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 D5A82C433E0 for ; Tue, 19 May 2020 15:18:29 +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 A8BC22081A for ; Tue, 19 May 2020 15:18:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A8BC22081A 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 1jb40S-0007lV-9I; Tue, 19 May 2020 15:18:12 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jb40R-0007lQ-HR for xen-devel@lists.xenproject.org; Tue, 19 May 2020 15:18:11 +0000 X-Inumbo-ID: f2eb2f24-99e3-11ea-b07b-bc764e2007e4 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id f2eb2f24-99e3-11ea-b07b-bc764e2007e4; Tue, 19 May 2020 15:18:10 +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 D6670B227; Tue, 19 May 2020 15:18:11 +0000 (UTC) Subject: Re: [PATCH v3 1/5] xen/common: introduce a new framework for save/restore of 'domain' context To: paul@xen.org References: <20200514104416.16657-1-paul@xen.org> <20200514104416.16657-2-paul@xen.org> <000401d62de6$7cb6efa0$7624cee0$@xen.org> <080a1fa3-eb1e-e3b2-c52e-5c7ffdabc6eb@suse.com> <000601d62def$b4f64380$1ee2ca80$@xen.org> From: Jan Beulich Message-ID: <0ee39765-bc1a-e795-5b20-52ba7026e8d4@suse.com> Date: Tue, 19 May 2020 17:18:07 +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: <000601d62def$b4f64380$1ee2ca80$@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, 'Volodymyr Babchuk' , =?UTF-8?B?J1JvZ2VyIFBhdSBNb25uw6kn?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 19.05.2020 17:10, Paul Durrant wrote: >> From: Jan Beulich >> Sent: 19 May 2020 15:24 >> >> On 19.05.2020 16:04, Paul Durrant wrote: >>>> From: Jan Beulich >>>> Sent: 19 May 2020 14:04 >>>> >>>> On 14.05.2020 12:44, Paul Durrant wrote: >>>>> +/* >>>>> + * Register save and restore handlers. Save handlers will be invoked >>>>> + * in order of DOMAIN_SAVE_CODE(). >>>>> + */ >>>>> +#define DOMAIN_REGISTER_SAVE_RESTORE(_x, _save, _load) \ >>>>> + static int __init __domain_register_##_x##_save_restore(void) \ >>>>> + { \ >>>>> + domain_register_save_type( \ >>>>> + DOMAIN_SAVE_CODE(_x), \ >>>>> + #_x, \ >>>>> + &(_save), \ >>>>> + &(_load)); \ >>>>> + \ >>>>> + return 0; \ >>>>> + } \ >>>>> + __initcall(__domain_register_##_x##_save_restore); >>>> >>>> I'm puzzled by part of the comment: Invoking by save code looks >>>> reasonable for the saving side (albeit END doesn't match this rule >>>> afaics), but is this going to be good enough for the consuming side? >>> >>> No, this only relates to the save side which is why the comment >>> says 'Save handlers'. I do note that it would be more consistent >>> to use 'load' rather than 'restore' here though. >>> >>>> There may be dependencies between types, and with fixed ordering >>>> there may be no way to insert a depended upon type ahead of an >>>> already defined one (at least as long as the codes are meant to be >>>> stable). >>>> >>> >>> The ordering of load handlers is determined by the stream. I'll >>> add a sentence saying that. >> >> I.e. the consumer of the "get" interface (and producer of the stream) >> is supposed to take apart the output it gets, bring records into >> suitable order (which implies it knows of all the records, and which >> hence means this code may need updating in cases where I'd expect >> only the hypervisor needs), and only then issue to the stream? > > The intention is that the stream is always in a suitable order so the > load side does not have to do any re-ordering. I understood this to be the intention, but what I continue to not understand is where / how the save side orders it suitably. "Save handlers will be invoked in order of DOMAIN_SAVE_CODE()" does not allow for any ordering, unless at the time of the introduction of a particular code you already know what others it may depend on in the future, reserving appropriate codes. And as said - END also doesn't look to fit this comment. Jan