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Re: [lwip-users] p->payload == iphdr failed...


From: Simon Goldschmidt
Subject: Re: [lwip-users] p->payload == iphdr failed...
Date: Mon, 10 Nov 2008 08:54:56 +0100

Jonathan Larmour wrote:
> [..]
> It's possible to come up with a solution despite this. For example, the 
> ref count is currently 16-bit which is probably overkill. Or the type and 
> flags field could be merged[1]. I think I'd prefer the former - I can't 
> imagine more than 255 references to a single pbuf. Even with a pbuf chain 
> with only 128 byte pbufs, that would still be equivalent to nearly 32Kbyte
> jumbo frames (and the obvious solution if somehow this was likely would be
> to use larger pbufs!). Anyway, with a u8_t of extra space, you can't store
> the base address, but you can store the offset from the payload pointer to
> the real start of the packet - pbuf_header could adjust it every time.

As you write below, I think a diff between original and current payload of 255 
only may lead to problems... (even if not with TCP options, which _may_ be 
longer as 255 even if we don't support them).

I thought about adding an extra payload pointer after the struct PBUF_REF which 
only would have to make the PBUF_REF/ROM specific pool elements larger. Also, 
only pbuf.c would have to know about PBUF_REF structs being larger than the 
other ones. I think that would be less invasive to the rest of the code.

Simon
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