Re: [PATCH net-next 1/3] ip: discard IPv4 datagrams with overlapping segments.

[Eric Dumazet <eric.dumazet@gmail.com>]

On 08/02/2018 03:54 PM, Stephen Hemminger wrote:
> On Thu,  2 Aug 2018 22:45:58 +0000
> Peter Oskolkov <posk@google.com> wrote:
> 
>> diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
>> index e5ebc83827ab..da1a144f1a51 100644
>> --- a/include/uapi/linux/snmp.h
>> +++ b/include/uapi/linux/snmp.h
>> @@ -40,6 +40,7 @@ enum
>>  	IPSTATS_MIB_REASMREQDS,			/* ReasmReqds */
>>  	IPSTATS_MIB_REASMOKS,			/* ReasmOKs */
>>  	IPSTATS_MIB_REASMFAILS,			/* ReasmFails */
>> +	IPSTATS_MIB_REASM_OVERLAPS,		/* ReasmOverlaps */
>>  	IPSTATS_MIB_FRAGOKS,			/* FragOKs */
>>  	IPSTATS_MIB_FRAGFAILS,			/* FragFails */
>>  	IPSTATS_MIB_FRAGCREATES,		/* FragCreates */
> 
> Inserting new entries in the middle of an enum means the numeric
> values will change. Isn't this going to break userspace ABI?
> 

I would argue the only exported thing from the kernel are the Key:Val in the /proc files.

Not sure why these enum are uapi.

Commit 46c2fa39877ed70415ee2b1acfb9129e956f6de4 added LINUX_MIB_TCPFASTOPENBLACKHOLE in the middle,
and really nobody complained.


Commit 0604475119de5f80dc051a5db055c6a2a75bd542 added LINUX_MIBSTCPMEMORYPRESSURESCHRONO
in the middle as well.

I am pretty sure we should maintain locality of these counters to lower number
of dirtied cache lines, say under IP frag DDOS ;)