From nobody Fri May 3 00:34:14 2024 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1553853507138270.14985229692184; Fri, 29 Mar 2019 02:58:27 -0700 (PDT) Received: from localhost ([127.0.0.1]:49773 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h9oHF-0000Iu-44 for importer@patchew.org; Fri, 29 Mar 2019 05:58:21 -0400 Received: from eggs.gnu.org ([209.51.188.92]:34096) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h9oGH-0008Ql-Id for qemu-devel@nongnu.org; Fri, 29 Mar 2019 05:57:22 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1h9oGG-0004X2-Fr for qemu-devel@nongnu.org; Fri, 29 Mar 2019 05:57:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44902) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1h9oGG-0004Wi-8l for qemu-devel@nongnu.org; Fri, 29 Mar 2019 05:57:20 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4B76E3082E05 for ; Fri, 29 Mar 2019 09:57:19 +0000 (UTC) Received: from xz-x1.nay.redhat.com (dhcp-14-116.nay.redhat.com [10.66.14.116]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4C407D1D8; Fri, 29 Mar 2019 09:57:15 +0000 (UTC) From: Peter Xu To: qemu-devel@nongnu.org Date: Fri, 29 Mar 2019 17:57:13 +0800 Message-Id: <20190329095713.14177-1-peterx@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Fri, 29 Mar 2019 09:57:19 +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: [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 , "Dr . David Alan Gilbert" , peterx@redhat.com, Juan Quintela Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" 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 Reviewed-by: Dr. David Alan Gilbert --- 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_buff= er, _size) =20 +/* + * 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=3D=3D1 + * rather than size=3D=3Dsizeof(bool). + */ #define VMSTATE_UNUSED_V(_v, _size) \ VMSTATE_UNUSED_BUFFER(NULL, _v, _size) =20 --=20 2.17.1