鎺ュ彛鍑芥暟璇存槑

简单的watchdog驱动,实现了定时重启

watchdog驱动接口函数有2个：
                 1,open 函数
                 2,ioctl函数

open 函数原型：int open(const char *pathname,int flags)

        参数：
              pathname: 设备文件路径
                 flags: 打开文件的方式。
        返回值：
                  成功时，返回文件描述符
                  失败时，返回-1值
        

ioctl函数原型：int ioctl(int fileID,unsigned int cmd,unsigned long arg)

        参数：
             fileID: 文件描述符
                arg: 传变量的地址
                cmd： 为实现接口的不同功能而设定，
                            具体cmd值如下：
 	                *  WDIOC_KEEPALIVE:  Ping the keepalive to keep us alive for another timeout.
                             *
                      *  WDIOC_SETTIMEOUT: Set the timeout for the watchdog. The parameter is generally
                      *                   an integer number of milliseconds, the watchdog times will
                      *                   be set to the first value larger than the given time. It will
                      *                   return EINVAL if the timeout is beyond the capability of the 
                      *                   watchdog timer. For some boards. it is a custom timeout that 
                      *                   is board dependent. Note that this function will automatically
                      *                   does the keepalive for the watchdog.
                            *
                      * WDIOC_GETTIMEOUT: Get the timeout for programmer.
                            *  
                      * WDIOS_DISABLECARD: Turn off the watchdog timer.
                

       返回值：
 
                成功时，返回非负值
                失败是，返回负值