Linux设备模型之input子系统详解(二)

六:event事件的处理

在开始的时候曾以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 <= REP_MAX && value >= 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, 忽略掉具体事件的处理. 到最后,如果该事件需要input device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_HANDLERS.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input device->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：

到此，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.

最后调用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.

这里可以看到.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;

         /* No load-on-demand here? */

         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struct input_handler全局数组.先将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.这里可以看到.一 个handler代表1<<5个设备节点(因为在input_table中取值是以次备号右移5位为索引的.即低5位相同的次备号对应的是同一 个索引).终于看到了input_talbe大显身手的地方了.input_talbe[ ]中取值和input_talbe[ ]的赋值,这两个过程是相对应的.

在input_table中找到对应的handler之后,就会检验这个handler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.

         /*

         * That's _really_ odd. Usually NULL ->open means "nothing special",

         * not "no device". Oh, well...

         */

         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file的fops.如果handler的fops中有open()函数,则调用它.(如果以evdev为例的话，这里的open()函数应该就是evdev_open()函数)

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)~(13,64+32).

从之前的分析知道.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 },     /* Matches all devices */

         { },                       /* Terminating zero entry */

};

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.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 < EVDEV_MINORS; 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.这个结构封装了一个handle结构,这结构与之前所讨论的handler是不相同的.注意有一个字母的差别哦.可以把handle看成是handler和input device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,如果成功,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,则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.