G_PART macro definitions

[perryh at pluto.rain.com]

I am trying to understand, in some detail, the operation of the
g_part_taste and g_part_probe functions in sys/geom/part/g_part.c,
and am having trouble figuring out exactly what the G_PART_PROBE
and G_PART_READ macros do.  Where will I find their definitions
(in 8.1-RELEASE)?

They don't seem to be in sys/geom/part/g_part.c itself, nor in
sys/geom/part/g_part.h -- at least, not in a form that I've been
able to recognize.