linux中input_register_device注册函数分析

17.1.2  注册函数input_register_device()（1）

button_init()函数中的28行调用了input_register_device()函数注册输入设备结构体。input_register_device()函数是输入子系统核心（input core）提供的函数。该函数将input_dev结构体注册到输入子系统核心中，input_dev结构体必须由前面讲的input_allocate_device()函数来分配。input_register_device()函数如果注册失败，必须调用input_free_device()函数释放分配的空间。如果该函数注册成功，在卸载函数中应该调用input_unregister_device()函数来注销输入设备结构体。

1．input_register_device()函数

input_register_device()函数的代码如下：

/**
 * input_register_device - register device with input core
 * @dev: device to be registered
 *
 * This function registers device with input core. The device must be
 * allocated with input_allocate_device() and all it's capabilities
 * set up before registering.
 * If function fails the device must be freed with input_free_device().
 * Once device has been successfully registered it can be unregistered
 * with input_unregister_device(); input_free_device() should not be
 * called in this case.
 */
int input_register_device(struct input_dev *dev)
{
    static atomic_t input_no = ATOMIC_INIT(0);
    struct input_handler *handler;
    const char *path;
    int error;

    /* Every input device generates EV_SYN/SYN_REPORT events. */
    __set_bit(EV_SYN, dev->evbit);

    /* KEY_RESERVED is not supposed to be transmitted to userspace. */
    __clear_bit(KEY_RESERVED, dev->keybit);

    /* Make sure that bitmasks not mentioned in dev->evbit are clean. */
    input_cleanse_bitmasks(dev);

    /*
     * If delay and period are pre-set by the driver, then autorepeating
     * is handled by the driver itself and we don't do it in input.c.
     */
    init_timer(&dev->timer);
    if (!dev->rep[REP_DELAY] && !dev->rep[REP_PERIOD]) {
        dev->timer.data = (long) dev;
        dev->timer.function = input_repeat_key;
        dev->rep[REP_DELAY] = 250;
        dev->rep[REP_PERIOD] = 33;
    }

    if (!dev->getkeycode)
        dev->getkeycode = input_default_getkeycode;

    if (!dev->setkeycode)
        dev->setkeycode = input_default_setkeycode;

    dev_set_name(&dev->dev, "input%ld",
             (unsigned long) atomic_inc_return(&input_no) - 1);

    error = device_add(&dev->dev);
    if (error)
        return error;

    path = kobject_get_path(&dev->dev.kobj, GFP_KERNEL);
    printk(KERN_INFO "input: %s as %s\n",
        dev->name ? dev->name : "Unspecified device", path ? path : "N/A");
    kfree(path);

    error = mutex_lock_interruptible(&input_mutex);
    if (error) {
        device_del(&dev->dev);
        return error;
    }

    list_add_tail(&dev->node, &input_dev_list);

    list_for_each_entry(handler, &input_handler_list, node)
        input_attach_handler(dev, handler);

    input_wakeup_procfs_readers();

    mutex_unlock(&input_mutex);

    return 0;
}

/**
 * input_register_device - register device with input core
 * @dev: device to be registered
 *
 * This function registers device with input core. The device must be
 * allocated with input_allocate_device() and all it's capabilities
 * set up before registering.
 * If function fails the device must be freed with input_free_device().
 * Once device has been successfully registered it can be unregistered
 * with input_unregister_device(); input_free_device() should not be
 * called in this case.
 */
int input_register_device(struct input_dev *dev)
{
	static atomic_t input_no = ATOMIC_INIT(0);
	struct input_handler *handler;
	const char *path;
	int error;

	/* Every input device generates EV_SYN/SYN_REPORT events. */
	__set_bit(EV_SYN, dev->evbit);

	/* KEY_RESERVED is not supposed to be transmitted to userspace. */
	__clear_bit(KEY_RESERVED, dev->keybit);

	/* Make sure that bitmasks not mentioned in dev->evbit are clean. */
	input_cleanse_bitmasks(dev);

	/*
	 * If delay and period are pre-set by the driver, then autorepeating
	 * is handled by the driver itself and we don't do it in input.c.
	 */
	init_timer(&dev->timer);
	if (!dev->rep[REP_DELAY] && !dev->rep[REP_PERIOD]) {
		dev->timer.data = (long) dev;
		dev->timer.function = input_repeat_key;
		dev->rep[REP_DELAY] = 250;
		dev->rep[REP_PERIOD] = 33;
	}

	if (!dev->getkeycode)
		dev->getkeycode = input_default_getkeycode;

	if (!dev->setkeycode)
		dev->setkeycode = input_default_setkeycode;

	dev_set_name(&dev->dev, "input%ld",
		     (unsigned long) atomic_inc_return(&input_no) - 1);

	error = device_add(&dev->dev);
	if (error)
		return error;

	path = kobject_get_path(&dev->dev.kobj, GFP_KERNEL);
	printk(KERN_INFO "input: %s as %s\n",
		dev->name ? dev->name : "Unspecified device", path ? path : "N/A");
	kfree(path);

	error = mutex_lock_interruptible(&input_mutex);
	if (error) {
		device_del(&dev->dev);
		return error;
	}

	list_add_tail(&dev->node, &input_dev_list);

	list_for_each_entry(handler, &input_handler_list, node)
		input_attach_handler(dev, handler);

	input_wakeup_procfs_readers();

	mutex_unlock(&input_mutex);

	return 0;
}

 

 

下面对该函数的主要代码进行分析。

第03～06行，定义了一些函数中将要用到的局部变量。

第07行，调用__set_bit()函数设置input_dev所支持的事件类型。事件类型由input_dev的evbit成员来表示，在这里将其EV_SYN置位，表示设备支持所有的事件。注意，一个设备可以支持一种或者多种事件类型。常用的事件类型如下：

#define EV_SYN          0x00    /*表示设备支持所有的事件*/
#define EV_KEY          0x01    /*键盘或者按键，表示一个键码*/
#define EV_REL          0x02    /*鼠标设备，表示一个相对的光标位置结果*/
#define EV_ABS          0x03    /*手写板产生的值，其是一个绝对整数值*/
#define EV_MSC          0x04    /*其他类型*/
#define EV_LED          0x11    /*LED灯设备*/
#define EV_SND          0x12    /*蜂鸣器，输入声音*/
#define EV_REP          0x14    /*允许重复按键类型*/
#define EV_PWR          0x16    /*电源管理事件*/

dev_set_name设置input_dev中的device的名字，名字以input0、input1、input2、input3、input4等的形式出现在sysfs文件系统中。

使用device_add()函数将input_dev包含的device结构注册到Linux设备模型中，并可以在sysfs文件系统中表现出来。

打印设备的路径，输出调试信息。

调用list_add_tail()函数将input_dev加入input_dev_list链表中，input_dev_list链表中包含了系统中所有的input_dev设备。