linux内核input子系统解析

Android、X windows、qt等众多应用对于linux系统中键盘、鼠标、触摸屏等输入设备的支持都通过、或越来越倾向于标准的input输入子系统。

因为input子系统已经完成了字符驱动的文件操作接口，所以编写驱动的核心工作是完成input系统留出的接口，工作量不大。但如果你想更灵活的应用它，就需要好好的分析下input子系统了。

一、input输入子系统框架

下图是input输入子系统框架，输入子系统由输入子系统核心层（ Input Core ），驱动层和事件处理层（Event Handler）三部份组成。一个输入事件，如鼠标移动，键盘按键按下，joystick的移动等等通过input driver -> Input core -> Event handler -> userspace到达用户空间传给应用程序。

注意：keyboard.c不会在/dev/input下产生节点，而是作为ttyn终端（不包括串口终端）的输入。

二、Input driver编写要点

1、分配、注册、注销input设备

struct input_dev *input_allocate_device(void)

????????int input_register_device(struct input_dev *dev)

????????void input_unregister_device(struct input_dev *dev)

2、设置input设备支持的事件类型、事件码、事件值的范围、input_id等信息

参见usb键盘驱动：usbkbd.c

usb_to_input_id(dev, &input_dev->id);//设置bustype、vendo、PRoduct等

????????input_dev->evbit[0] = BIT(EV_KEY) | BIT(EV_LED) | BIT(EV_REP);//支持的事件类型

????????input_dev->ledbit[0] = BIT(LED_NUML) | BIT(LED_CAPSL) | BIT(LED_SCROLLL) | BIT(LED_COMPOSE) | BIT(LED_KANA);// EV_LED事件支持的事件码

????????for (i = 0; i < 255; i++)

????????????????set_bit(usb_kbd_keycode[i], input_dev->keybit); //EV_KEY事件支持的事件码

include/linux/input.h中定义了支持的类型（下面列出的是2.6.22内核的情况）

#define EV_SYN???????????0x00

????????#define EV_KEY???????????0x01

????????#define EV_REL???????????0x02

????????#define EV_ABS???????????0x03

????????#define EV_MSC??????????0x04

????????#define EV_SW????????????0x05

????????#define EV_LED??????????0x11

????????#define EV_SND?????????0x12

????????#define EV_REP?????????0x14

????????#define EV_FF ????????????0x15

????????#define EV_PWR????????0x16

????????#define EV_FF_STATUS????????0x17

????????#define EV_MAX??????????0x1f

一个设备可以支持一个或多个事件类型。每个事件类型下面还需要设置具体的触发事件码。比如：EV_KEY事件，需要定义其支持哪些按键事件码。

3、如果需要，设置input设备的打开、关闭、写入数据时的处理方法

参见usb键盘驱动：usbkbd.c

input_dev->open = usb_kbd_open;

????????input_dev->close = usb_kbd_close;

????????input_dev->event = usb_kbd_event;

4、在发生输入事件时，向子系统报告事件

用于报告EV_KEY、EV_REL、EV_ABS等事件的函数有：

void input_report_key(struct input_dev *dev, unsigned int code, int value)

????????void input_report_rel(struct input_dev *dev, unsigned int code, int value)

????????void input_report_abs(struct input_dev *dev, unsigned int code, int value)

如果你觉得麻烦，你也可以只记住1个函数（因为上述函数都是通过它实现的）

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

三、Event Handler层解析

1、Input输入子系统数据结构关系图

2、input_handler结构体

以evdev.c中的evdev_handler为例：

static struct input_handler evdev_handler = {

????????????????.event = evdev_event, //向系统报告input事件，系统通过read方法读取

????????????????.connect = evdev_connect, //和input_dev匹配后调用connect构建

????????????????.disconnect = evdev_disconnect,

????????????????.fops = &evdev_fops, //event设备文件的操作方法

????????????????.minor = EVDEV_MINOR_BASE, //次设备号基准值

????????????????.name = "evdev",

????????????????.id_table = evdev_ids, //匹配规则

????????};

3、input字符设备注册过程

drivers/input/input.c中：

????????static int __init input_init(void)

????????{

????????????????int err;

????????????????err = class_register(&input_class);

????????????????……

????????????????err = register_chrdev(INPUT_MAJOR, "input", &input_fops);

????????????????……

????????}

input_fops定义：

static const struct file_Operations input_fops = {

????????????????.owner = THIS_MODULE,

????????????????.open = input_open_file,

????????};

Input_dev和input_handler匹配后调用input_handler的connect。以evdev_handler为例：

static int evdev_connect(struct input_handler *handler, struct input_dev *dev,const struct input_device_id *id)

????????{

????????????????struct evdev *evdev;?

????????????????struct class_device *cdev;

????????????????dev_t devt;

????????????????int minor;

????????????????int error;

????????for (minor = 0; minor < EVDEV_MINORS && evdev_table[minor]; minor++);

????????????????if (minor == EVDEV_MINORS) {

????????????????????????printk(KERN_ERR "evdev: no more free evdev devices/n");

????????????????????????return -ENFILE;

????????????????}

????????evdev = kzalloc(sizeof(struct evdev), GFP_KERNEL);//为每个匹配evdev_handler的设备创建一个evdev。

????????????????if (!evdev)

????????????????????????return -ENOMEM;

????????INIT_LIST_HEAD(&evdev->client_list);

????????????????init_waitqueue_head(&evdev->wait);

????????evdev->exist = 1;

????????????????evdev->minor = minor;

????????????????evdev->handle.dev = dev;

????????????????evdev->handle.name = evdev->name;

????????????????evdev->handle.handler = handler;

????????????????evdev->handle.private = evdev;

????????????????sprintf(evdev->name, "event%d", minor);

????????evdev_table[minor] = evdev;//记录evdev的位置，字符设备/dev/input/evnetx访问时根据次设备号及EVDEV_MINOR_BASE最终在evdev_open中找到对应的evdev

????????????????devt = MKDEV(INPUT_MAJOR, EVDEV_MINOR_BASE + minor),

????????????????cdev = class_device_create(&input_class, &dev->cdev, devt,dev->cdev.dev, evdev->name);//创建了event字符设备节点

????????????????……

????????}

4、input字符设备的打开过程

static int input_open_file(struct inode *inode, struct file *file)

????????{

????????????????struct input_handler *handler = input_table[iminor(inode) >> 5];

????????????????//得到对应的input_handler

????????????????const struct file_operations *old_fops, *new_fops = NULL;

????????????????int err;

????????????????if (!handler || !(new_fops = fops_get(handler->fops)))

????????????????//取出对应input_handler的file_operations

????????????????????????return -ENODEV;

????????????????if (!new_fops->open) {

????????????????????????fops_put(new_fops);

????????????????????????return -ENODEV;

????????????????}

????????????????old_fops = file->f_op;

????????????????file->f_op = new_fops;//重定位打开的设备文件的操作方法

????????????????err = new_fops->open(inode, file);

????????????????if (err) {

????????????????????????fops_put(file->f_op);

????????????????????????file->f_op = fops_get(old_fops);

????????????????}

????????????????fops_put(old_fops);

????????????????return err;

????????}

5、input字符设备的其它操作

由于在open阶段已经把设备文件的操作操作方法重定位了到了具体的input_handler，所以其它接口操作（read、write、ioctl等），由各个input_handler的fops方法决定。如evdev.c中的：evdev_fops。

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input_register_device(&button_dev);

用来注册一个input device.

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