wait_inotify.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Wait until an inotify event on the given cgroup file.
 */
#include <linux/limits.h>
#include <sys/inotify.h>
#include <sys/mman.h>
#include <sys/ptrace.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <errno.h>
#include <fcntl.h>
#include <poll.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static const char usage[] = "Usage: %s [-v] <cgroup_file>\n";
static char *file;
static int verbose;

static inline void fail_message(char *msg)
{
	fprintf(stderr, msg, file);
	exit(1);
}

int main(int argc, char *argv[])
{
	char *cmd = argv[0];
	int c, fd;
	struct pollfd fds = { .events = POLLIN, };

	while ((c = getopt(argc, argv, "v")) != -1) {
		switch (c) {
		case 'v':
			verbose++;
			break;
		}
		argv++, argc--;
	}

	if (argc != 2) {
		fprintf(stderr, usage, cmd);
		return -1;
	}
	file = argv[1];
	fd = open(file, O_RDONLY);
	if (fd < 0)
		fail_message("Cgroup file %s not found!\n");
	close(fd);

	fd = inotify_init();
	if (fd < 0)
		fail_message("inotify_init() fails on %s!\n");
	if (inotify_add_watch(fd, file, IN_MODIFY) < 0)
		fail_message("inotify_add_watch() fails on %s!\n");
	fds.fd = fd;

	/*
	 * poll waiting loop
	 */
	for (;;) {
		int ret = poll(&fds, 1, 10000);

		if (ret < 0) {
			if (errno == EINTR)
				continue;
			perror("poll");
			exit(1);
		}
		if ((ret > 0) && (fds.revents & POLLIN))
			break;
	}
	if (verbose) {
		struct inotify_event events[10];
		long len;

		usleep(1000);
		len = read(fd, events, sizeof(events));
		printf("Number of events read = %ld\n",
			len/sizeof(struct inotify_event));
	}
	close(fd);
	return 0;
}