原创 linux内核input子系统解析

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。