driver core: make kobj_type constant.

This way instances of kobj_type (which contain function pointers) can be
stored in .rodata, which means that they cannot be [easily/accidentally]
modified at runtime.

Signed-off-by: Wedson Almeida Filho <wedsonaf@google.com>
Link: https://lore.kernel.org/r/20211224231345.777370-1-wedsonaf@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: wedsonaf

Documentation/core-api/kobject.rst

@@ -118,7 +118,7 @@ Initialization of kobjects
 Code which creates a kobject must, of course, initialize that object. Some
 of the internal fields are setup with a (mandatory) call to kobject_init()::
 
-    void kobject_init(struct kobject *kobj, struct kobj_type *ktype);
+    void kobject_init(struct kobject *kobj, const struct kobj_type *ktype);
 
 The ktype is required for a kobject to be created properly, as every kobject
 must have an associated kobj_type.  After calling kobject_init(), to
@@ -156,7 +156,7 @@ kobject_name()::
 There is a helper function to both initialize and add the kobject to the
 kernel at the same time, called surprisingly enough kobject_init_and_add()::
 
-    int kobject_init_and_add(struct kobject *kobj, struct kobj_type *ktype,
+    int kobject_init_and_add(struct kobject *kobj, const struct kobj_type *ktype,
                              struct kobject *parent, const char *fmt, ...);
 
 The arguments are the same as the individual kobject_init() and

drivers/base/bus.c

@@ -165,7 +165,7 @@ static struct kobj_type bus_ktype = {
 
 static int bus_uevent_filter(struct kset *kset, struct kobject *kobj)
 {
-	struct kobj_type *ktype = get_ktype(kobj);
+	const struct kobj_type *ktype = get_ktype(kobj);
 
 	if (ktype == &bus_ktype)
 		return 1;

drivers/base/core.c

@@ -2263,7 +2263,7 @@ static struct kobj_type device_ktype = {
 
 static int dev_uevent_filter(struct kset *kset, struct kobject *kobj)
 {
-	struct kobj_type *ktype = get_ktype(kobj);
+	const struct kobj_type *ktype = get_ktype(kobj);
 
 	if (ktype == &device_ktype) {
 		struct device *dev = kobj_to_dev(kobj);

include/linux/kobject.h

@@ -66,7 +66,7 @@ struct kobject {
 	struct list_head	entry;
 	struct kobject		*parent;
 	struct kset		*kset;
-	struct kobj_type	*ktype;
+	const struct kobj_type	*ktype;
 	struct kernfs_node	*sd; /* sysfs directory entry */
 	struct kref		kref;
 #ifdef CONFIG_DEBUG_KOBJECT_RELEASE
@@ -90,13 +90,13 @@ static inline const char *kobject_name(const struct kobject *kobj)
 	return kobj->name;
 }
 
-extern void kobject_init(struct kobject *kobj, struct kobj_type *ktype);
+extern void kobject_init(struct kobject *kobj, const struct kobj_type *ktype);
 extern __printf(3, 4) __must_check
 int kobject_add(struct kobject *kobj, struct kobject *parent,
 		const char *fmt, ...);
 extern __printf(4, 5) __must_check
 int kobject_init_and_add(struct kobject *kobj,
-			 struct kobj_type *ktype, struct kobject *parent,
+			 const struct kobj_type *ktype, struct kobject *parent,
 			 const char *fmt, ...);
 
 extern void kobject_del(struct kobject *kobj);
@@ -217,7 +217,7 @@ static inline void kset_put(struct kset *k)
 	kobject_put(&k->kobj);
 }
 
-static inline struct kobj_type *get_ktype(struct kobject *kobj)
+static inline const struct kobj_type *get_ktype(struct kobject *kobj)
 {
 	return kobj->ktype;
 }

kernel/params.c

@@ -928,7 +928,7 @@ static const struct sysfs_ops module_sysfs_ops = {
 
 static int uevent_filter(struct kset *kset, struct kobject *kobj)
 {
-	struct kobj_type *ktype = get_ktype(kobj);
+	const struct kobj_type *ktype = get_ktype(kobj);
 
 	if (ktype == &module_ktype)
 		return 1;

lib/kobject.c

@@ -65,7 +65,7 @@ void kobject_get_ownership(struct kobject *kobj, kuid_t *uid, kgid_t *gid)
  */
 static int populate_dir(struct kobject *kobj)
 {
-	struct kobj_type *t = get_ktype(kobj);
+	const struct kobj_type *t = get_ktype(kobj);
 	struct attribute *attr;
 	int error = 0;
 	int i;
@@ -346,7 +346,7 @@ EXPORT_SYMBOL(kobject_set_name);
  * to kobject_put(), not by a call to kfree directly to ensure that all of
  * the memory is cleaned up properly.
  */
-void kobject_init(struct kobject *kobj, struct kobj_type *ktype)
+void kobject_init(struct kobject *kobj, const struct kobj_type *ktype)
 {
 	char *err_str;
 
@@ -461,7 +461,7 @@ EXPORT_SYMBOL(kobject_add);
  * same type of error handling after a call to kobject_add() and kobject
  * lifetime rules are the same here.
  */
-int kobject_init_and_add(struct kobject *kobj, struct kobj_type *ktype,
+int kobject_init_and_add(struct kobject *kobj, const struct kobj_type *ktype,
 			 struct kobject *parent, const char *fmt, ...)
 {
 	va_list args;
@@ -679,7 +679,7 @@ EXPORT_SYMBOL(kobject_get_unless_zero);
 static void kobject_cleanup(struct kobject *kobj)
 {
 	struct kobject *parent = kobj->parent;
-	struct kobj_type *t = get_ktype(kobj);
+	const struct kobj_type *t = get_ktype(kobj);
 	const char *name = kobj->name;
 
 	pr_debug("kobject: '%s' (%p): %s, parent %p\n",