snd_pcm_oss_get_active_substream
err = snd_pcm_oss_get_active_substream(pcm_oss_file, &substream);
err = snd_pcm_oss_get_active_substream(pcm_oss_file, &substream);
err = snd_pcm_oss_get_active_substream(pcm_oss_file, &substream);
err = snd_pcm_oss_get_active_substream(pcm_oss_file, &substream);
err = snd_pcm_oss_get_active_substream(pcm_oss_file, &substream);