Re: [PATCH man] ebpf.2: various updates to address some fixmes

[Alexei Starovoitov <ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>]

On 7/28/15 10:35 AM, Daniel Borkmann wrote:
> On 07/28/2015 07:25 PM, Alexei Starovoitov wrote:
>> On 7/28/15 8:29 AM, Daniel Borkmann wrote:
>>> +.BR __sync_fetch_and_add()
>>> +can be used on map values in case the map has a value_size of
>>> sizeof(long).
>>> +This is quite often useful for aggregation and accounting of events.
>>
>> The above is a bit not clear, since both u32 and u64 can be used
>> as atomic counters.
>
> Right, it's unclear indeed. Perhaps the sizeof(long) should be dropped and
> it should say instead "the map has a value_size of 4 or 8 bytes".

that also probably not ideal, since value_size == sizeof(struct elemval)
struct elemval {
   u64 packet_rx;
   u64 byte_rx;
   u32 another_counter;
   ...
   u32 some_useful_field;
};
so the program can keep multiple counters in each map element.

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