linux/tools/gpio/gpio-watch.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * gpio-watch - monitor unrequested lines for property changes using the
 *              character device
 *
 * Copyright (C) 2019 BayLibre SAS
 * Author: Bartosz Golaszewski <bgolaszewski@baylibre.com>
 */

#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <linux/gpio.h>
#include <poll.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <unistd.h>

int main(int argc, char **argv)
{
	struct gpioline_info_changed chg;
	struct gpioline_info req;
	struct pollfd pfd;
	int fd, i, j, ret;
	char *event, *end;
	ssize_t rd;

	if (argc < 3)
		goto err_usage;

	fd = open(argv[1], O_RDWR | O_CLOEXEC);
	if (fd < 0) {
		perror("unable to open gpiochip");
		return EXIT_FAILURE;
	}

	for (i = 0, j = 2; i < argc - 2; i++, j++) {
		memset(&req, 0, sizeof(req));

		req.line_offset = strtoul(argv[j], &end, 0);
		if (*end != '\0')
			goto err_usage;

		ret = ioctl(fd, GPIO_GET_LINEINFO_WATCH_IOCTL, &req);
		if (ret) {
			perror("unable to set up line watch");
			return EXIT_FAILURE;
		}
	}

	pfd.fd = fd;
	pfd.events = POLLIN | POLLPRI;

	for (;;) {
		ret = poll(&pfd, 1, 5000);
		if (ret < 0) {
			perror("error polling the linechanged fd");
			return EXIT_FAILURE;
		} else if (ret > 0) {
			memset(&chg, 0, sizeof(chg));
			rd = read(pfd.fd, &chg, sizeof(chg));
			if (rd < 0 || rd != sizeof(chg)) {
				if (rd != sizeof(chg))
					errno = EIO;

				perror("error reading line change event");
				return EXIT_FAILURE;
			}

			switch (chg.event_type) {
			case GPIOLINE_CHANGED_REQUESTED:
				event = "requested";
				break;
			case GPIOLINE_CHANGED_RELEASED:
				event = "released";
				break;
			case GPIOLINE_CHANGED_CONFIG:
				event = "config changed";
				break;
			default:
				fprintf(stderr,
					"invalid event type received from the kernel\n");
				return EXIT_FAILURE;
			}

			printf("line %u: %s at %llu\n",
			       chg.info.line_offset, event, chg.timestamp);
		}
	}

	return 0;

err_usage:
	printf("%s: <gpiochip> <line0> <line1> ...\n", argv[0]);
	return EXIT_FAILURE;
}