#include <sys/mman.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>

int main( void )
{
  char *ptr;
  int fd;
  long i;
  char z;

  fd = open( "/dev/mem", O_RDONLY, 0666 );

  if( fd < 0 )
  {
    perror( "open /dev/mem" );
    exit( 1 );
  }

  /* map in 1G worth of physical RAM */
  ptr = mmap( NULL, 0x40000000L, PROT_READ, MAP_SHARED, fd, 0 );

  if( ptr == (void *) -1 )
  {
    perror( "mmap" );
    exit( 1 );
  }

  /* print out memory at 8 meg intervals.  8M * 128 = 1024M */
  for( i = 0; i < 128; i++ )
  {
    /* -> for mmap */
    printf( "%02lx -> %x\n", i, ptr[8 * 1024 * 1024 * i] );

    /* => for lseek/read */
    if( lseek( fd, 8 * 1024 * 1024 * i, SEEK_SET ) < 0 )
    {
      perror( "lseek" );
      exit( 1 );
    }

    if( read( fd, &z, 1 ) != 1 )
    {
      perror( "read" );
      exit( 1 );
    }

    printf( "%02lx => %x\n", i, z );
  }

  return 0;
}