Re: [lwip-devel] Packet queues (was Re: [bug #11400] ARP multi-packet-queue modifies TCP ...)

[Jonathan Larmour]

Kieran Mansley wrote:
> I'd like to avoid special cases if I can, so if it could sensibly be
> generalised to all pbuf types, that would be nice.  That way it would
> just become an additional flag on the pbuf->flags variable that was
> independent of type.  Doing so wouldn't add any additional code over
> your proposal I think - might even make it simpler - and would make it
> easier to use this feature from other places (e.g. the TCP side of
> things) if we find it necessary in the future.

That's a little more work than I was envisaging, but not much. Currently 
lwIP ubiquitously tests the flags with pure equality, for example:
 if (pbuf->flags == PBUF_FLAG_RAM)
so an extra bit ORd in will break that.

Unhelpfully, PBUF_FLAG_RAM is defined as "0x00U", so it isn't even a bit at 
all. It would have to be given a new value, but that's not a problem.

I guess the best solution would be to use test macros e.g.:
#define PBUF_FLAG_RAM 0x08U
#define PBUF_FLAG_NOCOPY 0x10U

#define PBUF_IS_RAM(_p) ((_p)->flags & PBUF_FLAG_RAM)
#define PBUF_NEEDS_COPY(_p) (0 == ((_p)->flags & PBUF_FLAG_NOCOPY))

> Perhaps we should add a this as a task to the savannah tracker.  Would
> you be willing to take ownership of this for the time being?  I'm in no
> hurry for a solution, but I think it would definitely be an improvement
> and shouldn't get forgotten.

My employer is keen to have a single copy implementation for some low 
memory System-On-Chips, so hopefully this should happen quite soon. But to 
make sure, I will create a task assigned to myself.

Jifl
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