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=-2.2 required=3.0 tests=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 0953ACA9EA9 for ; Fri, 18 Oct 2019 16:36:25 +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 D2F8E20663 for ; Fri, 18 Oct 2019 16:36:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D2F8E20663 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]:43108 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iLVEl-0002lt-V5 for qemu-devel@archiver.kernel.org; Fri, 18 Oct 2019 12:36:23 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:51944) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iLVDO-0001dF-TM for qemu-devel@nongnu.org; Fri, 18 Oct 2019 12:34:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iLVDN-0002bd-OV for qemu-devel@nongnu.org; Fri, 18 Oct 2019 12:34:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45096) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iLVDJ-0002Yc-TL; Fri, 18 Oct 2019 12:34:54 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DD4B61017C0D; Fri, 18 Oct 2019 16:34:52 +0000 (UTC) Received: from [10.3.116.168] (ovpn-116-168.phx2.redhat.com [10.3.116.168]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 765495C21A; Fri, 18 Oct 2019 16:34:49 +0000 (UTC) Subject: Re: [PATCH 08/10] nbd/server: introduce NBDExtentArray To: Vladimir Sementsov-Ogievskiy , "qemu-block@nongnu.org" References: <20190930151502.7829-1-vsementsov@virtuozzo.com> <20190930151502.7829-9-vsementsov@virtuozzo.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: <39449490-8cea-0387-6840-96bc06af55b2@redhat.com> Date: Fri, 18 Oct 2019 11:34:48 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.64]); Fri, 18 Oct 2019 16:34:52 +0000 (UTC) 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: 209.132.183.28 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: "kwolf@redhat.com" , "fam@euphon.net" , Denis Lunev , "qemu-devel@nongnu.org" , "mreitz@redhat.com" , "jsnow@redhat.com" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 10/18/19 11:07 AM, Vladimir Sementsov-Ogievskiy wrote: >>> =C2=A0 static int nbd_co_send_extents(NBDClient *client, uint64_t ha= ndle, >>> -=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 NBDExtent *extents, unsigned int nb_= extents, >>> -=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 uint64_t length, bool last, >>> -=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 uint32_t context_id, Error **errp) >>> +=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 NBDExtentArray *ea, >>> +=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 bool last, uint32_t context_id, Erro= r **errp) >>> =C2=A0 { >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 NBDStructuredMeta chunk; >>> - >>> +=C2=A0=C2=A0=C2=A0 size_t len =3D ea->count * sizeof(ea->extents[0])= ; >>> +=C2=A0=C2=A0=C2=A0 g_autofree NBDExtent *extents =3D g_memdup(ea->ex= tents, len); >> >> Why do we need memdup here?=C2=A0 What's wrong with modifying ea->exte= nts in place?... >=20 > To not make ea to be IN-OUT parameter.. I don't like functions with sid= e effects. > It will break the code if at some point we call nbd_co_send_extents twi= ce on same > ea object. >=20 > What is the true way? To not memdup, nbd_co_send_extents should consume= the whole > ea object.. >=20 > Seems, g_autoptr attribute can't be used for function parameter, gcc co= mplains: > nbd/server.c:1983:32: error: =E2=80=98cleanup=E2=80=99 attribute ignore= d [-Werror=3Dattributes] > 1983 | g_autoptr(NBDExtentArray) ea, > | ^~~~~~~~~ >=20 > so, is it better > to call nbd_co_send_external(... g_steal_pointer(&ea) ...) >=20 > and than in nbd_co_send_external do >=20 > g_autoptr(NBDExtentArray) local_ea =3D ea; > NBDExtent *extents =3D local_ea->extents; >=20 > ? >=20 No, that makes it worse. It's that much more confusing to track who is=20 allocating what and where it gets cleaned up. I personally don't see the need to avoid jumping through hoops to avoid=20 an in-out parameter (if we're going to rework code later, we'll notice=20 that we documented how things are supposed to be used), but if in-out=20 parameters bother you, then the approach you used, even with an extra=20 memdup(), is the simplest way to maintain, even if it is not the most=20 efficient. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org