[alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api

[Devin Heitmueller]

> this seems like a feature, not a bug. PulseAudio starts streaming before
> clients push any data and likewise keeps sources active even after for some
> time after clients stop recording. Closing VLC in your example doesn't
> immediately close the ALSA device. look for module-suspend-on-idle in your
> default.pa config file.

The ALSA userland emulation in PulseAudio is supposed to faithfully emulate
the behavior of the ALSA kernel ABI... except when it doesn't, then it's not
a bug but rather a feature.  :-)

> I also agree that the open/close of the alsa device is the only way to
> control exclusion.

I was also a proponent that we should have fairly coarse locking done
at open/close for the various device nodes (ALSA/V4L/DVB).  The challenge here
is that we have a large installed based of existing applications that
rely on kernel
behavior that isn't formally specified in any specification.  Hence
we're forced to try
to come up with a solution that minimizes the risk of ABI breakage.

If we were doing this from scratch then we could lay down some hard/fast rules
about things apps aren't supposed to do and how apps are supposed to respond
to those exception cases.  Unfortunately we don't have that luxury here.

Devin

-- 
Devin J. Heitmueller - Kernel Labs
http://www.kernellabs.com