mapcmp.c

/*
 * Simple program to compare two mmap'd areas.
 *
 * Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet
 * Copyright (C) 2001 O'Reilly & Associates
 *
 * The source code in this file can be freely used, adapted,
 * and redistributed in source or binary form, so long as an
 * acknowledgment appears in derived source files.  The citation
 * should list that the code comes from the book "Linux Device
 * Drivers" by Alessandro Rubini and Jonathan Corbet, published
 * by O'Reilly & Associates.   No warranty is attached;
 * we cannot take responsibility for errors or fitness for use.
 *
 * $Id: mapcmp.c,v 1.2 2004/03/05 17:35:41 corbet Exp $
 */

#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 *, unsigned long, unsigned long);
#define PAGE_SIZE 4096


int main(int argc, char **argv)
{
    unsigned long 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 = strtoul(argv[3], NULL, 16); // convert the offset to ul
    size = atoi(argv[4]) * PAGE_SIZE; // calculate total # of bytes
    printf("Offset is 0x%lx\n", offset);

    // map the two devices
    addr1 = mapdev(argv[1], offset, size);
    addr2 = mapdev(argv[2], offset, size);

    printf("Comparing...");
    
    // force a write of all user-space buffered data for stdout;
    // to make sure all data has been flushed to the device
    fflush(stdout);
    
    // do the comparison
    for(i = 0; i < size; i++){
        if(*addr1++ != *addr2++){
            printf("areas differ at byte %ld\n", i);
            exit(0);
        }
    }

    printf("areas are identical\n");
    exit(0);
}


static char *mapdev(const char *dev, unsigned long offset, unsigned long 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 (%lu @ %lx) at %p\n", dev, size, offset, addr);
    return (addr);
}