kernfs: move struct kernfs_root out of the public view.

There is no need to have struct kernfs_root be part of kernfs.h for
the whole kernel to see and poke around it. Move it internal to kernfs
code and provide a helper function, kernfs_root_to_node(), to handle the
one field that kernfs users were directly accessing from the structure.

Cc: Imran Khan <[e-mail]>
Acked-by: Tejun Heo <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

arch/x86/kernel/cpu/resctrl/rdtgroup.c

···
 
 	list_add(&rdtgroup_default.rdtgroup_list, &rdt_all_groups);
 
-	ret = rdtgroup_add_files(rdt_root->kn, RF_CTRL_BASE);
+	ret = rdtgroup_add_files(kernfs_root_to_node(rdt_root), RF_CTRL_BASE);
 	if (ret) {
 		kernfs_destroy_root(rdt_root);
 		goto out;
 	}
 
-	rdtgroup_default.kn = rdt_root->kn;
+	rdtgroup_default.kn = kernfs_root_to_node(rdt_root);
 	kernfs_activate(rdtgroup_default.kn);
 
 out:

fs/kernfs/dir.c

···
 }
 
 /**
+ * kernfs_root_to_node - return the kernfs_node associated with a kernfs_root
+ * @root: root to use to lookup
+ */
+struct kernfs_node *kernfs_root_to_node(struct kernfs_root *root)
+{
+	return root->kn;
+}
+
+/**
  * kernfs_create_dir_ns - create a directory
  * @parent: parent in which to create a new directory
  * @name: name of the new directory

fs/kernfs/kernfs-internal.h

···
 	atomic_t		user_xattr_size;
 };
 
+struct kernfs_root {
+	/* published fields */
+	struct kernfs_node	*kn;
+	unsigned int		flags;	/* KERNFS_ROOT_* flags */
+
+	/* private fields, do not use outside kernfs proper */
+	struct idr		ino_idr;
+	u32			last_id_lowbits;
+	u32			id_highbits;
+	struct kernfs_syscall_ops *syscall_ops;
+
+	/* list of kernfs_super_info of this root, protected by kernfs_rwsem */
+	struct list_head	supers;
+
+	wait_queue_head_t	deactivate_waitq;
+	struct rw_semaphore	kernfs_rwsem;
+};
+
 /* +1 to avoid triggering overflow warning when negating it */
 #define KN_DEACTIVATED_BIAS		(INT_MIN + 1)
 

fs/sysfs/mount.c

···
 	if (IS_ERR(sysfs_root))
 		return PTR_ERR(sysfs_root);
 
-	sysfs_root_kn = sysfs_root->kn;
+	sysfs_root_kn = kernfs_root_to_node(sysfs_root);
 
 	err = register_filesystem(&sysfs_fs_type);
 	if (err) {

include/linux/kernfs.h

···
 			 struct kernfs_root *root);
 };
 
+#if 0
 struct kernfs_root {
 	/* published fields */
 	struct kernfs_node	*kn;
···
 	wait_queue_head_t	deactivate_waitq;
 	struct rw_semaphore	kernfs_rwsem;
 };
+#endif
+
+struct kernfs_node *kernfs_root_to_node(struct kernfs_root *root);
 
 struct kernfs_open_file {
 	/* published fields */

kernel/cgroup/cgroup.c

···
 
 struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
 {
-	struct cgroup *root_cgrp = kf_root->kn->priv;
+	struct cgroup *root_cgrp = kernfs_root_to_node(kf_root)->priv;
 
 	return root_cgrp->root;
 }
···
 		ret = PTR_ERR(root->kf_root);
 		goto exit_root_id;
 	}
-	root_cgrp->kn = root->kf_root->kn;
+	root_cgrp->kn = kernfs_root_to_node(root->kf_root);
 	WARN_ON_ONCE(cgroup_ino(root_cgrp) != 1);
 	root_cgrp->ancestor_ids[0] = cgroup_id(root_cgrp);