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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 4907FC352A3 for ; Tue, 11 Feb 2020 15:38:14 +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 155862051A for ; Tue, 11 Feb 2020 15:38:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="WBHeuTO+" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 155862051A 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]:51686 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j1Xc5-0007vG-4i for qemu-devel@archiver.kernel.org; Tue, 11 Feb 2020 10:38:13 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:45120) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j1XbV-0007SE-FS for qemu-devel@nongnu.org; Tue, 11 Feb 2020 10:37:38 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1j1XbU-0004zu-Ef for qemu-devel@nongnu.org; Tue, 11 Feb 2020 10:37:37 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:59148 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1j1XbU-0004za-BL for qemu-devel@nongnu.org; Tue, 11 Feb 2020 10:37:36 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1581435454; 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=M0Ccpfqtvh5xhrwqeCxU+lK32upuAOFC8XAbpg8N2hs=; b=WBHeuTO+BF51K7ovRWlnxNQT2DIJZMNALbDCnaV7HXlohzxgOC+ykvvn73oBYZpFQMkzrM s0ioaTgnaCUNdIeJ5tfjfK9D2sX99Gt+4DsT9apspt73ufjsmd3MBwE75GsGi6SVmNI00N lsjo4bRXIS2GGv+/8eTXjjX32AJNSPA= 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-324-A3_j1GbxPFmGdYIgYp6uPQ-1; Tue, 11 Feb 2020 10:37:30 -0500 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 624668024FA; Tue, 11 Feb 2020 15:37:29 +0000 (UTC) Received: from [10.3.116.180] (ovpn-116-180.phx2.redhat.com [10.3.116.180]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E23A826E4C; Tue, 11 Feb 2020 15:37:28 +0000 (UTC) Subject: Re: [PATCH v2 04/33] block: Add BdrvChildRole to BdrvChild To: Max Reitz , qemu-block@nongnu.org References: <20200204170848.614480-1-mreitz@redhat.com> <20200204170848.614480-5-mreitz@redhat.com> <3113019f-797f-fe89-abbd-280bbddded31@redhat.com> <61ad1ad4-e118-c92c-bbe2-cdd03d02a8d8@redhat.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: <2f287423-10e6-f962-ae4e-5644fd8a37f4@redhat.com> Date: Tue, 11 Feb 2020 09:37:28 -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: <61ad1ad4-e118-c92c-bbe2-cdd03d02a8d8@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-MC-Unique: A3_j1GbxPFmGdYIgYp6uPQ-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] X-Received-From: 205.139.110.120 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: Kevin Wolf , Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2/6/20 4:53 AM, Max Reitz wrote: >>> +++ b/block.c >>> @@ -2381,6 +2381,7 @@ static void bdrv_replace_child(BdrvChild *child, >>> BlockDriverState *new_bs) >>> =C2=A0 BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs, >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 const ch= ar *child_name, >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 const Bd= rvChildClass *child_class, >>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 BdrvChildRole child_= role, >> >> Hmm - C is loose enough to allow the declaration of a parameter as an >> enum type even when its intended usage is to receive a bitwise-or >> derived from that enum but not declared in the enum.=C2=A0 For example, = if I >> understand intent correctly, a caller might pass in 0x3 >> (BDRV_CHILD_DATA|BDRV_CHILD_METADATA) which does NOT appear in >> BdrvChildRole.=C2=A0 It feels like it might be cleaner to document the >> interface as taking an unsigned int (although then you've lost the >> documentation that the int is derived from BdrvChildRole), than to abuse >> the typesystem to pass values that are not BdrvChildRole through the >> parameter. >=20 > I don=E2=80=99t necessarily disagree, but we have pre-existing examples o= f such > abuse, like BdrvRequestFlags. >=20 > The advantage of using BdrvChildRole as a type here is to show that we > expect values from that enum. I personally prefer that. Yeah, the self-documenting aspect is nice. >=20 > I mean, we could do something else entirely and name the enum > =E2=80=9CBdrvChildRoleBits=E2=80=9D and add a =E2=80=9Ctypedef unsigned i= nt BdrvChildRole;=E2=80=9D. I > don=E2=80=99t think we=E2=80=99ve ever done that before but maybe it=E2= =80=99d be the cleanest way? You're right that we haven't done it, but it is also the slickest=20 solution that preserves documentation intent. In C, such a typedef=20 serves only as documentation (and the compiler doesn't enforce it,=20 compared to what a strongly-typed language would do), but I do like the=20 idea. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org