From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57330) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UsVng-0003oc-4L for qemu-devel@nongnu.org; Fri, 28 Jun 2013 06:21:13 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UsVnd-0000wQ-78 for qemu-devel@nongnu.org; Fri, 28 Jun 2013 06:21:08 -0400 Received: from mx.ipv6.kamp.de ([2a02:248:0:51::16]:40975 helo=mx01.kamp.de) by eggs.gnu.org with smtp (Exim 4.71) (envelope-from ) id 1UsVnc-0000wE-TX for qemu-devel@nongnu.org; Fri, 28 Jun 2013 06:21:05 -0400 Message-ID: <51CD638E.20902@kamp.de> Date: Fri, 28 Jun 2013 12:21:02 +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. Do we need to check the return value of bdrv_has_zero_init(bs->backing_hd) in case bs-backing_hd != NULL?