Re: [dpdk-dev] Bulk dequeue of packets and the returned values, question

["Venkatesan, Venky" <venky.venkatesan@intel.com>]

Keith,

On 9/28/2014 11:04 AM, Wiles, Roger Keith wrote:
> I am also looking at the bulk dequeue routines, which the ring can be fixed or variable. On fixed  < 0 on error is returned and 0 if successful. On a variable ring < 0 on error or n on success, but I think n can be zero in the variable case, correct?
>
> If these are true then why not have the routines return  < 0 on error and >= 0 on success. Which means a dequeue from a fixed ring would return only ’requested size n’ or < 0 if you error off the 0 case. The 0 case could be OK, if you allow zero to be return on a empty ring for the fixed ring case.
>
> Does this make sense to anyone?
It won't make sense unless you're aware of the history behind these 
functions. The original functions that were implemented for the ring 
were only the bulk functions (i.e. FIXED). They would return exactly the 
number of items requested for dequeue (0 if success, negative if error), 
and not return any if the required number were not available.

The burst (i.e. VARIABLE) functions came in much later (think it was 
r1.3 where we introduced them), and by that time, there were already 
quite a number of deployments of DPDK in the field using the legacy ring 
functions. Therefore we made the decision to keep the legacy behavior 
intact & not impacting deployed code - and merging the burst functions 
into the code. Given that there was no "versioning" of the API/ABI in 
those releases :).

Hope that helps.
-Venky

>
> Thanks
> ++Keith
>
> Keith Wiles, Principal Technologist with CTO office, Wind River mobile 972-213-5533
>