What's the approved way to get access to the I/O bus?

Apropos of nothing, on Linux, in libc's
sysdeps/unix/sysv/linux/alpha/ioperm.c, the I/O bus is mmapped, and inb,
outb, etc., are provided.

On my NetBSD 1.4 system (a PC64+), I see in the kernel sources a `struct
alpha_isafcndesc` which seems to have function pointers to inb/outb type
functions; but I'm apparently not looking in the right places because I
can't find anything in the kernel that uses this apart from
arch/alpha/isa/isafcns_jensen.c, nor can I find anything in userland
that's analogous.

Any hints would be appreciated.

Thanks.

--
Kaleb