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=-3.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS 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 B5073C352A4 for ; Mon, 10 Feb 2020 18:14:27 +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 823BD2082F for ; Mon, 10 Feb 2020 18:14:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=igalia.com header.i=@igalia.com header.b="JRpN/7tm" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 823BD2082F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=igalia.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:37225 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j1DZi-00074G-Pc for qemu-devel@archiver.kernel.org; Mon, 10 Feb 2020 13:14:26 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:57778) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j1DZ7-0006bN-Bj for qemu-devel@nongnu.org; Mon, 10 Feb 2020 13:13:50 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1j1DZ6-0003uS-Fd for qemu-devel@nongnu.org; Mon, 10 Feb 2020 13:13:49 -0500 Received: from fanzine.igalia.com ([178.60.130.6]:46808) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1j1DZ6-0003s7-6f; Mon, 10 Feb 2020 13:13:48 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Type:MIME-Version:Message-ID:Date:References:In-Reply-To:Subject:Cc:To:From; bh=qWMlBpLMOw2Kqp+43+zTeTd8DI5zbbaMNH70aj22CYA=; b=JRpN/7tm4CUDThUK8jy0ip3ezVZQnz8Df1/4fwX7LbAtg4gOR1Vx0QV54GQAUv69x3FaCbXLKYBk8r3SxCieyLAglFb+EbZKftuoPBu4q1xyRExfJ/aVSyyO3hB7Mr9GJyFW73ajT1jS16wBVP/JZKX3KLbn0d42fVxR0egSpjpVF0z+YwjZF+Z9c57OmfI3uTW5pOkshZ3Eg+lT8Fo4c1bYZP/mskt+LVmWtawEtpHH62XFOLO9xpHmGANhoClFVcwcMv5jdFW0zOAxLTbDmFLs6RN9G1RqrFeIrImTZJXLoamR7lV6t1O6WsgyN+RWVQ7o1i1VP7ezMBQMRYQMdQ==; Received: from maestria.local.igalia.com ([192.168.10.14] helo=mail.igalia.com) by fanzine.igalia.com with esmtps (Cipher TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim) id 1j1DZ4-0004cB-Ro; Mon, 10 Feb 2020 19:13:46 +0100 Received: from berto by mail.igalia.com with local (Exim) id 1j1DZ4-0002KW-If; Mon, 10 Feb 2020 19:13:46 +0100 From: Alberto Garcia To: Eric Blake , qemu-devel@nongnu.org Subject: Re: [PATCH 06/17] block: Improve bdrv_has_zero_init_truncate with backing file In-Reply-To: <20200131174436.2961874-7-eblake@redhat.com> References: <20200131174436.2961874-1-eblake@redhat.com> <20200131174436.2961874-7-eblake@redhat.com> User-Agent: Notmuch/0.18.2 (http://notmuchmail.org) Emacs/24.4.1 (i586-pc-linux-gnu) Date: Mon, 10 Feb 2020 19:13:46 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x (no timestamps) [generic] [fuzzy] X-Received-From: 178.60.130.6 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: david.edmondson@oracle.com, Kevin Wolf , qemu-block@nongnu.org, mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri 31 Jan 2020 06:44:25 PM CET, Eric Blake wrote: > When we added bdrv_has_zero_init_truncate(), we chose to blindly > return 0 if a backing file was present, because we knew of the corner > case where a backing layer larger than the current layer might leak > the tail of the backing layer into the resized region. But as this > setup is rare, it penalizes the more common case of a backing layer > smaller than the current layer. > > Signed-off-by: Eric Blake Reviewed-by: Alberto Garcia Berto