Commit 884f8ce4 authored by Greg Kroah-Hartman's avatar Greg Kroah-Hartman
Browse files

driver core: class: implement class_get/put without the private pointer. 

Much like what was done in commit 273afac6 ("driver core: bus:
implement bus_get/put() without the private pointer"), it is time to
move the driver core away from using the internal private pointer in
struct class in order to enable it to be always a constant and be placed
in read-only memory in the future.

First step in doing this is to create a helper function that turns a
'struct class' into 'struct subsys_private' called class_to_subsys().

class_to_subsys() walks the list of registered busses in the system and
finds the matching one based on the pointer to the class itself.  As
this is a short list, and this function is not on any fast path, it
should not be noticable.

Implement class_get() and class_put() using this new helper function.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Link: https://lore.kernel.org/r/20230325194234.46588-1-gregkh@linuxfoundation.org


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 75a2d422

drivers/base/class.c

+63 −18
Original line number Diff line number Diff line
@@ -20,8 +20,70 @@ 
#include <linux/mutex.h>

#include "base.h"



/* /sys/class */

static struct kset *class_kset;



#define to_class_attr(_attr) container_of(_attr, struct class_attribute, attr)



/**

 * class_to_subsys - Turn a struct class into a struct subsys_private

 *

 * @class: pointer to the struct bus_type to look up

 *

 * The driver core internals need to work on the subsys_private structure, not

 * the external struct class pointer.  This function walks the list of

 * registered classes in the system and finds the matching one and returns the

 * internal struct subsys_private that relates to that class.

 *

 * Note, the reference count of the return value is INCREMENTED if it is not

 * NULL.  A call to subsys_put() must be done when finished with the pointer in

 * order for it to be properly freed.

 */

static struct subsys_private *class_to_subsys(const struct class *class)

{

	struct subsys_private *sp = NULL;

	struct kobject *kobj;



	if (!class || !class_kset)

		return NULL;



	spin_lock(&class_kset->list_lock);



	if (list_empty(&class_kset->list))

		goto done;



	list_for_each_entry(kobj, &class_kset->list, entry) {

		struct kset *kset = container_of(kobj, struct kset, kobj);



		sp = container_of_const(kset, struct subsys_private, subsys);

		if (sp->class == class)

			goto done;

	}

	sp = NULL;

done:

	sp = subsys_get(sp);

	spin_unlock(&class_kset->list_lock);

	return sp;

}



static const struct class *class_get(const struct class *class)

{

	struct subsys_private *sp = class_to_subsys(class);



	if (sp)

		return class;

	return NULL;

}



static void class_put(const struct class *class)

{

	struct subsys_private *sp = class_to_subsys(class);



	/* two puts are required as the call to bus_to_subsys incremented it again */

	subsys_put(sp);

	subsys_put(sp);

}



static ssize_t class_attr_show(struct kobject *kobj, struct attribute *attr,

			       char *buf)

{
@@ -83,10 +145,6 @@ static const struct kobj_type class_ktype = { 
	.child_ns_type	= class_child_ns_type,

};



/* Hotplug events for classes go to the class subsys */

static struct kset *class_kset;





int class_create_file_ns(const struct class *cls, const struct class_attribute *attr,

			 const void *ns)

{
@@ -109,19 +167,6 @@ void class_remove_file_ns(const struct class *cls, const struct class_attribute 
}

EXPORT_SYMBOL_GPL(class_remove_file_ns);



static struct class *class_get(struct class *cls)

{

	if (cls)

		kset_get(&cls->p->subsys);

	return cls;

}



static void class_put(struct class *cls)

{

	if (cls)

		kset_put(&cls->p->subsys);

}



static struct device *klist_class_to_dev(struct klist_node *n)

{

	struct device_private *p = to_device_private_class(n);
@@ -434,7 +479,7 @@ EXPORT_SYMBOL_GPL(class_find_device); 


int class_interface_register(struct class_interface *class_intf)

{

	struct class *parent;

	const struct class *parent;

	struct class_dev_iter iter;

	struct device *dev;