On Sat, Apr 6, 2024 at 2:20 AM Andrea Righi <andrea.righi@xxxxxxxxxxxxx> wrote:
>
> In some cases, instead of always consuming all items from ring buffers
> in a greedy way, we may want to consume up to a certain amount of items,
> for example when we need to copy items from the BPF ring buffer to a
> limited user buffer.
>
> This change allows to set an upper limit to the amount of items consumed
> from one or more ring buffers.
>
> Signed-off-by: Andrea Righi <andrea.righi@xxxxxxxxxxxxx>
> ---
> tools/lib/bpf/ringbuf.c | 23 +++++++++++++++--------
> 1 file changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
> index aacb64278a01..2c4031168413 100644
> --- a/tools/lib/bpf/ringbuf.c
> +++ b/tools/lib/bpf/ringbuf.c
> @@ -231,7 +231,7 @@ static inline int roundup_len(__u32 len)
> return (len + 7) / 8 * 8;
> }
>
> -static int64_t ringbuf_process_ring(struct ring *r)
> +static int64_t ringbuf_process_ring(struct ring *r, size_t n)
> {
> int *len_ptr, len, err;
> /* 64-bit to avoid overflow in case of extreme application behavior */
> @@ -268,6 +268,9 @@ static int64_t ringbuf_process_ring(struct ring *r)
> }
>
> smp_store_release(r->consumer_pos, cons_pos);
> +
> + if (cnt >= n)
> + goto done;
> }
> } while (got_new_data);
> done:
> @@ -287,13 +290,15 @@ int ring_buffer__consume(struct ring_buffer *rb)
> for (i = 0; i < rb->ring_cnt; i++) {
> struct ring *ring = rb->rings[i];
>
> - err = ringbuf_process_ring(ring);
> + err = ringbuf_process_ring(ring, INT_MAX);
> if (err < 0)
> return libbpf_err(err);
> res += err;
> + if (res > INT_MAX) {
> + res = INT_MAX;
> + break;
> + }
> }
> - if (res > INT_MAX)
> - return INT_MAX;
the idea here was to avoid returning overflown int, not really to stop
at INT_MAX samples. So I kept this part intact (res is int64_t, so no
overflow inside the loop can happen)
> return res;
> }
>
> @@ -314,13 +319,15 @@ int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms)
> __u32 ring_id = rb->events[i].data.fd;
> struct ring *ring = rb->rings[ring_id];
>
> - err = ringbuf_process_ring(ring);
> + err = ringbuf_process_ring(ring, INT_MAX);
> if (err < 0)
> return libbpf_err(err);
> res += err;
> + if (res > INT_MAX) {
> + res = INT_MAX;
> + break;
> + }
> }
> - if (res > INT_MAX)
> - return INT_MAX;
> return res;
> }
>
> @@ -375,7 +382,7 @@ int ring__consume(struct ring *r)
> {
> int64_t res;
>
> - res = ringbuf_process_ring(r);
> + res = ringbuf_process_ring(r, INT_MAX);
> if (res < 0)
> return libbpf_err(res);
>
> --
> 2.43.0
>
