Re: Documentation question

[Duncan Roe <duncan_roe@optusnet.com.au>]

On Fri, Dec 20, 2019 at 01:29:53AM +0100, Pablo Neira Ayuso wrote:
> On Sun, Dec 15, 2019 at 01:02:20PM +1100, Duncan Roe wrote:
> > Hi Pablo,
> >
> > In pktbuff.c, the doc for pktb_mangle states that "It is appropriate to use
> > pktb_mangle to change the MAC header".
> >
> > This is not true. pktb_mangle always mangles from the network header onwards.
> >
> > I can either:
> >
> > Whithdraw the offending doc items
> >
> > OR:
> >
> > Adjust pktb_mangle to make the doc correct. This involves changing pktb_mangle,
> > nfq_ip_mangle and (soon) nfq_ip6_mangle. The changes would be a no-op for
> > AF_INET and AF_INET6 packet buffers.
> >
> > What do you think?
>
> You could fix it through signed int dataoff. So the users could
> specify a negative offset to mangle the MAC address.
>
> This function was made to update layer 7 payload information to
> implement the helpers. So dataoff usually contains the transport
> header size.
>
> Let me know, thanks.
>
-ve offsets? There has to be a better way.

When I added documentation for pktb_mangle, I assumed it mangled from
pktb->data, rather than checking the source.

That is the function I documented, and I think we need a function like that.

Rather than change the behaviour of pktb_mangle when a MAC header is present, I
propose a new function pktb_mangle2 which mangles from pktb->data onwards.

pktb_mangle would call this new function, with dataoff incremented by
pktb->network_header - pktb->data (only nonzero for AF_BRIDGE)

Ok?

Cheers ... Duncan.