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

// not correctly in the headers yet!!
#define O_DIRECT	 040000	/* direct disk access hint */

int main(int argc, char **argv)
{
        int fd;
        char *buf;
        int pages;
        int rc; 

        if (argc != 3) { 
                printf("Usage: %s file nr_pages\n", argv[0]);
                return 1;
        }

        pages = strtoul(argv[2], 0, 0);
        printf("directio on %s for %d pages \n", argv[1], pages);

        buf = mmap(0, pages * 4096, PROT_READ|PROT_WRITE, 
                   MAP_PRIVATE|MAP_ANON, 0, 0);
        if (!buf) { 
                printf("No memory %s\n", strerror(errno));
                return 1;
        }

        fd = open(argv[1], O_DIRECT | O_RDWR | O_CREAT);
        if (fd == -1) { 
                printf("Cannot open %s:  %s\n", argv[1], strerror(errno));
                return 1;
        }

        rc = read(fd, buf, pages * 4096); 
        if (rc != pages * 4096) { 
                printf("Read error: %s, rc %d\n", strerror(errno), rc);
                return 1;
        }

        if ( lseek(fd, 0, SEEK_SET) != 0 ) { 
                printf("Cannot seek %s\n", strerror(errno));
                return 1;
        }

        rc = write(fd, buf, pages * 4096); 
        if (rc != pages * 4096) { 
                printf("Write error %s\n", strerror(errno));
                return 1;
        }

        return 0;
}