[PATCH 5/5] tiny-shmem: use call_once()

[Akinobu Mita <akinobu.mita@gmail.com>]

This patch defers mounting tmpfs till shmem_file_setup() is
called first time by using call_once().

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
---
 mm/tiny-shmem.c |   21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

Index: 2.6-rc/mm/tiny-shmem.c
===================================================================
--- 2.6-rc.orig/mm/tiny-shmem.c
+++ 2.6-rc/mm/tiny-shmem.c
@@ -19,6 +19,7 @@
 #include <linux/module.h>
 #include <linux/swap.h>
 #include <linux/ramfs.h>
+#include <linux/once.h>
 
 static struct file_system_type tmpfs_fs_type = {
 	.name		= "tmpfs",
@@ -26,19 +27,23 @@ static struct file_system_type tmpfs_fs_
 	.kill_sb	= kill_litter_super,
 };
 
-static struct vfsmount *shm_mnt;
-
 static int __init init_tmpfs(void)
 {
 	BUG_ON(register_filesystem(&tmpfs_fs_type) != 0);
 
-	shm_mnt = kern_mount(&tmpfs_fs_type);
-	BUG_ON(IS_ERR(shm_mnt));
-
 	return 0;
 }
 module_init(init_tmpfs)
 
+static struct vfsmount *shm_mnt;
+
+static int init_shm_mnt(void)
+{
+	shm_mnt = kern_mount(&tmpfs_fs_type);
+
+	return IS_ERR(shm_mnt) ? PTR_ERR(shm_mnt) : 0;
+}
+
 /*
  * shmem_file_setup - get an unlinked file living in tmpfs
  *
@@ -53,9 +58,11 @@ struct file *shmem_file_setup(char *name
 	struct inode *inode;
 	struct dentry *dentry, *root;
 	struct qstr this;
+	static DEFINE_ONCE(once);
 
-	if (IS_ERR(shm_mnt))
-		return (void *)shm_mnt;
+	error = call_once(&once, init_shm_mnt);
+	if (error)
+		return ERR_PTR(error);
 
 	error = -ENOMEM;
 	this.name = name;