linux驱动——input输入子系统（1）—输入子系统核心层（Input Core）

1、

上图是 input输入子系统框架，输入子系统由输入子系统核心层（ Input Core ），驱动层和事件处理层（EventHandler）三部份组成。一个输入事件，如鼠标移动，键盘按键按下，joystick的移动等等通过 input driver -> Input core ->Event handler -> userspace 到达用户空间传给应用程序。

2、先来说下Input Core输入子系统核心层。在Linux中，输入子系统作为一个模块存在，向上，为用户层提供接口函数，向下，为驱动层程序提供统一的接口函数。主要在Input.c (linux2.6.28\drivers\input)文件中：

subsys_initcall(input_init);
module_exit(input_exit);

static int __init input_init(void)
{
int err;

err = class_register(&input_class);//注册一个名为input的类

其中有：

struct class input_class = {
.name = "input",
};
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);注册了主设备号为INPUT_MAJOR的字符设备，操作函数集是：input_fops，如下所示：

static const struct file_operations input_fops = {
.owner = THIS_MODULE,
.open = input_open_file,
};
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)  //做和input_init函数做相反的工作
{
input_proc_exit();
unregister_chrdev(INPUT_MAJOR, "input");
class_unregister(&input_class);
}

2.1、接着看下input_open_file函数，源码如下：

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();
/* No load-on-demand here? */
handler = input_table[iminor(inode) >> 5];

其中iminor(inode)为打开文件所对应的次设备号。input_table是一个struct input_handler全局数组，只有8个元素，其定义为：
static struct input_handler *input_table[8];

首 先将设备结点的次设备号右移5位做为索引值到input_table中取对应项，从这里也可以看到，一个handler代表 32（1<<5）个设备结点，也就是一个handler最多可以处理32个设备结点。因为在input_table中取值是以次备号右移5位 为索引的，即第5位相同的次备号对应的是同一个索引。在input_register_handler()函数中 input_table[handler->minor >> 5] = handler，其将handler赋给了input_table数组，所使用的规则也是右移5位。

其中input_handler结构体如下所示：

/**
 * struct input_handler - implements one of interfaces for input devices
 * @private: driver-specific data
 * @event: event handler. This method is being called by input core with
 * interrupts disabled and dev->event_lock spinlock held and so
 * it may not sleep
 * @connect: called when attaching a handler to an input device
 * @disconnect: disconnects a handler from input device
 * @start: starts handler for given handle. This function is called by
 * input core right after connect() method and also when a process
 * that "grabbed" a device releases it
 * @fops: file operations this driver implements
 * @minor: beginning of range of 32 minors for devices this driver
 * can provide
 * @name: name of the handler, to be shown in /proc/bus/input/handlers
 * @id_table: pointer to a table of input_device_ids this driver can
 * handle
 * @blacklist: pointer to a table of input_device_ids this driver should
 * ignore even if they match @id_table
 * @h_list: list of input handles associated with the handler
 * @node: for placing the driver onto input_handler_list
 *
 * Input handlers attach to input devices and create input handles. There
 * are likely several handlers attached to any given input device at the
 * same time. All of them will get their copy of input event generated by
 * the device.
 *
 * Note that input core serializes calls to connect() and disconnect()
 * methods.
 */
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;
};


if (!handler || !(new_fops = fops_get(handler->fops))) {
 //检查handler是否存在
err = -ENODEV;
goto out;
}


/*
* That's _really_ odd. Usually NULL ->open means "nothing special",
* not "no device". Oh, well...
*/
if (!new_fops->open) {  //判断new_fops->open是否存在
fops_put(new_fops);
err = -ENODEV;
goto out;
}
old_fops = file->f_op;
file->f_op = new_fops;


err = new_fops->open(inode, file);  //使用新的open函数重新打开设备


if (err) {
fops_put(file->f_op);
file->f_op = fops_get(old_fops);
}
fops_put(old_fops);
out:
unlock_kernel();
return err;
}