From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:49406) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SufYQ-0005es-MJ for qemu-devel@nongnu.org; Fri, 27 Jul 2012 04:05:53 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SufYI-00065b-B1 for qemu-devel@nongnu.org; Fri, 27 Jul 2012 04:05:46 -0400 Received: from e06smtp11.uk.ibm.com ([195.75.94.107]:34566) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SufYI-000659-2F for qemu-devel@nongnu.org; Fri, 27 Jul 2012 04:05:38 -0400 Received: from /spool/local by e06smtp11.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 27 Jul 2012 09:05:37 +0100 Received: from d06av04.portsmouth.uk.ibm.com (d06av04.portsmouth.uk.ibm.com [9.149.37.216]) by d06nrmr1407.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q6R85WK5934072 for ; Fri, 27 Jul 2012 09:05:32 +0100 Received: from d06av04.portsmouth.uk.ibm.com (loopback [127.0.0.1]) by d06av04.portsmouth.uk.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q6R85VO1016741 for ; Fri, 27 Jul 2012 02:05:31 -0600 From: Stefan Hajnoczi Date: Fri, 27 Jul 2012 09:05:18 +0100 Message-Id: <1343376324-19458-2-git-send-email-stefanha@linux.vnet.ibm.com> In-Reply-To: <1343376324-19458-1-git-send-email-stefanha@linux.vnet.ibm.com> References: <1343376324-19458-1-git-send-email-stefanha@linux.vnet.ibm.com> Subject: [Qemu-devel] [PATCH v3 1/7] docs: add dirty bit to qcow2 specification List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Kevin Wolf , Khoa Huynh , Anthony Liguori , 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 | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/docs/specs/qcow2.txt b/docs/specs/qcow2.txt index 87bf785..339cdc1 100644 --- a/docs/specs/qcow2.txt +++ b/docs/specs/qcow2.txt @@ -75,7 +75,12 @@ 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 -- 1.7.10.4