1// SPDX-License-Identifier: GPL-2.0
 2// Copyright (c) 2020 Facebook
 3
 4#include <linux/bpf.h>
 5#include <bpf/bpf_helpers.h>
 6
 7char _license[] SEC("license") = "GPL";
 8
 9struct sample {
10	int pid;
11	int seq;
12	long value;
13	char comm[16];
14};
15
16struct {
17	__uint(type, BPF_MAP_TYPE_RINGBUF);
18	__uint(max_entries, 1 << 12);
19} ringbuf SEC(".maps");
20
21/* inputs */
22int pid = 0;
23long value = 0;
24long flags = 0;
25
26/* outputs */
27long total = 0;
28long discarded = 0;
29long dropped = 0;
30
31long avail_data = 0;
32long ring_size = 0;
33long cons_pos = 0;
34long prod_pos = 0;
35
36/* inner state */
37long seq = 0;
38
39SEC("tp/syscalls/sys_enter_getpgid")
40int test_ringbuf(void *ctx)
41{
42	int cur_pid = bpf_get_current_pid_tgid() >> 32;
43	struct sample *sample;
44	int zero = 0;
45
46	if (cur_pid != pid)
47		return 0;
48
49	sample = bpf_ringbuf_reserve(&ringbuf, sizeof(*sample), 0);
50	if (!sample) {
51		__sync_fetch_and_add(&dropped, 1);
52		return 1;
53	}
54
55	sample->pid = pid;
56	bpf_get_current_comm(sample->comm, sizeof(sample->comm));
57	sample->value = value;
58
59	sample->seq = seq++;
60	__sync_fetch_and_add(&total, 1);
61
62	if (sample->seq & 1) {
63		/* copy from reserved sample to a new one... */
64		bpf_ringbuf_output(&ringbuf, sample, sizeof(*sample), flags);
65		/* ...and then discard reserved sample */
66		bpf_ringbuf_discard(sample, flags);
67		__sync_fetch_and_add(&discarded, 1);
68	} else {
69		bpf_ringbuf_submit(sample, flags);
70	}
71
72	avail_data = bpf_ringbuf_query(&ringbuf, BPF_RB_AVAIL_DATA);
73	ring_size = bpf_ringbuf_query(&ringbuf, BPF_RB_RING_SIZE);
74	cons_pos = bpf_ringbuf_query(&ringbuf, BPF_RB_CONS_POS);
75	prod_pos = bpf_ringbuf_query(&ringbuf, BPF_RB_PROD_POS);
76
77	return 0;
78}