From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:49003) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TcyNT-0002HF-1e for qemu-devel@nongnu.org; Mon, 26 Nov 2012 08:05:40 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TcyNN-00050v-0t for qemu-devel@nongnu.org; Mon, 26 Nov 2012 08:05:34 -0500 Received: from nodalink.pck.nerim.net ([62.212.105.220]:44781 helo=paradis.irqsave.net) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TcyNM-00050n-Os for qemu-devel@nongnu.org; Mon, 26 Nov 2012 08:05:28 -0500 From: =?UTF-8?q?Beno=C3=AEt=20Canet?= Date: Mon, 26 Nov 2012 14:05:00 +0100 Message-Id: <1353935123-24199-2-git-send-email-benoit@irqsave.net> In-Reply-To: <1353935123-24199-1-git-send-email-benoit@irqsave.net> References: <1353935123-24199-1-git-send-email-benoit@irqsave.net> Subject: [Qemu-devel] [RFC V3 01/24] qcow2: Add deduplication to the qcow2 specification. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: kwolf@redhat.com, =?UTF-8?q?Beno=C3=AEt=20Canet?= , stefanha@redhat.com Signed-off-by: Benoit Canet --- docs/specs/qcow2.txt | 33 ++++++++++++++++++++++++++++++++- 1 file changed, 32 insertions(+), 1 deletion(-) diff --git a/docs/specs/qcow2.txt b/docs/specs/qcow2.txt index 36a559d..16eafd7 100644 --- a/docs/specs/qcow2.txt +++ b/docs/specs/qcow2.txt @@ -80,7 +80,10 @@ in the description of a field. tables to repair refcounts before accessing the image. - Bits 1-63: Reserved (set to 0) + Bit 1: Deduplication bit. If this bit is set then + deduplication is used on this image. + + Bits 2-63: Reserved (set to 0) 80 - 87: compatible_features Bitmask of compatible features. An implementation can @@ -116,6 +119,7 @@ be stored. Each extension has a structure like the following: 0x00000000 - End of the header extension area 0xE2792ACA - Backing file format name 0x6803f857 - Feature name table + 0xCD8E819B - Deduplication other - Unknown header extension, can be safely ignored @@ -159,6 +163,33 @@ the header extension data. Each entry look like this: terminated if it has full length) +== Deduplication == + +The deduplication extension contains the offset and size of the deduplication +table. + + Byte 0 - 7: Offset + + 8 - 11: Size + +== Deduplication table == + +The deduplication table contains 64 bits offsets to the level 2 deduplication +table clusters. +Each entry of these clusters contains a 32 bytes SHA256 hash followed by the +64 bits logical offset of the first encountered block having this hash. + +Entries in the deduplication table are orderered by physical cluster index. + +The number of entries in an l2 deduplication table cluster is : +l2_dedup_cluster_entries = cluster_size / (32 + 8) + +The index in the level 1 deduplication table is : +l1_dedup_index = physical_cluster_index / l2_dedup_cluster_entries + +The index in the level 2 deduplication table is: +l2_dedup_index = physical_cluster_index % l2_dedup_cluster_entries + == Host cluster management == qcow2 manages the allocation of host clusters by maintaining a reference count -- 1.7.10.4