netdev - Re: [PATCH 1/2] [IPV4] UDP: Always checksum even if without socket filter

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Date:	Sun, 18 Nov 2007 14:40:10 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	andi@...stfloor.org
Cc:	wangchen@...fujitsu.com, herbert@...dor.apana.org.au,
	netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] [IPV4] UDP: Always checksum even if without socket
 filter

From: Andi Kleen <andi@...stfloor.org>
Date: Sun, 18 Nov 2007 22:45:15 +0100

> > We could defer the increment until we check the checksum,
> > but that is likely to break even more things because people
> > (as Wang Chen did initially) will send a packet to some
> > port with an app that doesn't eat the packets, and expect the
> > InDatagrams counter to increase once the stack eats the packet.
> 
> Who expects that? Is there really any program who relies on that?
> 
> If it's just a human: there are a couple of "non intuitive" behaviours
> in the stack. This would be just another one. Not too big a deal.

I would consider this a legitimate thing to check in a test suite
such as TAHI or similar.

The networking stack DID receive the packet.  Just because a socket
owner is busy doing something else or blocked on some other event
is no excuse not to bump the InDataGgrams counter.

The behavior would suck.

> > But it won't until the application does the read.
> > 
> > All of our options suck, we just have to choose the least sucking one
> > and right now to me that's decrementing the counter as much as I
> > empathize with the SNMP application overflow detection issue.
> 
> If the SNMP monitor detects an false overflow the error it reports 
> will be much worse than a single missing packet. So you would replace 
> one error with a worse error.

This can be fixed, the above cannot.
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