netdev - Re: [PATCH] IP: Increment INADDRERRORS if routing for a packet is not successful

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Message-ID: <1275430054.2638.115.camel@edumazet-laptop>
Date:	Wed, 02 Jun 2010 00:07:34 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	netdev@...r.kernel.org, Stephen Hemminger <shemminger@...tta.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH] IP: Increment INADDRERRORS if routing for a packet is
 not successful

Le mardi 01 juin 2010 à 16:13 -0500, Christoph Lameter a écrit :
> Something like this would have been very helpful during recent debugging
> of multicast issues. Silent discards are bad.
> 

> 
> If the kernel perceives that something is wrong with an incoming packet then the
> IP stack currently silently discards packets. This makes it difficult to diagnose
> problems with the network configurations (such as a misbehaving kernel
> subsystem discarding multicast packets because the reverse path filter
> does not like multicast subscriptions on the second NIC with rp_filter=1).
> 
> It is also necessary to know how many inbound packets are discarded to
> assess networking issues in general with a NIC.
> 
> Signed-off-by: Christoph Lameter <cl@...ux-foundation.org>
> Acked-by: Stephen Hemminger <shemminger@...tta.com>
> 

I disagree with this patch.

IPSTATS_MIB_INADDRERRORS has a strong meaning, part of RFCS.

In this path, we simulate the routing of a virtual packet, not its
delivery.

This should not affect IPSTATS SNMP entries.

You should use another MIB entry, say LINUX_MIB_INROUTEERRORS ?

Dont inet_rtm_getroute() caller gets an error status anyway ?

> ---
>  net/ipv4/route.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> Index: linux-2.6/net/ipv4/route.c
> ===================================================================
> --- linux-2.6.orig/net/ipv4/route.c	2010-06-01 11:46:10.000000000 -0500
> +++ linux-2.6/net/ipv4/route.c	2010-06-01 11:52:55.000000000 -0500
> @@ -2981,6 +2981,9 @@ static int inet_rtm_getroute(struct sk_b
>  		rt = skb_rtable(skb);
>  		if (err == 0 && rt->u.dst.error)
>  			err = -rt->u.dst.error;
> +		if (err)
> +			IP_INC_STATS_BH(dev_net(skb->dev),
> +					IPSTATS_MIB_INADDRERRORS);
>  	} else {
>  		struct flowi fl = {
>  			.nl_u = {
> 
> 


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