/*
 *  Execution of this program creates a large (looking) file at
 *  local system.  The execution of this program stops at offset
 *  which is just beyond what the local filesystem can support.
 *
 *  In case the local filesystem is EXT2 or UFS, the triply-
 *  indirection scheme can support up to following sizes per
 *  filesystem basic block size:
 *
 *   512        2 GB + epsilon
 *    1k       16 GB + epsilon
 *    2k      128 GB + epsilon
 *    4k     1024 GB + epsilon
 *    8k     8192 GB + epsilon  ( not without PAGE_SIZE >= 8 kB )
 *
 *  However, the basic block device layer can support only up to
 *  4G blocks of 512 bytes; being at safe side, lets say 2G blocks
 *  of 512 bytes:  1024 GB without epsilon.
 *
 *  The basic filesystem block size supportable at given system is 
 *  currently dependent on what the system page cache page size is.
 *  If the filesystem basic block exceeds of the system page size,
 *  the system does not work currently. (2.2.* series kernels.)
 *
 *
 *        bb = sizeof(basic block)
 *        B  = bb / 4
 *        MaxSize = bb * (B^3 + B^2 + B + 10)
 *                = bb^4 / 4^3 + bb^3 / 4^2 + bb^2 / 4^1 + 10 * bb
 *                = bb^4 / 64  + bb^3 / 16  + bb^2 / 4   + 10 * bb
 *  
 *        The primary term (bb^4/64) yields that 16 GB for bb=1k
 *        The 'epsilon' is all the rest, and is less than 1/250 of
 *        the primary term for 1kB, even less for larger bb values.
 *
 *
 *  The EXT2 (and UFS) can address up to 4G of "basic blocks", however
 *  that limit will likely to be beyond of other limitations from other
 *  parts of the system.
 *
 */

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>

#define O_LARGEFILE     0100000 /* For i386 only ! */

extern loff_t llseek(int fd, loff_t pos, int whence);

#define LFS "lfs-test.dat"

int main()
{
  int fd;
  loff_t off, pos;
  int rc;

  fd = open(LFS,O_RDWR|O_CREAT|O_TRUNC|O_LARGEFILE,0644);
  if (fd < 0) {
    perror("open('"LFS"',O_RDWR|O_CREAT|O_TRUNC|O_LARGEFILE,0644)");
    exit(88);
  }

  off = 0LL;

  while (1) {
    off += 0x2000000LL; /* 32 MB */
    pos = llseek(fd, off - 4LL, SEEK_SET);
    if (pos == (loff_t)-1LL) {
      fprintf(stdout,"llseek(fd,off,SEEK_SET) off=%Ld; errno=%s\n",
	      off,strerror(errno));
      break;
    }
    fprintf(stdout,"llseek(fd,off,SEEK_SET) new pos = %Ld\n",pos);
    if (write(fd,"01234567",8) != 8) {
      perror("write(fd,'....',8) failed");
      break;
    }
  }
  close(fd);
  exit(99);
}