Re: [PATCH v2 1/2] can: fix multiple delivery of a single CAN frame for overlapping CAN filters

[Oliver Hartkopp <socketcan@hartkopp.net>]

On 18.03.2015 23:17, Ahmed S. Darwish wrote:

>> diff --git a/net/can/raw.c b/net/can/raw.c
>> index 00c13ef..0a6abf1 100644
>> --- a/net/can/raw.c
>> +++ b/net/can/raw.c
>> @@ -86,6 +86,8 @@ struct raw_sock {
>>   	struct can_filter dfilter; /* default/single filter */
>>   	struct can_filter *filter; /* pointer to filter(s) */
>>   	can_err_mask_t err_mask;
>> +	struct sk_buff *uniq_skb;
>> +	ktime_t uniq_tstamp;
>>   };
>>
>
> My knowledge of the networking internals are really shallow,
> but the `uniq_tstamp' field above feels a little bit redundant?

(..)

> If so, isn't the `uniq_skb' field, on its own, quite sufficient?

AFAIK the skbs are retrieved from a memory pool, so it can be that the skb 
pointer values can be the same by the time.

E.g. if you receive the CAN frames in a timely distance that the skb pointer 
accidentally is the same than the last time, you might unintentionally drop a 
new (changed) content.

With checking the timestamp this possibility of potentially identical skb 
pointers is removed.

Regards,
Oliver