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=-2.3 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 9DC40C433E0 for ; Tue, 19 May 2020 15:34:20 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 7B9342075F for ; Tue, 19 May 2020 15:34:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7B9342075F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jb4Fv-0001Tt-MU; Tue, 19 May 2020 15:34:11 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jb4Fu-0001Te-S2 for xen-devel@lists.xenproject.org; Tue, 19 May 2020 15:34:10 +0000 X-Inumbo-ID: 2f029626-99e6-11ea-b07b-bc764e2007e4 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 2f029626-99e6-11ea-b07b-bc764e2007e4; Tue, 19 May 2020 15:34:10 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id BCD4EAD88; Tue, 19 May 2020 15:34:11 +0000 (UTC) Subject: Re: [PATCH v3 4/5] common/domain: add a domain context record for shared_info... To: paul@xen.org References: <20200514104416.16657-1-paul@xen.org> <20200514104416.16657-5-paul@xen.org> <000a01d62df1$28e876e0$7ab964a0$@xen.org> From: Jan Beulich Message-ID: <035bded3-9542-31e1-aacf-515be43b8536@suse.com> Date: Tue, 19 May 2020 17:34:08 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <000a01d62df1$28e876e0$7ab964a0$@xen.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: 'Stefano Stabellini' , 'Julien Grall' , 'Wei Liu' , 'Andrew Cooper' , 'Paul Durrant' , 'Ian Jackson' , 'George Dunlap' , xen-devel@lists.xenproject.org Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 19.05.2020 17:21, Paul Durrant wrote: >> From: Jan Beulich >> Sent: 19 May 2020 15:08 >> >> On 14.05.2020 12:44, Paul Durrant wrote: >>> --- a/xen/include/public/save.h >>> +++ b/xen/include/public/save.h >>> @@ -73,7 +73,16 @@ struct domain_save_header { >>> }; >>> DECLARE_DOMAIN_SAVE_TYPE(HEADER, 1, struct domain_save_header); >>> >>> -#define DOMAIN_SAVE_CODE_MAX 1 >>> +struct domain_shared_info_context { >>> + uint8_t has_32bit_shinfo; >>> + uint8_t pad[3]; >> >> 32-(or 16-)bit flags, with just a single bit used for the purpose? >> > > I debated that. Given this is xen/tools-only would a bit-field be acceptable? Looking at domctl.h and sysctl.h, the only instance I can find is a live-patching struct, and I'd suppose the addition of bitfields there was missed in the hasty review back then. While it might be acceptable, I'd recommend against it. It'll bite us the latest with a port to an arch where endianness is not fixed, and hence may vary between hypercall caller and callee. The standard way of using #define-s looks more future proof. Jan