Where is file "channel_if.h"

[rhino64 at postmail.ch]

Hi All,
    I need to compile a sound driver which need the include file "channel_if.h".
This file seems to be part of FreeBSD kernel definition. The only file I can find
is "/usr/src/sys/dev/sound/pcm/channel_if.m".

It is similar to a header file but it seems that it should be modified
to have the C header file syntax. How to do this transformation ?

Thanks for the help,

Alain Aubord