aboutsummaryrefslogtreecommitdiffstats
path: root/fs/pipe.c
blob: e2f4f1d9ffc2578ff4d2da0404c459b819a260a0 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
/*
 *  linux/fs/pipe.c
 *
 *  Copyright (C) 1991, 1992, 1999  Linus Torvalds
 */

#include <linux/mm.h>
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/pipe_fs_i.h>
#include <linux/uio.h>
#include <linux/highmem.h>

#include <asm/uaccess.h>
#include <asm/ioctls.h>

/*
 * We use a start+len construction, which provides full use of the 
 * allocated memory.
 * -- Florian Coosmann (FGC)
 * 
 * Reads with count = 0 should always return 0.
 * -- Julian Bradfield 1999-06-07.
 *
 * FIFOs and Pipes now generate SIGIO for both readers and writers.
 * -- Jeremy Elson <jelson@circlemud.org> 2001-08-16
 *
 * pipe_read & write cleanup
 * -- Manfred Spraul <manfred@colorfullife.com> 2002-05-09
 */

/* Drop the inode semaphore and wait for a pipe event, atomically */
void pipe_wait(struct inode * inode)
{
	DEFINE_WAIT(wait);

	/*
	 * Pipes are system-local resources, so sleeping on them
	 * is considered a noninteractive wait:
	 */
	prepare_to_wait(PIPE_WAIT(*inode), &wait, TASK_INTERRUPTIBLE|TASK_NONINTERACTIVE);
	mutex_unlock(PIPE_MUTEX(*inode));
	schedule();
	finish_wait(PIPE_WAIT(*inode), &wait);
	mutex_lock(PIPE_MUTEX(*inode));
}

static int
pipe_iov_copy_from_user(void *to, struct iovec *iov, unsigned long len)
{
	unsigned long copy;

	while (len > 0) {
		while (!iov->iov_len)
			iov++;
		copy = min_t(unsigned long, len, iov->iov_len);

		if (copy_from_user(to, iov->iov_base, copy))
			return -EFAULT;
		to += copy;
		len -= copy;
		iov->iov_base += copy;
		iov->iov_len -= copy;
	}
	return 0;
}

static int
pipe_iov_copy_to_user(struct iovec *iov, const void *from, unsigned long len)
{
	unsigned long copy;

	while (len > 0) {
		while (!iov->iov_len)
			iov++;
		copy = min_t(unsigned long, len, iov->iov_len);

		if (copy_to_user(iov->iov_base, from, copy))
			return -EFAULT;
		from += copy;
		len -= copy;
		iov->iov_base += copy;
		iov->iov_len -= copy;
	}
	return 0;
}

static void anon_pipe_buf_release(struct pipe_inode_info *info, struct pipe_buffer *buf)
{
	struct page *page = buf->page;

	if (info->tmp_page) {
		__free_page(page);
		return;
	}
	info->tmp_page = page;
}

static void *anon_pipe_buf_map(struct file *file, struct pipe_inode_info *info, struct pipe_buffer *buf)
{
	return kmap(buf->page);
}

static void anon_pipe_buf_unmap(struct pipe_inode_info *info, struct pipe_buffer *buf)
{
	kunmap(buf->page);
}

static struct pipe_buf_operations anon_pipe_buf_ops = {
	.can_merge = 1,
	.map = anon_pipe_buf_map,
	.unmap = anon_pipe_buf_unmap,
	.release = anon_pipe_buf_release,
};

static ssize_t
pipe_readv(struct file *filp, const struct iovec *_iov,
	   unsigned long nr_segs, loff_t *ppos)
{
	struct inode *inode = filp->f_dentry->d_inode;
	struct pipe_inode_info *info;
	int do_wakeup;
	ssize_t ret;
	struct iovec *iov = (struct iovec *)_iov;
	size_t total_len;

	total_len = iov_length(iov, nr_segs);
	/* Null read succeeds. */
	if (unlikely(total_len == 0))
		return 0;

	do_wakeup = 0;
	ret = 0;
	mutex_lock(PIPE_MUTEX(*inode));
	info = inode->i_pipe;
	for (;;) {
		int bufs = info->nrbufs;
		if (bufs) {
			int curbuf = info->curbuf;
			struct pipe_buffer *buf = info->bufs + curbuf;
			struct pipe_buf_operations *ops = buf->ops;
			void *addr;
			size_t chars = buf->len;
			int error;

			if (chars > total_len)
				chars = total_len;

			addr = ops->map(filp, info, buf);
			error = pipe_iov_copy_to_user(iov, addr + buf->offset, chars);
			ops->unmap(info, buf);
			if (unlikely(error)) {
				if (!ret) ret = -EFAULT;
				break;
			}
			ret += chars;
			buf->offset += chars;
			buf->len -= chars;
			if (!buf->len) {
				buf->ops = NULL;
				ops->release(info, buf);
				curbuf = (curbuf + 1) & (PIPE_BUFFERS-1);
				info->curbuf = curbuf;
				info->nrbufs = --bufs;
				do_wakeup = 1;
			}
			total_len -= chars;
			if (!total_len)
				break;	/* common path: read succeeded */
		}
		if (bufs)	/* More to do? */
			continue;
		if (!PIPE_WRITERS(*inode))
			break;
		if (!PIPE_WAITING_WRITERS(*inode)) {
			/* syscall merging: Usually we must not sleep
			 * if O_NONBLOCK is set, or if we got some data.
			 * But if a writer sleeps in kernel space, then
			 * we can wait for that data without violating POSIX.
			 */
			if (ret)
				break;
			if (filp->f_flags & O_NONBLOCK) {
				ret = -EAGAIN;
				break;
			}
		}
		if (signal_pending(current)) {
			if (!ret) ret = -ERESTARTSYS;
			break;
		}
		if (do_wakeup) {
			wake_up_interruptible_sync(PIPE_WAIT(*inode));
 			kill_fasync(PIPE_FASYNC_WRITERS(*inode), SIGIO, POLL_OUT);
		}
		pipe_wait(inode);
	}
	mutex_unlock(PIPE_MUTEX(*inode));
	/* Signal writers asynchronously that there is more room.  */
	if (do_wakeup) {
		wake_up_interruptible(PIPE_WAIT(*inode));
		kill_fasync(PIPE_FASYNC_WRITERS(*inode), SIGIO, POLL_OUT);
	}
	if (ret > 0)
		file_accessed(filp);
	return ret;
}

static ssize_t
pipe_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
{
	struct iovec iov = { .iov_base = buf, .iov_len = count };
	return pipe_readv(filp, &iov, 1, ppos);
}

static ssize_t
pipe_writev(struct file *filp, const struct iovec *_iov,
	    unsigned long nr_segs, loff_t *ppos)
{
	struct inode *inode = filp->f_dentry->d_inode;
	struct pipe_inode_info *info;
	ssize_t ret;
	int do_wakeup;
	struct iovec *iov = (struct iovec *)_iov;
	size_t total_len;
	ssize_t chars;

	total_len = iov_length(iov, nr_segs);
	/* Null write succeeds. */
	if (unlikely(total_len == 0))
		return 0;

	do_wakeup = 0;
	ret = 0;
	mutex_lock(PIPE_MUTEX(*inode));
	info = inode->i_pipe;

	if (!PIPE_READERS(*inode)) {
		send_sig(SIGPIPE, current, 0);
		ret = -EPIPE;
		goto out;
	}

	/* We try to merge small writes */
	chars = total_len & (PAGE_SIZE-1); /* size of the last buffer */
	if (info->nrbufs && chars != 0) {
		int lastbuf = (info->curbuf + info->nrbufs - 1) & (PIPE_BUFFERS-1);
		struct pipe_buffer *buf = info->bufs + lastbuf;
		struct pipe_buf_operations *ops = buf->ops;
		int offset = buf->offset + buf->len;
		if (ops->can_merge && offset + chars <= PAGE_SIZE) {
			void *addr = ops->map(filp, info, buf);
			int error = pipe_iov_copy_from_user(offset + addr, iov, chars);
			ops->unmap(info, buf);
			ret = error;
			do_wakeup = 1;
			if (error)
				goto out;
			buf->len += chars;
			total_len -= chars;
			ret = chars;
			if (!total_len)
				goto out;
		}
	}

	for (;;) {
		int bufs;
		if (!PIPE_READERS(*inode)) {
			send_sig(SIGPIPE, current, 0);
			if (!ret) ret = -EPIPE;
			break;
		}
		bufs = info->nrbufs;
		if (bufs < PIPE_BUFFERS) {
			int newbuf = (info->curbuf + bufs) & (PIPE_BUFFERS-1);
			struct pipe_buffer *buf = info->bufs + newbuf;
			struct page *page = info->tmp_page;
			int error;

			if (!page) {
				page = alloc_page(GFP_HIGHUSER);
				if (unlikely(!page)) {
					ret = ret ? : -ENOMEM;
					break;
				}
				info->tmp_page = page;
			}
			/* Always wakeup, even if the copy fails. Otherwise
			 * we lock up (O_NONBLOCK-)readers that sleep due to
			 * syscall merging.
			 * FIXME! Is this really true?
			 */
			do_wakeup = 1;
			chars = PAGE_SIZE;
			if (chars > total_len)
				chars = total_len;

			error = pipe_iov_copy_from_user(kmap(page), iov, chars);
			kunmap(page);
			if (unlikely(error)) {
				if (!ret) ret = -EFAULT;
				break;
			}
			ret += chars;

			/* Insert it into the buffer array */
			buf->page = page;
			buf->ops = &anon_pipe_buf_ops;
			buf->offset = 0;
			buf->len = chars;
			info->nrbufs = ++bufs;
			info->tmp_page = NULL;

			total_len -= chars;
			if (!total_len)
				break;
		}
		if (bufs < PIPE_BUFFERS)
			continue;
		if (filp->f_flags & O_NONBLOCK) {
			if (!ret) ret = -EAGAIN;
			break;
		}
		if (signal_pending(current)) {
			if (!ret) ret = -ERESTARTSYS;
			break;
		}
		if (do_wakeup) {
			wake_up_interruptible_sync(PIPE_WAIT(*inode));
			kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO, POLL_IN);
			do_wakeup = 0;
		}
		PIPE_WAITING_WRITERS(*inode)++;
		pipe_wait(inode);
		PIPE_WAITING_WRITERS(*inode)--;
	}
out:
	mutex_unlock(PIPE_MUTEX(*inode));
	if (do_wakeup) {
		wake_up_interruptible(PIPE_WAIT(*inode));
		kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO, POLL_IN);
	}
	if (ret > 0)
		file_update_time(filp);
	return ret;
}

static ssize_t
pipe_write(struct file *filp, const char __user *buf,
	   size_t count, loff_t *ppos)
{
	struct iovec iov = { .iov_base = (void __user *)buf, .iov_len = count };
	return pipe_writev(filp, &iov, 1, ppos);
}

static ssize_t
bad_pipe_r(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
{
	return -EBADF;
}

static ssize_t
bad_pipe_w(struct file *filp, const char __user *buf, size_t count, loff_t *ppos)
{
	return -EBADF;
}

static int
pipe_ioctl(struct inode *pino, struct file *filp,
	   unsigned int cmd, unsigned long arg)
{
	struct inode *inode = filp->f_dentry->d_inode;
	struct pipe_inode_info *info;
	int count, buf, nrbufs;

	switch (cmd) {
		case FIONREAD:
			mutex_lock(PIPE_MUTEX(*inode));
			info =  inode->i_pipe;
			count = 0;
			buf = info->curbuf;
			nrbufs = info->nrbufs;
			while (--nrbufs >= 0) {
				count += info->bufs[buf].len;
				buf = (buf+1) & (PIPE_BUFFERS-1);
			}
			mutex_unlock(PIPE_MUTEX(*inode));
			return put_user(count, (int __user *)arg);
		default:
			return -EINVAL;
	}
}

/* No kernel lock held - fine */
static unsigned int
pipe_poll(struct file *filp, poll_table *wait)
{
	unsigned int mask;
	struct inode *inode = filp->f_dentry->d_inode;
	struct pipe_inode_info *info = inode->i_pipe;
	int nrbufs;

	poll_wait(filp, PIPE_WAIT(*inode), wait);

	/* Reading only -- no need for acquiring the semaphore.  */
	nrbufs = info->nrbufs;
	mask = 0;
	if (filp->f_mode & FMODE_READ) {
		mask = (nrbufs > 0) ? POLLIN | POLLRDNORM : 0;
		if (!PIPE_WRITERS(*inode) && filp->f_version != PIPE_WCOUNTER(*inode))
			mask |= POLLHUP;
	}

	if (filp->f_mode & FMODE_WRITE) {
		mask |= (nrbufs < PIPE_BUFFERS) ? POLLOUT | POLLWRNORM : 0;
		/*
		 * Most Unices do not set POLLERR for FIFOs but on Linux they
		 * behave exactly like pipes for poll().
		 */
		if (!PIPE_READERS(*inode))
			mask |= POLLERR;
	}

	return mask;
}

static int
pipe_release(struct inode *inode, int decr, int decw)
{
	mutex_lock(PIPE_MUTEX(*inode));
	PIPE_READERS(*inode) -= decr;
	PIPE_WRITERS(*inode) -= decw;
	if (!PIPE_READERS(*inode) && !PIPE_WRITERS(*inode)) {
		free_pipe_info(inode);
	} else {
		wake_up_interruptible(PIPE_WAIT(*inode));
		kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO, POLL_IN);
		kill_fasync(PIPE_FASYNC_WRITERS(*inode), SIGIO, POLL_OUT);
	}
	mutex_unlock(PIPE_MUTEX(*inode));

	return 0;
}

static int
pipe_read_fasync(int fd, struct file *filp, int on)
{
	struct inode *inode = filp->f_dentry->d_inode;
	int retval;

	mutex_lock(PIPE_MUTEX(*inode));
	retval = fasync_helper(fd, filp, on, PIPE_FASYNC_READERS(*inode));
	mutex_unlock(PIPE_MUTEX(*inode));

	if (retval < 0)
		return retval;

	return 0;
}


static int
pipe_write_fasync(int fd, struct file *filp, int on)
{
	struct inode *inode = filp->f_dentry->d_inode;
	int retval;

	mutex_lock(PIPE_MUTEX(*inode));
	retval = fasync_helper(fd, filp, on, PIPE_FASYNC_WRITERS(*inode));
	mutex_unlock(PIPE_MUTEX(*inode));

	if (retval < 0)
		return retval;

	return 0;
}


static int
pipe_rdwr_fasync(int fd, struct file *filp, int on)
{
	struct inode *inode = filp->f_dentry->d_inode;
	int retval;

	mutex_lock(PIPE_MUTEX(*inode));

	retval = fasync_helper(fd, filp, on, PIPE_FASYNC_READERS(*inode));

	if (retval >= 0)
		retval = fasync_helper(fd, filp, on, PIPE_FASYNC_WRITERS(*inode));

	mutex_unlock(PIPE_MUTEX(*inode));

	if (retval < 0)
		return retval;

	return 0;
}


static int
pipe_read_release(struct inode *inode, struct file *filp)
{
	pipe_read_fasync(-1, filp, 0);
	return pipe_release(inode, 1, 0);
}

static int
pipe_write_release(struct inode *inode, struct file *filp)
{
	pipe_write_fasync(-1, filp, 0);
	return pipe_release(inode, 0, 1);
}

static int
pipe_rdwr_release(struct inode *inode, struct file *filp)
{
	int decr, decw;

	pipe_rdwr_fasync(-1, filp, 0);
	decr = (filp->f_mode & FMODE_READ) != 0;
	decw = (filp->f_mode & FMODE_WRITE) != 0;
	return pipe_release(inode, decr, decw);
}

static int
pipe_read_open(struct inode *inode, struct file *filp)
{
	/* We could have perhaps used atomic_t, but this and friends
	   below are the only places.  So it doesn't seem worthwhile.  */
	mutex_lock(PIPE_MUTEX(*inode));
	PIPE_READERS(*inode)++;
	mutex_unlock(PIPE_MUTEX(*inode));

	return 0;
}

static int
pipe_write_open(struct inode *inode, struct file *filp)
{
	mutex_lock(PIPE_MUTEX(*inode));
	PIPE_WRITERS(*inode)++;
	mutex_unlock(PIPE_MUTEX(*inode));

	return 0;
}

static int
pipe_rdwr_open(struct inode *inode, struct file *filp)
{
	mutex_lock(PIPE_MUTEX(*inode));
	if (filp->f_mode & FMODE_READ)
		PIPE_READERS(*inode)++;
	if (filp->f_mode & FMODE_WRITE)
		PIPE_WRITERS(*inode)++;
	mutex_unlock(PIPE_MUTEX(*inode));

	return 0;
}

/*
 * The file_operations structs are not static because they
 * are also used in linux/fs/fifo.c to do operations on FIFOs.
 */
const struct file_operations read_fifo_fops = {
	.llseek		= no_llseek,
	.read		= pipe_read,
	.readv		= pipe_readv,
	.write		= bad_pipe_w,
	.poll		= pipe_poll,
	.ioctl		= pipe_ioctl,
	.open		= pipe_read_open,
	.release	= pipe_read_release,
	.fasync		= pipe_read_fasync,
};

const struct file_operations write_fifo_fops = {
	.llseek		= no_llseek,
	.read		= bad_pipe_r,
	.write		= pipe_write,
	.writev		= pipe_writev,
	.poll		= pipe_poll,
	.ioctl		= pipe_ioctl,
	.open		= pipe_write_open,
	.release	= pipe_write_release,
	.fasync		= pipe_write_fasync,
};

const struct file_operations rdwr_fifo_fops = {
	.llseek		= no_llseek,
	.read		= pipe_read,
	.readv		= pipe_readv,
	.write		= pipe_write,
	.writev		= pipe_writev,
	.poll		= pipe_poll,
	.ioctl		= pipe_ioctl,
	.open		= pipe_rdwr_open,
	.release	= pipe_rdwr_release,
	.fasync		= pipe_rdwr_fasync,
};

static struct file_operations read_pipe_fops = {
	.llseek		= no_llseek,
	.read		= pipe_read,
	.readv		= pipe_readv,
	.write		= bad_pipe_w,
	.poll		= pipe_poll,
	.ioctl		= pipe_ioctl,
	.open		= pipe_read_open,
	.release	= pipe_read_release,
	.fasync		= pipe_read_fasync,
};

static struct file_operations write_pipe_fops = {
	.llseek		= no_llseek,
	.read		= bad_pipe_r,
	.write		= pipe_write,
	.writev		= pipe_writev,
	.poll		= pipe_poll,
	.ioctl		= pipe_ioctl,
	.open		= pipe_write_open,
	.release	= pipe_write_release,
	.fasync		= pipe_write_fasync,
};

static struct file_operations rdwr_pipe_fops = {
	.llseek		= no_llseek,
	.read		= pipe_read,
	.readv		= pipe_readv,
	.write		= pipe_write,
	.writev		= pipe_writev,
	.poll		= pipe_poll,
	.ioctl		= pipe_ioctl,
	.open		= pipe_rdwr_open,
	.release	= pipe_rdwr_release,
	.fasync		= pipe_rdwr_fasync,
};

void free_pipe_info(struct inode *inode)
{
	int i;
	struct pipe_inode_info *info = inode->i_pipe;

	inode->i_pipe = NULL;
	for (i = 0; i < PIPE_BUFFERS; i++) {
		struct pipe_buffer *buf = info->bufs + i;
		if (buf->ops)
			buf->ops->release(info, buf);
	}
	if (info->tmp_page)
		__free_page(info->tmp_page);
	kfree(info);
}

struct inode* pipe_new(struct inode* inode)
{
	struct pipe_inode_info *info;

	info = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL);
	if (!info)
		goto fail_page;
	inode->i_pipe = info;

	init_waitqueue_head(PIPE_WAIT(*inode));
	PIPE_RCOUNTER(*inode) = PIPE_WCOUNTER(*inode) = 1;

	return inode;
fail_page:
	return NULL;
}

static struct vfsmount *pipe_mnt __read_mostly;
static int pipefs_delete_dentry(struct dentry *dentry)
{
	return 1;
}
static struct dentry_operations pipefs_dentry_operations = {
	.d_delete	= pipefs_delete_dentry,
};

static struct inode * get_pipe_inode(void)
{
	struct inode *inode = new_inode(pipe_mnt->mnt_sb);

	if (!inode)
		goto fail_inode;

	if(!pipe_new(inode))
		goto fail_iput;
	PIPE_READERS(*inode) = PIPE_WRITERS(*inode) = 1;
	inode->i_fop = &rdwr_pipe_fops;

	/*
	 * Mark the inode dirty from the very beginning,
	 * that way it will never be moved to the dirty
	 * list because "mark_inode_dirty()" will think
	 * that it already _is_ on the dirty list.
	 */
	inode->i_state = I_DIRTY;
	inode->i_mode = S_IFIFO | S_IRUSR | S_IWUSR;
	inode->i_uid = current->fsuid;
	inode->i_gid = current->fsgid;
	inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
	inode->i_blksize = PAGE_SIZE;
	return inode;

fail_iput:
	iput(inode);
fail_inode:
	return NULL;
}

int do_pipe(int *fd)
{
	struct qstr this;
	char name[32];
	struct dentry *dentry;
	struct inode * inode;
	struct file *f1, *f2;
	int error;
	int i,j;

	error = -ENFILE;
	f1 = get_empty_filp();
	if (!f1)
		goto no_files;

	f2 = get_empty_filp();
	if (!f2)
		goto close_f1;

	inode = get_pipe_inode();
	if (!inode)
		goto close_f12;

	error = get_unused_fd();
	if (error < 0)
		goto close_f12_inode;
	i = error;

	error = get_unused_fd();
	if (error < 0)
		goto close_f12_inode_i;
	j = error;

	error = -ENOMEM;
	sprintf(name, "[%lu]", inode->i_ino);
	this.name = name;
	this.len = strlen(name);
	this.hash = inode->i_ino; /* will go */
	dentry = d_alloc(pipe_mnt->mnt_sb->s_root, &this);
	if (!dentry)
		goto close_f12_inode_i_j;
	dentry->d_op = &pipefs_dentry_operations;
	d_add(dentry, inode);
	f1->f_vfsmnt = f2->f_vfsmnt = mntget(mntget(pipe_mnt));
	f1->f_dentry = f2->f_dentry = dget(dentry);
	f1->f_mapping = f2->f_mapping = inode->i_mapping;

	/* read file */
	f1->f_pos = f2->f_pos = 0;
	f1->f_flags = O_RDONLY;
	f1->f_op = &read_pipe_fops;
	f1->f_mode = FMODE_READ;
	f1->f_version = 0;

	/* write file */
	f2->f_flags = O_WRONLY;
	f2->f_op = &write_pipe_fops;
	f2->f_mode = FMODE_WRITE;
	f2->f_version = 0;

	fd_install(i, f1);
	fd_install(j, f2);
	fd[0] = i;
	fd[1] = j;
	return 0;

close_f12_inode_i_j:
	put_unused_fd(j);
close_f12_inode_i:
	put_unused_fd(i);
close_f12_inode:
	free_pipe_info(inode);
	iput(inode);
close_f12:
	put_filp(f2);
close_f1:
	put_filp(f1);
no_files:
	return error;	
}

/*
 * pipefs should _never_ be mounted by userland - too much of security hassle,
 * no real gain from having the whole whorehouse mounted. So we don't need
 * any operations on the root directory. However, we need a non-trivial
 * d_name - pipe: will go nicely and kill the special-casing in procfs.
 */

static struct super_block *pipefs_get_sb(struct file_system_type *fs_type,
	int flags, const char *dev_name, void *data)
{
	return get_sb_pseudo(fs_type, "pipe:", NULL, PIPEFS_MAGIC);
}

static struct file_system_type pipe_fs_type = {
	.name		= "pipefs",
	.get_sb		= pipefs_get_sb,
	.kill_sb	= kill_anon_super,
};

static int __init init_pipe_fs(void)
{
	int err = register_filesystem(&pipe_fs_type);
	if (!err) {
		pipe_mnt = kern_mount(&pipe_fs_type);
		if (IS_ERR(pipe_mnt)) {
			err = PTR_ERR(pipe_mnt);
			unregister_filesystem(&pipe_fs_type);
		}
	}
	return err;
}

static void __exit exit_pipe_fs(void)
{
	unregister_filesystem(&pipe_fs_type);
	mntput(pipe_mnt);
}

fs_initcall(init_pipe_fs);
module_exit(exit_pipe_fs);