I see this kind of type in the execve syscall:
asmlinkage long sys_execve(const char __user *filename,
const char __user *const __user *argv,
const char __user *const __user *envp);
do_execve(struct filename *filename,
const char __user *const __user *__argv,
const char __user *const __user *__envp)
What is the meaning of
const char __user *const __user *
?
As you read through the list of file_operations methods, you will note that a number of parameters include the string __user. 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.