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=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,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 D7AA9C433DB for ; Mon, 22 Mar 2021 07:02:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AF5BE6196E for ; Mon, 22 Mar 2021 07:02:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229961AbhCVHBh (ORCPT ); Mon, 22 Mar 2021 03:01:37 -0400 Received: from mx2.suse.de ([195.135.220.15]:47420 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229995AbhCVHBU (ORCPT ); Mon, 22 Mar 2021 03:01:20 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1616396479; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ikdRbjYwrh6jMOeo5QgfZnIqyWaL0H+nMzfLn9qBY+0=; b=i3fuAO3/9AJ6D78I8hJbTgo7/dJINVsaVaiq5rqBsLQNwwLHqBLM63NvFuspPOh6OtKms3 JEW/vNHZP7NjQlMgSS4Z91h7zr03OQOF1wMHQsVW1O6on2indryxLVZMHx4Qq85zP/j4H8 1oNf/90t4g4YFYaYuYQK5o40fWdf0pE= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 00DD3AD4A; Mon, 22 Mar 2021 07:01:18 +0000 (UTC) To: Leon Romanovsky Cc: "Hsu, Chiahao" , Andrew Lunn , netdev@vger.kernel.org, wei.liu@kernel.org, paul@xen.org, davem@davemloft.net, kuba@kernel.org, xen-devel@lists.xenproject.org References: <64f5c7a8-cc09-3a7f-b33b-a64d373aed60@amazon.com> <12f643b5-7a35-d960-9b1f-22853aea4b4c@amazon.com> From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Subject: Re: [net-next 1/2] xen-netback: add module parameter to disable ctrl-ring Message-ID: Date: Mon, 22 Mar 2021 08:01:17 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="XNey0EOIqh5lWhHqjRdvYYllC8uxFqu6T" Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --XNey0EOIqh5lWhHqjRdvYYllC8uxFqu6T Content-Type: multipart/mixed; boundary="Ov0WnZb01U1s0agqQzQ7tBpupQeAGgOZ7"; protected-headers="v1" From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= To: Leon Romanovsky Cc: "Hsu, Chiahao" , Andrew Lunn , netdev@vger.kernel.org, wei.liu@kernel.org, paul@xen.org, davem@davemloft.net, kuba@kernel.org, xen-devel@lists.xenproject.org Message-ID: Subject: Re: [net-next 1/2] xen-netback: add module parameter to disable ctrl-ring References: <64f5c7a8-cc09-3a7f-b33b-a64d373aed60@amazon.com> <12f643b5-7a35-d960-9b1f-22853aea4b4c@amazon.com> In-Reply-To: --Ov0WnZb01U1s0agqQzQ7tBpupQeAGgOZ7 Content-Type: multipart/mixed; boundary="------------8A2B5EA9D8912C96E9D361F3" Content-Language: en-US This is a multi-part message in MIME format. --------------8A2B5EA9D8912C96E9D361F3 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 22.03.21 07:48, Leon Romanovsky wrote: > On Mon, Mar 22, 2021 at 06:58:34AM +0100, J=C3=BCrgen Gro=C3=9F wrote: >> On 22.03.21 06:39, Leon Romanovsky wrote: >>> On Sun, Mar 21, 2021 at 06:54:52PM +0100, Hsu, Chiahao wrote: >>>> >>> >>> <...> >>> >>>>>> Typically there should be one VM running netback on each host, >>>>>> and having control over what interfaces or features it exposes is = also >>>>>> important for stability. >>>>>> How about we create a 'feature flags' modparam, each bits is speci= fied for >>>>>> different new features? >>>>> At the end, it will be more granular module parameter that user sti= ll >>>>> will need to guess. >>>> I believe users always need to know any parameter or any tool's flag= before >>>> they use it. >>>> For example, before user try to set/clear this ctrl_ring_enabled, th= ey >>>> should already have basic knowledge about this feature, >>>> or else they shouldn't use it (the default value is same as before),= and >>>> that's also why we use the 'ctrl_ring_enabled' as parameter name. >>> >>> It solves only forward migration flow. Move from machine A with no >>> option X to machine B with option X. It doesn't work for backward >>> flow. Move from machine B to A back will probably break. >>> >>> In your flow, you want that users will set all module parameters for >>> every upgrade and keep those parameters differently per-version. >> >> I think the flag should be a per guest config item. Adding this item t= o >> the backend Xenstore nodes for netback to consume it should be rather >> easy. >> >> Yes, this would need a change in Xen tools, too, but it is the most >> flexible way to handle it. And in case of migration the information >> would be just migrated to the new host with the guest's config data. >=20 > Yes, it will overcome global nature of module parameters, but how does > it solve backward compatibility concern? When creating a guest on A the (unknown) feature will not be set to any value in the guest's config data. A migration stream not having any value for that feature on B should set it to "false". When creating a guest on B it will either have the feature value set explicitly in the guest config (either true or false), or it will get the server's default (this value should be configurable in a global config file, default for that global value would be "true"). So with the guest created on B with feature specified as "false" (either for this guest only, or per global config), it will be migratable to machine A without problem. Migrating it back to B would work the same way as above. Trying to migrate a guest with feature set to "true" to B would not work, but this would be the host admin's fault due to not configuring the guest correctly. 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