Input Core和evdev基本知识 - Kernel3.0.8

1. 基本数据结构和使用示例

input_event数据结构如下：

struct input_event {
    struct timeval time;
    __u16 type;
    __u16 code;
    __s32 value;
};

input_dev数据结构如下：

struct input_dev {
    const char *name;
    const char *phys;
    const char *uniq;
    struct input_id id;

    unsigned long propbit[BITS_TO_LONGS(INPUT_PROP_CNT)];

    unsigned long evbit[BITS_TO_LONGS(EV_CNT)];
    unsigned long keybit[BITS_TO_LONGS(KEY_CNT)];
    unsigned long relbit[BITS_TO_LONGS(REL_CNT)];
    unsigned long absbit[BITS_TO_LONGS(ABS_CNT)];
    unsigned long mscbit[BITS_TO_LONGS(MSC_CNT)];
    unsigned long ledbit[BITS_TO_LONGS(LED_CNT)];
    unsigned long sndbit[BITS_TO_LONGS(SND_CNT)];
    unsigned long ffbit[BITS_TO_LONGS(FF_CNT)];
    unsigned long swbit[BITS_TO_LONGS(SW_CNT)];

    unsigned int hint_events_per_packet;

    unsigned int keycodemax;
    unsigned int keycodesize;
    void *keycode;

    int (*setkeycode)(struct input_dev *dev,
              const struct input_keymap_entry *ke,
              unsigned int *old_keycode);
    int (*getkeycode)(struct input_dev *dev,
              struct input_keymap_entry *ke);

    struct ff_device *ff;

    unsigned int repeat_key;
    struct timer_list timer;

    int rep[REP_CNT];

    struct input_mt_slot *mt;
    int mtsize;
    int slot;
    int trkid;

    struct input_absinfo *absinfo;

    unsigned long key[BITS_TO_LONGS(KEY_CNT)];
    unsigned long led[BITS_TO_LONGS(LED_CNT)];
    unsigned long snd[BITS_TO_LONGS(SND_CNT)];
    unsigned long sw[BITS_TO_LONGS(SW_CNT)];

    int (*open)(struct input_dev *dev);
    void (*close)(struct input_dev *dev);
    int (*flush)(struct input_dev *dev, struct file *file);
    int (*event)(struct input_dev *dev, unsigned int type, unsigned int code, int value);

    struct input_handle __rcu *grab;

    spinlock_t event_lock;
    struct mutex mutex;

    unsigned int users;
    bool going_away;

    bool sync;

    struct device dev;

    struct list_head    h_list;
    struct list_head    node;
}

比如TouchScrenn报告一个TouchDown事件给Input子系统，其代码如下：

input_report_abs(inputdevice, ABS_X, 100);
input_report_abs(inputdevice, ABS_Y, 200);
input_report_key(inputdevice, BTN_TOUCH,  1);

static inline void input_report_abs(struct input_dev *dev, unsigned int code, int value)
{
    input_event(dev, EV_ABS, code, value);
}

static inline void input_report_key(struct input_dev *dev, unsigned int code, int value)
{
    input_event(dev, EV_KEY, code, !!value);
}

/**
 * input_event() - report new input event
 * @dev: device that generated the event
 * @type: type of the event
 * @code: event code
 * @value: value of the event
 *
 * This function should be used by drivers implementing various input
 * devices to report input events. See also input_inject_event().
 */
void input_event(struct input_dev *dev,
         unsigned int type, unsigned int code, int value)
{
    unsigned long flags;

    if (is_event_supported(type, dev->evbit, EV_MAX)) {

        spin_lock_irqsave(&dev->event_lock, flags);
        add_input_randomness(type, code, value);
        input_handle_event(dev, type, code, value);
        spin_unlock_irqrestore(&dev->event_lock, flags);
    }
}

它将调用input_pass_event，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_handler *handler;
    struct input_handle *handle;

    rcu_read_lock();

    handle = rcu_dereference(dev->grab);
    if (handle)
        handle->handler->event(handle, type, code, value);
    else {
        bool filtered = false;

        list_for_each_entry_rcu(handle, &dev->h_list, d_node) {
            if (!handle->open)
                continue;

            handler = handle->handler;
            if (!handler->filter) {
                if (filtered)
                    break;

                handler->event(handle, type, code, value);

            } else if (handler->filter(handle, type, code, value))
                filtered = true;
        }
    }

    rcu_read_unlock();
}

上面的handler就是下面的evdev_handler.
2. evdev & input core & input_dev初始化

在kernel中，调用函数evdev_read,此函数从client->buffer中（evdev_client *client = file->private_data;）copy对应的input_event到用户提供的buffer。这些input_event数据如何从input_handle_event到client->buffer中的呢? 它是在evdev_event中实现的。

<span style="font-size:10px;">static struct input_handler evdev_handler = {
    .event      = evdev_event,
    .connect    = evdev_connect,
    .disconnect = evdev_disconnect,
    .fops       = &evdev_fops,
    .minor      = EVDEV_MINOR_BASE,
    .name       = "evdev",
    .id_table   = evdev_ids,
};</span>

    input_dev如何与evdev_handler关联起来的呢？ 它只在evdev_init中调用input_register_handler(&evdev_handler)被注册了。其关联关系如下：   

   a）在input_register_handler中，把evdev_handler增加到input_handler_list中   

   b）在input_register_device中，通过input_attach_handler(dev, handler)，寻找input_handler_list中哪一个input_handler与需要注册的设备相匹配，找到匹配的，则调用此input_handler的connect把input_handler与注册的input_device关联起来，这样新注册的input_device就有对应的处理方法了。

 

<span style="font-size:10px;">static int input_attach_handler(struct input_dev *dev, struct input_handler *handler)
{
    const struct input_device_id *id;
    int error;

    id = input_match_device(handler, dev);
    if (!id)
        return -ENODEV;

    error = handler->connect(handler, dev, id);
    if (error && error != -ENODEV)
        pr_err("failed to attach handler %s to device %s, error: %d\n",
               handler->name, kobject_name(&dev->dev.kobj), error);

    return error;
} </span>

     c）如果匹配上了，就调用evdev_handler->connect函数(evdev_connect),它把此evdev_handler保存在新设备的handle->handler中(evdev->handle.handler = handler;)。这样在input_pass_event就可以调用evdev->handle.handler.event了。        

    d）input_handle把input_device和input_handler关联起来，其数据结构如下： 

 

struct input_handle {

    void *private;

    int open;
    const char *name;

    struct input_dev *dev;
    struct input_handler *handler;

    struct list_head    d_node;
    struct list_head    h_node;
};

  e）evdev为事件字符设备( Event char devices)提供了访问原始输入设备事件的方法，即它是做具体事的东东，对于事件字符设备，当我们调用open, read, write最终都会调用它的函数，即evdev_fops中的对应函数。有了evdev和input core，设备驱动程序就很简单了.

   e.1）首先调用input_allocate_device 创建一个input_dev对象

   e.2）然后设备input_dev的各种属性以告诉input core你将提供哪些事件

   e.3）最后调用input_register_device把input_dev注册到input core

   f）input_register_device

       前面讲过，在input_register_device中，它将在input_handler_list 寻找与input_dev匹配的input_handler，然后调用input_handler的connect函数，即evdev_connect。在evdev_connect中，它将创建evdev对象，并以evdev->minor作为索引把它放在evdev_table数组中。evdev数据结构如下：

struct evdev {
    int open;
    int minor;   //在evdev_table中的索引
    struct input_handle handle;  //连接input_dev和input_handler
    wait_queue_head_t wait;
    struct evdev_client __rcu *grab;   // 用户每调用一次open,将创建一个evdev_client
    struct list_head client_list;
    spinlock_t client_lock; /* protects client_list */
    struct mutex mutex;
    struct device dev;
    bool exist;
};

struct evdev_client {
    unsigned int head;
    unsigned int tail;
    unsigned int packet_head; /* [future] position of the first element of next packet */
    spinlock_t buffer_lock; /* protects access to buffer, head and tail */
    struct wake_lock wake_lock;
    char name[28];
    struct fasync_struct *fasync;
    struct evdev *evdev;
    struct list_head node;
    unsigned int bufsize;
    struct input_event buffer[];  //存放所有这个设备产生的input_event,由evdev_event写入
};

        在evdev_connect，它设置设备名，初始化input_handle中各个数据成员（关键是其input_dev和input_handler），然后再调用input_register_handle把evdev中的input_handle添加到input_dev的h_lis链表中，并且把此input_handle添加到input_handler的h_list链表中。从此它们的三角关系建立完成。注：当用户每打开一次它就要创建一个evdev_client，并加入到client_list链表中，当input_dev产生事件时，evdev_event函数将把此input_event放入evdev->client_list链表中的每个evdev_client的buffer中。它们的关系如下图所示：

3. Kernel中数据读取流程

     在kernel中调用evdev_read来读取数据，其函数原型如下：

static ssize_t evdev_read(struct file *file, char __user *buffer, size_t count, loff_t *ppos)

    其读取流程为：

    1）从前面得知在打开设备文件时，创建了一个evdev_client，并把此client保存在file的private_data中，所以现在从file->private_data中取出evdev_client

    2）从前面得知此evdev_client中保存有在evdev_connect时创建的evdev，从而可以得到对应的evdev对象

    3）从client->buffer中读取事件，并copy到用户提供的buffer中。前面讲过，client->buffer中的事件是当input_dev报告事件给Input core时，由evdev_event把input_event事件放入client->buffer中的。