Linux设备模型之bus,device,driver分析
Linux设备模型之bus,device,driver分析
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:
[cpp]
- 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:1; //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:
[cpp]
- 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 = 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
- 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 0;
- 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:
[cpp]
- 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:
[cpp]
- 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 = 0;
- 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 0;
- 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 = 0;
- 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 0;
- 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 0;
- }
- /*********************************************
- × 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) : 1; //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 = 0;
- 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 = 0;
- 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 = 1;
- 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 = 0;
- 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。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的分析放到下一篇《linux设备模型之bus,device,driver分析<二>》 ^_^!
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