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=-20.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS autolearn=ham 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 3F535C433E6 for ; Fri, 5 Mar 2021 17:02:56 +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 D99346507C for ; Fri, 5 Mar 2021 17:02:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D99346507C 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]:55646 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lIDqo-0005Hl-Tj for qemu-devel@archiver.kernel.org; Fri, 05 Mar 2021 12:02:54 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:60934) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lIDkD-0006sg-T6 for qemu-devel@nongnu.org; Fri, 05 Mar 2021 11:56:06 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:38293) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lIDjz-0007AB-Bq for qemu-devel@nongnu.org; Fri, 05 Mar 2021 11:56:05 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614963349; 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=hNkuWjOrI8SckSnRLnxx+FN4aL9raBAHm2X/LISDeaE=; b=bbex7f/PMO/gYYtlyFfLeL+wufXkWDifji2/TqeZSzpnAvwZE9+GZ8POeL792QLKF2i4sk wYHk9yJeIQhAKDyNu9P5gDDlo/LgRzAqw5Z+4XOo95JjoFmHlgHAEOmXglDRAUBAEzbQhk /umgZM4c1bVnIHZk1MqHA1pekyrgJ1w= 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-298-rJQGhuAxN6CpmPnMHuqXeQ-1; Fri, 05 Mar 2021 11:55:44 -0500 X-MC-Unique: rJQGhuAxN6CpmPnMHuqXeQ-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 1C03410059D7; Fri, 5 Mar 2021 16:55:21 +0000 (UTC) Received: from merkur.redhat.com (ovpn-112-36.phx2.redhat.com [10.3.112.36]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0BDF460BF3; Fri, 5 Mar 2021 16:55:19 +0000 (UTC) From: Kevin Wolf To: qemu-block@nongnu.org Subject: [PULL 10/31] docs: show how to spawn qemu-storage-daemon with fd passing Date: Fri, 5 Mar 2021 17:54:33 +0100 Message-Id: <20210305165454.356840-11-kwolf@redhat.com> In-Reply-To: <20210305165454.356840-1-kwolf@redhat.com> References: <20210305165454.356840-1-kwolf@redhat.com> 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=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=kwolf@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: kwolf@redhat.com, peter.maydell@linaro.org, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" From: Stefan Hajnoczi The QMP monitor, NBD server, and vhost-user-blk export all support file descriptor passing. This is a useful technique because it allows the parent process to spawn and wait for qemu-storage-daemon without busy waiting, which may delay startup due to arbitrary sleep() calls. This Python example is inspired by the test case written for libnbd by Richard W.M. Jones : https://gitlab.com/nbdkit/libnbd/-/commit/89113f484effb0e6c322314ba75c1cbe07a04543 Thanks to Daniel P. Berrangé for suggestions on how to get this working. Now let's document it! Reported-by: Richard W.M. Jones Cc: Kevin Wolf Cc: Daniel P. Berrangé Signed-off-by: Stefan Hajnoczi Message-Id: <20210301172728.135331-2-stefanha@redhat.com> Reviewed-by: Daniel P. Berrangé Reviewed-by: Richard W.M. Jones Signed-off-by: Kevin Wolf --- docs/tools/qemu-storage-daemon.rst | 42 ++++++++++++++++++++++++++++-- 1 file changed, 40 insertions(+), 2 deletions(-) diff --git a/docs/tools/qemu-storage-daemon.rst b/docs/tools/qemu-storage-daemon.rst index 6ce85f2f7d..5714794775 100644 --- a/docs/tools/qemu-storage-daemon.rst +++ b/docs/tools/qemu-storage-daemon.rst @@ -101,10 +101,12 @@ Standard options: .. option:: --nbd-server addr.type=inet,addr.host=,addr.port=[,tls-creds=][,tls-authz=][,max-connections=] --nbd-server addr.type=unix,addr.path=[,tls-creds=][,tls-authz=][,max-connections=] + --nbd-server addr.type=fd,addr.str=[,tls-creds=][,tls-authz=][,max-connections=] is a server for NBD exports. Both TCP and UNIX domain sockets are supported. - TLS encryption can be configured using ``--object`` tls-creds-* and authz-* - secrets (see below). + A listen socket can be provided via file descriptor passing (see Examples + below). TLS encryption can be configured using ``--object`` tls-creds-* and + authz-* secrets (see below). To configure an NBD server on UNIX domain socket path ``/tmp/nbd.sock``:: @@ -141,6 +143,42 @@ QMP commands:: --chardev socket,path=qmp.sock,server=on,wait=off,id=char1 \ --monitor chardev=char1 +Launch the daemon from Python with a QMP monitor socket using file descriptor +passing so there is no need to busy wait for the QMP monitor to become +available:: + + #!/usr/bin/env python3 + import subprocess + import socket + + sock_path = '/var/run/qmp.sock' + + with socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) as listen_sock: + listen_sock.bind(sock_path) + listen_sock.listen() + + fd = listen_sock.fileno() + + subprocess.Popen( + ['qemu-storage-daemon', + '--chardev', f'socket,fd={fd},server=on,id=char1', + '--monitor', 'chardev=char1'], + pass_fds=[fd], + ) + + # listen_sock was automatically closed when leaving the 'with' statement + # body. If the daemon process terminated early then the following connect() + # will fail with "Connection refused" because no process has the listen + # socket open anymore. Launch errors can be detected this way. + + qmp_sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) + qmp_sock.connect(sock_path) + ...QMP interaction... + +The same socket spawning approach also works with the ``--nbd-server +addr.type=fd,addr.str=`` and ``--export +type=vhost-user-blk,addr.type=fd,addr.str=`` options. + Export raw image file ``disk.img`` over NBD UNIX domain socket ``nbd.sock``:: $ qemu-storage-daemon \ -- 2.29.2