Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756954AbYH1V1y (ORCPT ); Thu, 28 Aug 2008 17:27:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755060AbYH1V1q (ORCPT ); Thu, 28 Aug 2008 17:27:46 -0400 Received: from terminus.zytor.com ([198.137.202.10]:49685 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753563AbYH1V1q (ORCPT ); Thu, 28 Aug 2008 17:27:46 -0400 Message-ID: <48B7183E.3010100@kernel.org> Date: Thu, 28 Aug 2008 14:27:26 -0700 From: "H. Peter Anvin" Organization: Linux Kernel Organization, Inc. User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Miklos Szeredi CC: tj@kernel.org, fuse-devel@lists.sourceforge.net, greg@kroah.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 5/7] FUSE: implement ioctl support References: <1219945263-21074-1-git-send-email-tj@kernel.org> <1219945263-21074-6-git-send-email-tj@kernel.org> <48B6EC83.1070207@kernel.org> <48B6EE36.5070209@kernel.org> <48B6F7C5.3020204@kernel.org> <48B708C4.4000405@kernel.org> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 979 Lines: 25 Miklos Szeredi wrote: > On Thu, 28 Aug 2008, H. Peter Anvin wrote: >> This is *hard* to get right, and we screw this up in the kernel with >> painful regularity. The throught of having user-space processes, which >> don't have access to the kernel locking primitives and functions like >> copy_from_user() dealing with this stuff scares me crazy. > > What issues exactly are you thinking of? Memory changing underneath you. It can be dealt with by very careful sequencing only. >> That is why I'm suggesting using an in-kernel linearizer. > > Lots of complexity, ugh... Even Tejun's current scheme is better IMO. And then you get *no* privilege separation, for one thing, so why even bother doing it in userspace? -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/