[lwip-users] Re: [lwip] Recent change in pbuf.c

[David Haas]

Kieran,

OK, I think you might be right. I was thinking that the ethernet driver was
at the link layer, but I'll accept that this is really the physical layer
and I should be using PBUF_RAW. That will certainly solve this issue.

Thanks,
David.

----- Original Message -----
From: "Kieran Mansley" <address@hidden>
To: <address@hidden>
Sent: Wednesday, December 04, 2002 4:32 PM
Subject: Re: [lwip] Recent change in pbuf.c


> On Wed, 4 Dec 2002, David Haas wrote:
> > I still have to question the need for the offset at the link layer. In
> > fact the only thing I can think of is if you are running a remote-access
> > server where the ethernet header is removed and a PPP header is
> > inserted. I would claim that this is a somewhat specialized use and lwip
> > should not be optimized for this. (or at least it should be documented).
>
> I think the reason for your problem is not the code, but the way you are
> thinking about it!  ;)
>
> You are trying to put a physical layer packet (ie. one with an ethernet
> header) into a "link layer" pbuf, and finding that they aren't really
> suited to each other.  Instead you should put your physical layer packet
> into a raw pbuf, and then everything will be happy.
>
> The reason (I think) it is this way is because it is more suited to when
> you are allocating pbufs for transmit, rather than receive.  When
> transmitting a packet at the link layer you need to leave room for a
> physical layer header to be added later, and so that is the reason for the
> offset.
>
> So, I guess I'm with Jani on this one I'm afraid!
>
> Kieran
>
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