From nobody Tue Apr 15 11:38:42 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1552051302095742.0248413577996; Fri, 8 Mar 2019 05:21:42 -0800 (PST) Received: from localhost ([127.0.0.1]:42995 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h2FRO-0001Jl-VR for importer@patchew.org; Fri, 08 Mar 2019 08:21:37 -0500 Received: from eggs.gnu.org ([209.51.188.92]:60121) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h2F6A-0000TA-Cg for qemu-devel@nongnu.org; Fri, 08 Mar 2019 07:59:41 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1h2F65-0000oJ-Go for qemu-devel@nongnu.org; Fri, 08 Mar 2019 07:59:36 -0500 Received: from mx1.redhat.com ([209.132.183.28]:46748) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1h2F60-0000Lb-Kj; Fri, 08 Mar 2019 07:59:28 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DD2E2307D874; Fri, 8 Mar 2019 12:59:27 +0000 (UTC) Received: from localhost.localdomain.com (ovpn-117-27.ams2.redhat.com [10.36.117.27]) by smtp.corp.redhat.com (Postfix) with ESMTP id C8E255D704; Fri, 8 Mar 2019 12:59:26 +0000 (UTC) From: Kevin Wolf To: qemu-block@nongnu.org Date: Fri, 8 Mar 2019 13:58:23 +0100 Message-Id: <20190308125823.32535-34-kwolf@redhat.com> In-Reply-To: <20190308125823.32535-1-kwolf@redhat.com> References: <20190308125823.32535-1-kwolf@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Fri, 08 Mar 2019 12:59:27 +0000 (UTC) Content-Transfer-Encoding: quoted-printable 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] [PULL 33/33] qcow2 spec: Describe string header extensions 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, peter.maydell@linaro.org, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Type: text/plain; charset="utf-8" Be more specific about the string representation in header extensions. Suggested-by: Stefan Hajnoczi Signed-off-by: Kevin Wolf Reviewed-by: Eric Blake Reviewed-by: Stefan Hajnoczi --- docs/interop/qcow2.txt | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt index bfb97cfde3..8c3098d8d9 100644 --- a/docs/interop/qcow2.txt +++ b/docs/interop/qcow2.txt @@ -170,11 +170,11 @@ be stored. Each extension has a structure like the fo= llowing: =20 Byte 0 - 3: Header extension type: 0x00000000 - End of the header extension area - 0xE2792ACA - Backing file format name + 0xE2792ACA - Backing file format name string 0x6803f857 - Feature name table 0x23852875 - Bitmaps extension 0x0537be77 - Full disk encryption header pointer - 0x44415441 - External data file name + 0x44415441 - External data file name string other - Unknown header extension, can be safe= ly ignored =20 @@ -196,6 +196,16 @@ data of compatible features that it doesn't support. C= ompatible features that need space for additional data can use a header extension. =20 =20 +=3D=3D String header extensions =3D=3D + +Some header extensions (such as the backing file format name and the exter= nal +data file name) are just a single string. In this case, the header extensi= on +length is the string length and the string is not '\0' terminated. (The he= ader +extension padding can make it look like a string is '\0' terminated, but +neither is padding always necessary nor is there a guarantee that zero byt= es +are used for padding.) + + =3D=3D Feature name table =3D=3D =20 The feature name table is an optional header extension that contains the n= ame --=20 2.20.1