Commit 273afac6 authored by Greg Kroah-Hartman's avatar Greg Kroah-Hartman
Browse files

driver core: bus: implement bus_get/put() without the private pointer 

In the quest to make 'struct bus_type' constant and in read-only memory,
we need to stop using the private pointer to the subsys_private
structure.  First step in doing this is to create a helper function that
turns a 'struct bus_type' into 'struct subsys_private' called
bus_to_subsys().

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

Implement bus_get() and bus_put() using this new helper function.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Link: https://lore.kernel.org/r/20230208111330.439504-3-gregkh@linuxfoundation.org


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 789be03a

drivers/base/bus.c

+53 −8
Original line number Original line Diff line number Diff line
@@ -24,6 +24,9 @@ 
/* /sys/devices/system */

/* /sys/devices/system */

static struct kset *system_kset;

static struct kset *system_kset;





/* /sys/bus */

static struct kset *bus_kset;



#define to_bus_attr(_attr) container_of(_attr, struct bus_attribute, attr)

#define to_bus_attr(_attr) container_of(_attr, struct bus_attribute, attr)





/*

/*
@@ -39,19 +42,63 @@ static struct kset *system_kset; 
static int __must_check bus_rescan_devices_helper(struct device *dev,

static int __must_check bus_rescan_devices_helper(struct device *dev,

						void *data);

						void *data);





/**

 * bus_to_subsys - Turn a struct bus_type into a struct subsys_private

 *

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

 *

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

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

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

 * internal struct subsys_private that relates to that bus.

 *

 * 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 *bus_to_subsys(const struct bus_type *bus)

{

	struct subsys_private *sp = NULL;

	struct kobject *kobj;



	if (!bus)

		return NULL;



	spin_lock(&bus_kset->list_lock);



	if (list_empty(&bus_kset->list))

		goto done;



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

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



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

		if (sp->bus == bus)

			goto done;

	}

	sp = NULL;

done:

	sp = subsys_get(sp);

	spin_unlock(&bus_kset->list_lock);

	return sp;

}



static struct bus_type *bus_get(struct bus_type *bus)

static struct bus_type *bus_get(struct bus_type *bus)

{

{

	if (bus) {

	struct subsys_private *sp = bus_to_subsys(bus);

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



	if (sp)

		return bus;

		return bus;

	}

	return NULL;

	return NULL;

}

}





static void bus_put(struct bus_type *bus)

static void bus_put(const struct bus_type *bus)

{

{

	if (bus)

	struct subsys_private *sp = bus_to_subsys(bus);

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



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

	subsys_put(sp);

	subsys_put(sp);

}

}





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

static ssize_t drv_attr_show(struct kobject *kobj, struct attribute *attr,
@@ -177,8 +224,6 @@ static const struct kset_uevent_ops bus_uevent_ops = { 
	.filter = bus_uevent_filter,

	.filter = bus_uevent_filter,

};

};





static struct kset *bus_kset;



/* Manually detach a device from its associated driver. */

/* Manually detach a device from its associated driver. */

static ssize_t unbind_store(struct device_driver *drv, const char *buf,

static ssize_t unbind_store(struct device_driver *drv, const char *buf,

			    size_t count)

			    size_t count)