sound(4) vs alsa oss plugin

[Andriy Gapon]

I think I discovered an interesting/unusual problem.

For some reason ALSA OSS plugin developers decided to use SNDCTL_DSP_GETOPTR and
SNDCTL_DSP_GETIPTR to track state of playback/recording.
http://manuals.opensound.com/developer/SNDCTL_DSP_GETOPTR.html
http://manuals.opensound.com/developer/SNDCTL_DSP_GETIPTR.html
Of all information returned by these ioctl they use just 'ptr' to track the
progress by hardware.

Now I see that under a "right mix" of circumstances the following is possible:
- a buffer is completely empty for recording or completely full for playback
- an application / ALSA checks the buffer pointer and gets some value P
- the application sleeps for some time, perhaps oversleeps due to system load or
something else
- the buffer is completely filled or drained depending on the direction
- the application / ALSA checks the buffer pointer and gets the same value P
- the application assumes that the buffer is in the old state and waits further
- sound(4) code knows that the buffer is in the new state and does nothing

The above is only possible, obviously, if the buffer size is a multiple of a
sample size.

So, couple of questions:
- apparently this used to work (works?) in Linux - how?
- is there any trick that we can do in our sound(4) code to prevent this 'ptr'
full cycle from happening?

Ideally, it's the logic in the ALSA OSS plugin that should be fixed, but...
The upstream is not very responsive.  I wonder if they still care about OSS at all.
While patching audio/alsa-plugins is relatively easy, fixing a binary package
for audio/linux-f10-alsa-plugins-oss is not.  And it's needed for things like
skype, etc.

What do you think?

P.S.
it's because of audio problems with skype that I found this issue.

-- 
Andriy Gapon