#include <sys/types.h>
#include <sys/stat.h>
/* Normal <fcntl.h> doesn't include O_DIRECT on the host used */
#include <linux/fcntl.h>
#include <stdio.h>
#include <errno.h>

/*

  This is a test snippet that fails on Linux kernel 2.4.
  The source is a slightly modified version of

    https://mail.clusterfs.com/pipermail/lustre-discuss/2006-March/001344.html
    
  You need to create the file before running this program,

    % touch testfile.dat

  If you replace 512 below with 'block_size', write works.

*/

int main(int argc, char **argv)
{
  int         i, err, fd, block_size;
  mode_t      io_mode;
  char       *buf, *filename;
  long long   offset = 0;
  struct stat statBuf;

  filename = "testfile.dat";

  /* get system block size */
  stat(filename, &statBuf);
  block_size = statBuf.st_blksize;
  printf("Writing to file: %s   block_size=%d\n",filename,block_size);

  buf = (char*) malloc(block_size * 2);
  buf += block_size - ((long)buf % 512); 

  printf("Pointer is : 0x%x, block_size=0x%x\n",buf, block_size);

  for (i=0; i<block_size; i++) buf[i] = 'z';

  io_mode = O_CREAT | O_WRONLY | O_DIRECT;

  fd = open(filename, io_mode, 0600);
  if (fd == -1) printf("Error when open file %s\n", filename);

  err = write(fd, buf, block_size);
  if (err == -1)
    printf("WRITE Error: offset=%lld len=%d - errno=%d(EINVAL=%d)\n",offset,block_size,errno,EINVAL);
  else
    printf("WRITE Success: offset=%lld len=%d err=%d\n",offset,block_size,err);

  close(fd);
  free(buf);
  return 0;
}