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 3CCC5C3DA4A for ; Fri, 16 Aug 2024 15:17:27 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1seyhP-0007kB-Pk; Fri, 16 Aug 2024 11:17:07 -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 1seyhO-0007ek-99 for qemu-devel@nongnu.org; Fri, 16 Aug 2024 11:17:06 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1seyhM-0007yQ-AD for qemu-devel@nongnu.org; Fri, 16 Aug 2024 11:17:06 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1723821422; 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:in-reply-to:in-reply-to: references:references; bh=h268iraODaINcGNSXqFo17MOMSjBV5lzLDaKD99mPpI=; b=iTrjkBBpixlWcMNhz0zGuCqGqHx7uDfzNBorxDB5V2R6Id/VQkHOrQytgaMY2Y9kswMMpd Ofi242N3X8q6T8ejqaYX/QpO354/GtSQGrr+PijoXBlgcANPPYxn3B1bQ9+kU5mhp1gPUD z5EXZBxaBbNJdYV6TJZEfbnrnfnmBz8= Received: from mx-prod-mc-04.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-671-XNZYqBDbMdCelGLaJd8Z8A-1; Fri, 16 Aug 2024 11:16:59 -0400 X-MC-Unique: XNZYqBDbMdCelGLaJd8Z8A-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-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id DAF731955BF9; Fri, 16 Aug 2024 15:16:57 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.143]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 95C3B19560A3; Fri, 16 Aug 2024 15:16:54 +0000 (UTC) Date: Fri, 16 Aug 2024 16:16:50 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Peter Xu Cc: Steven Sistare , qemu-devel@nongnu.org, Fabiano Rosas , David Hildenbrand , Marcel Apfelbaum , Eduardo Habkost , Philippe Mathieu-Daude , Paolo Bonzini , Markus Armbruster Subject: Re: [PATCH V2 00/11] Live update: cpr-exec Message-ID: References: <1719776434-435013-1-git-send-email-steven.sistare@oracle.com> <5776f6b4-c55f-4e56-aac5-bee7e441ad15@oracle.com> <46b63356-9602-4fa2-9d31-186f5f85151f@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: 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=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.131, 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, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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, Aug 16, 2024 at 11:06:10AM -0400, Peter Xu wrote: > On Thu, Aug 15, 2024 at 04:55:20PM -0400, Steven Sistare wrote: > > On 8/13/2024 3:46 PM, Peter Xu wrote: > > > On Tue, Aug 06, 2024 at 04:56:18PM -0400, Steven Sistare wrote: > > > > > The flipside, however, is that localhost migration via 2 separate QEMU > > > > > processes has issues where both QEMUs want to be opening the very same > > > > > file, and only 1 of them can ever have them open. > > > > > > I thought we used to have similar issue with block devices, but I assume > > > it's solved for years (and whoever owns it will take proper file lock, > > > IIRC, and QEMU migration should properly serialize the time window on who's > > > going to take the file lock). > > > > > > Maybe this is about something else? > > > > I don't have an example where this fails. > > > > I can cause "Failed to get "write" lock" errors if two qemu instances open > > the same block device, but the error is suppressed if you add the -incoming > > argument, due to this code: > > > > blk_attach_dev() > > if (runstate_check(RUN_STATE_INMIGRATE)) > > blk->disable_perm = true; > > Yep, this one is pretty much expected. > > > > > > > Indeed, and "files" includes unix domain sockets. > > > > More on this -- the second qemu to bind a unix domain socket for listening > > wins, and the first qemu loses it (because second qemu unlinks and recreates > > the socket path before binding on the assumption that it is stale). > > > > One must use a different name for the socket for second qemu, and clients > > that wish to connect must be aware of the new port. > > > > > > Network ports also conflict. > > > > cpr-exec avoids such problems, and is one of the advantages of the method that > > > > I forgot to promote. > > > > > > I was thinking that's fine, as the host ports should be the backend of the > > > VM ports only anyway so they don't need to be identical on both sides? > > > > > > IOW, my understanding is it's the guest IP/ports/... which should still be > > > stable across migrations, where the host ports can be different as long as > > > the host ports can forward guest port messages correctly? > > > > Yes, one must use a different host port number for the second qemu, and clients > > that wish to connect must be aware of the new port. > > > > That is my point -- cpr-transfer requires fiddling with such things. > > cpr-exec does not. > > Right, and my understanding is all these facilities are already there, so > no new code should be needed on reconnect issues if to support cpr-transfer > in Libvirt or similar management layers that supports migrations. Note Libvirt explicitly blocks localhost migration today because solving all these clashing resource problems is a huge can of worms and it can't be made invisible to the user of libvirt in any practical way. 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 :|