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=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 09046C43470 for ; Fri, 23 Apr 2021 16:57:11 +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 8D07061006 for ; Fri, 23 Apr 2021 16:57:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8D07061006 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]:42050 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lZz77-0001ja-NJ for qemu-devel@archiver.kernel.org; Fri, 23 Apr 2021 12:57:09 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:36548) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lZz4V-0008Ko-AO for qemu-devel@nongnu.org; Fri, 23 Apr 2021 12:54:29 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:54015) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lZz4K-0008Ar-Bk for qemu-devel@nongnu.org; Fri, 23 Apr 2021 12:54:24 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1619196854; h=from:from: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=nFmKihOZ13MtuisFQ6/Ztg0w1zdx/xt6O5SsoVc+DmA=; b=UOZpogtoyGEhwr0UgAiFUESqpQSVua4ta9oYXxIS0Z8WIAjlM43q2+tX1A1Kr8SuIpQCsQ eKkqMzwGqyU1DdB5vZ5kCPenmrnOk6mvWmHslcDAKzO4mlqEPOH3V+iHdO/tg+vpfpLWHb p6CSkfZOagEzc4vz1lcGqXtvS/bft6c= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-470-Vyvrez5QOa2czRIQ1rYHDw-1; Fri, 23 Apr 2021 12:54:12 -0400 X-MC-Unique: Vyvrez5QOa2czRIQ1rYHDw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B812383DD20; Fri, 23 Apr 2021 16:54:11 +0000 (UTC) Received: from maya.cloud.tilaa.com (unknown [10.36.110.6]) by smtp.corp.redhat.com (Postfix) with ESMTP id 527B060C4A; Fri, 23 Apr 2021 16:54:11 +0000 (UTC) Received: from localhost (238-055-210-188.ip-addr.inexio.net [188.210.55.238]) by maya.cloud.tilaa.com (Postfix) with ESMTPSA id 880DE4009B; Fri, 23 Apr 2021 18:54:10 +0200 (CEST) Date: Fri, 23 Apr 2021 18:54:08 +0200 From: Stefano Brivio To: "Daniel P. =?UTF-8?B?QmVycmFuZ8Op?=" Subject: Re: socket.c added support for unix domain socket datagram transport Message-ID: <20210423185408.6d5d14f0@redhat.com> In-Reply-To: References: <1C0E1BC5-904F-46B0-8044-68E43E67BE60@gmail.com> <20210423172940.14f48b49@elisabeth> Organization: Red Hat MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=sbrivio@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=170.10.133.124; envelope-from=sbrivio@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Ralph Schmieder , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, 23 Apr 2021 17:21:38 +0100 Daniel P. Berrang=C3=A9 wrote: > On Fri, Apr 23, 2021 at 05:29:40PM +0200, Stefano Brivio wrote: > > Hi Ralph, > >=20 > > On Fri, 23 Apr 2021 08:56:48 +0200 > > Ralph Schmieder wrote: > > =20 > > > Hey... new to this list. I was looking for a way to use Unix domain > > > sockets as a network transport between local VMs. > > >=20 > > > I'm part of a team where we run dozens if not hundreds of VMs on a > > > single compute instance which are highly interconnected. > > >=20 > > > In the current implementation, I use UDP sockets (e.g. something like= =20 > > >=20 > > > -netdev > > > id=3Dbla,type=3Dsocket,udp=3Dlocalhost:1234,localaddr=3Dlocalhost:567= 8)=20 > > >=20 > > > which works great. > > >=20 > > > The downside of this approach is that I need to keep track of all the > > > UDP ports in use and that there's a potential for clashes. Clearly, > > > having Unix domain sockets where I could store the sockets in the > > > VM's directory would be much easier to manage. > > >=20 > > > However, even though there is some AF_UNIX support in net/socket.c, > > > it's > > >=20 > > > - not configurable > > > - it doesn't work =20 > >=20 > > I hate to say this, but I've been working on something very similar > > just in the past days, with the notable difference that I'm using > > stream-oriented AF_UNIX sockets instead of datagram-oriented. > >=20 > > I have a similar use case, and after some experiments I picked a > > stream-oriented socket over datagram-oriented because: > >=20 > > - overhead appears to be the same > >=20 > > - message boundaries make little sense here -- you already have a > > 32-bit vnet header with the message size defining the message > > boundaries > >=20 > > - datagram-oriented AF_UNIX sockets are actually reliable and there's > > no packet reordering on Linux, but this is not "formally" guaranteed > >=20 > > - it's helpful for me to know when a qemu instance disconnects for any > > reason =20 >=20 > The current IP socket impl for the net socket backend uses SOCK_DGRAM, > so from a consistency POV it feels sensible todo the same for UNIX > sockets too. That's just for UDP though -- it also supports TCP with the "connect=3D" parameter, and given that a stream-oriented AF_UNIX socket behaves very similarly, I recycled that parameter and just extended that bit of documentation. > None the less, your last point in particular about wanting to know > about disconnects feels valid, and if its useful to you for UNIX > sockets, then it ought to be useful for IP sockets too. >=20 > IOW, I wonder if we should use DGRAM for UNIX sockets too by default > to match current behaviour, but then also add a CLI option that allows > choice of DGRAM vs STREAM, and wire that up for IP & UNIX sockets. The choice would only apply to AF_UNIX (that is, not to TCP and UDP). The current situation isn't entirely consistent, because for TCP you have "connect=3D", for UDP it's "udp=3D" or "mcast=3D", and I'm extending t= he "connect=3D" case to support stream-oriented AF_UNIX, which I think is consistent. However, to have it symmetric for the datagram-oriented case (UDP and AF_UNIX), ideally it should be changed to "dgram=3Dhost:port|path" -- which I guess we can't do. I see two alternatives: 1. - "connect=3D" (TCP only) - "unix=3Dpath,type=3Ddgram|stream" - "udp=3D" (UDP only) 2. - "connect=3D" (TCP and AF_UNIX stream) - "unix_dgram=3D" - "udp=3D" (UDP only) The major thing I like of 2. is that we save some code and a further option, but other than that I don't have a strong preference. --=20 Stefano