这是内核启动之后要调用的驱动模型的开始代码：
drivers/base/init.c
/** * driver_init - initialize driver model. * * Call the driver model init functions to initialize their * subsystems. Called early from init/main.c. */ void __init driver_init(void) { /* These are the core pieces */ devices_init(); // /sys/devices buses_init(); // /sys/bus classes_init(); // /sys/class firmware_init(); hypervisor_init(); /* These are also core pieces, but must come after the * core core pieces. */ platform_bus_init(); system_bus_init(); cpu_dev_init(); memory_dev_init(); }
且看platform_bus_init
drivers/base/platform.c
struct device platform_bus = { .bus_id = "platform", };
struct bus_type platform_bus_type = { .name = "platform", .dev_attrs = platform_dev_attrs, .match = platform_match, .uevent = platform_uevent, .pm = PLATFORM_PM_OPS_PTR, };
int __init platform_bus_init(void) { int error;
/* /sys/devices/platform (this platform is bus_id's value) */
error = device_register(&platform_bus);
if (error)
return error;
/* /sys/bus/platform (this platform is the value of bus_type's name field) */
error = bus_register(&platform_bus_type);
if (error)
device_unregister(&platform_bus);
return error;
}
这里讲述 bus_register(&platform_bus_type)：
/** * struct bus_type_private - structure to hold the private to the driver core portions of the bus_type structure. * * @subsys - the struct kset that defines this bus. This is the main kobject * @drivers_kset - the list of drivers associated with this bus * @devices_kset - the list of devices associated with this bus * @klist_devices - the klist to iterate over the @devices_kset * @klist_drivers - the klist to iterate over the @drivers_kset * @bus_notifier - the bus notifier list for anything that cares about things * on this bus. * @bus - pointer back to the struct bus_type that this structure is associated * with. * * This structure is the one that is the actual kobject allowing struct * bus_type to be statically allocated safely. Nothing outside of the driver * core should ever touch these fields. */ struct bus_type_private { struct kset subsys; struct kset *drivers_kset; struct kset *devices_kset; struct klist klist_devices; struct klist klist_drivers; struct blocking_notifier_head bus_notifier; unsigned int drivers_autoprobe:1; struct bus_type *bus; };
int bus_register(struct bus_type *bus) { int retval; struct bus_type_private *priv; priv = kzalloc(sizeof(struct bus_type_private), GFP_KERNEL); if (!priv) return -ENOMEM; priv->bus = bus; bus->p = priv; BLOCKING_INIT_NOTIFIER_HEAD(&priv->bus_notifier); retval = kobject_set_name(&priv->subsys.kobj, "%s", bus->name); if (retval) goto out; priv->subsys.kobj.kset = bus_kset; priv->subsys.kobj.ktype = &bus_ktype; priv->drivers_autoprobe = 1; retval = kset_register(&priv->subsys); if (retval) goto out; retval = bus_create_file(bus, &bus_attr_uevent); if (retval) goto bus_uevent_fail; priv->devices_kset = kset_create_and_add("devices", NULL, &priv->subsys.kobj); if (!priv->devices_kset) { retval = -ENOMEM; goto bus_devices_fail; } priv->drivers_kset = kset_create_and_add("drivers", NULL, &priv->subsys.kobj); if (!priv->drivers_kset) { retval = -ENOMEM; goto bus_drivers_fail; } klist_init(&priv->klist_devices, klist_devices_get, klist_devices_put); klist_init(&priv->klist_drivers, NULL, NULL); retval = add_probe_files(bus); if (retval) goto bus_probe_files_fail; retval = bus_add_attrs(bus); if (retval) goto bus_attrs_fail; pr_debug("bus: '%s': registered ", bus->name); return 0;
struct bus_type_private *priv指向struct bus_type，这里会显示/sys/bus/platform
retval = kobject_set_name(&priv->subsys.kobj, "%s", bus->name);
priv->subsys.kobj.kset = bus_kset;
retval = kset_register(&priv->subsys);// subsys is a kset.
这里显示/sys/bus/platform/devices
priv->devices_kset = kset_create_and_add("devices", NULL, &priv->subsys.kobj);
这里显示/sys/bus/platform/drivers
priv->drivers_kset = kset_create_and_add("drivers", NULL, &priv->subsys.kobj);
kset_create_and_add--->kset_register
/** * kset_register - initialize and add a kset. * @k: kset. */ int kset_register(struct kset *k) { int err; if (!k) return -EINVAL; kset_init(k); // INIT_LIST_HEAD(&k->kobj->entry); INIT_LIST_HEAD(&k->list); err = kobject_add_internal(&k->kobj); if (err) return err; kobject_uevent(&k->kobj, KOBJ_ADD); return 0; }
static int kobject_add_internal(struct kobject *kobj) { kobj_kset_join(kobj); error = create_dir(kobj); // /sys/bus/platform }
/* add the kobject to its kset's list */ static void kobj_kset_join(struct kobject *kobj) { if (!kobj->kset) return; kset_get(kobj->kset); spin_lock(&kobj->kset->list_lock); list_add_tail(&kobj->entry, &kobj->kset->list); spin_unlock(&kobj->kset->list_lock); }
If a kset is associated with a kobject, then the parent for the kobject can be set to
NULL in the call to kobject_add() and then the kobject's parent will be the kset itself.
确切的说是kobject's parent赋值为kobject关联的kset's kobjcect
struct kobject { const char *name; struct list_head entry; struct kobject *parent; struct kset *kset; struct kobj_type *ktype; struct sysfs_dirent *sd; struct kref kref; unsigned int state_initialized:1; unsigned int state_in_sysfs:1; unsigned int state_add_uevent_sent:1; unsigned int state_remove_uevent_sent:1; };
* * A kset defines a group of kobjects. They can be individually * different "types" but overall these kobjects all want to be grouped * together and operated on in the same manner. ksets are used to * define the attribute callbacks and other common events that happen to * a kobject. * * @list: the list of all kobjects for this kset * @list_lock: a lock for iterating over the kobjects * @kobj: the embedded kobject for this kset (recursion, isn't it fun...) * @uevent_ops: the set of uevent operations for this kset. These are * called whenever a kobject has something happen to it so that the kset * can add new environment variables, or filter out the uevents if so * desired. */ struct kset { struct list_head list; spinlock_t list_lock; struct kobject kobj; struct kset_uevent_ops *uevent_ops; };
struct list_head { struct list_head *next, *prev; };
从list_add_tail(&kobj->entry, &kobj->kset->list); 调用中，我们一下子就明白了，
bus =&struct bus_type platform_bus_type;
bus->p->->subsys.kobj.kset = bus_kset;// bus_kset = kset_create_and_add("bus", &bus_uevent_ops, NULL); 创建了bus的kset显示/sys/bus
所以&kobj->kset->list就是bus_kset->list,list_add_tail就是把bus->p->->subsys.kobj.entry加入到bus_kset->list链表中。
bus_kset包含不同bus的subsys的kset，而代表subsys的kset的就是这个kset中的kobject。所以把kobjetct的entry加入到表示kset的kset->list中。
换句话说，struct kset这个集合包含的内容由其嵌入的struct list_head list来表示，这个struct kset自身由其嵌入的struct kobject kobj来表示。
所以这里就是把platform这个kset加入到bus这个kset中。用户空间的视图表示就是/sys/bus/platform。