/*
       *  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/malloc.h>
      #include <linux/smp_lock.h>
      
  16  static void wait_for_partner(struct inode* inode, unsigned int* cnt)
      {
      	int cur = *cnt;	
  19  	while(cur == *cnt) {
      		pipe_wait(inode);
  21  		if(signal_pending(current))
  22  			break;
      	}
      }
      
  26  static void wake_up_partner(struct inode* inode)
      {
      	wake_up_interruptible(PIPE_WAIT(*inode));
      }
      
  31  static int fifo_open(struct inode *inode, struct file *filp)
      {
      	int ret;
      
      	ret = -ERESTARTSYS;
  36  	lock_kernel();
  37  	if (down_interruptible(PIPE_SEM(*inode)))
  38  		goto err_nolock_nocleanup;
      
  40  	if (!inode->i_pipe) {
      		ret = -ENOMEM;
  42  		if(!pipe_new(inode))
  43  			goto err_nocleanup;
      	}
      	filp->f_version = 0;
      
  47  	switch (filp->f_mode) {
  48  	case 1:
      	/*
      	 *  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_fifo_fops;
      		PIPE_RCOUNTER(*inode)++;
  56  		if (PIPE_READERS(*inode)++ == 0)
      			wake_up_partner(inode);
      
  59  		if (!PIPE_WRITERS(*inode)) {
  60  			if ((filp->f_flags & O_NONBLOCK)) {
      				/* suppress POLLHUP until we have
      				 * seen a writer */
      				filp->f_version = PIPE_WCOUNTER(*inode);
  64  			} else 
      			{
      				wait_for_partner(inode, &PIPE_WCOUNTER(*inode));
  67  				if(signal_pending(current))
  68  					goto err_rd;
      			}
      		}
  71  		break;
      	
  73  	case 2:
      	/*
      	 *  O_WRONLY
      	 *  POSIX.1 says that O_NONBLOCK means return -1 with
      	 *  errno=ENXIO when there is no process reading the FIFO.
      	 */
      		ret = -ENXIO;
  80  		if ((filp->f_flags & O_NONBLOCK) && !PIPE_READERS(*inode))
  81  			goto err;
      
      		filp->f_op = &write_fifo_fops;
      		PIPE_WCOUNTER(*inode)++;
  85  		if (!PIPE_WRITERS(*inode)++)
      			wake_up_partner(inode);
      
  88  		if (!PIPE_READERS(*inode)) {
      			wait_for_partner(inode, &PIPE_RCOUNTER(*inode));
  90  			if (signal_pending(current))
  91  				goto err_wr;
      		}
  93  		break;
      	
  95  	case 3:
      	/*
      	 *  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_fifo_fops;
      
      		PIPE_READERS(*inode)++;
      		PIPE_WRITERS(*inode)++;
      		PIPE_RCOUNTER(*inode)++;
      		PIPE_WCOUNTER(*inode)++;
 108  		if (PIPE_READERS(*inode) == 1 || PIPE_WRITERS(*inode) == 1)
      			wake_up_partner(inode);
 110  		break;
      
 112  	default:
      		ret = -EINVAL;
 114  		goto err;
      	}
      
      	/* Ok! */
      	up(PIPE_SEM(*inode));
 119  	unlock_kernel();
 120  	return 0;
      
      err_rd:
 123  	if (!--PIPE_READERS(*inode))
      		wake_up_interruptible(PIPE_WAIT(*inode));
      	ret = -ERESTARTSYS;
 126  	goto err;
      
      err_wr:
 129  	if (!--PIPE_WRITERS(*inode))
      		wake_up_interruptible(PIPE_WAIT(*inode));
      	ret = -ERESTARTSYS;
 132  	goto err;
      
      err:
 135  	if (!PIPE_READERS(*inode) && !PIPE_WRITERS(*inode)) {
      		struct pipe_inode_info *info = inode->i_pipe;
      		inode->i_pipe = NULL;
      		free_page((unsigned long)info->base);
      		kfree(info);
      	}
      
      err_nocleanup:
      	up(PIPE_SEM(*inode));
      
      err_nolock_nocleanup:
 146  	unlock_kernel();
 147  	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...
       */
      struct file_operations def_fifo_fops = {
      	open:		fifo_open,	/* will set read or write pipe_fops */
      };