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#include "bpf_misc.h"
7
8char _license[] SEC("license") = "GPL";
9
10struct sample {
11	int pid;
12	int seq;
13	long value;
14	char comm[16];
15};
16
17struct {
18	__uint(type, BPF_MAP_TYPE_RINGBUF);
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("fentry/" SYS_PREFIX "sys_getpgid")
40int test_ringbuf(void *ctx)
41{
42	int cur_pid = bpf_get_current_pid_tgid() >> 32;
43	struct sample *sample;
44
45	if (cur_pid != pid)
46		return 0;
47
48	sample = bpf_ringbuf_reserve(&ringbuf, sizeof(*sample), 0);
49	if (!sample) {
50		__sync_fetch_and_add(&dropped, 1);
51		return 0;
52	}
53
54	sample->pid = pid;
55	bpf_get_current_comm(sample->comm, sizeof(sample->comm));
56	sample->value = value;
57
58	sample->seq = seq++;
59	__sync_fetch_and_add(&total, 1);
60
61	if (sample->seq & 1) {
62		/* copy from reserved sample to a new one... */
63		bpf_ringbuf_output(&ringbuf, sample, sizeof(*sample), flags);
64		/* ...and then discard reserved sample */
65		bpf_ringbuf_discard(sample, flags);
66		__sync_fetch_and_add(&discarded, 1);
67	} else {
68		bpf_ringbuf_submit(sample, flags);
69	}
70
71	avail_data = bpf_ringbuf_query(&ringbuf, BPF_RB_AVAIL_DATA);
72	ring_size = bpf_ringbuf_query(&ringbuf, BPF_RB_RING_SIZE);
73	cons_pos = bpf_ringbuf_query(&ringbuf, BPF_RB_CONS_POS);
74	prod_pos = bpf_ringbuf_query(&ringbuf, BPF_RB_PROD_POS);
75
76	return 0;
77}
78