Linux输入子系统(2):input.c实现细节

注:内核版本为 kernel-2.6.30.4

一、input子系统初始化
整个input子系统是作为一个字符设备驱动,它们的主设备号是13，不同的设备次设备号不同,input驱动注册的时候提供的fops

里面只包括一个open函数.

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

static int __init input_init(void)
{
int err;
input_init_abs_bypass();
err = class_register(&input_class);//新建类
if (err) {
printk(KERN_ERR "input: unable to register input_dev class\n");
return err;
}
err = input_proc_init();//新建/proc入口
if (err)
goto fail1;
err = register_chrdev(INPUT_MAJOR, "input", &input_fops);//注册输入子系统,主设备号为13
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 int input_open_file(struct inode *inode, struct file *file)
{
struct input_handler *handler;
/*static struct input_handler *input_table[8];input子系统最多维护8个事件处理方法
*每个事件处理方法可以处理32个次设备号
*调用input_register_handler的时候将input_handler按次设备号放在该数组中
*/
handler = input_table[iminor(inode)>>5];//根据次设备号，获取该设备input_handler
if (!handler || !(new_fops = fops_get(handler->fops))) { //提取handler里面的file_operations
err = -ENODEV;
goto out; }
file->f_op = new_fops; //将设备的fops赋值给它的文件描述符的f_op
err = new_fops->open(inode, file); //调用handler->fops->open实现文件的打开
}

二、设备驱动层设备链表建立过程

1.分配struct input_dev结构体

struct input_dev *input_allocate_device(void)
{
struct input_dev *dev;dev = kzalloc(sizeof(struct input_dev), GFP_KERNEL);//分配一个struct input_dev结构体
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);//初始该设备的input_handle链表头
INIT_LIST_HEAD(&dev->node);
__module_get(THIS_MODULE);
return dev;
}

2.设置struct input_dev结构体

/* 能产生哪类事件 */
set_bit(EV_KEY, buttons_dev->evbit);//能产生按键类型事件
set_bit(EV_REP, buttons_dev->evbit);//能产生重复类型事件

/* 能产生该类操作里的哪些事件: L,S,ENTER,LEFTSHIT */
set_bit(KEY_L, buttons_dev->keybit);//能产生按键类型下的L键事件
set_bit(KEY_S, buttons_dev->keybit);//能产生按键类型下的S键事件
set_bit(KEY_ENTER, buttons_dev->keybit);//能产生按键类型下的ENTER键事件
set_bit(KEY_LEFTSHIFT, buttons_dev->keybit);//能产生按键类型下的SHIFT键事件

3.注册struct input_dev结构体

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);//设置支持同步事件,每次事件上报结束就发送这个事件
/*
* 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;
dev_set_name(&dev->dev, "input%ld",(unsigned long) atomic_inc_return(&input_no) - 1);
error = device_add(&dev->dev);//将设备注册到设备模型中去,这样在/sys目录下将新建一个以目录
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);//将input_dev加入到input子系统维护的全局input_dev链表中去
list_for_each_entry(handler, &input_handler_list, node)//取出input子系统维护的全局input_handler链表的元素
input_attach_handler(dev, handler);//找出能处理新注册的input_dev的设备方法input_handler
input_wakeup_procfs_readers();
mutex_unlock(&input_mutex);
return 0;
}

4.input_dev和input_handler匹配过程

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))//input_dev在input_handler的黑名单中,就直接返回
return -ENODEV;
id = input_match_device(handler->id_table, dev);//比较input_handler的id_table是否支持input_dev
if (!id)
return -ENODEV;
error = handler->connect(handler, dev, id);//如果input_hander能支持该设备就调用它的connect函数
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;
}

5.匹配成功




input_dev和input_handler匹配成功后将调用handler的connect函数,现在以内核中evdev提供的evdev_handler的connect为例

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);

snprintf(evdev->name, sizeof(evdev->name), "event%d", minor);
evdev->exist = 1;
evdev->minor = minor;

evdev->handle.dev = input_get_device(dev);
evdev->handle.name = evdev->name;
evdev->handle.handler = handler;
evdev->handle.private = evdev;

dev_set_name(&evdev->dev, evdev->name);
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);//新建一个input_handle,用于联系匹配的input_dev和input_handler
if (error)
goto err_free_evdev;
error = evdev_install_chrdev(evdev);
if (error)
goto err_unregister_handle;
error = device_add(&evdev->dev);//将该evdev加入到设备模型中去
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;
}

input_register_handle用于将handle挂靠在dev和handler的h_list链表上

int input_register_handle(struct input_handle *handle)
{
struct input_handler *handler = handle->handler;//获得input_handle关联的input_handler
struct input_dev *dev = handle->dev;//获得input_handle关联的input_dev
int error;

error = mutex_lock_interruptible(&dev->mutex);
if (error)
return error;
list_add_tail_rcu(&handle->d_node, &dev->h_list);//将input_handle挂在input_dev的h_list链表上
mutex_unlock(&dev->mutex);
list_add_tail(&handle->h_node, &handler->h_list);//将input_handle挂在input_handler的h_list链表上

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

return 0;
}

二、事件处理层的设备处理方法链表建立过程

内核自带很多的设备处理方法，当有新的设备,evdev.c里面注册的evdev_handler就可以处理任何的input_dev设备。

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);//初始化input_handler的input_handle链表

if (handler->fops != NULL) {
if (input_table[handler->minor >> 5]) {
retval = -EBUSY;
goto out;
}
input_table[handler->minor >> 5] = handler;//根据次设备号找到新handler存放位置
}

list_add_tail(&handler->node, &input_handler_list);//将该新建的handler加入到input子系统维护的全局handler链表中
list_for_each_entry(dev, &input_dev_list, node)//遍历input子系统维护的全局dev链表
input_attach_handler(dev, handler);//找到和它匹配的input_dev
input_wakeup_procfs_readers();
out:
mutex_unlock(&input_mutex);
return retval;
}

三、应用程序访问input设备节点

1.打开设备节点

当应用程序调用open("/dev/eventxx",O_RDWR)，会调用驱动层的input_open_file.该函数会根据设备的次设备号在 struct input_handler *input_table[8]找到它对应的input_handler,然后取出里面的fops赋值给文件描述符使用。

2.读写设备节点(evdev.c为例)

当应用程序调用read后将调用到input_handler的read函数,如果设备现在没有数据可读,那个调用read的进程将休眠等待

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;
/*缓冲队列为空&&*evdev存在&&文件为非阻塞/
if (client->head == client->tail && evdev->exist &&(file->f_flags & O_NONBLOCK))
return -EAGAIN;
/*将进程休眠等待在evdev->wait上,至到缓冲区有数据或者evdev不存在*/
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;
}
3.硬件设备有动作,唤醒读等待进程

当设备驱动层有数据的时候，就会调用input_event，这将导致input_handler的event函数被调用。(evdev.c为例)

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();
//唤醒因读这个evdev设备而休眠的设备
wake_up_interruptible(&evdev->wait);
}

参考文章:
http://www.cnblogs.com/myblesh/articles/2367648.html