From 884f8ce42ccec9d0bf11d8bf9f111e5961ca1c82 Mon Sep 17 00:00:00 2001 From: Greg Kroah-Hartman Date: Sat, 25 Mar 2023 20:42:33 +0100 Subject: [PATCH] driver core: class: implement class_get/put without the private pointer. Much like what was done in commit 273afac615ad ("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" Link: https://lore.kernel.org/r/20230325194234.46588-1-gregkh@linuxfoundation.org Signed-off-by: Greg Kroah-Hartman --- drivers/base/class.c | 81 ++++++++++++++++++++++++++++++++++++++++------------ 1 file changed, 63 insertions(+), 18 deletions(-) diff --git a/drivers/base/class.c b/drivers/base/class.c index 04de20e..c53d6f9 100644 --- a/drivers/base/class.c +++ b/drivers/base/class.c @@ -20,8 +20,70 @@ #include #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; -- 2.7.4