From nobody Mon May 20 16:30:36 2024 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com ARC-Seal: i=1; a=rsa-sha256; t=1614612820; cv=none; d=zohomail.com; s=zohoarc; b=Ry1W18RcmVHRPBPCz1QM01Y9YL9yQIzhR4bbuBoCsXVbyFgbnx/kcsIqGlaCYXWa/v3i1l6M57+xuzHBbIKrDpH3G4dZlfUmmZzt5Ne7PT2A6342GI5XIAR37gDh+mSZ0yhYMctDg6MONUVAA2T690if5AW2iWHH0TCMYhheOGI= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1614612820; h=Content-Type:Content-Transfer-Encoding:Cc:Date:From:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:Sender:Subject:To; bh=vHslKbJrov1Sj5p7l3/ILTzgapFMZHegcDCUyzwPG4Q=; b=i1rWwk507MZaZ7IJuNzA31N/Hf+29wpSXT541R3bweUiFH0GopIbcc1288SWBtvCvgf/KFGrsXgPEZusVBnAIZzgQVhbTyYDqhyAekUJ4YB5OtZCX9wAS83SisbUvurHMvOZtfEvcfvJ2pWMmDDvLAe+PX+KFeSrrh6i6yiEt+s= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail header.from= (p=none dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1614612820287111.55511989472382; Mon, 1 Mar 2021 07:33:40 -0800 (PST) Received: from localhost ([::1]:47748 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lGkYF-0002e4-7z for importer@patchew.org; Mon, 01 Mar 2021 10:33:39 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:60516) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lGkWn-0001S0-7d for qemu-devel@nongnu.org; Mon, 01 Mar 2021 10:32:09 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:25558) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lGkWl-0002Fr-85 for qemu-devel@nongnu.org; Mon, 01 Mar 2021 10:32:08 -0500 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-420-KSBY1bzONI-SNRIfuc-g9w-1; Mon, 01 Mar 2021 10:32:04 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0109610CE780; Mon, 1 Mar 2021 15:32:04 +0000 (UTC) Received: from localhost (ovpn-115-54.ams2.redhat.com [10.36.115.54]) by smtp.corp.redhat.com (Postfix) with ESMTP id 92B7A5C1D1; Mon, 1 Mar 2021 15:32:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614612726; 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; bh=vHslKbJrov1Sj5p7l3/ILTzgapFMZHegcDCUyzwPG4Q=; b=es+pZ4XUTO4u08mYittFFJsox//0j3e8vvtETPEv6BkZ5UxzVIihFZpYm5Vdqk9tqtX3xC 1kjmjSRdg3oJUSb+3OVvY0Ll1acm2UYXbXxpl0hzpzYFHH9QVmy5cf9G1IpXB1iGYfr0AR WsfIQY9EqSe5VoZg4rE5J+5O+PsIfl8= X-MC-Unique: KSBY1bzONI-SNRIfuc-g9w-1 From: Stefan Hajnoczi To: qemu-devel@nongnu.org Subject: [PATCH] docs: show how to spawn qemu-storage-daemon with fd passing Date: Mon, 1 Mar 2021 15:31:59 +0000 Message-Id: <20210301153159.35660-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=63.128.21.124; envelope-from=stefanha@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: Kevin Wolf , =?UTF-8?q?Daniel=20P=20=2E=20Berrang=C3=A9?= , Stefan Hajnoczi , qemu-block@nongnu.org, "Richard W . M . Jones" Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" 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/89113f484effb0e6c322314ba75c1cbe0= 7a04543 Thanks to Daniel P. Berrang=C3=A9 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. Berrang=C3=A9 Signed-off-by: Stefan Hajnoczi Reviewed-by: Richard W.M. Jones --- docs/tools/qemu-storage-daemon.rst | 38 ++++++++++++++++++++++++++++-- 1 file changed, 36 insertions(+), 2 deletions(-) diff --git a/docs/tools/qemu-storage-daemon.rst b/docs/tools/qemu-storage-d= aemon.rst index f63627eaf6..45854c131e 100644 --- a/docs/tools/qemu-storage-daemon.rst +++ b/docs/tools/qemu-storage-daemon.rst @@ -101,10 +101,12 @@ Standard options: =20 .. option:: --nbd-server addr.type=3Dinet,addr.host=3D,addr.port=3D<= port>[,tls-creds=3D][,tls-authz=3D][,max-connections=3D] --nbd-server addr.type=3Dunix,addr.path=3D[,tls-creds=3D][,tls= -authz=3D][,max-connections=3D] + --nbd-server addr.type=3Dfd,addr.str=3D[,tls-creds=3D][,tls-auth= z=3D][,max-connections=3D] =20 is a server for NBD exports. Both TCP and UNIX domain sockets are suppor= ted. - TLS encryption can be configured using ``--object`` tls-creds-* and auth= z-* - 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). =20 To configure an NBD server on UNIX domain socket path ``/tmp/nbd.sock``:: =20 @@ -127,6 +129,38 @@ QMP commands:: --chardev socket,path=3Dqmp.sock,server,nowait,id=3Dchar1 \ --monitor chardev=3Dchar1 =20 +Launch the daemon from Python with a QMP monitor socket using file descrip= tor +passing so there is no need to busy wait for the QMP monitor to become +available:: + + #!/usr/bin/env python3 + import os + import subprocess + import socket + + sock_path =3D '/tmp/qmp-{}.sock'.format(os.getpid()) + + with socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) as listen_sock: + listen_sock.bind(sock_path) + listen_sock.listen() + + fd =3D listen_sock.fileno() + + subprocess.Popen( + ['qemu-storage-daemon', + '--chardev', f'socket,fd=3D{fd},server=3Don,id=3Dchar1', + '--monitor', 'chardev=3Dchar1'], + pass_fds=3D[fd], + ) + + qmp_sock =3D 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=3Dfd,addr.str=3D`` and ``--export +type=3Dvhost-user-blk,addr.type=3Dfd,addr.str=3D`` options. + Export raw image file ``disk.img`` over NBD UNIX domain socket ``nbd.sock`= `:: =20 $ qemu-storage-daemon \ --=20 2.29.2