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
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