Re: [lwip-members] static variables in ip.c

[leon . woestenberg]

Hello,

> A while back Leon spotted that struct netif * variable in ip_output was
> static
> and Adam confirmed it's a bug.But there are more such defs in ip.c.
> And that one was not yet fixed.
> It's a good idea to make them all local vars don't you think?
> 
This may sound strange, but it may not be a bug after all!

The ip module may not be called concurrently from two tasks, because most of
the code (roughly 60%) acts on private ip data structures (such as the
routing table).

So, given that fact, the ip module does not need to be re-entrant, and so
the usage of static to reduce stack size usage is actually a valid approach.

In a real neat approach, ip should be re-entrant and multi-threading safe,
but that needs entangling a lot of synchronization constructs (probably
semaphore/mutex locks).

If we do want to make the stack multi-threading safe, there is lot more work
to do besides ip. I suggest we defer this to later, there are more important
archtectural issues to tackle first.

Leon.

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