> > Thoughts on what to do about this?  There should certainly be room in front
> > of the packet for the link header, and we should try to avoid allocating
> > the extra mbuf.
>So, FWIW, I fixed this.  See M_READONLY() in sys/mbuf.h, and how it is
>used by M_LEADINGSPACE() and M_TRAILINGSPACE().

	traditionally it was a requirement for the caller of the M_*SPACE to
	check if the mbuf is under M_READONLY situation or not.  the check
	is not normally made on the input path as we are sure it is not
	shared on input path (WARNING: some packet filter directives, like
	"duplicate this traffic", break the assumption).
	the above change can choke certain code (which uses M_LEADINGSPACE when
	doing some mbuf length computation, not just for playing with m_data
	for example), IMHO.

itojun