1// SPDX-License-Identifier: GPL-2.0
2/*
3 * cgroup_event_listener.c - Simple listener of cgroup events
4 *
5 * Copyright (C) Kirill A. Shutemov <kirill@shutemov.name>
6 */
7
8#include <assert.h>
9#include <err.h>
10#include <errno.h>
11#include <fcntl.h>
12#include <libgen.h>
13#include <limits.h>
14#include <stdio.h>
15#include <string.h>
16#include <unistd.h>
17
18#include <sys/eventfd.h>
19
20#define USAGE_STR "Usage: cgroup_event_listener <path-to-control-file> <args>"
21
22int main(int argc, char **argv)
23{
24 int efd = -1;
25 int cfd = -1;
26 int event_control = -1;
27 char event_control_path[PATH_MAX];
28 char line[LINE_MAX];
29 int ret;
30
31 if (argc != 3)
32 errx(1, "%s", USAGE_STR);
33
34 cfd = open(argv[1], O_RDONLY);
35 if (cfd == -1)
36 err(1, "Cannot open %s", argv[1]);
37
38 ret = snprintf(event_control_path, PATH_MAX, "%s/cgroup.event_control",
39 dirname(argv[1]));
40 if (ret >= PATH_MAX)
41 errx(1, "Path to cgroup.event_control is too long");
42
43 event_control = open(event_control_path, O_WRONLY);
44 if (event_control == -1)
45 err(1, "Cannot open %s", event_control_path);
46
47 efd = eventfd(0, 0);
48 if (efd == -1)
49 err(1, "eventfd() failed");
50
51 ret = snprintf(line, LINE_MAX, "%d %d %s", efd, cfd, argv[2]);
52 if (ret >= LINE_MAX)
53 errx(1, "Arguments string is too long");
54
55 ret = write(event_control, line, strlen(line) + 1);
56 if (ret == -1)
57 err(1, "Cannot write to cgroup.event_control");
58
59 while (1) {
60 uint64_t result;
61
62 ret = read(efd, &result, sizeof(result));
63 if (ret == -1) {
64 if (errno == EINTR)
65 continue;
66 err(1, "Cannot read from eventfd");
67 }
68 assert(ret == sizeof(result));
69
70 ret = access(event_control_path, W_OK);
71 if ((ret == -1) && (errno == ENOENT)) {
72 puts("The cgroup seems to have removed.");
73 break;
74 }
75
76 if (ret == -1)
77 err(1, "cgroup.event_control is not accessible any more");
78
79 printf("%s %s: crossed\n", argv[1], argv[2]);
80 }
81
82 return 0;
83}
84

source code of linux/tools/cgroup/cgroup_event_listener.c