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Linux/Android——input_handler之evdev

    在前文Linux/Android——input子系统核心 中概括了总体的结构,以及介绍了input核心的职责,其中有说道注册input设备时会去匹配已有的事件处理器handler,

而这个handler也是存放在一个链表里面的,这里介绍下input子系统中的事件处理input_handler机制.


                                              撰写不易,转载需注明出处:http://blog.csdn.net/jscese/article/details/42238377#t6


evdev:

  /kernel/drivers/input下众多事件处理器handler其中的一个,可以看下源码/kernel/drivers/input/evdev.c中的模块init:

static int __init evdev_init(void)
{
	return input_register_handler(&evdev_handler);
}

这个初始化就是往input核心中注册一个input_handler类型的evdev_handler,调用的是input.c提供的接口,input_handler结构前文有介绍,看下evdev_handler的赋值:

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,
};

赋值各个函数指针!



input_register_handler:

 可以看到上面的evdev handler 就是调用这个接口注册到input核心中的,同样evdev.c同目录下也还有其它的handler,有兴趣可以看看它们的init函数,都是会调用到这个接口去注册的.

/**
 * input_register_handler - register a new input handler
 * @handler: handler to be registered
 *
 * This function registers a new input handler (interface) for input
 * devices in the system and attaches it to all input devices that
 * are compatible with the handler.
 */
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; //给input.c定义的全局handler 数组赋值,evdev handler的次设备号为64,这里除以32,赋值在input_table[2]
    }

    list_add_tail(&handler->node, &input_handler_list);  //添加进handler 链表

    list_for_each_entry(dev, &input_dev_list, node)   //同样遍历input_dev这个链表,依次调用下面的input_attach_handler去匹配input_dev,这个跟input_dev注册的时候的情形类似
        input_attach_handler(dev, handler);

    input_wakeup_procfs_readers();

 out:
    mutex_unlock(&input_mutex);
    return retval;
}

input核心中保存的handler数组:

static struct input_handler *input_table[8];

这是保存注册到input核心中的handler数组,因为在之前input注册的时候注册的字符设备主设备号为13.字符设备的次设备号为0~255,可以有256个设备,

这里后面会看到一个handler可以connect处理32个input设备,所以input体系中,最多拥有8个handler


这个匹配过程和上一篇中的过程是一样的,最后匹配上的话会调用匹配上的handler 中connect指针指向的函数.


另外可以注意的是evdev是匹配所有设备的,因为:

static const struct input_device_id evdev_ids[] = {
	{ .driver_info = 1 },	/* Matches all devices */
	{ },			/* Terminating zero entry */
};

如果没有特定的handler添加进handler链表,那么在匹配的时候,只要有这个evdev的handler,最后都会匹配到evdev,这个具体可以去看看上篇的匹配过程.

我这边调试的是usb触摸屏,所以用的是evdev的handler,下面看下evdev的connect.


evdev_connect:

 注册的evdev_handler中connect指向的函数为evdev_connect:

/*
 * Create new evdev device. Note that input core serializes calls
 * to connect and disconnect so we don't need to lock evdev_table here.
 */
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) {
        pr_err("no more free evdev devices\n");
        return -ENFILE;
    }

// 可以看到这里evdev handler匹配连接好的设备都以evdev 类型存在这个evdev_table数组的,这个数组大小为32个,这就是我上面说到的,为什么只有8个handler

//这里是判断evdev的32个位置中是否有空

    evdev = kzalloc(sizeof(struct evdev), GFP_KERNEL); //为上面定义的*evdev分配内存空间
    if (!evdev)
        return -ENOMEM;

    INIT_LIST_HEAD(&evdev->client_list); //以下都是对这个 evdev的初始化了
    spin_lock_init(&evdev->client_lock);
    mutex_init(&evdev->mutex);
    init_waitqueue_head(&evdev->wait);

    dev_set_name(&evdev->dev, "event%d", minor);  //给这个evdev命名
    evdev->exist = true;
    evdev->minor = minor;   // 以minor为索引赋值

    evdev->handle.dev = input_get_device(dev);  //evdev中的handle变量的初始化 ,后面分析这个handle ,这里面保存的就是已经匹配成功的input_dev 和 handler
    evdev->handle.name = dev_name(&evdev->dev);
    evdev->handle.handler = handler;
    evdev->handle.private = evdev;

    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);

    error = input_register_handle(&evdev->handle); //把这个evdev中初始化好的handle 注册到input核心中去,代表一个匹配成功的组合
    if (error)
        goto err_free_evdev;

    error = evdev_install_chrdev(evdev);  //把这个初始化好的evdev添加到上面说到过的evdev_table数组,以minor索引序号
    if (error)
        goto err_unregister_handle;

    error = device_add(&evdev->dev); //把这个device 添加到/sys/class/input/下面,所以我们可以看到/dev/input下面看到:event0~31 字样字符设备文件,这就是在上面命名的
    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;
}


evdev:

这里的evdev变量的结构如下:

struct evdev
{
	int open; //打开标志
	int minor; //次设备号
	struct input_handle handle; //包含的handle
	wait_queue_head_t wait; //等待队列

	struct evdev_client __rcu *grab; //强制绑定的evdev_client结构
	struct list_head client_list; //evdev_client 链表,这说明一个evdev设备可以处理多个evdev_client,可以有多个进程访问evdev设备

	spinlock_t client_lock; /* protects client_list */
	struct mutex mutex;
	struct device dev;
	bool exist;
};


关于这个结构变量我的理解是抽象出来一个设备,代表一个input_dev与其匹配好的handler的组合(handle),可以看作提供给事件处理层的一个封装.


input_handle:

这个代表一个匹配成功的input dev和 handler组合,定义在input.h中,每个evdev中包含一个input_handle,并且注册到input核心中:

/**
 * struct input_handle - links input device with an input handler
 * @private: handler-specific data
 * @open: counter showing whether the handle is 'open', i.e. should deliver
 *    events from its device
 * @name: name given to the handle by handler that created it
 * @dev: input device the handle is attached to
 * @handler: handler that works with the device through this handle
 * @d_node: used to put the handle on device's list of attached handles
 * @h_node: used to put the handle on handler's list of handles from which
 *    it gets events
 */
struct input_handle {

    void *private;  //指向上面封装的evdev

    int open;
    const char *name;

    struct input_dev *dev;   //input 设备
    struct input_handler *handler;  // 一个input的handler

    struct list_head    d_node;  //链表结构
    struct list_head    h_node;
};

input_register_handle:

 看看这个handle的注册,不要和handler搞混淆了,这不是一个概念~

/**
 * input_register_handle - register a new input handle
 * @handle: handle to register
 *
 * This function puts a new input handle onto device's
 * and handler's lists so that events can flow through
 * it once it is opened using input_open_device().
 *
 * This function is supposed to be called from handler's
 * connect() method.
 */
int input_register_handle(struct input_handle *handle)
{
    struct input_handler *handler = handle->handler;
    struct input_dev *dev = handle->dev;  //取出两个成员

...

    /*
     * Filters go to the head of the list, normal handlers
     * to the tail.
     */
    if (handler->filter)
        list_add_rcu(&handle->d_node, &dev->h_list);
    else
        list_add_tail_rcu(&handle->d_node, &dev->h_list);

//把这个handle的d_node 加到对应input_dev的h_list链表里面

...

    list_add_tail_rcu(&handle->h_node, &handler->h_list);

//把这个handle的h_node 加到对应input_handler的h_list链表里面

...

}

这个注册是把handle 本身的链表加入到它自己的input_dev 以及 input_handler的h_list链表中,这样以后就可以通过h_list遍历到这个handle,

这样就实现了三者的绑定联系.



另外在evdev中还有个结构:


struct evdev_client {
    unsigned int head;  //buffer数组的索引头
    unsigned int tail;   //buffer数组的索引尾
    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;
    bool use_wake_lock;
    char name[28];
    struct fasync_struct *fasync;    //异步通知函数
    struct evdev *evdev;  //包含一个evdev变量
    struct list_head node;  //链表
    unsigned int bufsize;
    struct input_event buffer[];   //input_event数据结构的数组,input_event代表一个事件,基本成员:类型(type),编码(code),值(value)
};

这个结构会在evdev被打开的时候 创建,这里关于evdev的初始以及在input系统中承接作用暂时介绍到这里,

前文 Linux/Android——输入子系统input_event传递 中有记录从设备驱动传递上来的event是怎么到input核心,然后接着往上传递的,接下来就是用到evdev传递了.下篇介绍.












Linux/Android——input_handler之evdev