From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:54708) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UDWaS-0003ls-2l for qemu-devel@nongnu.org; Thu, 07 Mar 2013 03:54:07 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UDWaP-00068H-86 for qemu-devel@nongnu.org; Thu, 07 Mar 2013 03:54:04 -0500 Received: from ssl.dlhnet.de ([91.198.192.8]:36066 helo=ssl.dlh.net) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UDWaP-00067t-2L for qemu-devel@nongnu.org; Thu, 07 Mar 2013 03:54:01 -0500 Message-ID: <513855A7.7070205@dlhnet.de> Date: Thu, 07 Mar 2013 09:53:59 +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> In-Reply-To: <5137A964.5020803@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: Paolo Bonzini Cc: kwolf@redhat.com, sw@weilnetz.de, Jeff Cody , qemu-devel@nongnu.org, stefanha@redhat.com On 06.03.2013 21:39, Paolo Bonzini wrote: > 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. >> >> 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. > > Then we can add bdrv_revalidate and, for block_resize, call > bdrv_revalidate+bdrv_truncate. For bs->growable = 0 && > !bs->drv->bdrv_truncate, bdrv_truncate can just check that the actual > size is the same or bigger as the one requested, and fail otherwise. > > Paolo > Regarding brd_drain_all(). Is the fix right to call it only on device shrink? In this case it has to be added to iscsi_truncate as well. Peter