bus，device，driver三个很重要的概念贯穿Linux内核驱动架构，特转载一篇博文：
（转载自http://blog.csdn.net/gdt_a20/article/details/6425894）
内核的开发者将总线，设备，驱动这三者用软件思想抽象了出来，巧妙的建立了其间的关系，使之更形象化。结合前面所学的知识，总的来说其三者间的关系为bus有两条链表，分别用于挂接设备和驱动，指定了其自身bus的device或者driver最后都会分别连接到对应bus的这两条链表上，而总线又有其始端，为bus_kset，一个driver可以对应于几个设备，因此driver同样有其设备链表，用于挂接可以操作的设备，其自身也有bus挂接点，用于将自身挂接到对应bus（每个driver只属于一条总线），而对于device，一个设备只属于一条总线，只能有一个driver与其对应，因此对于device，都是单一的，一个driver挂接点，一个bus挂接点，device与bus相同的是都有始端，device为devices_kset，因此device的注册同时会出现在对应的bus目录和device总目录下。好了，下面就以源码为例分别分析一下bus，device，driver的注册过程。
一、bus的注册
bus的注册比较简单，首先来看一下bus的结构：
struct bus_type {
const char *name; //名字
struct bus_attribute *bus_attrs; //bus属性集
struct device_attribute *dev_attrs; //device属性集
struct driver_attribute *drv_attrs; //driver属性集
int (*match)(struct device *dev, struct device_driver *drv);
int (*uevent)(struct device *dev, struct kobj_uevent_env *env);
int (*probe)(struct device *dev);
int (*remove)(struct device *dev);
void (*shutdown)(struct device *dev);
int (*suspend)(struct device *dev, pm_message_t state);
int (*resume)(struct device *dev);
const struct dev_pm_ops *pm;
struct bus_type_private *p; //bus的私有成员
};
//其中重点看一下私有成员结构体：
struct bus_type_private {
struct kset subsys; //bus内嵌的kset，代表其自身
struct kset *drivers_kset;
struct kset *devices_kset;
struct klist klist_devices; //包含devices链表及其操作函数
struct klist klist_drivers; //driver链表及其操作函数
struct blocking_notifier_head bus_notifier;
unsigned int drivers_autoprobe:; //匹配成功自动初始化标志
struct bus_type *bus;
};
无论是bus，driver，还是device其本身特征都放在私有成员里，其注册时，都会申请并填充这个结构体，下面具体分析一下bus的注册流程，从bus_register开始：
int bus_register(struct bus_type *bus)
{
int retval;
struct bus_type_private *priv;
priv = kzalloc(sizeof(struct bus_type_private), GFP_KERNEL); //进入时bus_type->bus_type_private为NULL
if (!priv) //该函数主要是对其的设置
return -ENOMEM;
priv->bus = bus; //私有成员的bus回指该bus
bus->p = priv; //初始化bus->p,即其私有属性
BLOCKING_INIT_NOTIFIER_HEAD(&priv->bus_notifier);
retval = kobject_set_name(&priv->subsys.kobj, "%s", bus->name); //设置该bus的名字，bus是kset的封装
if (retval)
goto out;
//bus_kset即为所有bus的总起始端点
//围绕bus内嵌的kset初始化，和kset的初始化时围绕
priv->subsys.kobj.kset = bus_kset; //kobj相似，没有parent时，就会用kset的kobj，此处即是
priv->subsys.kobj.ktype = &bus_ktype; //属性操作级别统一为bus_ktype
priv->drivers_autoprobe = ; //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
retval = kset_register(&priv->subsys); //注册kset，创建目录结构，以及层次关系
if (retval)
goto out;
retval = bus_create_file(bus, &bus_attr_uevent); //当前bus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, //初始化bus目录下的devices目录，里面级联了该bus下设备，
&priv->subsys.kobj); //仍然以kset为原型
if (!priv->devices_kset) {
retval = -ENOMEM;
goto bus_devices_fail;
}
priv->drivers_kset = kset_create_and_add("drivers", NULL, //初始化bus目录下的drivers目录，里面级联了该bus下设备的driver
&priv->subsys.kobj);
if (!priv->drivers_kset) {
retval = -ENOMEM;
goto bus_drivers_fail;
}
klist_init(&priv->klist_devices, klist_devices_get, klist_devices_put); //初始化klist_devices里的操作函数成员
klist_init(&priv->klist_drivers, NULL, NULL); //klist_drivers里的操作函数置空
retval = add_probe_files(bus); //增加bus_attr_drivers_probe和bus_attr_drivers_autoprobe
if (retval) //属性文件
goto bus_probe_files_fail;
retval = bus_add_attrs(bus); //增加默认的属性文件
if (retval)
goto bus_attrs_fail;
pr_debug("bus: '%s': registered/n", bus->name);
return ;
bus_attrs_fail: //以下为错误处理
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;
}
由此可见，bus又是kset的封装，bus_register主要完成了其私有成员bus_type_private的初始化，并初始化了其下的两个目录devices和drivers，及其属性文件，bus有个自己的根目录也就是bus有个起始端点，是bus_kset，经过此番的注册，bus目录下将会出现我们注册的bus，并且其下会有device和driver两个子目录，代表它下面的driver和device链表。
二、driver的注册
下面看一下driver是怎么和bus关联起来的，首先看下driver的结构：
struct device_driver {
const char *name; //名字
struct bus_type *bus; //其所在的bus
struct module *owner;
const char *mod_name; /* used for built-in modules */
bool suppress_bind_attrs; /* disables bind/unbind via sysfs */
#if defined(CONFIG_OF)
const struct of_device_id *of_match_table;
#endif
int (*probe) (struct device *dev); //匹配成功时可能会调用到的函数
int (*remove) (struct device *dev);
void (*shutdown) (struct device *dev);
int (*suspend) (struct device *dev, pm_message_t state);
int (*resume) (struct device *dev);
const struct attribute_group **groups;
const struct dev_pm_ops *pm;
struct driver_private *p; //私有成员，表示driver
};
//重点看下driver的私有成员
struct driver_private {
struct kobject kobj; //代表driver自身
struct klist klist_devices; //可以操控的设备链表
struct klist_node knode_bus; //挂接到bus的节点
struct module_kobject *mkobj; //模块相关
struct device_driver *driver; //回指该driver
};
如同bus一样，重点的仍是可以代表其自身的私有属性，下面具体看一下driver的注册过程，从driver_register开始：
int driver_register(struct device_driver *drv)
{
int ret;
struct device_driver *other;
BUG_ON(!drv->bus->p);
if ((drv->bus->probe && drv->probe) || //driver和bus的同名操作函数如果同时存在，会出现警告
(drv->bus->remove && drv->remove) || //并且会优先选用bus的
(drv->bus->shutdown && drv->shutdown))
printk(KERN_WARNING "Driver '%s' needs updating - please use "
"bus_type methods/n", drv->name);
other = driver_find(drv->name, drv->bus); //进入bus的driver链表，确认该driver是否已经注册
if (other) {
put_driver(other); //找到了再减少引用计数，并且报错退出
printk(KERN_ERR "Error: Driver '%s' is already registered, "
"aborting.../n", drv->name);
return -EBUSY;
}
ret = bus_add_driver(drv); //如果没有注册，那么把该driver加入所在bus
if (ret)
return ret;
ret = driver_add_groups(drv, drv->groups);
if (ret)
bus_remove_driver(drv);
return ret;
}
/****************************************************
× 跟踪一下driver_find(drv->name, drv->bus)
****************************************************/
struct device_driver *driver_find(const char *name, struct bus_type *bus)
{
struct kobject *k = kset_find_obj(bus->p->drivers_kset, name); //bus->p->drivers_kset代表bus下
struct driver_private *priv; //的driver目录，此处会遍历bus的
//driver链表，通过driver内嵌的
if (k) { //kobj名字比较
priv = to_driver(k);
return priv->driver; //如果找到同名的kobj那么返回该driver
}
return NULL;
}
//看一下kset_find_obj吧:
struct kobject *kset_find_obj(struct kset *kset, const char *name)
{
struct kobject *k;
struct kobject *ret = NULL;
spin_lock(&kset->list_lock);
list_for_each_entry(k, &kset->list, entry) { //遍历bus下的driver链表，如果
if (kobject_name(k) && !strcmp(kobject_name(k), name)) { //找到那么返回找到的kobj，并且把
ret = kobject_get(k); //该driver的kobj引用计数+1
break;
}
}
spin_unlock(&kset->list_lock);
return ret;
}
/************************************************
× 再来跟踪一下driver_register里面的另外一个函数
× bus_add_driver(drv)
************************************************/
int bus_add_driver(struct device_driver *drv)
{
struct bus_type *bus;
struct driver_private *priv;
int error = ;
bus = bus_get(drv->bus); //取得其所在bus的指针
if (!bus)
return -EINVAL;
pr_debug("bus: '%s': add driver %s/n", bus->name, drv->name); //开始初始化这个driver的私有成员，
//和bus类似
priv = kzalloc(sizeof(*priv), GFP_KERNEL);
if (!priv) {
error = -ENOMEM;
goto out_put_bus;
}
klist_init(&priv->klist_devices, NULL, NULL); //设备操作函数清空，设备链表初始化
priv->driver = drv;
drv->p = priv;
priv->kobj.kset = bus->p->drivers_kset; //kset指定到bus下面
error = kobject_init_and_add(&priv->kobj, &driver_ktype, NULL, //建立层次结构和属性文件
"%s", drv->name);
if (error)
goto out_unregister;
if (drv->bus->p->drivers_autoprobe) { //bus的自动匹配如果设置为真，
error = driver_attach(drv); //那么到bus的devices上去匹配设备
if (error)
goto out_unregister;
}
klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers); //把driver挂接到bus的driver链表
module_add_driver(drv->owner, drv);
error = driver_create_file(drv, &driver_attr_uevent); //以下添加该driver相关属性文件
if (error) {
printk(KERN_ERR "%s: uevent attr (%s) failed/n",
__func__, drv->name);
}
error = driver_add_attrs(bus, drv);
if (error) {
/* How the hell do we get out of this pickle? Give up */
printk(KERN_ERR "%s: driver_add_attrs(%s) failed/n",
__func__, drv->name);
}
if (!drv->suppress_bind_attrs) {
error = add_bind_files(drv);
if (error) {
/* Ditto */
printk(KERN_ERR "%s: add_bind_files(%s) failed/n",
__func__, drv->name);
}
}
kobject_uevent(&priv->kobj, KOBJ_ADD);
return ;
out_unregister:
kobject_put(&priv->kobj);
kfree(drv->p);
drv->p = NULL;
out_put_bus:
bus_put(bus);
return error;
}
/****************************************************************
× 接下来就剩下最终要的匹配函数driver_attach(drv)了，我们来看一下：
****************************************************************/
int driver_attach(struct device_driver *drv) //遍历bus的设备链表找到
{ //合适的设备就调用__driver_attach，
return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach); //NULL表示从头开始遍历
}
//============
int bus_for_each_dev(struct bus_type *bus, struct device *start,
void *data, int (*fn)(struct device *, void *))
{
struct klist_iter i;
struct device *dev;
int error = ;
if (!bus)
return -EINVAL;
klist_iter_init_node(&bus->p->klist_devices, &i, //进入bus的devices链表
(start ? &start->p->knode_bus : NULL));
while ((dev = next_device(&i)) && !error) //设备存在则调用fn即__driver_attach
error = fn(dev, data); //进行匹配
klist_iter_exit(&i);
return error;
}
/*********************************************
× 接着看一下__driver_attach这个函数
*********************************************/
static int __driver_attach(struct device *dev, void *data)
{
struct device_driver *drv = data;
if (!driver_match_device(drv, dev)) //进行匹配
return ;
if (dev->parent) /* Needed for USB */
device_lock(dev->parent);
device_lock(dev);
if (!dev->driver) //如果设备没有指定driver
driver_probe_device(drv, dev); //那么需要初始化匹配到的这个设备
device_unlock(dev);
if (dev->parent)
device_unlock(dev->parent);
return ;
}
/*********************************************
× 又遇到两个分支，囧，先看一下driver_match_device
*********************************************/
static inline int driver_match_device(struct device_driver *drv, //bus的match存在就用bus的
struct device *dev) //，否则就直接匹配成功...
{ //match通常实现为首先扫描
return drv->bus->match ? drv->bus->match(dev, drv) : ; //driver支持的id设备表，如果
} //为NULL就用名字进行匹配
/************************************
× 再来看一下driver_probe_device这个函数
************************************/
int driver_probe_device(struct device_driver *drv, struct device *dev)
{
int ret = ;
if (!device_is_registered(dev)) //判断该设备是否已经注册
return -ENODEV;
pr_debug("bus: '%s': %s: matched device %s with driver %s/n",
drv->bus->name, __func__, dev_name(dev), drv->name);
pm_runtime_get_noresume(dev);
pm_runtime_barrier(dev);
ret = really_probe(dev, drv); //调用really_probe
pm_runtime_put_sync(dev);
return ret;
}
/************************************
× 看一下device_is_registered
************************************/
static inline int device_is_registered(struct device *dev)
{
return dev->kobj.state_in_sysfs; //在sysfs中表示已经注册
}
/************************************
× 再看really_probe
************************************/
static int really_probe(struct device *dev, struct device_driver *drv)
{
int ret = ;
atomic_inc(&probe_count);
pr_debug("bus: '%s': %s: probing driver %s with device %s/n",
drv->bus->name, __func__, drv->name, dev_name(dev));
WARN_ON(!list_empty(&dev->devres_head));
dev->driver = drv; //device的driver初始化成该driver
if (driver_sysfs_add(dev)) {
printk(KERN_ERR "%s: driver_sysfs_add(%s) failed/n",
__func__, dev_name(dev));
goto probe_failed;
}
//利用probe初始化设备
if (dev->bus->probe) { //如果bus的probe存在就用bus的，
ret = dev->bus->probe(dev); //如果bus的不存在driver的存在
if (ret) //再用driver的
goto probe_failed;
} else if (drv->probe) {
ret = drv->probe(dev);
if (ret)
goto probe_failed;
}
driver_bound(dev); //调用driver_bound进行绑定
ret = ;
pr_debug("bus: '%s': %s: bound device %s to driver %s/n",
drv->bus->name, __func__, dev_name(dev), drv->name);
goto done;
probe_failed:
devres_release_all(dev);
driver_sysfs_remove(dev);
dev->driver = NULL;
if (ret != -ENODEV && ret != -ENXIO) {
/* driver matched but the probe failed */
printk(KERN_WARNING
"%s: probe of %s failed with error %d/n",
drv->name, dev_name(dev), ret);
}
/*
* Ignore errors returned by ->probe so that the next driver can try
* its luck.
*/
ret = ;
done:
atomic_dec(&probe_count);
wake_up(&probe_waitqueue);
return ret;
}
/**********************************
* 最后跟一下driver_bound(dev)这个函数
**********************************/
static void driver_bound(struct device *dev)
{
if (klist_node_attached(&dev->p->knode_driver)) { //判断是否已经绑定
printk(KERN_WARNING "%s: device %s already bound/n",
__func__, kobject_name(&dev->kobj));
return;
}
pr_debug("driver: '%s': %s: bound to device '%s'/n", dev_name(dev),
__func__, dev->driver->name);
klist_add_tail(&dev->p->knode_driver, &dev->driver->p->klist_devices); //将设备添加
//到driver的链表
if (dev->bus)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_BOUND_DRIVER, dev);
}
//all end
总结一下，driver的注册，主要涉及将自身挂接到bus的driver链表，并将匹配到的设备加入自己的device链表，并且将匹配到的device的driver成员初始化为该driver，私有属性的driver节点也挂到driver的设备链表下，其中匹配函数是利用利用bus的match函数，该函数通常判断如果driver有id表，就查表匹配，如果没有就用driver和device名字匹配。当匹配成功后如果自动初始化标志允许则调用初始化函数probe，bus的probe优先级始终高于driver的，而一般bus的probe最终也是调用bus-->dev-->driver的probe。另外注意一点driver是没有总的起始端点的，driver不是可具体描述的事物。
===========================================================================================================
由于篇幅比较长，device的分析单独放到以下：
三、device的注册
还是照例先看一下device的结构：
struct device {
struct device *parent;
struct device_private *p; //私有属性结构，重点
struct kobject kobj;
const char *init_name; /* initial name of the device */
struct device_type *type;
struct mutex mutex; /* mutex to synchronize calls to
* its driver.
*/
struct bus_type *bus; /* type of bus device is on */ //所在bus
struct device_driver *driver; /* which driver has allocated this //匹配的driver
device */
void *platform_data; /* Platform specific data, device
core doesn't touch it */
struct dev_pm_info power;
#ifdef CONFIG_NUMA
int numa_node; /* NUMA node this device is close to */
#endif
u64 *dma_mask; /* dma mask (if dma'able device) */
u64 coherent_dma_mask;/* Like dma_mask, but for
alloc_coherent mappings as
not all hardware supports
64 bit addresses for consistent
allocations such descriptors. */
struct device_dma_parameters *dma_parms;
struct list_head dma_pools; /* dma pools (if dma'ble) */
struct dma_coherent_mem *dma_mem; /* internal for coherent mem
override */
/* arch specific additions */
struct dev_archdata archdata;
#ifdef CONFIG_OF
struct device_node *of_node;
#endif
dev_t devt; /* dev_t, creates the sysfs "dev" */
spinlock_t devres_lock;
struct list_head devres_head;
struct klist_node knode_class;
struct class *class;
const struct attribute_group **groups; /* optional groups */
void (*release)(struct device *dev);
};
//重点看一下私有属性结构
struct device_private {
struct klist klist_children; //子集结构
struct klist_node knode_parent; //父级挂接点
struct klist_node knode_driver; //driver挂接点
struct klist_node knode_bus; //bus挂接点
void *driver_data;
struct device *device; //回指
};
接下来详细看一下device的注册device_register:
int device_register(struct device *dev)
{
device_initialize(dev); //初始化dev
return device_add(dev); //添加dev
}
/******************************
* 先看一下device_initialize(dev)
******************************/
void device_initialize(struct device *dev)
{
dev->kobj.kset = devices_kset; //可见device和bus都有其起始的kset，而driver没有
kobject_init(&dev->kobj, &device_ktype); //初始化这个kobj并建立层次关系以及属性文件，此时
INIT_LIST_HEAD(&dev->dma_pools); //是放到了总的device文件目录下面
mutex_init(&dev->mutex);
lockdep_set_novalidate_class(&dev->mutex);
spin_lock_init(&dev->devres_lock);
INIT_LIST_HEAD(&dev->devres_head);
device_pm_init(dev);
set_dev_node(dev, -);
}
/******************************
* 再来看一下device_add(dev)
******************************/
int device_add(struct device *dev)
{
struct device *parent = NULL;
struct class_interface *class_intf;
int error = -EINVAL;
dev = get_device(dev);
if (!dev)
goto done;
if (!dev->p) {
error = device_private_init(dev); //初始化dev的私有成员，及其链表操作函数
if (error)
goto done;
}
/*
* for statically allocated devices, which should all be converted
* some day, we need to initialize the name. We prevent reading back
* the name, and force the use of dev_name()
*/
if (dev->init_name) {
dev_set_name(dev, "%s", dev->init_name); //设置名字，给kobj
dev->init_name = NULL;
}
if (!dev_name(dev)) { //名字为空出错退出
error = -EINVAL;
goto name_error;
}
pr_debug("device: '%s': %s/n", dev_name(dev), __func__);
parent = get_device(dev->parent); //返回父节点，如果有返回，没有返回NULL
setup_parent(dev, parent);
/* use parent numa_node */
if (parent)
set_dev_node(dev, dev_to_node(parent));
/* first, register with generic layer. */
/* we require the name to be set before, and pass NULL */
error = kobject_add(&dev->kobj, dev->kobj.parent, NULL); //初始化kobj与其父节点的连接
if (error)
goto Error;
/* notify platform of device entry */
if (platform_notify)
platform_notify(dev);
error = device_create_file(dev, &uevent_attr); //产生属性文件
if (error)
goto attrError;
if (MAJOR(dev->devt)) {
error = device_create_file(dev, &devt_attr); //在sys下产生dev属性文件
if (error)
goto ueventattrError;
error = device_create_sys_dev_entry(dev);
if (error)
goto devtattrError;
devtmpfs_create_node(dev);
}
error = device_add_class_symlinks(dev);
if (error)
goto SymlinkError;
error = device_add_attrs(dev); //增加属性文件
if (error)
goto AttrsError;
error = bus_add_device(dev); //把device的bus节点挂到bus的设备节点上
if (error)
goto BusError;
error = dpm_sysfs_add(dev);
if (error)
goto DPMError;
device_pm_add(dev);
/* Notify clients of device addition. This call must come
* after dpm_sysf_add() and before kobject_uevent().
*/
if (dev->bus)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_ADD_DEVICE, dev);
kobject_uevent(&dev->kobj, KOBJ_ADD);
bus_probe_device(dev); //匹配driver
if (parent)
klist_add_tail(&dev->p->knode_parent, //把该设备的节点挂到其父节点的链表
&parent->p->klist_children);
if (dev->class) {
mutex_lock(&dev->class->p->class_mutex);
/* tie the class to the device */
klist_add_tail(&dev->knode_class,
&dev->class->p->class_devices);
/* notify any interfaces that the device is here */
list_for_each_entry(class_intf,
&dev->class->p->class_interfaces, node)
if (class_intf->add_dev)
class_intf->add_dev(dev, class_intf);
mutex_unlock(&dev->class->p->class_mutex);
}
done:
put_device(dev);
return error;
DPMError:
bus_remove_device(dev);
BusError:
device_remove_attrs(dev);
AttrsError:
device_remove_class_symlinks(dev);
SymlinkError:
if (MAJOR(dev->devt))
devtmpfs_delete_node(dev);
if (MAJOR(dev->devt))
device_remove_sys_dev_entry(dev);
devtattrError:
if (MAJOR(dev->devt))
device_remove_file(dev, &devt_attr);
ueventattrError:
device_remove_file(dev, &uevent_attr);
attrError:
kobject_uevent(&dev->kobj, KOBJ_REMOVE);
kobject_del(&dev->kobj);
Error:
cleanup_device_parent(dev);
if (parent)
put_device(parent);
name_error:
kfree(dev->p);
dev->p = NULL;
goto done;
}
/***********************************************
* 重点看一下bus_probe_device匹配driver以及初始化过程
***********************************************/
void bus_probe_device(struct device *dev)
{
struct bus_type *bus = dev->bus;
int ret;
if (bus && bus->p->drivers_autoprobe) { //设置了自动匹配初始化那么就开始匹配
ret = device_attach(dev);
WARN_ON(ret < );
}
}
/******************
* 继续device_attach
******************/
int device_attach(struct device *dev)
{
int ret = ;
device_lock(dev);
if (dev->driver) { //默认指定了driver就直接绑定
ret = device_bind_driver(dev);
if (ret == )
ret = ;
else {
dev->driver = NULL;
ret = ;
}
} else { //没有指定就进行遍历匹配
pm_runtime_get_noresume(dev);
ret = bus_for_each_drv(dev->bus, NULL, dev, __device_attach);
pm_runtime_put_sync(dev);
}
device_unlock(dev);
return ret;
}
/**************************
* 再来看device_bind_driver分支
**************************/
int device_bind_driver(struct device *dev)
{
int ret;
ret = driver_sysfs_add(dev);
if (!ret)
driver_bound(dev); //主要是完成了将私有成员的driver节点挂到
return ret; //了driver的设备链表
}
/**************************
* 先看bus_for_each_drv分支
**************************/
int bus_for_each_drv(struct bus_type *bus, struct device_driver *start,
void *data, int (*fn)(struct device_driver *, void *))
{
struct klist_iter i;
struct device_driver *drv;
int error = ;
if (!bus)
return -EINVAL;
klist_iter_init_node(&bus->p->klist_drivers, &i, //和driver遍历device类似，从头开始遍历bus的driver链表
start ? &start->p->knode_bus : NULL); //发现一个driver就调用fn即__device_attach进行匹配
while ((drv = next_driver(&i)) && !error)
error = fn(drv, data);
klist_iter_exit(&i);
return error;
}
/*********************************
* 最后来看一下__device_attach这个函数
*********************************/
static int __device_attach(struct device_driver *drv, void *data)
{
struct device *dev = data;
if (!driver_match_device(drv, dev))
return ;
return driver_probe_device(drv, dev);
}
/*
对比driver的注册最后调用的__driver_attach可以发现其实质是一样的，都最后归宿到了
这driver_match_device，driver_probe_device两个函数,本质参数的和谐做到了通用
性在这里就不继续分析了，不是很清楚的可以看前一篇文章driver最后一部分的分析 ^_^
*/
以上便是device的注册，可以发现device和driver围绕着bus最后有种殊途同归的感觉，下面结合driver的流程给出一个框图
以便更明确其间的流程：