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/devicesbuses_init(); // /sys/busclasses_init(); // /sys/classfirmware_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)
{interror;

　　　　 /* /sys/devices/platform (this platform is bus_id's value) */

　　　　error= device_register(&platform_bus);　　　　 if(error)　　　　　　　　returnerror;

　　　　  /* /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);　　　　　returnerror; }

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.*/
structbus_type_private {struct kset subsys;struct kset *drivers_kset;struct kset *devices_kset;structklist klist_devices;structklist klist_drivers;structblocking_notifier_head bus_notifier;unsignedint drivers_autoprobe:1;struct bus_type *bus;
};

int bus_register(struct bus_type *bus)
{intretval;struct bus_type_private *priv;                                          priv= kzalloc(sizeof(structbus_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)gotobus_uevent_fail;                                           priv->devices_kset = kset_create_and_add("devices", NULL,&priv->subsys.kobj);if (!priv->devices_kset) {                                              retval= -ENOMEM;gotobus_devices_fail;                                          }                                                                       priv->drivers_kset = kset_create_and_add("drivers", NULL,&priv->subsys.kobj);if (!priv->drivers_kset) {                                              retval= -ENOMEM;gotobus_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)gotobus_probe_files_fail;                                      retval=bus_add_attrs(bus);if(retval)gotobus_attrs_fail;                                            pr_debug("bus: '%s': registered\n", 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)
{interr;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)returnerr;                                                        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

structkobject {const char              *name;struct list_head        entry;struct kobject          *parent;struct kset             *kset;struct kobj_type        *ktype;struct sysfs_dirent     *sd;structkref             kref;                                              unsignedint state_initialized:1;                                          unsignedint state_in_sysfs:1;                                             unsignedint state_add_uevent_sent:1;                                                                                                    unsignedint 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 inthe 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 thiskset* @list_lock: a lock foriterating over the kobjects* @kobj: the embedded kobject for this kset (recursion, isn't it fun...)* @uevent_ops: the set of uevent operations for thiskset.  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 ifso*desired.*/
structkset {structlist_head list;                                                  spinlock_t list_lock;structkobject kobj;struct kset_uevent_ops *uevent_ops;
};

structlist_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。