From patchwork Wed Feb 27 17:22:39 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kevin Wolf X-Patchwork-Id: 10832101 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id CC48C922 for ; Wed, 27 Feb 2019 17:25:34 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id AC9FD2E8FC for ; Wed, 27 Feb 2019 17:25:34 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id A0BA92E917; Wed, 27 Feb 2019 17:25:34 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 3A6672E8FC for ; Wed, 27 Feb 2019 17:25:34 +0000 (UTC) Received: from localhost ([127.0.0.1]:47932 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gz2xZ-0004im-As for patchwork-qemu-devel@patchwork.kernel.org; Wed, 27 Feb 2019 12:25:33 -0500 Received: from eggs.gnu.org ([209.51.188.92]:51249) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gz2vq-00034K-4V for qemu-devel@nongnu.org; Wed, 27 Feb 2019 12:23:46 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gz2vp-0003Ir-6W for qemu-devel@nongnu.org; Wed, 27 Feb 2019 12:23:46 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45572) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gz2vN-0002wB-T2; Wed, 27 Feb 2019 12:23:23 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 0FB2430BCE63; Wed, 27 Feb 2019 17:23:14 +0000 (UTC) Received: from linux.fritz.box.com (ovpn-117-19.ams2.redhat.com [10.36.117.19]) by smtp.corp.redhat.com (Postfix) with ESMTP id CB05B171A0; Wed, 27 Feb 2019 17:23:12 +0000 (UTC) From: Kevin Wolf To: qemu-block@nongnu.org Date: Wed, 27 Feb 2019 18:22:39 +0100 Message-Id: <20190227172256.30368-4-kwolf@redhat.com> In-Reply-To: <20190227172256.30368-1-kwolf@redhat.com> References: <20190227172256.30368-1-kwolf@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.43]); Wed, 27 Feb 2019 17:23:14 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH 03/20] qcow2: Extend spec for external data files X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, qemu-devel@nongnu.org, mreitz@redhat.com Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP This adds external data file to the qcow2 spec as a new incompatible feature. Signed-off-by: Kevin Wolf --- docs/interop/qcow2.txt | 38 ++++++++++++++++++++++++++++++++++---- 1 file changed, 34 insertions(+), 4 deletions(-) diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt index fb5cb47245..1c1849dc26 100644 --- a/docs/interop/qcow2.txt +++ b/docs/interop/qcow2.txt @@ -97,7 +97,19 @@ in the description of a field. be written to (unless for regaining consistency). - Bits 2-63: Reserved (set to 0) + Bit 2: External data file bit. If this bit is set, an + external data file is used. Guest clusters are + then stored in the external data file. For such + images, clusters in the external data file are + not refcounted. The offset field in the + Standard Cluster Descriptor must match the + guest offset and neither compressed clusters + nor internal snapshots are supported. + + An external data file name header extension may + be present if this bit is set. + + Bits 3-63: Reserved (set to 0) 80 - 87: compatible_features Bitmask of compatible features. An implementation can @@ -126,7 +138,17 @@ in the description of a field. bit is unset, the bitmaps extension data must be considered inconsistent. - Bits 1-63: Reserved (set to 0) + Bit 1: If this bit is set, the external data file can + be read as a consistent standalone raw image + without looking at the qcow2 metadata. + + Setting this bit has a performance impact for + some operations on the image (e.g. writing + zeros requires writing to the data file instead + of only setting the zero flag in the L2 table + entry) and conflicts with backing files. + + Bits 2-63: Reserved (set to 0) 96 - 99: refcount_order Describes the width of a reference count block entry (width @@ -148,6 +170,7 @@ be stored. Each extension has a structure like the following: 0x6803f857 - Feature name table 0x23852875 - Bitmaps extension 0x0537be77 - Full disk encryption header pointer + 0x44415441 - External data file name other - Unknown header extension, can be safely ignored @@ -437,6 +460,11 @@ L2 table entry: This information is only accurate in L2 tables that are reachable from the active L1 table. + With external data files, all guest clusters have an + implicit refcount of 1 (because of the fixed host = guest + mapping for guest cluster offsets), so this bit should be 1 + for all allocated clusters. + Standard Cluster Descriptor: Bit 0: If set to 1, the cluster reads as all zeros. The host @@ -450,8 +478,10 @@ Standard Cluster Descriptor: 1 - 8: Reserved (set to 0) 9 - 55: Bits 9-55 of host cluster offset. Must be aligned to a - cluster boundary. If the offset is 0, the cluster is - unallocated. + cluster boundary. If the offset is 0 and bit 63 is clear, + the cluster is unallocated. The offset may only be 0 with + bit 63 set (indicating a host cluster offset of 0) when an + external data file is used. 56 - 61: Reserved (set to 0)