在linux下，按鍵、觸摸屏、滑鼠等都可以利用input接口函數來實作裝置驅動。
從上圖可知：
輸入子系統由三部分構成：
1 驅動
2 輸入子系統
3 處理函數
其中2,3都是核心已經完成，我們要完成的就是1驅動
裝置用input_dev結構體描述，使用input子系統實作輸入裝置驅動的時候，驅動的核心工作是向系統報告按鍵、觸摸屏、鍵盤、滑鼠等輸入事件（event，通過input_event結構體描述），不再需要關心檔案操作接口，因為input子系統已經完成了檔案操作接口。驅動報告的事件經過InputCore和Eventhandler最終到達使用者空間。
Input_dev 結構中比較重要的域有：
Name:名字
Evbit:裝置所支援的事件類型
Keybit：按鍵類型
注冊輸入裝置的函數為：
int input_register_device(struct input_dev *dev)
登出輸入裝置的函數為：
void input_unregister_device(struct input_dev *dev)
裝置所支援的事件類型有：
EV_RST Reset EV_KEY 按鍵
EV_REL 相對坐标EV_ABS絕對坐标
EV_MSC 其它EV_LED LED
EV_SND 聲音EV_REP Repeat
EV_FF 力回報
并使用set_bit(EV_KEY, button_dev.evbit)告知結構體支援哪種裝置類型
用于報告EV_KEY、EV_REL和EV_ABS事件的函數分别為：
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)
code：
事件的代碼。如果事件的類型是EV_KEY，該代碼code為裝置鍵盤代碼。代碼值0~127為鍵盤上的按鍵代碼，0x110~0x116為滑鼠上按鍵代碼，其中0x110(BTN_LEFT)為滑鼠左鍵，0x111(BTN_RIGHT)為滑鼠右鍵,0x112(BTN_ MIDDLE)為滑鼠中鍵。其它代碼含義請參看include/linux/input.h檔案
value
事件的值。如果事件的類型是EV_KEY,當按鍵按下時值為1,松開時值為0。
input_sync()用于事件同步，它告知事件的接收者：驅動已經發出了一個完整的報告。
在中斷中，使用input_report_key等函數想使用者空間報告，在應用程式中直接讀取狀态。
輸入子系統的裝置檔案名預設為event0 – event31主裝置号預設為13，類似于misc混雜裝置。
下面基于mini2440的input輸入按鍵驅動代碼：
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/poll.h>
#include <linux/irq.h>
#include <asm/irq.h>
#include <linux/interrupt.h>
#include <asm/uaccess.h>
#include <mach/regs-gpio.h>
#include <mach/hardware.h>
#include <linux/platform_device.h>
#include <linux/cdev.h>
#include <linux/miscdevice.h>
#include <linux/input.h>
struct input_dev *button_dev;
struct button_irq_desc {
int irq;
int pin;
int pin_setting;
int number;
char *name;
};
static struct button_irq_desc button_irqs [] = {
{IRQ_EINT8 , S3C2410_GPG0 , S3C2410_GPG0_EINT8 , 0, "KEY0"},
{IRQ_EINT11, S3C2410_GPG3 , S3C2410_GPG3_EINT11 , 1, "KEY1"},
{IRQ_EINT13, S3C2410_GPG5 , S3C2410_GPG5_EINT13 , 2, "KEY2"},
{IRQ_EINT14, S3C2410_GPG6 , S3C2410_GPG6_EINT14 , 3, "KEY3"},
{IRQ_EINT15, S3C2410_GPG7 , S3C2410_GPG7_EINT15 , 4, "KEY4"},
{IRQ_EINT19, S3C2410_GPG11, S3C2410_GPG11_EINT19, 5, "KEY5"},
};
static int key_values = 0;
static irqreturn_t buttons_interrupt(int irq, void *dev_id)
{
struct button_irq_desc *button_irqs = (struct button_irq_desc *)dev_id;
int down;
udelay(0);
down = !s3c2410_gpio_getpin(button_irqs->pin); //down: 1(按下)，0（彈起）
if (!down) {
key_values = button_irqs->number;
//printk("====>rising key_values=%d\n",key_values);
if(key_values==0)
input_report_key(button_dev, KEY_1, 0);
if(key_values==1)
input_report_key(button_dev, KEY_2, 0);
if(key_values==2)
input_report_key(button_dev, KEY_3, 0);
if(key_values==3)
input_report_key(button_dev, KEY_4, 0);
if(key_values==4)
input_report_key(button_dev, KEY_5, 0);
if(key_values==5)
input_report_key(button_dev, KEY_6, 0);
input_sync(button_dev);
}
else {
key_values = button_irqs->number;
//printk("====>falling key_values=%d\n",key_values);
if(key_values==0)
input_report_key(button_dev, KEY_1, 1);
if(key_values==1)
input_report_key(button_dev, KEY_2, 1);
if(key_values==2)
input_report_key(button_dev, KEY_3, 1);
if(key_values==3)
input_report_key(button_dev, KEY_4, 1);
if(key_values==4)
input_report_key(button_dev, KEY_5, 1);
if(key_values==5)
input_report_key(button_dev, KEY_6, 1);
input_sync(button_dev);
}
return IRQ_RETVAL(IRQ_HANDLED);
}
static int s3c24xx_request_irq(void)
{
int i;
int err = 0;
for (i = 0; i < sizeof(button_irqs)/sizeof(button_irqs[0]); i++) {
if (button_irqs[i].irq < 0) {
continue;
}
err = request_irq(button_irqs[i].irq, buttons_interrupt, IRQ_TYPE_EDGE_BOTH,
button_irqs[i].name, (void *)&button_irqs[i]);
if (err)
break;
}
if (err) {
i--;
for (; i >= 0; i--) {
if (button_irqs[i].irq < 0) {
continue;
}
disable_irq(button_irqs[i].irq);
free_irq(button_irqs[i].irq, (void *)&button_irqs[i]);
}
return -EBUSY;
}
return 0;
}
static int __init dev_init(void)
{
s3c24xx_request_irq();
button_dev = input_allocate_device();
if (!button_dev) {
printk(KERN_ERR "Unable to allocate the input device !!\n");
return -ENOMEM;
}
button_dev->name = "s3c2440_button";
button_dev->id.bustype = BUS_RS232;
button_dev->id.vendor = 0xDEAD;
button_dev->id.product = 0xBEEF;
button_dev->id.version = 0x0100;
button_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT(EV_SYN);
//set_bit(EV_KEY, button_dev->evbit)//支援EV_KEY事件
set_bit(KEY_1, button_dev->keybit);
set_bit(KEY_2, button_dev->keybit);
set_bit(KEY_3, button_dev->keybit);
set_bit(KEY_4, button_dev->keybit);
set_bit(KEY_5, button_dev->keybit);
set_bit(KEY_6, button_dev->keybit);
//printk("KEY_RESERVED=%d ,KEY_1=%d",KEY_RESERVED,KEY_1);
input_register_device(button_dev); //注冊input裝置
printk ("initialized\n");
return 0;
}
static void __exit dev_exit(void)
{
int i;
for (i = 0; i < sizeof(button_irqs)/sizeof(button_irqs[0]); i++) {
if (button_irqs[i].irq < 0) {
continue;
}
free_irq(button_irqs[i].irq, (void *)&button_irqs[i]);
}
input_unregister_device(button_dev);
}
module_init(dev_init);
module_exit(dev_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("David Xie");
應用程式：
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/select.h>
#include <sys/time.h>
#include <errno.h>
#include <linux/input.h>
int main(void)
{
int buttons_fd;
int key_value,i=0,count;
struct input_event ev_key;
buttons_fd = open("/dev/event0", O_RDWR);
if (buttons_fd < 0) {
perror("open device buttons");
exit(1);
}
for (;;) {
count = read(buttons_fd,&ev_key,sizeof(struct input_event));
// printf("count=%d\n",count);
for(i=0; i<(int)count/sizeof(struct input_event); i++)
if(EV_KEY==ev_key.type)
printf("type:%d,code:%d,value:%d\n", ev_key.type,ev_key.code-1,ev_key.value);
if(EV_SYN==ev_key.type)
printf("syn event\n\n");
}
close(buttons_fd);
return 0;
}
加載核心子產品：
多了event0裝置檔案
運作應用程式：
、
下面我們分析input子系統源碼：
在分析源代碼之前，我們要先了解幾個主要的結構：
Input_dev是代表一個輸入裝置。
struct input_dev {
const char *name;
const char *phys;
const char *uniq;
struct input_id id;
unsigned long evbit[BITS_TO_LONGS(EV_CNT)];
unsigned long keybit[BITS_TO_LONGS(KEY_CNT)];
unsigned long relbit[BITS_TO_LONGS(REL_CNT)];
unsigned long absbit[BITS_TO_LONGS(ABS_CNT)];
unsigned long mscbit[BITS_TO_LONGS(MSC_CNT)];
unsigned long ledbit[BITS_TO_LONGS(LED_CNT)];
unsigned long sndbit[BITS_TO_LONGS(SND_CNT)];
unsigned long ffbit[BITS_TO_LONGS(FF_CNT)];
unsigned long swbit[BITS_TO_LONGS(SW_CNT)];
unsigned int keycodemax;
unsigned int keycodesize;
void *keycode;
int (*setkeycode)(struct input_dev *dev, int scancode, int keycode);
int (*getkeycode)(struct input_dev *dev, int scancode, int *keycode);
struct ff_device *ff;
unsigned int repeat_key;
struct timer_list timer;
int sync;
int abs[ABS_MAX + 1];
int rep[REP_MAX + 1];
unsigned long key[BITS_TO_LONGS(KEY_CNT)];
unsigned long led[BITS_TO_LONGS(LED_CNT)];
unsigned long snd[BITS_TO_LONGS(SND_CNT)];
unsigned long sw[BITS_TO_LONGS(SW_CNT)];
int absmax[ABS_MAX + 1];
int absmin[ABS_MAX + 1];
int absfuzz[ABS_MAX + 1];
int absflat[ABS_MAX + 1];
int absres[ABS_MAX + 1];
int (*open)(struct input_dev *dev);
void (*close)(struct input_dev *dev);
int (*flush)(struct input_dev *dev, struct file *file);
int (*event)(struct input_dev *dev, unsigned int type, unsigned int code, int value);
struct input_handle *grab;
spinlock_t event_lock;
struct mutex mutex;
unsigned int users;
bool going_away;
struct device dev;
struct list_head h_list;
struct list_head node;
};
input_handler表示一個Input裝置對應的handler
struct input_handler {
void *private;
void (*event)(struct input_handle *handle, unsigned int type, unsigned int code, int value);
int (*connect)(struct input_handler *handler, struct input_dev *dev, const struct input_device_id *id);
void (*disconnect)(struct input_handle *handle);
void (*start)(struct input_handle *handle);
const struct file_operations *fops;
int minor;
const char *name;
const struct input_device_id *id_table;
const struct input_device_id *blacklist;
struct list_head h_list;
struct list_head node;
};
input_handle是用來連接配接input_handler和input_dev的結構
struct input_handle {
void *private;
int open;
const char *name;
struct input_dev *dev;
struct input_handler *handler;
struct list_head d_node;
struct list_head h_node;
};
在核心中，因為Input是作為子系統存在，跟其子系統一樣，首先會執行input.c的input_init,(如rtc子系統在加載具體裝置驅動程式之前會加載rtc_init,iic子系統會加載iic_init)。
其中input_init的标志是subsys_initcall(input_init);“優先級”比module_init更高。
static int __init input_init(void)
{
int err;
input_init_abs_bypass();
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;
}
有上可知 input_init主要功能（1）填充input_abs_bypass數組并注冊input類（2）在proc目錄下建立互動檔案（3）注冊cdev，主裝置号為13
我們在檢視input_fops結構：
static const struct file_operations input_fops = {
.owner = THIS_MODULE,
.open = input_open_file,
};
隻有open函數，為什麼呢，我們檢視input_open_file的源碼：
static int input_open_file(struct inode *inode, struct file *file)
{
struct input_handler *handler;
const struct file_operations *old_fops, *new_fops = NULL;
int err;
lock_kernel();
handler = input_table[iminor(inode) >> 5];
if (!handler || !(new_fops = fops_get(handler->fops))) {
err = -ENODEV;
goto out;
}
if (!new_fops->open) {
fops_put(new_fops);
err = -ENODEV;
goto out;
}
old_fops = file->f_op;
file->f_op = new_fops;
err = new_fops->open(inode, file);
if (err) {
fops_put(file->f_op);
file->f_op = fops_get(old_fops);
}
fops_put(old_fops);
out:
unlock_kernel();
return err;
}
由上可知：open函數最終會調用對應handler的open函數。
子系統初始化之後，下面就是事件的驅動了，在這裡我們支援的是按鍵，對應的驅動是evdev.c
static int __init evdev_init(void)
{
return input_register_handler(&evdev_handler);
}
static struct input_handler evdev_handler = {
.event = evdev_event,
.connect = evdev_connect,
.disconnect = evdev_disconnect,
.fops = &evdev_fops,
.minor = EVDEV_MINOR_BASE,
.name = "evdev",
.id_table = evdev_ids,
};
int input_register_handler(struct input_handler *handler)
{
struct input_dev *dev;
int retval;
retval = mutex_lock_interruptible(&input_mutex);
if (retval)
return retval;
INIT_LIST_HEAD(&handler->h_list);
if (handler->fops != NULL) {
if (input_table[handler->minor >> 5]) {
retval = -EBUSY;
goto out;
}
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();
out:
mutex_unlock(&input_mutex);
return retval;
}
事件層注冊完之後
下面就是具體按鍵驅動的注冊了：
首先：
struct input_dev *input_allocate_device(void)
{
struct input_dev *dev;
dev = kzalloc(sizeof(struct input_dev), GFP_KERNEL);
if (dev) {
dev->dev.type = &input_dev_type;
dev->dev.class = &input_class;
device_initialize(&dev->dev);
mutex_init(&dev->mutex);
spin_lock_init(&dev->event_lock);
INIT_LIST_HEAD(&dev->h_list);
INIT_LIST_HEAD(&dev->node);
__module_get(THIS_MODULE);
}
return dev;
}
input_allocate_device配置設定一個input_dev,并在/sys/device下建立目錄。
下面注冊dev結構
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);
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;
dev_set_name(&dev->dev, "input%ld",
(unsigned long) atomic_inc_return(&input_no) - 1);
error = device_add(&dev->dev);
if (error)
return error;
path = kobject_get_path(&dev->dev.kobj, GFP_KERNEL);
printk(KERN_INFO "input: %s as %s\n",
dev->name ? dev->name : "Unspecified device", path ? path : "N/A");
kfree(path);
error = mutex_lock_interruptible(&input_mutex);
if (error) {
device_del(&dev->dev);
return error;
}
list_add_tail(&dev->node, &input_dev_list);
list_for_each_entry(handler, &input_handler_list, node)
input_attach_handler(dev, handler);
input_wakeup_procfs_readers();
mutex_unlock(&input_mutex);
return 0;
}
input_register_device的主要作用是
（1） 對形參Input_dev結構的一些預設參數做填充，包括支援的事件類型，timer函數，getkeycode函數指針，setkeycode函數指針，并且對dev域的name填充。
（2） device_add 添加裝置到device核心
（3） 将該Input_dev結構加入到input_dev_list連結清單
（4） 周遊整個input_handler_list連結清單，找到一個handler的id_table和input_dev的id一直的handler結構，并将此hanlder和此input_dev結構聯系起來
對(4)要重點分析：
list_for_each_entry(handler, &input_handler_list, node)
input_attach_handler(dev, handler);
list_for_each_entry之前已經講過，就是對input_handler_list整個連結清單進行周遊。
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->dev.kobj), error);
return error;
}
當handler的id_table和dev的id一緻就執行handler的connect函數将dev和handler聯系起來。執行handler的connect函數。那麼在這裡對應的就是evdev_handler的evdev_connect函數。
static int evdev_connect(struct input_handler *handler, struct input_dev *dev,
const struct input_device_id *id)
{
struct evdev *evdev;
int minor;
int error;
for (minor = 0; minor < EVDEV_MINORS; minor++)
if (!evdev_table[minor])
break;
if (minor == EVDEV_MINORS) {
printk(KERN_ERR "evdev: no more free evdev devices\n");
return -ENFILE;
}
evdev = kzalloc(sizeof(struct evdev), GFP_KERNEL);
if (!evdev)
return -ENOMEM;
INIT_LIST_HEAD(&evdev->client_list);
spin_lock_init(&evdev->client_lock);
mutex_init(&evdev->mutex);
init_waitqueue_head(&evdev->wait);
dev_set_name(&evdev->dev, "event%d", minor);
evdev->exist = 1;
evdev->minor = minor;
evdev->handle.dev = input_get_device(dev);
evdev->handle.name = dev_name(&evdev->dev);
evdev->handle.handler = handler;
evdev->handle.private = evdev;
evdev->dev.devt = MKDEV(INPUT_MAJOR, EVDEV_MINOR_BASE + minor);
evdev->dev.class = &input_class;
evdev->dev.parent = &dev->dev;
evdev->dev.release = evdev_free;
device_initialize(&evdev->dev);
error = input_register_handle(&evdev->handle);
if (error)
goto err_free_evdev;
error = evdev_install_chrdev(evdev);
if (error)
goto err_unregister_handle;
error = device_add(&evdev->dev);
if (error)
goto err_cleanup_evdev;
return 0;
err_cleanup_evdev:
evdev_cleanup(evdev);
err_unregister_handle:
input_unregister_handle(&evdev->handle);
err_free_evdev:
put_device(&evdev->dev);
return error;
}
由上：evdev_connect的函數主要功能：（1）配置設定一個evdev，并将它填充到evdev_table中（友善以後調用），（2）調用input_register_handle将hander handle input_dev連接配接起來，其中handle分别和input_dev和handler相連。（3）調用device_add添加裝置。
調用完evdev_connect之後handle handler input_dev之間就通過連結清單關聯起來了。
對于(2)要分析一下：
int input_register_handle(struct input_handle *handle)
{
struct input_handler *handler = handle->handler;
struct input_dev *dev = handle->dev;
int error;
error = mutex_lock_interruptible(&dev->mutex);
if (error)
return error;
list_add_tail_rcu(&handle->d_node, &dev->h_list);
mutex_unlock(&dev->mutex);
list_add_tail(&handle->h_node, &handler->h_list);
if (handler->start)
handler->start(handle);
return 0;
}
通過input_register_handle就将handler handle input_dev3個結構通過連結清單聯系起來了。
當上面這些步驟完成之前，驅動就在核心注冊好了，驅動程式加載完後，在/dev/input目錄下就生成了even0裝置，它的主裝置号是13，次裝置号為64.
當應用程式使用open函數打開/dev/input/even0裝置時，在核心中Input子系統，open對應的驅動時input.c的input_open_file函數：
static int input_open_file(struct inode *inode, struct file *file)
{
struct input_handler *handler;
const struct file_operations *old_fops, *new_fops = NULL;
int err;
lock_kernel();
handler = input_table[iminor(inode) >> 5];
if (!handler || !(new_fops = fops_get(handler->fops))) {
err = -ENODEV;
goto out;
}
if (!new_fops->open) {
fops_put(new_fops);
err = -ENODEV;
goto out;
}
old_fops = file->f_op;
file->f_op = new_fops;
err = new_fops->open(inode, file);
if (err) {
fops_put(file->f_op);
file->f_op = fops_get(old_fops);
}
fops_put(old_fops);
out:
unlock_kernel();
return err;
}
input_open_file主要做了以下事情：（1）通過此裝置号右移5位（因為Input_register_handler中次裝置号左移5位存儲于Input_table中）擷取handler結構，在此處就是evdev_handler。（2）如果evdev_handler的open函數存在就執行evdev_handler的open函數。
上面已經提到：evdev_handler的fops：下面就執行evdev_handler的fops的open了。
static int evdev_open(struct inode *inode, struct file *file)
{
struct evdev *evdev;
struct evdev_client *client;
int i = iminor(inode) - EVDEV_MINOR_BASE;
int error;
if (i >= EVDEV_MINORS)
return -ENODEV;
error = mutex_lock_interruptible(&evdev_table_mutex);
if (error)
return error;
evdev = evdev_table[i];
if (evdev)
get_device(&evdev->dev);
mutex_unlock(&evdev_table_mutex);
if (!evdev)
return -ENODEV;
client = kzalloc(sizeof(struct evdev_client), GFP_KERNEL);
if (!client) {
error = -ENOMEM;
goto err_put_evdev;
}
spin_lock_init(&client->buffer_lock);
client->evdev = evdev;
evdev_attach_client(evdev, client);
error = evdev_open_device(evdev);
if (error)
goto err_free_client;
file->private_data = client;
return 0;
err_free_client:
evdev_detach_client(evdev, client);
kfree(client);
err_put_evdev:
put_device(&evdev->dev);
return error;
}
evdev_open函數主要做了以下事情：（1）通過次裝置号擷取evdev結構（2）配置設定一個endev_client結構并将client->evdev指向擷取的evdev結構（3）調用evdev_attach_client函數将client置于evdev的連結清單頭（4）調用evdev_open_device函數
evdev_open_device函數：
{
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;
}
函數調用input_open_device函數
int input_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) {
synchronize_rcu();
}
}
out:
mutex_unlock(&dev->mutex);
return retval;
}
因為在本按鍵驅動中，沒有設定button_dev的open域，是以這裡input_open_device無意義。
下面就是read函數監聽鍵值了：
Read函數對應的驅動程式是 evdev.c的evdev_read。
static ssize_t evdev_read(struct file *file, char __user *buffer, size_t count, loff_t *ppos)
{
struct evdev_client *client = file->private_data;
struct evdev *evdev = client->evdev;
struct input_event event;
int retval;
if (count < input_event_size())
return -EINVAL;
if (client->head == client->tail && evdev->exist &&
(file->f_flags & O_NONBLOCK))
return -EAGAIN;
retval = wait_event_interruptible(evdev->wait,
client->head != client->tail || !evdev->exist);
if (retval)
return retval;
if (!evdev->exist)
return -ENODEV;
while (retval + input_event_size() <= count &&
evdev_fetch_next_event(client, &event)) {
if (input_event_to_user(buffer + retval, &event))
return -EFAULT;
retval += input_event_size();
}
return retval;
}
這裡有必要提一下evdev_read函數中的client結構：
這裡有必要提一下evdev_read函數中的client結構：
struct evdev_client {
struct input_event buffer[EVDEV_BUFFER_SIZE];
int head;
int tail;
spinlock_t buffer_lock;
struct fasync_struct *fasync;
struct evdev *evdev;
struct list_head node;
};
這個結構中的head tail相當于一個循環隊列，隻有當head不等于tail的時候才表示buffer裡面不為空。那麼當調用evdev_read時運作到retval = wait_event_interruptible(evdev->wait,client->head != client->tail || !evdev->exist);時evdev_read會阻塞。這樣就會等待按鍵。
當按下鍵值，進入中斷函數，調用input_report_key報告event。
static inline void input_report_key(struct input_dev *dev, unsigned int code, int value)
{
input_event(dev, EV_KEY, code, !!value);
}
void input_event(struct input_dev *dev,
unsigned int type, unsigned int code, int value)
{
unsigned long flags;
if (is_event_supported(type, dev->evbit, EV_MAX)) {
spin_lock_irqsave(&dev->event_lock, flags);
add_input_randomness(type, code, value);
input_handle_event(dev, type, code, value);
spin_unlock_irqrestore(&dev->event_lock, flags);
}
}
函數最終調用input_handle_event
input_handle_event函數再根據type類型做相應處理，該驅動去type為EV_KEY，
static void input_handle_event(struct input_dev *dev,
unsigned int type, unsigned int code, int value)
{
int disposition = INPUT_IGNORE_EVENT;
switch (type) {
case EV_SYN:
switch (code) {
case SYN_CONFIG:
disposition = INPUT_PASS_TO_ALL;
break;
case SYN_REPORT:
if (!dev->sync) {
dev->sync = 1;
disposition = INPUT_PASS_TO_HANDLERS;
}
break;
case SYN_MT_REPORT:
dev->sync = 0;
disposition = INPUT_PASS_TO_HANDLERS;
break;
}
break;
case EV_KEY:
if (is_event_supported(code, dev->keybit, KEY_MAX) &&
!!test_bit(code, dev->key) != value) {
if (value != 2) {
__change_bit(code, dev->key);
if (value)
input_start_autorepeat(dev, code);
else
input_stop_autorepeat(dev);
}
disposition = INPUT_PASS_TO_HANDLERS;
}
break;
case EV_SW:
if (is_event_supported(code, dev->swbit, SW_MAX) &&
!!test_bit(code, dev->sw) != value) {
__change_bit(code, dev->sw);
disposition = INPUT_PASS_TO_HANDLERS;
}
break;
case EV_ABS:
if (is_event_supported(code, dev->absbit, ABS_MAX)) {
if (test_bit(code, input_abs_bypass)) {
disposition = INPUT_PASS_TO_HANDLERS;
break;
}
value = input_defuzz_abs_event(value,
dev->abs[code], dev->absfuzz[code]);
if (dev->abs[code] != value) {
dev->abs[code] = value;
disposition = INPUT_PASS_TO_HANDLERS;
}
}
break;
case EV_REL:
if (is_event_supported(code, dev->relbit, REL_MAX) && value)
disposition = INPUT_PASS_TO_HANDLERS;
break;
case EV_MSC:
if (is_event_supported(code, dev->mscbit, MSC_MAX))
disposition = INPUT_PASS_TO_ALL;
break;
case EV_LED:
if (is_event_supported(code, dev->ledbit, LED_MAX) &&
!!test_bit(code, dev->led) != value) {
__change_bit(code, dev->led);
disposition = INPUT_PASS_TO_ALL;
}
break;
case EV_SND:
if (is_event_supported(code, dev->sndbit, SND_MAX)) {
if (!!test_bit(code, dev->snd) != !!value)
__change_bit(code, dev->snd);
disposition = INPUT_PASS_TO_ALL;
}
break;
case EV_REP:
if (code <= REP_MAX && value >= 0 && dev->rep[code] != value) {
dev->rep[code] = value;
disposition = INPUT_PASS_TO_ALL;
}
break;
case EV_FF:
if (value >= 0)
disposition = INPUT_PASS_TO_ALL;
break;
case EV_PWR:
disposition = INPUT_PASS_TO_ALL;
break;
}
if (disposition != INPUT_IGNORE_EVENT && type != EV_SYN)
dev->sync = 0;
if ((disposition & INPUT_PASS_TO_DEVICE) && dev->event)
dev->event(dev, type, code, value);
if (disposition & INPUT_PASS_TO_HANDLERS)
input_pass_event(dev, type, code, value);
}
input_handle_event最終調用：input_pass_event
static void input_pass_event(struct input_dev *dev,
unsigned int type, unsigned int code, int value)
{
struct input_handle *handle;
rcu_read_lock();
handle = rcu_dereference(dev->grab);
if (handle)
handle->handler->event(handle, type, code, value);
else
list_for_each_entry_rcu(handle, &dev->h_list, d_node)
if (handle->open)
handle->handler->event(handle,
type, code, value);
rcu_read_unlock();
}
input_pass_event再調用evdev_event
static void evdev_event(struct input_handle *handle,
unsigned int type, unsigned int code, int value)
{
struct evdev *evdev = handle->private;
struct evdev_client *client;
struct input_event event;
do_gettimeofday(&event.time);
event.type = type;
event.code = code;
event.value = value;
rcu_read_lock();
client = rcu_dereference(evdev->grab);
if (client)
evdev_pass_event(client, &event);
else
list_for_each_entry_rcu(client, &evdev->client_list, node)
evdev_pass_event(client, &event);
rcu_read_unlock();
wake_up_interruptible(&evdev->wait);
}
evdev_event會調用evdev_pass_event函數：
static void evdev_pass_event(struct evdev_client *client,
struct input_event *event)
{
spin_lock(&client->buffer_lock);
client->buffer[client->head++] = *event;
client->head &= EVDEV_BUFFER_SIZE - 1;
spin_unlock(&client->buffer_lock);
kill_fasync(&client->fasync, SIGIO, POLL_IN);
}
從evdev_pass_event函數我們可以得到：将事件結構存在buffe,client的head指針加一，那麼head加一之後，也就是報告鍵值完畢了，回到了evdev_read函數中：此時的head是不等于tail的，是以喚醒等待隊列：
下面就會執行evdev_read的evdev_fetch_next_event函數：
static int evdev_fetch_next_event(struct evdev_client *client,
struct input_event *event)
{
int have_event;
spin_lock_irq(&client->buffer_lock);
have_event = client->head != client->tail;
if (have_event) {
*event = client->buffer[client->tail++];
client->tail &= EVDEV_BUFFER_SIZE - 1;
}
spin_unlock_irq(&client->buffer_lock);
return have_event;
}
evdev_fetch_next_event将client的尾節點加一(這時候head和tail又相等了)。
随後evdev_read調用input_event_to_user
int input_event_to_user(char __user *buffer,
const struct input_event *event)
{
if (copy_to_user(buffer, event, sizeof(struct input_event)))
return -EFAULT;
return 0;
}
這樣就将按鍵事件結構event傳遞到了使用者空間。
總結：由上我們看出，input子系統的确是很複雜的。下面畫一個簡單的流程圖。