RE: [PATCH] libbpf: add support for canceling cached_cons advance

["Li,Rongqing" <lirongqing@baidu.com>]

> -----Original Message-----
> From: Magnus Karlsson [mailto:magnus.karlsson@gmail.com]
> Sent: Monday, November 23, 2020 5:40 PM
> To: Li,Rongqing <lirongqing@baidu.com>
> Cc: Network Development <netdev@vger.kernel.org>; bpf
> <bpf@vger.kernel.org>
> Subject: Re: [PATCH] libbpf: add support for canceling cached_cons advance
> 
> On Sun, Nov 22, 2020 at 2:21 PM Li RongQing <lirongqing@baidu.com> wrote:
> >
> > It is possible to fail receiving packets after calling
> > xsk_ring_cons__peek, at this condition, cached_cons has been advanced,
> > should be cancelled.
> 
> Thanks RongQing,
> 
> I have needed this myself in various situations, so I think we should add this.
> But your motivation in the commit message is somewhat confusing. How about
> something like this?
> 
> 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.
> 
> Replace your commit message with this, fix the bug below, send a v2 and then I
> am happy to ack this.


Thank you very much
> 
> /Magnus
> 
> > Signed-off-by: Li RongQing <lirongqing@baidu.com>
> > ---
> >  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..4128215c246b 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) {
> > +       rx->cached_cons -= nb;
> 
> cons-> not rx->. Please make sure the v2 compiles and passes checkpatch.
> 

Sorry for building error
I will send V2

Thanks 

-Li


> > +}
> > +
> >  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
> >