From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:56038) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UDWfW-0007b5-JK for qemu-devel@nongnu.org; Thu, 07 Mar 2013 03:59:21 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UDWfV-00083K-9J for qemu-devel@nongnu.org; Thu, 07 Mar 2013 03:59:18 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48605) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UDWfV-00083E-0n for qemu-devel@nongnu.org; Thu, 07 Mar 2013 03:59:17 -0500 Date: Thu, 7 Mar 2013 09:59:12 +0100 From: Kevin Wolf Message-ID: <20130307085912.GD2536@dhcp-200-207.str.redhat.com> 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> <513855A7.7070205@dlhnet.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <513855A7.7070205@dlhnet.de> 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: Peter Lieven Cc: Paolo Bonzini , Jeff Cody , qemu-devel@nongnu.org, stefanha@redhat.com, sw@weilnetz.de Am 07.03.2013 um 09:53 hat Peter Lieven geschrieben: > 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. The real fix would bdrv_drain(bs). I hope we're not too far away from that today, even though we're not quite there. Kevin