Re: [PATCH] libbpf: Allow callbacks at consumption time

[Tamir Duberstein]

On Thu, Jun 11, 2026 at 10:03 PM <bot+bpf-ci@xxxxxxxxxx> wrote:
>
> >     libbpf: Allow callbacks at consumption time
> >
> >     Ring buffer callbacks and contexts are fixed when each ring is added to
> >     a manager. Callers that drain records into per-operation state, such as
> >     a bounded destination buffer, must therefore keep mutable dispatch state
> >     alive for the lifetime of the manager or rebuild it for each operation.
> >
> >     Add bounded manager and per-ring consumption APIs that take a callback
> >     and context for one operation. The supplied callback overrides the
> >     configured callback without changing it. This also allows managers used
> >     only through the new APIs to be created without a setup-time callback.
> >
> >     Make zero-record requests return without invoking callbacks so all
> >     bounded consumption APIs preserve their bound.
> >
> >     Signed-off-by: Tamir Duberstein <tamird@xxxxxxxxxx>
>
> Part of this change looks like a bug fix.  The early return added to
> ringbuf_process_ring():
>
>         if (n == 0)
>                 return 0;
>
> makes a request for zero records return without consuming or dispatching
> anything.  Before this, the cnt >= n limit was only checked after the
> sample callback ran, so an n == 0 request still consumed and dispatched
> one record and violated the requested bound.
>
> That bound-violation behavior came in with the bounded consumption APIs
> ring_buffer__consume_n() / ring__consume_n() and the n parameter on
> ringbuf_process_ring().  Should this carry:
>
>   Fixes: 4d22ea94ea33 ("libbpf: Add ring__consume_n / ring_buffer__consume_n")

Thanks. My clanker flagged the same. I will extract this fix into a
separate patch in v2.