Subject: Re: [PATCH] snmp: add missing counters for RFC 4293

From: Eric Dumazet <[email-masked]>
Date: Tue, 21 Apr 2009 22:45:49 +0200

Neil Horman a écrit :
> On Tue, Apr 21, 2009 at 09:58:51PM +0200, Eric Dumazet wrote:
>> Neil Horman a écrit :
>>> The IP MIB (RFC 4293) defines stats for InOctets, OutOctets, InMcastOctets and
>>> OutMcastOctets:
>>> http://tools.ietf.org/html/rfc4293
>>> But it seems we don't track those in any way that easy to separate from other
>>> protocols.  This patch adds those missing counters to the stats file.  Tested
>>> successfully by me
>>>
>>> Signed-off-by: Neil Horman <[email-masked]>
>>>
>>>
>>>  include/linux/snmp.h  |    4 ++++
>>>  net/ipv4/ip_input.c   |    4 ++++
>>>  net/ipv4/ip_output.c  |    3 +++
>>>  net/ipv4/proc.c       |    4 ++++
>>>  net/ipv6/ip6_input.c  |    4 ++++
>>>  net/ipv6/ip6_output.c |    8 ++++++++
>>>  net/ipv6/mcast.c      |    9 +++++++++
>>>  net/ipv6/ndisc.c      |    3 +++
>>>  net/ipv6/proc.c       |    4 ++++
>>>  net/ipv6/raw.c        |    6 ++++++
>>>  10 files changed, 49 insertions(+)
>>>
>>> diff --git a/include/linux/snmp.h b/include/linux/snmp.h
>>> index aee3f1e..95c17f6 100644
>>> --- a/include/linux/snmp.h
>>> +++ b/include/linux/snmp.h
>>> @@ -19,6 +19,8 @@ enum
>>>  {
>>>  	IPSTATS_MIB_NUM = 0,
>>>  	IPSTATS_MIB_INRECEIVES,			/* InReceives */
>>> +	IPSTATS_MIB_INOCTETS,			/* InOctets */
>>> +	IPSTATS_MIB_INMCASTOCTETS,		/* InMcastOctets */
>>>  	IPSTATS_MIB_INHDRERRORS,		/* InHdrErrors */
>>>  	IPSTATS_MIB_INTOOBIGERRORS,		/* InTooBigErrors */
>>>  	IPSTATS_MIB_INNOROUTES,			/* InNoRoutes */
>>> @@ -29,6 +31,8 @@ enum
>>>  	IPSTATS_MIB_INDELIVERS,			/* InDelivers */
>>>  	IPSTATS_MIB_OUTFORWDATAGRAMS,		/* OutForwDatagrams */
>>>  	IPSTATS_MIB_OUTREQUESTS,		/* OutRequests */
>>> +	IPSTATS_MIB_OUTOCTETS,			/* OutOctets */
>>> +	IPSTATS_MIB_OUTMCASTOCTETS,		/* OutMcastOctets */
>>>  	IPSTATS_MIB_OUTDISCARDS,		/* OutDiscards */
>>>  	IPSTATS_MIB_OUTNOROUTES,		/* OutNoRoutes */
>>>  	IPSTATS_MIB_REASMTIMEOUT,		/* ReasmTimeout */
>>> diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
>>> index 1a58a6f..bc9169b 100644
>>> --- a/net/ipv4/ip_input.c
>>> +++ b/net/ipv4/ip_input.c
>>> @@ -385,6 +385,7 @@ int ip_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt,
>>>  		goto drop;
>>>  
>>>  	IP_INC_STATS_BH(dev_net(dev), IPSTATS_MIB_INRECEIVES);
>>> +	IP_ADD_STATS_BH(dev_net(dev), IPSTATS_MIB_INOCTETS, skb->len);
>>>  
>>>  	if ((skb = skb_share_check(skb, GFP_ATOMIC)) == NULL) {
>>>  		IP_INC_STATS_BH(dev_net(dev), IPSTATS_MIB_INDISCARDS);
>>> @@ -396,6 +397,9 @@ int ip_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt,
>>>  
>>>  	iph = ip_hdr(skb);
>>>  
>>> +	if (ipv4_is_multicast(iph->daddr))
>>> +		IP_ADD_STATS_BH(dev_net(dev), IPSTATS_MIB_INMCASTOCTETS, skb->len);
>>> +
>>>  	/*
>>>  	 *	RFC1122: 3.2.1.2 MUST silently discard any IP frame that fails the checksum.
>>>  	 *
>>> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
>>> index 3e7e910..8a68dc2 100644
>>> --- a/net/ipv4/ip_output.c
>>> +++ b/net/ipv4/ip_output.c
>>> @@ -245,6 +245,8 @@ int ip_mc_output(struct sk_buff *skb)
>>>  	 *	If the indicated interface is up and running, send the packet.
>>>  	 */
>>>  	IP_INC_STATS(dev_net(dev), IPSTATS_MIB_OUTREQUESTS);
>>> +	IP_ADD_STATS_BH(dev_net(dev), IPSTATS_MIB_OUTOCTETS, skb->len);
>>> +	IP_ADD_STATS_BH(dev_net(dev), IPSTATS_MIB_OUTMCASTOCTETS, skb->len);
>> So you use the _BH variant right after IP_INC_STATS() ?
>> Which one is right (or which one is false ?)
>>
> 
> Both are correct (right now), at least as far as I can tell.  I'm not 100% sure why ADD
> was named ADD_BH, except for the fact that it doesn't toggle the use of the mib
> array passed in.  I think the right solution would be to simply rename
> IP_ADD_STATS_BH to IP_ADD_STATS, and modify its implementation to access
> mib[!in_softirq()] rather than just mib[0].  I had planned to do this in a
> followup cleanup patch.  Alternatively, I could add a new IP_ADD_STATS to be
> complete, but I don't really see the advantage (asside from not checking
> in_softirq quite as often).
> 

Both usages in the same function cannot be correct.

Either you use _BH variant because you know you are in softirq
(and non preemptable) context.

Either you use non_BH variant because you are in possibly preemptable context.

Mixing both just proves there is a problem.

And we use _BH variant because it is currently faster (this might change in 2.6.31
thanks to per_cpu infra changes)