xref: /openbmc/linux/fs/splice.c (revision a6978d1b7bb8f3a25305e8ff7d367f7289614c5d)
1  // SPDX-License-Identifier: GPL-2.0-only
2  /*
3   * "splice": joining two ropes together by interweaving their strands.
4   *
5   * This is the "extended pipe" functionality, where a pipe is used as
6   * an arbitrary in-memory buffer. Think of a pipe as a small kernel
7   * buffer that you can use to transfer data from one end to the other.
8   *
9   * The traditional unix read/write is extended with a "splice()" operation
10   * that transfers data buffers to or from a pipe buffer.
11   *
12   * Named by Larry McVoy, original implementation from Linus, extended by
13   * Jens to support splicing to files, network, direct splicing, etc and
14   * fixing lots of bugs.
15   *
16   * Copyright (C) 2005-2006 Jens Axboe <axboe@kernel.dk>
17   * Copyright (C) 2005-2006 Linus Torvalds <torvalds@osdl.org>
18   * Copyright (C) 2006 Ingo Molnar <mingo@elte.hu>
19   *
20   */
21  #include <linux/bvec.h>
22  #include <linux/fs.h>
23  #include <linux/file.h>
24  #include <linux/pagemap.h>
25  #include <linux/splice.h>
26  #include <linux/memcontrol.h>
27  #include <linux/mm_inline.h>
28  #include <linux/swap.h>
29  #include <linux/writeback.h>
30  #include <linux/export.h>
31  #include <linux/syscalls.h>
32  #include <linux/uio.h>
33  #include <linux/fsnotify.h>
34  #include <linux/security.h>
35  #include <linux/gfp.h>
36  #include <linux/net.h>
37  #include <linux/socket.h>
38  #include <linux/sched/signal.h>
39  
40  #include "internal.h"
41  
42  /*
43   * Splice doesn't support FMODE_NOWAIT. Since pipes may set this flag to
44   * indicate they support non-blocking reads or writes, we must clear it
45   * here if set to avoid blocking other users of this pipe if splice is
46   * being done on it.
47   */
48  static noinline void noinline pipe_clear_nowait(struct file *file)
49  {
50  	fmode_t fmode = READ_ONCE(file->f_mode);
51  
52  	do {
53  		if (!(fmode & FMODE_NOWAIT))
54  			break;
55  	} while (!try_cmpxchg(&file->f_mode, &fmode, fmode & ~FMODE_NOWAIT));
56  }
57  
58  /*
59   * Attempt to steal a page from a pipe buffer. This should perhaps go into
60   * a vm helper function, it's already simplified quite a bit by the
61   * addition of remove_mapping(). If success is returned, the caller may
62   * attempt to reuse this page for another destination.
63   */
64  static bool page_cache_pipe_buf_try_steal(struct pipe_inode_info *pipe,
65  		struct pipe_buffer *buf)
66  {
67  	struct folio *folio = page_folio(buf->page);
68  	struct address_space *mapping;
69  
70  	folio_lock(folio);
71  
72  	mapping = folio_mapping(folio);
73  	if (mapping) {
74  		WARN_ON(!folio_test_uptodate(folio));
75  
76  		/*
77  		 * At least for ext2 with nobh option, we need to wait on
78  		 * writeback completing on this folio, since we'll remove it
79  		 * from the pagecache.  Otherwise truncate wont wait on the
80  		 * folio, allowing the disk blocks to be reused by someone else
81  		 * before we actually wrote our data to them. fs corruption
82  		 * ensues.
83  		 */
84  		folio_wait_writeback(folio);
85  
86  		if (!filemap_release_folio(folio, GFP_KERNEL))
87  			goto out_unlock;
88  
89  		/*
90  		 * If we succeeded in removing the mapping, set LRU flag
91  		 * and return good.
92  		 */
93  		if (remove_mapping(mapping, folio)) {
94  			buf->flags |= PIPE_BUF_FLAG_LRU;
95  			return true;
96  		}
97  	}
98  
99  	/*
100  	 * Raced with truncate or failed to remove folio from current
101  	 * address space, unlock and return failure.
102  	 */
103  out_unlock:
104  	folio_unlock(folio);
105  	return false;
106  }
107  
108  static void page_cache_pipe_buf_release(struct pipe_inode_info *pipe,
109  					struct pipe_buffer *buf)
110  {
111  	put_page(buf->page);
112  	buf->flags &= ~PIPE_BUF_FLAG_LRU;
113  }
114  
115  /*
116   * Check whether the contents of buf is OK to access. Since the content
117   * is a page cache page, IO may be in flight.
118   */
119  static int page_cache_pipe_buf_confirm(struct pipe_inode_info *pipe,
120  				       struct pipe_buffer *buf)
121  {
122  	struct folio *folio = page_folio(buf->page);
123  	int err;
124  
125  	if (!folio_test_uptodate(folio)) {
126  		folio_lock(folio);
127  
128  		/*
129  		 * Folio got truncated/unhashed. This will cause a 0-byte
130  		 * splice, if this is the first page.
131  		 */
132  		if (!folio->mapping) {
133  			err = -ENODATA;
134  			goto error;
135  		}
136  
137  		/*
138  		 * Uh oh, read-error from disk.
139  		 */
140  		if (!folio_test_uptodate(folio)) {
141  			err = -EIO;
142  			goto error;
143  		}
144  
145  		/* Folio is ok after all, we are done */
146  		folio_unlock(folio);
147  	}
148  
149  	return 0;
150  error:
151  	folio_unlock(folio);
152  	return err;
153  }
154  
155  const struct pipe_buf_operations page_cache_pipe_buf_ops = {
156  	.confirm	= page_cache_pipe_buf_confirm,
157  	.release	= page_cache_pipe_buf_release,
158  	.try_steal	= page_cache_pipe_buf_try_steal,
159  	.get		= generic_pipe_buf_get,
160  };
161  
162  static bool user_page_pipe_buf_try_steal(struct pipe_inode_info *pipe,
163  		struct pipe_buffer *buf)
164  {
165  	if (!(buf->flags & PIPE_BUF_FLAG_GIFT))
166  		return false;
167  
168  	buf->flags |= PIPE_BUF_FLAG_LRU;
169  	return generic_pipe_buf_try_steal(pipe, buf);
170  }
171  
172  static const struct pipe_buf_operations user_page_pipe_buf_ops = {
173  	.release	= page_cache_pipe_buf_release,
174  	.try_steal	= user_page_pipe_buf_try_steal,
175  	.get		= generic_pipe_buf_get,
176  };
177  
178  static void wakeup_pipe_readers(struct pipe_inode_info *pipe)
179  {
180  	smp_mb();
181  	if (waitqueue_active(&pipe->rd_wait))
182  		wake_up_interruptible(&pipe->rd_wait);
183  	kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
184  }
185  
186  /**
187   * splice_to_pipe - fill passed data into a pipe
188   * @pipe:	pipe to fill
189   * @spd:	data to fill
190   *
191   * Description:
192   *    @spd contains a map of pages and len/offset tuples, along with
193   *    the struct pipe_buf_operations associated with these pages. This
194   *    function will link that data to the pipe.
195   *
196   */
197  ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
198  		       struct splice_pipe_desc *spd)
199  {
200  	unsigned int spd_pages = spd->nr_pages;
201  	unsigned int tail = pipe->tail;
202  	unsigned int head = pipe->head;
203  	unsigned int mask = pipe->ring_size - 1;
204  	int ret = 0, page_nr = 0;
205  
206  	if (!spd_pages)
207  		return 0;
208  
209  	if (unlikely(!pipe->readers)) {
210  		send_sig(SIGPIPE, current, 0);
211  		ret = -EPIPE;
212  		goto out;
213  	}
214  
215  	while (!pipe_full(head, tail, pipe->max_usage)) {
216  		struct pipe_buffer *buf = &pipe->bufs[head & mask];
217  
218  		buf->page = spd->pages[page_nr];
219  		buf->offset = spd->partial[page_nr].offset;
220  		buf->len = spd->partial[page_nr].len;
221  		buf->private = spd->partial[page_nr].private;
222  		buf->ops = spd->ops;
223  		buf->flags = 0;
224  
225  		head++;
226  		pipe->head = head;
227  		page_nr++;
228  		ret += buf->len;
229  
230  		if (!--spd->nr_pages)
231  			break;
232  	}
233  
234  	if (!ret)
235  		ret = -EAGAIN;
236  
237  out:
238  	while (page_nr < spd_pages)
239  		spd->spd_release(spd, page_nr++);
240  
241  	return ret;
242  }
243  EXPORT_SYMBOL_GPL(splice_to_pipe);
244  
245  ssize_t add_to_pipe(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
246  {
247  	unsigned int head = pipe->head;
248  	unsigned int tail = pipe->tail;
249  	unsigned int mask = pipe->ring_size - 1;
250  	int ret;
251  
252  	if (unlikely(!pipe->readers)) {
253  		send_sig(SIGPIPE, current, 0);
254  		ret = -EPIPE;
255  	} else if (pipe_full(head, tail, pipe->max_usage)) {
256  		ret = -EAGAIN;
257  	} else {
258  		pipe->bufs[head & mask] = *buf;
259  		pipe->head = head + 1;
260  		return buf->len;
261  	}
262  	pipe_buf_release(pipe, buf);
263  	return ret;
264  }
265  EXPORT_SYMBOL(add_to_pipe);
266  
267  /*
268   * Check if we need to grow the arrays holding pages and partial page
269   * descriptions.
270   */
271  int splice_grow_spd(const struct pipe_inode_info *pipe, struct splice_pipe_desc *spd)
272  {
273  	unsigned int max_usage = READ_ONCE(pipe->max_usage);
274  
275  	spd->nr_pages_max = max_usage;
276  	if (max_usage <= PIPE_DEF_BUFFERS)
277  		return 0;
278  
279  	spd->pages = kmalloc_array(max_usage, sizeof(struct page *), GFP_KERNEL);
280  	spd->partial = kmalloc_array(max_usage, sizeof(struct partial_page),
281  				     GFP_KERNEL);
282  
283  	if (spd->pages && spd->partial)
284  		return 0;
285  
286  	kfree(spd->pages);
287  	kfree(spd->partial);
288  	return -ENOMEM;
289  }
290  
291  void splice_shrink_spd(struct splice_pipe_desc *spd)
292  {
293  	if (spd->nr_pages_max <= PIPE_DEF_BUFFERS)
294  		return;
295  
296  	kfree(spd->pages);
297  	kfree(spd->partial);
298  }
299  
300  /**
301   * copy_splice_read -  Copy data from a file and splice the copy into a pipe
302   * @in: The file to read from
303   * @ppos: Pointer to the file position to read from
304   * @pipe: The pipe to splice into
305   * @len: The amount to splice
306   * @flags: The SPLICE_F_* flags
307   *
308   * This function allocates a bunch of pages sufficient to hold the requested
309   * amount of data (but limited by the remaining pipe capacity), passes it to
310   * the file's ->read_iter() to read into and then splices the used pages into
311   * the pipe.
312   *
313   * Return: On success, the number of bytes read will be returned and *@ppos
314   * will be updated if appropriate; 0 will be returned if there is no more data
315   * to be read; -EAGAIN will be returned if the pipe had no space, and some
316   * other negative error code will be returned on error.  A short read may occur
317   * if the pipe has insufficient space, we reach the end of the data or we hit a
318   * hole.
319   */
320  ssize_t copy_splice_read(struct file *in, loff_t *ppos,
321  			 struct pipe_inode_info *pipe,
322  			 size_t len, unsigned int flags)
323  {
324  	struct iov_iter to;
325  	struct bio_vec *bv;
326  	struct kiocb kiocb;
327  	struct page **pages;
328  	ssize_t ret;
329  	size_t used, npages, chunk, remain, keep = 0;
330  	int i;
331  
332  	/* Work out how much data we can actually add into the pipe */
333  	used = pipe_occupancy(pipe->head, pipe->tail);
334  	npages = max_t(ssize_t, pipe->max_usage - used, 0);
335  	len = min_t(size_t, len, npages * PAGE_SIZE);
336  	npages = DIV_ROUND_UP(len, PAGE_SIZE);
337  
338  	bv = kzalloc(array_size(npages, sizeof(bv[0])) +
339  		     array_size(npages, sizeof(struct page *)), GFP_KERNEL);
340  	if (!bv)
341  		return -ENOMEM;
342  
343  	pages = (struct page **)(bv + npages);
344  	npages = alloc_pages_bulk_array(GFP_USER, npages, pages);
345  	if (!npages) {
346  		kfree(bv);
347  		return -ENOMEM;
348  	}
349  
350  	remain = len = min_t(size_t, len, npages * PAGE_SIZE);
351  
352  	for (i = 0; i < npages; i++) {
353  		chunk = min_t(size_t, PAGE_SIZE, remain);
354  		bv[i].bv_page = pages[i];
355  		bv[i].bv_offset = 0;
356  		bv[i].bv_len = chunk;
357  		remain -= chunk;
358  	}
359  
360  	/* Do the I/O */
361  	iov_iter_bvec(&to, ITER_DEST, bv, npages, len);
362  	init_sync_kiocb(&kiocb, in);
363  	kiocb.ki_pos = *ppos;
364  	ret = call_read_iter(in, &kiocb, &to);
365  
366  	if (ret > 0) {
367  		keep = DIV_ROUND_UP(ret, PAGE_SIZE);
368  		*ppos = kiocb.ki_pos;
369  	}
370  
371  	/*
372  	 * Callers of ->splice_read() expect -EAGAIN on "can't put anything in
373  	 * there", rather than -EFAULT.
374  	 */
375  	if (ret == -EFAULT)
376  		ret = -EAGAIN;
377  
378  	/* Free any pages that didn't get touched at all. */
379  	if (keep < npages)
380  		release_pages(pages + keep, npages - keep);
381  
382  	/* Push the remaining pages into the pipe. */
383  	remain = ret;
384  	for (i = 0; i < keep; i++) {
385  		struct pipe_buffer *buf = pipe_head_buf(pipe);
386  
387  		chunk = min_t(size_t, remain, PAGE_SIZE);
388  		*buf = (struct pipe_buffer) {
389  			.ops	= &default_pipe_buf_ops,
390  			.page	= bv[i].bv_page,
391  			.offset	= 0,
392  			.len	= chunk,
393  		};
394  		pipe->head++;
395  		remain -= chunk;
396  	}
397  
398  	kfree(bv);
399  	return ret;
400  }
401  EXPORT_SYMBOL(copy_splice_read);
402  
403  const struct pipe_buf_operations default_pipe_buf_ops = {
404  	.release	= generic_pipe_buf_release,
405  	.try_steal	= generic_pipe_buf_try_steal,
406  	.get		= generic_pipe_buf_get,
407  };
408  
409  /* Pipe buffer operations for a socket and similar. */
410  const struct pipe_buf_operations nosteal_pipe_buf_ops = {
411  	.release	= generic_pipe_buf_release,
412  	.get		= generic_pipe_buf_get,
413  };
414  EXPORT_SYMBOL(nosteal_pipe_buf_ops);
415  
416  static void wakeup_pipe_writers(struct pipe_inode_info *pipe)
417  {
418  	smp_mb();
419  	if (waitqueue_active(&pipe->wr_wait))
420  		wake_up_interruptible(&pipe->wr_wait);
421  	kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
422  }
423  
424  /**
425   * splice_from_pipe_feed - feed available data from a pipe to a file
426   * @pipe:	pipe to splice from
427   * @sd:		information to @actor
428   * @actor:	handler that splices the data
429   *
430   * Description:
431   *    This function loops over the pipe and calls @actor to do the
432   *    actual moving of a single struct pipe_buffer to the desired
433   *    destination.  It returns when there's no more buffers left in
434   *    the pipe or if the requested number of bytes (@sd->total_len)
435   *    have been copied.  It returns a positive number (one) if the
436   *    pipe needs to be filled with more data, zero if the required
437   *    number of bytes have been copied and -errno on error.
438   *
439   *    This, together with splice_from_pipe_{begin,end,next}, may be
440   *    used to implement the functionality of __splice_from_pipe() when
441   *    locking is required around copying the pipe buffers to the
442   *    destination.
443   */
444  static int splice_from_pipe_feed(struct pipe_inode_info *pipe, struct splice_desc *sd,
445  			  splice_actor *actor)
446  {
447  	unsigned int head = pipe->head;
448  	unsigned int tail = pipe->tail;
449  	unsigned int mask = pipe->ring_size - 1;
450  	int ret;
451  
452  	while (!pipe_empty(head, tail)) {
453  		struct pipe_buffer *buf = &pipe->bufs[tail & mask];
454  
455  		sd->len = buf->len;
456  		if (sd->len > sd->total_len)
457  			sd->len = sd->total_len;
458  
459  		ret = pipe_buf_confirm(pipe, buf);
460  		if (unlikely(ret)) {
461  			if (ret == -ENODATA)
462  				ret = 0;
463  			return ret;
464  		}
465  
466  		ret = actor(pipe, buf, sd);
467  		if (ret <= 0)
468  			return ret;
469  
470  		buf->offset += ret;
471  		buf->len -= ret;
472  
473  		sd->num_spliced += ret;
474  		sd->len -= ret;
475  		sd->pos += ret;
476  		sd->total_len -= ret;
477  
478  		if (!buf->len) {
479  			pipe_buf_release(pipe, buf);
480  			tail++;
481  			pipe->tail = tail;
482  			if (pipe->files)
483  				sd->need_wakeup = true;
484  		}
485  
486  		if (!sd->total_len)
487  			return 0;
488  	}
489  
490  	return 1;
491  }
492  
493  /* We know we have a pipe buffer, but maybe it's empty? */
494  static inline bool eat_empty_buffer(struct pipe_inode_info *pipe)
495  {
496  	unsigned int tail = pipe->tail;
497  	unsigned int mask = pipe->ring_size - 1;
498  	struct pipe_buffer *buf = &pipe->bufs[tail & mask];
499  
500  	if (unlikely(!buf->len)) {
501  		pipe_buf_release(pipe, buf);
502  		pipe->tail = tail+1;
503  		return true;
504  	}
505  
506  	return false;
507  }
508  
509  /**
510   * splice_from_pipe_next - wait for some data to splice from
511   * @pipe:	pipe to splice from
512   * @sd:		information about the splice operation
513   *
514   * Description:
515   *    This function will wait for some data and return a positive
516   *    value (one) if pipe buffers are available.  It will return zero
517   *    or -errno if no more data needs to be spliced.
518   */
519  static int splice_from_pipe_next(struct pipe_inode_info *pipe, struct splice_desc *sd)
520  {
521  	/*
522  	 * Check for signal early to make process killable when there are
523  	 * always buffers available
524  	 */
525  	if (signal_pending(current))
526  		return -ERESTARTSYS;
527  
528  repeat:
529  	while (pipe_empty(pipe->head, pipe->tail)) {
530  		if (!pipe->writers)
531  			return 0;
532  
533  		if (sd->num_spliced)
534  			return 0;
535  
536  		if (sd->flags & SPLICE_F_NONBLOCK)
537  			return -EAGAIN;
538  
539  		if (signal_pending(current))
540  			return -ERESTARTSYS;
541  
542  		if (sd->need_wakeup) {
543  			wakeup_pipe_writers(pipe);
544  			sd->need_wakeup = false;
545  		}
546  
547  		pipe_wait_readable(pipe);
548  	}
549  
550  	if (eat_empty_buffer(pipe))
551  		goto repeat;
552  
553  	return 1;
554  }
555  
556  /**
557   * splice_from_pipe_begin - start splicing from pipe
558   * @sd:		information about the splice operation
559   *
560   * Description:
561   *    This function should be called before a loop containing
562   *    splice_from_pipe_next() and splice_from_pipe_feed() to
563   *    initialize the necessary fields of @sd.
564   */
565  static void splice_from_pipe_begin(struct splice_desc *sd)
566  {
567  	sd->num_spliced = 0;
568  	sd->need_wakeup = false;
569  }
570  
571  /**
572   * splice_from_pipe_end - finish splicing from pipe
573   * @pipe:	pipe to splice from
574   * @sd:		information about the splice operation
575   *
576   * Description:
577   *    This function will wake up pipe writers if necessary.  It should
578   *    be called after a loop containing splice_from_pipe_next() and
579   *    splice_from_pipe_feed().
580   */
581  static void splice_from_pipe_end(struct pipe_inode_info *pipe, struct splice_desc *sd)
582  {
583  	if (sd->need_wakeup)
584  		wakeup_pipe_writers(pipe);
585  }
586  
587  /**
588   * __splice_from_pipe - splice data from a pipe to given actor
589   * @pipe:	pipe to splice from
590   * @sd:		information to @actor
591   * @actor:	handler that splices the data
592   *
593   * Description:
594   *    This function does little more than loop over the pipe and call
595   *    @actor to do the actual moving of a single struct pipe_buffer to
596   *    the desired destination. See pipe_to_file, pipe_to_sendmsg, or
597   *    pipe_to_user.
598   *
599   */
600  ssize_t __splice_from_pipe(struct pipe_inode_info *pipe, struct splice_desc *sd,
601  			   splice_actor *actor)
602  {
603  	int ret;
604  
605  	splice_from_pipe_begin(sd);
606  	do {
607  		cond_resched();
608  		ret = splice_from_pipe_next(pipe, sd);
609  		if (ret > 0)
610  			ret = splice_from_pipe_feed(pipe, sd, actor);
611  	} while (ret > 0);
612  	splice_from_pipe_end(pipe, sd);
613  
614  	return sd->num_spliced ? sd->num_spliced : ret;
615  }
616  EXPORT_SYMBOL(__splice_from_pipe);
617  
618  /**
619   * splice_from_pipe - splice data from a pipe to a file
620   * @pipe:	pipe to splice from
621   * @out:	file to splice to
622   * @ppos:	position in @out
623   * @len:	how many bytes to splice
624   * @flags:	splice modifier flags
625   * @actor:	handler that splices the data
626   *
627   * Description:
628   *    See __splice_from_pipe. This function locks the pipe inode,
629   *    otherwise it's identical to __splice_from_pipe().
630   *
631   */
632  ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
633  			 loff_t *ppos, size_t len, unsigned int flags,
634  			 splice_actor *actor)
635  {
636  	ssize_t ret;
637  	struct splice_desc sd = {
638  		.total_len = len,
639  		.flags = flags,
640  		.pos = *ppos,
641  		.u.file = out,
642  	};
643  
644  	pipe_lock(pipe);
645  	ret = __splice_from_pipe(pipe, &sd, actor);
646  	pipe_unlock(pipe);
647  
648  	return ret;
649  }
650  
651  /**
652   * iter_file_splice_write - splice data from a pipe to a file
653   * @pipe:	pipe info
654   * @out:	file to write to
655   * @ppos:	position in @out
656   * @len:	number of bytes to splice
657   * @flags:	splice modifier flags
658   *
659   * Description:
660   *    Will either move or copy pages (determined by @flags options) from
661   *    the given pipe inode to the given file.
662   *    This one is ->write_iter-based.
663   *
664   */
665  ssize_t
666  iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
667  			  loff_t *ppos, size_t len, unsigned int flags)
668  {
669  	struct splice_desc sd = {
670  		.total_len = len,
671  		.flags = flags,
672  		.pos = *ppos,
673  		.u.file = out,
674  	};
675  	int nbufs = pipe->max_usage;
676  	struct bio_vec *array = kcalloc(nbufs, sizeof(struct bio_vec),
677  					GFP_KERNEL);
678  	ssize_t ret;
679  
680  	if (unlikely(!array))
681  		return -ENOMEM;
682  
683  	pipe_lock(pipe);
684  
685  	splice_from_pipe_begin(&sd);
686  	while (sd.total_len) {
687  		struct iov_iter from;
688  		unsigned int head, tail, mask;
689  		size_t left;
690  		int n;
691  
692  		ret = splice_from_pipe_next(pipe, &sd);
693  		if (ret <= 0)
694  			break;
695  
696  		if (unlikely(nbufs < pipe->max_usage)) {
697  			kfree(array);
698  			nbufs = pipe->max_usage;
699  			array = kcalloc(nbufs, sizeof(struct bio_vec),
700  					GFP_KERNEL);
701  			if (!array) {
702  				ret = -ENOMEM;
703  				break;
704  			}
705  		}
706  
707  		head = pipe->head;
708  		tail = pipe->tail;
709  		mask = pipe->ring_size - 1;
710  
711  		/* build the vector */
712  		left = sd.total_len;
713  		for (n = 0; !pipe_empty(head, tail) && left && n < nbufs; tail++) {
714  			struct pipe_buffer *buf = &pipe->bufs[tail & mask];
715  			size_t this_len = buf->len;
716  
717  			/* zero-length bvecs are not supported, skip them */
718  			if (!this_len)
719  				continue;
720  			this_len = min(this_len, left);
721  
722  			ret = pipe_buf_confirm(pipe, buf);
723  			if (unlikely(ret)) {
724  				if (ret == -ENODATA)
725  					ret = 0;
726  				goto done;
727  			}
728  
729  			bvec_set_page(&array[n], buf->page, this_len,
730  				      buf->offset);
731  			left -= this_len;
732  			n++;
733  		}
734  
735  		iov_iter_bvec(&from, ITER_SOURCE, array, n, sd.total_len - left);
736  		ret = vfs_iter_write(out, &from, &sd.pos, 0);
737  		if (ret <= 0)
738  			break;
739  
740  		sd.num_spliced += ret;
741  		sd.total_len -= ret;
742  		*ppos = sd.pos;
743  
744  		/* dismiss the fully eaten buffers, adjust the partial one */
745  		tail = pipe->tail;
746  		while (ret) {
747  			struct pipe_buffer *buf = &pipe->bufs[tail & mask];
748  			if (ret >= buf->len) {
749  				ret -= buf->len;
750  				buf->len = 0;
751  				pipe_buf_release(pipe, buf);
752  				tail++;
753  				pipe->tail = tail;
754  				if (pipe->files)
755  					sd.need_wakeup = true;
756  			} else {
757  				buf->offset += ret;
758  				buf->len -= ret;
759  				ret = 0;
760  			}
761  		}
762  	}
763  done:
764  	kfree(array);
765  	splice_from_pipe_end(pipe, &sd);
766  
767  	pipe_unlock(pipe);
768  
769  	if (sd.num_spliced)
770  		ret = sd.num_spliced;
771  
772  	return ret;
773  }
774  
775  EXPORT_SYMBOL(iter_file_splice_write);
776  
777  #ifdef CONFIG_NET
778  /**
779   * splice_to_socket - splice data from a pipe to a socket
780   * @pipe:	pipe to splice from
781   * @out:	socket to write to
782   * @ppos:	position in @out
783   * @len:	number of bytes to splice
784   * @flags:	splice modifier flags
785   *
786   * Description:
787   *    Will send @len bytes from the pipe to a network socket. No data copying
788   *    is involved.
789   *
790   */
791  ssize_t splice_to_socket(struct pipe_inode_info *pipe, struct file *out,
792  			 loff_t *ppos, size_t len, unsigned int flags)
793  {
794  	struct socket *sock = sock_from_file(out);
795  	struct bio_vec bvec[16];
796  	struct msghdr msg = {};
797  	ssize_t ret = 0;
798  	size_t spliced = 0;
799  	bool need_wakeup = false;
800  
801  	pipe_lock(pipe);
802  
803  	while (len > 0) {
804  		unsigned int head, tail, mask, bc = 0;
805  		size_t remain = len;
806  
807  		/*
808  		 * Check for signal early to make process killable when there
809  		 * are always buffers available
810  		 */
811  		ret = -ERESTARTSYS;
812  		if (signal_pending(current))
813  			break;
814  
815  		while (pipe_empty(pipe->head, pipe->tail)) {
816  			ret = 0;
817  			if (!pipe->writers)
818  				goto out;
819  
820  			if (spliced)
821  				goto out;
822  
823  			ret = -EAGAIN;
824  			if (flags & SPLICE_F_NONBLOCK)
825  				goto out;
826  
827  			ret = -ERESTARTSYS;
828  			if (signal_pending(current))
829  				goto out;
830  
831  			if (need_wakeup) {
832  				wakeup_pipe_writers(pipe);
833  				need_wakeup = false;
834  			}
835  
836  			pipe_wait_readable(pipe);
837  		}
838  
839  		head = pipe->head;
840  		tail = pipe->tail;
841  		mask = pipe->ring_size - 1;
842  
843  		while (!pipe_empty(head, tail)) {
844  			struct pipe_buffer *buf = &pipe->bufs[tail & mask];
845  			size_t seg;
846  
847  			if (!buf->len) {
848  				tail++;
849  				continue;
850  			}
851  
852  			seg = min_t(size_t, remain, buf->len);
853  
854  			ret = pipe_buf_confirm(pipe, buf);
855  			if (unlikely(ret)) {
856  				if (ret == -ENODATA)
857  					ret = 0;
858  				break;
859  			}
860  
861  			bvec_set_page(&bvec[bc++], buf->page, seg, buf->offset);
862  			remain -= seg;
863  			if (remain == 0 || bc >= ARRAY_SIZE(bvec))
864  				break;
865  			tail++;
866  		}
867  
868  		if (!bc)
869  			break;
870  
871  		msg.msg_flags = MSG_SPLICE_PAGES;
872  		if (flags & SPLICE_F_MORE)
873  			msg.msg_flags |= MSG_MORE;
874  		if (remain && pipe_occupancy(pipe->head, tail) > 0)
875  			msg.msg_flags |= MSG_MORE;
876  		if (out->f_flags & O_NONBLOCK)
877  			msg.msg_flags |= MSG_DONTWAIT;
878  
879  		iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, bvec, bc,
880  			      len - remain);
881  		ret = sock_sendmsg(sock, &msg);
882  		if (ret <= 0)
883  			break;
884  
885  		spliced += ret;
886  		len -= ret;
887  		tail = pipe->tail;
888  		while (ret > 0) {
889  			struct pipe_buffer *buf = &pipe->bufs[tail & mask];
890  			size_t seg = min_t(size_t, ret, buf->len);
891  
892  			buf->offset += seg;
893  			buf->len -= seg;
894  			ret -= seg;
895  
896  			if (!buf->len) {
897  				pipe_buf_release(pipe, buf);
898  				tail++;
899  			}
900  		}
901  
902  		if (tail != pipe->tail) {
903  			pipe->tail = tail;
904  			if (pipe->files)
905  				need_wakeup = true;
906  		}
907  	}
908  
909  out:
910  	pipe_unlock(pipe);
911  	if (need_wakeup)
912  		wakeup_pipe_writers(pipe);
913  	return spliced ?: ret;
914  }
915  #endif
916  
917  static int warn_unsupported(struct file *file, const char *op)
918  {
919  	pr_debug_ratelimited(
920  		"splice %s not supported for file %pD4 (pid: %d comm: %.20s)\n",
921  		op, file, current->pid, current->comm);
922  	return -EINVAL;
923  }
924  
925  /*
926   * Attempt to initiate a splice from pipe to file.
927   */
928  static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
929  			   loff_t *ppos, size_t len, unsigned int flags)
930  {
931  	if (unlikely(!out->f_op->splice_write))
932  		return warn_unsupported(out, "write");
933  	return out->f_op->splice_write(pipe, out, ppos, len, flags);
934  }
935  
936  /*
937   * Indicate to the caller that there was a premature EOF when reading from the
938   * source and the caller didn't indicate they would be sending more data after
939   * this.
940   */
941  static void do_splice_eof(struct splice_desc *sd)
942  {
943  	if (sd->splice_eof)
944  		sd->splice_eof(sd);
945  }
946  
947  /**
948   * vfs_splice_read - Read data from a file and splice it into a pipe
949   * @in:		File to splice from
950   * @ppos:	Input file offset
951   * @pipe:	Pipe to splice to
952   * @len:	Number of bytes to splice
953   * @flags:	Splice modifier flags (SPLICE_F_*)
954   *
955   * Splice the requested amount of data from the input file to the pipe.  This
956   * is synchronous as the caller must hold the pipe lock across the entire
957   * operation.
958   *
959   * If successful, it returns the amount of data spliced, 0 if it hit the EOF or
960   * a hole and a negative error code otherwise.
961   */
962  long vfs_splice_read(struct file *in, loff_t *ppos,
963  		     struct pipe_inode_info *pipe, size_t len,
964  		     unsigned int flags)
965  {
966  	unsigned int p_space;
967  	int ret;
968  
969  	if (unlikely(!(in->f_mode & FMODE_READ)))
970  		return -EBADF;
971  	if (!len)
972  		return 0;
973  
974  	/* Don't try to read more the pipe has space for. */
975  	p_space = pipe->max_usage - pipe_occupancy(pipe->head, pipe->tail);
976  	len = min_t(size_t, len, p_space << PAGE_SHIFT);
977  
978  	ret = rw_verify_area(READ, in, ppos, len);
979  	if (unlikely(ret < 0))
980  		return ret;
981  
982  	if (unlikely(len > MAX_RW_COUNT))
983  		len = MAX_RW_COUNT;
984  
985  	if (unlikely(!in->f_op->splice_read))
986  		return warn_unsupported(in, "read");
987  	/*
988  	 * O_DIRECT and DAX don't deal with the pagecache, so we allocate a
989  	 * buffer, copy into it and splice that into the pipe.
990  	 */
991  	if ((in->f_flags & O_DIRECT) || IS_DAX(in->f_mapping->host))
992  		return copy_splice_read(in, ppos, pipe, len, flags);
993  	return in->f_op->splice_read(in, ppos, pipe, len, flags);
994  }
995  EXPORT_SYMBOL_GPL(vfs_splice_read);
996  
997  /**
998   * splice_direct_to_actor - splices data directly between two non-pipes
999   * @in:		file to splice from
1000   * @sd:		actor information on where to splice to
1001   * @actor:	handles the data splicing
1002   *
1003   * Description:
1004   *    This is a special case helper to splice directly between two
1005   *    points, without requiring an explicit pipe. Internally an allocated
1006   *    pipe is cached in the process, and reused during the lifetime of
1007   *    that process.
1008   *
1009   */
1010  ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
1011  			       splice_direct_actor *actor)
1012  {
1013  	struct pipe_inode_info *pipe;
1014  	long ret, bytes;
1015  	size_t len;
1016  	int i, flags, more;
1017  
1018  	/*
1019  	 * We require the input to be seekable, as we don't want to randomly
1020  	 * drop data for eg socket -> socket splicing. Use the piped splicing
1021  	 * for that!
1022  	 */
1023  	if (unlikely(!(in->f_mode & FMODE_LSEEK)))
1024  		return -EINVAL;
1025  
1026  	/*
1027  	 * neither in nor out is a pipe, setup an internal pipe attached to
1028  	 * 'out' and transfer the wanted data from 'in' to 'out' through that
1029  	 */
1030  	pipe = current->splice_pipe;
1031  	if (unlikely(!pipe)) {
1032  		pipe = alloc_pipe_info();
1033  		if (!pipe)
1034  			return -ENOMEM;
1035  
1036  		/*
1037  		 * We don't have an immediate reader, but we'll read the stuff
1038  		 * out of the pipe right after the splice_to_pipe(). So set
1039  		 * PIPE_READERS appropriately.
1040  		 */
1041  		pipe->readers = 1;
1042  
1043  		current->splice_pipe = pipe;
1044  	}
1045  
1046  	/*
1047  	 * Do the splice.
1048  	 */
1049  	bytes = 0;
1050  	len = sd->total_len;
1051  
1052  	/* Don't block on output, we have to drain the direct pipe. */
1053  	flags = sd->flags;
1054  	sd->flags &= ~SPLICE_F_NONBLOCK;
1055  
1056  	/*
1057  	 * We signal MORE until we've read sufficient data to fulfill the
1058  	 * request and we keep signalling it if the caller set it.
1059  	 */
1060  	more = sd->flags & SPLICE_F_MORE;
1061  	sd->flags |= SPLICE_F_MORE;
1062  
1063  	WARN_ON_ONCE(!pipe_empty(pipe->head, pipe->tail));
1064  
1065  	while (len) {
1066  		size_t read_len;
1067  		loff_t pos = sd->pos, prev_pos = pos;
1068  
1069  		ret = vfs_splice_read(in, &pos, pipe, len, flags);
1070  		if (unlikely(ret <= 0))
1071  			goto read_failure;
1072  
1073  		read_len = ret;
1074  		sd->total_len = read_len;
1075  
1076  		/*
1077  		 * If we now have sufficient data to fulfill the request then
1078  		 * we clear SPLICE_F_MORE if it was not set initially.
1079  		 */
1080  		if (read_len >= len && !more)
1081  			sd->flags &= ~SPLICE_F_MORE;
1082  
1083  		/*
1084  		 * NOTE: nonblocking mode only applies to the input. We
1085  		 * must not do the output in nonblocking mode as then we
1086  		 * could get stuck data in the internal pipe:
1087  		 */
1088  		ret = actor(pipe, sd);
1089  		if (unlikely(ret <= 0)) {
1090  			sd->pos = prev_pos;
1091  			goto out_release;
1092  		}
1093  
1094  		bytes += ret;
1095  		len -= ret;
1096  		sd->pos = pos;
1097  
1098  		if (ret < read_len) {
1099  			sd->pos = prev_pos + ret;
1100  			goto out_release;
1101  		}
1102  	}
1103  
1104  done:
1105  	pipe->tail = pipe->head = 0;
1106  	file_accessed(in);
1107  	return bytes;
1108  
1109  read_failure:
1110  	/*
1111  	 * If the user did *not* set SPLICE_F_MORE *and* we didn't hit that
1112  	 * "use all of len" case that cleared SPLICE_F_MORE, *and* we did a
1113  	 * "->splice_in()" that returned EOF (ie zero) *and* we have sent at
1114  	 * least 1 byte *then* we will also do the ->splice_eof() call.
1115  	 */
1116  	if (ret == 0 && !more && len > 0 && bytes)
1117  		do_splice_eof(sd);
1118  out_release:
1119  	/*
1120  	 * If we did an incomplete transfer we must release
1121  	 * the pipe buffers in question:
1122  	 */
1123  	for (i = 0; i < pipe->ring_size; i++) {
1124  		struct pipe_buffer *buf = &pipe->bufs[i];
1125  
1126  		if (buf->ops)
1127  			pipe_buf_release(pipe, buf);
1128  	}
1129  
1130  	if (!bytes)
1131  		bytes = ret;
1132  
1133  	goto done;
1134  }
1135  EXPORT_SYMBOL(splice_direct_to_actor);
1136  
1137  static int direct_splice_actor(struct pipe_inode_info *pipe,
1138  			       struct splice_desc *sd)
1139  {
1140  	struct file *file = sd->u.file;
1141  
1142  	return do_splice_from(pipe, file, sd->opos, sd->total_len,
1143  			      sd->flags);
1144  }
1145  
1146  static void direct_file_splice_eof(struct splice_desc *sd)
1147  {
1148  	struct file *file = sd->u.file;
1149  
1150  	if (file->f_op->splice_eof)
1151  		file->f_op->splice_eof(file);
1152  }
1153  
1154  /**
1155   * do_splice_direct - splices data directly between two files
1156   * @in:		file to splice from
1157   * @ppos:	input file offset
1158   * @out:	file to splice to
1159   * @opos:	output file offset
1160   * @len:	number of bytes to splice
1161   * @flags:	splice modifier flags
1162   *
1163   * Description:
1164   *    For use by do_sendfile(). splice can easily emulate sendfile, but
1165   *    doing it in the application would incur an extra system call
1166   *    (splice in + splice out, as compared to just sendfile()). So this helper
1167   *    can splice directly through a process-private pipe.
1168   *
1169   */
1170  long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
1171  		      loff_t *opos, size_t len, unsigned int flags)
1172  {
1173  	struct splice_desc sd = {
1174  		.len		= len,
1175  		.total_len	= len,
1176  		.flags		= flags,
1177  		.pos		= *ppos,
1178  		.u.file		= out,
1179  		.splice_eof	= direct_file_splice_eof,
1180  		.opos		= opos,
1181  	};
1182  	long ret;
1183  
1184  	if (unlikely(!(out->f_mode & FMODE_WRITE)))
1185  		return -EBADF;
1186  
1187  	if (unlikely(out->f_flags & O_APPEND))
1188  		return -EINVAL;
1189  
1190  	ret = rw_verify_area(WRITE, out, opos, len);
1191  	if (unlikely(ret < 0))
1192  		return ret;
1193  
1194  	ret = splice_direct_to_actor(in, &sd, direct_splice_actor);
1195  	if (ret > 0)
1196  		*ppos = sd.pos;
1197  
1198  	return ret;
1199  }
1200  EXPORT_SYMBOL(do_splice_direct);
1201  
1202  static int wait_for_space(struct pipe_inode_info *pipe, unsigned flags)
1203  {
1204  	for (;;) {
1205  		if (unlikely(!pipe->readers)) {
1206  			send_sig(SIGPIPE, current, 0);
1207  			return -EPIPE;
1208  		}
1209  		if (!pipe_full(pipe->head, pipe->tail, pipe->max_usage))
1210  			return 0;
1211  		if (flags & SPLICE_F_NONBLOCK)
1212  			return -EAGAIN;
1213  		if (signal_pending(current))
1214  			return -ERESTARTSYS;
1215  		pipe_wait_writable(pipe);
1216  	}
1217  }
1218  
1219  static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
1220  			       struct pipe_inode_info *opipe,
1221  			       size_t len, unsigned int flags);
1222  
1223  long splice_file_to_pipe(struct file *in,
1224  			 struct pipe_inode_info *opipe,
1225  			 loff_t *offset,
1226  			 size_t len, unsigned int flags)
1227  {
1228  	long ret;
1229  
1230  	pipe_lock(opipe);
1231  	ret = wait_for_space(opipe, flags);
1232  	if (!ret)
1233  		ret = vfs_splice_read(in, offset, opipe, len, flags);
1234  	pipe_unlock(opipe);
1235  	if (ret > 0)
1236  		wakeup_pipe_readers(opipe);
1237  	return ret;
1238  }
1239  
1240  /*
1241   * Determine where to splice to/from.
1242   */
1243  long do_splice(struct file *in, loff_t *off_in, struct file *out,
1244  	       loff_t *off_out, size_t len, unsigned int flags)
1245  {
1246  	struct pipe_inode_info *ipipe;
1247  	struct pipe_inode_info *opipe;
1248  	loff_t offset;
1249  	long ret;
1250  
1251  	if (unlikely(!(in->f_mode & FMODE_READ) ||
1252  		     !(out->f_mode & FMODE_WRITE)))
1253  		return -EBADF;
1254  
1255  	ipipe = get_pipe_info(in, true);
1256  	opipe = get_pipe_info(out, true);
1257  
1258  	if (ipipe && opipe) {
1259  		if (off_in || off_out)
1260  			return -ESPIPE;
1261  
1262  		/* Splicing to self would be fun, but... */
1263  		if (ipipe == opipe)
1264  			return -EINVAL;
1265  
1266  		if ((in->f_flags | out->f_flags) & O_NONBLOCK)
1267  			flags |= SPLICE_F_NONBLOCK;
1268  
1269  		ret = splice_pipe_to_pipe(ipipe, opipe, len, flags);
1270  	} else if (ipipe) {
1271  		if (off_in)
1272  			return -ESPIPE;
1273  		if (off_out) {
1274  			if (!(out->f_mode & FMODE_PWRITE))
1275  				return -EINVAL;
1276  			offset = *off_out;
1277  		} else {
1278  			offset = out->f_pos;
1279  		}
1280  
1281  		if (unlikely(out->f_flags & O_APPEND))
1282  			return -EINVAL;
1283  
1284  		ret = rw_verify_area(WRITE, out, &offset, len);
1285  		if (unlikely(ret < 0))
1286  			return ret;
1287  
1288  		if (in->f_flags & O_NONBLOCK)
1289  			flags |= SPLICE_F_NONBLOCK;
1290  
1291  		file_start_write(out);
1292  		ret = do_splice_from(ipipe, out, &offset, len, flags);
1293  		file_end_write(out);
1294  
1295  		if (!off_out)
1296  			out->f_pos = offset;
1297  		else
1298  			*off_out = offset;
1299  	} else if (opipe) {
1300  		if (off_out)
1301  			return -ESPIPE;
1302  		if (off_in) {
1303  			if (!(in->f_mode & FMODE_PREAD))
1304  				return -EINVAL;
1305  			offset = *off_in;
1306  		} else {
1307  			offset = in->f_pos;
1308  		}
1309  
1310  		if (out->f_flags & O_NONBLOCK)
1311  			flags |= SPLICE_F_NONBLOCK;
1312  
1313  		ret = splice_file_to_pipe(in, opipe, &offset, len, flags);
1314  
1315  		if (!off_in)
1316  			in->f_pos = offset;
1317  		else
1318  			*off_in = offset;
1319  	} else {
1320  		ret = -EINVAL;
1321  	}
1322  
1323  	if (ret > 0) {
1324  		/*
1325  		 * Generate modify out before access in:
1326  		 * do_splice_from() may've already sent modify out,
1327  		 * and this ensures the events get merged.
1328  		 */
1329  		fsnotify_modify(out);
1330  		fsnotify_access(in);
1331  	}
1332  
1333  	return ret;
1334  }
1335  
1336  static long __do_splice(struct file *in, loff_t __user *off_in,
1337  			struct file *out, loff_t __user *off_out,
1338  			size_t len, unsigned int flags)
1339  {
1340  	struct pipe_inode_info *ipipe;
1341  	struct pipe_inode_info *opipe;
1342  	loff_t offset, *__off_in = NULL, *__off_out = NULL;
1343  	long ret;
1344  
1345  	ipipe = get_pipe_info(in, true);
1346  	opipe = get_pipe_info(out, true);
1347  
1348  	if (ipipe) {
1349  		if (off_in)
1350  			return -ESPIPE;
1351  		pipe_clear_nowait(in);
1352  	}
1353  	if (opipe) {
1354  		if (off_out)
1355  			return -ESPIPE;
1356  		pipe_clear_nowait(out);
1357  	}
1358  
1359  	if (off_out) {
1360  		if (copy_from_user(&offset, off_out, sizeof(loff_t)))
1361  			return -EFAULT;
1362  		__off_out = &offset;
1363  	}
1364  	if (off_in) {
1365  		if (copy_from_user(&offset, off_in, sizeof(loff_t)))
1366  			return -EFAULT;
1367  		__off_in = &offset;
1368  	}
1369  
1370  	ret = do_splice(in, __off_in, out, __off_out, len, flags);
1371  	if (ret < 0)
1372  		return ret;
1373  
1374  	if (__off_out && copy_to_user(off_out, __off_out, sizeof(loff_t)))
1375  		return -EFAULT;
1376  	if (__off_in && copy_to_user(off_in, __off_in, sizeof(loff_t)))
1377  		return -EFAULT;
1378  
1379  	return ret;
1380  }
1381  
1382  static int iter_to_pipe(struct iov_iter *from,
1383  			struct pipe_inode_info *pipe,
1384  			unsigned flags)
1385  {
1386  	struct pipe_buffer buf = {
1387  		.ops = &user_page_pipe_buf_ops,
1388  		.flags = flags
1389  	};
1390  	size_t total = 0;
1391  	int ret = 0;
1392  
1393  	while (iov_iter_count(from)) {
1394  		struct page *pages[16];
1395  		ssize_t left;
1396  		size_t start;
1397  		int i, n;
1398  
1399  		left = iov_iter_get_pages2(from, pages, ~0UL, 16, &start);
1400  		if (left <= 0) {
1401  			ret = left;
1402  			break;
1403  		}
1404  
1405  		n = DIV_ROUND_UP(left + start, PAGE_SIZE);
1406  		for (i = 0; i < n; i++) {
1407  			int size = min_t(int, left, PAGE_SIZE - start);
1408  
1409  			buf.page = pages[i];
1410  			buf.offset = start;
1411  			buf.len = size;
1412  			ret = add_to_pipe(pipe, &buf);
1413  			if (unlikely(ret < 0)) {
1414  				iov_iter_revert(from, left);
1415  				// this one got dropped by add_to_pipe()
1416  				while (++i < n)
1417  					put_page(pages[i]);
1418  				goto out;
1419  			}
1420  			total += ret;
1421  			left -= size;
1422  			start = 0;
1423  		}
1424  	}
1425  out:
1426  	return total ? total : ret;
1427  }
1428  
1429  static int pipe_to_user(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
1430  			struct splice_desc *sd)
1431  {
1432  	int n = copy_page_to_iter(buf->page, buf->offset, sd->len, sd->u.data);
1433  	return n == sd->len ? n : -EFAULT;
1434  }
1435  
1436  /*
1437   * For lack of a better implementation, implement vmsplice() to userspace
1438   * as a simple copy of the pipes pages to the user iov.
1439   */
1440  static long vmsplice_to_user(struct file *file, struct iov_iter *iter,
1441  			     unsigned int flags)
1442  {
1443  	struct pipe_inode_info *pipe = get_pipe_info(file, true);
1444  	struct splice_desc sd = {
1445  		.total_len = iov_iter_count(iter),
1446  		.flags = flags,
1447  		.u.data = iter
1448  	};
1449  	long ret = 0;
1450  
1451  	if (!pipe)
1452  		return -EBADF;
1453  
1454  	pipe_clear_nowait(file);
1455  
1456  	if (sd.total_len) {
1457  		pipe_lock(pipe);
1458  		ret = __splice_from_pipe(pipe, &sd, pipe_to_user);
1459  		pipe_unlock(pipe);
1460  	}
1461  
1462  	if (ret > 0)
1463  		fsnotify_access(file);
1464  
1465  	return ret;
1466  }
1467  
1468  /*
1469   * vmsplice splices a user address range into a pipe. It can be thought of
1470   * as splice-from-memory, where the regular splice is splice-from-file (or
1471   * to file). In both cases the output is a pipe, naturally.
1472   */
1473  static long vmsplice_to_pipe(struct file *file, struct iov_iter *iter,
1474  			     unsigned int flags)
1475  {
1476  	struct pipe_inode_info *pipe;
1477  	long ret = 0;
1478  	unsigned buf_flag = 0;
1479  
1480  	if (flags & SPLICE_F_GIFT)
1481  		buf_flag = PIPE_BUF_FLAG_GIFT;
1482  
1483  	pipe = get_pipe_info(file, true);
1484  	if (!pipe)
1485  		return -EBADF;
1486  
1487  	pipe_clear_nowait(file);
1488  
1489  	pipe_lock(pipe);
1490  	ret = wait_for_space(pipe, flags);
1491  	if (!ret)
1492  		ret = iter_to_pipe(iter, pipe, buf_flag);
1493  	pipe_unlock(pipe);
1494  	if (ret > 0) {
1495  		wakeup_pipe_readers(pipe);
1496  		fsnotify_modify(file);
1497  	}
1498  	return ret;
1499  }
1500  
1501  static int vmsplice_type(struct fd f, int *type)
1502  {
1503  	if (!f.file)
1504  		return -EBADF;
1505  	if (f.file->f_mode & FMODE_WRITE) {
1506  		*type = ITER_SOURCE;
1507  	} else if (f.file->f_mode & FMODE_READ) {
1508  		*type = ITER_DEST;
1509  	} else {
1510  		fdput(f);
1511  		return -EBADF;
1512  	}
1513  	return 0;
1514  }
1515  
1516  /*
1517   * Note that vmsplice only really supports true splicing _from_ user memory
1518   * to a pipe, not the other way around. Splicing from user memory is a simple
1519   * operation that can be supported without any funky alignment restrictions
1520   * or nasty vm tricks. We simply map in the user memory and fill them into
1521   * a pipe. The reverse isn't quite as easy, though. There are two possible
1522   * solutions for that:
1523   *
1524   *	- memcpy() the data internally, at which point we might as well just
1525   *	  do a regular read() on the buffer anyway.
1526   *	- Lots of nasty vm tricks, that are neither fast nor flexible (it
1527   *	  has restriction limitations on both ends of the pipe).
1528   *
1529   * Currently we punt and implement it as a normal copy, see pipe_to_user().
1530   *
1531   */
1532  SYSCALL_DEFINE4(vmsplice, int, fd, const struct iovec __user *, uiov,
1533  		unsigned long, nr_segs, unsigned int, flags)
1534  {
1535  	struct iovec iovstack[UIO_FASTIOV];
1536  	struct iovec *iov = iovstack;
1537  	struct iov_iter iter;
1538  	ssize_t error;
1539  	struct fd f;
1540  	int type;
1541  
1542  	if (unlikely(flags & ~SPLICE_F_ALL))
1543  		return -EINVAL;
1544  
1545  	f = fdget(fd);
1546  	error = vmsplice_type(f, &type);
1547  	if (error)
1548  		return error;
1549  
1550  	error = import_iovec(type, uiov, nr_segs,
1551  			     ARRAY_SIZE(iovstack), &iov, &iter);
1552  	if (error < 0)
1553  		goto out_fdput;
1554  
1555  	if (!iov_iter_count(&iter))
1556  		error = 0;
1557  	else if (type == ITER_SOURCE)
1558  		error = vmsplice_to_pipe(f.file, &iter, flags);
1559  	else
1560  		error = vmsplice_to_user(f.file, &iter, flags);
1561  
1562  	kfree(iov);
1563  out_fdput:
1564  	fdput(f);
1565  	return error;
1566  }
1567  
1568  SYSCALL_DEFINE6(splice, int, fd_in, loff_t __user *, off_in,
1569  		int, fd_out, loff_t __user *, off_out,
1570  		size_t, len, unsigned int, flags)
1571  {
1572  	struct fd in, out;
1573  	long error;
1574  
1575  	if (unlikely(!len))
1576  		return 0;
1577  
1578  	if (unlikely(flags & ~SPLICE_F_ALL))
1579  		return -EINVAL;
1580  
1581  	error = -EBADF;
1582  	in = fdget(fd_in);
1583  	if (in.file) {
1584  		out = fdget(fd_out);
1585  		if (out.file) {
1586  			error = __do_splice(in.file, off_in, out.file, off_out,
1587  						len, flags);
1588  			fdput(out);
1589  		}
1590  		fdput(in);
1591  	}
1592  	return error;
1593  }
1594  
1595  /*
1596   * Make sure there's data to read. Wait for input if we can, otherwise
1597   * return an appropriate error.
1598   */
1599  static int ipipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
1600  {
1601  	int ret;
1602  
1603  	/*
1604  	 * Check the pipe occupancy without the inode lock first. This function
1605  	 * is speculative anyways, so missing one is ok.
1606  	 */
1607  	if (!pipe_empty(pipe->head, pipe->tail))
1608  		return 0;
1609  
1610  	ret = 0;
1611  	pipe_lock(pipe);
1612  
1613  	while (pipe_empty(pipe->head, pipe->tail)) {
1614  		if (signal_pending(current)) {
1615  			ret = -ERESTARTSYS;
1616  			break;
1617  		}
1618  		if (!pipe->writers)
1619  			break;
1620  		if (flags & SPLICE_F_NONBLOCK) {
1621  			ret = -EAGAIN;
1622  			break;
1623  		}
1624  		pipe_wait_readable(pipe);
1625  	}
1626  
1627  	pipe_unlock(pipe);
1628  	return ret;
1629  }
1630  
1631  /*
1632   * Make sure there's writeable room. Wait for room if we can, otherwise
1633   * return an appropriate error.
1634   */
1635  static int opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
1636  {
1637  	int ret;
1638  
1639  	/*
1640  	 * Check pipe occupancy without the inode lock first. This function
1641  	 * is speculative anyways, so missing one is ok.
1642  	 */
1643  	if (!pipe_full(pipe->head, pipe->tail, pipe->max_usage))
1644  		return 0;
1645  
1646  	ret = 0;
1647  	pipe_lock(pipe);
1648  
1649  	while (pipe_full(pipe->head, pipe->tail, pipe->max_usage)) {
1650  		if (!pipe->readers) {
1651  			send_sig(SIGPIPE, current, 0);
1652  			ret = -EPIPE;
1653  			break;
1654  		}
1655  		if (flags & SPLICE_F_NONBLOCK) {
1656  			ret = -EAGAIN;
1657  			break;
1658  		}
1659  		if (signal_pending(current)) {
1660  			ret = -ERESTARTSYS;
1661  			break;
1662  		}
1663  		pipe_wait_writable(pipe);
1664  	}
1665  
1666  	pipe_unlock(pipe);
1667  	return ret;
1668  }
1669  
1670  /*
1671   * Splice contents of ipipe to opipe.
1672   */
1673  static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
1674  			       struct pipe_inode_info *opipe,
1675  			       size_t len, unsigned int flags)
1676  {
1677  	struct pipe_buffer *ibuf, *obuf;
1678  	unsigned int i_head, o_head;
1679  	unsigned int i_tail, o_tail;
1680  	unsigned int i_mask, o_mask;
1681  	int ret = 0;
1682  	bool input_wakeup = false;
1683  
1684  
1685  retry:
1686  	ret = ipipe_prep(ipipe, flags);
1687  	if (ret)
1688  		return ret;
1689  
1690  	ret = opipe_prep(opipe, flags);
1691  	if (ret)
1692  		return ret;
1693  
1694  	/*
1695  	 * Potential ABBA deadlock, work around it by ordering lock
1696  	 * grabbing by pipe info address. Otherwise two different processes
1697  	 * could deadlock (one doing tee from A -> B, the other from B -> A).
1698  	 */
1699  	pipe_double_lock(ipipe, opipe);
1700  
1701  	i_tail = ipipe->tail;
1702  	i_mask = ipipe->ring_size - 1;
1703  	o_head = opipe->head;
1704  	o_mask = opipe->ring_size - 1;
1705  
1706  	do {
1707  		size_t o_len;
1708  
1709  		if (!opipe->readers) {
1710  			send_sig(SIGPIPE, current, 0);
1711  			if (!ret)
1712  				ret = -EPIPE;
1713  			break;
1714  		}
1715  
1716  		i_head = ipipe->head;
1717  		o_tail = opipe->tail;
1718  
1719  		if (pipe_empty(i_head, i_tail) && !ipipe->writers)
1720  			break;
1721  
1722  		/*
1723  		 * Cannot make any progress, because either the input
1724  		 * pipe is empty or the output pipe is full.
1725  		 */
1726  		if (pipe_empty(i_head, i_tail) ||
1727  		    pipe_full(o_head, o_tail, opipe->max_usage)) {
1728  			/* Already processed some buffers, break */
1729  			if (ret)
1730  				break;
1731  
1732  			if (flags & SPLICE_F_NONBLOCK) {
1733  				ret = -EAGAIN;
1734  				break;
1735  			}
1736  
1737  			/*
1738  			 * We raced with another reader/writer and haven't
1739  			 * managed to process any buffers.  A zero return
1740  			 * value means EOF, so retry instead.
1741  			 */
1742  			pipe_unlock(ipipe);
1743  			pipe_unlock(opipe);
1744  			goto retry;
1745  		}
1746  
1747  		ibuf = &ipipe->bufs[i_tail & i_mask];
1748  		obuf = &opipe->bufs[o_head & o_mask];
1749  
1750  		if (len >= ibuf->len) {
1751  			/*
1752  			 * Simply move the whole buffer from ipipe to opipe
1753  			 */
1754  			*obuf = *ibuf;
1755  			ibuf->ops = NULL;
1756  			i_tail++;
1757  			ipipe->tail = i_tail;
1758  			input_wakeup = true;
1759  			o_len = obuf->len;
1760  			o_head++;
1761  			opipe->head = o_head;
1762  		} else {
1763  			/*
1764  			 * Get a reference to this pipe buffer,
1765  			 * so we can copy the contents over.
1766  			 */
1767  			if (!pipe_buf_get(ipipe, ibuf)) {
1768  				if (ret == 0)
1769  					ret = -EFAULT;
1770  				break;
1771  			}
1772  			*obuf = *ibuf;
1773  
1774  			/*
1775  			 * Don't inherit the gift and merge flags, we need to
1776  			 * prevent multiple steals of this page.
1777  			 */
1778  			obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
1779  			obuf->flags &= ~PIPE_BUF_FLAG_CAN_MERGE;
1780  
1781  			obuf->len = len;
1782  			ibuf->offset += len;
1783  			ibuf->len -= len;
1784  			o_len = len;
1785  			o_head++;
1786  			opipe->head = o_head;
1787  		}
1788  		ret += o_len;
1789  		len -= o_len;
1790  	} while (len);
1791  
1792  	pipe_unlock(ipipe);
1793  	pipe_unlock(opipe);
1794  
1795  	/*
1796  	 * If we put data in the output pipe, wakeup any potential readers.
1797  	 */
1798  	if (ret > 0)
1799  		wakeup_pipe_readers(opipe);
1800  
1801  	if (input_wakeup)
1802  		wakeup_pipe_writers(ipipe);
1803  
1804  	return ret;
1805  }
1806  
1807  /*
1808   * Link contents of ipipe to opipe.
1809   */
1810  static int link_pipe(struct pipe_inode_info *ipipe,
1811  		     struct pipe_inode_info *opipe,
1812  		     size_t len, unsigned int flags)
1813  {
1814  	struct pipe_buffer *ibuf, *obuf;
1815  	unsigned int i_head, o_head;
1816  	unsigned int i_tail, o_tail;
1817  	unsigned int i_mask, o_mask;
1818  	int ret = 0;
1819  
1820  	/*
1821  	 * Potential ABBA deadlock, work around it by ordering lock
1822  	 * grabbing by pipe info address. Otherwise two different processes
1823  	 * could deadlock (one doing tee from A -> B, the other from B -> A).
1824  	 */
1825  	pipe_double_lock(ipipe, opipe);
1826  
1827  	i_tail = ipipe->tail;
1828  	i_mask = ipipe->ring_size - 1;
1829  	o_head = opipe->head;
1830  	o_mask = opipe->ring_size - 1;
1831  
1832  	do {
1833  		if (!opipe->readers) {
1834  			send_sig(SIGPIPE, current, 0);
1835  			if (!ret)
1836  				ret = -EPIPE;
1837  			break;
1838  		}
1839  
1840  		i_head = ipipe->head;
1841  		o_tail = opipe->tail;
1842  
1843  		/*
1844  		 * If we have iterated all input buffers or run out of
1845  		 * output room, break.
1846  		 */
1847  		if (pipe_empty(i_head, i_tail) ||
1848  		    pipe_full(o_head, o_tail, opipe->max_usage))
1849  			break;
1850  
1851  		ibuf = &ipipe->bufs[i_tail & i_mask];
1852  		obuf = &opipe->bufs[o_head & o_mask];
1853  
1854  		/*
1855  		 * Get a reference to this pipe buffer,
1856  		 * so we can copy the contents over.
1857  		 */
1858  		if (!pipe_buf_get(ipipe, ibuf)) {
1859  			if (ret == 0)
1860  				ret = -EFAULT;
1861  			break;
1862  		}
1863  
1864  		*obuf = *ibuf;
1865  
1866  		/*
1867  		 * Don't inherit the gift and merge flag, we need to prevent
1868  		 * multiple steals of this page.
1869  		 */
1870  		obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
1871  		obuf->flags &= ~PIPE_BUF_FLAG_CAN_MERGE;
1872  
1873  		if (obuf->len > len)
1874  			obuf->len = len;
1875  		ret += obuf->len;
1876  		len -= obuf->len;
1877  
1878  		o_head++;
1879  		opipe->head = o_head;
1880  		i_tail++;
1881  	} while (len);
1882  
1883  	pipe_unlock(ipipe);
1884  	pipe_unlock(opipe);
1885  
1886  	/*
1887  	 * If we put data in the output pipe, wakeup any potential readers.
1888  	 */
1889  	if (ret > 0)
1890  		wakeup_pipe_readers(opipe);
1891  
1892  	return ret;
1893  }
1894  
1895  /*
1896   * This is a tee(1) implementation that works on pipes. It doesn't copy
1897   * any data, it simply references the 'in' pages on the 'out' pipe.
1898   * The 'flags' used are the SPLICE_F_* variants, currently the only
1899   * applicable one is SPLICE_F_NONBLOCK.
1900   */
1901  long do_tee(struct file *in, struct file *out, size_t len, unsigned int flags)
1902  {
1903  	struct pipe_inode_info *ipipe = get_pipe_info(in, true);
1904  	struct pipe_inode_info *opipe = get_pipe_info(out, true);
1905  	int ret = -EINVAL;
1906  
1907  	if (unlikely(!(in->f_mode & FMODE_READ) ||
1908  		     !(out->f_mode & FMODE_WRITE)))
1909  		return -EBADF;
1910  
1911  	/*
1912  	 * Duplicate the contents of ipipe to opipe without actually
1913  	 * copying the data.
1914  	 */
1915  	if (ipipe && opipe && ipipe != opipe) {
1916  		if ((in->f_flags | out->f_flags) & O_NONBLOCK)
1917  			flags |= SPLICE_F_NONBLOCK;
1918  
1919  		/*
1920  		 * Keep going, unless we encounter an error. The ipipe/opipe
1921  		 * ordering doesn't really matter.
1922  		 */
1923  		ret = ipipe_prep(ipipe, flags);
1924  		if (!ret) {
1925  			ret = opipe_prep(opipe, flags);
1926  			if (!ret)
1927  				ret = link_pipe(ipipe, opipe, len, flags);
1928  		}
1929  	}
1930  
1931  	if (ret > 0) {
1932  		fsnotify_access(in);
1933  		fsnotify_modify(out);
1934  	}
1935  
1936  	return ret;
1937  }
1938  
1939  SYSCALL_DEFINE4(tee, int, fdin, int, fdout, size_t, len, unsigned int, flags)
1940  {
1941  	struct fd in, out;
1942  	int error;
1943  
1944  	if (unlikely(flags & ~SPLICE_F_ALL))
1945  		return -EINVAL;
1946  
1947  	if (unlikely(!len))
1948  		return 0;
1949  
1950  	error = -EBADF;
1951  	in = fdget(fdin);
1952  	if (in.file) {
1953  		out = fdget(fdout);
1954  		if (out.file) {
1955  			error = do_tee(in.file, out.file, len, flags);
1956  			fdput(out);
1957  		}
1958   		fdput(in);
1959   	}
1960  
1961  	return error;
1962  }
1963