前言在键盘驱动代码分析的笔记中,接触到了input子系统.键盘驱动,键盘驱动将检测到的所有按键都上报给了input子系统。Input子系统是所有I/O设备驱动的中间层,为上层提供了一个统一的界面。例如,在终端系统中,我们不需要去管有多少个键盘,多少个鼠标。它只要从input子系统中去取对应的事件(按键,鼠标移位等)就可以了。今天就对input子系统做一个详尽的分析.下面的代码是基于linux kernel 2.6.25.分析的代码主要位于kernel2.6.25/drivers/input下面.二:使用input子系统的例子在内核自带的文档Documentation/input/input-programming.txt中。有一个使用input子系统的例子,并附带相应的说明。以此为例分析如下:#include handler->name, kobject_name(&dev->dev.kobj), error);          return error;}如果handle的blacklist被赋值。要先匹配blacklist中的数据跟dev->id的数据是否匹配。匹配成功过后再来匹配handle->id和dev->id中的数据。如果匹配成功,则调用handler->connect().来看一下具体的数据匹配过程,这是在input_match_device()中完成的。代码如下:static const struct input_device_id *input_match_device(const struct input_device_id *id,                                                                 struct input_dev *dev){         int i;          for (; id->flags || id->driver_info; id++) {                    if (id->flags & INPUT_DEVICE_ID_MATCH_BUS)                            if (id->bustype != dev->id.bustype)                                     continue;                    if (id->flags & INPUT_DEVICE_ID_MATCH_VENDOR)                            if (id->vendor != dev->id.vendor)                                     continue;                    if (id->flags & INPUT_DEVICE_ID_MATCH_PRODUCT)                            if (id->product != dev->id.product)                                     continue;                    if (id->flags & INPUT_DEVICE_ID_MATCH_VERSION)                            if (id->version != dev->id.version)                                     continue;                    MATCH_BIT(evbit,  EV_MAX);                   MATCH_BIT(,, KEY_MAX);                   MATCH_BIT(relbit, REL_MAX);                   MATCH_BIT(absbit, ABS_MAX);                   MATCH_BIT(mscbit, MSC_MAX);                   MATCH_BIT(ledbit, LED_MAX);                   MATCH_BIT(sndbit, SND_MAX);                   MATCH_BIT(ffbit,  FF_MAX);                   MATCH_BIT(swbit,  SW_MAX);                    return id;         }          return NULL;}MATCH_BIT宏的定义如下:#define MATCH_BIT(bit, max)                   for (i = 0; i                             if ((id->bit[i] & dev->bit[i]) != id->bit[i])                                     break;                   if (i != BITS_TO_LONGS(max))                            continue; 由此看到。在id->flags中定义了要匹配的项。定义INPUT_DEVICE_ID_MATCH_BUS。则是要比较inputdevice和inputhandler的总线类型。INPUT_DEVICE_ID_MATCH_VENDOR,INPUT_DEVICE_ID_MATCH_PRODUCT,INPUT_DEVICE_ID_MATCH_VERSION分别要求设备厂商。设备号和设备版本.如果id->flags定义的类型匹配成功。或者是id->flags没有定义,就会进入到MATCH_BIT的匹配项了.从MATCH_BIT宏的定义可以看出。只有当iput device和inputhandler的id成员在evbit, keybit,… swbit项相同才会匹配成功。而且匹配的顺序是从evbit,keybit到swbit.只要有一项不同,就会循环到id中的下一项进行比较.简而言之,注册input device的过程就是为input device设置默认值,并将其挂以input_dev_list.与挂载在input_handler_list中的handler相匹配。如果匹配成功,就会调用handler的connect函数. 四:handler注册分析Handler注册的接口如下所示:int input_register_handler(struct input_handler *handler){         struct input_dev *dev;         int retval;          retval = mutex_lock_interruptible(&input_mutex);         if (retval)                   return retval;          INIT_LIST_HEAD(&handler->h_list);          if (handler->fops != NULL) {                   if (input_table[handler->minor >> 5]) {                            retval = -EBUSY;                            goto out;                   }                   input_table[handler->minor >> 5] = handler;         }          list_add_tail(&handler->node, &input_handler_list);          list_for_each_entry(dev, &input_dev_list, node)                   input_attach_handler(dev, handler);          input_wakeup_procfs_readers();  out:         mutex_unlock(&input_mutex);         return retval;}handler->minor表示对应input设备节点的次设备号.以handler->minor右移五位做为索引值插入到input_table[ ]中..之后再来分析input_talbe[ ]的作用.然后将handler挂到input_handler_list中.然后将其与挂在input_dev_list中的input device匹配.这个过程和input device的注册有相似的地方.都是注册到各自的链表,.然后与另外一条链表的对象相匹配.handle的注册int input_register_handle(struct input_handle *handle){         struct input_handler *handler = handle->handler;         struct input_dev *dev = handle->dev;         int error;          /*          * We take dev->mutex here to prevent race with          * input_release_device().          */         error = mutex_lock_interruptible(&dev->mutex);         if (error)                   return error;         list_add_tail_rcu(&handle->d_node, &dev->h_list);         mutex_unlock(&dev->mutex);         synchronize_rcu();                  list_add_tail(&handle->h_node, &handler->h_list);          if (handler->start)                   handler->start(handle);          return 0;}在这个函数里所做的处理其实很简单.将handle挂到所对应input device的h_list链表上.还将handle挂到对应的handler的hlist链表上.如果handler定义了start函数,将调用之.到这里,我们已经看到了input device, handler和handle是怎么关联起来的了.以图的方式总结如下:      六:event事件的处理我们在开篇的时候曾以linux kernel文档中自带的代码作分析.提出了几个事件上报的API.这些API其实都是input_event()的封装.代码如下:void input_event(struct input_dev *dev,                    unsigned int type, unsigned int code, int value){         unsigned long flags;          //判断设备是否支持这类事件         if (is_event_supported(type, dev->evbit, EV_MAX)) {                    spin_lock_irqsave(&dev->event_lock, flags);                   //利用键盘输入来调整随机数产生器                   add_input_randomness(type, code, value);                   input_handle_event(dev, type, code, value);                   spin_unlock_irqrestore(&dev->event_lock, flags);         }}首先,先判断设备产生的这个事件是否合法.如果合法,流程转入到input_handle_event()中.代码如下:static void input_handle_event(struct input_dev *dev,                                   unsigned int type, unsigned int code, int value){         int disposition = INPUT_IGNORE_EVENT;          switch (type) {          case EV_SYN:                   switch (code) {                   case SYN_CONFIG:                            disposition = INPUT_PASS_TO_ALL;                            break;                    case SYN_REPORT:                            if (!dev->sync) {                                     dev->sync = 1;                                     disposition = INPUT_PASS_TO_HANDLERS;                            }                            break;                   }                   break;          case EV_KEY:                   //判断按键值是否被支持                   if (is_event_supported(code, dev->keybit, KEY_MAX) &&                       !!test_bit(code, dev->key) != value) {                             if (value != 2) {                                     __change_bit(code, dev->key);                                     if (value)                                               input_start_autorepeat(dev, code);                            }                             disposition = INPUT_PASS_TO_HANDLERS;                   }                   break;          case EV_SW:                   if (is_event_supported(code, dev->swbit, SW_MAX) &&                       !!test_bit(code, dev->sw) != value) {                             __change_bit(code, dev->sw);                            disposition = INPUT_PASS_TO_HANDLERS;                   }                   break;case EV_ABS:                   if (is_event_supported(code, dev->absbit, ABS_MAX)) {                             value = input_defuzz_abs_event(value,                                               dev->abs[code], dev->absfuzz[code]);                             if (dev->abs[code] != value) {                                     dev->abs[code] = value;                                     disposition = INPUT_PASS_TO_HANDLERS;                            }                   }                   break;          case EV_REL:                   if (is_event_supported(code, dev->relbit, REL_MAX) && value)                            disposition = INPUT_PASS_TO_HANDLERS;                    break;          case EV_MSC:                   if (is_event_supported(code, dev->mscbit, MSC_MAX))                            disposition = INPUT_PASS_TO_ALL;                    break;          case EV_LED:                   if (is_event_supported(code, dev->ledbit, LED_MAX) &&                       !!test_bit(code, dev->led) != value) {                             __change_bit(code, dev->led);                            disposition = INPUT_PASS_TO_ALL;                   }                   break;          case EV_SND:                   if (is_event_supported(code, dev->sndbit, SND_MAX)) {                             if (!!test_bit(code, dev->snd) != !!value)                                     __change_bit(code, dev->snd);                            disposition = INPUT_PASS_TO_ALL;                   }                   break;          case EV_REP:                   if (code = 0 && dev->rep[code] != value) {                            dev->rep[code] = value;                            disposition = INPUT_PASS_TO_ALL;                   }                   break;          case EV_FF:                   if (value >= 0)                            disposition = INPUT_PASS_TO_ALL;                   break;          case EV_PWR:                   disposition = INPUT_PASS_TO_ALL;                   break;         }          if (type != EV_SYN)                   dev->sync = 0;          if ((disposition & INPUT_PASS_TO_DEVICE) && dev->event)                   dev->event(dev, type, code, value);          if (disposition & INPUT_PASS_TO_HANDLERS)                   input_pass_event (dev, type, code, value);}在这里,我们忽略掉具体事件的处理.到最后,如果该事件需要inputdevice来完成的,就会将disposition设置成INPUT_PASS_TO_DEVICE.如果需要handler来完成的,就将dispostion设为INPUT_PASS_TO_DEVICE.如果需要两者都参与,将disposition设置为INPUT_PASS_TO_ALL.需要输入设备参与的,回调设备的event函数.如果需要handler参与的.调用input_pass_event().代码如下:static void input_pass_event(struct input_dev *dev,                                 unsigned int type, unsigned int code, int value){         struct input_handle *handle;          rcu_read_lock();          handle = rcu_dereference(dev->grab);         if (handle)                   handle->handler->event(handle, type, code, value);         else                   list_for_each_entry_rcu(handle, &dev->h_list, d_node)                            if (handle->open)                                     handle->handler->event(handle,type, code, value);         rcu_read_unlock();}如果input device被强制指定了handler,则调用该handler的event函数.结合handle注册的分析.我们知道.会将handle挂到input device的h_list链表上.如果没有为input device强制指定handler.就会遍历inputdevice->h_list上的handle成员.如果该handle被打开,则调用与输入设备对应的handler的event()函数.注意,只有在handle被打开的情况下才会接收到事件.另外,输入设备的handler强制设置一般是用带EVIOCGRAB标志的ioctl来完成的.如下是发图的方示总结evnet的处理过程:       我们已经分析了input device,handler和handle的注册过程以及事件的上报和处理.下面以evdev为实例做分析.来贯穿理解一下整个过程. 七:evdev概述 Evdev对应的设备节点一般位于/dev/input/event0 ~ /dev/input/event4.理论上可以对应32个设备节点.分别代表被handler匹配的32个input device.可以用cat /dev/input/event0.然后移动鼠标或者键盘按键就会有数据输出(两者之间只能选一.因为一个设备文件只能关能一个输入设备).还可以往这个文件里写数据,使其产生特定的事件.这个过程我们之后再详细分析.为了分析这一过程,必须从input子系统的初始化说起. 八:input子系统的初始化Input子系统的初始化函数为input_init().代码如下:static int __init input_init(void){         int err;          err = class_register(&input_class);         if (err) {                   printk(KERN_ERR "input: unable to register input_dev class\n");                   return err;         }          err = input_proc_init();         if (err)                   goto fail1;          err = register_chrdev(INPUT_MAJOR, "input", &input_fops);         if (err) {                   printk(KERN_ERR "input: unable to register char major %d", INPUT_MAJOR);                   goto fail2;         }          return 0;  fail2:        input_proc_exit(); fail1:        class_unregister(&input_class);         return err;}在这个初始化函数里,先注册了一个名为”input”的类.所有input device都属于这个类.在sysfs中表现就是.所有input device所代表的目录都位于/dev/class/input下面.然后调用input_proc_init()在/proc下面建立相关的交互文件.再后调用register_chrdev()注册了主设备号为INPUT_MAJOR(13).次设备号为0~255的字符设备.它的操作指针为input_fops.在这里,我们看到.所有主设备号13的字符设备的操作最终都会转入到input_fops中.在前面分析的/dev/input/event0~/dev/input/event4的主设备号为13.操作也不例外的落在了input_fops中.Input_fops定义如下:static const struct file_operations input_fops = {         .owner = THIS_MODULE,         .open = input_open_file,};打开文件所对应的操作函数为input_open_file.代码如下示:static int input_open_file(struct inode *inode, struct file *file){         struct input_handler *handler = input_table[iminor(inode) >> 5];         const struct file_operations *old_fops, *new_fops = NULL;         int err;                  if (!handler || !(new_fops = fops_get(handler->fops)))                   return -ENODEV; iminor(inode)为打开文件所对应的次设备号.input_table是一个structinput_handler全局数组.在这里.它先设备结点的次设备号右移5位做为索引值到input_table中取对应项.从这里我们也可以看到.一个handle代表1 在input_table中找到对应的handler之后,就会检验这个handle是否存,是否带有fops文件操作集.如果没有.则返回一个设备不存在的错误.                 if (!new_fops->open) {                   fops_put(new_fops);                   return -ENODEV;         }         old_fops = file->f_op;         file->f_op = new_fops;          err = new_fops->open(inode, file);          if (err) {                   fops_put(file->f_op);                   file->f_op = fops_get(old_fops);         }         fops_put(old_fops);         return err;}然后将handler中的fops替换掉当前的fops.如果新的fops中有open()函数,则调用它. 九:evdev的初始化Evdev的模块初始化函数为evdev_init().代码如下:static int __init evdev_init(void){         return input_register_handler(&evdev_handler);}它调用了input_register_handler注册了一个handler.注意到,在这里evdev_handler中定义的minor为EVDEV_MINOR_BASE(64).也就是说evdev_handler所表示的设备文件范围为(13,64)à(13,64+32).从之前的分析我们知道.匹配成功的关键在于handler中的blacklist和id_talbe. Evdev_handler的id_table定义如下:static const struct input_device_id evdev_ids[] = {         { .driver_info = 1 },             { },                      };它没有定义flags.也没有定义匹配属性值.这个handler是匹配所有input device的.从前面的分析我们知道.匹配成功之后会调用handler->connect函数.在Evdev_handler中,该成员函数如下所示: static int evdev_connect(struct input_handler *handler, struct input_dev *dev,                             const struct input_device_id *id){         struct evdev *evdev;         int minor;         int error;          for (minor = 0; minor                    if (!evdev_table[minor])                            break;          if (minor == EVDEV_MINORS) {                   printk(KERN_ERR "evdev: no more free evdev devices\n");                   return -ENFILE;         }EVDEV_MINORS定义为32.表示evdev_handler所表示的32个设备文件.evdev_talbe是一个struct evdev类型的数组.struct evdev是模块使用的封装结构.在接下来的代码中我们可以看到这个结构的使用.这一段代码的在evdev_talbe找到为空的那一项.minor就是数组中第一项为空的序号.          evdev = kzalloc(sizeof(struct evdev), GFP_KERNEL);         if (!evdev)                   return -ENOMEM;          INIT_LIST_HEAD(&evdev->client_list);         spin_lock_init(&evdev->client_lock);mutex_init(&evdev->mutex);         init_waitqueue_head(&evdev->wait);          snprintf(evdev->name, sizeof(evdev->name), "event%d", minor);         evdev->exist = 1;         evdev->minor = minor;          evdev->handle.dev = input_get_device(dev);         evdev->handle.name = evdev->name;         evdev->handle.handler = handler;         evdev->handle.private = evdev;接下来,分配了一个evdev结构,并对这个结构进行初始化.在这里我们可以看到,这个结构封装了一个handle结构,这结构与我们之前所讨论的handler是不相同的.注意有一个字母的差别哦.我们可以把handle看成是handler和inputdevice的信息集合体.在这个结构里集合了匹配成功的handler和input device          strlcpy(evdev->dev.bus_id, evdev->name, sizeof(evdev->dev.bus_id));         evdev->dev.devt = MKDEV(INPUT_MAJOR, EVDEV_MINOR_BASE + minor);         evdev->dev.class = &input_class;         evdev->dev.parent = &dev->dev;         evdev->dev.release = evdev_free;         device_initialize(&evdev->dev);在这段代码里主要完成evdev封装的device的初始化.注意在这里,使它所属的类指向input_class.这样在/sysfs中创建的设备目录就会在/sys/class/input/下面显示.          error = input_register_handle(&evdev->handle);         if (error)                   goto err_free_evdev;         error = evdev_install_chrdev(evdev);         if (error)                   goto err_unregister_handle;          error = device_add(&evdev->dev);         if (error)                   goto err_cleanup_evdev;          return 0;  err_cleanup_evdev:         evdev_cleanup(evdev); err_unregister_handle:         input_unregister_handle(&evdev->handle); err_free_evdev:         put_device(&evdev->dev);         return error;}注册handle,如果是成功的,那么调用evdev_install_chrdev将evdev_table的minor项指向evdev. 然后将evdev->device注册到sysfs.如果失败,将进行相关的错误处理.万事俱备了,但是要接收事件,还得要等”东风”.这个”东风”就是要打开相应的handle.这个打开过程是在文件的open()中完成的. 十:evdev设备结点的open()操作我们知道.对主设备号为INPUT_MAJOR的设备节点进行操作,会将操作集转换成handler的操作集.在evdev中,这个操作集就是evdev_fops.对应的open函数如下示:static int evdev_open(struct inode *inode, struct file *file){         struct evdev *evdev;         struct evdev_client *client;         int i = iminor(inode) - EVDEV_MINOR_BASE;         int error;          if (i >= EVDEV_MINORS)                   return -ENODEV;          error = mutex_lock_interruptible(&evdev_table_mutex);         if (error)                   return error;         evdev = evdev_table[i];         if (evdev)                   get_device(&evdev->dev);         mutex_unlock(&evdev_table_mutex);          if (!evdev)                   return -ENODEV;          client = kzalloc(sizeof(struct evdev_client), GFP_KERNEL);         if (!client) {                   error = -ENOMEM;                   goto err_put_evdev;         }         spin_lock_init(&client->buffer_lock);         client->evdev = evdev;         evdev_attach_client(evdev, client);          error = evdev_open_device(evdev);         if (error)                   goto err_free_client;          file->private_data = client;         return 0;  err_free_client:         evdev_detach_client(evdev, client);         kfree(client); err_put_evdev:         put_device(&evdev->dev);         return error;}iminor(inode) - EVDEV_MINOR_BASE就得到了在evdev_table[ ]中的序号.然后将数组中对应的evdev取出.递增devdev中device的引用计数.分配并初始化一个client.并将它和evdev关联起来: client->evdev指向它所表示的evdev. 将client挂到evdev->client_list上. 将client赋为file的私有区.对应handle的打开是在此evdev_open_device()中完成的.代码如下:static int evdev_open_device(struct evdev *evdev){         int retval;          retval = mutex_lock_interruptible(&evdev->mutex);         if (retval)                   return retval;          if (!evdev->exist)                   retval = -ENODEV;         else if (!evdev->open++) {                   retval = input_open_device(&evdev->handle);                   if (retval)                            evdev->open--;         }          mutex_unlock(&evdev->mutex);         return retval;}如果evdev是第一次打开,就会调用input_open_device()打开evdev对应的handle.跟踪一下这个函数:int input_open_device(struct input_handle *handle){         struct input_dev *dev = handle->dev;         int retval;          retval = mutex_lock_interruptible(&dev->mutex);         if (retval)                   return retval;          if (dev->going_away) {                   retval = -ENODEV;                   goto out;         }          handle->open++;          if (!dev->users++ && dev->open)                   retval = dev->open(dev);          if (retval) {                   dev->users--;if (!--handle->open) {                                                       synchronize_rcu();                   }         }  out:         mutex_unlock(&dev->mutex);         return retval;}在这个函数中,我们看到.递增handle的打开计数.如果是第一次打开.则调用input device的open()函数. 十一:evdev的事件处理经过上面的分析.每当input device上报一个事件时,会将其交给和它匹配的handler的event函数处理.在evdev中.这个event函数对应的代码为:static void evdev_event(struct input_handle *handle,                            unsigned int type, unsigned int code, int value){         struct evdev *evdev = handle->private;         struct evdev_client *client;         struct input_event event;          do_gettimeofday(&event.time);         event.type = type;         event.code = code;         event.value = value;          rcu_read_lock();          client = rcu_dereference(evdev->grab);         if (client)                   evdev_pass_event(client, &event);         else                   list_for_each_entry_rcu(client, &evdev->client_list, node)                            evdev_pass_event(client, &event);          rcu_read_unlock();          wake_up_interruptible(&evdev->wait);}首先构造一个struct input_event结构.并设备它的type.code,value为处理事件的相关属性.如果该设备被强制设置了handle.则调用如之对应的client.我们在open的时候分析到.会初始化clinet并将其链入到evdev->client_list. 这样,就可以通过evdev->client_list找到这个client了.对于找到的第一个client都会调用evdev_pass_event( ).代码如下:static void evdev_pass_event(struct evdev_client *client,                                 struct input_event *event){                 spin_lock(&client->buffer_lock);         client->buffer[client->head++] = *event;         client->head &= EVDEV_BUFFER_SIZE - 1;         spin_unlock(&client->buffer_lock);          kill_fasync(&client->fasync, SIGIO, POLL_IN);}这里的操作很简单.就是将event保存到client->buffer中.而client->head就是当前的数据位置.注意这里是一个环形缓存区.写数据是从client->head写.而读数据则是从client->tail中读. 十二:设备节点的read处理对于evdev设备节点的read操作都会由evdev_read()完成.它的代码如下:static ssize_t evdev_read(struct file *file, char __user *buffer,                              size_t count, loff_t *ppos){         struct evdev_client *client = file->private_data;         struct evdev *evdev = client->evdev;         struct input_event event;         int retval;          if (count                    return -EINVAL;          if (client->head == client->tail && evdev->exist &&             (file->f_flags & O_NONBLOCK))                   return -EAGAIN;          retval = wait_event_interruptible(evdev->wait,                   client->head != client->tail || !evdev->exist);         if (retval)                   return retval;          if (!evdev->exist)                   return -ENODEV;          while (retval + evdev_event_size()                 evdev_fetch_next_event(client, &event)) {                    if (evdev_event_to_user(buffer + retval, &event))                            return -EFAULT;                    retval += evdev_event_size();         }          return retval;}首先,它判断缓存区大小是否足够.在读取数据的情况下,可能当前缓存区内没有数据可读.在这里先睡眠等待缓存区中有数据.如果在睡眠的时候,.条件满足.是不会进行睡眠状态而直接返回的.然后根据read()提够的缓存区大小.将client中的数据写入到用户空间的缓存区中.十三:设备节点的写操作同样.对设备节点的写操作是由evdev_write()完成的.代码如下: static ssize_t evdev_write(struct file *file, const char __user *buffer,                               size_t count, loff_t *ppos){         struct evdev_client *client = file->private_data;         struct evdev *evdev = client->evdev;         struct input_event event;         int retval;          retval = mutex_lock_interruptible(&evdev->mutex);         if (retval)                   return retval;          if (!evdev->exist) {                   retval = -ENODEV;                   goto out;         }          while (retval                     if (evdev_event_from_user(buffer + retval, &event)) {                            retval = -EFAULT;bsp;               goto out;                   }                    input_inject_event(&evdev->handle,                                        event.type, event.code, event.value);                   retval += evdev_event_size();         }  out:         mutex_unlock(&evdev->mutex);         return retval;}首先取得操作设备文件所对应的evdev.实际上,这里写入设备文件的是一个event结构的数组.我们在之前分析过,这个结构里包含了事件的type.code和event.将写入设备的event数组取出.然后对每一项调用event_inject_event().这个函数的操作和input_event()差不多.就是将第一个参数handle转换为输入设备结构.然后这个设备再产生一个事件.代码如下:void input_inject_event(struct input_handle *handle,                            unsigned int type, unsigned int code, int value){         struct input_dev *dev = handle->dev;         struct input_handle *grab;         unsigned long flags;          if (is_event_supported(type, dev->evbit, EV_MAX)) {                   spin_lock_irqsave(&dev->event_lock, flags);                    rcu_read_lock();                   grab = rcu_dereference(dev->grab);                   if (!grab || grab == handle)                            input_handle_event(dev, type, code, value);                   rcu_read_unlock();                    spin_unlock_irqrestore(&dev->event_lock, flags);         }}我们在这里也可以跟input_event()对比一下,这里设备可以产生任意事件,而不需要和设备所支持的事件类型相匹配.由此可见.对于写操作而言.就是让与设备文件相关的输入设备产生一个特定的事件.将上述设备文件的操作过程以图的方式表示如下:     十四:小结在这一节点,分析了整个input子系统的架构,各个环节的流程.最后还以evdev为例.将各个流程贯穿在一起.以加深对input子系统的理解.由此也可以看出.linux设备驱动采用了分层的模式.从最下层的设备模型到设备,驱动,总线再到input子系统最后到inputdevice.这样的分层结构使得最上层的驱动不必关心下层是怎么实现的.而下层驱动又为多种型号同样功能的驱动提供了一个统一的接口.
10-26 04:30
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