1/*
  2 *  linux/fs/fifo.c
  3 *
  4 *  written by Paul H. Hargrove
  5 *
  6 *  Fixes:
  7 *	10-06-1999, AV: fixed OOM handling in fifo_open(), moved
  8 *			initialization there, switched to external
  9 *			allocation of pipe_inode_info.
 10 */
 11
 12#include <linux/mm.h>
 13#include <linux/fs.h>
 14#include <linux/sched.h>
 15#include <linux/pipe_fs_i.h>
 16
 17static void wait_for_partner(struct inode* inode, unsigned int *cnt)
 18{
 19	int cur = *cnt;	
 20
 21	while (cur == *cnt) {
 22		pipe_wait(inode->i_pipe);
 23		if (signal_pending(current))
 24			break;
 25	}
 26}
 27
 28static void wake_up_partner(struct inode* inode)
 29{
 30	wake_up_interruptible(&inode->i_pipe->wait);
 31}
 32
 33static int fifo_open(struct inode *inode, struct file *filp)
 34{
 35	struct pipe_inode_info *pipe;
 36	int ret;
 37
 38	mutex_lock(&inode->i_mutex);
 39	pipe = inode->i_pipe;
 40	if (!pipe) {
 41		ret = -ENOMEM;
 42		pipe = alloc_pipe_info(inode);
 43		if (!pipe)
 44			goto err_nocleanup;
 45		inode->i_pipe = pipe;
 46	}
 47	filp->f_version = 0;
 48
 49	/* We can only do regular read/write on fifos */
 50	filp->f_mode &= (FMODE_READ | FMODE_WRITE);
 51
 52	switch (filp->f_mode) {
 53	case FMODE_READ:
 54	/*
 55	 *  O_RDONLY
 56	 *  POSIX.1 says that O_NONBLOCK means return with the FIFO
 57	 *  opened, even when there is no process writing the FIFO.
 58	 */
 59		filp->f_op = &read_pipefifo_fops;
 60		pipe->r_counter++;
 61		if (pipe->readers++ == 0)
 62			wake_up_partner(inode);
 63
 64		if (!pipe->writers) {
 65			if ((filp->f_flags & O_NONBLOCK)) {
 66				/* suppress POLLHUP until we have
 67				 * seen a writer */
 68				filp->f_version = pipe->w_counter;
 69			} else {
 70				wait_for_partner(inode, &pipe->w_counter);
 71				if(signal_pending(current))
 72					goto err_rd;
 73			}
 74		}
 75		break;
 76	
 77	case FMODE_WRITE:
 78	/*
 79	 *  O_WRONLY
 80	 *  POSIX.1 says that O_NONBLOCK means return -1 with
 81	 *  errno=ENXIO when there is no process reading the FIFO.
 82	 */
 83		ret = -ENXIO;
 84		if ((filp->f_flags & O_NONBLOCK) && !pipe->readers)
 85			goto err;
 86
 87		filp->f_op = &write_pipefifo_fops;
 88		pipe->w_counter++;
 89		if (!pipe->writers++)
 90			wake_up_partner(inode);
 91
 92		if (!pipe->readers) {
 93			wait_for_partner(inode, &pipe->r_counter);
 94			if (signal_pending(current))
 95				goto err_wr;
 96		}
 97		break;
 98	
 99	case FMODE_READ | FMODE_WRITE:
100	/*
101	 *  O_RDWR
102	 *  POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
103	 *  This implementation will NEVER block on a O_RDWR open, since
104	 *  the process can at least talk to itself.
105	 */
106		filp->f_op = &rdwr_pipefifo_fops;
107
108		pipe->readers++;
109		pipe->writers++;
110		pipe->r_counter++;
111		pipe->w_counter++;
112		if (pipe->readers == 1 || pipe->writers == 1)
113			wake_up_partner(inode);
114		break;
115
116	default:
117		ret = -EINVAL;
118		goto err;
119	}
120
121	/* Ok! */
122	mutex_unlock(&inode->i_mutex);
123	return 0;
124
125err_rd:
126	if (!--pipe->readers)
127		wake_up_interruptible(&pipe->wait);
128	ret = -ERESTARTSYS;
129	goto err;
130
131err_wr:
132	if (!--pipe->writers)
133		wake_up_interruptible(&pipe->wait);
134	ret = -ERESTARTSYS;
135	goto err;
136
137err:
138	if (!pipe->readers && !pipe->writers)
139		free_pipe_info(inode);
140
141err_nocleanup:
142	mutex_unlock(&inode->i_mutex);
143	return ret;
144}
145
146/*
147 * Dummy default file-operations: the only thing this does
148 * is contain the open that then fills in the correct operations
149 * depending on the access mode of the file...
150 */
151const struct file_operations def_fifo_fops = {
152	.open		= fifo_open,	/* will set read_ or write_pipefifo_fops */
153	.llseek		= noop_llseek,
154};