_interval,
+		.maxlen		= sizeof(dirtytime_expire_interval),
+		.mode		= 0644,
+		.proc_handler	= dirtytime_interval_handler,
+		.extra1		= SYSCTL_ZERO,
+	},
+};
+
+static int __init start_dirtytime_writeback(void)
+{
+	schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
+	register_sysctl_init("vm", vm_fs_writeback_table);
+	return 0;
+}
+__initcall(start_dirtytime_writeback);
 
 /**
  * __mark_inode_dirty -	internal function to mark an inode dirty

include/linux/writeback.h

···
 /* These are exported to sysctl. */
 extern unsigned int dirty_writeback_interval;
 extern unsigned int dirty_expire_interval;
-extern unsigned int dirtytime_expire_interval;
 extern int laptop_mode;
-
-int dirtytime_interval_handler(const struct ctl_table *table, int write,
-		void *buffer, size_t *lenp, loff_t *ppos);
 
 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty);
 unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh);

kernel/sysctl.c

···
 
 static const struct ctl_table vm_table[] = {
 	{
-		.procname	= "dirtytime_expire_seconds",
-		.data		= &dirtytime_expire_interval,
-		.maxlen		= sizeof(dirtytime_expire_interval),
-		.mode		= 0644,
-		.proc_handler	= dirtytime_interval_handler,
-		.extra1		= SYSCTL_ZERO,
-	},
-	{
 		.procname	= "drop_caches",
 		.data		= &sysctl_drop_caches,
 		.maxlen		= sizeof(int),