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


#define BUFSZ 1000000000  // 10GB
// adjust above for smaller tests
// requires 10GB io_benchmark.dat file in the working directory filled with random data
static unsigned char buf[BUFSZ];

int main(int argc, char *argv[])
{
        unsigned int total, msize, offset, secs;
        int fd, i, j, rslt;
        void * p;
        char c;
        struct timeval start, end;

// Time 1000 mmaps and munmaps from random offsets for various
// sizes of mapped chunk.
        for (msize = 4096; msize <= 1048576; msize *= 16) {
                gettimeofday(&start, NULL);
                fd = open("io_benchmark.dat", O_RDONLY); // file
                if (fd  < 0 ) abort();
                for (i = 0; i < 1000; i++) {
                // Make sure the block to be mapped doesn't start in the
                // last meg and is multiply of 4096.
                offset = (off_t) random() % (BUFSZ - 1048576) /10000 * 4096;
                p = mmap(0, (size_t) msize, PROT_READ, MAP_PRIVATE, fd, offset);
                if (p == MAP_FAILED){
                        printf("map failed: %s offset: %i \n", strerror(errno), offset);
                }
                for (j = 1; j < msize; j++) {
                        c = *((char *)p+j);
                        }
                munmap(p, (size_t) msize);
                }
        gettimeofday(&end, NULL);
        secs = ((end.tv_sec * 1000) + (end.tv_usec /1000)) - ((start.tv_sec * 1000) + (start.tv_usec /1000)) ;
        printf("1000 mmaps %d kB blocks: %i ms\n", msize/1024, secs);
  rslt = close(fd);
  if (fd  < 0 ) abort();
  }
    return 0;
}