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 lists1p.gnu.org (lists1p.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 410D2C4452B for ; Mon, 20 Jul 2026 11:21:42 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wlm3u-0005LV-Gs; Mon, 20 Jul 2026 07:21:30 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wlm3s-0005JJ-RZ for qemu-arm@nongnu.org; Mon, 20 Jul 2026 07:21:28 -0400 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 1wlm3r-0006JS-77 for qemu-arm@nongnu.org; Mon, 20 Jul 2026 07:21:28 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1784546486; 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=CbY95mxV5ei+0P0HY54yC9Kcg5bRwKf3usDUHzvfs1A=; b=PsTXJtYdOyaekLpBJUdZCGxQrHO+1kmZV3wegZni0uQgJTxOdX2f3UXkau04NDcA6rNUXi 5GVXLiTWnoxwLJ3CGIWdf/VvjDKToTKOkcQ9jzIvtbv0T+4Qn334PVLLCtGhK/5VJxkms1 DJDzh/3UIMiT+NOQodMs5ofmioF/OFE= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-509-Nxxdt3x0OXexPndfcfk_jQ-1; Mon, 20 Jul 2026 07:21:22 -0400 X-MC-Unique: Nxxdt3x0OXexPndfcfk_jQ-1 X-Mimecast-MFC-AGG-ID: Nxxdt3x0OXexPndfcfk_jQ_1784546480 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A0B871800662; Mon, 20 Jul 2026 11:21:19 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.4]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 6D6D330001BE; Mon, 20 Jul 2026 11:21:18 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id E2EA421E6920; Mon, 20 Jul 2026 13:21:15 +0200 (CEST) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Cc: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Peter Maydell , qemu-devel@nongnu.org, Jan Kiszka , qemu-arm@nongnu.org, BALATON Zoltan , qemu-ppc@nongnu.org, Huacai Chen , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Jiaxun Yang , Gerd Hoffmann Subject: Re: A few Machines crash when "no default audio driver available" In-Reply-To: ("Daniel P. =?utf-8?Q?Berrang?= =?utf-8?Q?=C3=A9=22's?= message of "Thu, 9 Jul 2026 16:58:48 +0100") References: <87o6gge6b0.fsf@pond.sub.org> <87zf00cn7m.fsf@pond.sub.org> Date: Mon, 20 Jul 2026 13:21:15 +0200 Message-ID: <87wlupvrdg.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-Mimecast-MFC-PROC-ID: elMjniBbqrT3BbnxGOrNff-dsA7sthgm4SOHrku2ltw_1784546480 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: permerror client-ip=170.10.129.124; envelope-from=armbru@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, 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_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.01, SPF_HELO_PASS=-0.001, T_SPF_PERMERROR=0.01 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-arm@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-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Sender: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Daniel P. Berrang=C3=A9 writes: > On Thu, Jul 09, 2026 at 07:31:31PM +0400, Marc-Andr=C3=A9 Lureau wrote: >> Hi >>=20 >> On Thu, Jul 9, 2026 at 6:02=E2=80=AFPM Daniel P. Berrang=C3=A9 wrote: >> > >> > On Thu, Jul 09, 2026 at 05:54:30PM +0400, Marc-Andr=C3=A9 Lureau wrote= : >> > > Hi >> > > >> > > On Thu, Jul 9, 2026 at 5:44=E2=80=AFPM Peter Maydell wrote: >> > > > >> > > > On Thu, 9 Jul 2026 at 14:32, Daniel P. Berrang=C3=A9 wrote: >> > > > > >> > > > > On Thu, Jul 09, 2026 at 03:22:05PM +0200, Markus Armbruster wrot= e: >> > > > > > Cc: mainainters for "Overall Audio backends" >> > > > > > Peter Maydell writes: >> > > > > > >> > > > > > > On Thu, 9 Jul 2026 at 12:44, Markus Armbruster wrote: >> > > > > > >> >> > > > > > >> I stumbled over ARM machine musicpal, PPC machines pegasos1= , pegasos2, >> > > > > > >> and MIPS machine fuloong2e crashes. >> > > > > > >> >> > > > > > >> I run them like this: >> > > > > > >> >> > > > > > >> $ qemu-system-aarch64 -M musicpal -nodefaults -S -display n= one -monitor stdio >> > > > > > > >> > > > > > >> Died when device_set_realized() tried to propagate a "no de= fault audio >> > > > > > >> driver available" error to &error_abort. >> > > > > > > >> > > > > > > Is this something we want to have be a possibility the devic= es >> > > > > > > have to cope with? Can we have the "ignores all audio data" >> > > > > > > backend be always available instead? >> > > > > > >> > > > > > There's plenty of precedence for /dev/null-like backends. >> > > > > > >> > > > > > > Otherwise every audio device needs to cope with "there is no >> > > > > > > audio backend available" and implement "do nothing with the >> > > > > > > audio data" itself. >> > > > > > >> > > > > > Yes. >> > > > > >> > > > > We've got a bit of tension between "no defaults" and "builtin au= dio >> > > > > devices" here. >> > > > > >> > > > > Cnosider if I had instead done >> > > > > >> > > > > qemu-system-x86_64 -M pc -device ac97 -nodefaults >> > > > > >> > > > > It is not unreasonable to expect to see an error because you ask= ed >> > > > > explicitly for 'ac97' and forgot to wire up the required audio >> > > > > backend, and asked to NOT have any defaults. Even then, a crash is unequivocally wrong. Fatal error would be defensible. >> > > > > But with your 'musicpal' machine example, you never asked for th= e >> > > > > frontend device, so you should be forgiven for also not asking >> > > > > for a audio backend. Indeed. >> > > > Ah, so this is because of -nodefaults, not because QEMU was >> > > > somehow built with no audio backends in it. Yes. There are more ways to end up with no audio backend. >> > > > > If we guarantee a /dev/null audio backend always exists, we help >> > > > > the second case but degrade the first case >> > > > >> > > > As a possible analogy, for network devices we just warn in >> > > > the analogous "device created but no backend wired up": >> > > > >> > > > ./build/x86/qemu-system-x86_64 -nodefaults -device e1000 -display= none >> > > > qemu-system-x86_64: warning: nic e1000.0 has no peer >> > > > >> > > > and the effective behaviour is that output packets are dropped. When a network device lacks a backend, we make it behave as if it's not connected to anything, and also tell the user that this is the case. Makes sense, especially for onboard devices: the user may not care for such an onboard device, and can't remove it. When an audio device lacks a backend, could we make it behave as if it's not connected to anything? Longwinded way to say ... >> > > > We could make audio devices do that (which would be basically >> > > > equivalent to "if we need an audio backend and we don't have >> > > > one, warn and create the null backend"). ... yes, please. >> > > Note that we don't have a real "null" backend. The "none" backend do= es >> > > mixing/resampling/volume before dropping the audio (its parent is >> > > MIXENG_BACKEND). I think it would be worth to add (so one day we can >> > > compile qemu without the whole audio/ engine) >> > >> > Rather than adding "null" backend, IMHO, we should make "none" do >> > what its name suggests, by removing the MIGENG_BACKEND from it. >> > >>=20 >> It's a bit more complicated, the "none" backend can be used by vnc >> (not spice or dbus), and we have the now-deprecated HMP wavcapture >> command. > > Oh right because VNC used the capture APIs to receive the audio. > It should probably have had an explicit "vnc" audio backend like > spice did :-( Is this fixable? "Certain audio commands only work when you actually have an audio backend" would be perfectly reasonable, wouldn'it ? >> Note, the new "qemu-vnc" server does not mix/resample audio at this >> point, it takes the first audio stream instead. > >>=20 >> Fwiw, a "null" audio backend would still need to process audio data at >> a correct pace. I'm dense today: why?