Input子系统 - Kernel驱动程序 - Android

1、Input子系统相关定义
2、input core 初始化
- 2.1 input_init 初始化入口
3、 input_dev设备注册
4、input_handler注册
- 4.1 常见的input_handler
- 4.2 input_register_handler注册函数
5、input_dev和input_handler匹配input_handle
6、input事件上报
7、Input事件内核空间传递到用户空间
- 7.1 evdev_fetch_next_event
- 7.2 input_event_to_user
参考文献

android-goldfish-5.4-dev
AOSP > 文档 > 核心主题 > 输入

https://www.kernel.org/doc/Documentation/input/input.txt
https://www.kernel.org/doc/Documentation/input/event-codes.txt
https://www.kernel.org/doc/Documentation/input/multi-touch-protocol.txt

1、Input子系统相关定义

在这里插入图片描述

1.1 代码位置

Android_Kernel\goldfish\drivers\input
Android_Kernel\goldfish\include\linux\input.h 定义了一组标准事件类型和代码
在这里插入图片描述

1.2 input_dev结构体：表示输入设备

Name： 设备名称
Phys： 系统层次结构中设备的物理路径
Uniq： 设备的唯一标识码（如果设备有）
Id： 设备的Id（struct input_Id）
Propbit： 设备属性和怪癖的位图。
Evbit： 设备支持的事件类型的位图（EV_KEY、EV_REL等）
Keybit： 此设备具有的keys/buttons位图
Relbit： 设备的相对轴位图
Absbit： 设备的绝对轴位图
Mscbit： 设备支持的杂项事件的位图
Ledbit： 设备上存在的LED位图
Sndbit: 设备支持的音效位图
Ffbit： 设备支持的力反馈效果位图
Swbit： 设备上存在的开关位图
Hint_events_per_packet： 设备在数据包中生成的平均事件数（EV_SYN/SYN_REPORT事件之间）。由事件处理程序用于估计容纳事件所需的缓冲区大小。
Keycodemax： 键代码表的大小
Keycodesize： 键代码表中元素的大小
Keycode： 此设备的扫描码到密钥码的映射
Getkeycode： 用于检索当前密钥映射的可选遗留方法。
Setkeycode： 更改当前密钥映射的可选方法，用于实现稀疏密钥映射。如果未提供，将使用默认机制。该方法在保持event_lock时被调用，因此不能休眠
Ff： 如果设备支持力反馈效应，则与设备相关的力反馈结构
Poller： 如果设备设置为使用轮询模式，则与设备关联的轮询器结构
Repeat_key： 存储上次按键的按键代码；用于实现软件自动监管
Timer: 软件自动恢复的计时器
Rep： 自动回放参数的当前值（延迟、速率）
Mt： 指向多点触摸状态的指针
Absinfo： 包含绝对轴信息（当前值、最小值、最大值、平坦值、模糊值、分辨率）的&struct input_Absinfo元素数组
Key： 反映设备按键/按钮的当前状态
Led： 反映设备Led的当前状态
Snd： 反映音效的当前状态
Sw： 反映设备开关的当前状态
Open： 当第一个用户调用input_Open_device()时，会调用此方法。驱动程序必须准备设备开始生成事件（启动轮询线程、请求IRQ、提交URB等）
Close： 当最后一个用户调用input_Close_device（）时，会调用此方法。
Flush： 清除设备。最常用于消除与设备断开连接时加载到设备中的力反馈效应
Event： 发送到设备的事件的事件处理程序，如EV_LED或EV_SND。该设备应执行请求的操作（打开LED、播放声音等）呼叫受保护
Event_lock：并且不能休眠
Grab： 当前抓取设备的输入句柄（通过EVIOCGRAB ioctl）。当句柄抓取设备时，它将成为来自该设备的所有输入事件的唯一接收者
Event_lock： 当input core接收并处理设备的新事件时（在input_Event()中），将获取此spinlock。在设备向输入核心注册后，访问和/或修改设备参数（如keymap或absmin、absmax、absfuzz等）的代码必须使用此锁。
Mutex： 序列化对open()、close()和flush()方法的调用
Users： 存储打开此设备的用户数（输入处理程序）。input_open_device()和input_close_device()使用它来确保dev->open()仅在第一个用户打开设备时调用，dev->close()在最后一个用户关闭设备时调用
Going_away： 标记正在注销的设备，并使用-ENODEV导致input_open_device*()失败。
Dev: 此设备的驱动程序模型视图
H_list： 与设备相关联的输入句柄列表。访问列表时，必须持有dev->mutex
Node： 用于将设备放置在input_dev_list上
Num_vals： 当前帧中排队的值数
Max_vals： 帧中排队的最大值数
Vals： 当前帧中排队的值数组
Devres_managed： 表示设备使用Devres框架进行管理，不需要显式注销或释放。
Timestamp： 存储由驱动程序调用的input_set_Timestamp设置的时间戳

include/linux/input.h

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;

	struct input_dev_poller *poller;

	unsigned int repeat_key;
	struct timer_list timer;

	int rep[REP_CNT];

	struct input_mt *mt;

	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;

	struct device dev;

	struct list_head	h_list;
	struct list_head	node;

	unsigned int num_vals;
	unsigned int max_vals;
	struct input_value *vals;

	bool devres_managed;

	ktime_t timestamp[INPUT_CLK_MAX];
};
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1.3 input_handler结构体：struct input_handler - implements one of interfaces for input devices

Private： 驱动程序特定数据
Event： 事件处理程序。此方法由输入核心调用，同时禁用中断并保持dev->event_lock spinlock，因此它可能不会休眠
Events： 事件序列处理程序。此方法由输入核心调用，同时禁用中断并保持dev->event_lock spinlock，因此它可能不会休眠
Filter： 类似于event；将普通事件处理程序与“Filter”分离。
Match： 在比较设备的id和处理程序的id_table后调用，以便在设备和处理程序之间进行细粒度匹配
Connect： 在将处理程序附加到输入设备时调用
Disconnect： 断开处理程序与输入设备的连接
**Start：**启动给定句柄的处理程序。这个函数是在connect()方法之后由输入核心调用的，当“抓取”设备的进程释放它时也是如此
Legacy_minors: 由使用旧版次要范围的驱动程序设置为%true
Minor： 此驱动程序可以提供的设备的32个遗留次要范围的开始
Name： 处理程序的名称，显示在/proc/bus/input/handlers中
Id_table： 指向此驱动程序可以处理的input_device_Id表的指针
H_list： 与处理程序关联的输入处理程序列表
Node： 用于将驱动程序放置到input_handler_list上

Input handlers附加到input devices并创建input handles。可能有多个处理程序同时连接到任何给定的输入设备。他们所有人都将获得设备生成的输入事件的副本。使用完全相同的结构来实现输入过滤器。 Input core允许过滤器首先运行，并且如果任何过滤器指示应该过滤事件（通过从其filter()方法返回%true），则不会将事件传递给常规处理程序。请注意，输入核心序列化对connect()和disconnect()方法的调用。

include/linux/input.h

struct input_handler {

	void *private;

	void (*event)(struct input_handle *handle, unsigned int type, unsigned int code, int value);
	void (*events)(struct input_handle *handle,
		       const struct input_value *vals, unsigned int count);
	bool (*filter)(struct input_handle *handle, unsigned int type, unsigned int code, int value);
	bool (*match)(struct input_handler *handler, struct input_dev *dev);
	int (*connect)(struct input_handler *handler, struct input_dev *dev, const struct input_device_id *id);
	void (*disconnect)(struct input_handle *handle);
	void (*start)(struct input_handle *handle);

	bool legacy_minors;
	int minor;
	const char *name;

	const struct input_device_id *id_table;

	struct list_head	h_list;
	struct list_head	node;
};
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1.4 input_handle结构体：将输入设备与输入处理程序链接

一个input_dev上报的事件可以被多个input_handler接收处理，一个input_handler也可以处理多个input_dev上报的事件，这样多个input_dev和多个input_handler之间可能会形成交织的网状。在这种情况下，需要一个桥梁来搭建两者之间的联系，两边的函数调用都可以通过这个“中介”进行，input_handle就是这个桥梁。

Private： 特定于处理程序的数据
Open： 显示句柄是否“打开”的计数器，即应从其设备传递事件
Name： 创建句柄的处理程序赋予句柄的名称
Dev： 句柄所连接的输入设备
Handler： 通过该句柄与设备一起工作的句柄
D_node： 用于将句柄放在设备的附加句柄列表中
H_node： 用于将句柄放在处理程序的句柄列表中，从中获取事件

include/linux/input.h

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;
};
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2、input core 初始化

include/linux/input.h
drivers/input/input.c

sybsys_initcall注册设定启动等级，保证其初始化会早于input设备和input_handler的注册
module_init方式注册input设备和input_handler

subsys_initcall(input_init);
module_exit(input_exit);
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2.1 input_init 初始化入口

drivers/input/input.c

class_register(&input_class) input类注册，放在/sys/class
input_proc_init(); 主要用于input_handler和devices信息查看，Proc文件创建
register_chrdev_region(MKDEV(INPUT_MAJOR, 0), INPUT_MAX_CHAR_DEVICES, "input") 注册字符设备

static int __init input_init(void)
{
	int err;

	err = class_register(&input_class);
	if (err) {
		pr_err("unable to register input_dev class\n");
		return err;
	}

	err = input_proc_init();
	if (err)
		goto fail1;

	err = register_chrdev_region(MKDEV(INPUT_MAJOR, 0),
				     INPUT_MAX_CHAR_DEVICES, "input");
	if (err) {
		pr_err("unable to register char major %d", INPUT_MAJOR);
		goto fail2;
	}

	return 0;

 fail2:	input_proc_exit();
 fail1:	class_unregister(&input_class);
	return err;
}
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2.1.1 class_register

class_register(&input_class) input类注册，放在/sys/class

Linux内核API class_register|极客笔记

drivers/input/input.c

struct class input_class = {
	.name		= "input",
	.devnode	= input_devnode,
};
EXPORT_SYMBOL_GPL(input_class);
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include/linux/device.h
drivers/base/class.c

/* This is a #define to keep the compiler from merging different
 * instances of the __key variable */
#define class_register(class)			\
({						\
	static struct lock_class_key __key;	\
	__class_register(class, &__key);	\
})
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2.1.2 input_proc_init

input_proc_init() 主要用于input_handler和devices信息查看，Proc文件创建

static int __init input_proc_init(void)
{
	struct proc_dir_entry *entry;

	proc_bus_input_dir = proc_mkdir("bus/input", NULL);
	if (!proc_bus_input_dir)
		return -ENOMEM;

	entry = proc_create("devices", 0, proc_bus_input_dir,
			    &input_devices_fileops);
	if (!entry)
		goto fail1;

	entry = proc_create("handlers", 0, proc_bus_input_dir,
			    &input_handlers_fileops);
	if (!entry)
		goto fail2;

	return 0;

 fail2:	remove_proc_entry("devices", proc_bus_input_dir);
 fail1: remove_proc_entry("bus/input", NULL);
	return -ENOMEM;
}
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2.1.3 register_chrdev_region

register_chrdev_region(MKDEV(INPUT_MAJOR, 0), INPUT_MAX_CHAR_DEVICES, "input") 注册字符设备；创建一个主设备为13的“input”设备

include/uapi/linux/major.h

#define INPUT_MAJOR		13
1

drivers/input/input.c

#define INPUT_MAX_CHAR_DEVICES		1024
1

fs/char_dev.c

/**
 * register_chrdev_region() - register a range of device numbers
 * @from: the first in the desired range of device numbers; must include
 *        the major number.
 * @count: the number of consecutive device numbers required
 * @name: the name of the device or driver.
 *
 * Return value is zero on success, a negative error code on failure.
 */
int register_chrdev_region(dev_t from, unsigned count, const char *name)
{
	struct char_device_struct *cd;
	dev_t to = from + count;
	dev_t n, next;

	for (n = from; n < to; n = next) {
		next = MKDEV(MAJOR(n)+1, 0);
		if (next > to)
			next = to;
		cd = __register_chrdev_region(MAJOR(n), MINOR(n),
			       next - n, name);
		if (IS_ERR(cd))
			goto fail;
	}
	return 0;
fail:
	to = n;
	for (n = from; n < to; n = next) {
		next = MKDEV(MAJOR(n)+1, 0);
		kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
	}
	return PTR_ERR(cd);
}
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3、 input_dev设备注册

3.1 input_allocate_device：分配input_dev结构体内存

input_allocate_device-为新的输入设备分配内存
返回准备好的结构input_dev或%NULL。
注意：使用input_free_device()释放尚未注册的设备；input_unregister_device()应用于已注册的设备。

drivers/input/input.c

struct input_dev *devm_input_allocate_device(struct device *dev)
{
	struct input_dev *input;
	struct input_devres *devres;

	devres = devres_alloc(devm_input_device_release,
			      sizeof(*devres), GFP_KERNEL);
	if (!devres)
		return NULL;

	input = input_allocate_device();
	if (!input) {
		devres_free(devres);
		return NULL;
	}

	input->dev.parent = dev;
	input->devres_managed = true;

	devres->input = input;
	devres_add(dev, devres);

	return input;
}
EXPORT_SYMBOL(devm_input_allocate_device);
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/**
 * input_allocate_device - allocate memory for new input device
 *
 * Returns prepared struct input_dev or %NULL.
 *
 * NOTE: Use input_free_device() to free devices that have not been
 * registered; input_unregister_device() should be used for already
 * registered devices.
 */
struct input_dev *input_allocate_device(void)
{
	static atomic_t input_no = ATOMIC_INIT(-1);
	struct input_dev *dev;

	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
	if (dev) {
		dev->dev.type = &input_dev_type;
		dev->dev.class = &input_class;
		device_initialize(&dev->dev);
		mutex_init(&dev->mutex);
		spin_lock_init(&dev->event_lock);
		timer_setup(&dev->timer, NULL, 0);
		INIT_LIST_HEAD(&dev->h_list);
		INIT_LIST_HEAD(&dev->node);

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

		__module_get(THIS_MODULE);
	}

	return dev;
}
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3.2 input_register_device：带输入核心的寄存器设备

此函数将设备注册到 input core 。在注册之前，必须为设备分配input_allocate_device()及其所有功能。如果函数失败，则必须使用input_free_device()释放设备。一旦设备成功注册，就可以使用input_unregister_device()进行注销；在这种情况下，不应调用input_free_device()。请注意，此函数还用于注册托管输入设备（使用devm_input_allocate_device()分配的设备）。这样的托管输入设备不需要明确地注销或释放，它们的拆除由devres基础设施控制。同样值得注意的是，删除托管输入设备在内部是一个两步过程：注册的托管输入设备首先未注册，但保留在内存中，并且仍然可以处理input_event()调用（尽管事件不会传递到任何地方）。稍后，当devres堆栈展开到进行设备分配的点时，将释放托管输入设备。

device_add(&dev->dev)：将设备注册为linux设备
list_add_tail(&dev->node, &input_dev_list)：将设备添加到linux内核全局列表input_dev_list
list_for_each_entry(handler, &input_handler_list, node)
input_attach_handler(dev, handler);：遍历input_handler_list，为设备找到自己的handler

drivers/input/input.c

int input_register_device(struct input_dev *dev)
{
	struct input_devres *devres = NULL;
	struct input_handler *handler;
	unsigned int packet_size;
	const char *path;
	int error;

	if (test_bit(EV_ABS, dev->evbit) && !dev->absinfo) {
		dev_err(&dev->dev,
			"Absolute device without dev->absinfo, refusing to register\n");
		return -EINVAL;
	}

	if (dev->devres_managed) {
		devres = devres_alloc(devm_input_device_unregister,
				      sizeof(*devres), GFP_KERNEL);
		if (!devres)
			return -ENOMEM;

		devres->input = dev;
	}

	/* 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);

	packet_size = input_estimate_events_per_packet(dev);
	if (dev->hint_events_per_packet < packet_size)
		dev->hint_events_per_packet = packet_size;

	dev->max_vals = dev->hint_events_per_packet + 2;
	dev->vals = kcalloc(dev->max_vals, sizeof(*dev->vals), GFP_KERNEL);
	if (!dev->vals) {
		error = -ENOMEM;
		goto err_devres_free;
	}

	/*
	 * 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.
	 */
	if (!dev->rep[REP_DELAY] && !dev->rep[REP_PERIOD])
		input_enable_softrepeat(dev, 250, 33);

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

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

	if (dev->poller)
		input_dev_poller_finalize(dev->poller);

	error = device_add(&dev->dev);
	if (error)
		goto err_free_vals;

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

	error = mutex_lock_interruptible(&input_mutex);
	if (error)
		goto err_device_del;

	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);

	if (dev->devres_managed) {
		dev_dbg(dev->dev.parent, "%s: registering %s with devres.\n",
			__func__, dev_name(&dev->dev));
		devres_add(dev->dev.parent, devres);
	}
	return 0;

err_device_del:
	device_del(&dev->dev);
err_free_vals:
	kfree(dev->vals);
	dev->vals = NULL;
err_devres_free:
	devres_free(devres);
	return error;
}
EXPORT_SYMBOL(input_register_device);
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3.3 案例："gpio-keys"设备注册

在这里插入图片描述

drivers/input/keyboard/gpio_keys.c
“gpio-keys”： platform_driver_register(&gpio_keys_device_driver) -> gpio_keys_probe -> devm_input_allocate_device -> input_register_device

如其它案例等查看如下等目录：
drivers/input/gameport
drivers/input/joystick
drivers/input/keyboard
drivers/input/misc
drivers/input/mouse
drivers/input/rmi4
drivers/input/serio
drivers/input/tablet
drivers/input/touchscreen

static struct platform_driver gpio_keys_device_driver = {
	.probe		= gpio_keys_probe,
	.shutdown	= gpio_keys_shutdown,
	.driver		= {
		.name	= "gpio-keys",
		.pm	= &gpio_keys_pm_ops,
		.of_match_table = gpio_keys_of_match,
		.dev_groups	= gpio_keys_groups,
	}
};

static int __init gpio_keys_init(void)
{
	return platform_driver_register(&gpio_keys_device_driver);
}
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static int gpio_keys_probe(struct platform_device *pdev)
{
	struct device *dev = &pdev->dev;
	const struct gpio_keys_platform_data *pdata = dev_get_platdata(dev);
	struct fwnode_handle *child = NULL;
	struct gpio_keys_drvdata *ddata;
	struct input_dev *input;
	int i, error;
	int wakeup = 0;

	if (!pdata) {
		pdata = gpio_keys_get_devtree_pdata(dev);
		if (IS_ERR(pdata))
			return PTR_ERR(pdata);
	}

	ddata = devm_kzalloc(dev, struct_size(ddata, data, pdata->nbuttons),
			     GFP_KERNEL);
	if (!ddata) {
		dev_err(dev, "failed to allocate state\n");
		return -ENOMEM;
	}

	ddata->keymap = devm_kcalloc(dev,
				     pdata->nbuttons, sizeof(ddata->keymap[0]),
				     GFP_KERNEL);
	if (!ddata->keymap)
		return -ENOMEM;

	input = devm_input_allocate_device(dev);
	if (!input) {
		dev_err(dev, "failed to allocate input device\n");
		return -ENOMEM;
	}

	ddata->pdata = pdata;
	ddata->input = input;
	mutex_init(&ddata->disable_lock);

	platform_set_drvdata(pdev, ddata);
	input_set_drvdata(input, ddata);

	input->name = pdata->name ? : pdev->name;
	input->phys = "gpio-keys/input0";
	input->dev.parent = dev;
	input->open = gpio_keys_open;
	input->close = gpio_keys_close;

	input->id.bustype = BUS_HOST;
	input->id.vendor = 0x0001;
	input->id.product = 0x0001;
	input->id.version = 0x0100;

	input->keycode = ddata->keymap;
	input->keycodesize = sizeof(ddata->keymap[0]);
	input->keycodemax = pdata->nbuttons;

	/* Enable auto repeat feature of Linux input subsystem */
	if (pdata->rep)
		__set_bit(EV_REP, input->evbit);

	for (i = 0; i < pdata->nbuttons; i++) {
		const struct gpio_keys_button *button = &pdata->buttons[i];

		if (!dev_get_platdata(dev)) {
			child = device_get_next_child_node(dev, child);
			if (!child) {
				dev_err(dev,
					"missing child device node for entry %d\n",
					i);
				return -EINVAL;
			}
		}

		error = gpio_keys_setup_key(pdev, input, ddata,
					    button, i, child);
		if (error) {
			fwnode_handle_put(child);
			return error;
		}

		if (button->wakeup)
			wakeup = 1;
	}

	fwnode_handle_put(child);

	error = input_register_device(input);
	if (error) {
		dev_err(dev, "Unable to register input device, error: %d\n",
			error);
		return error;
	}

	device_init_wakeup(dev, wakeup);

	return 0;
}
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4、input_handler注册

4.1 常见的input_handler

一般来说input_handler注册会在input_dev设备注册之前，常见的input_handler：

evdev_handler：响应绝大部分事件，默认input处理事件
mousedev_handler：鼠标类input事件
joydev_handler ：游戏遥感类input事件
kbd_handler：键盘类事件
input_leds_handler
apmpower_handler

drivers/input/evdev.c

static struct input_handler evdev_handler = {
	.event		= evdev_event,
	.events		= evdev_events,
	.connect	= evdev_connect,
	.disconnect	= evdev_disconnect,
	.legacy_minors	= true,
	.minor		= EVDEV_MINOR_BASE,
	.name		= "evdev",
	.id_table	= evdev_ids,
};
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drivers/tty/vt/keyboard.c

static struct input_handler kbd_handler = {
	.event		= kbd_event,
	.match		= kbd_match,
	.connect	= kbd_connect,
	.disconnect	= kbd_disconnect,
	.start		= kbd_start,
	.name		= "kbd",
	.id_table	= kbd_ids,
};
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drivers/input/mousedev.c

static struct input_handler mousedev_handler = {
	.event		= mousedev_event,
	.connect	= mousedev_connect,
	.disconnect	= mousedev_disconnect,
	.legacy_minors	= true,
	.minor		= MOUSEDEV_MINOR_BASE,
	.name		= "mousedev",
	.id_table	= mousedev_ids,
};
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drivers/input/joydev.c

static struct input_handler joydev_handler = {
	.event		= joydev_event,
	.match		= joydev_match,
	.connect	= joydev_connect,
	.disconnect	= joydev_disconnect,
	.legacy_minors	= true,
	.minor		= JOYDEV_MINOR_BASE,
	.name		= "joydev",
	.id_table	= joydev_ids,
};
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drivers/input/input-leds.c

static struct input_handler input_leds_handler = {
	.event =	input_leds_event,
	.connect =	input_leds_connect,
	.disconnect =	input_leds_disconnect,
	.name =		"leds",
	.id_table =	input_leds_ids,
};
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drivers/input/apm-power.c

static struct input_handler apmpower_handler = {
	.event =	apmpower_event,
	.connect =	apmpower_connect,
	.disconnect =	apmpower_disconnect,
	.name =		"apm-power",
	.id_table =	apmpower_ids,
};
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4.2 input_register_handler注册函数

此函数为系统中的输入设备注册一个新的input_handler（接口），并将其连接到与该处理程序兼容的所有input devices。

INIT_LIST_HEAD(&handler->h_list)：初始化在Linux的内核链表
list_add_tail(&handler->node, &input_handler_list)：将handler添加到linux内核全局列表input_handler_list
list_for_each_entry(handler, &input_handler_list, node)
input_attach_handler(dev, handler);：遍历input_handler_list，为设备找到自己的handler

/**
 * 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 error;

	error = mutex_lock_interruptible(&input_mutex);
	if (error)
		return error;

	INIT_LIST_HEAD(&handler->h_list);

	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();

	mutex_unlock(&input_mutex);
	return 0;
}
EXPORT_SYMBOL(input_register_handler);
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5、input_dev和input_handler匹配input_handle

5.1 input_match_device匹配

input_dev设备注册和input_handler注册都会调用input_attach_handler

input_match_device：匹配成功返回handler->id_table，即input_device_id
handler->connect(handler, dev, id)：匹配成功调用connect函数，如drivers/input/evdev.c#evdev_connect、drivers/input/mousedev.c#mousedev_connect

static const struct input_device_id *input_match_device(struct input_handler *handler,
							struct input_dev *dev)
{
	const struct input_device_id *id;

	for (id = handler->id_table; id->flags || id->driver_info; id++) {
		if (input_match_device_id(dev, id) &&
		    (!handler->match || handler->match(handler, dev))) {
			return id;
		}
	}

	return NULL;
}

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;
}
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5.2 connect函数

如drivers/input/evdev.c#evdev_connect、drivers/input/mousedev.c#mousedev_connect等；查看通用事件处理evdev.c：

.driver_info = 1：其中evdev_ids匹配所有设备，
evdev_connect：一旦注册就会evdev的connect；
1》input_register_handle注册一个新的input_handle，主要将handle分别挂载在input_dev和input_handler成员链表；
(evdev->handle.dev = input_get_device(dev);、evdev->handle.handler = handler;)
2》input_get_new_minor最多能创建32个event设备#define EVDEV_MINORS 32；
3》cdev_device_add最终调用device_add，向Linux系统新创建一个event设备/dev/input/eventX

drivers/input/evdev.c

struct evdev {
	int open;
	struct input_handle handle;
	wait_queue_head_t wait;
	struct evdev_client __rcu *grab;
	struct list_head client_list;
	spinlock_t client_lock; /* protects client_list */
	struct mutex mutex;
	struct device dev;
	struct cdev cdev;
	bool exist;
};

/*
 * Create new evdev device. Note that input core serializes calls
 * to connect and disconnect.
 */
static int evdev_connect(struct input_handler *handler, struct input_dev *dev,
			 const struct input_device_id *id)
{
	struct evdev *evdev;
	int minor;
	int dev_no;
	int error;

	minor = input_get_new_minor(EVDEV_MINOR_BASE, EVDEV_MINORS, true);
	if (minor < 0) {
		error = minor;
		pr_err("failed to reserve new minor: %d\n", error);
		return error;
	}

	evdev = kzalloc(sizeof(struct evdev), GFP_KERNEL);
	if (!evdev) {
		error = -ENOMEM;
		goto err_free_minor;
	}

	INIT_LIST_HEAD(&evdev->client_list);
	spin_lock_init(&evdev->client_lock);
	mutex_init(&evdev->mutex);
	init_waitqueue_head(&evdev->wait);
	evdev->exist = true;

	dev_no = minor;
	/* Normalize device number if it falls into legacy range */
	if (dev_no < EVDEV_MINOR_BASE + EVDEV_MINORS)
		dev_no -= EVDEV_MINOR_BASE;
	dev_set_name(&evdev->dev, "event%d", dev_no);

	evdev->handle.dev = input_get_device(dev);
	evdev->handle.name = dev_name(&evdev->dev);
	evdev->handle.handler = handler;
	evdev->handle.private = evdev;

	evdev->dev.devt = MKDEV(INPUT_MAJOR, 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);
	if (error)
		goto err_free_evdev;

	cdev_init(&evdev->cdev, &evdev_fops);

	error = cdev_device_add(&evdev->cdev, &evdev->dev);
	if (error)
		goto err_cleanup_evdev;

	return 0;

 err_cleanup_evdev:
	evdev_cleanup(evdev);
	input_unregister_handle(&evdev->handle);
 err_free_evdev:
	put_device(&evdev->dev);
 err_free_minor:
	input_free_minor(minor);
	return error;
}

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

MODULE_DEVICE_TABLE(input, evdev_ids);

static struct input_handler evdev_handler = {
	.event		= evdev_event,
	.events		= evdev_events,
	.connect	= evdev_connect,
	.disconnect	= evdev_disconnect,
	.legacy_minors	= true,
	.minor		= EVDEV_MINOR_BASE,
	.name		= "evdev",
	.id_table	= evdev_ids,
};
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5.3 input_register_handle

input_register_handle-注册一个新的输入句柄

Handle：用于注册的Handle

这个函数将一个新的输入句柄放在input_dev和input_handler的列表中，这样，一旦使用input_open_device()打开它，事件就可以在其中流动。这个函数应该从处理程序的connect()方法调用。

/**
 * 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;
	int error;

	/*
	 * We take dev->mutex here to prevent race with
	 * input_release_device().
	 */
	error = mutex_lock_interruptible(&dev->mutex);
	if (error)
		return error;

	/*
	 * 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);

	mutex_unlock(&dev->mutex);

	/*
	 * Since we are supposed to be called from ->connect()
	 * which is mutually exclusive with ->disconnect()
	 * we can't be racing with input_unregister_handle()
	 * and so separate lock is not needed here.
	 */
	list_add_tail_rcu(&handle->h_node, &handler->h_list);

	if (handler->start)
		handler->start(handle);

	return 0;
}
EXPORT_SYMBOL(input_register_handle);
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5.4 input_dev \ input_handler \ input_handle 关系

在这里插入图片描述

input_dev 是硬件驱动层，代表一个input设备
input_handler 是事件处理层，代表一个事件处理器
input_handle 属于核心层，代表一个配对的input设备与input事件处理器

input_dev 通过全局的input_dev_list链接在一起。设备注册的时候实现这个操作。
input_handler 通过全局的input_handler_list链接在一起。事件处理器注册的时候实现这个操作。

input_hande 没有一个全局的链表，它注册的时候将自己分别挂在了input_dev 和 input_handler 的h_list上了。
通过input_dev 和input_handler就可以找到input_handle 在设备注册和事件处理器，注册的时候都要进行配对工作，配对后就会实现链接。
通过input_handle也可以找到input_dev和input_handler。

6、input事件上报

input事件一般采用中断方式上报，相关方法input_report_abs、input_report_key、input_sync等。最终input_sync来表示一次事件上报，最终调用input_event处理。

6.1 底层Input事件上报

AOSP > 文档 > 核心主题 > 键盘设备、AOSP > 文档 > 核心主题 > 触摸设备

不同的input设备上报的input事件的格式不同，常用的按键或者触摸屏采用的中断方式上报。
比如触摸屏上报input事件时一般需要上报手指的id、x坐标、y坐标等信息。

https://www.kernel.org/doc/Documentation/input/input.txt
https://www.kernel.org/doc/Documentation/input/event-codes.txt
https://www.kernel.org/doc/Documentation/input/multi-touch-protocol.txt

input_report_abs(input, ABS_MT_POSITION_X, x);
input_report_abs(input, ABS_MT_POSITION_Y, y);
input_sync(input);
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-	type	code	value
第1个点	EV_ABS	ABS_MT_SLOT	0
\	EV_ABS	ABS_MT_TRACKING_ID	id
\	EV_ABS	ABS_MT_POSITION_X	x
\	EV_ABS	ABS_MT_POSITION_Y	y
…	…	…	…
第2个点	EV_ABS	ABS_MT_SLOT	n
\	EV_ABS	ABS_MT_TRACKING_ID	id
\	EV_ABS	ABS_MT_POSITION_X	x
\	EV_ABS	ABS_MT_POSITION_Y	y

6.2 input_event 报告新的input事件

实现各种输入设备的驱动程序应使用此功能来报告输入事件。另请参见input_inject_event()。
注意：input_event()可以在使用input_allocate_device()分配输入设备之后立即安全使用，甚至在使用input_register_device()注册之前也是如此，但该事件不会到达任何输入处理程序。input_event()的这种早期调用可以用于“种子”开关的初始状态或绝对轴的初始位置等

input_handle_event：每一个事件上报都是通过input_event接口来完成，在判定事件类型是否支持后，主要是调用input_handle_event来完成
input_get_disposition：根据上报信息判断怎么处理
handler->events()/handler->event()：input_dev对应input_handler，如evdev_handler等(input_event -> input_handle_event -> input_pass_values -> input_to_handler -> handler->events()/handler->event())

drivers/input/input.c

/*
 * Pass event first through all filters and then, if event has not been
 * filtered out, through all open handles. This function is called with
 * dev->event_lock held and interrupts disabled.
 */
static unsigned int input_to_handler(struct input_handle *handle,
			struct input_value *vals, unsigned int count)
{
	struct input_handler *handler = handle->handler;
	struct input_value *end = vals;
	struct input_value *v;

	if (handler->filter) {
		for (v = vals; v != vals + count; v++) {
			if (handler->filter(handle, v->type, v->code, v->value))
				continue;
			if (end != v)
				*end = *v;
			end++;
		}
		count = end - vals;
	}

	if (!count)
		return 0;

	if (handler->events)
		handler->events(handle, vals, count);
	else if (handler->event)
		for (v = vals; v != vals + count; v++)
			handler->event(handle, v->type, v->code, v->value);

	return count;
}


/*
 * Pass values first through all filters and then, if event has not been
 * filtered out, through all open handles. This function is called with
 * dev->event_lock held and interrupts disabled.
 */
static void input_pass_values(struct input_dev *dev,
			      struct input_value *vals, unsigned int count)
{
	struct input_handle *handle;
	struct input_value *v;

	if (!count)
		return;

	rcu_read_lock();

	handle = rcu_dereference(dev->grab);
	if (handle) {
		count = input_to_handler(handle, vals, count);
	} else {
		list_for_each_entry_rcu(handle, &dev->h_list, d_node)
			if (handle->open) {
				count = input_to_handler(handle, vals, count);
				if (!count)
					break;
			}
	}

	rcu_read_unlock();

	/* trigger auto repeat for key events */
	if (test_bit(EV_REP, dev->evbit) && test_bit(EV_KEY, dev->evbit)) {
		for (v = vals; v != vals + count; v++) {
			if (v->type == EV_KEY && v->value != 2) {
				if (v->value)
					input_start_autorepeat(dev, v->code);
				else
					input_stop_autorepeat(dev);
			}
		}
	}
}


/**
 * 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().
 *
 * NOTE: input_event() may be safely used right after input device was
 * allocated with input_allocate_device(), even before it is registered
 * with input_register_device(), but the event will not reach any of the
 * input handlers. Such early invocation of input_event() may be used
 * to 'seed' initial state of a switch or initial position of absolute
 * axis, etc.
 */
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);
		input_handle_event(dev, type, code, value);
		spin_unlock_irqrestore(&dev->event_lock, flags);
	}
}
EXPORT_SYMBOL(input_event);


static void input_handle_event(struct input_dev *dev,
			       unsigned int type, unsigned int code, int value)
{
	int disposition = input_get_disposition(dev, type, code, &value);

	if (disposition != INPUT_IGNORE_EVENT && type != EV_SYN)
		add_input_randomness(type, code, value);

	if ((disposition & INPUT_PASS_TO_DEVICE) && dev->event)
		dev->event(dev, type, code, value);

	if (!dev->vals)
		return;

	if (disposition & INPUT_PASS_TO_HANDLERS) {
		struct input_value *v;

		if (disposition & INPUT_SLOT) {
			v = &dev->vals[dev->num_vals++];
			v->type = EV_ABS;
			v->code = ABS_MT_SLOT;
			v->value = dev->mt->slot;
		}

		v = &dev->vals[dev->num_vals++];
		v->type = type;
		v->code = code;
		v->value = value;
	}

	if (disposition & INPUT_FLUSH) {
		if (dev->num_vals >= 2)
			input_pass_values(dev, dev->vals, dev->num_vals);
		dev->num_vals = 0;
		/*
		 * Reset the timestamp on flush so we won't end up
		 * with a stale one. Note we only need to reset the
		 * monolithic one as we use its presence when deciding
		 * whether to generate a synthetic timestamp.
		 */
		dev->timestamp[INPUT_CLK_MONO] = ktime_set(0, 0);
	} else if (dev->num_vals >= dev->max_vals - 2) {
		dev->vals[dev->num_vals++] = input_value_sync;
		input_pass_values(dev, dev->vals, dev->num_vals);
		dev->num_vals = 0;
	}

}
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6.3 evdev_handler中evdev_events处理

evdev_events将传入事件传递给所有连接的客户端
evdev_event/evdev_events -> evdev_pass_values -> __pass_event ->

input事件存储在client->buffer中；kill_fasync用于发送通知事件，告诉上层client->buffer中有数据可以读了。

drivers/input/evdev.c

static void __pass_event(struct evdev_client *client,
			 const struct input_event *event)
{
	client->buffer[client->head++] = *event;
	client->head &= client->bufsize - 1;

	if (unlikely(client->head == client->tail)) {
		/*
		 * This effectively "drops" all unconsumed events, leaving
		 * EV_SYN/SYN_DROPPED plus the newest event in the queue.
		 */
		client->tail = (client->head - 2) & (client->bufsize - 1);

		client->buffer[client->tail] = (struct input_event) {
			.input_event_sec = event->input_event_sec,
			.input_event_usec = event->input_event_usec,
			.type = EV_SYN,
			.code = SYN_DROPPED,
			.value = 0,
		};

		client->packet_head = client->tail;
	}

	if (event->type == EV_SYN && event->code == SYN_REPORT) {
		client->packet_head = client->head;
		kill_fasync(&client->fasync, SIGIO, POLL_IN);
	}
}

static void evdev_pass_values(struct evdev_client *client,
			const struct input_value *vals, unsigned int count,
			ktime_t *ev_time)
{
	struct evdev *evdev = client->evdev;
	const struct input_value *v;
	struct input_event event;
	struct timespec64 ts;
	bool wakeup = false;

	if (client->revoked)
		return;

	ts = ktime_to_timespec64(ev_time[client->clk_type]);
	event.input_event_sec = ts.tv_sec;
	event.input_event_usec = ts.tv_nsec / NSEC_PER_USEC;

	/* Interrupts are disabled, just acquire the lock. */
	spin_lock(&client->buffer_lock);

	for (v = vals; v != vals + count; v++) {
		if (__evdev_is_filtered(client, v->type, v->code))
			continue;

		if (v->type == EV_SYN && v->code == SYN_REPORT) {
			/* drop empty SYN_REPORT */
			if (client->packet_head == client->head)
				continue;

			wakeup = true;
		}

		event.type = v->type;
		event.code = v->code;
		event.value = v->value;
		__pass_event(client, &event);
	}

	spin_unlock(&client->buffer_lock);

	if (wakeup)
		wake_up_interruptible(&evdev->wait);
}

/*
 * Pass incoming events to all connected clients.
 */
static void evdev_events(struct input_handle *handle,
			 const struct input_value *vals, unsigned int count)
{
	struct evdev *evdev = handle->private;
	struct evdev_client *client;
	ktime_t *ev_time = input_get_timestamp(handle->dev);

	rcu_read_lock();

	client = rcu_dereference(evdev->grab);

	if (client)
		evdev_pass_values(client, vals, count, ev_time);
	else
		list_for_each_entry_rcu(client, &evdev->client_list, node)
			evdev_pass_values(client, vals, count, ev_time);

	rcu_read_unlock();
}

/*
 * Pass incoming event to all connected clients.
 */
static void evdev_event(struct input_handle *handle,
			unsigned int type, unsigned int code, int value)
{
	struct input_value vals[] = { { type, code, value } };

	evdev_events(handle, vals, 1);
}
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7、Input事件内核空间传递到用户空间

EventHub::getEvents -> resd：input事件存储在client->buffer中，当应用层或框架层调用read函数读取/dev/input/event*文件时，例如evdev.c会调用evdev_read返回数据，
event_fetch_next_event：判断client->buffer这个循环缓冲区中的头尾指针是否相等（相等时buffer中没有数据），不相等时取出一个input_event类型的事件放入到event中；
input_event_to_user：将此事件copy到应用层，input_event_size函数是用来获取一个input_event事件的大小，循环复制client->buffer中的事件到应用层的buffer中。

frameworks/native/services/inputflinger/reader/EventHub.cpp

size_t EventHub::getEvents(int timeoutMillis, RawEvent* buffer, size_t bufferSize) {
    ALOG_ASSERT(bufferSize >= 1);

    std::scoped_lock _l(mLock);

    struct input_event readBuffer[bufferSize];

    RawEvent* event = buffer;
    size_t capacity = bufferSize;
    bool awoken = false;
    for (;;) {
        nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);

        // Reopen input devices if needed.
        if (mNeedToReopenDevices) {
            mNeedToReopenDevices = false;

            ALOGI("Reopening all input devices due to a configuration change.");

            closeAllDevicesLocked();
            mNeedToScanDevices = true;
            break; // return to the caller before we actually rescan
        }

        // Report any devices that had last been added/removed.
        for (auto it = mClosingDevices.begin(); it != mClosingDevices.end();) {
            std::unique_ptr<Device> device = std::move(*it);
            ALOGV("Reporting device closed: id=%d, name=%s\n", device->id, device->path.c_str());
            event->when = now;
            event->deviceId = (device->id == mBuiltInKeyboardId)
                    ? ReservedInputDeviceId::BUILT_IN_KEYBOARD_ID
                    : device->id;
            event->type = DEVICE_REMOVED;
            event += 1;
            it = mClosingDevices.erase(it);
            mNeedToSendFinishedDeviceScan = true;
            if (--capacity == 0) {
                break;
            }
        }

        if (mNeedToScanDevices) {
            mNeedToScanDevices = false;
            scanDevicesLocked();
            mNeedToSendFinishedDeviceScan = true;
        }

        while (!mOpeningDevices.empty()) {
            std::unique_ptr<Device> device = std::move(*mOpeningDevices.rbegin());
            mOpeningDevices.pop_back();
            ALOGV("Reporting device opened: id=%d, name=%s\n", device->id, device->path.c_str());
            event->when = now;
            event->deviceId = device->id == mBuiltInKeyboardId ? 0 : device->id;
            event->type = DEVICE_ADDED;
            event += 1;

            // Try to find a matching video device by comparing device names
            for (auto it = mUnattachedVideoDevices.begin(); it != mUnattachedVideoDevices.end();
                 it++) {
                std::unique_ptr<TouchVideoDevice>& videoDevice = *it;
                if (tryAddVideoDeviceLocked(*device, videoDevice)) {
                    // videoDevice was transferred to 'device'
                    it = mUnattachedVideoDevices.erase(it);
                    break;
                }
            }

            auto [dev_it, inserted] = mDevices.insert_or_assign(device->id, std::move(device));
            if (!inserted) {
                ALOGW("Device id %d exists, replaced.", device->id);
            }
            mNeedToSendFinishedDeviceScan = true;
            if (--capacity == 0) {
                break;
            }
        }

        if (mNeedToSendFinishedDeviceScan) {
            mNeedToSendFinishedDeviceScan = false;
            event->when = now;
            event->type = FINISHED_DEVICE_SCAN;
            event += 1;
            if (--capacity == 0) {
                break;
            }
        }

        // Grab the next input event.
        bool deviceChanged = false;
        while (mPendingEventIndex < mPendingEventCount) {
            const struct epoll_event& eventItem = mPendingEventItems[mPendingEventIndex++];
            if (eventItem.data.fd == mINotifyFd) {
                if (eventItem.events & EPOLLIN) {
                    mPendingINotify = true;
                } else {
                    ALOGW("Received unexpected epoll event 0x%08x for INotify.", eventItem.events);
                }
                continue;
            }

            if (eventItem.data.fd == mWakeReadPipeFd) {
                if (eventItem.events & EPOLLIN) {
                    ALOGV("awoken after wake()");
                    awoken = true;
                    char wakeReadBuffer[16];
                    ssize_t nRead;
                    do {
                        nRead = read(mWakeReadPipeFd, wakeReadBuffer, sizeof(wakeReadBuffer));
                    } while ((nRead == -1 && errno == EINTR) || nRead == sizeof(wakeReadBuffer));
                } else {
                    ALOGW("Received unexpected epoll event 0x%08x for wake read pipe.",
                          eventItem.events);
                }
                continue;
            }

            Device* device = getDeviceByFdLocked(eventItem.data.fd);
            if (device == nullptr) {
                ALOGE("Received unexpected epoll event 0x%08x for unknown fd %d.", eventItem.events,
                      eventItem.data.fd);
                ALOG_ASSERT(!DEBUG);
                continue;
            }
            if (device->videoDevice && eventItem.data.fd == device->videoDevice->getFd()) {
                if (eventItem.events & EPOLLIN) {
                    size_t numFrames = device->videoDevice->readAndQueueFrames();
                    if (numFrames == 0) {
                        ALOGE("Received epoll event for video device %s, but could not read frame",
                              device->videoDevice->getName().c_str());
                    }
                } else if (eventItem.events & EPOLLHUP) {
                    // TODO(b/121395353) - consider adding EPOLLRDHUP
                    ALOGI("Removing video device %s due to epoll hang-up event.",
                          device->videoDevice->getName().c_str());
                    unregisterVideoDeviceFromEpollLocked(*device->videoDevice);
                    device->videoDevice = nullptr;
                } else {
                    ALOGW("Received unexpected epoll event 0x%08x for device %s.", eventItem.events,
                          device->videoDevice->getName().c_str());
                    ALOG_ASSERT(!DEBUG);
                }
                continue;
            }
            // This must be an input event
            if (eventItem.events & EPOLLIN) {
                int32_t readSize =
                        read(device->fd, readBuffer, sizeof(struct input_event) * capacity);
                if (readSize == 0 || (readSize < 0 && errno == ENODEV)) {
                    // Device was removed before INotify noticed.
                    ALOGW("could not get event, removed? (fd: %d size: %" PRId32
                          " bufferSize: %zu capacity: %zu errno: %d)\n",
                          device->fd, readSize, bufferSize, capacity, errno);
                    deviceChanged = true;
                    closeDeviceLocked(*device);
                } else if (readSize < 0) {
                    if (errno != EAGAIN && errno != EINTR) {
                        ALOGW("could not get event (errno=%d)", errno);
                    }
                } else if ((readSize % sizeof(struct input_event)) != 0) {
                    ALOGE("could not get event (wrong size: %d)", readSize);
                } else {
                    int32_t deviceId = device->id == mBuiltInKeyboardId ? 0 : device->id;

                    size_t count = size_t(readSize) / sizeof(struct input_event);
                    for (size_t i = 0; i < count; i++) {
                        struct input_event& iev = readBuffer[i];
                        event->when = processEventTimestamp(iev);
                        event->readTime = systemTime(SYSTEM_TIME_MONOTONIC);
                        event->deviceId = deviceId;
                        event->type = iev.type;
                        event->code = iev.code;
                        event->value = iev.value;
                        event += 1;
                        capacity -= 1;
                    }
                    if (capacity == 0) {
                        // The result buffer is full.  Reset the pending event index
                        // so we will try to read the device again on the next iteration.
                        mPendingEventIndex -= 1;
                        break;
                    }
                }
            } else if (eventItem.events & EPOLLHUP) {
                ALOGI("Removing device %s due to epoll hang-up event.",
                      device->identifier.name.c_str());
                deviceChanged = true;
                closeDeviceLocked(*device);
            } else {
                ALOGW("Received unexpected epoll event 0x%08x for device %s.", eventItem.events,
                      device->identifier.name.c_str());
            }
        }

        // readNotify() will modify the list of devices so this must be done after
        // processing all other events to ensure that we read all remaining events
        // before closing the devices.
        if (mPendingINotify && mPendingEventIndex >= mPendingEventCount) {
            mPendingINotify = false;
            readNotifyLocked();
            deviceChanged = true;
        }

        // Report added or removed devices immediately.
        if (deviceChanged) {
            continue;
        }

        // Return now if we have collected any events or if we were explicitly awoken.
        if (event != buffer || awoken) {
            break;
        }

        // Poll for events.
        // When a device driver has pending (unread) events, it acquires
        // a kernel wake lock.  Once the last pending event has been read, the device
        // driver will release the kernel wake lock, but the epoll will hold the wakelock,
        // since we are using EPOLLWAKEUP. The wakelock is released by the epoll when epoll_wait
        // is called again for the same fd that produced the event.
        // Thus the system can only sleep if there are no events pending or
        // currently being processed.
        //
        // The timeout is advisory only.  If the device is asleep, it will not wake just to
        // service the timeout.
        mPendingEventIndex = 0;

        mLock.unlock(); // release lock before poll

        int pollResult = epoll_wait(mEpollFd, mPendingEventItems, EPOLL_MAX_EVENTS, timeoutMillis);

        mLock.lock(); // reacquire lock after poll

        if (pollResult == 0) {
            // Timed out.
            mPendingEventCount = 0;
            break;
        }

        if (pollResult < 0) {
            // An error occurred.
            mPendingEventCount = 0;

            // Sleep after errors to avoid locking up the system.
            // Hopefully the error is transient.
            if (errno != EINTR) {
                ALOGW("poll failed (errno=%d)\n", errno);
                usleep(100000);
            }
        } else {
            // Some events occurred.
            mPendingEventCount = size_t(pollResult);
        }
    }

    // All done, return the number of events we read.
    return event - buffer;
}
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drivers/input/evdev.c

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;
	size_t read = 0;
	int error;

	if (count != 0 && count < input_event_size())
		return -EINVAL;

	for (;;) {
		if (!evdev->exist || client->revoked)
			return -ENODEV;

		if (client->packet_head == client->tail &&
		    (file->f_flags & O_NONBLOCK))
			return -EAGAIN;

		/*
		 * count == 0 is special - no IO is done but we check
		 * for error conditions (see above).
		 */
		if (count == 0)
			break;

		while (read + input_event_size() <= count &&
		       evdev_fetch_next_event(client, &event)) {

			if (input_event_to_user(buffer + read, &event))
				return -EFAULT;

			read += input_event_size();
		}

		if (read)
			break;

		if (!(file->f_flags & O_NONBLOCK)) {
			error = wait_event_interruptible(evdev->wait,
					client->packet_head != client->tail ||
					!evdev->exist || client->revoked);
			if (error)
				return error;
		}
	}

	return read;
}
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7.1 evdev_fetch_next_event

event_fetch_next_event：判断client->buffer这个循环缓冲区中的头尾指针是否相等（相等时buffer中没有数据），不相等时取出一个input_event类型的事件放入到event中

drivers/input/evdev.c

static int evdev_fetch_next_event(struct evdev_client *client,
				  struct input_event *event)
{
	int have_event;

	spin_lock_irq(&client->buffer_lock);

	have_event = client->packet_head != client->tail;
	if (have_event) {
		*event = client->buffer[client->tail++];
		client->tail &= client->bufsize - 1;
	}

	spin_unlock_irq(&client->buffer_lock);

	return have_event;
}
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7.2 input_event_to_user

input_event_to_user：将此事件copy到应用层，input_event_size函数是用来获取一个input_event事件的大小，循环复制client->buffer中的事件到应用层的buffer中

drivers/input/input-compat.c

#ifdef CONFIG_COMPAT

int input_event_to_user(char __user *buffer,
			const struct input_event *event)
{
	if (in_compat_syscall() && !COMPAT_USE_64BIT_TIME) {
		struct input_event_compat compat_event;

		compat_event.sec = event->input_event_sec;
		compat_event.usec = event->input_event_usec;
		compat_event.type = event->type;
		compat_event.code = event->code;
		compat_event.value = event->value;

		if (copy_to_user(buffer, &compat_event,
				 sizeof(struct input_event_compat)))
			return -EFAULT;

	} else {
		if (copy_to_user(buffer, event, sizeof(struct input_event)))
			return -EFAULT;
	}

	return 0;
}

#else

int input_event_to_user(char __user *buffer,
			const struct input_event *event)
{
	if (copy_to_user(buffer, event, sizeof(struct input_event)))
		return -EFAULT;

	return 0;
}

#endif /* CONFIG_COMPAT */
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参考文献

https://www.kernel.org/doc/Documentation/input/input.txt
Linux值输入子系统分析(详解)
input输入子系统

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原文地址：https://blog.csdn.net/qq_23452385/article/details/132859426