poll.c

 1// SPDX-License-Identifier: GPL-2.0
 2/*
 3 * Simple poll on a file.
 4 *
 5 * Copyright (c) 2024 Google LLC.
 6 */
 7
 8#include <errno.h>
 9#include <fcntl.h>
10#include <poll.h>
11#include <stdio.h>
12#include <stdlib.h>
13#include <string.h>
14#include <unistd.h>
15
16#define BUFSIZE 4096
17
18/*
19 * Usage:
20 *  poll [-I|-P] [-t timeout] FILE
21 */
22int main(int argc, char *argv[])
23{
24	struct pollfd pfd = {.events = POLLIN};
25	char buf[BUFSIZE];
26	int timeout = -1;
27	int ret, opt;
28
29	while ((opt = getopt(argc, argv, "IPt:")) != -1) {
30		switch (opt) {
31		case 'I':
32			pfd.events = POLLIN;
33			break;
34		case 'P':
35			pfd.events = POLLPRI;
36			break;
37		case 't':
38			timeout = atoi(optarg);
39			break;
40		default:
41			fprintf(stderr, "Usage: %s [-I|-P] [-t timeout] FILE\n",
42				argv[0]);
43			return -1;
44		}
45	}
46	if (optind >= argc) {
47		fprintf(stderr, "Error: Polling file is not specified\n");
48		return -1;
49	}
50
51	pfd.fd = open(argv[optind], O_RDONLY);
52	if (pfd.fd < 0) {
53		fprintf(stderr, "failed to open %s", argv[optind]);
54		perror("open");
55		return -1;
56	}
57
58	/* Reset poll by read if POLLIN is specified. */
59	if (pfd.events & POLLIN)
60		do {} while (read(pfd.fd, buf, BUFSIZE) == BUFSIZE);
61
62	ret = poll(&pfd, 1, timeout);
63	if (ret < 0 && errno != EINTR) {
64		perror("poll");
65		return -1;
66	}
67	close(pfd.fd);
68
69	/* If timeout happned (ret == 0), exit code is 1 */
70	if (ret == 0)
71		return 1;
72
73	return 0;
74}