kernfs: move the last knowledge of sysfs out from kernfs

There is still one residue of sysfs remaining: the sb_magic
SYSFS_MAGIC. However this should be kernfs user specific,
so this patch moves it out. Kerrnfs user should specify their
magic number while mouting.

Signed-off-by: Jianyu Zhan <[e-mail]>
Acked-by: Tejun Heo <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

fs/kernfs/mount.c

···
 	return NULL;
 }
 
-static int kernfs_fill_super(struct super_block *sb)
+static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
 {
 	struct kernfs_super_info *info = kernfs_info(sb);
 	struct inode *inode;
···
 	info->sb = sb;
 	sb->s_blocksize = PAGE_CACHE_SIZE;
 	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
-	sb->s_magic = SYSFS_MAGIC;
+	sb->s_magic = magic;
 	sb->s_op = &kernfs_sops;
 	sb->s_time_gran = 1;
 
···
  * @fs_type: file_system_type of the fs being mounted
  * @flags: mount flags specified for the mount
  * @root: kernfs_root of the hierarchy being mounted
+ * @magic: file system specific magic number
  * @new_sb_created: tell the caller if we allocated a new superblock
  * @ns: optional namespace tag of the mount
  *
···
  * The return value can be passed to the vfs layer verbatim.
  */
 struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
-			       struct kernfs_root *root, bool *new_sb_created,
-			       const void *ns)
+				struct kernfs_root *root, unsigned long magic,
+				bool *new_sb_created, const void *ns)
 {
 	struct super_block *sb;
 	struct kernfs_super_info *info;
···
 	if (!sb->s_root) {
 		struct kernfs_super_info *info = kernfs_info(sb);
 
-		error = kernfs_fill_super(sb);
+		error = kernfs_fill_super(sb, magic);
 		if (error) {
 			deactivate_locked_super(sb);
 			return ERR_PTR(error);

fs/sysfs/mount.c

···
 #define DEBUG
 
 #include <linux/fs.h>
+#include <linux/magic.h>
 #include <linux/mount.h>
 #include <linux/init.h>
 #include <linux/user_namespace.h>
···
 	}
 
 	ns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
-	root = kernfs_mount_ns(fs_type, flags, sysfs_root, &new_sb, ns);
+	root = kernfs_mount_ns(fs_type, flags, sysfs_root,
+				SYSFS_MAGIC, &new_sb, ns);
 	if (IS_ERR(root) || !new_sb)
 		kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
 	return root;

include/linux/kernfs.h

···
 
 const void *kernfs_super_ns(struct super_block *sb);
 struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
-			       struct kernfs_root *root, bool *new_sb_created,
-			       const void *ns);
+			       struct kernfs_root *root, unsigned long magic,
+			       bool *new_sb_created, const void *ns);
 void kernfs_kill_sb(struct super_block *sb);
 
 void kernfs_init(void);
···
 
 static inline struct dentry *
 kernfs_mount_ns(struct file_system_type *fs_type, int flags,
-		struct kernfs_root *root, bool *new_sb_created, const void *ns)
+		struct kernfs_root *root, unsigned long magic,
+		bool *new_sb_created, const void *ns)
 { return ERR_PTR(-ENOSYS); }
 
 static inline void kernfs_kill_sb(struct super_block *sb) { }
···
 
 static inline struct dentry *
 kernfs_mount(struct file_system_type *fs_type, int flags,
-	     struct kernfs_root *root, bool *new_sb_created)
+		struct kernfs_root *root, unsigned long magic,
+		bool *new_sb_created)
 {
-	return kernfs_mount_ns(fs_type, flags, root, new_sb_created, NULL);
+	return kernfs_mount_ns(fs_type, flags, root,
+				magic, new_sb_created, NULL);
 }
 
 #endif	/* __LINUX_KERNFS_H */

kernel/cgroup.c

···
 #include <linux/init_task.h>
 #include <linux/kernel.h>
 #include <linux/list.h>
+#include <linux/magic.h>
 #include <linux/mm.h>
 #include <linux/mutex.h>
 #include <linux/mount.h>
···
 	if (ret)
 		return ERR_PTR(ret);
 
-	dentry = kernfs_mount(fs_type, flags, root->kf_root, &new_sb);
+	dentry = kernfs_mount(fs_type, flags, root->kf_root,
+				CGROUP_SUPER_MAGIC, &new_sb);
 	if (IS_ERR(dentry) || !new_sb)
 		cgroup_put(&root->cgrp);
 	return dentry;