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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 5D44EC3A5A0 for ; Mon, 20 Apr 2020 15:55:01 +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 286F3206DD for ; Mon, 20 Apr 2020 15:55:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="BD4nXzWJ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 286F3206DD 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]:38202 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jQYlA-0000Jr-CX for qemu-devel@archiver.kernel.org; Mon, 20 Apr 2020 11:55:00 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42730 helo=eggs1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jQYkM-0008Gt-Lx for qemu-devel@nongnu.org; Mon, 20 Apr 2020 11:54:11 -0400 Received: from Debian-exim by eggs1p.gnu.org with spam-scanned (Exim 4.90_1) (envelope-from ) id 1jQYkM-0004zw-BJ for qemu-devel@nongnu.org; Mon, 20 Apr 2020 11:54:10 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:21499 helo=us-smtp-1.mimecast.com) by eggs1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jQYkL-0004v3-Qy for qemu-devel@nongnu.org; Mon, 20 Apr 2020 11:54:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1587398048; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=E8VYH79oipZhKGruaeFhIL40GGcCXwcxdYwECT7PSo4=; b=BD4nXzWJiIWQmsiivM2vo+boCMiXZMrRhQPgt4XbRGmfGWAxEmjVAL2Uzt90LBHxeFKrf4 OInwxAofNsnk7JhU/YGuB/i+j7Bd6Zi1waaeBGIQl4NP2Jv8+sToJ+AX6q6rpJUCtCBOT/ GB48p4PKClproVaQKDkM1pXG5RHHNAg= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-479-rMFED9B3MSqq9xhmfSBiXw-1; Mon, 20 Apr 2020 11:54:03 -0400 X-MC-Unique: rMFED9B3MSqq9xhmfSBiXw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EF25685EE70; Mon, 20 Apr 2020 15:54:01 +0000 (UTC) Received: from [10.10.116.80] (ovpn-116-80.rdu2.redhat.com [10.10.116.80]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3AEE960C99; Mon, 20 Apr 2020 15:53:57 +0000 (UTC) Subject: Re: [PATCH v4 5/9] raw-format: Support BDRV_REQ_ZERO_WRITE for truncate To: Kevin Wolf References: <20200420133214.28921-1-kwolf@redhat.com> <20200420133214.28921-6-kwolf@redhat.com> <20200420153217.GA29316@linux.fritz.box> From: Eric Blake Organization: Red Hat, Inc. Message-ID: <7d313fb3-d2c4-54f8-fc03-4d471ee084fc@redhat.com> Date: Mon, 20 Apr 2020 10:53:51 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200420153217.GA29316@linux.fritz.box> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=207.211.31.120; envelope-from=eblake@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs1p.gnu.org: First seen = 2020/04/20 03:29:13 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 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: vsementsov@virtuozzo.com, berto@igalia.com, qemu-devel@nongnu.org, qemu-block@nongnu.org, mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 4/20/20 10:32 AM, Kevin Wolf wrote: >>> @@ -445,6 +445,7 @@ static int raw_open(BlockDriverState *bs, QDict *options, int flags, >>> bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED | >>> ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) & >>> bs->file->bs->supported_zero_flags); >>> + bs->supported_truncate_flags = BDRV_REQ_ZERO_WRITE; >> >> Shouldn't this be: >> >> bs->supported_truncate_flags = (bs->file->bs->supported_truncate_flags & >> BDRV_REQ_ZERO_WRITE); >> >> rather than unconditionally advertising something that the underlying layer >> may lack? > > Maybe that makes more sense, yes. If nothing else, it is more consistent with what we are doing for supported_zero_flags. I also argue that having a reference to the passthrough is easier to grep for, if we ever add new flags in the future. That is, while keeping passthrough as opt-in rather than blind copying or blind assignment is slightly more code, it is easier to maintain. > > I think in practice it wouldn't make a difference because the nested > bdrv_co_truncate() would still fail rather than silently ignoring the > flag. It would behave the same as filter drivers, which also recursively > call bdrv_co_truncate() without checking the flag first (which is, of > course, because I don't want to modify each filter driver). Probably true, but consistency and ease of maintenance are better than proving action at a distance :) -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org