/*
 * $Id: zerofile.c,v 1.5 2013/01/09 04:48:36 grog Exp $
 *
 * Create a file with zero content.  Continue until the file system is full or
 * the optionally specified number of bytes have been written.
 *
 * This seemingly useless program makes the file system more easily compressible
 * for a physical backup.
 */
#include <errno.h>
#include <sys/limits.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define MANYMANY 131072
#ifndef O_LARGEFILE                             /* This *horrible* Linux kludge */
#ifdef linux                                    /* ... which Linux even hides */
#define O_LARGEFILE 0100000
#else
#define O_LARGEFILE 0
#endif
#endif

int main (int argc, char *argv [])
{
  char *buf;
  int myfile;
  int count;
  long size;

  buf = malloc (MANYMANY);
  memset (buf, 0, MANYMANY);

  if ((argc > 3) || (argc < 2))
    {
    fprintf (stderr, "Usage:\n\t%s filename [size in MB]\n", argv [0]);
    exit (1);
    }
  if (argc == 3)
    size = atol (argv [2]) * 8;			/* number of I/O transfers */
  else
    size = INT_MAX;
  myfile = open (argv [1], O_CREAT | O_RDWR | O_LARGEFILE, 0666);
  if (myfile < 0)
    {
    fprintf (stderr,
             "Can't open %s: %s (%d)\n",
             argv [1],
             strerror (errno),
             errno);
    exit (1);
    }
  while (size--)
    {
    count = write (myfile, buf, MANYMANY);
    if (count < 0)
      {
      fprintf (stderr,
               "Can't write to %s: %s (%d)\n",
               argv [1],
               strerror (errno),
               errno );
      exit (1);
      }
    else if (count == 0)
      exit (0);
    }
  /* NOTREACHED */
  return 0;
}