From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:41188) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UDL7G-00031K-PA for qemu-devel@nongnu.org; Wed, 06 Mar 2013 15:39:12 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UDL7A-0008G4-Kz for qemu-devel@nongnu.org; Wed, 06 Mar 2013 15:39:10 -0500 Received: from mail-wi0-x230.google.com ([2a00:1450:400c:c05::230]:61931) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UDL7A-0008Fq-Fg for qemu-devel@nongnu.org; Wed, 06 Mar 2013 15:39:04 -0500 Received: by mail-wi0-f176.google.com with SMTP id hm14so456121wib.15 for ; Wed, 06 Mar 2013 12:39:03 -0800 (PST) Sender: Paolo Bonzini Message-ID: <5137A964.5020803@redhat.com> Date: Wed, 06 Mar 2013 21:39:00 +0100 From: Paolo Bonzini 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> In-Reply-To: <51379304.50307@dlhnet.de> Content-Type: text/plain; charset=ISO-8859-1 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: Peter Lieven Cc: kwolf@redhat.com, sw@weilnetz.de, Jeff Cody , qemu-devel@nongnu.org, stefanha@redhat.com 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