From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45123) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bIFUC-00031i-Q7 for qemu-devel@nongnu.org; Wed, 29 Jun 2016 09:25:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bIFU8-0001hA-ML for qemu-devel@nongnu.org; Wed, 29 Jun 2016 09:25:00 -0400 Received: from mailhub.sw.ru ([195.214.232.25]:1355 helo=relay.sw.ru) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bIFU8-0001h6-A8 for qemu-devel@nongnu.org; Wed, 29 Jun 2016 09:24:56 -0400 References: <1467202967-497386-1-git-send-email-vsementsov@virtuozzo.com> From: Vladimir Sementsov-Ogievskiy Message-ID: <5773CC1F.7020802@virtuozzo.com> Date: Wed, 29 Jun 2016 16:24:47 +0300 MIME-Version: 1.0 In-Reply-To: <1467202967-497386-1-git-send-email-vsementsov@virtuozzo.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] spec/qcow2: bitmaps: zero bitmap table offset List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, den@openvz.org, kwolf@redhat.com, eblake@redhat.com, jsnow@redhat.com, stefanha@redhat.com, famz@redhat.com, mreitz@redhat.com On 29.06.2016 15:22, Vladimir Sementsov-Ogievskiy wrote: > This allows effectively free in_use bitmap clusters including bitmap > table without loss of meaningful data. > > Now it is possible only to free end-point clusters and zero-out (not > free) bitmap table > > Signed-off-by: Vladimir Sementsov-Ogievskiy > --- > > Hi all! > > Here is one small but significant addition to specification of bitmaps in qcow2. > > Can we apply it just like this or I'll have to inroduce new incompatible feature flag? > > If there is existing implementation of the format, it may break image, saved by > software, using extended spec. But is there are any implementations except not > finished my one? > > > docs/specs/qcow2.txt | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/docs/specs/qcow2.txt b/docs/specs/qcow2.txt > index 80cdfd0..dd07a82 100644 > --- a/docs/specs/qcow2.txt > +++ b/docs/specs/qcow2.txt > @@ -435,6 +435,8 @@ Structure of a bitmap directory entry: > Offset into the image file at which the bitmap table > (described below) for the bitmap starts. Must be aligned to > a cluster boundary. > + Zero value means that bitmap table is not allocated and the > + bitmap should be considered as empty (all bits are zero). > > 8 - 11: bitmap_table_size > Number of entries in the bitmap table of the bitmap. + bitmap_table_size must be zero if bitmap_table_size is zero. -- Best regards, Vladimir