The _ssize() function in ossaudiodev.c (2.4.3, but it's
the same in svn) calls SNDCTL_SET_CHANNELS with
channels=0 as part of an attempt to determine the total
number of samples per second for the current
configuration of the audio device, but as far as I can
tell this is not guaranteed to act as a query and at
least two implementations treat it as a request for a
monaural format (the ALSA pcm-oss module and the
alsa-oss library).

What this can safely be replaced with I don't know;
both Linux's OSS drivers and ALSA support
SOUND_PCM_READ_CHANNELS but this is not standard to the
best of my knowledge.  Storing the value returned when
the program calls .setfmt or .setparameters may be an
option.