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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3FFCED0C61D for ; Fri, 25 Oct 2024 14:50:26 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1t4Ld9-0001Ka-MR; Fri, 25 Oct 2024 10:49:35 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1t4Ld7-0001KK-FD for qemu-devel@nongnu.org; Fri, 25 Oct 2024 10:49:33 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1t4Ld5-0004My-DB for qemu-devel@nongnu.org; Fri, 25 Oct 2024 10:49:33 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1729867769; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=YJxptOmw9jGtOgabnvTpv/oQjkImldbv0ThhqEH9vcQ=; b=admxQxGtXLVX+Rdmu+nSU47oCzmP3Kzs1Dx+PtS2/A2MRJ+/vtzPJXRH2kEsPvU2Ajzy2x XfffLtix2PzlpCv94vlcOBUZtJC5f0kYHy0Te1s5vHp1vv6w7ndj20c4gKXryxka1axMuv y9oBUt/yFs+ofvLKuIs8F76ty7OFi+A= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-530-WU5pzOElOo-T4FNZrH24AQ-1; Fri, 25 Oct 2024 10:49:25 -0400 X-MC-Unique: WU5pzOElOo-T4FNZrH24AQ-1 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 34E6419560A2; Fri, 25 Oct 2024 14:49:23 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.164]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D8002196BB7D; Fri, 25 Oct 2024 14:49:18 +0000 (UTC) Date: Fri, 25 Oct 2024 15:49:15 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Steven Sistare Cc: Paolo Bonzini , qemu-devel@nongnu.org, Peter Xu , Fabiano Rosas , David Hildenbrand , Marcel Apfelbaum , Eduardo Habkost , Philippe Mathieu-Daude , Markus Armbruster Subject: Re: [RFC V1 00/14] precreate phase Message-ID: References: <1729178055-207271-1-git-send-email-steven.sistare@oracle.com> <922177b7-216f-4176-a57a-a86f32252664@oracle.com> <380c6b5f-c888-4cc3-80ee-4f082037aa88@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <380c6b5f-c888-4cc3-80ee-4f082037aa88@oracle.com> User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.454, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Fri, Oct 25, 2024 at 10:32:15AM -0400, Steven Sistare wrote: > On 10/25/2024 9:43 AM, Daniel P. Berrangé wrote: > > On Fri, Oct 25, 2024 at 09:33:51AM -0400, Steven Sistare wrote: > > > On 10/25/2024 4:46 AM, Daniel P. Berrangé wrote: > > > > On Thu, Oct 24, 2024 at 05:16:14PM -0400, Steven Sistare wrote: > > > > > > > > > > Regarding: "what you want is effectively to execute monitor commands > > > > > from the migration stream" > > > > > > > > > > That is not the goal of this series. It could be someone else's goal, when > > > > > fully developing a precreate phase, and in that context I understand and > > > > > agree with your comments. I have a narrower immediate problem to solve, > > > > > however. > > > > > > > > > > For CPR, src qemu sends file descriptors to dst qemu using SCM_RIGHTS over > > > > > a dedicated channel, then src qemu sends migration state over the normal > > > > > migration channel. > > > > > > > > > > Dst qemu reads the fds early, then calls the backend and device creation > > > > > functions which use them. Dst qemu then accepts and reads the migration > > > > > channel. > > > > > > > > > > We need a way to send monitor commands that set dst migration capabilities, > > > > > before src qemu starts the migration. Hence the dst cannot proceed to > > > > > backend and device creation because the src has not sent fd's yet. Hence > > > > > we need a dst monitor before device creation. The precreate phase does that. > > > > > > > > Sigh, what we obviously need here, is what we've always talked about as our > > > > long term design goal: > > > > > > > > A way to launch QEMU with the CLI only specifying the QMP socket, and every > > > > other config aspect done by issuing QMP commands, which are processed in the > > > > order the mgmt app sends them, so QEMU hasn't have to hardcode processing > > > > of different pieces in different phases. > > > > > > > > Anything that isn't that, is piling more hacks on top of our existing > > > > mountain of hacks. That's OK if it does something useful as a side effect > > > > that moves us incrementally closer towards that desired end goal. > > > > > > > > > Regarding: "This series makes this much more complex." > > > > > > > > > > I could simplify it if I abandon CPR for chardevs. Then qemu_create_early_backends > > > > > and other early dependencies can remain as is. I would drop the notion of > > > > > a precreate phase, and instead leverage the preconfig phase. I would move > > > > > qemu_create_late_backends, and a small part at the end of qemu_init, to > > > > > qmp_x_exit_preconfig. > > > > > > > > Is CPR still going to useful enough in the real world if you drop chardev > > > > support ? Every VM has at least one chardev for a serial device doesn't > > > > it, and often more since we wire chardevs into all kinds of places. > > > > > > CPR for chardev is not as useful for cpr-transfer mode because the mgmt layer already > > > knows how to create and manage new connections to dest qemu, as it would for normal > > > migration. > > > > > > CPR for chardev is very useful for cpr-exec mode. And cpr-exec mode does not need any > > > of these monitor patches, because old qemu exec's new qemu, and they are never active > > > at the same time. One must completely specify the migration using src qemu before > > > initiating the exec. I mourn cpr-exec mode. > > > > > > Which begs the question, do we really need to allow migration parameters to be set > > > in the dest monitor when using cpr? CPR is a very restricted mode of migration. > > > Let me discuss this with Peter. > > > > The migration QAPI design has always felt rather odd to me, in that we > > have perfectly good commands "migrate" & "migrate-incoming" that are able > > to accept an arbitrary list of parameters when invoked. Instead of passing > > parameters to them though, we instead require apps use the separate > > migreate-set-parameters/capabiltiies commands many times over to set > > global variables which the later 'migrate' command then uses. > > > > The reason for this is essentially a historical mistake - we copied the > > way we did it from HMP, which was this way because HMP was bad at supporting > > arbitrary customizable paramters to commands. I wish we hadn't copied this > > design over to QMP. > > > > To bring it back on topic, we need QMP on the dest to set parameters, > > because -incoming was limited to only take the URI. > > > > If the "migrate-incoming" command accepted all parameters directly, > > then we could use QAPI visitor to usupport a "-incoming ..." command > > that took an arbitrary JSON document and turned it into a call to > > "migrate-incoming". > > > > With that we would never need QMP on the target for cpr-exec, avoiding > > this ordering poblem you're facing....assuming we put processing of > > -incoming at the right point in the code flow > > > > Can we fix this design and expose the full configurability on the > > CLI using QAPI schema & inline JSON, like we do for other QAPI-ified > > CLI args. > > > > It seems entirely practical to me to add parameters to 'migrate-incoming' > > in a backwards compatible manner and deprecate set-parameters/capabilities > > Hi Daniel, should we ever need to set caps or parameters for CPR, that sounds > like a good way forward. And a good idea independently of CPR. However, I > am hoping to proceed with CPR with the initial restriction that one cannot > set them. The case that motivated my exploration of precreate is artificial -- > qtest wanting to enable migration events -- and I can fix that. I know of no > real cases where caps must be set for CPR. > > The other screw case which motivated this thread is a dynamically chosen TCP > port number for the migration listen socket. One must query dest qemu to get it. > Your suggestions here for new incoming syntax would not help. However, for CPR, > we always migrate to the same host, so a unix domain socket can be used. FWIW, at least in libvirt usage, IIRC, libvirt will choose the listener port number upfront itself With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|