Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751320AbWJEB5z (ORCPT ); Wed, 4 Oct 2006 21:57:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751322AbWJEB5z (ORCPT ); Wed, 4 Oct 2006 21:57:55 -0400 Received: from smtp.osdl.org ([65.172.181.4]:42464 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S1751320AbWJEB5y (ORCPT ); Wed, 4 Oct 2006 21:57:54 -0400 Date: Wed, 4 Oct 2006 18:57:47 -0700 From: Andrew Morton To: Inaky Perez-Gonzalez Cc: Reinette Chatre , Joe Korty , Paul Jackson , linux-kernel@vger.kernel.org Subject: Re: [PATCH] bitmap: separate bitmap parsing for user buffer and kernel buffer Message-Id: <20061004185747.4cb64048.akpm@osdl.org> In-Reply-To: <200610041833.40866.inaky@linux.intel.com> References: <200610041756.30528.reinette.chatre@linux.intel.com> <20061004181003.6dae6065.akpm@osdl.org> <200610041833.40866.inaky@linux.intel.com> X-Mailer: Sylpheed version 2.2.7 (GTK+ 2.8.17; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1291 Lines: 32 On Wed, 4 Oct 2006 18:33:37 -0700 Inaky Perez-Gonzalez wrote: > On Wednesday 04 October 2006 18:10, Andrew Morton wrote: > > On Wed, 4 Oct 2006 17:56:30 -0700 > > Reinette Chatre wrote: > > > + if (is_user) { > > > + if (__get_user(c, buf++)) > > > + return -EFAULT; > > > + } > > > + else > > > + c = *buf++; > > > > Is this actually needed? __get_user(kernel_address) works OK and (believe > > it or not, given all the stuff it involves) boils down to a single > > instruction. > > We weren't too sure if that'd be true in all kinds of arches and > memory models. If it works for kernel space too, then we can fold > out a lot of code... We use __get_user() in this fashion in several places in core kernel already, although it's usually to find out "will this address give me a fault", rather than to actually read a value. There's some precedent for the `is_user' approach as well - it has the advantage of being more sparse-friendly, and perhaps clearer to read. - 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/