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=-2.2 required=3.0 tests=FROM_EXCESS_BASE64, 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 7A4B7C606C1 for ; Mon, 8 Jul 2019 16:07:45 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 46807204EC for ; Mon, 8 Jul 2019 16:07:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 46807204EC Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:43162 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hkWB4-0006zo-IU for qemu-devel@archiver.kernel.org; Mon, 08 Jul 2019 12:07:42 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42719) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hkW8N-0005uh-Iy for qemu-devel@nongnu.org; Mon, 08 Jul 2019 12:04:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hkW8L-0006bZ-M3 for qemu-devel@nongnu.org; Mon, 08 Jul 2019 12:04:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48010) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hkW8L-0006T7-FM for qemu-devel@nongnu.org; Mon, 08 Jul 2019 12:04:53 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 48FF883F51 for ; Mon, 8 Jul 2019 16:04:48 +0000 (UTC) Received: from redhat.com (unknown [10.42.17.95]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 154691001B19; Mon, 8 Jul 2019 16:04:44 +0000 (UTC) Date: Mon, 8 Jul 2019 17:04:42 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau Message-ID: <20190708160442.GL3082@redhat.com> References: <20190708072437.3339-1-marcandre.lureau@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190708072437.3339-1-marcandre.lureau@redhat.com> User-Agent: Mutt/1.12.0 (2019-05-25) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Mon, 08 Jul 2019 16:04:48 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH 0/3] Add dbus-vmstate X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Laurent Vivier , Thomas Huth , Juan Quintela , qemu-devel@nongnu.org, "Dr. David Alan Gilbert" , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Jul 08, 2019 at 11:24:34AM +0400, Marc-Andr=C3=A9 Lureau wrote: > Hi, >=20 > With external processes or helpers participating to the VM support, it > becomes necessary to handle their migration. Various options exist to > transfer their state: > 1) as the VM memory, RAM or devices (we could say that's how > vhost-user devices can be handled today, they are expected to > restore from ring state) > 2) other "vmstate" (as with TPM emulator state blobs) > 3) left to be handled by management layer >=20 > 1) is not practical, since an external processes may legitimatelly > need arbitrary state date to back a device or a service, or may not > even have an associated device. >=20 > 2) needs ad-hoc code for each helper, but is simple and working >=20 > 3) is complicated for management layer, QEMU has the migration timing >=20 > The proposed "dbus-vmstate" object will connect to a given D-Bus > address, and save/load from org.qemu.VMState1 owners on migration. >=20 > Thus helpers can easily have their state migrated with QEMU, without > implementing ad-hoc support (such as done for TPM emulation) >=20 > I chose D-Bus as it is ubiquitous on Linux (it is systemd IPC), and > can be made to work on various other OSes. There are several > implementations and good bindings for various languages. > (the tests/dbus-vmstate-test.c is a good example of how simple > the implementation of services can be, even in C) >=20 > The D-Bus protocol can be made to work peer-to-peer, but the most > common and practical way is through a bus daemon. This also has the > advantage of increased debuggability (you can eavesdrop on the bus and > introspect it). The downside of using the bus daemon is that we have to spawn a new instance of dbus-daemon for every QEMU VM that's running on the host, which is yet more memory overhead for each VM & another process to manage, and yet another thing to go wrong. QEMU already has a direct UNIX socket connection to the helper processes in question. I'd much rather we just had another direct UNIX socket connection to that helper, using D-Bus peer-to-peer. The benefit of debugging doesn't feel compelling enough to justify running an extra daemon for each VM. Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|