From NAS-Central Buffalo - The Linkstation Wiki

Do I need to install a new kernel?

No you don't.
At least with firmware 1.36, Buffalo already built the kernel with NFSD (NFS version 3) support enabled.

What is missing?

The "only" missing stuff are the nfs_utils.
Unfortunately the optware feed for the LS-VL does not contain the complete nfs_utils due to build problems.
Serendipitously (I always wanted to use this word ;-) ) I built the necessary tools and scripts when I built the Ready-to-use NFS kernel.Do not use this kernel for the LS-VL!

You DO need the packages "portmap" and "e2fslibs" from Optware installed!

What do you have to do?

Download this tarball to the share "share":

  http://downloads.buffalo.nas-central.org/Users/kenatonline/NFSKernel/nfstools.tar.gz

Then connect as user "root" to your LS-VL via ssh. Change to the root directory.

  cd /

Unpack the tarball.

  tar xvzf /mnt/disk1/share/nfstools.tar.gz

Configure nfsd.

  NFS for Beginners

Either reboot the box or just start the nfsd.

  /etc/rc.d/extensions.d/S98_nfs.sh start

Wait at least one minute before you check for success.

  /etc/rc.d/extensions.d/S98_nfs.sh status

It should return this:

 portmap is running.
 mountd is running.
 nfsd is running.
 statd is running.
 lockd is running.
 All kernel NFS services running.