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@canonical.com --- 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; 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);

Introduce a new API to consume items from a ring buffer, limited to a specified amount, and return to the caller the actual number of items consumed.

Link: https://lore.kernel.org/lkml/20240310154726.734289-1-andrea.righi@canonical.... Signed-off-by: Andrea Righi andrea.righi@canonical.com --- tools/lib/bpf/libbpf.h | 12 ++++++++++++ tools/lib/bpf/libbpf.map | 3 +++ tools/lib/bpf/ringbuf.c | 38 +++++++++++++++++++++++++++++++++++--- 3 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h index f88ab50c0229..4f775a6dcaa0 100644 --- a/tools/lib/bpf/libbpf.h +++ b/tools/lib/bpf/libbpf.h @@ -1293,6 +1293,7 @@ LIBBPF_API int ring_buffer__add(struct ring_buffer *rb, int map_fd, ring_buffer_sample_fn sample_cb, void *ctx); LIBBPF_API int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms); LIBBPF_API int ring_buffer__consume(struct ring_buffer *rb); +LIBBPF_API int ring_buffer__consume_n(struct ring_buffer *rb, size_t n); LIBBPF_API int ring_buffer__epoll_fd(const struct ring_buffer *rb);

/** @@ -1367,6 +1368,17 @@ LIBBPF_API int ring__map_fd(const struct ring *r); */ LIBBPF_API int ring__consume(struct ring *r);

+/** + * @brief **ring__consume_n()** consumes up to a requested amount of items from + * a ringbuffer without event polling. + * + * @param r A ringbuffer object. + * @param n Maximum amount of items to consume. + * @return The number of items consumed, or a negative number if any of the + * callbacks return an error. + */ +LIBBPF_API int ring__consume_n(struct ring *r, size_t n); + struct user_ring_buffer_opts { size_t sz; /* size of this struct, for forward/backward compatibility */ }; diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map index 5dd81a7b96b5..23d82bba021a 100644 --- a/tools/lib/bpf/libbpf.map +++ b/tools/lib/bpf/libbpf.map @@ -418,4 +418,7 @@ LIBBPF_1.4.0 { } LIBBPF_1.3.0;

LIBBPF_1.5.0 { + global: + ring__consume_n; + ring_buffer__consume_n; } LIBBPF_1.4.0; diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c index 2c4031168413..19cd34883011 100644 --- a/tools/lib/bpf/ringbuf.c +++ b/tools/lib/bpf/ringbuf.c @@ -277,6 +277,33 @@ static int64_t ringbuf_process_ring(struct ring *r, size_t n) return cnt; }

+/* Consume available ring buffer(s) data without event polling, up to n + * records. + * + * Returns number of records consumed across all registered ring buffers (or + * n, whichever is less), or negative number if any of the callbacks return + * error. + */ +int ring_buffer__consume_n(struct ring_buffer *rb, size_t n) +{ + int64_t err, res = 0; + int i; + + for (i = 0; i < rb->ring_cnt; i++) { + struct ring *ring = rb->rings[i]; + + err = ringbuf_process_ring(ring, n); + if (err < 0) + return libbpf_err(err); + res += err; + n -= err; + + if (n == 0) + break; + } + return res; +} + /* Consume available ring buffer(s) data without event polling. * Returns number of records consumed across all registered ring buffers (or * INT_MAX, whichever is less), or negative number if any of the callbacks @@ -378,17 +405,22 @@ int ring__map_fd(const struct ring *r) return r->map_fd; }

-int ring__consume(struct ring *r) +int ring__consume_n(struct ring *r, size_t n) { - int64_t res; + int res;

- res = ringbuf_process_ring(r, INT_MAX); + res = ringbuf_process_ring(r, n); if (res < 0) return libbpf_err(res);

return res > INT_MAX ? INT_MAX : res; }

+int ring__consume(struct ring *r) +{ + return ring__consume_n(r, INT_MAX); +} + static void user_ringbuf_unmap_ring(struct user_ring_buffer *rb) { if (rb->consumer_pos) {