Re: Headroom for bridging and wireless

On Mon, Dec 08, 2003 at 08:16:30PM +0100, Bart De Schuymer wrote:
> On Sunday 07 December 2003 00:22, Tom Marshall wrote:
> > I tried setting br->dev->hard_header_len to the max of the ports (see
> > attached patch).  Then I hardcoded hard_header_len to ETH_HLEN+4 for the
> > wireless driver.  I verified the kernel messages -- the bridge sets hh_len
> > to 18 when I add the wireless device to the bridge and back to 14 when I
> > remove it.  Unfortunately, it doesn't seem to be working.  Both bridged
> > traffic and traffic from the bridge itself still has 0 headroom in the
> > wireless tx function.  :-(
> 
> Your patch to br_if.c does seem to use an uninitialized p pointer.

I'm afraid that I am not familiar with the kernel list functions.  It was an
ugly copy/paste job.  ;-)

> Apart from that, I've just changed the hard_header_len for my bridge box and 
> the headroom did increase as it should, for packets originating from the 
> bridge and going through br0.

Nice, but it would be most useful to have the bridged packets use the
increased headroom.  I don't suppose there is a way to do that easily.  The
only thing I can think of right now is to have the skb functions always
reserve the maximum headroom for all devices in the system.  Seems a small
price to pay for a huge decrease in reallocs.

Note this is not just a bridge problem, it should also apply to routing.

-- 
Perfection in design is achieved not when there is nothing left to add, but 
rather when there is nothing left to take away.                          
        - Antoine de Saint-Exupery

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