unlocked_ioctl和compat_ioctl

參考：

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內核中struct file_operations含有下面兩個函數指針：

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必須要實現的ioctl，當有32bit的userspace application call 64bit kernel的IOCTL的時候，這個callback會被調用到。如果沒有實現compat_ioctl，那么32位的用戶程序在64位的kernel上執行ioctl時會返回錯誤：Not a typewriter

2、如果是64位的用戶程序運行在64位的kernel上，調用的是unlocked_ioctl，如果是32位的APP運行在32位的kernel上，調用的也是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。