Re: [libvirt] [PATCH] qemu: Allow using regular audio backends with VNC

On 05/24/2010 10:31 AM, Daniel P. Berrange wrote: > On Mon, May 24, 2010 at 10:26:43AM -0400, Cole Robinson wrote: >> On 05/24/2010 10:14 AM, Daniel P. Berrange wrote: >>> On Thu, May 20, 2010 at 12:04:04PM -0400, Cole Robinson wrote: >>>> Currently all host audio backends are disabled if a VM is using VNC, in >>>> favor of the QEMU VNC audio extension. Unfortunately no released VNC >>>> client supports this extension, so users have no way of getting audio >>>> to work if using VNC. >>>> >>>> Add a new config option in qemu.conf which allows changing libvirt's >>>> behavior, but keep the default intact. >>>> >>>> Signed-off-by: Cole Robinson <crobinso(a)redhat.com&gt; >>>> --- >>>> src/qemu/qemu.conf | 10 ++++++++++ >>>> src/qemu/qemu_conf.c | 17 ++++++++++++----- >>>> src/qemu/qemu_conf.h | 2 ++ >>>> 3 files changed, 24 insertions(+), 5 deletions(-) >>>> >>>> diff --git a/src/qemu/qemu.conf b/src/qemu/qemu.conf >>>> index 3da332f..fec946d 100644 >>>> --- a/src/qemu/qemu.conf >>>> +++ b/src/qemu/qemu.conf >>>> @@ -168,3 +168,13 @@ >>>> # be assigned to guests. >>>> # >>>> # relaxed_acs_check = 1 >>>> + >>>> + >>>> +# QEMU implements anextension for providing audio over a VNC connection, >>>> +# though if your VNC client does not support it, your only chance for getting >>>> +# sound output is through regular audio backends. By default, libvirt will >>>> +# disable all QEMU sound backends if using VNC, since they can cause >>>> +# permissions issues. Enabling this option will make libvirtd honor the >>>> +# QEMU_AUDIO_DRV environment variable when using VNC. >>>> +# >>>> +# vnc_enable_audio_backend = 0 >>> >>> I think this would be better named as 'vnc_allow_host_audio' >>> since its not toggling VNC audio, just whether it is allowed >>> to use the host audio drivers. >>> >> >> Okay, I'll change and resend. >> >>> NB, even with this toggled things are unlikely to magically >>> 'just work'. If QEMU is running as 'qemu' user ID, that user >>> won't have any permissions to use /dev/snd/* devices. And >>> if running as 'root' then pulseaudio won't autospawn so will >>> need to be run manually. >>> >> >> Right. Currently getting sound to work in Fedora is a big pain, and >> there have been quite a few user complaints. I'm going to write up a >> 'known bug' page, documenting a workaround of qemu.conf user/group = >> $USER to fix the issue, but this patch will still need to be backported. > > I'd really recommend against telling people to configure libvirt to run > the guests as their own $USER because that'll open a huge can of worms. > What exactly are the downsides, besides the security implications? It should exercise all the same code as user/group = 'qemu', but solves issues like: - Making sure emulator user can access $HOME for install media - Audio - PTY access - SDL (if someone insists on it)

> Better to tell them to add an ACL to /dev/snd/* using setfacl to add the > qemu user to the ACL for the sound card, or drop in a udev rule todo the > same. > I'll try that out, but I wonder will my local user actually hear that sound? Will the audio go to my pulseaudio session?