From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [RFC PATCH 07/20] Introduce qemu_put_vector() and qemu_put_vector_prepare() to use put_vector() in QEMUFile. Date: Fri, 23 Apr 2010 08:23:46 -0500 Message-ID: <4BD19F62.1060001@linux.vnet.ibm.com> References: <1271829445-5328-1-git-send-email-tamura.yoshiaki@lab.ntt.co.jp> <1271829445-5328-8-git-send-email-tamura.yoshiaki@lab.ntt.co.jp> <4BD0A3B0.8040609@linux.vnet.ibm.com> <4BD11BCC.2050908@lab.ntt.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, qemu-devel@nongnu.org, avi@redhat.com, Anthony Liguori , mtosatti@redhat.com, ohmura.kei@lab.ntt.co.jp, yoshikawa.takuya@oss.ntt.co.jp To: Yoshiaki Tamura Return-path: Received: from e36.co.us.ibm.com ([32.97.110.154]:60554 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755260Ab0DWNXv (ORCPT ); Fri, 23 Apr 2010 09:23:51 -0400 Received: from d03relay03.boulder.ibm.com (d03relay03.boulder.ibm.com [9.17.195.228]) by e36.co.us.ibm.com (8.14.3/8.13.1) with ESMTP id o3NDKftu004647 for ; Fri, 23 Apr 2010 07:20:41 -0600 Received: from d03av01.boulder.ibm.com (d03av01.boulder.ibm.com [9.17.195.167]) by d03relay03.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id o3NDNmZa040488 for ; Fri, 23 Apr 2010 07:23:48 -0600 Received: from d03av01.boulder.ibm.com (loopback [127.0.0.1]) by d03av01.boulder.ibm.com (8.14.3/8.13.1/NCO v10.0 AVout) with ESMTP id o3NDNlvT005651 for ; Fri, 23 Apr 2010 07:23:48 -0600 In-Reply-To: <4BD11BCC.2050908@lab.ntt.co.jp> Sender: kvm-owner@vger.kernel.org List-ID: On 04/22/2010 11:02 PM, Yoshiaki Tamura wrote: > Anthony Liguori wrote: >> On 04/21/2010 12:57 AM, Yoshiaki Tamura wrote: >>> For fool proof purpose, qemu_put_vector_parepare should be called >>> before qemu_put_vector. Then, if qemu_put_* functions except this is >>> called after qemu_put_vector_prepare, program will abort(). >>> >>> Signed-off-by: Yoshiaki Tamura >> >> I don't get it. What's this protecting against? > > This was introduced to prevent mixing the order of normal write and > vector write, and flush QEMUFile buffer before handling vectors. > While qemu_put_buffer copies data to QEMUFile buffer, > qemu_put_vector() will bypass that buffer. > > It's just fool proof purpose for what we encountered at beginning, and > if the user of qemu_put_vector() is careful enough, we can remove > qemu_put_vectore_prepare(). While writing this message, I started to > think that just calling qemu_fflush() in qemu_put_vector() would be > enough... I definitely think removing the vector stuff in the first version would simplify the process of getting everything merged. I'd prefer not to have two apis so if vector operations were important from a performance perspective, I'd want to see everything converted to a vector API. Regards, Anthony Liguori