From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by passt.top (Postfix) with ESMTP id D54E15A005E for ; Thu, 9 Feb 2023 11:31:12 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1675938671; 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=Vur81fNvGyzTA17YWj4lN54RVS9kk8x+nu6niRJ+JNw=; b=ExKeKPuNvbEK1hC/0xjWVw6pptUXxWSBffucuCtZymmNlGf14P0pgF3rmsvSf4q2pS6wQW H2lMgPDO1OXA3AvnKyAZKDUaRGgpp0jqe5FPv7YMT6cvPhNMgeHPaj2s7XT6VqwspIatDq Bh4jp1plKtVFj4nBE2A5C1av0A79OAA= 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-269-F4BEEjS4OH2lyhTHnKkHPw-1; Thu, 09 Feb 2023 05:31:04 -0500 X-MC-Unique: F4BEEjS4OH2lyhTHnKkHPw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 80DBB802C1D for ; Thu, 9 Feb 2023 10:31:04 +0000 (UTC) Received: from maya.cloud.tilaa.com (ovpn-208-4.brq.redhat.com [10.40.208.4]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BAFE9C16022; Thu, 9 Feb 2023 10:31:03 +0000 (UTC) Date: Thu, 9 Feb 2023 11:31:01 +0100 From: Stefano Brivio To: Michal =?UTF-8?B?UHLDrXZvem7DrWs=?= Subject: Re: [libvirt PATCH] qemu: allow passt to self-daemonize Message-ID: <20230209113101.057d986c@elisabeth> In-Reply-To: <41d2c66b-cb07-6e4a-4dd9-615ce46d5497@redhat.com> References: <20230208231310.1728051-1-laine@redhat.com> <41d2c66b-cb07-6e4a-4dd9-615ce46d5497@redhat.com> Organization: Red Hat MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Message-ID-Hash: 3QP3DEUTMV5RAFGEAELAKJH4EA5GGVWR X-Message-ID-Hash: 3QP3DEUTMV5RAFGEAELAKJH4EA5GGVWR X-MailFrom: sbrivio@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: Laine Stump , libvir-list@redhat.com, passt-dev@passt.top X-Mailman-Version: 3.3.3 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Thu, 9 Feb 2023 09:52:00 +0100 Michal Pr=C3=ADvozn=C3=ADk wrote: > On 2/9/23 00:13, Laine Stump wrote: > > I initially had the passt process being started in an identical > > fashion to the slirp-helper - libvirt was daemonizing the new process > > and recording its pid in a pidfile. The problem with this is that, > > since it is daemonized immediately, any startup error in passt happens > > after the daemonization, and thus isn't seen by libvirt - libvirt > > believes that the process has started successfully and continues on > > its merry way. The result was that sometimes a guest would be started, > > but there would be no passt process for qemu to use for network > > traffic. > >=20 > > Instead, we should be starting passt in the same manner we start > > dnsmasq - we just exec it as normal (along with a request that passt > > create the pidfile, which is just another option on the passt > > commandline) and wait for the child process to exit; passt then has a > > chance to parse its commandline and complete all the setup prior to > > daemonizing itself; if it encounters an error and exits with a non-0 > > code, libvirt will see the code and know about the failure. We can > > then grab the output from stderr, log that so the "user" has some idea > > of what went wrong, and then fail the guest startup. > >=20 > > Signed-off-by: Laine Stump > > --- > > src/qemu/qemu_passt.c | 9 ++++----- > > 1 file changed, 4 insertions(+), 5 deletions(-) > >=20 > > diff --git a/src/qemu/qemu_passt.c b/src/qemu/qemu_passt.c > > index 0f09bf3db8..f640a69c00 100644 > > --- a/src/qemu/qemu_passt.c > > +++ b/src/qemu/qemu_passt.c > > @@ -141,24 +141,23 @@ qemuPasstStart(virDomainObj *vm, > > g_autofree char *passtSocketName =3D qemuPasstCreateSocketPath(vm,= net); > > g_autoptr(virCommand) cmd =3D NULL; > > g_autofree char *pidfile =3D qemuPasstCreatePidFilename(vm, net); > > + g_autofree char *errbuf =3D NULL; > > char macaddr[VIR_MAC_STRING_BUFLEN]; > > size_t i; > > pid_t pid =3D (pid_t) -1; > > int exitstatus =3D 0; > > int cmdret =3D 0; > > - VIR_AUTOCLOSE errfd =3D -1; > > =20 > > cmd =3D virCommandNew(PASST); > > =20 > > virCommandClearCaps(cmd); > > - virCommandSetPidFile(cmd, pidfile); > > - virCommandSetErrorFD(cmd, &errfd); > > - virCommandDaemonize(cmd); > > + virCommandSetErrorBuffer(cmd, &errbuf); > > =20 > > virCommandAddArgList(cmd, > > "--one-off", > > "--socket", passtSocketName, > > "--mac-addr", virMacAddrFormat(&net->mac, mac= addr), > > + "--pid", pidfile, =20 >=20 > The only problem with this approach is that our virPidFile*() functions > rely on locking the very first byte. And when reading the pidfile, we > try to lock the file and if we succeeded it means the file wasn't locked > which means the process holding the lock died and thus the pid in the > pidfile is stale. >=20 > Now, I don't see passt locking the pidfile at all. So effectively, after > this patch qemuPasstStop() would do nothing (well, okay, it'll remove > the pidfile), qemuPasstSetupCgroup() does nothing, etc. And it doesn't need to do anything, actually! passt is started with the --one-off option: -1, --one-off Quit after handling a single client connection, that is, o= nce the client closes the socket, or once we get a socket error. well, removing the PID file is nice (passt can't do it as it won't see the filesystem after starting up), but that's about it. --=20 Stefano