1 /*
2 * cgroup_event_listener.c - Simple listener of cgroup events
3 *
4 * Copyright (C) Kirill A. Shutemov <kirill@shutemov.name>
5 */
6
7 #include <assert.h>
8 #include <errno.h>
9 #include <fcntl.h>
10 #include <libgen.h>
11 #include <limits.h>
12 #include <stdio.h>
13 #include <string.h>
14 #include <unistd.h>
15
16 #include <sys/eventfd.h>
17
18 #define USAGE_STR "Usage: cgroup_event_listener <path-to-control-file> <args>\n"
19
main(int argc,char ** argv)20 int main(int argc, char **argv)
21 {
22 int efd = -1;
23 int cfd = -1;
24 int event_control = -1;
25 char event_control_path[PATH_MAX];
26 char line[LINE_MAX];
27 int ret;
28
29 if (argc != 3) {
30 fputs(USAGE_STR, stderr);
31 return 1;
32 }
33
34 cfd = open(argv[1], O_RDONLY);
35 if (cfd == -1) {
36 fprintf(stderr, "Cannot open %s: %s\n", argv[1],
37 strerror(errno));
38 goto out;
39 }
40
41 ret = snprintf(event_control_path, PATH_MAX, "%s/cgroup.event_control",
42 dirname(argv[1]));
43 if (ret >= PATH_MAX) {
44 fputs("Path to cgroup.event_control is too long\n", stderr);
45 goto out;
46 }
47
48 event_control = open(event_control_path, O_WRONLY);
49 if (event_control == -1) {
50 fprintf(stderr, "Cannot open %s: %s\n", event_control_path,
51 strerror(errno));
52 goto out;
53 }
54
55 efd = eventfd(0, 0);
56 if (efd == -1) {
57 perror("eventfd() failed");
58 goto out;
59 }
60
61 ret = snprintf(line, LINE_MAX, "%d %d %s", efd, cfd, argv[2]);
62 if (ret >= LINE_MAX) {
63 fputs("Arguments string is too long\n", stderr);
64 goto out;
65 }
66
67 ret = write(event_control, line, strlen(line) + 1);
68 if (ret == -1) {
69 perror("Cannot write to cgroup.event_control");
70 goto out;
71 }
72
73 while (1) {
74 uint64_t result;
75
76 ret = read(efd, &result, sizeof(result));
77 if (ret == -1) {
78 if (errno == EINTR)
79 continue;
80 perror("Cannot read from eventfd");
81 break;
82 }
83 assert(ret == sizeof(result));
84
85 ret = access(event_control_path, W_OK);
86 if ((ret == -1) && (errno == ENOENT)) {
87 puts("The cgroup seems to have removed.");
88 ret = 0;
89 break;
90 }
91
92 if (ret == -1) {
93 perror("cgroup.event_control "
94 "is not accessible any more");
95 break;
96 }
97
98 printf("%s %s: crossed\n", argv[1], argv[2]);
99 }
100
101 out:
102 if (efd >= 0)
103 close(efd);
104 if (event_control >= 0)
105 close(event_control);
106 if (cfd >= 0)
107 close(cfd);
108
109 return (ret != 0);
110 }
111