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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 X-GL_Whitelist: yes 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) 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+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP 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). - 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 checked + for compatibility. + + Bits 3-63: Reserved (set to 0) 80 - 87: compatible_features Bitmask of compatible features. An implementation can @@ -135,6 +140,7 @@ be stored. Each extension has a structure like the following: 0xE2792ACA - Backing file format name 0x6803f857 - Feature name table 0x23852875 - Bitmaps extension + 0xC03183A3 - Compress format extension other - Unknown header extension, can be safely ignored @@ -208,6 +214,41 @@ The fields of the bitmaps extension are: starts. Must be aligned to a cluster boundary. +== Compress format extension == + +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 absent +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 = default compress level + 1 = lowest compress level + x = 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 extension + to the next multiple of 8. All bytes of the padding must be + zero. + + == Host cluster management == qcow2 manages the allocation of host clusters by maintaining a reference count