/*
   *  linux/fs/fifo.c
   *
   *  written by Paul H. Hargrove
   *
   *  Fixes:
   *	10-06-1999, AV: fixed OOM handling in fifo_open(), moved
   *			initialization there, switched to external
   *			allocation of pipe_inode_info.
   */
  
  #include <linux/mm.h>
  #include <linux/slab.h>

  #include <linux/fs.h>

  #include <linux/sched.h>

  #include <linux/pipe_fs_i.h>

  static void wait_for_partner(struct inode* inode, unsigned int *cnt)

  {
  	int cur = *cnt;	

  
  	while (cur == *cnt) {
  		pipe_wait(inode->i_pipe);
  		if (signal_pending(current))

  			break;
  	}
  }
  
  static void wake_up_partner(struct inode* inode)
  {

  	wake_up_interruptible(&inode->i_pipe->wait);

  }
  
  static int fifo_open(struct inode *inode, struct file *filp)
  {

  	struct pipe_inode_info *pipe;

  	int ret;

  	mutex_lock(&inode->i_mutex);

  	pipe = inode->i_pipe;
  	if (!pipe) {

  		ret = -ENOMEM;

  		pipe = alloc_pipe_info(inode);
  		if (!pipe)

  			goto err_nocleanup;

  		inode->i_pipe = pipe;

  	}
  	filp->f_version = 0;
  
  	/* We can only do regular read/write on fifos */
  	filp->f_mode &= (FMODE_READ | FMODE_WRITE);
  
  	switch (filp->f_mode) {

  	case FMODE_READ:

  	/*
  	 *  O_RDONLY
  	 *  POSIX.1 says that O_NONBLOCK means return with the FIFO
  	 *  opened, even when there is no process writing the FIFO.
  	 */

  		filp->f_op = &read_pipefifo_fops;

  		pipe->r_counter++;
  		if (pipe->readers++ == 0)

  			wake_up_partner(inode);

  		if (!pipe->writers) {

  			if ((filp->f_flags & O_NONBLOCK)) {
  				/* suppress POLLHUP until we have
  				 * seen a writer */

  				filp->f_version = pipe->w_counter;

  			} else 
  			{

  				wait_for_partner(inode, &pipe->w_counter);

  				if(signal_pending(current))
  					goto err_rd;
  			}
  		}
  		break;
  	

  	case FMODE_WRITE:

  	/*
  	 *  O_WRONLY
  	 *  POSIX.1 says that O_NONBLOCK means return -1 with
  	 *  errno=ENXIO when there is no process reading the FIFO.
  	 */
  		ret = -ENXIO;

  		if ((filp->f_flags & O_NONBLOCK) && !pipe->readers)

  			goto err;

  		filp->f_op = &write_pipefifo_fops;

  		pipe->w_counter++;
  		if (!pipe->writers++)

  			wake_up_partner(inode);

  		if (!pipe->readers) {
  			wait_for_partner(inode, &pipe->r_counter);

  			if (signal_pending(current))
  				goto err_wr;
  		}
  		break;
  	

  	case FMODE_READ | FMODE_WRITE:

  	/*
  	 *  O_RDWR
  	 *  POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
  	 *  This implementation will NEVER block on a O_RDWR open, since
  	 *  the process can at least talk to itself.
  	 */

  		filp->f_op = &rdwr_pipefifo_fops;

  		pipe->readers++;
  		pipe->writers++;
  		pipe->r_counter++;
  		pipe->w_counter++;
  		if (pipe->readers == 1 || pipe->writers == 1)

  			wake_up_partner(inode);
  		break;
  
  	default:
  		ret = -EINVAL;
  		goto err;
  	}
  
  	/* Ok! */

  	mutex_unlock(&inode->i_mutex);

  	return 0;
  
  err_rd:

  	if (!--pipe->readers)
  		wake_up_interruptible(&pipe->wait);

  	ret = -ERESTARTSYS;
  	goto err;
  
  err_wr:

  	if (!--pipe->writers)
  		wake_up_interruptible(&pipe->wait);

  	ret = -ERESTARTSYS;
  	goto err;
  
  err:

  	if (!pipe->readers && !pipe->writers)

  		free_pipe_info(inode);
  
  err_nocleanup:

  	mutex_unlock(&inode->i_mutex);

  	return ret;
  }
  
  /*
   * Dummy default file-operations: the only thing this does
   * is contain the open that then fills in the correct operations
   * depending on the access mode of the file...
   */

  const struct file_operations def_fifo_fops = {

  	.open		= fifo_open,	/* will set read_ or write_pipefifo_fops */

  };