Subject: Re: purpose of mbuf type MT_HEADER
To: =?iso-8859-2?Q?J=F6rn?= Seger <>
From: Pavel Cahyna <>
List: tech-net
Date: 10/03/2004 18:08:46
> Am Freitag, 1. Oktober 2004 11:38 schrieb Pavel Cahyna:
> > Hello,
> >
> > what is the purpose of mbuf type MT_HEADER? How is it different from
> > MT_DATA? The manual page says only "data is a packet header", which is not
> > clear - aren't headers of upper-layer protocols just data for lower-layer
> > ones?
> There are different aproached for TCP and UDP.
> Stevens TCP/IP Illustrated Volume 2:
> The first mbuf with the packet header for the UDP datagram has a type of 
> MT_DATA, but the first mbuf with the packet header for the TCP segment has a 
> type of MT_HEADER. This [..] makes no difference. Mbufs of these two types 
> are essentially the same.

This only seems to confirm my suspicion that the difference is only
vaguely defined, so there should not be KASSERTs which compare mbuf types.
(such as in m_cat in kern/uipc_mbuf.c)
Could please somebody look at kern/26937 and confirm (or disprove) it?

Thanks and bye	Pavel