[转] linux设备模型之bus，device，driver分析
[本文转自：http://blog.csdn.net/gdt_a20]
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: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：
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：
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 = 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, //通知链 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。
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, -1); } /****************************** * 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 < 0); } } /****************** * 继续device_attach ******************/ int device_attach(struct device *dev) { int ret = 0; device_lock(dev); if (dev->driver) { //默认指定了driver就直接绑定 ret = device_bind_driver(dev); if (ret == 0) ret = 1; else { dev->driver = NULL; ret = 0; } } 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 = 0; 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 0; 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：
