From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:54314) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Si5U0-0005Zv-PC for qemu-devel@nongnu.org; Fri, 22 Jun 2012 11:09:17 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Si5Tq-0007tC-M2 for qemu-devel@nongnu.org; Fri, 22 Jun 2012 11:09:12 -0400 Received: from e06smtp16.uk.ibm.com ([195.75.94.112]:48339) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Si5Tq-0007sc-Dl for qemu-devel@nongnu.org; Fri, 22 Jun 2012 11:09:02 -0400 Received: from /spool/local by e06smtp16.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 22 Jun 2012 16:08:58 +0100 Received: from d06av12.portsmouth.uk.ibm.com (d06av12.portsmouth.uk.ibm.com [9.149.37.247]) by d06nrmr1407.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q5MF8sr62445514 for ; Fri, 22 Jun 2012 16:08:54 +0100 Received: from d06av12.portsmouth.uk.ibm.com (loopback [127.0.0.1]) by d06av12.portsmouth.uk.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q5MF8ski013867 for ; Fri, 22 Jun 2012 09:08:54 -0600 From: Stefan Hajnoczi Date: Fri, 22 Jun 2012 16:08:40 +0100 Message-Id: <1340377726-5896-2-git-send-email-stefanha@linux.vnet.ibm.com> In-Reply-To: <1340377726-5896-1-git-send-email-stefanha@linux.vnet.ibm.com> References: <1340377726-5896-1-git-send-email-stefanha@linux.vnet.ibm.com> Subject: [Qemu-devel] [RFC 1/7] docs: add dirty bit to qcow2 specification List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: qemu-devel@nongnu.org, Stefan Hajnoczi The dirty bit will make it possible to perform lazy refcount updates, where the image file is not kept consistent all the time. Upon opening a dirty image file, it is necessary to perform a consistency check and repair any incorrect refcounts. Therefore the dirty bit must be an incompatible feature bit. We don't want old programs accessing a file with stale refcounts. Signed-off-by: Stefan Hajnoczi --- docs/specs/qcow2.txt | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/docs/specs/qcow2.txt b/docs/specs/qcow2.txt index 87bf785..3a789ce 100644 --- a/docs/specs/qcow2.txt +++ b/docs/specs/qcow2.txt @@ -75,7 +75,11 @@ in the description of a field. Bitmask of incompatible features. An implementation must fail to open an image if an unknown bit is set. - Bits 0-63: Reserved (set to 0) + Bit 0: Dirty bit. If this bit is set then refcounts may be + inconsistent, make sure to scan L1/L2 tables to + repair refcounts before accessing the image. + + Bits 1-63: Reserved (set to 0) 80 - 87: compatible_features Bitmask of compatible features. An implementation can -- 1.7.10