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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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Greg Kroah-Hartman 2023-02-08 12:13:11 +01:00
parent 789be03a60
commit 273afac615
1 changed files with 53 additions and 8 deletions
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61
drivers/base/bus.c
View File

@ -24,6 +24,9 @@
/* /sys/devices/system */
static struct kset *system_kset;
/* /sys/bus */
static struct kset *bus_kset;
#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,
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)
{
if (bus) {
kset_get(&bus->p->subsys);
struct subsys_private *sp = bus_to_subsys(bus);
if (sp)
return bus;
}
return NULL;
}
static void bus_put(struct bus_type *bus)
static void bus_put(const struct bus_type *bus)
{
if (bus)
kset_put(&bus->p->subsys);
struct subsys_private *sp = bus_to_subsys(bus);
/* 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,
@ -177,8 +224,6 @@ static const struct kset_uevent_ops bus_uevent_ops = {
.filter = bus_uevent_filter,
};
static struct kset *bus_kset;
/* Manually detach a device from its associated driver. */
static ssize_t unbind_store(struct device_driver *drv, const char *buf,
size_t count)