class_create动态创建设备的逻辑类，并完成部分字段的初始化，然后将其添加到内核中。创建的逻辑类位于/sys/class/。
参数：
     owner, 拥有者。一般赋值为THIS_MODULE。
     name, 创建的逻辑类的名称。

alloc_chrdev_region — register a range of char device numbers 

int alloc_chrdev_region ( dev_t * dev,  
  unsigned baseminor,  
  unsigned count,  
  const char * name); 

dev_t * dev
output parameter for first assigned number 
unsigned baseminor
first of the requested range of minor numbers 
unsigned count
the number of minor numbers required 
const char * name
the name of the associated device or driver