kernfs: introduce kernfs_pin_sb()

	kernfs_put(root_kn);

}

/**

 * kernfs_pin_sb: try to pin the superblock associated with a kernfs_root

 * @kernfs_root: the kernfs_root in question

 * @ns: the namespace tag

 *

 * Pin the superblock so the superblock won't be destroyed in subsequent

 * operations.  This can be used to block ->kill_sb() which may be useful

 * for kernfs users which dynamically manage superblocks.

 *

 * Returns NULL if there's no superblock associated to this kernfs_root, or

 * -EINVAL if the superblock is being freed.

 */

struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns)

{

	struct kernfs_super_info *info;

	struct super_block *sb = NULL;

	mutex_lock(&kernfs_mutex);

	list_for_each_entry(info, &root->supers, node) {

		if (info->ns == ns) {

			sb = info->sb;

			if (!atomic_inc_not_zero(&info->sb->s_active))

				sb = ERR_PTR(-EINVAL);

			break;

		}

	}

	mutex_unlock(&kernfs_mutex);

	return sb;

}

void __init kernfs_init(void)

{

	kernfs_node_cache = kmem_cache_create("kernfs_node_cache",

			       struct kernfs_root *root, unsigned long magic,

			       bool *new_sb_created, const void *ns);

void kernfs_kill_sb(struct super_block *sb);

struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns);

void kernfs_init(void);