From patchwork Mon Aug 6 20:44:43 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kevin Wolf X-Patchwork-Id: 175449 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 38C402C009D for ; Tue, 7 Aug 2012 06:45:27 +1000 (EST) Received: from localhost ([::1]:58871 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SyUB3-0008Um-AT for incoming@patchwork.ozlabs.org; Mon, 06 Aug 2012 16:45:25 -0400 Received: from eggs.gnu.org ([208.118.235.92]:60091) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SyUAh-0008Ir-CX for qemu-devel@nongnu.org; Mon, 06 Aug 2012 16:45:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SyUAf-0004Ox-Nn for qemu-devel@nongnu.org; Mon, 06 Aug 2012 16:45:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:22686) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SyUAf-0004OK-GD for qemu-devel@nongnu.org; Mon, 06 Aug 2012 16:45:01 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q76Kj0kP021671 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Mon, 6 Aug 2012 16:45:00 -0400 Received: from dhcp-5-188.str.redhat.com (vpn1-7-164.ams2.redhat.com [10.36.7.164]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id q76KiqGE002690; Mon, 6 Aug 2012 16:44:59 -0400 From: Kevin Wolf To: anthony@codemonkey.ws Date: Mon, 6 Aug 2012 22:44:43 +0200 Message-Id: <1344285891-6578-5-git-send-email-kwolf@redhat.com> In-Reply-To: <1344285891-6578-1-git-send-email-kwolf@redhat.com> References: <1344285891-6578-1-git-send-email-kwolf@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.22 X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 209.132.183.28 Cc: kwolf@redhat.com, qemu-devel@nongnu.org Subject: [Qemu-devel] [PATCH 04/12] docs: add dirty bit to qcow2 specification X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org From: Stefan Hajnoczi The dirty bit will make it possible to perform lazy refcount updates, where the image file is not kept consistent all the time. Upon opening a dirty image file, it is necessary to perform a consistency check and repair any incorrect refcounts. Therefore the dirty bit must be an incompatible feature bit. We don't want old programs accessing a file with stale refcounts. Signed-off-by: Stefan Hajnoczi Signed-off-by: Kevin Wolf --- docs/specs/qcow2.txt | 7 ++++++- 1 files changed, 6 insertions(+), 1 deletions(-) diff --git a/docs/specs/qcow2.txt b/docs/specs/qcow2.txt index 87bf785..339cdc1 100644 --- a/docs/specs/qcow2.txt +++ b/docs/specs/qcow2.txt @@ -75,7 +75,12 @@ in the description of a field. Bitmask of incompatible features. An implementation must fail to open an image if an unknown bit is set. - Bits 0-63: Reserved (set to 0) + Bit 0: Dirty bit. If this bit is set then refcounts + may be inconsistent, make sure to scan L1/L2 + tables to repair refcounts before accessing the + image. + + Bits 1-63: Reserved (set to 0) 80 - 87: compatible_features Bitmask of compatible features. An implementation can