From patchwork Wed Oct 17 16:00:10 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [RFC,V2,01/20] qcow2: Add deduplication to the qcow2 specification. Date: Wed, 17 Oct 2012 06:00:10 -0000 From: =?utf-8?q?Beno=C3=AEt_Canet_=3Cbenoit=40irqsave=2Enet=3E?= X-Patchwork-Id: 192087 Message-Id: <1350489629-1838-2-git-send-email-benoit@irqsave.net> To: qemu-devel@nongnu.org Cc: kwolf@redhat.com, =?UTF-8?q?Beno=C3=AEt=20Canet?= , stefanha@redhat.com --- docs/specs/qcow2.txt | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/docs/specs/qcow2.txt b/docs/specs/qcow2.txt index 36a559d..013a16b 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 +163,16 @@ 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 + + == Host cluster management == qcow2 manages the allocation of host clusters by maintaining a reference count