question on mbuf(m_copyback) code

[Swami Pichumani]

Hi all,
I had a question on the m_copyback code (I use pretty old version but feel 
this might still be same).
Inside the while(len>0) loop, the first line kinda seems odd. It subtracts 
the off (which becomes after first iteration) from m_len(which is supposed 
to tell the amount of data in the particular mbuf) to find the free space 
i nthe mbuf. This obviously would not work without m_len getting initialized 
to MLEN (or MHLEN), which is not the right thing to do (since when an 
mbuf has 0 data when initialized and m_len would be zero).

thanks in advance for any comments on this,

-swami