From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266475AbUGKB76 (ORCPT ); Sat, 10 Jul 2004 21:59:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266477AbUGKB76 (ORCPT ); Sat, 10 Jul 2004 21:59:58 -0400 Received: from chaos.analogic.com ([204.178.40.224]:39809 "EHLO chaos.analogic.com") by vger.kernel.org with ESMTP id S266475AbUGKB74 (ORCPT ); Sat, 10 Jul 2004 21:59:56 -0400 Date: Sat, 10 Jul 2004 21:59:47 -0400 (EDT) From: "Richard B. Johnson" X-X-Sender: root@chaos Reply-To: root@chaos.analogic.com To: Qiuyu Zhang cc: linux-kernel@vger.kernel.org Subject: Re: Question about copy_from_user/copy_to_user In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 10 Jul 2004, Qiuyu Zhang wrote: > Hi all, > > I am working on a module driver. A user application alloc a bunch of > memory for storing packet. And module driver can read /write data > from/into the memory in user space. I use ioctl function to pass the > pointer of memory of user space to module driver. What I want to do > is to store the pointer in kernel space and when I need to write or > read data from memory of user space, I try to use copy_from_user or > copy_to_user to get/put data. But I always get wrong data. I don't > know the reason. Would you guys give me some help? > > Simple description of the code: > > device_ioctl() { > // get the pointer of memory of user space, and assign the > pointer to kernel variable. > } > > > > device_xmit(){ > // when upper layer send a packet to this device. > // I try to use the copy_from_user to get some information from > user space buf > // but I cannot get correct information. > } > > Thx > - The kernel executes functions upon behalf of the caller. The caller's pointer is only valid when the caller calls the kernel. At another time, the kernel has its data-segment set to KERNEL_DS and other times set to the virtual address space of other callers. Anything written like you propose is likely to vomit and take your corner of the galaxy with it. Please get a good book about kernel device drivers first before you start. Cheers, Dick Johnson Penguin : Linux version 2.4.26 on an i686 machine (5570.56 BogoMips). Note 96.31% of all statistics are fiction.