Robert Love wrote:
Thanks for your answer! It seems that I got confused. :)Think about what devnetfs is asking. The function is prototyped as copy_to_user(to, from, len) where to and from are pointers. If current->mm is invalid, then exactly whose "from" are you copying to? Remember, Linux is a virtual memory operating system: there can be many mappings at the same address. Likewise, with copy_from_user(), without a valid ->mm from where exactly are you copying from? The functions pull the to/from user addresses from the loaded user address space. Without a user address space, these functions do not work. Nor could they. In short, to answer the original question, kernel threads cannot copy from user-space since they have no user-space. If you want to get data into and out of a kernel thread, expose an interface (procfs, sysfs, syscall, device file, etc.)
So it seems that copy_from_user could only happen within a task? I mean, if the user-process get into the kernel with a syscall, then the syscall could do copy_from_user, then do some stuff with that data in kernel-space. But it's all happening within a task. Is that right?
Thanks for the clarification! :)
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