unlocked_ioctl和compat_ioctl

参考：

https://www.cnblogs.com/super119/archive/2012/12/03/2799967.html

https://lwn.net/Articles/119652/

http://b8807053.pixnet.net/blog/post/3610561-ioctl%2cunlocked_ioctl%e5%92%8ccompat_ioctl

Linux内核中struct file_operations含有下面两个函数指针：

struct file_operations {
        ... ...
    long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
    long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
        ... ...
}；

注意：

1、compat_ioctl：支持64bit的driver必须要实现的ioctl，当有32bit的userspace application call 64bit kernel的IOCTL的时候，这个callback会被调用到。如果没有实现compat_ioctl，那么32位的用户程序在64位的kernel上执行ioctl时会返回错误：Not a typewriter

2、如果是64位的用户程序运行在64位的kernel上，调用的是unlocked_ioctl，如果是32位的APP运行在32位的kernel上，调用的也是unlocked_ioctl

示例：

 #ifdef CONFIG_COMPAT
 static long debussy_compat_ioctl (struct file *filp, unsigned int cmd, unsigned long arg)
 {
     return debussy_ioctl(filp, cmd, (unsigned long)compat_ptr(arg));
 }
 #endif

 static const struct file_operations debussy_fops = {
     .owner        = THIS_MODULE,
     .unlocked_ioctl = debussy_ioctl,
 #ifdef CONFIG_COMPAT
     .compat_ioctl = debussy_compat_ioctl,
 #endif
 };

完。