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 lists1p.gnu.org (lists1p.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 6960BC43458 for ; Mon, 13 Jul 2026 18:38:51 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wjLXp-0008VP-Lw; Mon, 13 Jul 2026 14:38:22 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wjLXm-0008VE-1B for qemu-devel@nongnu.org; Mon, 13 Jul 2026 14:38:18 -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 1wjLXa-0001j3-8W for qemu-devel@nongnu.org; Mon, 13 Jul 2026 14:38:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1783967884; 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=6yngjYaZLXJGmfqSKjJQIi/LZe3hW7VOv6sUvCb/1kQ=; b=CGPqL9/8fujQ9hZw/fnMWPgt53t8pkXgHASh+J8ix59LFcYj4+vclXT1pWW6T7UAqCBd5Z 9QhJ4N9gQv7S9P2UWUwMX+prdDXhxygM+Kac5KRJeL9fhPsnsEt2jx9tz8ydsPsXIj3hav y5lqzDouQ7OzF8R5gJbd6fOKYhPfFUY= 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-604-I52ay6JmPEuFIHk58SgXgg-1; Mon, 13 Jul 2026 14:38:01 -0400 X-MC-Unique: I52ay6JmPEuFIHk58SgXgg-1 X-Mimecast-MFC-AGG-ID: I52ay6JmPEuFIHk58SgXgg_1783967880 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (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 2E3261955DC1; Mon, 13 Jul 2026 18:37:59 +0000 (UTC) Received: from redhat.com (unknown [10.44.50.22]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5B8AE180065F; Mon, 13 Jul 2026 18:37:53 +0000 (UTC) Date: Mon, 13 Jul 2026 19:37:50 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Vladimir Sementsov-Ogievskiy Cc: jasowang@redhat.com, mst@redhat.com, armbru@redhat.com, peterx@redhat.com, farosas@suse.de, raphael.s.norwitz@gmail.com, bchaney@akamai.com, qemu-devel@nongnu.org, pbonzini@redhat.com, yc-core@yandex-team.ru, mark.caveayland@nutanix.com, Eric Blake Subject: Re: [PATCH v18 09/14] qapi: add local migration parameter Message-ID: References: <20260710191809.721154-1-vsementsov@yandex-team.ru> <20260710191809.721154-10-vsementsov@yandex-team.ru> <05c89310-7bec-4aac-addc-b5ef377e09a7@yandex-team.ru> <25b5e9a6-e563-4ab0-9075-04a3a00d3b33@yandex-team.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <25b5e9a6-e563-4ab0-9075-04a3a00d3b33@yandex-team.ru> User-Agent: Mutt/2.3.2 (2026-04-26) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: permerror client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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=-0.01, RCVD_IN_MSPIKE_WL=-0.01, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, T_SPF_PERMERROR=0.01 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development 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 Mon, Jul 13, 2026 at 08:55:37PM +0300, Vladimir Sementsov-Ogievskiy wrote: > On 13.07.26 14:21, Daniel P. Berrangé wrote: > > On Mon, Jul 13, 2026 at 01:55:48PM +0300, Vladimir Sementsov-Ogievskiy wrote: > > > On 13.07.26 12:51, Daniel P. Berrangé wrote: > > > > On Fri, Jul 10, 2026 at 10:17:58PM +0300, Vladimir Sementsov-Ogievskiy wrote: > > > > > We are going to implement local-migration feature: some devices will be > > > > > able to transfer open file descriptors through migration stream (which > > > > > must UNIX domain socket for that purpose). This allows to transfer the > > > > > whole backend state without reconnecting and restarting the backend > > > > > service. For example, virtio-net will migrate its attached TAP netdev, > > > > > together with its connected file descriptors. > > > > > > > > > > In this commit we introduce a migration parameter, which enables > > > > > the feature for devices that support it (none at the moment). > > > > > > > > > > Signed-off-by: Vladimir Sementsov-Ogievskiy > > > > > Acked-by: Markus Armbruster > > > > > Acked-by: Peter Xu > > > > > Reviewed-by: Ben Chaney > > > > > --- > > > > > include/migration/misc.h | 2 ++ > > > > > migration/options.c | 18 +++++++++++++++++- > > > > > qapi/migration.json | 12 ++++++++++-- > > > > > 3 files changed, 29 insertions(+), 3 deletions(-) > > > > > > > > > > > > > diff --git a/qapi/migration.json b/qapi/migration.json > > > > > index 66bd900465a..03bdf19f3a6 100644 > > > > > --- a/qapi/migration.json > > > > > +++ b/qapi/migration.json > > > > > @@ -830,7 +830,8 @@ > > > > > 'zero-page-detection', > > > > > 'direct-io', > > > > > { 'name': 'x-rdma-chunk-size', 'features': [ 'unstable' ] }, > > > > > - 'cpr-exec-command'] } > > > > > + 'cpr-exec-command', > > > > > + 'local'] } > > > > > ## > > > > > # @migrate-set-parameters: > > > > > @@ -1012,6 +1013,12 @@ > > > > > # Must be set to the same value on both source and destination > > > > > # before migration starts. (Since 11.1) > > > > > # > > > > > +# @local: Enable local migration for devices that support it. Backend > > > > > +# state and its file descriptors can then be passed to the > > > > > +# destination in the migration channel. The migration channel > > > > > +# must be a Unix domain socket. Usually needs to be enabled per > > > > > +# device. (Since 11.2) > > > > > > > > What happens when this is enabled and there are devices which > > > > don't support it ? > > > > > > These devices are migrated as usual, ignoring "local" option. > > > > > > > > > > > What happens when this is enabled and a device on the src > > > > does not support it but a device on the (newer) QEMU dest > > > > does support it ? How does the mgmt app know which devices > > > > support it ? > > > > > > The only supporting device (TAP-backend) declares support by > > > "local-migration-supported", so mgmt app should care to set > > > same value for it on host and target (like for other options > > > actually). Or simply relay on default, which is true starting > > > from 11.2 Machine Type. > > > > > > > > > > > Can we document the semantics in these cases. > > > > > > That's: "Usually needs to be enabled per device." > > > > ....except that we have it enabled by default for TAP backends > > in new machine types.... except that it will then break if the > > app/user has enabled any of the "forbidden" options. > > > > The way this doc is written makes it sound like "local" is an > > optimization you can turn on in any scenario, and it will do > > the right thing if the device supports it. That is very much > > not the case - enabling this flag will definitely break many > > configs out of the box, with new machine types due to the TAP > > device defaults & incompatible options. > > Ok, now we decided to NOT make default support for TAP in newer > machine types. > > So, enabling "local" is safe in existing scenarios, only explicit > enabling TAP.local-migration-supported will change the behavior. > > Keep "local" documentation as is? > > I see the only way to make it more informative: directly describe > connection with TAP.local-migration-supported, without general > phrases about "devices that support" and "usual". We'll have to > update it when more devices added (my next step is vhost-user-blk), > but at least, it would be absolutely correct at the moment. How about.... # @local: Permit the use of optimizations for local migration. # This must only be set when both the source and destination # QEMU processes are on the same OS and directly connected # with a UNIX domain socket as the migration channel to enable # use of file descriptor passing. Individual device backends # may need additional configuration flags set to enable local # migration optimizations. This will be documented against the # device backends where it applies. (Since 11.2) With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|