Linux驱动学习笔记之输入子系统（1）

之所以要引入子系统，是为了让程序更标准化。之前的按键程序，虽然最后相对比较完善，但是不是通用的，别人在不熟悉的情况下是不能随心所欲调用的。显然这与实际应用不合.input输入子系统是内核源码自带的，如果按他这种框架来写，写出的程序就可以很方便地被上层调用，而不用过份关注一些其他的问题。

首先，分析一个驱动程序，先从入口函数开始。static int __init input_init（）中有一句err = register_chrdev(INPUT_MAJOR, "input", &input_fops);是用来注册设备的，接下来再看注册设备的信息。
在
static const struct file_operations input_fops = {
    .owner = THIS_MODULE,
    .open = input_open_file,
};
想调用open肯定要进入input_open_file中执行，打开input_open_file 分析见代码中的注释。根据实际情况构造新的new_fops.
err = new_fops->open(inode, file);   // 返回新的fops
应用程序中要读就要执行：
read > ... > file->f_op->read
input_table数组由谁构造
MODULE_DEVICE_TABLE(input, evdev_ids);   // 源自drivers\input\Evdev.c

static struct input_handler evdev_handler = {
    .event =    evdev_event,                   // 事件
    .connect =    evdev_connect,               // 连接
    .disconnect =    evdev_disconnect,         // 断开连接，关联
    .fops =        &evdev_fops,                // fops
    .minor =    EVDEV_MINOR_BASE,              // 次设备号
    .name =        "evdev",                    // 设备名
    .id_table =    evdev_ids,                  // id_table 表示可以支持的设备 如果id_table支持设备则调用connect函数。让input_device(硬件上的）和input_handler(软件上的）建立一个连接。
};

input_register_handler（软件上的）

注册input_handler:
input_register_handler:
input_table[handler->minor >> 5] = handler  // 数组
list_add_tail(&handler->node, &input_handler_list);  // 放入链表

list_for_each_entry(dev, &input_dev_list, node)      // 对于每一个input_dev调用input_attach_handler
    input_attach_handler(dev, handler);              // 根据input_handler中的id_table来判断能否支持这个input_dev
          
注册输入设备
input_register_device
    list_add_tail(&dev->node, &input_dev_list)   // 放入链表
   
    list_for_each_entry(handler, &input_handler_list, node) // 对input_handler_list中的每一个条目都调用input_attach_handler（）;
        input_attach_handler(dev, handler);  // 根据input_handler中的id_table来判断能否支持这个input_dev

   
   
input_attach_handler:

id = input_match_device(handler->id_table, dev);

error = handler->connect(handler, dev, id);

根据注册input_dev或input_handler时，会两两比较input_dev和input_handler
根据input_handler的id_table判断这个input_handler能否支持这个input_dev,如果可以则调用
input_handler的connect函数建立“连接”

怎么建立连接：
1，分配一个input_handle结构体
2，设置
    input_handle.dev = input_dev;
    input_handle.handler = input_handler;
3,注册
    input_handler->h_list = &input_handle
    input_dev->h_list     = &input_handle
   
Evdev.c
evdev_connect()

evdev = kzalloc(sizeof(struct evdev), GFP_KERNEL);    // 分配一个input_handle结构

    // 设置
    evdev->handle.dev = dev;            // 指向input_dev结构体
    evdev->handle.name = evdev->name;   //
    evdev->handle.handler = handler;    // 指向input_handler结构体
    evdev->handle.private = evdev;
   
error = input_register_handle(&evdev->handle);  //  注册这个handle
   
怎么读按键：
app: read
---------------------------------------------
   ..............
        evdev_read
            // 无数据并且是非阻塞方式打开，则立刻返回。
            if (client->head == client->tail && evdev->exist && (file->f_flags & O_NONBLOCK))
            return -EAGAIN; // client缓冲，如果环形缓冲头和尾是一样。表示数据是空的。并且文件是以非阻塞方式打开
                                 则再次尝试。
            // 否则休眠
            retval = wait_event_interruptible(evdev->wait  // 如果是以阻塞方式打开则马上进入休眠。
                client->head != client->tail || !evdev->exist);
               
        谁来唤醒：
        evdev_event事件里面唤醒
            wake_up_interruptible(&evdev->wait);
           
        evdev_event被谁来调用
        
        怎么写符合输入子系统框架的驱动程序？
        1，分配一个input_dev结构体
        2，设置
        3，注册
        4，硬件相关的代码，比如在中断服务程序里面上报事件。

/*
 * The input core
 *
 * Copyright (c) 1999-2002 Vojtech Pavlik
 */

/*
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published by
 * the Free Software Foundation.
 */

#include <linux/init.h>
#include <linux/input.h>
#include <linux/module.h>
#include <linux/random.h>
#include <linux/major.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/interrupt.h>
#include <linux/poll.h>
#include <linux/device.h>
#include <linux/mutex.h>

MODULE_AUTHOR("Vojtech Pavlik ");
MODULE_DESCRIPTION("Input core");
MODULE_LICENSE("GPL");

#define INPUT_DEVICES    256

static LIST_HEAD(input_dev_list);
static LIST_HEAD(input_handler_list);

static struct input_handler *input_table[8];

/**
 * 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
 * See also input_inject_event()
 */
void input_event(struct input_dev *dev, unsigned int type, unsigned int code, int value)
{
    struct input_handle *handle;

    if (type > EV_MAX || !test_bit(type, dev->evbit))
        return;

    add_input_randomness(type, code, value);

    switch (type) {

        case EV_SYN:
            switch (code) {
                case SYN_CONFIG:
                    if (dev->event)
                        dev->event(dev, type, code, value);
                    break;

                case SYN_REPORT:
                    if (dev->sync)
                        return;
                    dev->sync = 1;
                    break;
            }
            break;

        case EV_KEY:

            if (code > KEY_MAX || !test_bit(code, dev->keybit) || !!test_bit(code, dev->key) == value)
                return;

            if (value == 2)
                break;

            change_bit(code, dev->key);

            if (test_bit(EV_REP, dev->evbit) && dev->rep[REP_PERIOD] && dev->rep[REP_DELAY] && dev->timer.data && value) {
                dev->repeat_key = code;
                mod_timer(&dev->timer, jiffies + msecs_to_jiffies(dev->rep[REP_DELAY]));
            }

            break;

        case EV_SW:

            if (code > SW_MAX || !test_bit(code, dev->swbit) || !!test_bit(code, dev->sw) == value)
                return;

            change_bit(code, dev->sw);

            break;

        case EV_ABS:

            if (code > ABS_MAX || !test_bit(code, dev->absbit))
                return;

            if (dev->absfuzz[code]) {
                if ((value > dev->abs[code] - (dev->absfuzz[code] >> 1)) &&
                 (value < dev->abs[code] + (dev->absfuzz[code] >> 1)))
                    return;

                if ((value > dev->abs[code] - dev->absfuzz[code]) &&
                 (value < dev->abs[code] + dev->absfuzz[code]))
                    value = (dev->abs[code] * 3 + value) >> 2;

                if ((value > dev->abs[code] - (dev->absfuzz[code] << 1)) &&
                 (value < dev->abs[code] + (dev->absfuzz[code] << 1)))
                    value = (dev->abs[code] + value) >> 1;
            }

            if (dev->abs[code] == value)
                return;

            dev->abs[code] = value;
            break;

        case EV_REL:

            if (code > REL_MAX || !test_bit(code, dev->relbit) || (value == 0))
                return;

            break;

        case EV_MSC:

            if (code > MSC_MAX || !test_bit(code, dev->mscbit))
                return;

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

            break;

        case EV_LED:

            if (code > LED_MAX || !test_bit(code, dev->ledbit) || !!test_bit(code, dev->led) == value)
                return;

            change_bit(code, dev->led);

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

            break;

        case EV_SND:

            if (code > SND_MAX || !test_bit(code, dev->sndbit))
                return;

            if (!!test_bit(code, dev->snd) != !!value)
                change_bit(code, dev->snd);

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

            break;

        case EV_REP:

            if (code > REP_MAX || value < 0 || dev->rep[code] == value)
                return;

            dev->rep[code] = value;
            if (dev->event)
                dev->event(dev, type, code, value);

            break;

        case EV_FF:

            if (value < 0)
                return;

            if (dev->event)
                dev->event(dev, type, code, value);
            break;
    }

    if (type != EV_SYN)
        dev->sync = 0;

    if (dev->grab)
        dev->grab->handler->event(dev->grab, type, code, value);
    else
        list_for_each_entry(handle, &dev->h_list, d_node)
            if (handle->open)
                handle->handler->event(handle, type, code, value);
}
EXPORT_SYMBOL(input_event);

/**
 * input_inject_event() - send input event from input handler
 * @handle: input handle to send event through
 * @type: type of the event
 * @code: event code
 * @value: value of the event
 *
 * Similar to input_event() but will ignore event if device is "grabbed" and handle
 * injecting event is not the one that owns the device.
 */
void input_inject_event(struct input_handle *handle, unsigned int type, unsigned int code, int value)
{
    if (!handle->dev->grab || handle->dev->grab == handle)
        input_event(handle->dev, type, code, value);
}
EXPORT_SYMBOL(input_inject_event);

static void input_repeat_key(unsigned long data)
{
    struct input_dev *dev = (void *) data;

    if (!test_bit(dev->repeat_key, dev->key))
        return;

    input_event(dev, EV_KEY, dev->repeat_key, 2);
    input_sync(dev);

    if (dev->rep[REP_PERIOD])
        mod_timer(&dev->timer, jiffies + msecs_to_jiffies(dev->rep[REP_PERIOD]));
}

int input_grab_device(struct input_handle *handle)
{
    if (handle->dev->grab)
        return -EBUSY;

    handle->dev->grab = handle;
    return 0;
}
EXPORT_SYMBOL(input_grab_device);

void input_release_device(struct input_handle *handle)
{
    struct input_dev *dev = handle->dev;

    if (dev->grab == handle) {
        dev->grab = NULL;

        list_for_each_entry(handle, &dev->h_list, d_node)
            if (handle->handler->start)
                handle->handler->start(handle);
    }
}
EXPORT_SYMBOL(input_release_device);

int input_open_device(struct input_handle *handle)
{
    struct input_dev *dev = handle->dev;
    int err;

    err = mutex_lock_interruptible(&dev->mutex);
    if (err)
        return err;

    handle->open++;

    if (!dev->users++ && dev->open)
        err = dev->open(dev);

    if (err)
        handle->open--;

    mutex_unlock(&dev->mutex);

    return err;
}
EXPORT_SYMBOL(input_open_device);

int input_flush_device(struct input_handle* handle, struct file* file)
{
    if (handle->dev->flush)
        return handle->dev->flush(handle->dev, file);

    return 0;
}
EXPORT_SYMBOL(input_flush_device);

void input_close_device(struct input_handle *handle)
{
    struct input_dev *dev = handle->dev;

    input_release_device(handle);

    mutex_lock(&dev->mutex);

    if (!--dev->users && dev->close)
        dev->close(dev);
    handle->open--;

    mutex_unlock(&dev->mutex);
}
EXPORT_SYMBOL(input_close_device);

static int input_fetch_keycode(struct input_dev *dev, int scancode)
{
    switch (dev->keycodesize) {
        case 1:
            return ((u8 *)dev->keycode)[scancode];

        case 2:
            return ((u16 *)dev->keycode)[scancode];

        default:
            return ((u32 *)dev->keycode)[scancode];
    }
}

static int input_default_getkeycode(struct input_dev *dev,
                 int scancode, int *keycode)
{
    if (!dev->keycodesize)
        return -EINVAL;

    if (scancode < 0 || scancode >= dev->keycodemax)
        return -EINVAL;

    *keycode = input_fetch_keycode(dev, scancode);

    return 0;
}

static int input_default_setkeycode(struct input_dev *dev,
                 int scancode, int keycode)
{
    int old_keycode;
    int i;

    if (scancode < 0 || scancode >= dev->keycodemax)
        return -EINVAL;

    if (keycode < 0 || keycode > KEY_MAX)
        return -EINVAL;

    if (!dev->keycodesize)
        return -EINVAL;

    if (dev->keycodesize < sizeof(keycode) && (keycode >> (dev->keycodesize * 8)))
        return -EINVAL;

    switch (dev->keycodesize) {
        case 1: {
            u8 *k = (u8 *)dev->keycode;
            old_keycode = k[scancode];
            k[scancode] = keycode;
            break;
        }
        case 2: {
            u16 *k = (u16 *)dev->keycode;
            old_keycode = k[scancode];
            k[scancode] = keycode;
            break;
        }
        default: {
            u32 *k = (u32 *)dev->keycode;
            old_keycode = k[scancode];
            k[scancode] = keycode;
            break;
        }
    }

    clear_bit(old_keycode, dev->keybit);
    set_bit(keycode, dev->keybit);

    for (i = 0; i < dev->keycodemax; i++) {
        if (input_fetch_keycode(dev, i) == old_keycode) {
            set_bit(old_keycode, dev->keybit);
            break; /* Setting the bit twice is useless, so break */
        }
    }

    return 0;
}


#define MATCH_BIT(bit, max) \
        for (i = 0; i < NBITS(max); i++) \
            if ((id->bit[i] & dev->bit[i]) != id->bit[i]) \
                break; \
        if (i != NBITS(max)) \
            continue;

static const struct input_device_id *input_match_device(const struct input_device_id *id,
                            struct input_dev *dev)
{
    int i;

    for (; id->flags || id->driver_info; id++) {

        if (id->flags & INPUT_DEVICE_ID_MATCH_BUS)
            if (id->bustype != dev->id.bustype)
                continue;

        if (id->flags & INPUT_DEVICE_ID_MATCH_VENDOR)
            if (id->vendor != dev->id.vendor)
                continue;

        if (id->flags & INPUT_DEVICE_ID_MATCH_PRODUCT)
            if (id->product != dev->id.product)
                continue;

        if (id->flags & INPUT_DEVICE_ID_MATCH_VERSION)
            if (id->version != dev->id.version)
                continue;

        MATCH_BIT(evbit, EV_MAX);
        MATCH_BIT(keybit, KEY_MAX);
        MATCH_BIT(relbit, REL_MAX);
        MATCH_BIT(absbit, ABS_MAX);
        MATCH_BIT(mscbit, MSC_MAX);
        MATCH_BIT(ledbit, LED_MAX);
        MATCH_BIT(sndbit, SND_MAX);
        MATCH_BIT(ffbit, FF_MAX);
        MATCH_BIT(swbit, SW_MAX);

        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;

    if (handler->blacklist && input_match_device(handler->blacklist, dev))
        return -ENODEV;

    id = input_match_device(handler->id_table, dev);
    if (!id)
        return -ENODEV;

    error = handler->connect(handler, dev, id);
    if (error && error != -ENODEV)
        printk(KERN_ERR
            "input: failed to attach handler %s to device %s, "
            "error: %d\n",
            handler->name, kobject_name(&dev->cdev.kobj), error);

    return error;
}


#ifdef CONFIG_PROC_FS

static struct proc_dir_entry *proc_bus_input_dir;
static DECLARE_WAIT_QUEUE_HEAD(input_devices_poll_wait);
static int input_devices_state;

static inline void input_wakeup_procfs_readers(void)
{
    input_devices_state++;
    wake_up(&input_devices_poll_wait);
}

static unsigned int input_proc_devices_poll(struct file *file, poll_table *wait)
{
    int state = input_devices_state;

    poll_wait(file, &input_devices_poll_wait, wait);
    if (state != input_devices_state)
        return POLLIN | POLLRDNORM;

    return 0;
}

static struct list_head *list_get_nth_element(struct list_head *list, loff_t *pos)
{
    struct list_head *node;
    loff_t i = 0;

    list_for_each(node, list)
        if (i++ == *pos)
            return node;

    return NULL;
}

static struct list_head *list_get_next_element(struct list_head *list, struct list_head *element, loff_t *pos)
{
    if (element->next == list)
        return NULL;

    ++(*pos);
    return element->next;
}

static void *input_devices_seq_start(struct seq_file *seq, loff_t *pos)
{
    /* acquire lock here ... Yes, we do need locking, I knowi, I know... */

    return list_get_nth_element(&input_dev_list, pos);
}

static void *input_devices_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
    return list_get_next_element(&input_dev_list, v, pos);
}

static void input_devices_seq_stop(struct seq_file *seq, void *v)
{
    /* release lock here */
}

static void input_seq_print_bitmap(struct seq_file *seq, const char *name,
                 unsigned long *bitmap, int max)
{
    int i;

    for (i = NBITS(max) - 1; i > 0; i--)
        if (bitmap[i])
            break;

    seq_printf(seq, "B: %s=", name);
    for (; i >= 0; i--)
        seq_printf(seq, "%lx%s", bitmap[i], i > 0 ? " " : "");
    seq_putc(seq, '\n');
}

static int input_devices_seq_show(struct seq_file *seq, void *v)
{
    struct input_dev *dev = container_of(v, struct input_dev, node);
    const char *path = kobject_get_path(&dev->cdev.kobj, GFP_KERNEL);
    struct input_handle *handle;

    seq_printf(seq, "I: Bus=%04x Vendor=%04x Product=%04x Version=%04x\n",
         dev->id.bustype, dev->id.vendor, dev->id.product, dev->id.version);

    seq_printf(seq, "N: Name=\"%s\"\n", dev->name ? dev->name : "");
    seq_printf(seq, "P: Phys=%s\n", dev->phys ? dev->phys : "");
    seq_printf(seq, "S: Sysfs=%s\n", path ? path : "");
    seq_printf(seq, "U: Uniq=%s\n", dev->uniq ? dev->uniq : "");
    seq_printf(seq, "H: Handlers=");

    list_for_each_entry(handle, &dev->h_list, d_node)
        seq_printf(seq, "%s ", handle->name);
    seq_putc(seq, '\n');

    input_seq_print_bitmap(seq, "EV", dev->evbit, EV_MAX);
    if (test_bit(EV_KEY, dev->evbit))
        input_seq_print_bitmap(seq, "KEY", dev->keybit, KEY_MAX);
    if (test_bit(EV_REL, dev->evbit))
        input_seq_print_bitmap(seq, "REL", dev->relbit, REL_MAX);
    if (test_bit(EV_ABS, dev->evbit))
        input_seq_print_bitmap(seq, "ABS", dev->absbit, ABS_MAX);
    if (test_bit(EV_MSC, dev->evbit))
        input_seq_print_bitmap(seq, "MSC", dev->mscbit, MSC_MAX);
    if (test_bit(EV_LED, dev->evbit))
        input_seq_print_bitmap(seq, "LED", dev->ledbit, LED_MAX);
    if (test_bit(EV_SND, dev->evbit))
        input_seq_print_bitmap(seq, "SND", dev->sndbit, SND_MAX);
    if (test_bit(EV_FF, dev->evbit))
        input_seq_print_bitmap(seq, "FF", dev->ffbit, FF_MAX);
    if (test_bit(EV_SW, dev->evbit))
        input_seq_print_bitmap(seq, "SW", dev->swbit, SW_MAX);

    seq_putc(seq, '\n');

    kfree(path);
    return 0;
}

static struct seq_operations input_devices_seq_ops = {
    .start    = input_devices_seq_start,
    .next    = input_devices_seq_next,
    .stop    = input_devices_seq_stop,
    .show    = input_devices_seq_show,
};

static int input_proc_devices_open(struct inode *inode, struct file *file)
{
    return seq_open(file, &input_devices_seq_ops);
}

static const struct file_operations input_devices_fileops = {
    .owner        = THIS_MODULE,
    .open        = input_proc_devices_open,
    .poll        = input_proc_devices_poll,
    .read        = seq_read,
    .llseek        = seq_lseek,
    .release    = seq_release,
};

static void *input_handlers_seq_start(struct seq_file *seq, loff_t *pos)
{
    /* acquire lock here ... Yes, we do need locking, I knowi, I know... */
    seq->private = (void *)(unsigned long)*pos;
    return list_get_nth_element(&input_handler_list, pos);
}

static void *input_handlers_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
    seq->private = (void *)(unsigned long)(*pos + 1);
    return list_get_next_element(&input_handler_list, v, pos);
}

static void input_handlers_seq_stop(struct seq_file *seq, void *v)
{
    /* release lock here */
}

static int input_handlers_seq_show(struct seq_file *seq, void *v)
{
    struct input_handler *handler = container_of(v, struct input_handler, node);

    seq_printf(seq, "N: Number=%ld Name=%s",
         (unsigned long)seq->private, handler->name);
    if (handler->fops)
        seq_printf(seq, " Minor=%d", handler->minor);
    seq_putc(seq, '\n');

    return 0;
}
static struct seq_operations input_handlers_seq_ops = {
    .start    = input_handlers_seq_start,
    .next    = input_handlers_seq_next,
    .stop    = input_handlers_seq_stop,
    .show    = input_handlers_seq_show,
};

static int input_proc_handlers_open(struct inode *inode, struct file *file)
{
    return seq_open(file, &input_handlers_seq_ops);
}

static const struct file_operations input_handlers_fileops = {
    .owner        = THIS_MODULE,
    .open        = input_proc_handlers_open,
    .read        = seq_read,
    .llseek        = seq_lseek,
    .release    = seq_release,
};

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

    proc_bus_input_dir = proc_mkdir("input", proc_bus);
    if (!proc_bus_input_dir)
        return -ENOMEM;

    proc_bus_input_dir->owner = THIS_MODULE;

    entry = create_proc_entry("devices", 0, proc_bus_input_dir);
    if (!entry)
        goto fail1;

    entry->owner = THIS_MODULE;
    entry->proc_fops = &input_devices_fileops;

    entry = create_proc_entry("handlers", 0, proc_bus_input_dir);
    if (!entry)
        goto fail2;

    entry->owner = THIS_MODULE;
    entry->proc_fops = &input_handlers_fileops;

    return 0;

 fail2:    remove_proc_entry("devices", proc_bus_input_dir);
 fail1: remove_proc_entry("input", proc_bus);
    return -ENOMEM;
}

static void input_proc_exit(void)
{
    remove_proc_entry("devices", proc_bus_input_dir);
    remove_proc_entry("handlers", proc_bus_input_dir);
    remove_proc_entry("input", proc_bus);
}

#else /* !CONFIG_PROC_FS */
static inline void input_wakeup_procfs_readers(void) { }
static inline int input_proc_init(void) { return 0; }
static inline void input_proc_exit(void) { }
#endif

#define INPUT_DEV_STRING_ATTR_SHOW(name)                    \
static ssize_t input_dev_show_##name(struct class_device *dev, char *buf)    \
{                                        \
    struct input_dev *input_dev = to_input_dev(dev);            \
                                        \
    return scnprintf(buf, PAGE_SIZE, "%s\n",                \
             input_dev->name ? input_dev->name : "");        \
}                                        \
static CLASS_DEVICE_ATTR(name, S_IRUGO, input_dev_show_##name, NULL);

INPUT_DEV_STRING_ATTR_SHOW(name);
INPUT_DEV_STRING_ATTR_SHOW(phys);
INPUT_DEV_STRING_ATTR_SHOW(uniq);

static int input_print_modalias_bits(char *buf, int size,
                 char name, unsigned long *bm,
                 unsigned int min_bit, unsigned int max_bit)
{
    int len = 0, i;

    len += snprintf(buf, max(size, 0), "%c", name);
    for (i = min_bit; i < max_bit; i++)
        if (bm[LONG(i)] & BIT(i))
            len += snprintf(buf + len, max(size - len, 0), "%X,", i);
    return len;
}

static int input_print_modalias(char *buf, int size, struct input_dev *id,
                int add_cr)
{
    int len;

    len = snprintf(buf, max(size, 0),
         "input:b%04Xv%04Xp%04Xe%04X-",
         id->id.bustype, id->id.vendor,
         id->id.product, id->id.version);

    len += input_print_modalias_bits(buf + len, size - len,
                'e', id->evbit, 0, EV_MAX);
    len += input_print_modalias_bits(buf + len, size - len,
                'k', id->keybit, KEY_MIN_INTERESTING, KEY_MAX);
    len += input_print_modalias_bits(buf + len, size - len,
                'r', id->relbit, 0, REL_MAX);
    len += input_print_modalias_bits(buf + len, size - len,
                'a', id->absbit, 0, ABS_MAX);
    len += input_print_modalias_bits(buf + len, size - len,
                'm', id->mscbit, 0, MSC_MAX);
    len += input_print_modalias_bits(buf + len, size - len,
                'l', id->ledbit, 0, LED_MAX);
    len += input_print_modalias_bits(buf + len, size - len,
                's', id->sndbit, 0, SND_MAX);
    len += input_print_modalias_bits(buf + len, size - len,
                'f', id->ffbit, 0, FF_MAX);
    len += input_print_modalias_bits(buf + len, size - len,
                'w', id->swbit, 0, SW_MAX);

    if (add_cr)
        len += snprintf(buf + len, max(size - len, 0), "\n");

    return len;
}

static ssize_t input_dev_show_modalias(struct class_device *dev, char *buf)
{
    struct input_dev *id = to_input_dev(dev);
    ssize_t len;

    len = input_print_modalias(buf, PAGE_SIZE, id, 1);

    return min_t(int, len, PAGE_SIZE);
}
static CLASS_DEVICE_ATTR(modalias, S_IRUGO, input_dev_show_modalias, NULL);

static struct attribute *input_dev_attrs[] = {
    &class_device_attr_name.attr,
    &class_device_attr_phys.attr,
    &class_device_attr_uniq.attr,
    &class_device_attr_modalias.attr,
    NULL
};

static struct attribute_group input_dev_attr_group = {
    .attrs    = input_dev_attrs,
};

#define INPUT_DEV_ID_ATTR(name)                            \
static ssize_t input_dev_show_id_##name(struct class_device *dev, char *buf)    \
{                                        \
    struct input_dev *input_dev = to_input_dev(dev);            \
    return scnprintf(buf, PAGE_SIZE, "%04x\n", input_dev->id.name);        \
}                                        \
static CLASS_DEVICE_ATTR(name, S_IRUGO, input_dev_show_id_##name, NULL);

INPUT_DEV_ID_ATTR(bustype);
INPUT_DEV_ID_ATTR(vendor);
INPUT_DEV_ID_ATTR(product);
INPUT_DEV_ID_ATTR(version);

static struct attribute *input_dev_id_attrs[] = {
    &class_device_attr_bustype.attr,
    &class_device_attr_vendor.attr,
    &class_device_attr_product.attr,
    &class_device_attr_version.attr,
    NULL
};

static struct attribute_group input_dev_id_attr_group = {
    .name    = "id",
    .attrs    = input_dev_id_attrs,
};

static int input_print_bitmap(char *buf, int buf_size, unsigned long *bitmap,
             int max, int add_cr)
{
    int i;
    int len = 0;

    for (i = NBITS(max) - 1; i > 0; i--)
        if (bitmap[i])
            break;

    for (; i >= 0; i--)
        len += snprintf(buf + len, max(buf_size - len, 0),
                "%lx%s", bitmap[i], i > 0 ? " " : "");

    if (add_cr)
        len += snprintf(buf + len, max(buf_size - len, 0), "\n");

    return len;
}

#define INPUT_DEV_CAP_ATTR(ev, bm)                        \
static ssize_t input_dev_show_cap_##bm(struct class_device *dev, char *buf)    \
{                                        \
    struct input_dev *input_dev = to_input_dev(dev);            \
    int len = input_print_bitmap(buf, PAGE_SIZE,                \
                 input_dev->bm##bit, ev##_MAX, 1);        \
    return min_t(int, len, PAGE_SIZE);                    \
}                                        \
static CLASS_DEVICE_ATTR(bm, S_IRUGO, input_dev_show_cap_##bm, NULL);

INPUT_DEV_CAP_ATTR(EV, ev);
INPUT_DEV_CAP_ATTR(KEY, key);
INPUT_DEV_CAP_ATTR(REL, rel);
INPUT_DEV_CAP_ATTR(ABS, abs);
INPUT_DEV_CAP_ATTR(MSC, msc);
INPUT_DEV_CAP_ATTR(LED, led);
INPUT_DEV_CAP_ATTR(SND, snd);
INPUT_DEV_CAP_ATTR(FF, ff);
INPUT_DEV_CAP_ATTR(SW, sw);

static struct attribute *input_dev_caps_attrs[] = {
    &class_device_attr_ev.attr,
    &class_device_attr_key.attr,
    &class_device_attr_rel.attr,
    &class_device_attr_abs.attr,
    &class_device_attr_msc.attr,
    &class_device_attr_led.attr,
    &class_device_attr_snd.attr,
    &class_device_attr_ff.attr,
    &class_device_attr_sw.attr,
    NULL
};

static struct attribute_group input_dev_caps_attr_group = {
    .name    = "capabilities",
    .attrs    = input_dev_caps_attrs,
};

static struct attribute_group *input_dev_attr_groups[] = {
    &input_dev_attr_group,
    &input_dev_id_attr_group,
    &input_dev_caps_attr_group,
    NULL
};

static void input_dev_release(struct class_device *class_dev)
{
    struct input_dev *dev = to_input_dev(class_dev);

    input_ff_destroy(dev);
    kfree(dev);

    module_put(THIS_MODULE);
}

/*
 * Input uevent interface - loading event handlers based on
 * device bitfields.
 */
static int input_add_uevent_bm_var(char **envp, int num_envp, int *cur_index,
                 char *buffer, int buffer_size, int *cur_len,
                 const char *name, unsigned long *bitmap, int max)
{
    if (*cur_index >= num_envp - 1)
        return -ENOMEM;

    envp[*cur_index] = buffer + *cur_len;

    *cur_len += snprintf(buffer + *cur_len, max(buffer_size - *cur_len, 0), name);
    if (*cur_len >= buffer_size)
        return -ENOMEM;

    *cur_len += input_print_bitmap(buffer + *cur_len,
                    max(buffer_size - *cur_len, 0),
                    bitmap, max, 0) + 1;
    if (*cur_len > buffer_size)
        return -ENOMEM;

    (*cur_index)++;
    return 0;
}

static int input_add_uevent_modalias_var(char **envp, int num_envp, int *cur_index,
                     char *buffer, int buffer_size, int *cur_len,
                     struct input_dev *dev)
{
    if (*cur_index >= num_envp - 1)
        return -ENOMEM;

    envp[*cur_index] = buffer + *cur_len;

    *cur_len += snprintf(buffer + *cur_len, max(buffer_size - *cur_len, 0),
             "MODALIAS=");
    if (*cur_len >= buffer_size)
        return -ENOMEM;

    *cur_len += input_print_modalias(buffer + *cur_len,
                     max(buffer_size - *cur_len, 0),
                     dev, 0) + 1;
    if (*cur_len > buffer_size)
        return -ENOMEM;

    (*cur_index)++;
    return 0;
}

#define INPUT_ADD_HOTPLUG_VAR(fmt, val...)                \
    do {                                \
        int err = add_uevent_var(envp, num_envp, &i,        \
                    buffer, buffer_size, &len,    \
                    fmt, val);            \
        if (err)                        \
            return err;                    \
    } while (0)

#define INPUT_ADD_HOTPLUG_BM_VAR(name, bm, max)                \
    do {                                \
        int err = input_add_uevent_bm_var(envp, num_envp, &i,    \
                    buffer, buffer_size, &len,    \
                    name, bm, max);            \
        if (err)                        \
            return err;                    \
    } while (0)

#define INPUT_ADD_HOTPLUG_MODALIAS_VAR(dev)                \
    do {                                \
        int err = input_add_uevent_modalias_var(envp,        \
                    num_envp, &i,            \
                    buffer, buffer_size, &len,    \
                    dev);                \
        if (err)                        \
            return err;                    \
    } while (0)

static int input_dev_uevent(struct class_device *cdev, char **envp,
             int num_envp, char *buffer, int buffer_size)
{
    struct input_dev *dev = to_input_dev(cdev);
    int i = 0;
    int len = 0;

    INPUT_ADD_HOTPLUG_VAR("PRODUCT=%x/%x/%x/%x",
                dev->id.bustype, dev->id.vendor,
                dev->id.product, dev->id.version);
    if (dev->name)
        INPUT_ADD_HOTPLUG_VAR("NAME=\"%s\"", dev->name);
    if (dev->phys)
        INPUT_ADD_HOTPLUG_VAR("PHYS=\"%s\"", dev->phys);
    if (dev->uniq)
        INPUT_ADD_HOTPLUG_VAR("UNIQ=\"%s\"", dev->uniq);

    INPUT_ADD_HOTPLUG_BM_VAR("EV=", dev->evbit, EV_MAX);
    if (test_bit(EV_KEY, dev->evbit))
        INPUT_ADD_HOTPLUG_BM_VAR("KEY=", dev->keybit, KEY_MAX);
    if (test_bit(EV_REL, dev->evbit))
        INPUT_ADD_HOTPLUG_BM_VAR("REL=", dev->relbit, REL_MAX);
    if (test_bit(EV_ABS, dev->evbit))
        INPUT_ADD_HOTPLUG_BM_VAR("ABS=", dev->absbit, ABS_MAX);
    if (test_bit(EV_MSC, dev->evbit))
        INPUT_ADD_HOTPLUG_BM_VAR("MSC=", dev->mscbit, MSC_MAX);
    if (test_bit(EV_LED, dev->evbit))
        INPUT_ADD_HOTPLUG_BM_VAR("LED=", dev->ledbit, LED_MAX);
    if (test_bit(EV_SND, dev->evbit))
        INPUT_ADD_HOTPLUG_BM_VAR("SND=", dev->sndbit, SND_MAX);
    if (test_bit(EV_FF, dev->evbit))
        INPUT_ADD_HOTPLUG_BM_VAR("FF=", dev->ffbit, FF_MAX);
    if (test_bit(EV_SW, dev->evbit))
        INPUT_ADD_HOTPLUG_BM_VAR("SW=", dev->swbit, SW_MAX);

    INPUT_ADD_HOTPLUG_MODALIAS_VAR(dev);

    envp[i] = NULL;
    return 0;
}

struct class input_class = {
    .name            = "input",
    .release        = input_dev_release,
    .uevent            = input_dev_uevent,
};
EXPORT_SYMBOL_GPL(input_class);

/**
 * 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)
{
    struct input_dev *dev;

    dev = kzalloc(sizeof(struct input_dev), GFP_KERNEL);
    if (dev) {
        dev->cdev.class = &input_class;
        dev->cdev.groups = input_dev_attr_groups;
        class_device_initialize(&dev->cdev);
        mutex_init(&dev->mutex);
        INIT_LIST_HEAD(&dev->h_list);
        INIT_LIST_HEAD(&dev->node);

        __module_get(THIS_MODULE);
    }

    return dev;
}
EXPORT_SYMBOL(input_allocate_device);

/**
 * input_free_device - free memory occupied by input_dev structure
 * @dev: input device to free
 *
 * This function should only be used if input_register_device()
 * was not called yet or if it failed. Once device was registered
 * use input_unregister_device() and memory will be freed once last
 * refrence to the device is dropped.
 *
 * Device should be allocated by input_allocate_device().
 *
 * NOTE: If there are references to the input device then memory
 * will not be freed until last reference is dropped.
 */
void input_free_device(struct input_dev *dev)
{
    if (dev)
        input_put_device(dev);
}
EXPORT_SYMBOL(input_free_device);

/**
 * input_set_capability - mark device as capable of a certain event
 * @dev: device that is capable of emitting or accepting event
 * @type: type of the event (EV_KEY, EV_REL, etc...)
 * @code: event code
 *
 * In addition to setting up corresponding bit in appropriate capability
 * bitmap the function also adjusts dev->evbit.
 */
void input_set_capability(struct input_dev *dev, unsigned int type, unsigned int code)
{
    switch (type) {
    case EV_KEY:
        __set_bit(code, dev->keybit);
        break;

    case EV_REL:
        __set_bit(code, dev->relbit);
        break;

    case EV_ABS:
        __set_bit(code, dev->absbit);
        break;

    case EV_MSC:
        __set_bit(code, dev->mscbit);
        break;

    case EV_SW:
        __set_bit(code, dev->swbit);
        break;

    case EV_LED:
        __set_bit(code, dev->ledbit);
        break;

    case EV_SND:
        __set_bit(code, dev->sndbit);
        break;

    case EV_FF:
        __set_bit(code, dev->ffbit);
        break;

    default:
        printk(KERN_ERR
            "input_set_capability: unknown type %u (code %u)\n",
            type, code);
        dump_stack();
        return;
    }

    __set_bit(type, dev->evbit);
}
EXPORT_SYMBOL(input_set_capability);

int input_register_device(struct input_dev *dev)
{
    static atomic_t input_no = ATOMIC_INIT(0);
    struct input_handler *handler;
    const char *path;
    int error;

    set_bit(EV_SYN, dev->evbit);

    /*
     * 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.
     */

    init_timer(&dev->timer);
    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)
        dev->getkeycode = input_default_getkeycode;

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

    list_add_tail(&dev->node, &input_dev_list);

    snprintf(dev->cdev.class_id, sizeof(dev->cdev.class_id),
         "input%ld", (unsigned long) atomic_inc_return(&input_no) - 1);

    if (!dev->cdev.dev)
        dev->cdev.dev = dev->dev.parent;

    error = class_device_add(&dev->cdev);
    if (error)
        return error;

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

    list_for_each_entry(handler, &input_handler_list, node)
        input_attach_handler(dev, handler);

    input_wakeup_procfs_readers();

    return 0;
}
EXPORT_SYMBOL(input_register_device);

void input_unregister_device(struct input_dev *dev)
{
    struct input_handle *handle, *next;
    int code;

    for (code = 0; code <= KEY_MAX; code++)
        if (test_bit(code, dev->key))
            input_report_key(dev, code, 0);
    input_sync(dev);

    del_timer_sync(&dev->timer);

    list_for_each_entry_safe(handle, next, &dev->h_list, d_node)
        handle->handler->disconnect(handle);
    WARN_ON(!list_empty(&dev->h_list));

    list_del_init(&dev->node);

    class_device_unregister(&dev->cdev);

    input_wakeup_procfs_readers();
}
EXPORT_SYMBOL(input_unregister_device);

int input_register_handler(struct input_handler *handler)
{
    struct input_dev *dev;

    INIT_LIST_HEAD(&handler->h_list);

    if (handler->fops != NULL) {
        if (input_table[handler->minor >> 5])
            return -EBUSY;

        input_table[handler->minor >> 5] = handler;
    }

    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();
    return 0;
}
EXPORT_SYMBOL(input_register_handler);

void input_unregister_handler(struct input_handler *handler)
{
    struct input_handle *handle, *next;

    list_for_each_entry_safe(handle, next, &handler->h_list, h_node)
        handler->disconnect(handle);
    WARN_ON(!list_empty(&handler->h_list));

    list_del_init(&handler->node);

    if (handler->fops != NULL)
        input_table[handler->minor >> 5] = NULL;

    input_wakeup_procfs_readers();
}
EXPORT_SYMBOL(input_unregister_handler);

int input_register_handle(struct input_handle *handle)
{
    struct input_handler *handler = handle->handler;

    list_add_tail(&handle->d_node, &handle->dev->h_list);
    list_add_tail(&handle->h_node, &handler->h_list);

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

    return 0;
}
EXPORT_SYMBOL(input_register_handle);

void input_unregister_handle(struct input_handle *handle)
{
    list_del_init(&handle->h_node);
    list_del_init(&handle->d_node);
}
EXPORT_SYMBOL(input_unregister_handle);

static int input_open_file(struct inode *inode, struct file *file)
{   // 根据所打开文件的次设备号，得到一个input_handler
    struct input_handler *handler = input_table[iminor(inode) >> 5]; // 分配一个input_handler结构体
    const struct file_operations *old_fops, *new_fops = NULL;
    int err;

    /* No load-on-demand here? */
    if (!handler || !(new_fops = fops_get(handler->fops))) // new_fops与handler中的fops不一样则返回。
        return -ENODEV;

    /*
     * That's _really_ odd. Usually NULL ->open means "nothing special",
     * not "no device". Oh, well...
     */
    if (!new_fops->open) {       // 如果新的fops中的open没有被打开。
        fops_put(new_fops);      // 就将fpos放入新的fops中。
        return -ENODEV;
    }                            // 否则将新fops写入旧的fops中。
    old_fops = file->f_op;
    file->f_op = new_fops;     // 将新的fops传入旧的fops

    err = new_fops->open(inode, file);   // 返回新的fops

    if (err) {                           // 如果新的fops被打开
        fops_put(file->f_op);
        file->f_op = fops_get(old_fops);
    }
    fops_put(old_fops);
    return err;                           //  返回fops
}

static const struct file_operations input_fops = {
    .owner = THIS_MODULE,
    .open = input_open_file,
};

static int __init input_init(void)
{
    int err;

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

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

    err = register_chrdev(INPUT_MAJOR, "input", &input_fops);
    if (err) {
        printk(KERN_ERR "input: unable to register char major %d", INPUT_MAJOR);
        goto fail2;
    }

    return 0;

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

static void __exit input_exit(void)
{
    input_proc_exit();
    unregister_chrdev(INPUT_MAJOR, "input");
    class_unregister(&input_class);
}

subsys_initcall(input_init);
module_exit(input_exit);

要看一个驱动程序，首先要从入口函数开始看。