From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35965) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UsTht-0005Sn-Ct for qemu-devel@nongnu.org; Fri, 28 Jun 2013 04:07:02 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UsThs-0001rP-0c for qemu-devel@nongnu.org; Fri, 28 Jun 2013 04:07:01 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49906) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UsThr-0001rJ-PC for qemu-devel@nongnu.org; Fri, 28 Jun 2013 04:06:59 -0400 Date: Fri, 28 Jun 2013 10:06:44 +0200 From: Kevin Wolf Message-ID: <20130628080644.GA3095@dhcp-200-207.str.redhat.com> References: <1372341154-3594-1-git-send-email-pl@kamp.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1372341154-3594-1-git-send-email-pl@kamp.de> Subject: Re: [Qemu-devel] [PATCH] block: change default of .has_zero_init to 0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Lieven Cc: josh.durgin@dreamhost.com, morita.kazutaka@gmail.com, tailai.ly@taobao.com, rjones@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com, bharata@linux.vnet.ibm.com, famz@redhat.com Am 27.06.2013 um 15:52 hat Peter Lieven geschrieben: > .has_zero_init defaults to 1 for all formats and protocols. > > this is a dangerous default since this means that all > new added drivers need to manually overwrite it to 0 if > they do not ensure that a device is zero initialized > after bdrv_create(). > > if a driver needs to explicitly set this value to > 1 its easier to verify the correctness in the review process. > > during review of the existing drivers it turned out > that ssh and gluster had a wrong default of 1. > both protocols support host_devices as backend > which are not by default zero initialized. this > wrong assumption will lead to possible corruption > if qemu-img convert is used to write to such a backend. > > a similar problem with the wrong default existed for > iscsi mose likely because the driver developer did > oversee the default value of 1. > > Signed-off-by: Peter Lieven > --- > block.c | 8 +++++++- > block/qcow.c | 1 + > block/qcow2.c | 1 + > block/qed.c | 1 + > block/raw-posix.c | 10 +--------- > block/raw-win32.c | 7 +------ > block/rbd.c | 1 + > block/sheepdog.c | 1 + > block/vdi.c | 1 + > block/vmdk.c | 1 + > include/block/block.h | 1 + > 11 files changed, 17 insertions(+), 16 deletions(-) You forgot cow, which is also a simple case that can be handled in this patch. vpc is still easy, but a bit more complicated than a constant return 1, because it depends on the subformat whether a new image will inherit the has_zero_init property from the underlying storage or whether it always produces zeros (for VHD_FIXED type images, it's basically raw + footer). I'll send a separate patch for this. A similar situation exists for vmdk, I think, just that the difference can be per extent there. I guess we need to return 0 if one of the extents is flat and has an underlying storage returning 0. I'll leave this part to Fam. For now, please remove the bdrv_has_zero_init_1 for vmdk from this patch as it's unsafe. Kevin