[PATCH] vfs: use kstrdup() and check failing allocation

- use kstrdup() instead of kmalloc() + memcpy()
- return NULL if allocating ->mnt_devname failed
- mnt_devname should be const

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/mount.h

@@ -47,7 +47,7 @@ struct vfsmount {
 	struct list_head mnt_child;	/* and going through their mnt_child */
 	int mnt_flags;
 	/* 4 bytes hole on 64bits arches */
-	char *mnt_devname;		/* Name of device e.g. /dev/dsk/hda1 */
+	const char *mnt_devname;	/* Name of device e.g. /dev/dsk/hda1 */
 	struct list_head mnt_list;
 	struct list_head mnt_expire;	/* link in fs-specific expiry list */
 	struct list_head mnt_share;	/* circular list of shared mounts */