sio_write blocking?

Hi all,

The manual page for sndio currently says:

> using the buffer usage to guess if sio_write() would block is false and 
> leads to unreliable programs

Why is this?  Is it perhaps talking about using bufsz instead of appbufsz?

(Additionally, is there a way to tell how much can be written without 
blocking?  An equivalent to alsa's snd_pcm_avail or SNDCTL_DSP_GETOSPACE?)

  -E