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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,T_HK_NAME_DR, USER_AGENT_MUTT 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 9E100C04AB4 for ; Tue, 14 May 2019 11:30:51 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 72A9C208CA for ; Tue, 14 May 2019 11:30:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 72A9C208CA 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 ([127.0.0.1]:46023 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hQVdy-0004aX-LZ for qemu-devel@archiver.kernel.org; Tue, 14 May 2019 07:30:50 -0400 Received: from eggs.gnu.org ([209.51.188.92]:49324) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hQVZF-0000ih-Jn for qemu-devel@nongnu.org; Tue, 14 May 2019 07:25:58 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hQVZE-0004qd-G2 for qemu-devel@nongnu.org; Tue, 14 May 2019 07:25:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58556) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hQVZE-0004pe-9q for qemu-devel@nongnu.org; Tue, 14 May 2019 07:25:56 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 06948356FF for ; Tue, 14 May 2019 11:25:55 +0000 (UTC) Received: from work-vm (ovpn-117-232.ams2.redhat.com [10.36.117.232]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 07940608A6; Tue, 14 May 2019 11:25:51 +0000 (UTC) Date: Tue, 14 May 2019 12:25:49 +0100 From: "Dr. David Alan Gilbert" To: Peter Xu Message-ID: <20190514112548.GB8632@work-vm> References: <20190329095713.14177-1-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190329095713.14177-1-peterx@redhat.com> User-Agent: Mutt/1.11.4 (2019-03-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Tue, 14 May 2019 11:25:55 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH] migration: comment VMSTATE_UNUSED*() properly X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Laurent Vivier , qemu-devel@nongnu.org, Juan Quintela Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Peter Xu (peterx@redhat.com) wrote: > It is error prone to use VMSTATE_UNUSED*() sometimes especially when > the size of the migration stream of the field is not the same as the > size of the structure (boolean is one example). Comment it well so > people will be aware of this when people want to use it. > > Signed-off-by: Peter Xu Queued > --- > include/migration/vmstate.h | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h > index a668ec75b8..9224370ed5 100644 > --- a/include/migration/vmstate.h > +++ b/include/migration/vmstate.h > @@ -1035,6 +1035,20 @@ extern const VMStateInfo vmstate_info_qtailq; > #define VMSTATE_BUFFER_UNSAFE(_field, _state, _version, _size) \ > VMSTATE_BUFFER_UNSAFE_INFO(_field, _state, _version, vmstate_info_buffer, _size) > > +/* > + * These VMSTATE_UNUSED*() macros can be used to fill in the holes > + * when some of the vmstate fields are obsolete to be compatible with > + * migrations between new/old binaries. > + * > + * CAUTION: when using any of the VMSTATE_UNUSED*() macros please be > + * sure that the size passed in is the size that was actually *sent* > + * rather than the size of the *structure*. One example is the > + * boolean type - the size of the structure can vary depending on the > + * definition of boolean, however the size we actually sent is always > + * 1 byte (please refer to implementation of VMSTATE_BOOL_V and > + * vmstate_info_bool). So here we should always pass in size==1 > + * rather than size==sizeof(bool). > + */ > #define VMSTATE_UNUSED_V(_v, _size) \ > VMSTATE_UNUSED_BUFFER(NULL, _v, _size) > > -- > 2.17.1 > > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK