The man page for bpf(4) says:

	STANDARD IOCTLS
	     bpf now supports several standard ioctl(2)'s which allow the user to do
	     async and/or non-blocking I/O to an open file descriptor.
	...
           SIOCGIFADDR (struct ifreq)
                    Returns the address associated with the interface.

There's no evidence in the code (1.5 and -current) to support this, and 
ioctl(bpf_dev, SIOCGIFADDR, &ifreq) returns EINVAL (on 1.5 at least).  There 
*is* code to support the rest of the calls listed under that heading.  Either 
the code or the doc is wrong, anybody know which?
-- 
Ross A. Patterson
Chief Technology Officer
CatchFIRE Systems, Inc.
5885 Trinity Parkway, Suite 220
Centreville, VA  20120
(703) 563-4164