Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/hid/hid
[platform/kernel/linux-starfive.git] / fs / pipe.c
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  *  linux/fs/pipe.c
4  *
5  *  Copyright (C) 1991, 1992, 1999  Linus Torvalds
6  */
7
8 #include <linux/mm.h>
9 #include <linux/file.h>
10 #include <linux/poll.h>
11 #include <linux/slab.h>
12 #include <linux/module.h>
13 #include <linux/init.h>
14 #include <linux/fs.h>
15 #include <linux/log2.h>
16 #include <linux/mount.h>
17 #include <linux/pseudo_fs.h>
18 #include <linux/magic.h>
19 #include <linux/pipe_fs_i.h>
20 #include <linux/uio.h>
21 #include <linux/highmem.h>
22 #include <linux/pagemap.h>
23 #include <linux/audit.h>
24 #include <linux/syscalls.h>
25 #include <linux/fcntl.h>
26 #include <linux/memcontrol.h>
27 #include <linux/watch_queue.h>
28
29 #include <linux/uaccess.h>
30 #include <asm/ioctls.h>
31
32 #include "internal.h"
33
34 /*
35  * New pipe buffers will be restricted to this size while the user is exceeding
36  * their pipe buffer quota. The general pipe use case needs at least two
37  * buffers: one for data yet to be read, and one for new data. If this is less
38  * than two, then a write to a non-empty pipe may block even if the pipe is not
39  * full. This can occur with GNU make jobserver or similar uses of pipes as
40  * semaphores: multiple processes may be waiting to write tokens back to the
41  * pipe before reading tokens: https://lore.kernel.org/lkml/1628086770.5rn8p04n6j.none@localhost/.
42  *
43  * Users can reduce their pipe buffers with F_SETPIPE_SZ below this at their
44  * own risk, namely: pipe writes to non-full pipes may block until the pipe is
45  * emptied.
46  */
47 #define PIPE_MIN_DEF_BUFFERS 2
48
49 /*
50  * The max size that a non-root user is allowed to grow the pipe. Can
51  * be set by root in /proc/sys/fs/pipe-max-size
52  */
53 unsigned int pipe_max_size = 1048576;
54
55 /* Maximum allocatable pages per user. Hard limit is unset by default, soft
56  * matches default values.
57  */
58 unsigned long pipe_user_pages_hard;
59 unsigned long pipe_user_pages_soft = PIPE_DEF_BUFFERS * INR_OPEN_CUR;
60
61 /*
62  * We use head and tail indices that aren't masked off, except at the point of
63  * dereference, but rather they're allowed to wrap naturally.  This means there
64  * isn't a dead spot in the buffer, but the ring has to be a power of two and
65  * <= 2^31.
66  * -- David Howells 2019-09-23.
67  *
68  * Reads with count = 0 should always return 0.
69  * -- Julian Bradfield 1999-06-07.
70  *
71  * FIFOs and Pipes now generate SIGIO for both readers and writers.
72  * -- Jeremy Elson <jelson@circlemud.org> 2001-08-16
73  *
74  * pipe_read & write cleanup
75  * -- Manfred Spraul <manfred@colorfullife.com> 2002-05-09
76  */
77
78 static void pipe_lock_nested(struct pipe_inode_info *pipe, int subclass)
79 {
80         if (pipe->files)
81                 mutex_lock_nested(&pipe->mutex, subclass);
82 }
83
84 void pipe_lock(struct pipe_inode_info *pipe)
85 {
86         /*
87          * pipe_lock() nests non-pipe inode locks (for writing to a file)
88          */
89         pipe_lock_nested(pipe, I_MUTEX_PARENT);
90 }
91 EXPORT_SYMBOL(pipe_lock);
92
93 void pipe_unlock(struct pipe_inode_info *pipe)
94 {
95         if (pipe->files)
96                 mutex_unlock(&pipe->mutex);
97 }
98 EXPORT_SYMBOL(pipe_unlock);
99
100 static inline void __pipe_lock(struct pipe_inode_info *pipe)
101 {
102         mutex_lock_nested(&pipe->mutex, I_MUTEX_PARENT);
103 }
104
105 static inline void __pipe_unlock(struct pipe_inode_info *pipe)
106 {
107         mutex_unlock(&pipe->mutex);
108 }
109
110 void pipe_double_lock(struct pipe_inode_info *pipe1,
111                       struct pipe_inode_info *pipe2)
112 {
113         BUG_ON(pipe1 == pipe2);
114
115         if (pipe1 < pipe2) {
116                 pipe_lock_nested(pipe1, I_MUTEX_PARENT);
117                 pipe_lock_nested(pipe2, I_MUTEX_CHILD);
118         } else {
119                 pipe_lock_nested(pipe2, I_MUTEX_PARENT);
120                 pipe_lock_nested(pipe1, I_MUTEX_CHILD);
121         }
122 }
123
124 static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
125                                   struct pipe_buffer *buf)
126 {
127         struct page *page = buf->page;
128
129         /*
130          * If nobody else uses this page, and we don't already have a
131          * temporary page, let's keep track of it as a one-deep
132          * allocation cache. (Otherwise just release our reference to it)
133          */
134         if (page_count(page) == 1 && !pipe->tmp_page)
135                 pipe->tmp_page = page;
136         else
137                 put_page(page);
138 }
139
140 static bool anon_pipe_buf_try_steal(struct pipe_inode_info *pipe,
141                 struct pipe_buffer *buf)
142 {
143         struct page *page = buf->page;
144
145         if (page_count(page) != 1)
146                 return false;
147         memcg_kmem_uncharge_page(page, 0);
148         __SetPageLocked(page);
149         return true;
150 }
151
152 /**
153  * generic_pipe_buf_try_steal - attempt to take ownership of a &pipe_buffer
154  * @pipe:       the pipe that the buffer belongs to
155  * @buf:        the buffer to attempt to steal
156  *
157  * Description:
158  *      This function attempts to steal the &struct page attached to
159  *      @buf. If successful, this function returns 0 and returns with
160  *      the page locked. The caller may then reuse the page for whatever
161  *      he wishes; the typical use is insertion into a different file
162  *      page cache.
163  */
164 bool generic_pipe_buf_try_steal(struct pipe_inode_info *pipe,
165                 struct pipe_buffer *buf)
166 {
167         struct page *page = buf->page;
168
169         /*
170          * A reference of one is golden, that means that the owner of this
171          * page is the only one holding a reference to it. lock the page
172          * and return OK.
173          */
174         if (page_count(page) == 1) {
175                 lock_page(page);
176                 return true;
177         }
178         return false;
179 }
180 EXPORT_SYMBOL(generic_pipe_buf_try_steal);
181
182 /**
183  * generic_pipe_buf_get - get a reference to a &struct pipe_buffer
184  * @pipe:       the pipe that the buffer belongs to
185  * @buf:        the buffer to get a reference to
186  *
187  * Description:
188  *      This function grabs an extra reference to @buf. It's used in
189  *      the tee() system call, when we duplicate the buffers in one
190  *      pipe into another.
191  */
192 bool generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
193 {
194         return try_get_page(buf->page);
195 }
196 EXPORT_SYMBOL(generic_pipe_buf_get);
197
198 /**
199  * generic_pipe_buf_release - put a reference to a &struct pipe_buffer
200  * @pipe:       the pipe that the buffer belongs to
201  * @buf:        the buffer to put a reference to
202  *
203  * Description:
204  *      This function releases a reference to @buf.
205  */
206 void generic_pipe_buf_release(struct pipe_inode_info *pipe,
207                               struct pipe_buffer *buf)
208 {
209         put_page(buf->page);
210 }
211 EXPORT_SYMBOL(generic_pipe_buf_release);
212
213 static const struct pipe_buf_operations anon_pipe_buf_ops = {
214         .release        = anon_pipe_buf_release,
215         .try_steal      = anon_pipe_buf_try_steal,
216         .get            = generic_pipe_buf_get,
217 };
218
219 /* Done while waiting without holding the pipe lock - thus the READ_ONCE() */
220 static inline bool pipe_readable(const struct pipe_inode_info *pipe)
221 {
222         unsigned int head = READ_ONCE(pipe->head);
223         unsigned int tail = READ_ONCE(pipe->tail);
224         unsigned int writers = READ_ONCE(pipe->writers);
225
226         return !pipe_empty(head, tail) || !writers;
227 }
228
229 static ssize_t
230 pipe_read(struct kiocb *iocb, struct iov_iter *to)
231 {
232         size_t total_len = iov_iter_count(to);
233         struct file *filp = iocb->ki_filp;
234         struct pipe_inode_info *pipe = filp->private_data;
235         bool was_full, wake_next_reader = false;
236         ssize_t ret;
237
238         /* Null read succeeds. */
239         if (unlikely(total_len == 0))
240                 return 0;
241
242         ret = 0;
243         __pipe_lock(pipe);
244
245         /*
246          * We only wake up writers if the pipe was full when we started
247          * reading in order to avoid unnecessary wakeups.
248          *
249          * But when we do wake up writers, we do so using a sync wakeup
250          * (WF_SYNC), because we want them to get going and generate more
251          * data for us.
252          */
253         was_full = pipe_full(pipe->head, pipe->tail, pipe->max_usage);
254         for (;;) {
255                 unsigned int head = pipe->head;
256                 unsigned int tail = pipe->tail;
257                 unsigned int mask = pipe->ring_size - 1;
258
259 #ifdef CONFIG_WATCH_QUEUE
260                 if (pipe->note_loss) {
261                         struct watch_notification n;
262
263                         if (total_len < 8) {
264                                 if (ret == 0)
265                                         ret = -ENOBUFS;
266                                 break;
267                         }
268
269                         n.type = WATCH_TYPE_META;
270                         n.subtype = WATCH_META_LOSS_NOTIFICATION;
271                         n.info = watch_sizeof(n);
272                         if (copy_to_iter(&n, sizeof(n), to) != sizeof(n)) {
273                                 if (ret == 0)
274                                         ret = -EFAULT;
275                                 break;
276                         }
277                         ret += sizeof(n);
278                         total_len -= sizeof(n);
279                         pipe->note_loss = false;
280                 }
281 #endif
282
283                 if (!pipe_empty(head, tail)) {
284                         struct pipe_buffer *buf = &pipe->bufs[tail & mask];
285                         size_t chars = buf->len;
286                         size_t written;
287                         int error;
288
289                         if (chars > total_len) {
290                                 if (buf->flags & PIPE_BUF_FLAG_WHOLE) {
291                                         if (ret == 0)
292                                                 ret = -ENOBUFS;
293                                         break;
294                                 }
295                                 chars = total_len;
296                         }
297
298                         error = pipe_buf_confirm(pipe, buf);
299                         if (error) {
300                                 if (!ret)
301                                         ret = error;
302                                 break;
303                         }
304
305                         written = copy_page_to_iter(buf->page, buf->offset, chars, to);
306                         if (unlikely(written < chars)) {
307                                 if (!ret)
308                                         ret = -EFAULT;
309                                 break;
310                         }
311                         ret += chars;
312                         buf->offset += chars;
313                         buf->len -= chars;
314
315                         /* Was it a packet buffer? Clean up and exit */
316                         if (buf->flags & PIPE_BUF_FLAG_PACKET) {
317                                 total_len = chars;
318                                 buf->len = 0;
319                         }
320
321                         if (!buf->len) {
322                                 pipe_buf_release(pipe, buf);
323                                 spin_lock_irq(&pipe->rd_wait.lock);
324 #ifdef CONFIG_WATCH_QUEUE
325                                 if (buf->flags & PIPE_BUF_FLAG_LOSS)
326                                         pipe->note_loss = true;
327 #endif
328                                 tail++;
329                                 pipe->tail = tail;
330                                 spin_unlock_irq(&pipe->rd_wait.lock);
331                         }
332                         total_len -= chars;
333                         if (!total_len)
334                                 break;  /* common path: read succeeded */
335                         if (!pipe_empty(head, tail))    /* More to do? */
336                                 continue;
337                 }
338
339                 if (!pipe->writers)
340                         break;
341                 if (ret)
342                         break;
343                 if (filp->f_flags & O_NONBLOCK) {
344                         ret = -EAGAIN;
345                         break;
346                 }
347                 __pipe_unlock(pipe);
348
349                 /*
350                  * We only get here if we didn't actually read anything.
351                  *
352                  * However, we could have seen (and removed) a zero-sized
353                  * pipe buffer, and might have made space in the buffers
354                  * that way.
355                  *
356                  * You can't make zero-sized pipe buffers by doing an empty
357                  * write (not even in packet mode), but they can happen if
358                  * the writer gets an EFAULT when trying to fill a buffer
359                  * that already got allocated and inserted in the buffer
360                  * array.
361                  *
362                  * So we still need to wake up any pending writers in the
363                  * _very_ unlikely case that the pipe was full, but we got
364                  * no data.
365                  */
366                 if (unlikely(was_full))
367                         wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM);
368                 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
369
370                 /*
371                  * But because we didn't read anything, at this point we can
372                  * just return directly with -ERESTARTSYS if we're interrupted,
373                  * since we've done any required wakeups and there's no need
374                  * to mark anything accessed. And we've dropped the lock.
375                  */
376                 if (wait_event_interruptible_exclusive(pipe->rd_wait, pipe_readable(pipe)) < 0)
377                         return -ERESTARTSYS;
378
379                 __pipe_lock(pipe);
380                 was_full = pipe_full(pipe->head, pipe->tail, pipe->max_usage);
381                 wake_next_reader = true;
382         }
383         if (pipe_empty(pipe->head, pipe->tail))
384                 wake_next_reader = false;
385         __pipe_unlock(pipe);
386
387         if (was_full)
388                 wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM);
389         if (wake_next_reader)
390                 wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
391         kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
392         if (ret > 0)
393                 file_accessed(filp);
394         return ret;
395 }
396
397 static inline int is_packetized(struct file *file)
398 {
399         return (file->f_flags & O_DIRECT) != 0;
400 }
401
402 /* Done while waiting without holding the pipe lock - thus the READ_ONCE() */
403 static inline bool pipe_writable(const struct pipe_inode_info *pipe)
404 {
405         unsigned int head = READ_ONCE(pipe->head);
406         unsigned int tail = READ_ONCE(pipe->tail);
407         unsigned int max_usage = READ_ONCE(pipe->max_usage);
408
409         return !pipe_full(head, tail, max_usage) ||
410                 !READ_ONCE(pipe->readers);
411 }
412
413 static ssize_t
414 pipe_write(struct kiocb *iocb, struct iov_iter *from)
415 {
416         struct file *filp = iocb->ki_filp;
417         struct pipe_inode_info *pipe = filp->private_data;
418         unsigned int head;
419         ssize_t ret = 0;
420         size_t total_len = iov_iter_count(from);
421         ssize_t chars;
422         bool was_empty = false;
423         bool wake_next_writer = false;
424
425         /* Null write succeeds. */
426         if (unlikely(total_len == 0))
427                 return 0;
428
429         __pipe_lock(pipe);
430
431         if (!pipe->readers) {
432                 send_sig(SIGPIPE, current, 0);
433                 ret = -EPIPE;
434                 goto out;
435         }
436
437 #ifdef CONFIG_WATCH_QUEUE
438         if (pipe->watch_queue) {
439                 ret = -EXDEV;
440                 goto out;
441         }
442 #endif
443
444         /*
445          * If it wasn't empty we try to merge new data into
446          * the last buffer.
447          *
448          * That naturally merges small writes, but it also
449          * page-aligns the rest of the writes for large writes
450          * spanning multiple pages.
451          */
452         head = pipe->head;
453         was_empty = pipe_empty(head, pipe->tail);
454         chars = total_len & (PAGE_SIZE-1);
455         if (chars && !was_empty) {
456                 unsigned int mask = pipe->ring_size - 1;
457                 struct pipe_buffer *buf = &pipe->bufs[(head - 1) & mask];
458                 int offset = buf->offset + buf->len;
459
460                 if ((buf->flags & PIPE_BUF_FLAG_CAN_MERGE) &&
461                     offset + chars <= PAGE_SIZE) {
462                         ret = pipe_buf_confirm(pipe, buf);
463                         if (ret)
464                                 goto out;
465
466                         ret = copy_page_from_iter(buf->page, offset, chars, from);
467                         if (unlikely(ret < chars)) {
468                                 ret = -EFAULT;
469                                 goto out;
470                         }
471
472                         buf->len += ret;
473                         if (!iov_iter_count(from))
474                                 goto out;
475                 }
476         }
477
478         for (;;) {
479                 if (!pipe->readers) {
480                         send_sig(SIGPIPE, current, 0);
481                         if (!ret)
482                                 ret = -EPIPE;
483                         break;
484                 }
485
486                 head = pipe->head;
487                 if (!pipe_full(head, pipe->tail, pipe->max_usage)) {
488                         unsigned int mask = pipe->ring_size - 1;
489                         struct pipe_buffer *buf = &pipe->bufs[head & mask];
490                         struct page *page = pipe->tmp_page;
491                         int copied;
492
493                         if (!page) {
494                                 page = alloc_page(GFP_HIGHUSER | __GFP_ACCOUNT);
495                                 if (unlikely(!page)) {
496                                         ret = ret ? : -ENOMEM;
497                                         break;
498                                 }
499                                 pipe->tmp_page = page;
500                         }
501
502                         /* Allocate a slot in the ring in advance and attach an
503                          * empty buffer.  If we fault or otherwise fail to use
504                          * it, either the reader will consume it or it'll still
505                          * be there for the next write.
506                          */
507                         spin_lock_irq(&pipe->rd_wait.lock);
508
509                         head = pipe->head;
510                         if (pipe_full(head, pipe->tail, pipe->max_usage)) {
511                                 spin_unlock_irq(&pipe->rd_wait.lock);
512                                 continue;
513                         }
514
515                         pipe->head = head + 1;
516                         spin_unlock_irq(&pipe->rd_wait.lock);
517
518                         /* Insert it into the buffer array */
519                         buf = &pipe->bufs[head & mask];
520                         buf->page = page;
521                         buf->ops = &anon_pipe_buf_ops;
522                         buf->offset = 0;
523                         buf->len = 0;
524                         if (is_packetized(filp))
525                                 buf->flags = PIPE_BUF_FLAG_PACKET;
526                         else
527                                 buf->flags = PIPE_BUF_FLAG_CAN_MERGE;
528                         pipe->tmp_page = NULL;
529
530                         copied = copy_page_from_iter(page, 0, PAGE_SIZE, from);
531                         if (unlikely(copied < PAGE_SIZE && iov_iter_count(from))) {
532                                 if (!ret)
533                                         ret = -EFAULT;
534                                 break;
535                         }
536                         ret += copied;
537                         buf->offset = 0;
538                         buf->len = copied;
539
540                         if (!iov_iter_count(from))
541                                 break;
542                 }
543
544                 if (!pipe_full(head, pipe->tail, pipe->max_usage))
545                         continue;
546
547                 /* Wait for buffer space to become available. */
548                 if (filp->f_flags & O_NONBLOCK) {
549                         if (!ret)
550                                 ret = -EAGAIN;
551                         break;
552                 }
553                 if (signal_pending(current)) {
554                         if (!ret)
555                                 ret = -ERESTARTSYS;
556                         break;
557                 }
558
559                 /*
560                  * We're going to release the pipe lock and wait for more
561                  * space. We wake up any readers if necessary, and then
562                  * after waiting we need to re-check whether the pipe
563                  * become empty while we dropped the lock.
564                  */
565                 __pipe_unlock(pipe);
566                 if (was_empty)
567                         wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
568                 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
569                 wait_event_interruptible_exclusive(pipe->wr_wait, pipe_writable(pipe));
570                 __pipe_lock(pipe);
571                 was_empty = pipe_empty(pipe->head, pipe->tail);
572                 wake_next_writer = true;
573         }
574 out:
575         if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
576                 wake_next_writer = false;
577         __pipe_unlock(pipe);
578
579         /*
580          * If we do do a wakeup event, we do a 'sync' wakeup, because we
581          * want the reader to start processing things asap, rather than
582          * leave the data pending.
583          *
584          * This is particularly important for small writes, because of
585          * how (for example) the GNU make jobserver uses small writes to
586          * wake up pending jobs
587          *
588          * Epoll nonsensically wants a wakeup whether the pipe
589          * was already empty or not.
590          */
591         if (was_empty || pipe->poll_usage)
592                 wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
593         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
594         if (wake_next_writer)
595                 wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM);
596         if (ret > 0 && sb_start_write_trylock(file_inode(filp)->i_sb)) {
597                 int err = file_update_time(filp);
598                 if (err)
599                         ret = err;
600                 sb_end_write(file_inode(filp)->i_sb);
601         }
602         return ret;
603 }
604
605 static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
606 {
607         struct pipe_inode_info *pipe = filp->private_data;
608         int count, head, tail, mask;
609
610         switch (cmd) {
611         case FIONREAD:
612                 __pipe_lock(pipe);
613                 count = 0;
614                 head = pipe->head;
615                 tail = pipe->tail;
616                 mask = pipe->ring_size - 1;
617
618                 while (tail != head) {
619                         count += pipe->bufs[tail & mask].len;
620                         tail++;
621                 }
622                 __pipe_unlock(pipe);
623
624                 return put_user(count, (int __user *)arg);
625
626 #ifdef CONFIG_WATCH_QUEUE
627         case IOC_WATCH_QUEUE_SET_SIZE: {
628                 int ret;
629                 __pipe_lock(pipe);
630                 ret = watch_queue_set_size(pipe, arg);
631                 __pipe_unlock(pipe);
632                 return ret;
633         }
634
635         case IOC_WATCH_QUEUE_SET_FILTER:
636                 return watch_queue_set_filter(
637                         pipe, (struct watch_notification_filter __user *)arg);
638 #endif
639
640         default:
641                 return -ENOIOCTLCMD;
642         }
643 }
644
645 /* No kernel lock held - fine */
646 static __poll_t
647 pipe_poll(struct file *filp, poll_table *wait)
648 {
649         __poll_t mask;
650         struct pipe_inode_info *pipe = filp->private_data;
651         unsigned int head, tail;
652
653         /* Epoll has some historical nasty semantics, this enables them */
654         pipe->poll_usage = 1;
655
656         /*
657          * Reading pipe state only -- no need for acquiring the semaphore.
658          *
659          * But because this is racy, the code has to add the
660          * entry to the poll table _first_ ..
661          */
662         if (filp->f_mode & FMODE_READ)
663                 poll_wait(filp, &pipe->rd_wait, wait);
664         if (filp->f_mode & FMODE_WRITE)
665                 poll_wait(filp, &pipe->wr_wait, wait);
666
667         /*
668          * .. and only then can you do the racy tests. That way,
669          * if something changes and you got it wrong, the poll
670          * table entry will wake you up and fix it.
671          */
672         head = READ_ONCE(pipe->head);
673         tail = READ_ONCE(pipe->tail);
674
675         mask = 0;
676         if (filp->f_mode & FMODE_READ) {
677                 if (!pipe_empty(head, tail))
678                         mask |= EPOLLIN | EPOLLRDNORM;
679                 if (!pipe->writers && filp->f_version != pipe->w_counter)
680                         mask |= EPOLLHUP;
681         }
682
683         if (filp->f_mode & FMODE_WRITE) {
684                 if (!pipe_full(head, tail, pipe->max_usage))
685                         mask |= EPOLLOUT | EPOLLWRNORM;
686                 /*
687                  * Most Unices do not set EPOLLERR for FIFOs but on Linux they
688                  * behave exactly like pipes for poll().
689                  */
690                 if (!pipe->readers)
691                         mask |= EPOLLERR;
692         }
693
694         return mask;
695 }
696
697 static void put_pipe_info(struct inode *inode, struct pipe_inode_info *pipe)
698 {
699         int kill = 0;
700
701         spin_lock(&inode->i_lock);
702         if (!--pipe->files) {
703                 inode->i_pipe = NULL;
704                 kill = 1;
705         }
706         spin_unlock(&inode->i_lock);
707
708         if (kill)
709                 free_pipe_info(pipe);
710 }
711
712 static int
713 pipe_release(struct inode *inode, struct file *file)
714 {
715         struct pipe_inode_info *pipe = file->private_data;
716
717         __pipe_lock(pipe);
718         if (file->f_mode & FMODE_READ)
719                 pipe->readers--;
720         if (file->f_mode & FMODE_WRITE)
721                 pipe->writers--;
722
723         /* Was that the last reader or writer, but not the other side? */
724         if (!pipe->readers != !pipe->writers) {
725                 wake_up_interruptible_all(&pipe->rd_wait);
726                 wake_up_interruptible_all(&pipe->wr_wait);
727                 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
728                 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
729         }
730         __pipe_unlock(pipe);
731
732         put_pipe_info(inode, pipe);
733         return 0;
734 }
735
736 static int
737 pipe_fasync(int fd, struct file *filp, int on)
738 {
739         struct pipe_inode_info *pipe = filp->private_data;
740         int retval = 0;
741
742         __pipe_lock(pipe);
743         if (filp->f_mode & FMODE_READ)
744                 retval = fasync_helper(fd, filp, on, &pipe->fasync_readers);
745         if ((filp->f_mode & FMODE_WRITE) && retval >= 0) {
746                 retval = fasync_helper(fd, filp, on, &pipe->fasync_writers);
747                 if (retval < 0 && (filp->f_mode & FMODE_READ))
748                         /* this can happen only if on == T */
749                         fasync_helper(-1, filp, 0, &pipe->fasync_readers);
750         }
751         __pipe_unlock(pipe);
752         return retval;
753 }
754
755 unsigned long account_pipe_buffers(struct user_struct *user,
756                                    unsigned long old, unsigned long new)
757 {
758         return atomic_long_add_return(new - old, &user->pipe_bufs);
759 }
760
761 bool too_many_pipe_buffers_soft(unsigned long user_bufs)
762 {
763         unsigned long soft_limit = READ_ONCE(pipe_user_pages_soft);
764
765         return soft_limit && user_bufs > soft_limit;
766 }
767
768 bool too_many_pipe_buffers_hard(unsigned long user_bufs)
769 {
770         unsigned long hard_limit = READ_ONCE(pipe_user_pages_hard);
771
772         return hard_limit && user_bufs > hard_limit;
773 }
774
775 bool pipe_is_unprivileged_user(void)
776 {
777         return !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN);
778 }
779
780 struct pipe_inode_info *alloc_pipe_info(void)
781 {
782         struct pipe_inode_info *pipe;
783         unsigned long pipe_bufs = PIPE_DEF_BUFFERS;
784         struct user_struct *user = get_current_user();
785         unsigned long user_bufs;
786         unsigned int max_size = READ_ONCE(pipe_max_size);
787
788         pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL_ACCOUNT);
789         if (pipe == NULL)
790                 goto out_free_uid;
791
792         if (pipe_bufs * PAGE_SIZE > max_size && !capable(CAP_SYS_RESOURCE))
793                 pipe_bufs = max_size >> PAGE_SHIFT;
794
795         user_bufs = account_pipe_buffers(user, 0, pipe_bufs);
796
797         if (too_many_pipe_buffers_soft(user_bufs) && pipe_is_unprivileged_user()) {
798                 user_bufs = account_pipe_buffers(user, pipe_bufs, PIPE_MIN_DEF_BUFFERS);
799                 pipe_bufs = PIPE_MIN_DEF_BUFFERS;
800         }
801
802         if (too_many_pipe_buffers_hard(user_bufs) && pipe_is_unprivileged_user())
803                 goto out_revert_acct;
804
805         pipe->bufs = kcalloc(pipe_bufs, sizeof(struct pipe_buffer),
806                              GFP_KERNEL_ACCOUNT);
807
808         if (pipe->bufs) {
809                 init_waitqueue_head(&pipe->rd_wait);
810                 init_waitqueue_head(&pipe->wr_wait);
811                 pipe->r_counter = pipe->w_counter = 1;
812                 pipe->max_usage = pipe_bufs;
813                 pipe->ring_size = pipe_bufs;
814                 pipe->nr_accounted = pipe_bufs;
815                 pipe->user = user;
816                 mutex_init(&pipe->mutex);
817                 return pipe;
818         }
819
820 out_revert_acct:
821         (void) account_pipe_buffers(user, pipe_bufs, 0);
822         kfree(pipe);
823 out_free_uid:
824         free_uid(user);
825         return NULL;
826 }
827
828 void free_pipe_info(struct pipe_inode_info *pipe)
829 {
830         int i;
831
832 #ifdef CONFIG_WATCH_QUEUE
833         if (pipe->watch_queue) {
834                 watch_queue_clear(pipe->watch_queue);
835                 put_watch_queue(pipe->watch_queue);
836         }
837 #endif
838
839         (void) account_pipe_buffers(pipe->user, pipe->nr_accounted, 0);
840         free_uid(pipe->user);
841         for (i = 0; i < pipe->ring_size; i++) {
842                 struct pipe_buffer *buf = pipe->bufs + i;
843                 if (buf->ops)
844                         pipe_buf_release(pipe, buf);
845         }
846         if (pipe->tmp_page)
847                 __free_page(pipe->tmp_page);
848         kfree(pipe->bufs);
849         kfree(pipe);
850 }
851
852 static struct vfsmount *pipe_mnt __read_mostly;
853
854 /*
855  * pipefs_dname() is called from d_path().
856  */
857 static char *pipefs_dname(struct dentry *dentry, char *buffer, int buflen)
858 {
859         return dynamic_dname(dentry, buffer, buflen, "pipe:[%lu]",
860                                 d_inode(dentry)->i_ino);
861 }
862
863 static const struct dentry_operations pipefs_dentry_operations = {
864         .d_dname        = pipefs_dname,
865 };
866
867 static struct inode * get_pipe_inode(void)
868 {
869         struct inode *inode = new_inode_pseudo(pipe_mnt->mnt_sb);
870         struct pipe_inode_info *pipe;
871
872         if (!inode)
873                 goto fail_inode;
874
875         inode->i_ino = get_next_ino();
876
877         pipe = alloc_pipe_info();
878         if (!pipe)
879                 goto fail_iput;
880
881         inode->i_pipe = pipe;
882         pipe->files = 2;
883         pipe->readers = pipe->writers = 1;
884         inode->i_fop = &pipefifo_fops;
885
886         /*
887          * Mark the inode dirty from the very beginning,
888          * that way it will never be moved to the dirty
889          * list because "mark_inode_dirty()" will think
890          * that it already _is_ on the dirty list.
891          */
892         inode->i_state = I_DIRTY;
893         inode->i_mode = S_IFIFO | S_IRUSR | S_IWUSR;
894         inode->i_uid = current_fsuid();
895         inode->i_gid = current_fsgid();
896         inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
897
898         return inode;
899
900 fail_iput:
901         iput(inode);
902
903 fail_inode:
904         return NULL;
905 }
906
907 int create_pipe_files(struct file **res, int flags)
908 {
909         struct inode *inode = get_pipe_inode();
910         struct file *f;
911         int error;
912
913         if (!inode)
914                 return -ENFILE;
915
916         if (flags & O_NOTIFICATION_PIPE) {
917                 error = watch_queue_init(inode->i_pipe);
918                 if (error) {
919                         free_pipe_info(inode->i_pipe);
920                         iput(inode);
921                         return error;
922                 }
923         }
924
925         f = alloc_file_pseudo(inode, pipe_mnt, "",
926                                 O_WRONLY | (flags & (O_NONBLOCK | O_DIRECT)),
927                                 &pipefifo_fops);
928         if (IS_ERR(f)) {
929                 free_pipe_info(inode->i_pipe);
930                 iput(inode);
931                 return PTR_ERR(f);
932         }
933
934         f->private_data = inode->i_pipe;
935
936         res[0] = alloc_file_clone(f, O_RDONLY | (flags & O_NONBLOCK),
937                                   &pipefifo_fops);
938         if (IS_ERR(res[0])) {
939                 put_pipe_info(inode, inode->i_pipe);
940                 fput(f);
941                 return PTR_ERR(res[0]);
942         }
943         res[0]->private_data = inode->i_pipe;
944         res[1] = f;
945         stream_open(inode, res[0]);
946         stream_open(inode, res[1]);
947         return 0;
948 }
949
950 static int __do_pipe_flags(int *fd, struct file **files, int flags)
951 {
952         int error;
953         int fdw, fdr;
954
955         if (flags & ~(O_CLOEXEC | O_NONBLOCK | O_DIRECT | O_NOTIFICATION_PIPE))
956                 return -EINVAL;
957
958         error = create_pipe_files(files, flags);
959         if (error)
960                 return error;
961
962         error = get_unused_fd_flags(flags);
963         if (error < 0)
964                 goto err_read_pipe;
965         fdr = error;
966
967         error = get_unused_fd_flags(flags);
968         if (error < 0)
969                 goto err_fdr;
970         fdw = error;
971
972         audit_fd_pair(fdr, fdw);
973         fd[0] = fdr;
974         fd[1] = fdw;
975         return 0;
976
977  err_fdr:
978         put_unused_fd(fdr);
979  err_read_pipe:
980         fput(files[0]);
981         fput(files[1]);
982         return error;
983 }
984
985 int do_pipe_flags(int *fd, int flags)
986 {
987         struct file *files[2];
988         int error = __do_pipe_flags(fd, files, flags);
989         if (!error) {
990                 fd_install(fd[0], files[0]);
991                 fd_install(fd[1], files[1]);
992         }
993         return error;
994 }
995
996 /*
997  * sys_pipe() is the normal C calling standard for creating
998  * a pipe. It's not the way Unix traditionally does this, though.
999  */
1000 static int do_pipe2(int __user *fildes, int flags)
1001 {
1002         struct file *files[2];
1003         int fd[2];
1004         int error;
1005
1006         error = __do_pipe_flags(fd, files, flags);
1007         if (!error) {
1008                 if (unlikely(copy_to_user(fildes, fd, sizeof(fd)))) {
1009                         fput(files[0]);
1010                         fput(files[1]);
1011                         put_unused_fd(fd[0]);
1012                         put_unused_fd(fd[1]);
1013                         error = -EFAULT;
1014                 } else {
1015                         fd_install(fd[0], files[0]);
1016                         fd_install(fd[1], files[1]);
1017                 }
1018         }
1019         return error;
1020 }
1021
1022 SYSCALL_DEFINE2(pipe2, int __user *, fildes, int, flags)
1023 {
1024         return do_pipe2(fildes, flags);
1025 }
1026
1027 SYSCALL_DEFINE1(pipe, int __user *, fildes)
1028 {
1029         return do_pipe2(fildes, 0);
1030 }
1031
1032 /*
1033  * This is the stupid "wait for pipe to be readable or writable"
1034  * model.
1035  *
1036  * See pipe_read/write() for the proper kind of exclusive wait,
1037  * but that requires that we wake up any other readers/writers
1038  * if we then do not end up reading everything (ie the whole
1039  * "wake_next_reader/writer" logic in pipe_read/write()).
1040  */
1041 void pipe_wait_readable(struct pipe_inode_info *pipe)
1042 {
1043         pipe_unlock(pipe);
1044         wait_event_interruptible(pipe->rd_wait, pipe_readable(pipe));
1045         pipe_lock(pipe);
1046 }
1047
1048 void pipe_wait_writable(struct pipe_inode_info *pipe)
1049 {
1050         pipe_unlock(pipe);
1051         wait_event_interruptible(pipe->wr_wait, pipe_writable(pipe));
1052         pipe_lock(pipe);
1053 }
1054
1055 /*
1056  * This depends on both the wait (here) and the wakeup (wake_up_partner)
1057  * holding the pipe lock, so "*cnt" is stable and we know a wakeup cannot
1058  * race with the count check and waitqueue prep.
1059  *
1060  * Normally in order to avoid races, you'd do the prepare_to_wait() first,
1061  * then check the condition you're waiting for, and only then sleep. But
1062  * because of the pipe lock, we can check the condition before being on
1063  * the wait queue.
1064  *
1065  * We use the 'rd_wait' waitqueue for pipe partner waiting.
1066  */
1067 static int wait_for_partner(struct pipe_inode_info *pipe, unsigned int *cnt)
1068 {
1069         DEFINE_WAIT(rdwait);
1070         int cur = *cnt;
1071
1072         while (cur == *cnt) {
1073                 prepare_to_wait(&pipe->rd_wait, &rdwait, TASK_INTERRUPTIBLE);
1074                 pipe_unlock(pipe);
1075                 schedule();
1076                 finish_wait(&pipe->rd_wait, &rdwait);
1077                 pipe_lock(pipe);
1078                 if (signal_pending(current))
1079                         break;
1080         }
1081         return cur == *cnt ? -ERESTARTSYS : 0;
1082 }
1083
1084 static void wake_up_partner(struct pipe_inode_info *pipe)
1085 {
1086         wake_up_interruptible_all(&pipe->rd_wait);
1087 }
1088
1089 static int fifo_open(struct inode *inode, struct file *filp)
1090 {
1091         struct pipe_inode_info *pipe;
1092         bool is_pipe = inode->i_sb->s_magic == PIPEFS_MAGIC;
1093         int ret;
1094
1095         filp->f_version = 0;
1096
1097         spin_lock(&inode->i_lock);
1098         if (inode->i_pipe) {
1099                 pipe = inode->i_pipe;
1100                 pipe->files++;
1101                 spin_unlock(&inode->i_lock);
1102         } else {
1103                 spin_unlock(&inode->i_lock);
1104                 pipe = alloc_pipe_info();
1105                 if (!pipe)
1106                         return -ENOMEM;
1107                 pipe->files = 1;
1108                 spin_lock(&inode->i_lock);
1109                 if (unlikely(inode->i_pipe)) {
1110                         inode->i_pipe->files++;
1111                         spin_unlock(&inode->i_lock);
1112                         free_pipe_info(pipe);
1113                         pipe = inode->i_pipe;
1114                 } else {
1115                         inode->i_pipe = pipe;
1116                         spin_unlock(&inode->i_lock);
1117                 }
1118         }
1119         filp->private_data = pipe;
1120         /* OK, we have a pipe and it's pinned down */
1121
1122         __pipe_lock(pipe);
1123
1124         /* We can only do regular read/write on fifos */
1125         stream_open(inode, filp);
1126
1127         switch (filp->f_mode & (FMODE_READ | FMODE_WRITE)) {
1128         case FMODE_READ:
1129         /*
1130          *  O_RDONLY
1131          *  POSIX.1 says that O_NONBLOCK means return with the FIFO
1132          *  opened, even when there is no process writing the FIFO.
1133          */
1134                 pipe->r_counter++;
1135                 if (pipe->readers++ == 0)
1136                         wake_up_partner(pipe);
1137
1138                 if (!is_pipe && !pipe->writers) {
1139                         if ((filp->f_flags & O_NONBLOCK)) {
1140                                 /* suppress EPOLLHUP until we have
1141                                  * seen a writer */
1142                                 filp->f_version = pipe->w_counter;
1143                         } else {
1144                                 if (wait_for_partner(pipe, &pipe->w_counter))
1145                                         goto err_rd;
1146                         }
1147                 }
1148                 break;
1149
1150         case FMODE_WRITE:
1151         /*
1152          *  O_WRONLY
1153          *  POSIX.1 says that O_NONBLOCK means return -1 with
1154          *  errno=ENXIO when there is no process reading the FIFO.
1155          */
1156                 ret = -ENXIO;
1157                 if (!is_pipe && (filp->f_flags & O_NONBLOCK) && !pipe->readers)
1158                         goto err;
1159
1160                 pipe->w_counter++;
1161                 if (!pipe->writers++)
1162                         wake_up_partner(pipe);
1163
1164                 if (!is_pipe && !pipe->readers) {
1165                         if (wait_for_partner(pipe, &pipe->r_counter))
1166                                 goto err_wr;
1167                 }
1168                 break;
1169
1170         case FMODE_READ | FMODE_WRITE:
1171         /*
1172          *  O_RDWR
1173          *  POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
1174          *  This implementation will NEVER block on a O_RDWR open, since
1175          *  the process can at least talk to itself.
1176          */
1177
1178                 pipe->readers++;
1179                 pipe->writers++;
1180                 pipe->r_counter++;
1181                 pipe->w_counter++;
1182                 if (pipe->readers == 1 || pipe->writers == 1)
1183                         wake_up_partner(pipe);
1184                 break;
1185
1186         default:
1187                 ret = -EINVAL;
1188                 goto err;
1189         }
1190
1191         /* Ok! */
1192         __pipe_unlock(pipe);
1193         return 0;
1194
1195 err_rd:
1196         if (!--pipe->readers)
1197                 wake_up_interruptible(&pipe->wr_wait);
1198         ret = -ERESTARTSYS;
1199         goto err;
1200
1201 err_wr:
1202         if (!--pipe->writers)
1203                 wake_up_interruptible_all(&pipe->rd_wait);
1204         ret = -ERESTARTSYS;
1205         goto err;
1206
1207 err:
1208         __pipe_unlock(pipe);
1209
1210         put_pipe_info(inode, pipe);
1211         return ret;
1212 }
1213
1214 const struct file_operations pipefifo_fops = {
1215         .open           = fifo_open,
1216         .llseek         = no_llseek,
1217         .read_iter      = pipe_read,
1218         .write_iter     = pipe_write,
1219         .poll           = pipe_poll,
1220         .unlocked_ioctl = pipe_ioctl,
1221         .release        = pipe_release,
1222         .fasync         = pipe_fasync,
1223         .splice_write   = iter_file_splice_write,
1224 };
1225
1226 /*
1227  * Currently we rely on the pipe array holding a power-of-2 number
1228  * of pages. Returns 0 on error.
1229  */
1230 unsigned int round_pipe_size(unsigned long size)
1231 {
1232         if (size > (1U << 31))
1233                 return 0;
1234
1235         /* Minimum pipe size, as required by POSIX */
1236         if (size < PAGE_SIZE)
1237                 return PAGE_SIZE;
1238
1239         return roundup_pow_of_two(size);
1240 }
1241
1242 /*
1243  * Resize the pipe ring to a number of slots.
1244  */
1245 int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
1246 {
1247         struct pipe_buffer *bufs;
1248         unsigned int head, tail, mask, n;
1249
1250         /*
1251          * We can shrink the pipe, if arg is greater than the ring occupancy.
1252          * Since we don't expect a lot of shrink+grow operations, just free and
1253          * allocate again like we would do for growing.  If the pipe currently
1254          * contains more buffers than arg, then return busy.
1255          */
1256         mask = pipe->ring_size - 1;
1257         head = pipe->head;
1258         tail = pipe->tail;
1259         n = pipe_occupancy(pipe->head, pipe->tail);
1260         if (nr_slots < n)
1261                 return -EBUSY;
1262
1263         bufs = kcalloc(nr_slots, sizeof(*bufs),
1264                        GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
1265         if (unlikely(!bufs))
1266                 return -ENOMEM;
1267
1268         /*
1269          * The pipe array wraps around, so just start the new one at zero
1270          * and adjust the indices.
1271          */
1272         if (n > 0) {
1273                 unsigned int h = head & mask;
1274                 unsigned int t = tail & mask;
1275                 if (h > t) {
1276                         memcpy(bufs, pipe->bufs + t,
1277                                n * sizeof(struct pipe_buffer));
1278                 } else {
1279                         unsigned int tsize = pipe->ring_size - t;
1280                         if (h > 0)
1281                                 memcpy(bufs + tsize, pipe->bufs,
1282                                        h * sizeof(struct pipe_buffer));
1283                         memcpy(bufs, pipe->bufs + t,
1284                                tsize * sizeof(struct pipe_buffer));
1285                 }
1286         }
1287
1288         head = n;
1289         tail = 0;
1290
1291         kfree(pipe->bufs);
1292         pipe->bufs = bufs;
1293         pipe->ring_size = nr_slots;
1294         if (pipe->max_usage > nr_slots)
1295                 pipe->max_usage = nr_slots;
1296         pipe->tail = tail;
1297         pipe->head = head;
1298
1299         /* This might have made more room for writers */
1300         wake_up_interruptible(&pipe->wr_wait);
1301         return 0;
1302 }
1303
1304 /*
1305  * Allocate a new array of pipe buffers and copy the info over. Returns the
1306  * pipe size if successful, or return -ERROR on error.
1307  */
1308 static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
1309 {
1310         unsigned long user_bufs;
1311         unsigned int nr_slots, size;
1312         long ret = 0;
1313
1314 #ifdef CONFIG_WATCH_QUEUE
1315         if (pipe->watch_queue)
1316                 return -EBUSY;
1317 #endif
1318
1319         size = round_pipe_size(arg);
1320         nr_slots = size >> PAGE_SHIFT;
1321
1322         if (!nr_slots)
1323                 return -EINVAL;
1324
1325         /*
1326          * If trying to increase the pipe capacity, check that an
1327          * unprivileged user is not trying to exceed various limits
1328          * (soft limit check here, hard limit check just below).
1329          * Decreasing the pipe capacity is always permitted, even
1330          * if the user is currently over a limit.
1331          */
1332         if (nr_slots > pipe->max_usage &&
1333                         size > pipe_max_size && !capable(CAP_SYS_RESOURCE))
1334                 return -EPERM;
1335
1336         user_bufs = account_pipe_buffers(pipe->user, pipe->nr_accounted, nr_slots);
1337
1338         if (nr_slots > pipe->max_usage &&
1339                         (too_many_pipe_buffers_hard(user_bufs) ||
1340                          too_many_pipe_buffers_soft(user_bufs)) &&
1341                         pipe_is_unprivileged_user()) {
1342                 ret = -EPERM;
1343                 goto out_revert_acct;
1344         }
1345
1346         ret = pipe_resize_ring(pipe, nr_slots);
1347         if (ret < 0)
1348                 goto out_revert_acct;
1349
1350         pipe->max_usage = nr_slots;
1351         pipe->nr_accounted = nr_slots;
1352         return pipe->max_usage * PAGE_SIZE;
1353
1354 out_revert_acct:
1355         (void) account_pipe_buffers(pipe->user, nr_slots, pipe->nr_accounted);
1356         return ret;
1357 }
1358
1359 /*
1360  * Note that i_pipe and i_cdev share the same location, so checking ->i_pipe is
1361  * not enough to verify that this is a pipe.
1362  */
1363 struct pipe_inode_info *get_pipe_info(struct file *file, bool for_splice)
1364 {
1365         struct pipe_inode_info *pipe = file->private_data;
1366
1367         if (file->f_op != &pipefifo_fops || !pipe)
1368                 return NULL;
1369 #ifdef CONFIG_WATCH_QUEUE
1370         if (for_splice && pipe->watch_queue)
1371                 return NULL;
1372 #endif
1373         return pipe;
1374 }
1375
1376 long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
1377 {
1378         struct pipe_inode_info *pipe;
1379         long ret;
1380
1381         pipe = get_pipe_info(file, false);
1382         if (!pipe)
1383                 return -EBADF;
1384
1385         __pipe_lock(pipe);
1386
1387         switch (cmd) {
1388         case F_SETPIPE_SZ:
1389                 ret = pipe_set_size(pipe, arg);
1390                 break;
1391         case F_GETPIPE_SZ:
1392                 ret = pipe->max_usage * PAGE_SIZE;
1393                 break;
1394         default:
1395                 ret = -EINVAL;
1396                 break;
1397         }
1398
1399         __pipe_unlock(pipe);
1400         return ret;
1401 }
1402
1403 static const struct super_operations pipefs_ops = {
1404         .destroy_inode = free_inode_nonrcu,
1405         .statfs = simple_statfs,
1406 };
1407
1408 /*
1409  * pipefs should _never_ be mounted by userland - too much of security hassle,
1410  * no real gain from having the whole whorehouse mounted. So we don't need
1411  * any operations on the root directory. However, we need a non-trivial
1412  * d_name - pipe: will go nicely and kill the special-casing in procfs.
1413  */
1414
1415 static int pipefs_init_fs_context(struct fs_context *fc)
1416 {
1417         struct pseudo_fs_context *ctx = init_pseudo(fc, PIPEFS_MAGIC);
1418         if (!ctx)
1419                 return -ENOMEM;
1420         ctx->ops = &pipefs_ops;
1421         ctx->dops = &pipefs_dentry_operations;
1422         return 0;
1423 }
1424
1425 static struct file_system_type pipe_fs_type = {
1426         .name           = "pipefs",
1427         .init_fs_context = pipefs_init_fs_context,
1428         .kill_sb        = kill_anon_super,
1429 };
1430
1431 static int __init init_pipe_fs(void)
1432 {
1433         int err = register_filesystem(&pipe_fs_type);
1434
1435         if (!err) {
1436                 pipe_mnt = kern_mount(&pipe_fs_type);
1437                 if (IS_ERR(pipe_mnt)) {
1438                         err = PTR_ERR(pipe_mnt);
1439                         unregister_filesystem(&pipe_fs_type);
1440                 }
1441         }
1442         return err;
1443 }
1444
1445 fs_initcall(init_pipe_fs);