linux-libusb takes advantage of FreeBSD libusb(8) library, which got
prepared to work correctly within linux(4) emulation layer. It lets
you to take Linux binary linked with libusb.so and use it on
FreeBSD.

Additional information: This port has been prepared under FreeBSD
with kern.osreldate = 1000510. It relies on the fact the libusb(8)
API seems to be stable and no changes have been made to internal API
for a long time. If this assumption isn't true, port won't work.
Please submit bug report to the port maintainter in that case.

WWW: http://lists.freebsd.org/pipermail/freebsd-usb/2014-March/012854.html