The current libpci branch uses the pciutils library
(/usr/lib/libpci*.so*) to discover the hierarchy of PCI bridges/devices.
pciutils works on many platforms, including windows (even if I never
actually tried it). Unfortunately, there is no official support for
MacOSX. I tried libpciaccess (used by X) which offers almost the same
abilities but it doesn't seem to work on MacOSX either. Does anybody
have any idea what we could use on MacOSX?