Re: [PATCH] selftests/bpf: Add ring_buffer__consume_n test.

[Jiri Olsa <olsajiri@gmail.com>]

On Sat, Apr 20, 2024 at 05:59:04PM +0200, Andrea Righi wrote:
> Add a testcase for the ring_buffer__consume_n() API.
> 
> The test produces multiple samples in a ring buffer, using a
> sys_getpid() fentry prog, and consumes them from user-space in batches,
> rather than consuming all of them greedily, like ring_buffer__consume()
> does.
> 

SNIP

> diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> index 48c5695b7abf..7e085bfce9b5 100644
> --- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> +++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> @@ -13,6 +13,7 @@
>  #include <linux/perf_event.h>
>  #include <linux/ring_buffer.h>
>  #include "test_ringbuf.lskel.h"
> +#include "test_ringbuf_n.lskel.h"
>  #include "test_ringbuf_map_key.lskel.h"
>  
>  #define EDONE 7777
> @@ -60,6 +61,7 @@ static int process_sample(void *ctx, void *data, size_t len)
>  }
>  
>  static struct test_ringbuf_map_key_lskel *skel_map_key;
> +static struct test_ringbuf_n_lskel *skel_n;

seems like there's no need for this to be static variable

>  static struct test_ringbuf_lskel *skel;
>  static struct ring_buffer *ringbuf;
>  
> @@ -326,6 +328,67 @@ static void ringbuf_subtest(void)
>  	test_ringbuf_lskel__destroy(skel);
>  }
>  
> +/*
> + * Test ring_buffer__consume_n() by producing N_TOT_SAMPLES samples in the ring
> + * buffer, via getpid(), and consuming them in chunks of N_SAMPLES.
> + */
> +#define N_TOT_SAMPLES	32
> +#define N_SAMPLES	4
> +
> +/* Sample value to verify the callback validity */
> +#define SAMPLE_VALUE	42L
> +
> +static int process_n_sample(void *ctx, void *data, size_t len)
> +{
> +	struct sample *s = data;
> +
> +	CHECK(s->value != SAMPLE_VALUE,
> +	      "sample_value", "exp %ld, got %ld\n", SAMPLE_VALUE, s->value);

I think we should use ASSERT macros instead in the new code

> +
> +	return 0;
> +}
> +
> +static void ringbuf_n_subtest(void)
> +{
> +	int err, i;
> +
> +	skel_n = test_ringbuf_n_lskel__open();
> +	if (!ASSERT_OK_PTR(skel_n, "test_ringbuf_n_lskel__open"))
> +		return;
> +
> +	skel_n->maps.ringbuf.max_entries = getpagesize();
> +	skel_n->bss->pid = getpid();
> +
> +	err = test_ringbuf_n_lskel__load(skel_n);
> +	if (!ASSERT_OK(err, "test_ringbuf_n_lskel__load"))
> +		goto cleanup;
> +
> +	ringbuf = ring_buffer__new(skel_n->maps.ringbuf.map_fd,
> +				   process_n_sample, NULL, NULL);
> +	if (!ASSERT_OK_PTR(ringbuf, "ring_buffer__new"))
> +		goto cleanup;
> +
> +	err = test_ringbuf_n_lskel__attach(skel_n);
> +	if (!ASSERT_OK(err, "test_ringbuf_n_lskel__attach"))
> +		goto cleanup_ringbuf;
> +
> +	/* Produce N_TOT_SAMPLES samples in the ring buffer by calling getpid() */
> +	skel->bss->value = SAMPLE_VALUE;

skel_n ?

> +	for (i = 0; i < N_TOT_SAMPLES; i++)
> +		syscall(__NR_getpgid);
> +
> +	/* Consume all samples from the ring buffer in batches of N_SAMPLES */
> +	for (i = 0; i < N_TOT_SAMPLES; i += err) {
> +		err = ring_buffer__consume_n(ringbuf, N_SAMPLES);
> +		ASSERT_EQ(err, N_SAMPLES, "rb_consume");
> +	}
> +

SNIP

> diff --git a/tools/testing/selftests/bpf/progs/test_ringbuf_n.c b/tools/testing/selftests/bpf/progs/test_ringbuf_n.c
> new file mode 100644
> index 000000000000..b98b5bb20699
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_ringbuf_n.c
> @@ -0,0 +1,52 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (c) 2024 Andrea Righi <andrea.righi@canonical.com>
> +
> +#include <linux/bpf.h>
> +#include <sched.h>
> +#include <unistd.h>
> +#include <bpf/bpf_helpers.h>
> +#include "bpf_misc.h"
> +
> +char _license[] SEC("license") = "GPL";
> +
> +#define TASK_COMM_LEN 16
> +
> +struct sample {
> +	int pid;
> +	int seq;

seq does not seem to be checked, is it needed?

jirka

> +	long value;
> +	char comm[16];
> +};
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_RINGBUF);
> +} ringbuf SEC(".maps");
> +
> +int pid = 0;
> +long value = 0;
> +
> +/* inner state */
> +long seq = 0;
> +
> +SEC("fentry/" SYS_PREFIX "sys_getpgid")
> +int test_ringbuf_n(void *ctx)
> +{
> +	int cur_pid = bpf_get_current_pid_tgid() >> 32;
> +	struct sample *sample;
> +
> +	if (cur_pid != pid)
> +		return 0;
> +
> +	sample = bpf_ringbuf_reserve(&ringbuf, sizeof(*sample), 0);
> +	if (!sample)
> +		return 0;
> +
> +	sample->pid = pid;
> +	sample->seq = seq++;
> +	sample->value = value;
> +	bpf_get_current_comm(sample->comm, sizeof(sample->comm));
> +
> +	bpf_ringbuf_submit(sample, 0);
> +
> +	return 0;
> +}
> -- 
> 2.43.0
> 
>