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 
8 char _license[] SEC("license") = "GPL";
9 
10 struct sample {
11 	int pid;
12 	int seq;
13 	long value;
14 	char comm[16];
15 };
16 
17 struct {
18 	__uint(type, BPF_MAP_TYPE_RINGBUF);
19 } ringbuf SEC(".maps");
20 
21 /* inputs */
22 int pid = 0;
23 long value = 0;
24 long flags = 0;
25 
26 /* outputs */
27 long total = 0;
28 long discarded = 0;
29 long dropped = 0;
30 
31 long avail_data = 0;
32 long ring_size = 0;
33 long cons_pos = 0;
34 long prod_pos = 0;
35 
36 /* inner state */
37 long seq = 0;
38 
39 SEC("fentry/" SYS_PREFIX "sys_getpgid")
40 int 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