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 1EB4AC27C76 for ; Sat, 28 Jan 2023 07:51:51 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pLfzS-0001xw-Ha; Sat, 28 Jan 2023 02:51:11 -0500 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 1pLfzO-0001vQ-PX for qemu-devel@nongnu.org; Sat, 28 Jan 2023 02:51:06 -0500 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 1pLfzJ-00055S-SR for qemu-devel@nongnu.org; Sat, 28 Jan 2023 02:51:06 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1674892261; 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: in-reply-to:in-reply-to:references:references; bh=NKhFxAMR8g325BDIgIg+y3a5WRV0QjaPLiyYEkF+pR4=; b=BBZbEhZgzzoV6Szy7Y4HBLi9374FfAN7FI+GHBc9QMlFhhjIa9jOvbrk0hPuw8wgF05BFA qFpmSeE4UinZJzBsFeJCMWUV1SPHpOTFM1cOyLKTFj2gtviInbMEUW7dLV+m0nBc+rhTKL yh6+7yrKRYtjbwP2fPy3E4rqBOrYLXQ= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-515-3MCYCe-wNYu60bEQbf8odA-1; Sat, 28 Jan 2023 02:49:38 -0500 X-MC-Unique: 3MCYCe-wNYu60bEQbf8odA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 9F96585C069; Sat, 28 Jan 2023 07:49:37 +0000 (UTC) Received: from localhost (unknown [10.39.195.119]) by smtp.corp.redhat.com (Postfix) with ESMTP id F2A392166B26; Sat, 28 Jan 2023 07:49:36 +0000 (UTC) Date: Sat, 28 Jan 2023 07:49:35 +0000 From: "Richard W.M. Jones" To: Eric Blake Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, berrange@redhat.com, kwolf@redhat.com Subject: Re: RFC: towards systemd socket activation in q-s-d Message-ID: <20230128074935.GO7636@redhat.com> References: <20230127212233.k6rlqkmubhovjxs4@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230127212233.k6rlqkmubhovjxs4@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 Received-SPF: pass client-ip=170.10.129.124; envelope-from=rjones@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, 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_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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: , 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, Jan 27, 2023 at 03:26:15PM -0600, Eric Blake wrote: > In https://bugzilla.redhat.com/show_bug.cgi?id=2055229, the question > was raised on how to make qemu-storage-daemon sufficiently powerful to > be a full-blown replacement to qemu-nbd. One of the features still > lacking is the ability to do systemd socket activation (qemu-nbd does > this, qemu-storage-daemon needs a way to do it). > > But that bug further noted that systemd supports LISTEN_FDNAMES to > supply names to a passed-in fd (right now, qemu-nbd does not use > names, but merely expects one fd in LISTEN_FDS). Dan had the idea > that it would be nice to write a systemd file that passes in a socket > name for a QMP socket, as in: > > [Socket] > ListenStream=/var/run/myapp/qsd.qmp > FileDescriptorName=qmp > Service=myapp-qsd.service > > and further notes that QAPI SocketAddressType supports @fd which is a > name in QMP (a previously-added fd passed through the older 'getfd' > command, rather than the newer 'add-fd' command), but an integer on > the command line. With LISTEN_FDNAMES, we could mix systemd socket > activation with named fds for any command line usage that already > supports SocketAddressType (not limited to just q-s-d usage). I couldn't find a good description of LISTEN_FDNAMES anywhere, and we don't use it in libnbd / nbdkit / qemu-nbd right now. So here's my interpretation of what this environment variable means ... Currently systemd socket activation in qemu-nbd or nbdkit uses only LISTEN_PID and LISTEN_FDS, usually with a single fd being passed. (I'll ignore LISTEN_PID.) So: LISTEN_FDS=1 fd 3 --> NBD socket This works because there's only one NBD protocol, it doesn't need to be named. However if we imagine that a superserver wants to run a webserver, it might need to pass two sockets carrying distinct protocols (HTTP and HTTPS). In this case it would use: LISTEN_FDS=2 fd 3 --> HTTP socket fd 4 --> HTTPS socket LISTEN_FDNAMES=http:https LISTEN_FDNAMES is telling the webserver that the first socket is HTTP and the second is HTTPS, so it knows which protocol to negotiate on each socket. I believe what you're saying above is that you'd like to have the ability to pass multiple sockets to q-s-d carrying distinct protocols, with the obvious ones being NBD + QMP (although other combinations could be possible, eg. NBD + vhost + QMP?): LISTEN_FDS=2 fd 3 --> NBD socket fd 4 --> QMP socket LISTEN_FDNAMES=nbd:qmp If my understanding is correct, then this makes sense. We might also modify libnbd to pass LISTEN_FDNAMES=nbd in: https://gitlab.com/nbdkit/libnbd/-/blob/master/generator/states-connect-socket-activation.c (Current servers would ignore the new environment variable.) > I'm at a point where I can take a shot at implementing this, but want > some feedback on whether it is better to try to shoehorn a generic > solution into the existing @fd member of the SocketAddressType union, > or whether it would be better to add yet another union member > @systemd-fd or some similar name to make it explicit when a command > line parameter wants to refer to an fd being passed through systemd > socket activation LISTEN_FDS and friends. It sounds like the q-s-d command lines will be even more convoluted and inelegant than before. That's fine, but please keep qemu-nbd around as a sane alternative. It might in the end just be a wrapper that translates the command line to q-s-d. I don't believe it's ever going to be possible or desirable to deprecate or remove qemu-nbd. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-builder quickly builds VMs from scratch http://libguestfs.org/virt-builder.1.html