devprot - (un)set write protection flag in block devices

devprot.c

/*
   devprot - (un)set write protection flag in block devices
   
   Copyright (C) 2012 Fernando Mercês

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/fs.h>
#include <unistd.h>

void fatal(const char *msg)
{
	fprintf(stderr, msg);
	exit(1);
}

void usage()
{
	printf("Usage:\n\t"
			 "devprot <device>\n"
			 "Example:\n\t"
			 "devprot /dev/sdc\n");
}

int main(int argc, char *argv[])
{
	int fd, state;

	if (argc != 2)
	{
		usage();
		exit(1);
	}

	// tenta abri-lo
	if ((fd = open(argv[1], O_RDONLY|O_NONBLOCK)) == -1)
		fatal("unable to open device\n");

	// pega o estado atual
	if (ioctl(fd, BLKROGET, &state) == -1)
		fatal("error getting device status - are you ruth?\n");

	// inverte a logica da coisa
	state = !state;

	// configura o novo estado
	if (ioctl(fd, BLKROSET, &state) == -1)
		fatal("error setting device status - are you ruth?\n");

	printf("%s%sprotected!\n", argv[1], !state ? " un" : " ");
	close(fd);
	return 0;
}