Linux: check CD-ROM tray status

trayopen.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <libgen.h>
#include <linux/cdrom.h>

#define DEFAULT_CDROM_DEV "/dev/cdrom"
#define PROGNAME_TRAYOPEN "trayopen"
#define PROGNAME_TRAYCLOSED "trayclosed"
#define FATAL_ERROR_EXIT_CODE -1
#define UNKNOWN_EXIT_CODE -2

#if defined(__GNUC__) && !defined(DONT_EXPECT)
#define trayopen_unlikely(x) (__builtin_expect(!!(x), 0))
#define trayopen_likely(x) (__builtin_expect(!!(x), 1))
#else
#define trayopen_unlikely(x) (!!(x))
#define trayopen_likely(x) (!!(x))
#endif

const char name_trayopen[] = PROGNAME_TRAYOPEN;
const char name_trayclosed[] = PROGNAME_TRAYCLOSED;

int main(int argc, char **argv)
{
	int expect_open, r, exit_code;
	const char *dev, *invoked_name;
	size_t prog_path_len;
	char *program_path;
	int fd;

	if (trayopen_unlikely(argc < 1))
	{
		return FATAL_ERROR_EXIT_CODE;
	}

	prog_path_len = strlen(argv[0]);
	program_path = malloc(prog_path_len + 1);
	if (trayopen_unlikely(program_path == NULL))
	{
		return FATAL_ERROR_EXIT_CODE;
	}
	strncpy(program_path, argv[0], prog_path_len);
	program_path[prog_path_len] = '\0';

	invoked_name = basename(program_path);
	if (strcmp(invoked_name, name_trayopen) == 0)
	{
		expect_open = 1;
	}
	else if (strcmp(invoked_name, name_trayclosed) == 0)
	{
		expect_open = 0;
	}
	else
	{
		free(program_path);
		fprintf(stderr, "%s: this program must be invoked as either `%s` or `%s`.\n",
				argv[0], name_trayopen, name_trayclosed);
		return FATAL_ERROR_EXIT_CODE;
	}
	free(program_path);

	if (trayopen_unlikely(argc > 2))
	{
		fprintf(stderr, "Usage:\n"
				"	%s [<name>] - determine if tray is opened.\n"
				"	%s [<name>] - determine if tray is closed.\n",
				name_trayopen, name_trayclosed);
		return FATAL_ERROR_EXIT_CODE;
	}

	dev = argc < 2 ? DEFAULT_CDROM_DEV : argv[1];
	if ((fd = open(dev, O_RDONLY | O_NONBLOCK)) < 0)
	{
		perror("opening cd-rom device");
		return FATAL_ERROR_EXIT_CODE;
	}

	if ((r = ioctl(fd, CDROM_DRIVE_STATUS)) < 0)
	{
		perror("ioctl CDROM_DRIVE_STATUS");
		close(fd);
		return FATAL_ERROR_EXIT_CODE;
	}
	close(fd);

	if (r == CDS_NO_INFO)
	{
		fprintf(stderr, "%s: CDROM_DRIVE_STATUS not implemented\n", argv[0]);
		fflush(stderr);
		puts("unknown");
		return UNKNOWN_EXIT_CODE;
	}
	else if (r == CDS_TRAY_OPEN)
	{
		exit_code = (expect_open ? EXIT_SUCCESS : EXIT_FAILURE);
	}
	else
	{
		exit_code = (expect_open ? EXIT_FAILURE : EXIT_SUCCESS);
	}

	return exit_code;
}