From nobody Mon Feb 9 01:20:20 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zoho.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1498734126389425.5989056664206; Thu, 29 Jun 2017 04:02:06 -0700 (PDT) Received: from localhost ([::1]:38330 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dQXD0-0002be-VE for importer@patchew.org; Thu, 29 Jun 2017 07:02:03 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51640) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dQX8d-00071m-Kg for qemu-devel@nongnu.org; Thu, 29 Jun 2017 06:57:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dQX8W-0007vR-Hq for qemu-devel@nongnu.org; Thu, 29 Jun 2017 06:57:28 -0400 Received: from mx-v6.kamp.de ([2a02:248:0:51::16]:42868 helo=mx01.kamp.de) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dQX8W-0007r3-8N for qemu-devel@nongnu.org; Thu, 29 Jun 2017 06:57:24 -0400 Received: (qmail 8776 invoked by uid 89); 29 Jun 2017 10:57:19 -0000 Received: from [195.62.97.28] by client-16-kamp (envelope-from , uid 89) with qmail-scanner-2010/03/19-MF (clamdscan: 0.99.2/23517. avast: 1.2.2/17010300. spamassassin: 3.4.1. 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Processed in 0.296473 secs); 29 Jun 2017 10:57:19 -0000 Received: from smtp.kamp.de (HELO submission.kamp.de) ([195.62.97.28]) by mx01.kamp.de with ESMTPS (DHE-RSA-AES256-GCM-SHA384 encrypted); 29 Jun 2017 10:57:16 -0000 Received: (qmail 12757 invoked from network); 29 Jun 2017 10:57:15 -0000 Received: from lieven-pc.kamp-intra.net (HELO lieven-pc) (relay@kamp.de@::ffff:172.21.12.60) by submission.kamp.de with ESMTPS (DHE-RSA-AES256-GCM-SHA384 encrypted) ESMTPA; 29 Jun 2017 10:57:15 -0000 Received: by lieven-pc (Postfix, from userid 1000) id 9EC69208AB; Thu, 29 Jun 2017 12:57:15 +0200 (CEST) X-GL_Whitelist: yes From: Peter Lieven To: qemu-block@nongnu.org Date: Thu, 29 Jun 2017 12:57:04 +0200 Message-Id: <1498733831-15254-2-git-send-email-pl@kamp.de> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1498733831-15254-1-git-send-email-pl@kamp.de> References: <1498733831-15254-1-git-send-email-pl@kamp.de> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 2a02:248:0:51::16 Subject: [Qemu-devel] [PATCH V2 1/8] docs: add compress format extension to qcow2 spec 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 Lieven , qemu-devel@nongnu.org, mreitz@redhat.com, den@openvz.org, lersek@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Signed-off-by: Peter Lieven --- docs/interop/qcow2.txt | 43 ++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 42 insertions(+), 1 deletion(-) diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt index 80cdfd0..c01daf3 100644 --- a/docs/interop/qcow2.txt +++ b/docs/interop/qcow2.txt @@ -85,7 +85,12 @@ in the description of a field. be written to (unless for regaining consistency). =20 - Bits 2-63: Reserved (set to 0) + Bit 2: Compress format bit. If and only if this = bit + is set then the compress format extension + MUST be present and MUST be parsed and che= cked + for compatibility. + + Bits 3-63: Reserved (set to 0) =20 80 - 87: compatible_features Bitmask of compatible features. An implementation can @@ -135,6 +140,7 @@ be stored. Each extension has a structure like the foll= owing: 0xE2792ACA - Backing file format name 0x6803f857 - Feature name table 0x23852875 - Bitmaps extension + 0xC03183A3 - Compress format extension other - Unknown header extension, can be safe= ly ignored =20 @@ -208,6 +214,41 @@ The fields of the bitmaps extension are: starts. Must be aligned to a cluster boundary. =20 =20 +=3D=3D Compress format extension =3D=3D + +The compress format extension is an optional header extension. It provides +the ability to specify the compress algorithm and compress parameters +that are used for compressed clusters. This new header MUST be present if +the incompatible-feature bit "compress format bit" is set and MUST be abse= nt +otherwise. + +The fields of the compress format extension are: + + Byte 0 - 15: compress_format_name (padded with zeros, but not + necessarily null terminated if it has full length) + + 16: compress_level (uint8_t) + 0 =3D default compress level + 1 =3D lowest compress level + x =3D highest compress level (the highest compress + level may vary for different compress formats) + + 17 - 19: Reserved for future use, must be zero. + + 20 - 23: extra_data_size + Size of compress format specific extra data. + For now, as no format specifies extra data, + extra_data_size is reserved and should be zero. + + variable: extra_data + Extra data with additional parameters for the compress + format, occupying extra_data_size bytes. + + variable: Padding to round up the size of compress format extensi= on + to the next multiple of 8. All bytes of the padding mus= t be + zero. + + =3D=3D Host cluster management =3D=3D =20 qcow2 manages the allocation of host clusters by maintaining a reference c= ount --=20 1.9.1