When does skbs get fragmented?

I'm writing a small kernel module that is similar to a Ethernet device
driver
and it receives skbs from the kernel.  I'd like to generate some skbs
with
fragments (i.e. skb_shinfo(skb)->nr_frag > 0) to test my module, but I
don't
know how.

If you can help, I'd highly appreciate it.  Basically, I'd like to know
under what
circumstances my driver can get fragmented skbs in its
hard_start_xmit()
function.

(I tried to send it large packet > than the Ethernet frame size, but
that didn't
seem to work.)

Please post or email, I'll summarize any responses received:

frank_6014 @ yahoo dot com.

Thanks!
-Frank H.