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From: David Miller <davem@davemloft.net>
Subject: Re: [ PATCH 2.6.17-rc6 1/1] udp.c: counting InDatagrams which are
 never delivered
Date: Sun, 11 Jun 2006 23:13:00 -0700 (PDT)
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To: gerrit@erg.abdn.ac.uk
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From: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Date: Mon, 12 Jun 2006 07:02:45 +0100

> This is clearly preferable - would it look like this:
> 
> csum_copy_err:
>      UDP_INC_STATS_BH(UDP_MIB_INERRORS);
>      UDP_DEC_STATS_BH(UDP_MIB_INDATAGRAMS); /* requires new macro */
> 
>      skb_kill_datagram(sk, skb, flags);
>      /* ... */
> 
> in udp_recvmsg? Here I must pass - there is no xxx_DEC_BH macro in 
> include/net/snmp.h and I don't know whether the following guess is correct:
> 
> #define SNMP_DEC_STATS_BH(mib, field) 	\
> 	(per_cpu_ptr(mib[0], raw_smp_processor_id())->mibs[field]--)
> 
> If this is correct, then it seems done; one could use this macro or add
> a corresponding UDP_DEC_STATS_BH to include/net/udp.h .

The index of mib[] in those macros is always "!in_softirq()", the
*_BH() variants use zero for the index because they are called in
contexts where we know that "!in_sortirq()" evaluates to false.

So your SNMP_DEC_STATS_BH() macro is correct.

Can you cook up the patch, which adds your SNMP_DEC_STATS_BH() macro,
the UDP_DEC_STATS_BH counterpart, and the change that uses it in
net/ipv4/udp.c?

I'd appreciate this, thanks a lot.