From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:55498) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UDWco-00056q-Ic for qemu-devel@nongnu.org; Thu, 07 Mar 2013 03:56:32 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UDWcm-0007Ve-4f for qemu-devel@nongnu.org; Thu, 07 Mar 2013 03:56:30 -0500 Received: from ssl.dlhnet.de ([91.198.192.8]:36088 helo=ssl.dlh.net) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UDWcl-0007Ui-U4 for qemu-devel@nongnu.org; Thu, 07 Mar 2013 03:56:28 -0500 Message-ID: <5138563A.4040005@dlhnet.de> Date: Thu, 07 Mar 2013 09:56:26 +0100 From: Peter Lieven MIME-Version: 1.0 References: <51378200.5010705@dlhnet.de> <513785A0.1010001@redhat.com> <20130306181454.GB3743@localhost.localdomain> <51378B97.2000709@redhat.com> <20130306184800.GB22782@localhost.localdomain> <51379304.50307@dlhnet.de> <5137A964.5020803@redhat.com> <20130307085038.GB2536@dhcp-200-207.str.redhat.com> In-Reply-To: <20130307085038.GB2536@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 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: Paolo Bonzini , Jeff Cody , qemu-devel@nongnu.org, stefanha@redhat.com, sw@weilnetz.de On 07.03.2013 09:50, Kevin Wolf wrote: > Am 06.03.2013 um 21:39 hat Paolo Bonzini geschrieben: >> Il 06/03/2013 20:03, Peter Lieven ha scritto: >>> Am 06.03.2013 19:48, schrieb Jeff Cody: >>>> On Wed, Mar 06, 2013 at 07:31:51PM +0100, Paolo Bonzini wrote: >>>>> Il 06/03/2013 19:14, Jeff Cody ha scritto: >>>>>> QCOW breaks with it using a normal raw posix file as a device. As a >>>>>> test: qemu-img create -f qcow test.qcow 5G. Now run qemu with that >>>>>> drive mounted, and try to partition and format it. QEMU now asserts. >>>>>> >>>>>> The nicety of being able to using truncate during a write call, >>>>>> especially for VHDX (which can have relatively large block/cluster >>>>>> sizes), so to grow the file sparsely in a dynamically allocated file. >>>>> >>>>> Perhaps we need two APIs, "truncate" and "revalidate". >>>>> >>>>> Truncate should be a no-op if (!bs->growable). >>>>> >>>>> Revalidate could be called by the block_resize monitor command with no >>>>> size specified. >>>>> >>>>> Paolo >>>> >>>> I think that is a good solution. Is it better to have "truncate" and >>>> "revalidate", or "truncate" and "grow", with grow being a subset of >>>> truncate, with fewer restrictions? There may still be operations >>>> where it is OK to grow a file, but not OK to shrink it. > > What semantics would the both operations have? Is truncate the same as > it used to be? I don't really understand what "revalidate" would do, it > sounds like a read-only operation from its name? > >>> Or as a first step: >>> >>> a) Call brdv_drain_all() only if the device is shrinked (independently of !bs->growable) >>> b) Call brdv_drain_all() inside iscsi_truncate() because it is a special requirement there >>> c) Fix the value of bs->growable for all drivers >> >> Let's start from (c). bdrv_file_open sets bs->growable = 1. I think it >> should be removed and only the file protocol should set it. > > This is probably right. If bs->growable is 1 for all drivers, whats the fix status of CVE-2008-0928? This flag was introduced as a fix for this problem. bdrv_check_byte_request() does nothing useful if bs->growable is 1. Peter