Installing ffp on a D-Link DIR-685 is slightly more difficult than on
a DNS-323. Currently, ffp can be run chroot'ed from a hard disk. For
the installation, you need a serial console.

A number of additional utility programs are needed that are not
included in the firmware. We therefore use a statically linked busybox
binary that has everything we need. To start the chroot'ed ffp,
there's the ffp-chroot.sh script. Download from:

  http://www.inreto.de/dir685/busybox-static
  http://www.inreto.de/dir685/ffp-chroot.sh

We also need the ffp 0.5 installation tarball fun_plug.tgz available
at:

  http://www.inreto.de/dns323/fun-plug/0.5/fun_plug.tgz

To install ffp, create an empty directory named fun_plug, and download
the three files (busybox-static, fun_plug.tgz, ffp-chroot.sh) to the
new directory on the DIR-685. Then switch to the serial console.

Then, find the mountpoint of the installed disk,

 # mount | grep /dev/sd
 /dev/sda on /var/tmp/storage_dev/HD_Hitachi_HTS54251 type ext3 (rw,data=ordered)

change to the fun_plug directory, and check that all required files
are present:

 # cd /var/tmp/storage_dev/HD_Hitachi_HTS54251
 # cd fun_plug
 # ls
 ffp-chroot.sh   fun_plug.tgz    busybox-static
 
Make sure, ffp-chroot.sh is executable:

 # chmod 0755 ffp-chroot.sh

Unpack and start ffp with:

 # ./ffp-chroot.sh 
 Unpacking fun_plug.tgz ...
 ...
 * /ffp/start/telnetd.sh ...
 Starting /ffp/sbin/telnetd -l /ffp/bin/sh
 ...

You should now be able to connect via telnet.

Note that most example config files in /ffp/etc/examples are specific
to the DNS-323 firmware and cannot be used unmodified. For unfsd, you
have to create the /etc directory, and an /ffp/etc/exports file
manually.