Re: [PATCH][V2] libbpf: add support for canceling cached_cons advance

[Daniel Borkmann <daniel@iogearbox.net>]

On 11/24/20 9:12 AM, Magnus Karlsson wrote:
> On Tue, Nov 24, 2020 at 8:33 AM Li RongQing <lirongqing@baidu.com> wrote:
>>
>> Add a new function for returning descriptors the user received
>> after an xsk_ring_cons__peek call. After the application has
>> gotten a number of descriptors from a ring, it might not be able
>> to or want to process them all for various reasons. Therefore,
>> it would be useful to have an interface for returning or
>> cancelling a number of them so that they are returned to the ring.
>>
>> This patch adds a new function called xsk_ring_cons__cancel that
>> performs this operation on nb descriptors counted from the end of
>> the batch of descriptors that was received through the peek call.
>>
>> Signed-off-by: Li RongQing <lirongqing@baidu.com>
>> [ Magnus Karlsson: rewrote changelog ]
>> Cc: Magnus Karlsson <magnus.karlsson@intel.com>
>> ---
>> diff with v1: fix the building, and rewrote changelog
>>
>>   tools/lib/bpf/xsk.h | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
>> index 1069c46364ff..1719a327e5f9 100644
>> --- a/tools/lib/bpf/xsk.h
>> +++ b/tools/lib/bpf/xsk.h
>> @@ -153,6 +153,12 @@ static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons,
>>          return entries;
>>   }
>>
>> +static inline void xsk_ring_cons__cancel(struct xsk_ring_cons *cons,
>> +                                        size_t nb)
>> +{
>> +       cons->cached_cons -= nb;
>> +}
>> +
>>   static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)
>>   {
>>          /* Make sure data has been read before indicating we are done
>> --
>> 2.17.3
> 
> Thank you RongQing.
> 
> Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>

@Magnus: shouldn't the xsk_ring_cons__cancel() nb type be '__u32 nb' instead?

Thanks,
Daniel