Re: [uml-devel] SOLVED: uml "ip header error" for large (fragmented) udp packets

[BlaisorBlade <blaisorblade_spam@yahoo.it>]

On Tuesday 12 October 2004 02:03, Lars Ellenberg wrote:
> / 2004-10-11 19:55:12 +0200
>
> \ Lars Ellenberg:
> > since UML => Host does not work, but
> > Host => UML does, this suggests that
> > the bug is somewhere on the sending side.
> >
> > I was not able to track it down.
>
> just so you know, finally:

> =======================
> --- linux-2.6.6/arch/um/include/sysdep-i386/checksum.h.orig	2004-10-12
> 01:50:49.000000000 +0200 +++
> linux-2.6.6/arch/um/include/sysdep-i386/checksum.h	2004-10-12
> 01:50:58.000000000 +0200 @@ -102,8 +102,7 @@
>  	   are modified, we must also specify them as outputs, or gcc
>  	   will assume they contain their original values. */
>
>  	: "=r" (sum), "=r" (iph), "=r" (ihl)
>
> -	: "1" (iph), "2" (ihl)
> -	: "memory");
> +	: "1" (iph), "2" (ihl));
>  	return(sum);
>  }
The patch you posted REMOVES a memory barrier - you reversed it. I actually 
checked the barrier is missing in the source code; but the strange thing is 
that you modified checksum.h.orig and not checksum.h! Are you sure that you 
compiled the corrected header? However, the patch is correct, and I assume 
you posted it the right way. I'm going to send it to Andrew Morton for 2.6.9 
(hoping he wants to accept all these patches - they are rushing for 2.6.9).

> that's all, folks. only a missing memory barrier.
Thanks a lot, folks! Yes, the patch is right.
> WTF :-/
>
> same patch applies to 2.6.8.1 - uml and probably all other umls.
> since that is a one-to-one copy anyways, maybe UML should better use the
> original (in include/asm-i386/checksum.h) right away??
I could do this later - too much checks for the other header code for a 
one-minute patch.
> there may be similar bugs hiding in various areas of uml...
I think there are even worse ones.
> btw,
> anyone wants to give me a hint how to tune it best?
> maybe how to up the mtu of the UML "nics"?
Impossible with the current code - it emulates an ethernet card, so I don't 
think you can do anything for this. However I hope it does not cause too much 
problems. Search for the network howtos: someone explained how to set the 
interface packet scheduler (maybe even Jeff Dike on the main UML site).

Bye
-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729


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