----Original Message---- From: kernelnewbies-bounce@xxxxxxxxxxxx [mailto:kernelnewbies-bounce@xxxxxxxxxxxx]On Behalf Of Mulyadi Santosa Sent: Wednesday, November 21, 2007 9:49 AM To: Sikandar Khan Cc: kernelnewbies Subject: Re: Question regarding User Space and the Kernel > Hi... >> 1) Can the kernel access User Address Space. Yes >> If yes thats wat i found from >> net ( but it is poorly written driver if it allows the same) >> then why cant the kernel directly copy data from the user . Why do >> we need copy_to_user and copy_from_user. >> Is it because some protection mechanisms. >> > we need to make sure the user space address is valid. It means: > 1. It is within valid user space address range (in 3:1 VM split, it's > 0-3 GB) > 2. It is within valid segment range (mentioned in related segment > descriptor) 3. It is not swapped out to disk. Thanks, Rajat ��.n��������+%����w�j)p���{.n����z�ޖw�n'���q���b�������v��m�����Y�����
