1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Wait until an inotify event on the given cgroup file.
4  */
5 #include <linux/limits.h>
6 #include <sys/inotify.h>
7 #include <sys/mman.h>
8 #include <sys/ptrace.h>
9 #include <sys/stat.h>
10 #include <sys/types.h>
11 #include <errno.h>
12 #include <fcntl.h>
13 #include <poll.h>
14 #include <stdio.h>
15 #include <stdlib.h>
16 #include <string.h>
17 #include <unistd.h>
18 
19 static const char usage[] = "Usage: %s [-v] <cgroup_file>\n";
20 static char *file;
21 static int verbose;
22 
23 static inline void fail_message(char *msg)
24 {
25 	fprintf(stderr, msg, file);
26 	exit(1);
27 }
28 
29 int main(int argc, char *argv[])
30 {
31 	char *cmd = argv[0];
32 	int c, fd;
33 	struct pollfd fds = { .events = POLLIN, };
34 
35 	while ((c = getopt(argc, argv, "v")) != -1) {
36 		switch (c) {
37 		case 'v':
38 			verbose++;
39 			break;
40 		}
41 		argv++, argc--;
42 	}
43 
44 	if (argc != 2) {
45 		fprintf(stderr, usage, cmd);
46 		return -1;
47 	}
48 	file = argv[1];
49 	fd = open(file, O_RDONLY);
50 	if (fd < 0)
51 		fail_message("Cgroup file %s not found!\n");
52 	close(fd);
53 
54 	fd = inotify_init();
55 	if (fd < 0)
56 		fail_message("inotify_init() fails on %s!\n");
57 	if (inotify_add_watch(fd, file, IN_MODIFY) < 0)
58 		fail_message("inotify_add_watch() fails on %s!\n");
59 	fds.fd = fd;
60 
61 	/*
62 	 * poll waiting loop
63 	 */
64 	for (;;) {
65 		int ret = poll(&fds, 1, 10000);
66 
67 		if (ret < 0) {
68 			if (errno == EINTR)
69 				continue;
70 			perror("poll");
71 			exit(1);
72 		}
73 		if ((ret > 0) && (fds.revents & POLLIN))
74 			break;
75 	}
76 	if (verbose) {
77 		struct inotify_event events[10];
78 		long len;
79 
80 		usleep(1000);
81 		len = read(fd, events, sizeof(events));
82 		printf("Number of events read = %ld\n",
83 			len/sizeof(struct inotify_event));
84 	}
85 	close(fd);
86 	return 0;
87 }
88