From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757928Ab2BXRIp (ORCPT ); Fri, 24 Feb 2012 12:08:45 -0500 Received: from imr3.ericy.com ([198.24.6.13]:38406 "EHLO imr3.ericy.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753570Ab2BXRIo (ORCPT ); Fri, 24 Feb 2012 12:08:44 -0500 Message-ID: <1330103229.23014.130.camel@groeck-laptop> Subject: Re: Can we move device drivers into user-space? From: Guenter Roeck Reply-To: guenter.roeck@ericsson.com To: Greg KH CC: Jidong Xiao , Kernel development list Date: Fri, 24 Feb 2012 09:07:09 -0800 In-Reply-To: <20120224153811.GA16535@kroah.com> References: <20120224153811.GA16535@kroah.com> Organization: Ericsson Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.2- Content-Transfer-Encoding: 7bit MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2012-02-24 at 10:38 -0500, Greg KH wrote: > On Fri, Feb 24, 2012 at 10:19:36AM -0500, Jidong Xiao wrote: > > On Wed, Feb 22, 2012 at 11:56 PM, Jidong Xiao wrote: > > > Hi, > > > > > > I am just curious. Since the concept user-space device drivers has > > > been proposed for several years, and some related projects and > > > research papers have demonstrated the feasibility of of moving device > > > drivers into use space. In particular, this paper: > > > > > > Tolerating Malicious Device Drivers in Linux. > > > http://pdos.csail.mit.edu/papers/sud:usenix10.pdf > > > > > > In this paper, existing device driver code need not to be changed, > > > which should help the idea to be applied in practice. > > > > > > The advantage and disadvantage of move device drivers into use space > > > of both obvious: > > > > > > Advantage: Since most of kernel bugs are caused by device drivers > > > issues, moving device drivers into user space can reduce the impact of > > > device driver bugs. From security perspective, the system can be more > > > secure and robust if most device drivers are working in user space. > > > Disadvantage: At least, existing techniques as well as the above paper > > > showed a relatively high overhead. > > > > > > So is it mainly because the high overhead that prevents the user-space > > > device drivers ideas being accepted in Linux? > > > > > > > Actually, my major concern is, since UIO has been accepted, then why > > don't we move all the rest device drivers into user space as well. As > > I understand, currently, some of device drivers are running on user > > space, while the other (or say the majority of) device drivers are > > running on kernel space, so why don't we maintain a consistent device > > drivers infrastructure, say, either all in user space, or all in > > kernel space. (Sure some critical device drivers still need to be kept > > in kernel space.) > > Feel free to create patches to do so, and handle all of the userspace > changes needed in order to implement this. > > I think you haven't thought through the true reason we have device > drivers, and why Linux isn't a microkernel... > > And I'd take exception to your "advantage:" line above, I don't believe > that is true at all. I second that. Worse, the real disadvantages are ignored. Crappy user-space code, code is kept proprietary, code is no longer submitted upstream, people don't care about implementing interrupts and instead implement polling loops, porting to later kernel versions is a pain. The list goes on and on. This is all more than annoying. I would prefer another approach: Fix the problematic drivers, and spend time researching how to improve forced module unload to a point where modules can be re-loaded after an OOPS. How about dropping UIO support from the kernel ? That would make more sense to me. Guenter