Re: Sound devices under vservers?

Hi Sirs,

Den 10. sep. 2016 17:34, skrev Herbert Poetzl:
> On Sun, Sep 11, 2016 at 12:26:22AM +1200, Andrew Ruthven wrote:
>
>> On Wed, 2016-09-07 at 18:57 +0200, Herbert Poetzl wrote:
>>> On Wed, Sep 07, 2016 at 11:33:48PM +1200, Andrew Ruthven wrote:
>>>>   
>>>> I run slimserver and squeezelite within a vserver, and until
>>>> recently they've worked nicely. But now squzeelite (which
>>>> actually plays the music out a soundcard) has stopped working.
>>> The files in /dev/snd within the container still match what is
>>>> on the hypervisor.
>>> There is no hypervisor in Linux-VServer.
>>> There is a kernel and a host system and a number of guests.
>> Yeah, I was just stealing the language from elsewhere. ;)
> Don't do that ;)
>
>>>> Running strace when I start squeezelite gives me:
>>>> open("/dev/snd/controlC0", O_RDONLY|O_CLOEXEC) = 4
>>>> fcntl(4, F_SETFD, FD_CLOEXEC)           = 0
>>>> ioctl(4, SNDRV_CTL_IOCTL_CARD_INFO or UI_DEV_CREATE,
>>>> 0x7ffcc50789d0) =
>>>> -1 ENOTTY (Inappropriate ioctl for device)
>>> Try to run squeezelite with strace in a chroot into the guest
>>> and see if the result differs.
>>> If you get the same result, then the isolation (Linux-VServer
>>> is not involved).
>>> If it works inside the chroot but fails inside the guest, then
>>> you might have insufficient capabilities.
>> Okay, fails within a chroot as well. Relevant lines:
>>>  From the host (setting LD_LIBRARY_PATH to pick up the libraries within
>> the guest):
>> open("/dev/snd/controlC0", O_RDONLY|O_CLOEXEC) = 4
>> fcntl(4, F_SETFD, FD_CLOEXEC)           = 0
>> ioctl(4, SNDRV_CTL_IOCTL_CARD_INFO or UI_DEV_CREATE, 0x7ffc646fd6d0) =
>> 0
>> close(4)                                = 0
>> Within a chroot:
>> open("/dev/snd/controlC0", O_RDONLY|O_CLOEXEC) = 4
>> fcntl(4, F_SETFD, FD_CLOEXEC)           = 0
>> ioctl(4, SNDRV_CTL_IOCTL_CARD_INFO or UI_DEV_CREATE, 0x7ffd93373400) =
>> -1 ENOTTY (Inappropriate ioctl for device)
>> close(4)                                = 0
>> Within the guest:
>> open("/dev/snd/controlC0", O_RDONLY|O_CLOEXEC) = 4
>> fcntl(4, F_SETFD, FD_CLOEXEC)           = 0
>> ioctl(4, SNDRV_CTL_IOCTL_CARD_INFO or UI_DEV_CREATE, 0x7ffd6119bd40) =
>> -1 ENOTTY (Inappropriate ioctl for device)
>> close(4)
>> Aw crap. Turns out the minor numbers were different for
>> /dev/snd/controlC0 between the host and the guest. I had
>> initially looked at those and thought they matched, guess I
>> read them wrong.
>> I guess I should add a step to my start script for the guest to
>> always copy over the contents of /dev/snd.  ;)  Actually, now
>> it's a bind mount.
> A bind mount should be fine, either of the snd dir if you
> want to share all audio devices with the guest or of the
> individual entries. Copy works also if the devices do not
> change during the lifetime of the guest.

Although unrelated to the original question, how would you suggest to 
share and/or prioritize/select sound output from potentially a range of 
guests (or other sources) on the host? Giving /dev access to each guest 
would probably just work for the guest that first grabs the device ---- 
or maybe all sound just would be mixed together? - I have no idea!

aRts, Phonon, PulseAudio, virtual sound device that pipes sound from 
guest to network stream....????  (I am just throwing out buzzwords here, 
as I have near to no clue on how the Linux sound system actually works 
and the state of it...! ;-) )

BR,
Tor Rune Skoglund, [email protected]
>> Sorry to distract folks, but I thought I'd respond with the
>> details and the cause in case other folks hit it.
> No problem! Thanks for the update though!
>
> All the best,
> Herbert
>
>> Cheers,
>> Andrew
>> -- 
>> Andrew Ruthven, Wellington, New Zealand
>> MIITP, ITCP
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