From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37534) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UsTrZ-0008Gb-Rf for qemu-devel@nongnu.org; Fri, 28 Jun 2013 04:17:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UsTrW-00053R-Uu for qemu-devel@nongnu.org; Fri, 28 Jun 2013 04:17:01 -0400 Received: from mx.ipv6.kamp.de ([2a02:248:0:51::16]:55795 helo=mx01.kamp.de) by eggs.gnu.org with smtp (Exim 4.71) (envelope-from ) id 1UsTrW-00053G-LG for qemu-devel@nongnu.org; Fri, 28 Jun 2013 04:16:58 -0400 Message-ID: <51CD4677.4070406@kamp.de> Date: Fri, 28 Jun 2013 10:16:55 +0200 From: Peter Lieven MIME-Version: 1.0 References: <1372341154-3594-1-git-send-email-pl@kamp.de> <20130628080644.GA3095@dhcp-200-207.str.redhat.com> In-Reply-To: <20130628080644.GA3095@dhcp-200-207.str.redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit 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: Kevin Wolf 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 On 28.06.2013 10:06, Kevin Wolf wrote: > 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. ups. > > 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. shall I leave this to the new 0 default until your patch is ready? > > 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. ok I will mention that the value is changed for vmdk (and vpc) in the commit message. thanks peter