[PATCH v4 0/4] libbpf: API to partially consume items from ringbuffer

[PATCH v4 0/4] libbpf: API to partially consume items from ringbuffer

[Andrea Righi]

Introduce ring__consume_n() and ring_buffer__consume_n() API to
partially consume items from one (or more) ringbuffer(s).

This can be useful, for example, to consume just a single item or when
we need to copy multiple items to a limited user-space buffer from the
ringbuffer callback.

Practical example (where this API can be used):
https://github.com/sched-ext/scx/blob/b7c06b9ed9f72cad83c31e39e9c4e2cfd8683a55/rust/scx_rustland_core/src/bpf.rs#L217

See also:
https://lore.kernel.org/lkml/20240310154726.734289-1-andrea.righi@canonical.com/T/#u

v4:
 - add a selftest to test the new API
 - open a new 1.5.0 cycle

v3:
 - rename ring__consume_max() -> ring__consume_n() and
   ring_buffer__consume_max() -> ring_buffer__consume_n()
 - add new API to a new 1.5.0 cycle
 - fixed minor nits / comments

v2:
 - introduce a new API instead of changing the callback's retcode
   behavior

Andrea Righi (4):
      libbpf: Start v1.5 development cycle
      libbpf: ringbuf: allow to consume up to a certain amount of items
      libbpf: Add ring__consume_n / ring_buffer__consume_n
      selftests/bpf: Add tests for ring__consume_n and ring_buffer__consume_n

 tools/lib/bpf/libbpf.h                           | 12 +++++
 tools/lib/bpf/libbpf.map                         |  6 +++
 tools/lib/bpf/libbpf_version.h                   |  2 +-
 tools/lib/bpf/ringbuf.c                          | 59 ++++++++++++++++++++----
 tools/testing/selftests/bpf/prog_tests/ringbuf.c |  8 ++++
 5 files changed, 76 insertions(+), 11 deletions(-)

[PATCH v4 1/4] libbpf: Start v1.5 development cycle

[Andrea Righi]

Bump libbpf.map to v1.5.0 to start a new libbpf version cycle.

Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
---
 tools/lib/bpf/libbpf.map       | 3 +++
 tools/lib/bpf/libbpf_version.h | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 51732ecb1385..5dd81a7b96b5 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -416,3 +416,6 @@ LIBBPF_1.4.0 {
 		btf__new_split;
 		btf_ext__raw_data;
 } LIBBPF_1.3.0;
+
+LIBBPF_1.5.0 {
+} LIBBPF_1.4.0;
diff --git a/tools/lib/bpf/libbpf_version.h b/tools/lib/bpf/libbpf_version.h
index e783a47da815..d6e5eff967cb 100644
--- a/tools/lib/bpf/libbpf_version.h
+++ b/tools/lib/bpf/libbpf_version.h
@@ -4,6 +4,6 @@
 #define __LIBBPF_VERSION_H
 
 #define LIBBPF_MAJOR_VERSION 1
-#define LIBBPF_MINOR_VERSION 4
+#define LIBBPF_MINOR_VERSION 5
 
 #endif /* __LIBBPF_VERSION_H */
-- 
2.43.0

[PATCH v4 2/4] libbpf: ringbuf: allow to consume up to a certain amount of items

[Andrea Righi]

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);
 
-- 
2.43.0

[PATCH v4 3/4] libbpf: Add ring__consume_n / ring_buffer__consume_n

[Andrea Righi]

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.com/T
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) {
-- 
2.43.0

[PATCH v4 4/4] selftests/bpf: Add tests for ring__consume_n and ring_buffer__consume_n

[Andrea Righi]

Add tests for new API ring__consume_n() and ring_buffer__consume_n().

Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
---
 tools/testing/selftests/bpf/prog_tests/ringbuf.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
index 48c5695b7abf..33aba7684ab9 100644
--- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c
+++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
@@ -304,10 +304,18 @@ static void ringbuf_subtest(void)
 	err = ring_buffer__consume(ringbuf);
 	CHECK(err < 0, "rb_consume", "failed: %d\b", err);
 
+	/* try to consume up to one item */
+	err = ring_buffer__consume_n(ringbuf, 1);
+	CHECK(err < 0 || err > 1, "rb_consume_n", "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");
 
+	/* try to consume up to one item */
+	err = ring__consume_n(ring, 1);
+	CHECK(err < 0 || err > 1, "ring_consume_n", "failed: %d\b", err);
+
 	/* 3 rounds, 2 samples each */
 	cnt = atomic_xchg(&sample_cnt, 0);
 	CHECK(cnt != 6, "cnt", "exp %d samples, got %d\n", 6, cnt);
-- 
2.43.0

Re: [PATCH v4 4/4] selftests/bpf: Add tests for ring__consume_n and ring_buffer__consume_n

[Andrii Nakryiko]

On Sat, Apr 6, 2024 at 2:20 AM Andrea Righi <andrea.righi@canonical.com> wrote:
>
> Add tests for new API ring__consume_n() and ring_buffer__consume_n().
>
> Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
> ---
>  tools/testing/selftests/bpf/prog_tests/ringbuf.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> index 48c5695b7abf..33aba7684ab9 100644
> --- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> +++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> @@ -304,10 +304,18 @@ static void ringbuf_subtest(void)
>         err = ring_buffer__consume(ringbuf);
>         CHECK(err < 0, "rb_consume", "failed: %d\b", err);
>
> +       /* try to consume up to one item */
> +       err = ring_buffer__consume_n(ringbuf, 1);
> +       CHECK(err < 0 || err > 1, "rb_consume_n", "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");
>
> +       /* try to consume up to one item */
> +       err = ring__consume_n(ring, 1);
> +       CHECK(err < 0 || err > 1, "ring_consume_n", "failed: %d\b", err);
> +

Did you actually run this test? There is ring_buffer__consume() and
ring__consume() calls right before your added calls, so consume_n will
return zero.

I dropped this broken patch. Please send a proper test as a follow up.

>         /* 3 rounds, 2 samples each */
>         cnt = atomic_xchg(&sample_cnt, 0);
>         CHECK(cnt != 6, "cnt", "exp %d samples, got %d\n", 6, cnt);
> --
> 2.43.0
>

Re: [PATCH v4 2/4] libbpf: ringbuf: allow to consume up to a certain amount of items

[Andrii Nakryiko]

On Sat, Apr 6, 2024 at 2:20 AM Andrea Righi <andrea.righi@canonical.com> 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@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;

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
>

Re: [PATCH v4 0/4] libbpf: API to partially consume items from ringbuffer

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Sat,  6 Apr 2024 11:15:40 +0200 you wrote:
> Introduce ring__consume_n() and ring_buffer__consume_n() API to
> partially consume items from one (or more) ringbuffer(s).
> 
> This can be useful, for example, to consume just a single item or when
> we need to copy multiple items to a limited user-space buffer from the
> ringbuffer callback.
> 
> [...]

Here is the summary with links:
  - [v4,1/4] libbpf: Start v1.5 development cycle
    https://git.kernel.org/bpf/bpf-next/c/5bd2ed658231
  - [v4,2/4] libbpf: ringbuf: allow to consume up to a certain amount of items
    https://git.kernel.org/bpf/bpf-next/c/13e8125a2276
  - [v4,3/4] libbpf: Add ring__consume_n / ring_buffer__consume_n
    https://git.kernel.org/bpf/bpf-next/c/4d22ea94ea33
  - [v4,4/4] selftests/bpf: Add tests for ring__consume_n and ring_buffer__consume_n
    (no matching commit)

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

Re: [PATCH v4 4/4] selftests/bpf: Add tests for ring__consume_n and ring_buffer__consume_n

[Andrii Nakryiko]

On Sat, Apr 6, 2024 at 10:39 AM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Sat, Apr 6, 2024 at 2:20 AM Andrea Righi <andrea.righi@canonical.com> wrote:
> >
> > Add tests for new API ring__consume_n() and ring_buffer__consume_n().
> >
> > Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
> > ---
> >  tools/testing/selftests/bpf/prog_tests/ringbuf.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> > index 48c5695b7abf..33aba7684ab9 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> > @@ -304,10 +304,18 @@ static void ringbuf_subtest(void)
> >         err = ring_buffer__consume(ringbuf);
> >         CHECK(err < 0, "rb_consume", "failed: %d\b", err);
> >
> > +       /* try to consume up to one item */
> > +       err = ring_buffer__consume_n(ringbuf, 1);
> > +       CHECK(err < 0 || err > 1, "rb_consume_n", "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");
> >
> > +       /* try to consume up to one item */
> > +       err = ring__consume_n(ring, 1);
> > +       CHECK(err < 0 || err > 1, "ring_consume_n", "failed: %d\b", err);
> > +
>
> Did you actually run this test? There is ring_buffer__consume() and
> ring__consume() calls right before your added calls, so consume_n will
> return zero.
>
> I dropped this broken patch. Please send a proper test as a follow up.

Sorry, technically, it's not broken, it just doesn't test much (CHECK
conditions confused me, I didn't realize you allow zero initially). We
will never consume anything and the result will be zero, which isn't
very meaningful.

"Interesting" test would set up things so that we have >1 item in
ringbuf and we consume exactly one at a time, because that's the new
logic you added.

I think it will be simpler to add a dedicated and simpler ringbuf test
for this, where you can specify how many items to submit, and then do
a bunch of consume/consume_n invocations, checking exact results.

Plus, please don't add new CHECK() uses, use ASSERT_XXX() ones instead.

I've applied first three patches because they look correct and it's
good to setup libbpf 1.5 dev cycle, but please do follow up with a
better test. Thanks.

>
> >         /* 3 rounds, 2 samples each */
> >         cnt = atomic_xchg(&sample_cnt, 0);
> >         CHECK(cnt != 6, "cnt", "exp %d samples, got %d\n", 6, cnt);
> > --
> > 2.43.0
> >

Re: [PATCH v4 4/4] selftests/bpf: Add tests for ring__consume_n and ring_buffer__consume_n

[Andrea Righi]

On Sat, Apr 06, 2024 at 10:52:10AM -0700, Andrii Nakryiko wrote:
> On Sat, Apr 6, 2024 at 10:39 AM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
> >
> > On Sat, Apr 6, 2024 at 2:20 AM Andrea Righi <andrea.righi@canonical.com> wrote:
> > >
> > > Add tests for new API ring__consume_n() and ring_buffer__consume_n().
> > >
> > > Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
> > > ---
> > >  tools/testing/selftests/bpf/prog_tests/ringbuf.c | 8 ++++++++
> > >  1 file changed, 8 insertions(+)
> > >
> > > diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> > > index 48c5695b7abf..33aba7684ab9 100644
> > > --- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> > > +++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> > > @@ -304,10 +304,18 @@ static void ringbuf_subtest(void)
> > >         err = ring_buffer__consume(ringbuf);
> > >         CHECK(err < 0, "rb_consume", "failed: %d\b", err);
> > >
> > > +       /* try to consume up to one item */
> > > +       err = ring_buffer__consume_n(ringbuf, 1);
> > > +       CHECK(err < 0 || err > 1, "rb_consume_n", "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");
> > >
> > > +       /* try to consume up to one item */
> > > +       err = ring__consume_n(ring, 1);
> > > +       CHECK(err < 0 || err > 1, "ring_consume_n", "failed: %d\b", err);
> > > +
> >
> > Did you actually run this test? There is ring_buffer__consume() and
> > ring__consume() calls right before your added calls, so consume_n will
> > return zero.
> >
> > I dropped this broken patch. Please send a proper test as a follow up.
> 
> Sorry, technically, it's not broken, it just doesn't test much (CHECK
> conditions confused me, I didn't realize you allow zero initially). We
> will never consume anything and the result will be zero, which isn't
> very meaningful.
> 
> "Interesting" test would set up things so that we have >1 item in
> ringbuf and we consume exactly one at a time, because that's the new
> logic you added.
> 
> I think it will be simpler to add a dedicated and simpler ringbuf test
> for this, where you can specify how many items to submit, and then do
> a bunch of consume/consume_n invocations, checking exact results.
> 
> Plus, please don't add new CHECK() uses, use ASSERT_XXX() ones instead.
> 
> I've applied first three patches because they look correct and it's
> good to setup libbpf 1.5 dev cycle, but please do follow up with a
> better test. Thanks.

Yeah, sorry, I tried to add a minimal test to the existing one, but I
agree that it not very meaningful.

I already have a better dedicated test case for this
(https://github.com/arighi/ebpf-maps/blob/libbpf-consume-n/src/main.c#L118),
I just need to integrate it in the kselftest properly (and maybe
pre-generate more than N records in the ring buffer, so that we can
better test if the limit works as expected).

I'll send another patch to add a proper test case.

Thanks for applying the other patches!
-Andrea

> 
> >
> > >         /* 3 rounds, 2 samples each */
> > >         cnt = atomic_xchg(&sample_cnt, 0);
> > >         CHECK(cnt != 6, "cnt", "exp %d samples, got %d\n", 6, cnt);
> > > --
> > > 2.43.0
> > >