/* *  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/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 */	.llseek		= noop_llseek,};