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=-8.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 C22D6C35247 for ; Tue, 4 Feb 2020 15:17:48 +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 9217420730 for ; Tue, 4 Feb 2020 15:17:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="OsTd/eS3" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9217420730 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]:60262 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iyzxT-0000i0-QW for qemu-devel@archiver.kernel.org; Tue, 04 Feb 2020 10:17:47 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:36932) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iyzwV-0008Gi-5W for qemu-devel@nongnu.org; Tue, 04 Feb 2020 10:16:48 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iyzwU-0005lS-0z for qemu-devel@nongnu.org; Tue, 04 Feb 2020 10:16:47 -0500 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:28382 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iyzwT-0005fN-TZ for qemu-devel@nongnu.org; Tue, 04 Feb 2020 10:16:45 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1580829405; 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=L8CrNrhBDrEK7OFjhoGeldkhzYhJDK7VVrXkAcE3CJU=; b=OsTd/eS3CJsChxDSlDN0zAdrAPUdc7OmmOdqZyWEHrkhhZFDCq9jMJCR60yz4AFbvmGjbH C5oiSrY3B80KetI+SF/83y2kVvRQ2OHllPhnzNi31Ux0Gm4hJGn/DKuA07Z/MWmlQzKuwR zA6dGGeEoHk1aq6cKLnwgy70bHvSj58= 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-355-7S1ry94oND6CGTZU5I85Fg-1; Tue, 04 Feb 2020 10:16:24 -0500 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 44A068010E6; Tue, 4 Feb 2020 15:16:23 +0000 (UTC) Received: from [10.3.116.181] (ovpn-116-181.phx2.redhat.com [10.3.116.181]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A9A761001920; Tue, 4 Feb 2020 15:16:22 +0000 (UTC) Subject: Re: [PATCH 04/17] block: Improve documentation of .bdrv_has_zero_init To: Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org References: <20200131174436.2961874-1-eblake@redhat.com> <20200131174436.2961874-5-eblake@redhat.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: Date: Tue, 4 Feb 2020 09:16:20 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-MC-Unique: 7S1ry94oND6CGTZU5I85Fg-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 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 2/4/20 9:03 AM, Vladimir Sementsov-Ogievskiy wrote: > 31.01.2020 20:44, Eric Blake wrote: >> Several drivers supply .bdrv_has_zero_init that returns 1, but lack >> the .bdrv_has_zero_init_truncate callback (parallels and qed outright, >> vdi in some scenarios).=C2=A0 A literal reading of the existing >> documentation says such drivers are broken, because >> bdrv_has_zero_init_truncate() defaults to zero if the callback is >> missing; but in practice, the tie between the two functions is only >> relevant when truncate is supported.=C2=A0 Clarify the documentation to >> make it obvious that this is okay. >> >> Fixes: 1dcaf527 >> Signed-off-by: Eric Blake >> --- >> =C2=A0 include/block/block_int.h | 3 ++- >> =C2=A0 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/include/block/block_int.h b/include/block/block_int.h >> index 640fb82c789e..77ab45dc87cf 100644 >> --- a/include/block/block_int.h >> +++ b/include/block/block_int.h >> @@ -444,7 +444,8 @@ struct BlockDriver { >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * Returns 1 if newly created images= are guaranteed to contain only >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * zeros, 0 otherwise. >> -=C2=A0=C2=A0=C2=A0=C2=A0 * Must return 0 if .bdrv_has_zero_init_truncat= e() returns 0. >> +=C2=A0=C2=A0=C2=A0=C2=A0 * Must return 0 if .bdrv_co_truncate is set an= d >> +=C2=A0=C2=A0=C2=A0=C2=A0 * .bdrv_has_zero_init_truncate() returns 0. >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */ >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 int (*bdrv_has_zero_init)(BlockDriverStat= e *bs); >> >=20 > I doubt, shouldn't 1dcaf527 be fixed by adding all needed=20 > bdrv_has_zero_init_truncate functions? That was my original thought. But looking at callers of=20 bdrv_has_zero_init_truncate() shows that they all plan to perform=20 bdrv_co_truncate(PREALLOC_MODE_OFF) and want to know if that will leak=20 non-zero data; if you can't truncate, it doesn't matter what=20 init_truncate() returns, but since init_truncate() defaults to 0, it=20 shouldn't invalidate init() returning 1 - fixing the docs was easier=20 than adding useless callbacks to parallels, qed, and vdi just to rip=20 them back out again in patch 9. As you noted later, sheepdog was the only driver that violated this rule=20 (and it is fixed in patch 8). I could reorder the series to get the bug=20 fix in before the documentation change, if that would help. >=20 > (sorry, I started to dig in the code and patches around=20 > bdrv_has_zero_init_truncate and tired :(., > =C2=A0hope Max will comment this). >=20 --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org