From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39164) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UsU00-0004U3-TS for qemu-devel@nongnu.org; Fri, 28 Jun 2013 04:25:47 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UsTzy-0007tN-Hb for qemu-devel@nongnu.org; Fri, 28 Jun 2013 04:25:44 -0400 Received: from mx.ipv6.kamp.de ([2a02:248:0:51::16]:60154 helo=mx01.kamp.de) by eggs.gnu.org with smtp (Exim 4.71) (envelope-from ) id 1UsTzy-0007tE-7i for qemu-devel@nongnu.org; Fri, 28 Jun 2013 04:25:42 -0400 Message-ID: <51CD4879.1010800@kamp.de> Date: Fri, 28 Jun 2013 10:25:29 +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> <51CD4677.4070406@kamp.de> <20130628082047.GC3095@dhcp-200-207.str.redhat.com> In-Reply-To: <20130628082047.GC3095@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 10:20, Kevin Wolf wrote: > Am 28.06.2013 um 10:16 hat Peter Lieven geschrieben: >> 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? > Yes, please leave vpc alone. I guess my patch will be queued before > yours anyway. ;-) once v2 is ready and noone has objections maybe you can put it in your queue? ;-) Peter