From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38243) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dVxLU-0003fC-Hj for qemu-devel@nongnu.org; Fri, 14 Jul 2017 05:57:13 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dVxLR-0007zv-GS for qemu-devel@nongnu.org; Fri, 14 Jul 2017 05:57:12 -0400 Received: from mx-v6.kamp.de ([2a02:248:0:51::16]:45011 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 1dVxLR-0007yK-73 for qemu-devel@nongnu.org; Fri, 14 Jul 2017 05:57:09 -0400 From: Peter Lieven Date: Fri, 14 Jul 2017 11:56:37 +0200 Message-Id: <1500026205-15542-2-git-send-email-pl@kamp.de> In-Reply-To: <1500026205-15542-1-git-send-email-pl@kamp.de> References: <1500026205-15542-1-git-send-email-pl@kamp.de> Subject: [Qemu-devel] [PATCH V3 1/9] specs/qcow2: add compress format extension List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, kwolf@redhat.com, lersek@redhat.com, den@openvz.org, mreitz@redhat.com, eblake@redhat.com, berrange@redhat.com, Peter Lieven Signed-off-by: Peter Lieven --- docs/interop/qcow2.txt | 35 ++++++++++++++++++++++++++++++++++- 1 file changed, 34 insertions(+), 1 deletion(-) diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt index d7fdb1f..c2d3dab 100644 --- a/docs/interop/qcow2.txt +++ b/docs/interop/qcow2.txt @@ -86,7 +86,12 @@ 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 @@ -137,6 +142,7 @@ be stored. Each extension has a structure like the following: 0x6803f857 - Feature name table 0x23852875 - Bitmaps extension 0x0537be77 - Full disk encryption header pointer + 0xC03183A3 - Compress format extension other - Unknown header extension, can be safely ignored @@ -311,6 +317,33 @@ The algorithms used for encryption vary depending on the method in the LUKS header, with the physical disk sector as the input tweak. + +== 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). + Valid compression format names currently are: + + zlib: Standard zlib deflate compression + + 16: compress_level (uint8_t) + + 0 = default compress level (valid for all formats, default) + + Additional valid compression levels for zlib compression: + + All values between 1 and 9. 1 gives best speed, 9 gives best + compression. + + == Host cluster management == qcow2 manages the allocation of host clusters by maintaining a reference count -- 1.9.1