[alsa-devel] External plugin question

I'm new to alsa dev and I'm trying to write a very simple external pcm plugin. I want my pcm plugin to output sound to multiple slave pcms when sound is being writei'd to it. So:

snd_pcm_myplugin_writei(pcm, buffer, size) { foreach slave pcm { snd_pcm_writei(slave_pcm, buffer, size); } }

I'm having trouble implementing this plugin because the external plugin sdk does not allow me to define the writei function for my plugin, but lets me define the transfer function which has a very different signature than writei:

transfer(snd_pcm_ioplug_t *io, const snd_pcm_channel_area_t *areas, snd_pcm_uframes_t offset, snd_pcm_uframes_t size)

how do I extract buffer and size from these arguments? Any tips on how I write my plugin.

Mina