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

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Message-ID: <20071118214515.GA8161@one.firstfloor.org>
Date:	Sun, 18 Nov 2007 22:45:15 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	David Miller <davem@...emloft.net>
Cc:	andi@...stfloor.org, 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

> 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.

> 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.

-Andi
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