From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BF476C742B1 for ; Fri, 12 Jul 2019 09:49:39 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9626B2064B for ; Fri, 12 Jul 2019 09:49:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9626B2064B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:47808 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hlsBO-0004Wt-Bu for qemu-devel@archiver.kernel.org; Fri, 12 Jul 2019 05:49:38 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:48713) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hlsBF-000443-1z for qemu-devel@nongnu.org; Fri, 12 Jul 2019 05:49:29 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hlsBE-0002d5-11 for qemu-devel@nongnu.org; Fri, 12 Jul 2019 05:49:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48422) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hlsBB-0002SI-Gx; Fri, 12 Jul 2019 05:49:25 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 0D3E2308FF23; Fri, 12 Jul 2019 09:49:24 +0000 (UTC) Received: from dhcp-200-226.str.redhat.com (dhcp-200-226.str.redhat.com [10.33.200.226]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A86511001B00; Fri, 12 Jul 2019 09:49:20 +0000 (UTC) Date: Fri, 12 Jul 2019 11:49:19 +0200 From: Kevin Wolf To: Max Reitz Message-ID: <20190712094919.GC4514@dhcp-200-226.str.redhat.com> References: <20190711195804.30703-1-mreitz@redhat.com> <20190711195804.30703-3-mreitz@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190711195804.30703-3-mreitz@redhat.com> User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.49]); Fri, 12 Jul 2019 09:49:24 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [RFC 2/5] block: Generic truncation fallback X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Stefan Hajnoczi , qemu-devel@nongnu.org, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 11.07.2019 um 21:58 hat Max Reitz geschrieben: > If a protocol driver does not support truncation, we call fall back to > effectively not doing anything if the new size is less than the actual > file size. This is what we have been doing for some host device drivers > already. Specifically, we're doing it for drivers that access a fixed-size image, i.e. block devices rather than regular files. We don't want to do this for drivers where the file size could be changed, but just didn't implement it. So I would suggest calling the function more specifically something like bdrv_co_truncate_blockdev(), and not using it as an automatic fallback in bdrv_co_truncate(), but just make it the BlockDriver.bdrv_co_truncate implementation for those drivers where it makes sense. And of course, we only need these fake implementations because qemu-img (or .bdrv_co_create_opts) always wants to create the protocol level. If we could avoid this, then we wouldn't need any of this. Kevin