/* * Simple program to compare two mmap'd areas. */#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <sys/mman.h>#include <sys/errno.h>#include <fcntl.h>static char *mapdev (const char *, int, int);/* * memcmp dev1 dev2 offset pages */int main (int argc, char **argv){	unsigned int offset, size, i;	char *addr1, *addr2;/* * Sanity check. */	if (argc != 5)	{		fprintf (stderr, "Usage: mapcmp dev1 dev2 offset pages\n");		exit (1);	}/* * Map the two devices. */	offset = atoi (argv[3]);	size = atoi (argv[4]);	addr1 = mapdev (argv[1], offset, size);	addr2 = mapdev (argv[2], offset, size);/* * Do the comparison. */	printf ("Comparing...");	fflush (stdout);	for (i = 0; i < size; i++)		if (*addr1++ != *addr2++)		{			printf ("areas differ at byte %d\n", i);			exit (0);		}	printf ("areas are identical.\n");	exit (0);}static char *mapdev (const char *dev, int offset, int size){	char *addr;	int fd = open (dev, O_RDONLY);	if (fd < 0)	{		perror (dev);		exit (1);	}	addr = mmap (0, size, PROT_READ, MAP_PRIVATE, fd, offset);	if (addr == MAP_FAILED)	{		perror (dev);		exit (1);	}	printf ("Mapped %s (%d @ %d) at 0x%p\n", dev, size, offset, addr);	return (addr);}