转载：https://blog.csdn.net/u010550992/article/details/50710567
http://www.techbulo.com/1903.html

上图说明了总线通过两个数据结构：devices_ket和driver_kset来管理注册在此总线上的所有的设备和驱动，为了方便遍历，linux增加了klist_devices和klist_drivers用来实现设备和驱动的遍历

struct bus_type mini_bus_type ={.name = "mini",.match = mini_match
};static int __init test_init(void)
{return bus_register(&mini_bus_type);	
}bus_register:工作就是完成bus_type_private的初始化.创建 注册的这条总线需要的目录文件.在这条总线目录下创建/device  /driver 目录初始化这条总线上的设备链表：struct klist klist_devices;初始化这条总线上的驱动链表：struct klist klist_drivers;int bus_register(struct bus_type *bus)
{int retval;struct bus_type_private *priv;						//是上面mini_bus_type的成员.priv = kzalloc(sizeof(struct bus_type_private), GFP_KERNEL);if (!priv)return -ENOMEM;priv->bus = bus;							//struct bus_type_private *p;所指向的内容动态分配.bus->p = priv;								//p关联到mini_bus_typeBLOCKING_INIT_NOTIFIER_HEAD(&priv->bus_notifier);retval = kobject_set_name(&priv->subsys.kobj, "%s", bus->name);		//kobject对应一个目录,这个目录就是我们看到的总线名字/bus/miniif (retval)goto out; //bus_kset = kset_create_and_add("bus", &bus_uevent_ops, NULL);priv->subsys.kobj.kset = bus_kset;					//mini目录在bus下,即/bus/mini:初始化kset的成员kobject,为kset_register()做准备.   priv->subsys.kobj.ktype = &bus_ktype;					//static struct kobj_type bus_ktype = {    .sysfs_ops = &bus_sysfs_ops, };    priv->drivers_autoprobe = 1;						//设置该标志，	当有driver注册时,会自动匹配devices上的设备并用probe初始化，//		当有device注册时,也同样找到driver并会初始化  //int bus_add_driver(struct device_driver *drv)//	if (drv->bus->p->drivers_autoprobe) { error = driver_attach(drv); }retval = kset_register(&priv->subsys);					//注册kset，创建目录结构，以及层次关系  生成/bus/mini                               if (retval)                                                                                                                           goto out;                                 //kset_register(&priv->subsys);//kobject_add_internal(&k->kobj);//error = create_dir(kobj); //error = sysfs_create_dir(kobj);//&priv->subsys---->mini_bus_type->p->subsys  		//priv->subsys.kobj.kset = bus_kset;retval = bus_create_file(bus, &bus_attr_uevent);			//mini目录下生成bus_attr_uevent属性文件 if (retval)goto bus_uevent_fail;priv->devices_kset = kset_create_and_add("devices", NULL,		//在mini下面创建一个mini/device,是mini这条总线的device的根目录.&priv->subsys.kobj);		//为什么在mini目录下?  (device这个目录:kset->kobj) kset->kobj.parent = &priv->subsys.kobj;//在某个目录下:kset->kob.kset =  x    	这个目录在x目录下，这个目录下面“还可有”目录//             kobj.parent =     y	这个目录在y目录下，这个目录下面“没有”有目录if (!priv->devices_kset) {retval = -ENOMEM;goto bus_devices_fail;}priv->drivers_kset = kset_create_and_add("drivers", NULL,		//在mini下面创建一个mini/driver,是mini这条总线的driver的根目录.&priv->subsys.kobj);		//struct kset *drivers_kset  指针.  if (!priv->drivers_kset) {retval = -ENOMEM;goto bus_drivers_fail;}klist_init(&priv->klist_devices, klist_devices_get, klist_devices_put);	//初始化 mini_bus_type->p->klist_devices  就是初始化device的list_headklist_init(&priv->klist_drivers, NULL, NULL);				//					 就是初始化driver的list_head//device,driver注册都挂在对应的链表上.retval = add_probe_files(bus);						//创建文件if (retval)goto bus_probe_files_fail;retval = bus_add_attrs(bus);if (retval)goto bus_attrs_fail;pr_debug("bus: '%s': registered\n", bus->name);return 0;bus_attrs_fail:remove_probe_files(bus);
bus_probe_files_fail:kset_unregister(bus->p->drivers_kset);
bus_drivers_fail:kset_unregister(bus->p->devices_kset);
bus_devices_fail:bus_remove_file(bus, &bus_attr_uevent);
bus_uevent_fail:kset_unregister(&bus->p->subsys);
out:kfree(bus->p);bus->p = NULL;return retval;
}struct bus_type {const char		*name;							//总线名称struct bus_attribute	*bus_attrs;						//总线属性(设备节点和这个有关系么?)struct device_attribute	*dev_attrs;						//设备属性   struct driver_attribute	*drv_attrs;						//驱动属性int (*match)(struct device *dev, struct device_driver *drv);			//用于匹配总线下的dev和driverint (*uevent)(struct device *dev, struct kobj_uevent_env *env);			//用于总线环境变量的添加int (*probe)(struct device *dev);						//总线和驱动匹配成功调用，platform不是设备和驱动匹配才调用么?没搞清楚.int (*remove)(struct device *dev);void (*shutdown)(struct device *dev);						//关机int (*suspend)(struct device *dev, pm_message_t state);				//挂起int (*resume)(struct device *dev);const struct dev_pm_ops *pm;							//电源管理.struct bus_type_private *p;							//将bus device sysfs关联起来，怎么关联的不明白呀
};struct bus_type_private {struct kset subsys;								//sysfsstruct kset *drivers_kset;							//bus目录下的 drvier子目录struct kset *devices_kset;							//bus目录下的 device子目录struct klist klist_devices;							//bus目录下的设备列表struct klist klist_drivers;							//bus目录下的驱动列表struct blocking_notifier_head bus_notifier;unsigned int drivers_autoprobe:1;struct bus_type *bus;
};struct bus_attribute {struct attribute	attr;ssize_t (*show)(struct bus_type *bus, char *buf);ssize_t (*store)(struct bus_type *bus, const char *buf, size_t count);
};#define BUS_ATTR(_name, _mode, _show, _store)	\
struct bus_attribute bus_attr_##_name = __ATTR(_name, _mode, _show, _store)#define __ATTR(_name,_mode,_show,_store) { \.attr = {.name = __stringify(_name), .mode = _mode },	\.show	= _show,					\.store	= _store,					\
}#define __stringify_1(x...)	#x
#define __stringify(x...)	__stringify_1(x)struct klist {spinlock_t		k_lock;struct list_head	k_list;void			(*get)(struct klist_node *);void			(*put)(struct klist_node *);
} __attribute__ ((aligned (sizeof(void *))));

------------------------------------------------------------------------------------

int bus_register(struct bus_type *bus){int retval;struct bus_type_private *priv;//分配存储空间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;首先,先为struct bus_type的私有区分配空间,然后将其和struct bus_type关联起来.由于struct bus_type也要在sysfs文件中表示一个节点,因此,它也内嵌也一个kset的结构.这就是priv->subsys.首先,它为这个kset的名称赋值为bus的名称,然后将priv->subsys.kobj.kset指向bus_kset. priv->subsys.kobj.ktype指向bus_ktype;然后调用kset_reqister()将priv->subsys注册.这里涉及到的接口都在之前分析过.注册过后,应该会在bus_kset所表示的目录下创建一个总线名称的目录.并且用户空间的hotplug应该会检测到一个add事件.我们来看一下bus_kset到底指向的是什么:bus_kset = kset_create_and_add("bus", &bus_uevent_ops, NULL);从此可以看出.这个bus_kset在sysfs中的结点就是/sys/bus.在这里注册的struct bus_types就会在/sys/bus/下面出现；bus_create_file()就是在priv->subsys.kobj的这个kobject上建立一个普通属性的文件.这个文件的属性对应在bus_attr_uevent.读写操作对应在priv->subsys.kobj.ktype中.我们到后面才统一分析bus注册时候的文件创建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);这段代码会在bus所在的目录下建立两个目录,分别为devices和drivers.并初始化挂载设备和驱动的链表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/n", bus->name);return 0;在这里,会为bus_attr_drivers_probe, bus_attr_drivers_autoprobe.注册bus_type中的属性建立文件bus_attrs_fail:remove_probe_files(bus);bus_probe_files_fail:kset_unregister(bus->p->drivers_kset);bus_drivers_fail:kset_unregister(bus->p->devices_kset);bus_devices_fail:bus_remove_file(bus, &bus_attr_uevent);bus_uevent_fail:kset_unregister(&bus->p->subsys);kfree(bus->p);out:return retval;}这段代码为出错处理;struct kset *kset_create_and_add(const char *name,  struct kset_uevent_ops *uevent_ops,struct kobject *parent_kobj){struct kset *kset;int error;//创建一个ksetkset = kset_create(name, uevent_ops, parent_kobj);if (!kset)return NULL;//注册kseterror = kset_register(kset);if (error){//如果注册失败,释放ksetkfree(kset);return NULL;}return kset;}Kset_create()用来创建一个struct kset结构.代码如下:static struct kset *kset_create(const char *name,struct kset_uevent_ops *uevent_ops,struct kobject *parent_kobj){struct kset *kset;kset = kzalloc(sizeof(*kset), GFP_KERNEL);if (!kset)return NULL;kobject_set_name(&kset->kobj, name);kset->uevent_ops = uevent_ops;kset->kobj.parent = parent_kobj;kset->kobj.ktype = &kset_ktype;kset->kobj.kset = NULL;return kset;}我们注意,在这里创建kset时.为其内嵌的kobject指定其struct kobj_type ktype结构为kset_ktype.这个结构的定义如下:static struct kobj_type kset_ktype = {.sysfs_ops    = &kobj_sysfs_ops,.release = kset_release,};属性文件的读写操作全部都包含在sysfs_ops成员里.kobj_sysfs_ops的定义如下:struct sysfs_ops kobj_sysfs_ops = {.show    = kobj_attr_show,.store   = kobj_attr_store,};创建好了kset之后,会调用kset_register().这个函数就是kset操作的核心代码了.如下:int kset_register(struct kset *k){int err;if (!k)return -EINVAL;kset_init(k);err = kobject_add_internal(&k->kobj);if (err)return err;kobject_uevent(&k->kobj, KOBJ_ADD);return 0;}void kset_init(struct kset *k)
{
kobject_init_internal(&k->kobj);             //只是对kobj中的成员变量做一些赋值的初始化
INIT_LIST_HEAD(&k->list);
spin_lock_init(&k->list_lock);
}static int kobject_add_internal(struct kobject *kobj){int error = 0;struct kobject *parent;if (!kobj)return -ENOENT;//如果kobject的名字为空.退出if (!kobj->name || !kobj->name[0]) {pr_debug("kobject: (%p): attempted to be registered with empty ""name!/n", kobj);WARN_ON(1);return -EINVAL;}//取kobject的父结点parent = kobject_get(kobj->parent);//如果kobject的父结点没有指定，就将kset->kobject做为它的父结点/* join kset if set, use it as parent if we do not already have one */if (kobj->kset) {if (!parent)parent = kobject_get(&kobj->kset->kobj);kobj_kset_join(kobj);kobj->parent = parent;}//调试用pr_debug("kobject: '%s' (%p): %s: parent: '%s', set: '%s'/n",kobject_name(kobj), kobj, __FUNCTION__,parent ? kobject_name(parent) : "<NULL>",kobj->kset ? kobject_name(&kobj->kset->kobj) : "<NULL>");//在sysfs中创建kobject的相关元素error = create_dir(kobj);if (error) {//v如果创建失败。减少相关的引用计数kobj_kset_leave(kobj);kobject_put(parent);kobj->parent = NULL;/* be noisy on error issues */if (error == -EEXIST)printk(KERN_ERR "%s failed for %s with ""-EEXIST, don't try to register things with ""the same name in the same directory./n",__FUNCTION__, kobject_name(kobj));elseprintk(KERN_ERR "%s failed for %s (%d)/n",__FUNCTION__, kobject_name(kobj), error);dump_stack();} else//如果创建成功。将state_in_sysfs建为1。表示该object已经在sysfs中了kobj->state_in_sysfs = 1;return error;}这段代码比较简单，它主要完成kobject父结点的判断和选定，然后再调用create_dir（）在sysfs创建相关信息。该函数代码如下：static int create_dir(struct kobject *kobj){int error = 0;if (kobject_name(kobj)) {//为kobject创建目录error = sysfs_create_dir(kobj);if (!error) {//为kobject->ktype中的属性创建文件error = populate_dir(kobj);if (error)sysfs_remove_dir(kobj);}}return error;}int sysfs_create_dir(struct kobject * kobj){struct sysfs_dirent *parent_sd, *sd;int error = 0;BUG_ON(!kobj);/*如果kobject的parnet存在。就在目录点的目录下创建这个目录。如果没有父结点不存在，就在/sys下面创建结点。*/if (kobj->parent)parent_sd = kobj->parent->sd;elseparent_sd = &sysfs_root;//在sysfs中创建目录//create_dir（）就是在sysfs中创建目录的接口，在之前已经详细分析过了error = create_dir(kobj, parent_sd, kobject_name(kobj), &sd);if (!error)kobj->sd = sd;return error;}接着看为kobject->ktype中的属性创建文件。这是在populate_dir（）中完成的。代码如下：static int populate_dir(struct kobject *kobj){struct kobj_type *t = get_ktype(kobj);struct attribute *attr;int error = 0;int i;if (t && t->default_attrs) {for (i = 0; (attr = t->default_attrs[i]) != NULL; i++) {error = sysfs_create_file(kobj, attr);if (error)break;}}return error;}这段代码比较简单。它遍历ktype中的属性。然后为其建立文件。请注意：文件的操作最后都会回溯到ktype->sysfs_ops的show和store这两个函数中.假如对于上面的bus_register()函数传入的参数为：struct bus_type ldd_bus_type = {
.name = "ldd",
.match = ldd_match,
.hotplug  = ldd_hotplug,
};