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

warning: implicit declaration of function ‘fstat’ [-Wimplicit-function-declaration]
  if((fstat(op, &buf)) != 0){