Linux 输入子系统核心层的实现

// 输入设备核心结构体（定义在 include/linux/input.h）struct input_dev {const char *name;          // 设备名称（如 "usb-mouse"）const char *phys;          // 物理路径（如 "usb-0000:00:14.0-1/input0"）struct input_id id;        // 设备ID（总线类型、厂商ID、产品ID等）unsigned long evbit[BITS_TO_LONGS(EV_CNT)]; // 支持的事件类型（EV_KEY/EV_REL/EV_ABS等）unsigned long keybit[BITS_TO_LONGS(KEY_CNT)]; // 支持的按键unsigned long relbit[BITS_TO_LONGS(REL_CNT)]; // 支持的相对坐标（鼠标）unsigned long absbit[BITS_TO_LONGS(ABS_CNT)]; // 支持的绝对坐标（触摸屏）struct list_head node;     // 挂入核心层设备链表的节点struct input_handler *grab; // 独占该设备的handlerstruct mutex mutex;        // 保护设备的互斥锁// 其他成员（事件队列、定时器、电源管理等）};// 输入事件处理者结构体（Handler）struct input_handler {void (*event)(struct input_handle *handle, unsignedint type, unsignedint code, int value); // 事件处理函数int (*connect)(struct input_handler *handler, struct input_dev *dev, conststruct input_device_id *id); // 匹配设备的函数void (*disconnect)(struct input_handle *handle); // 断开匹配的函数struct list_head node;     // 挂入核心层handler链表的节点const struct input_device_id *id_table; // 支持的设备ID表struct list_head h_list;   // 关联的input_handle链表};// 设备与Handler的连接结构体（核心层的“桥梁”）struct input_handle {struct input_dev *dev;     // 关联的输入设备struct input_handler *handler; // 关联的Handlerstruct list_head d_node;   // 挂入input_dev的h_liststruct list_head h_node;   // 挂入input_handler的h_list};

// 注册输入设备intinput_register_device(struct input_dev *dev);// 注销输入设备voidinput_unregister_device(struct input_dev *dev);

// 注册事件处理器intinput_register_handler(struct input_handler *handler);// 注销事件处理器voidinput_unregister_handler(struct input_handler *handler);

// 核心层事件上报函数voidinput_event(struct input_dev *dev, unsignedint type, unsignedint code, int value);

struct input_dev *input_dev;input_dev = input_allocate_device(); // 分配input_dev// 设置设备属性input_dev->name = "my_input_device";input_dev->id.bustype = BUS_I2C;// 设置支持的事件类型set_bit(EV_KEY, input_dev->evbit);set_bit(KEY_A, input_dev->keybit);// 注册设备input_register_device(input_dev);

input_register_device()	list_for_each_entry(handler, &input_handler_list, node)	input_attach_handler()			input_match_device()				handler->connect()

intinput_register_device(struct input_dev *dev){static atomic_t input_no = ATOMIC_INIT(0);struct input_devres *devres = NULL;struct input_handler *handler;unsigned int packet_size;const char *path;int error;if (dev->devres_managed) {		devres = devres_alloc(devm_input_device_unregister,				      sizeof(struct input_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);/* 将KEY_RESERVED位清零 */	__clear_bit(KEY_RESERVED, dev->keybit);/* 确保dev->evbit中没有设置的位都被清零 */input_cleanse_bitmasks(dev);	packet_size = input_estimate_events_per_packet(dev);	......//初始化定时器init_timer(&dev->timer);        //REP_DELAY和REP_PERIOD是关于重复按键的，如果没有设置就赋值为默认值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)//获取键的扫描码		dev->getkeycode = input_default_getkeycode;if (!dev->setkeycode)//设置键的扫描码		dev->setkeycode = input_default_setkeycode;dev_set_name(&dev->dev, "input%ld",//设置内嵌dev的名字		     (unsigned long) atomic_inc_return(&input_no) - 1);	error = device_add(&dev->dev);//将input_dev内嵌的dev注册到sysfsif (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);//上锁if (error)goto err_device_del;list_add_tail(&dev->node, &input_dev_list);//将输入设备挂载到input_dev_list链表上list_for_each_entry(handler, &input_handler_list, node)input_attach_handler(dev, handler);      //遍历事件处理驱动，如果找到匹配的事件处理驱动就将该设备依附上去，//生成一个handle        input_wakeup_procfs_readers();mutex_unlock(&input_mutex);   ..........}EXPORT_SYMBOL(input_register_device);

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);// 匹配成功，调用connectif (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;}

int (*connect)(struct input_handler *handler, struct input_dev *dev, const struct input_device_id *id);

static struct input_handler evdev_handler = {    // ...    .connect    = evdev_connect,    // ...};staticintevdev_connect(struct input_handler *handler, struct input_dev *dev, conststruct 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);...............    evdev = kzalloc(sizeof(struct evdev), GFP_KERNEL);    evdev->dev = dev;    evdev->handle.dev = dev;    evdev->handle.handler = handler;    evdev->handle.private = evdev;    // 创建设备节点    evdev->devno = input_alloc_device_id();    dev_set_name(&evdev->dev->dev, "event%d", evdev->devno);    cdev_init(&evdev->cdev, &evdev_fops);    cdev_add(&evdev->cdev, MKDEV(INPUT_MAJOR, evdev->devno), 1);    input_register_handle(&evdev->handle);    return 0;} cdev_add(&evdev->cdev, MKDEV(INPUT_MAJOR, evdev->devno), 1);加入到了字符设备中。

Input Core（撮合/转发）—— drivers/input/input.c  - 维护设备/handler 列表  - 匹配：input_match_device()  - 绑定：handler->connect()  - 转发：input_event()

staticinlinevoidinput_sync(struct input_dev *dev){    input_event(dev, EV_SYN, SYN_REPORT, 0);}

voidinput_event(struct input_dev *dev,		 unsigned int type, unsigned int code, int value){unsigned long flags;//判断设备驱动是否支持该输入事件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);

staticvoidinput_handle_event(struct input_dev *dev,			       unsigned int type, unsigned int code, int value)

事件处理层 Handler（Consumer）—— 以 evdev 为例  - /dev/input/eventX（字符设备接口）  - evdev_event()/evdev_read()/ioctl

static const struct file_operations evdev_fops = {	.owner		= THIS_MODULE,	.read		= evdev_read,	.write		= evdev_write,	.poll		= evdev_poll,	.open		= evdev_open,	.release	= evdev_release,	.unlocked_ioctl	= evdev_ioctl,#ifdef CONFIG_COMPAT	.compat_ioctl	= evdev_ioctl_compat,#endif	.fasync		= evdev_fasync,	.flush		= evdev_flush,	.llseek		= no_llseek,};

staticintevdev_open(struct inode *inode, structfile *file){struct evdev *evdev = container_of(inode->i_cdev, struct evdev, cdev);	unsigned int bufsize = evdev_compute_buffer_size(evdev->handle.dev);	unsigned int size = sizeof(struct evdev_client) +					bufsize * sizeof(struct input_event);struct evdev_client *client;int error;	client = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);// 第二，给evdev_client结构分配内存空间。if (!client)		client = vzalloc(size);if (!client)return -ENOMEM;	client->bufsize = bufsize;	spin_lock_init(&client->buffer_lock);	snprintf(client->name, sizeof(client->name), "%s-%d",			dev_name(&evdev->dev), task_tgid_vnr(current));	client->evdev = evdev;// 第三，将client的evdev指向当前evdev，并且将client挂接到evdev的链表上	evdev_attach_client(evdev, client);	error = evdev_open_device(evdev); // 第四，调用evdev_open_device()if (error)goto err_free_client;file->private_data = client;	nonseekable_open(inode, file);// 第五，设置文件的模式return 0; err_free_client:	evdev_detach_client(evdev, client);	kfree(client);return error;}

struct evdev {    int open;  // open，当用户open此设备时，open的值加1。    struct input_handle handle; // 包括了匹配的 dev 与 handler    wait_queue_head_t wait; // 等待队列    struct evdev_client __rcu *grab; // 可以为evdev实例指定一个struct evdev_client实例，这样在传递Input消息时就只会传递给这一个struct evdev_client实例，而不会传递给所有的struct evdev_client实例。每open一次就会生成一个struct evdev_client实例。    struct list_head client_list; // 用来把所有的struct client_list实例连接在一起    spinlock_t client_lock; /* protects client_list */    struct mutex mutex; // 同步相关的锁    struct device dev; // dev，用来嵌入到设备模型中。    struct cdev cdev; //    bool exist;  // struct evdev被成功实例化后，exist的值就为true};

client = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);

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;bool use_wake_lock;char name[28];struct fasync_struct *fasync;struct evdev *evdev;struct list_head node;int clkid;unsigned int bufsize;struct input_event buffer[];};

staticunsignedintevdev_compute_buffer_size(struct input_dev *dev){unsigned int n_events =max(dev->hint_events_per_packet * EVDEV_BUF_PACKETS,		    EVDEV_MIN_BUFFER_SIZE);return roundup_pow_of_two(n_events);}

client->evdev = evdev;// 第三，将client的evdev指向当前evdev，并且将client挂接到evdev的链表上	evdev_attach_client(evdev, client);staticvoidevdev_attach_client(struct evdev *evdev,struct evdev_client *client){	spin_lock(&evdev->client_lock);	list_add_tail_rcu(&client->node, &evdev->client_list);	spin_unlock(&evdev->client_lock);}

staticintevdev_open_device(struct evdev *evdev){int retval;	retval = mutex_lock_interruptible(&evdev->mutex);if (retval)return retval;if (!evdev->exist)		retval = -ENODEV;else if (!evdev->open++) {		retval = input_open_device(&evdev->handle);if (retval)			evdev->open--;	}mutex_unlock(&evdev->mutex);return retval;}intinput_open_device(struct input_handle *handle){struct input_dev *dev = handle->dev;int retval;	retval = mutex_lock_interruptible(&dev->mutex);if (retval)return retval;if (dev->going_away) {		retval = -ENODEV;goto out;	}	handle->open++;if (!dev->users++ && dev->open)		retval = dev->open(dev);if (retval) {		dev->users--;if (!--handle->open) {/*			 * Make sure we are not delivering any more events			 * through this handle			 */synchronize_rcu();		}	} out:mutex_unlock(&dev->mutex);return retval;}EXPORT_SYMBOL(input_open_device);