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 D0442C73C7C for ; Wed, 10 Jul 2019 09:11:37 +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 9FEBD20665 for ; Wed, 10 Jul 2019 09:11:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9FEBD20665 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]:59224 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hl8dU-00042J-JZ for qemu-devel@archiver.kernel.org; Wed, 10 Jul 2019 05:11:36 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42782) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hl8cW-0003bU-UC for qemu-devel@nongnu.org; Wed, 10 Jul 2019 05:10:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hl8cU-0002If-Uk for qemu-devel@nongnu.org; Wed, 10 Jul 2019 05:10:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48210) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hl8cO-0001t0-K6 for qemu-devel@nongnu.org; Wed, 10 Jul 2019 05:10:30 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 68E5C30917AB; Wed, 10 Jul 2019 09:10:24 +0000 (UTC) Received: from redhat.com (ovpn-112-53.ams2.redhat.com [10.36.112.53]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 07EAF5D9CC; Wed, 10 Jul 2019 09:10:18 +0000 (UTC) Date: Wed, 10 Jul 2019 10:10:13 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau Message-ID: <20190710091013.GD30831@redhat.com> References: <20190708072437.3339-1-marcandre.lureau@redhat.com> <20190708160442.GL3082@redhat.com> <20190709090153.GD8664@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.0 (2019-05-25) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Wed, 10 Jul 2019 09:10:24 +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 , "Dr. David Alan Gilbert" , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Jul 09, 2019 at 02:47:32PM +0400, Marc-Andr=C3=A9 Lureau wrote: > Hi >=20 > On Tue, Jul 9, 2019 at 1:02 PM Daniel P. Berrang=C3=A9 wrote: > > > > On Tue, Jul 09, 2019 at 12:26:38PM +0400, Marc-Andr=C3=A9 Lureau wrot= e: > > > Hi > > > > > > On Mon, Jul 8, 2019 at 8:04 PM Daniel P. Berrang=C3=A9 wrote: > > > > 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 justif= y > > > > running an extra daemon for each VM. > > > > > > I wouldn't minor the need for easier debugging. Debugging multiple > > > processes talking to each other is really hard. Having a bus is > > > awesome (if not required) in this case. > > > > > > There are other advantages of using a bus, those come to my mind: > > > > > > - less connections (bus topology) > > > > That applies to general use of DBus, but doesn't really apply to > > the proposed QEMU usage, as every single helper is talking to the > > same QEMU endpoint. So if we have 10 helpers, in p2p mode, we > > get 10 sockets open between the helper & QEMU. In bus mode, we > > get 10 sockets open between the helper & dbus and another socket > > open between dbus & QEMU. The bus is only a win in connections > > if you have a mesh-like connection topology not hub & spoke. >=20 > The mesh already exist, as it's not just QEMU that want to talk to the > helpers, but the management layer, and 3rd parties (debug tools, > audit, other management tools etc). There are also cases where helpers > may want to talk to each other. Taking networking as an example, 2 > slirp interfaces may want to share the same DHCP, bootp/TFTP, > filter/service provider. Redirection/forwarding may be provided on > demand (chardev-like services). The same is probably true for block > layers, security, GPU/display etc. In this case, the bus topology > makes more sense than hiding it under. These are alot of scenarios / use cases not described in the cover letter for this series. I'm reviewing this series from the POV of the need to transfer vmstate from a helper back to QEMU, which was the scenario in the cover letter. From this I see no need for a bus. If you think there's a more general use cases involving QEMU backends that will need the bus, then I think the bigger picture needs to be described when proposing the use of the bus, instead of only describing the very simple vmstate use case as the motivation. 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 :|