Merge branch 'add libbpf getters for individual ringbuffers'

Martin Kelly says:

====================
This patch series adds a new ring__ API to libbpf exposing getters for
accessing the individual ringbuffers inside a struct ring_buffer. This is
useful for polling individually, getting available data, or similar use
cases. The API looks like this, and was roughly proposed by Andrii Nakryiko
in another thread:

Getting a ring struct:
struct ring *ring_buffer__ring(struct ring_buffer *rb, unsigned int idx);

Using the ring struct:
unsigned long ring__consumer_pos(const struct ring *r);
unsigned long ring__producer_pos(const struct ring *r);
size_t ring__avail_data_size(const struct ring *r);
size_t ring__size(const struct ring *r);
int ring__map_fd(const struct ring *r);
int ring__consume(struct ring *r);

Changes in v2:
- Addressed all feedback from Andrii Nakryiko
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

tools/lib/bpf/libbpf.h

@@ -1229,6 +1229,7 @@ LIBBPF_API int bpf_tc_query(const struct bpf_tc_hook *hook,
 
 /* Ring buffer APIs */
 struct ring_buffer;
+struct ring;
 struct user_ring_buffer;
 
 typedef int (*ring_buffer_sample_fn)(void *ctx, void *data, size_t size);
@@ -1249,6 +1250,78 @@ 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__epoll_fd(const struct ring_buffer *rb);
 
+/**
+ * @brief **ring_buffer__ring()** returns the ringbuffer object inside a given
+ * ringbuffer manager representing a single BPF_MAP_TYPE_RINGBUF map instance.
+ *
+ * @param rb A ringbuffer manager object.
+ * @param idx An index into the ringbuffers contained within the ringbuffer
+ * manager object. The index is 0-based and corresponds to the order in which
+ * ring_buffer__add was called.
+ * @return A ringbuffer object on success; NULL and errno set if the index is
+ * invalid.
+ */
+LIBBPF_API struct ring *ring_buffer__ring(struct ring_buffer *rb,
+					  unsigned int idx);
+
+/**
+ * @brief **ring__consumer_pos()** returns the current consumer position in the
+ * given ringbuffer.
+ *
+ * @param r A ringbuffer object.
+ * @return The current consumer position.
+ */
+LIBBPF_API unsigned long ring__consumer_pos(const struct ring *r);
+
+/**
+ * @brief **ring__producer_pos()** returns the current producer position in the
+ * given ringbuffer.
+ *
+ * @param r A ringbuffer object.
+ * @return The current producer position.
+ */
+LIBBPF_API unsigned long ring__producer_pos(const struct ring *r);
+
+/**
+ * @brief **ring__avail_data_size()** returns the number of bytes in the
+ * ringbuffer not yet consumed. This has no locking associated with it, so it
+ * can be inaccurate if operations are ongoing while this is called. However, it
+ * should still show the correct trend over the long-term.
+ *
+ * @param r A ringbuffer object.
+ * @return The number of bytes not yet consumed.
+ */
+LIBBPF_API size_t ring__avail_data_size(const struct ring *r);
+
+/**
+ * @brief **ring__size()** returns the total size of the ringbuffer's map data
+ * area (excluding special producer/consumer pages). Effectively this gives the
+ * amount of usable bytes of data inside the ringbuffer.
+ *
+ * @param r A ringbuffer object.
+ * @return The total size of the ringbuffer map data area.
+ */
+LIBBPF_API size_t ring__size(const struct ring *r);
+
+/**
+ * @brief **ring__map_fd()** returns the file descriptor underlying the given
+ * ringbuffer.
+ *
+ * @param r A ringbuffer object.
+ * @return The underlying ringbuffer file descriptor
+ */
+LIBBPF_API int ring__map_fd(const struct ring *r);
+
+/**
+ * @brief **ring__consume()** consumes available ringbuffer data without event
+ * polling.
+ *
+ * @param r A ringbuffer object.
+ * @return The number of records consumed (or INT_MAX, whichever is less), or
+ * a negative number if any of the callbacks return an error.
+ */
+LIBBPF_API int ring__consume(struct ring *r);
+
 struct user_ring_buffer_opts {
 	size_t sz; /* size of this struct, for forward/backward compatibility */
 };

tools/lib/bpf/libbpf.map

@@ -400,4 +400,11 @@ LIBBPF_1.3.0 {
 		bpf_program__attach_netfilter;
 		bpf_program__attach_tcx;
 		bpf_program__attach_uprobe_multi;
+		ring__avail_data_size;
+		ring__consume;
+		ring__consumer_pos;
+		ring__map_fd;
+		ring__producer_pos;
+		ring__size;
+		ring_buffer__ring;
 } LIBBPF_1.2.0;

tools/lib/bpf/ringbuf.c

@@ -34,7 +34,7 @@ struct ring {
 
 struct ring_buffer {
 	struct epoll_event *events;
-	struct ring *rings;
+	struct ring **rings;
 	size_t page_size;
 	int epoll_fd;
 	int ring_cnt;
@@ -57,7 +57,7 @@ struct ringbuf_hdr {
 	__u32 pad;
 };
 
-static void ringbuf_unmap_ring(struct ring_buffer *rb, struct ring *r)
+static void ringbuf_free_ring(struct ring_buffer *rb, struct ring *r)
 {
 	if (r->consumer_pos) {
 		munmap(r->consumer_pos, rb->page_size);
@@ -67,6 +67,8 @@ static void ringbuf_unmap_ring(struct ring_buffer *rb, struct ring *r)
 		munmap(r->producer_pos, rb->page_size + 2 * (r->mask + 1));
 		r->producer_pos = NULL;
 	}
+
+	free(r);
 }
 
 /* Add extra RINGBUF maps to this ring buffer manager */
@@ -107,8 +109,10 @@ int ring_buffer__add(struct ring_buffer *rb, int map_fd,
 		return libbpf_err(-ENOMEM);
 	rb->events = tmp;
 
-	r = &rb->rings[rb->ring_cnt];
-	memset(r, 0, sizeof(*r));
+	r = calloc(1, sizeof(*r));
+	if (!r)
+		return libbpf_err(-ENOMEM);
+	rb->rings[rb->ring_cnt] = r;
 
 	r->map_fd = map_fd;
 	r->sample_cb = sample_cb;
@@ -121,7 +125,7 @@ int ring_buffer__add(struct ring_buffer *rb, int map_fd,
 		err = -errno;
 		pr_warn("ringbuf: failed to mmap consumer page for map fd=%d: %d\n",
 			map_fd, err);
-		return libbpf_err(err);
+		goto err_out;
 	}
 	r->consumer_pos = tmp;
 
@@ -131,16 +135,16 @@ int ring_buffer__add(struct ring_buffer *rb, int map_fd,
 	 */
 	mmap_sz = rb->page_size + 2 * (__u64)info.max_entries;
 	if (mmap_sz != (__u64)(size_t)mmap_sz) {
+		err = -E2BIG;
 		pr_warn("ringbuf: ring buffer size (%u) is too big\n", info.max_entries);
-		return libbpf_err(-E2BIG);
+		goto err_out;
 	}
 	tmp = mmap(NULL, (size_t)mmap_sz, PROT_READ, MAP_SHARED, map_fd, rb->page_size);
 	if (tmp == MAP_FAILED) {
 		err = -errno;
-		ringbuf_unmap_ring(rb, r);
 		pr_warn("ringbuf: failed to mmap data pages for map fd=%d: %d\n",
 			map_fd, err);
-		return libbpf_err(err);
+		goto err_out;
 	}
 	r->producer_pos = tmp;
 	r->data = tmp + rb->page_size;
@@ -152,14 +156,17 @@ int ring_buffer__add(struct ring_buffer *rb, int map_fd,
 	e->data.fd = rb->ring_cnt;
 	if (epoll_ctl(rb->epoll_fd, EPOLL_CTL_ADD, map_fd, e) < 0) {
 		err = -errno;
-		ringbuf_unmap_ring(rb, r);
 		pr_warn("ringbuf: failed to epoll add map fd=%d: %d\n",
 			map_fd, err);
-		return libbpf_err(err);
+		goto err_out;
 	}
 
 	rb->ring_cnt++;
 	return 0;
+
+err_out:
+	ringbuf_free_ring(rb, r);
+	return libbpf_err(err);
 }
 
 void ring_buffer__free(struct ring_buffer *rb)
@@ -170,7 +177,7 @@ void ring_buffer__free(struct ring_buffer *rb)
 		return;
 
 	for (i = 0; i < rb->ring_cnt; ++i)
-		ringbuf_unmap_ring(rb, &rb->rings[i]);
+		ringbuf_free_ring(rb, rb->rings[i]);
 	if (rb->epoll_fd >= 0)
 		close(rb->epoll_fd);
 
@@ -278,7 +285,7 @@ int ring_buffer__consume(struct ring_buffer *rb)
 	int i;
 
 	for (i = 0; i < rb->ring_cnt; i++) {
-		struct ring *ring = &rb->rings[i];
+		struct ring *ring = rb->rings[i];
 
 		err = ringbuf_process_ring(ring);
 		if (err < 0)
@@ -305,7 +312,7 @@ int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms)
 
 	for (i = 0; i < cnt; i++) {
 		__u32 ring_id = rb->events[i].data.fd;
-		struct ring *ring = &rb->rings[ring_id];
+		struct ring *ring = rb->rings[ring_id];
 
 		err = ringbuf_process_ring(ring);
 		if (err < 0)
@@ -323,6 +330,58 @@ int ring_buffer__epoll_fd(const struct ring_buffer *rb)
 	return rb->epoll_fd;
 }
 
+struct ring *ring_buffer__ring(struct ring_buffer *rb, unsigned int idx)
+{
+	if (idx >= rb->ring_cnt)
+		return errno = ERANGE, NULL;
+
+	return rb->rings[idx];
+}
+
+unsigned long ring__consumer_pos(const struct ring *r)
+{
+	/* Synchronizes with smp_store_release() in ringbuf_process_ring(). */
+	return smp_load_acquire(r->consumer_pos);
+}
+
+unsigned long ring__producer_pos(const struct ring *r)
+{
+	/* Synchronizes with smp_store_release() in __bpf_ringbuf_reserve() in
+	 * the kernel.
+	 */
+	return smp_load_acquire(r->producer_pos);
+}
+
+size_t ring__avail_data_size(const struct ring *r)
+{
+	unsigned long cons_pos, prod_pos;
+
+	cons_pos = ring__consumer_pos(r);
+	prod_pos = ring__producer_pos(r);
+	return prod_pos - cons_pos;
+}
+
+size_t ring__size(const struct ring *r)
+{
+	return r->mask + 1;
+}
+
+int ring__map_fd(const struct ring *r)
+{
+	return r->map_fd;
+}
+
+int ring__consume(struct ring *r)
+{
+	int64_t res;
+
+	res = ringbuf_process_ring(r);
+	if (res < 0)
+		return libbpf_err(res);
+
+	return res > INT_MAX ? INT_MAX : res;
+}
+
 static void user_ringbuf_unmap_ring(struct user_ring_buffer *rb)
 {
 	if (rb->consumer_pos) {

tools/testing/selftests/bpf/prog_tests/ringbuf.c

@@ -91,6 +91,9 @@ static void ringbuf_subtest(void)
 	int err, cnt, rb_fd;
 	int page_size = getpagesize();
 	void *mmap_ptr, *tmp_ptr;
+	struct ring *ring;
+	int map_fd;
+	unsigned long avail_data, ring_size, cons_pos, prod_pos;
 
 	skel = test_ringbuf_lskel__open();
 	if (CHECK(!skel, "skel_open", "skeleton open failed\n"))
@@ -162,6 +165,13 @@ static void ringbuf_subtest(void)
 
 	trigger_samples();
 
+	ring = ring_buffer__ring(ringbuf, 0);
+	if (!ASSERT_OK_PTR(ring, "ring_buffer__ring_idx_0"))
+		goto cleanup;
+
+	map_fd = ring__map_fd(ring);
+	ASSERT_EQ(map_fd, skel->maps.ringbuf.map_fd, "ring_map_fd");
+
 	/* 2 submitted + 1 discarded records */
 	CHECK(skel->bss->avail_data != 3 * rec_sz,
 	      "err_avail_size", "exp %ld, got %ld\n",
@@ -176,6 +186,18 @@ static void ringbuf_subtest(void)
 	      "err_prod_pos", "exp %ld, got %ld\n",
 	      3L * rec_sz, skel->bss->prod_pos);
 
+	/* verify getting this data directly via the ring object yields the same
+	 * results
+	 */
+	avail_data = ring__avail_data_size(ring);
+	ASSERT_EQ(avail_data, 3 * rec_sz, "ring_avail_size");
+	ring_size = ring__size(ring);
+	ASSERT_EQ(ring_size, page_size, "ring_ring_size");
+	cons_pos = ring__consumer_pos(ring);
+	ASSERT_EQ(cons_pos, 0, "ring_cons_pos");
+	prod_pos = ring__producer_pos(ring);
+	ASSERT_EQ(prod_pos, 3 * rec_sz, "ring_prod_pos");
+
 	/* poll for samples */
 	err = ring_buffer__poll(ringbuf, -1);
 
@@ -282,6 +304,10 @@ static void ringbuf_subtest(void)
 	err = ring_buffer__consume(ringbuf);
 	CHECK(err < 0, "rb_consume", "failed: %d\b", err);
 
+	/* also consume using ring__consume to make sure it works the same */
+	err = ring__consume(ring);
+	ASSERT_GE(err, 0, "ring_consume");
+
 	/* 3 rounds, 2 samples each */
 	cnt = atomic_xchg(&sample_cnt, 0);
 	CHECK(cnt != 6, "cnt", "exp %d samples, got %d\n", 6, cnt);

tools/testing/selftests/bpf/prog_tests/ringbuf_multi.c

@@ -42,6 +42,8 @@ void test_ringbuf_multi(void)
 {
 	struct test_ringbuf_multi *skel;
 	struct ring_buffer *ringbuf = NULL;
+	struct ring *ring_old;
+	struct ring *ring;
 	int err;
 	int page_size = getpagesize();
 	int proto_fd = -1;
@@ -84,11 +86,24 @@ void test_ringbuf_multi(void)
 	if (CHECK(!ringbuf, "ringbuf_create", "failed to create ringbuf\n"))
 		goto cleanup;
 
+	/* verify ring_buffer__ring returns expected results */
+	ring = ring_buffer__ring(ringbuf, 0);
+	if (!ASSERT_OK_PTR(ring, "ring_buffer__ring_idx_0"))
+		goto cleanup;
+	ring_old = ring;
+	ring = ring_buffer__ring(ringbuf, 1);
+	ASSERT_ERR_PTR(ring, "ring_buffer__ring_idx_1");
+
 	err = ring_buffer__add(ringbuf, bpf_map__fd(skel->maps.ringbuf2),
 			      process_sample, (void *)(long)2);
 	if (CHECK(err, "ringbuf_add", "failed to add another ring\n"))
 		goto cleanup;
 
+	/* verify adding a new ring didn't invalidate our older pointer */
+	ring = ring_buffer__ring(ringbuf, 0);
+	if (!ASSERT_EQ(ring, ring_old, "ring_buffer__ring_again"))
+		goto cleanup;
+
 	err = test_ringbuf_multi__attach(skel);
 	if (CHECK(err, "skel_attach", "skeleton attachment failed: %d\n", err))
 		goto cleanup;