On Fri, 2002-12-27 at 11:23, zw wrote: > > But I thought while doing copy_to_user() the task should have > > a valid task->mm. no? > > You mean the kernel thread, or the user task? I think you don't have > to do anything special on your kernel thread. You kernel thread, I > think, basically waiting there for a pointer from user space. Then > you call copy_to_user() in your kernel thread. That's it. I think. 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.) Robert Love -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
