Linux kernel 笔记 (38)——”__user”修饰符

kernel代码中,有时会看到函数声明中有的参数带有__user修饰符:

ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);

LDD给出的解释:

This annotation is a form of documentation, noting that a pointer is a user-space address that cannot be directly dereferenced. For normal compilation, __user has no effect, but it can be used by external checking software to find misuse of user-space addresses.

__user表明参数是一个用户空间的指针,不能在kernel代码中直接访问。也方便其它工具对代码进行检查。

 

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