Xen users - Nov 2006 - XEN sound emulation locks device exclusively

Hi there!

My problem is the following:

I am experimenting with virtualization with XEN.

I am running WinXP in a HVM host with a Debian Gnu/Linux (Etch) dom0.

I am also using audio emulation (sb16). This way, sounds from WinXP work fine.

And here comes the problem:

The HVM guest completely reserves the audio device; other software can not use
it.

(mplayer says this:

alsa-init: using ALSA 1.0.13
alsa-init: setup for 1/2 channel(s)
alsa-init: using device default
alsa-lib: pcm_hw.c:1248:(snd_pcm_hw_open) open /dev/snd/pcmC0D0p failed: Device
or resource busy
alsa-lib: pcm_dmix.c:864:(snd_pcm_dmix_open) unable to open slave
alsa-init: playback open error: Device or resource busy

)

This should not be like this; with alsa (including the dmix plugin) 
working fine on my system, different sounds sources could be mixed painlessly.

The problem seems to be that the HVM guest does not use the device
via the default device (which should go via the DMIX system), but directly.

How can this be fixed?

And where can I find more documentation about XEN audio emulation?

Thank you for your help:

      Kristof Csillag

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On 9 Nov 2006 at 11:58, Csillag, Kristof (GE Healthcare, consultan[Xen-users]
XEN sound emulation locks device excl wrote:

[...]
> The HVM guest completely reserves the audio device; other software can not
use it.
> 
[...]
> How can this be fixed?
> 
> And where can I find more documentation about XEN audio emulation?
As I think XEN has no "audio emulation", there''s probably no
fix other than using
VMware that has an audio emulation. What you are requesting is some magic driver
in XEN that saves the state of the sound card before it reinitializes the card
for
the next VM''s sound state, preferrably without disturbing sound. As you
can see,
that''s rather impossible. You could either use the sound hardware from
one VM only
and let XEN ignore it, or make the other machines use some higher level sound 
server that''s hosted on one machine.

Regards,
Ulrich


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You could use a sound server like pulseaudio. I believe it has a windows
driver.

On Thu, 2006-11-09 at 23:10 -0800, Ulrich Windl wrote:
> On 9 Nov 2006 at 11:58, Csillag, Kristof (GE Healthcare,
> consultan[Xen-users] XEN sound emulation locks device excl wrote:
> 
> [...]
> > The HVM guest completely reserves the audio device; other software
> can not use it.
> >
> [...]
> > How can this be fixed?
> >
> > And where can I find more documentation about XEN audio emulation?
> 
> As I think XEN has no "audio emulation", there''s
probably no fix other
> than using
> VMware that has an audio emulation. What you are requesting is some
> magic driver
> in XEN that saves the state of the sound card before it reinitializes
> the card for
> the next VM''s sound state, preferrably without disturbing sound.
As
> you can see,
> that''s rather impossible. You could either use the sound hardware
from
> one VM only
> and let XEN ignore it, or make the other machines use some higher
> level sound
> server that''s hosted on one machine.
> 
> Regards,
> Ulrich
> 
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
> 
> 
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> As I think XEN has no "audio emulation", there''s
probably no fix other than
> using VMware that has an audio emulation.
OK, so I have the wrong idea about how XEN handles sound.
(I found no documentation on this, so it was basically a guess.)

Here is what I know:

- In the notebook computer there is and Intel HDA sound card.
- In the configuration file for my HVM guest, I have
"soundhw=''sb16''".
- The WinXP running as HVM guest sees a Sound Blaster 16 sound device, and can
use it.

Here is what I thought:

- Either the XEN hypervisor, or some user-space tool (probably the later)
emulates
  the hardware interface of a SB16 for the HVM host, and
- it relays the sound to the sound system of DOM0.

If this is not how it goes, then what?
I thought that since there is no real SB16 in the host in question,
the SB16 interface must have been emulated,
but from what you say I seem to be mistaken.

Could someone please explain this, or give a link to the appropriate
documentation?

Thank you:


     Kristof Csillag


_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

> As I think XEN has no "audio emulation", there''s
probably no fix other than
> using VMware that has an audio emulation.
OK, so I have the wrong idea about how XEN handles sound.
(I found no documentation on this, so it was basically a guess.)

Here is what I know:

- In the notebook computer there is and Intel HDA sound card.
- In the configuration file for my HVM guest, I have
"soundhw=''sb16''".
- The WinXP running as HVM guest sees a Sound Blaster 16 sound device, and can
use it.

Here is what I thought:

- Either the XEN hypervisor, or some user-space tool (probably the later)
emulates
  the hardware interface of a SB16 for the HVM host, and
- it relays the sound to the sound system of DOM0.

If this is not how it goes, then what?
I thought that since there is no real SB16 in the host in question,
the SB16 interface must have been emulated,
but from what you say I seem to be mistaken.

Could someone please explain this, or give a link to the appropriate
documentation?

Thank you:


     Kristof Csillag

_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

> -----Original Message-----
> From: xen-users-bounces@lists.xensource.com 
> [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of 
> Csillag, Kristof (GE Healthcare, consultant)
> Sent: 13 November 2006 07:42
> To: xen-users@lists.xensource.com
> Subject: [Xen-users] Re: XEN sound emulation locks device exclusively
> 
> > As I think XEN has no "audio emulation", there''s
probably
> no fix other than
> > using VMware that has an audio emulation.
> 
> OK, so I have the wrong idea about how XEN handles sound.
> (I found no documentation on this, so it was basically a guess.)
> 
> Here is what I know:
> 
> - In the notebook computer there is and Intel HDA sound card.
> - In the configuration file for my HVM guest, I have
"soundhw=''sb16''".
> - The WinXP running as HVM guest sees a Sound Blaster 16 
> sound device, and can use it.
> 
> Here is what I thought:
> 
> - Either the XEN hypervisor, or some user-space tool 
> (probably the later) emulates
>   the hardware interface of a SB16 for the HVM host, and
> - it relays the sound to the sound system of DOM0.
> 
> If this is not how it goes, then what?
> I thought that since there is no real SB16 in the host in question,
> the SB16 interface must have been emulated,
> but from what you say I seem to be mistaken.
> 
> Could someone please explain this, or give a link to the 
> appropriate documentation?
If it''s a HVM guest, the sound emulation is done in QEMU-DM, the device
model for the HVM mode. 
In fact, qemu-dm is responsible for ALL hardware emulation with a few
exceptions (timer and interrupt controller functionality) that for
performance reasons are in Xen itself. 

So, yes, qemu-dm will have a SB16 type emulation layer that then
forwards the sound to be played to the real hardware. 

I would expect that this happens at a very low level, so it''s
"bare
samples" being sent to the hardware, which may mean that it needs to
lock the device exclusively to prevent other streams from interacting. 

--
Mats
> 
> Thank you:
> 
> 
>      Kristof Csillag
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
> 
> 
> 


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After checking the source code of ioemu (which is responsible for the audio
emulation),
I can see that there is a whole fully configurable audio system, with multiple
output
backands, including alsa output. (This whole stuff comes from QEMU.)

So it should be possible to send the sound to alsa via the normal channels,
using the dmix plugin.

So the question is: how can I configure the audio sub-system in qemu-dm?
How can I pass parameters to it?
(If I can not, then there should be a mechanism for that.)

     Kristof Csillag


-----Eredeti üzenet-----
Feladó: Petersson, Mats [mailto:Mats.Petersson@amd.com]
Küldve: 2006-11-13, H 16:15
Címzett: Csillag, Kristof (GE Healthcare, consultant);
xen-users@lists.xensource.com
Tárgy: RE: [Xen-users] Re: XEN sound emulation locks device exclusively
 
 
> -----Original Message-----
> From: xen-users-bounces@lists.xensource.com 
> [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of 
> Csillag, Kristof (GE Healthcare, consultant)
> Sent: 13 November 2006 07:42
> To: xen-users@lists.xensource.com
> Subject: [Xen-users] Re: XEN sound emulation locks device exclusively
> 
> > As I think XEN has no "audio emulation", there''s
probably
> no fix other than
> > using VMware that has an audio emulation.
> 
> OK, so I have the wrong idea about how XEN handles sound.
> (I found no documentation on this, so it was basically a guess.)
> 
> Here is what I know:
> 
> - In the notebook computer there is and Intel HDA sound card.
> - In the configuration file for my HVM guest, I have
"soundhw=''sb16''".
> - The WinXP running as HVM guest sees a Sound Blaster 16 
> sound device, and can use it.
> 
> Here is what I thought:
> 
> - Either the XEN hypervisor, or some user-space tool 
> (probably the later) emulates
>   the hardware interface of a SB16 for the HVM host, and
> - it relays the sound to the sound system of DOM0.
> 
> If this is not how it goes, then what?
> I thought that since there is no real SB16 in the host in question,
> the SB16 interface must have been emulated,
> but from what you say I seem to be mistaken.
> 
> Could someone please explain this, or give a link to the 
> appropriate documentation?
If it''s a HVM guest, the sound emulation is done in QEMU-DM, the device
model for the HVM mode. 
In fact, qemu-dm is responsible for ALL hardware emulation with a few
exceptions (timer and interrupt controller functionality) that for
performance reasons are in Xen itself. 

So, yes, qemu-dm will have a SB16 type emulation layer that then
forwards the sound to be played to the real hardware. 

I would expect that this happens at a very low level, so it''s
"bare
samples" being sent to the hardware, which may mean that it needs to
lock the device exclusively to prevent other streams from interacting. 

--
Mats
> 
> Thank you:
> 
> 
>      Kristof Csillag
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
> 
> 
> 



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Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

On Tue, 14 Nov 2006, Csillag, Kristof (GE Healthcare, consultant) wrote:
> After checking the source code of ioemu (which is responsible for the audio
emulation),
> I can see that there is a whole fully configurable audio system, with
multiple output
> backands, including alsa output. (This whole stuff comes from QEMU.)
>
> So it should be possible to send the sound to alsa via the normal channels,
> using the dmix plugin.
>
> So the question is: how can I configure the audio sub-system in qemu-dm?
> How can I pass parameters to it?
> (If I can not, then there should be a mechanism for that.)
<snip>

Audio in vanilla QEMU takes audio fine-tuning parameters from environment,
to use dmix:
QEMU_ALSA_DAC_DEV=dmix qemu <params>

--
vale

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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Csillag Kristof wrote:
>> As I think XEN has no "audio emulation", there''s
probably no fix other than
>> using VMware that has an audio emulation.
> 
> OK, so I have the wrong idea about how XEN handles sound.
> (I found no documentation on this, so it was basically a guess.)
> 
> Here is what I know:
> 
> - In the notebook computer there is and Intel HDA sound card.
> - In the configuration file for my HVM guest, I have
"soundhw=''sb16''".
> - The WinXP running as HVM guest sees a Sound Blaster 16 sound device, and
can use it.
> 
> Here is what I thought:
> 
> - Either the XEN hypervisor, or some user-space tool (probably the later)
emulates
>   the hardware interface of a SB16 for the HVM host, and
> - it relays the sound to the sound system of DOM0.
> 
> If this is not how it goes, then what?
> I thought that since there is no real SB16 in the host in question,
> the SB16 interface must have been emulated,
> but from what you say I seem to be mistaken.
Xen uses a stub version of qemu to emulate devices in hvm domains.  Your
best bet is probably searching with respect to qemu and sb16.

- -John McCullough
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