Android、X windows、qt等眾多應用對于linux系統中鍵盤、鼠標、觸摸屏等輸入設備的支持都通過、或越來越傾向于標準的input輸入子系統。

因為input子系統已經完成了字符驅動的文件操作接口，所以編寫驅動的核心工作是完成input系統留出的接口，工作量不大。但如果你想更靈活的應用它，就需要好好的分析下input子系統了。

一、input輸入子系統框架

下圖是input輸入子系統框架，輸入子系統由輸入子系統核心層（ Input Core ），驅動層和事件處理層（Event Handler）三部份組成。一個輸入事件，如鼠標移動，鍵盤按鍵按下，joystick的移動等等通過input driver -> Input core -> Event handler -> userspace到達用戶空間傳給應用程序。

注意：keyboard.c不會在/dev/input下產生節點，而是作為ttyn終端（不包括串口終端）的輸入。

二、Input driver編寫要點

1、分配、注冊、注銷input設備

struct input_dev *input_allocate_device(void)

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

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

2、設置input設備支持的事件類型、事件碼、事件值的范圍、input_id等信息

參見usb鍵盤驅動：usbkbd.c

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

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

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

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

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

include/linux/input.h中定義了支持的類型（下面列出的是2.6.22內核的情況）

#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

一個設備可以支持一個或多個事件類型。每個事件類型下面還需要設置具體的觸發事件碼。比如：EV_KEY事件，需要定義其支持哪些按鍵事件碼。

3、如果需要，設置input設備的打開、關閉、寫入數據時的處理方法

參見usb鍵盤驅動：usbkbd.c

input_dev->open = usb_kbd_open;

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

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

4、在發生輸入事件時，向子系統報告事件

用于報告EV_KEY、EV_REL、EV_ABS等事件的函數有：

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)

如果你覺得麻煩，你也可以只記住1個函數（因為上述函數都是通過它實現的）

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

三、Event Handler層解析

1、Input輸入子系統數據結構關系圖

2、input_handler結構體

以evdev.c中的evdev_handler為例：

static struct input_handler evdev_handler = {

????????????????.event = evdev_event, //向系統報告input事件，系統通過read方法讀取

????????????????.connect = evdev_connect, //和input_dev匹配后調用connect構建

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

????????????????.fops = &evdev_fops, //event設備文件的操作方法

????????????????.minor = EVDEV_MINOR_BASE, //次設備號基準值

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

????????????????.id_table = evdev_ids, //匹配規則

????????};

3、input字符設備注冊過程

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定義：

static const struct file_Operations input_fops = {

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

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

????????};

Input_dev和input_handler匹配后調用input_handler的connect。以evdev_handler為例：

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);//為每個匹配evdev_handler的設備創建一個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;//記錄evdev的位置，字符設備/dev/input/evnetx訪問時根據次設備號及EVDEV_MINOR_BASE最終在evdev_open中找到對應的evdev

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

????????????????cdev = class_device_create(&input_class, &dev->cdev, devt,dev->cdev.dev, evdev->name);//創建了event字符設備節點

????????????????……

????????}

4、input字符設備的打開過程

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

????????{

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

????????????????//得到對應的input_handler

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

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

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

????????????????//取出對應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;//重定位打開的設備文件的操作方法

????????????????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字符設備的其它操作

由于在open階段已經把設備文件的操作操作方法重定位了到了具體的input_handler，所以其它接口操作（read、write、ioctl等），由各個input_handler的fops方法決定。如evdev.c中的：evdev_fops。

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input_register_device(&button_dev);

用來注冊一個input device.

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