splice.c 34.0 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11
/*
 * "splice": joining two ropes together by interweaving their strands.
 *
 * This is the "extended pipe" functionality, where a pipe is used as
 * an arbitrary in-memory buffer. Think of a pipe as a small kernel
 * buffer that you can use to transfer data from one end to the other.
 *
 * The traditional unix read/write is extended with a "splice()" operation
 * that transfers data buffers to or from a pipe buffer.
 *
 * Named by Larry McVoy, original implementation from Linus, extended by
12 13
 * Jens to support splicing to files, network, direct splicing, etc and
 * fixing lots of bugs.
14
 *
15 16 17
 * Copyright (C) 2005-2006 Jens Axboe <axboe@suse.de>
 * Copyright (C) 2005-2006 Linus Torvalds <torvalds@osdl.org>
 * Copyright (C) 2006 Ingo Molnar <mingo@elte.hu>
18 19 20 21 22 23 24
 *
 */
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/pagemap.h>
#include <linux/pipe_fs_i.h>
#include <linux/mm_inline.h>
25
#include <linux/swap.h>
26 27
#include <linux/writeback.h>
#include <linux/buffer_head.h>
J
Jeff Garzik 已提交
28
#include <linux/module.h>
29
#include <linux/syscalls.h>
30
#include <linux/uio.h>
31

32 33 34 35 36 37
struct partial_page {
	unsigned int offset;
	unsigned int len;
};

/*
38
 * Passed to splice_to_pipe
39 40 41 42 43 44 45 46 47
 */
struct splice_pipe_desc {
	struct page **pages;		/* page map */
	struct partial_page *partial;	/* pages[] may not be contig */
	int nr_pages;			/* number of pages in map */
	unsigned int flags;		/* splice flags */
	struct pipe_buf_operations *ops;/* ops associated with output pipe */
};

48 49 50 51 52 53
/*
 * Attempt to steal a page from a pipe buffer. This should perhaps go into
 * a vm helper function, it's already simplified quite a bit by the
 * addition of remove_mapping(). If success is returned, the caller may
 * attempt to reuse this page for another destination.
 */
54
static int page_cache_pipe_buf_steal(struct pipe_inode_info *pipe,
55 56 57
				     struct pipe_buffer *buf)
{
	struct page *page = buf->page;
58
	struct address_space *mapping;
59

60 61
	lock_page(page);

62 63 64
	mapping = page_mapping(page);
	if (mapping) {
		WARN_ON(!PageUptodate(page));
65

66 67 68 69 70 71 72 73 74
		/*
		 * At least for ext2 with nobh option, we need to wait on
		 * writeback completing on this page, since we'll remove it
		 * from the pagecache.  Otherwise truncate wont wait on the
		 * page, allowing the disk blocks to be reused by someone else
		 * before we actually wrote our data to them. fs corruption
		 * ensues.
		 */
		wait_on_page_writeback(page);
75

76 77
		if (PagePrivate(page))
			try_to_release_page(page, mapping_gfp_mask(mapping));
78

79 80 81 82 83 84 85 86
		/*
		 * If we succeeded in removing the mapping, set LRU flag
		 * and return good.
		 */
		if (remove_mapping(mapping, page)) {
			buf->flags |= PIPE_BUF_FLAG_LRU;
			return 0;
		}
87
	}
88

89 90 91 92 93 94
	/*
	 * Raced with truncate or failed to remove page from current
	 * address space, unlock and return failure.
	 */
	unlock_page(page);
	return 1;
95 96
}

97
static void page_cache_pipe_buf_release(struct pipe_inode_info *pipe,
98 99 100
					struct pipe_buffer *buf)
{
	page_cache_release(buf->page);
J
Jens Axboe 已提交
101
	buf->flags &= ~PIPE_BUF_FLAG_LRU;
102 103
}

104
static int page_cache_pipe_buf_pin(struct pipe_inode_info *pipe,
105
				   struct pipe_buffer *buf)
106 107
{
	struct page *page = buf->page;
108
	int err;
109 110

	if (!PageUptodate(page)) {
111 112 113 114
		lock_page(page);

		/*
		 * Page got truncated/unhashed. This will cause a 0-byte
I
Ingo Molnar 已提交
115
		 * splice, if this is the first page.
116 117 118 119 120
		 */
		if (!page->mapping) {
			err = -ENODATA;
			goto error;
		}
121

122
		/*
I
Ingo Molnar 已提交
123
		 * Uh oh, read-error from disk.
124 125 126 127 128 129 130
		 */
		if (!PageUptodate(page)) {
			err = -EIO;
			goto error;
		}

		/*
131
		 * Page is ok afterall, we are done.
132
		 */
133 134 135
		unlock_page(page);
	}

136
	return 0;
137 138
error:
	unlock_page(page);
139
	return err;
140 141
}

142 143
static struct pipe_buf_operations page_cache_pipe_buf_ops = {
	.can_merge = 0,
144 145 146
	.map = generic_pipe_buf_map,
	.unmap = generic_pipe_buf_unmap,
	.pin = page_cache_pipe_buf_pin,
147
	.release = page_cache_pipe_buf_release,
148
	.steal = page_cache_pipe_buf_steal,
149
	.get = generic_pipe_buf_get,
150 151
};

152 153 154
static int user_page_pipe_buf_steal(struct pipe_inode_info *pipe,
				    struct pipe_buffer *buf)
{
155 156 157
	if (!(buf->flags & PIPE_BUF_FLAG_GIFT))
		return 1;

J
Jens Axboe 已提交
158
	buf->flags |= PIPE_BUF_FLAG_LRU;
159
	return generic_pipe_buf_steal(pipe, buf);
160 161 162 163
}

static struct pipe_buf_operations user_page_pipe_buf_ops = {
	.can_merge = 0,
164 165 166
	.map = generic_pipe_buf_map,
	.unmap = generic_pipe_buf_unmap,
	.pin = generic_pipe_buf_pin,
167 168
	.release = page_cache_pipe_buf_release,
	.steal = user_page_pipe_buf_steal,
169
	.get = generic_pipe_buf_get,
170 171
};

172 173 174 175
/*
 * Pipe output worker. This sets up our pipe format with the page cache
 * pipe buffer operations. Otherwise very similar to the regular pipe_writev().
 */
176 177
static ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
			      struct splice_pipe_desc *spd)
178
{
179
	int ret, do_wakeup, page_nr;
180 181 182

	ret = 0;
	do_wakeup = 0;
183
	page_nr = 0;
184

185 186
	if (pipe->inode)
		mutex_lock(&pipe->inode->i_mutex);
187 188

	for (;;) {
189
		if (!pipe->readers) {
190 191 192 193 194 195
			send_sig(SIGPIPE, current, 0);
			if (!ret)
				ret = -EPIPE;
			break;
		}

196 197
		if (pipe->nrbufs < PIPE_BUFFERS) {
			int newbuf = (pipe->curbuf + pipe->nrbufs) & (PIPE_BUFFERS - 1);
198
			struct pipe_buffer *buf = pipe->bufs + newbuf;
199

200 201 202 203
			buf->page = spd->pages[page_nr];
			buf->offset = spd->partial[page_nr].offset;
			buf->len = spd->partial[page_nr].len;
			buf->ops = spd->ops;
204 205 206
			if (spd->flags & SPLICE_F_GIFT)
				buf->flags |= PIPE_BUF_FLAG_GIFT;

207
			pipe->nrbufs++;
208 209 210
			page_nr++;
			ret += buf->len;

211 212
			if (pipe->inode)
				do_wakeup = 1;
213

214
			if (!--spd->nr_pages)
215
				break;
216
			if (pipe->nrbufs < PIPE_BUFFERS)
217 218 219 220 221
				continue;

			break;
		}

222
		if (spd->flags & SPLICE_F_NONBLOCK) {
223 224 225 226 227
			if (!ret)
				ret = -EAGAIN;
			break;
		}

228 229 230 231 232 233 234
		if (signal_pending(current)) {
			if (!ret)
				ret = -ERESTARTSYS;
			break;
		}

		if (do_wakeup) {
235
			smp_mb();
236 237 238
			if (waitqueue_active(&pipe->wait))
				wake_up_interruptible_sync(&pipe->wait);
			kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
239 240 241
			do_wakeup = 0;
		}

242 243 244
		pipe->waiting_writers++;
		pipe_wait(pipe);
		pipe->waiting_writers--;
245 246
	}

247 248
	if (pipe->inode)
		mutex_unlock(&pipe->inode->i_mutex);
249 250

	if (do_wakeup) {
251
		smp_mb();
252 253 254
		if (waitqueue_active(&pipe->wait))
			wake_up_interruptible(&pipe->wait);
		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
255 256
	}

257 258
	while (page_nr < spd->nr_pages)
		page_cache_release(spd->pages[page_nr++]);
259 260 261 262

	return ret;
}

263
static int
264 265 266
__generic_file_splice_read(struct file *in, loff_t *ppos,
			   struct pipe_inode_info *pipe, size_t len,
			   unsigned int flags)
267 268
{
	struct address_space *mapping = in->f_mapping;
269
	unsigned int loff, nr_pages;
270
	struct page *pages[PIPE_BUFFERS];
271
	struct partial_page partial[PIPE_BUFFERS];
272
	struct page *page;
273 274
	pgoff_t index, end_index;
	loff_t isize;
275
	size_t total_len;
276
	int error, page_nr;
277 278 279 280 281 282
	struct splice_pipe_desc spd = {
		.pages = pages,
		.partial = partial,
		.flags = flags,
		.ops = &page_cache_pipe_buf_ops,
	};
283

284
	index = *ppos >> PAGE_CACHE_SHIFT;
285 286
	loff = *ppos & ~PAGE_CACHE_MASK;
	nr_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
287 288 289 290 291

	if (nr_pages > PIPE_BUFFERS)
		nr_pages = PIPE_BUFFERS;

	/*
I
Ingo Molnar 已提交
292
	 * Initiate read-ahead on this page range. however, don't call into
293 294
	 * read-ahead if this is a non-zero offset (we are likely doing small
	 * chunk splice and the page is already there) for a single page.
295
	 */
296 297
	if (!loff || nr_pages > 1)
		page_cache_readahead(mapping, &in->f_ra, in, index, nr_pages);
298 299

	/*
I
Ingo Molnar 已提交
300
	 * Now fill in the holes:
301
	 */
302
	error = 0;
303
	total_len = 0;
304

305 306 307 308
	/*
	 * Lookup the (hopefully) full range of pages we need.
	 */
	spd.nr_pages = find_get_pages_contig(mapping, index, nr_pages, pages);
309

310 311 312 313 314 315
	/*
	 * If find_get_pages_contig() returned fewer pages than we needed,
	 * allocate the rest.
	 */
	index += spd.nr_pages;
	while (spd.nr_pages < nr_pages) {
316
		/*
317 318
		 * Page could be there, find_get_pages_contig() breaks on
		 * the first hole.
319
		 */
320 321
		page = find_get_page(mapping, index);
		if (!page) {
322 323 324 325 326 327
			/*
			 * Make sure the read-ahead engine is notified
			 * about this failure.
			 */
			handle_ra_miss(mapping, &in->f_ra, index);

328
			/*
329
			 * page didn't exist, allocate one.
330 331 332 333 334 335
			 */
			page = page_cache_alloc_cold(mapping);
			if (!page)
				break;

			error = add_to_page_cache_lru(page, mapping, index,
336
					      mapping_gfp_mask(mapping));
337 338
			if (unlikely(error)) {
				page_cache_release(page);
339 340
				if (error == -EEXIST)
					continue;
341 342
				break;
			}
343 344 345 346 347
			/*
			 * add_to_page_cache() locks the page, unlock it
			 * to avoid convoluting the logic below even more.
			 */
			unlock_page(page);
348 349
		}

350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372
		pages[spd.nr_pages++] = page;
		index++;
	}

	/*
	 * Now loop over the map and see if we need to start IO on any
	 * pages, fill in the partial map, etc.
	 */
	index = *ppos >> PAGE_CACHE_SHIFT;
	nr_pages = spd.nr_pages;
	spd.nr_pages = 0;
	for (page_nr = 0; page_nr < nr_pages; page_nr++) {
		unsigned int this_len;

		if (!len)
			break;

		/*
		 * this_len is the max we'll use from this page
		 */
		this_len = min_t(unsigned long, len, PAGE_CACHE_SIZE - loff);
		page = pages[page_nr];

373 374 375 376
		/*
		 * If the page isn't uptodate, we may need to start io on it
		 */
		if (!PageUptodate(page)) {
377 378 379 380 381 382 383
			/*
			 * If in nonblock mode then dont block on waiting
			 * for an in-flight io page
			 */
			if (flags & SPLICE_F_NONBLOCK)
				break;

384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401
			lock_page(page);

			/*
			 * page was truncated, stop here. if this isn't the
			 * first page, we'll just complete what we already
			 * added
			 */
			if (!page->mapping) {
				unlock_page(page);
				break;
			}
			/*
			 * page was already under io and is now done, great
			 */
			if (PageUptodate(page)) {
				unlock_page(page);
				goto fill_it;
			}
402

403 404 405 406
			/*
			 * need to read in the page
			 */
			error = mapping->a_ops->readpage(in, page);
407
			if (unlikely(error)) {
408 409 410 411 412 413
				/*
				 * We really should re-lookup the page here,
				 * but it complicates things a lot. Instead
				 * lets just do what we already stored, and
				 * we'll get it the next time we are called.
				 */
414
				if (error == AOP_TRUNCATED_PAGE)
415 416
					error = 0;

417 418
				break;
			}
419 420 421 422 423 424

			/*
			 * i_size must be checked after ->readpage().
			 */
			isize = i_size_read(mapping->host);
			end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
425
			if (unlikely(!isize || index > end_index))
426 427 428 429 430 431 432 433
				break;

			/*
			 * if this is the last page, see if we need to shrink
			 * the length and stop
			 */
			if (end_index == index) {
				loff = PAGE_CACHE_SIZE - (isize & ~PAGE_CACHE_MASK);
434
				if (total_len + loff > isize)
435 436 437 438
					break;
				/*
				 * force quit after adding this page
				 */
439
				len = this_len;
440
				this_len = min(this_len, loff);
441
				loff = 0;
442
			}
443
		}
444
fill_it:
445 446
		partial[page_nr].offset = loff;
		partial[page_nr].len = this_len;
447
		len -= this_len;
448
		total_len += this_len;
449
		loff = 0;
450 451
		spd.nr_pages++;
		index++;
452 453
	}

454 455 456 457 458 459 460
	/*
	 * Release any pages at the end, if we quit early. 'i' is how far
	 * we got, 'nr_pages' is how many pages are in the map.
	 */
	while (page_nr < nr_pages)
		page_cache_release(pages[page_nr++]);

461
	if (spd.nr_pages)
462
		return splice_to_pipe(pipe, &spd);
463

464
	return error;
465 466
}

467 468 469 470 471 472 473 474 475
/**
 * generic_file_splice_read - splice data from file to a pipe
 * @in:		file to splice from
 * @pipe:	pipe to splice to
 * @len:	number of bytes to splice
 * @flags:	splice modifier flags
 *
 * Will read pages from given file and fill them into a pipe.
 */
476 477 478
ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
				 struct pipe_inode_info *pipe, size_t len,
				 unsigned int flags)
479 480 481 482 483 484
{
	ssize_t spliced;
	int ret;

	ret = 0;
	spliced = 0;
485

486
	while (len) {
487
		ret = __generic_file_splice_read(in, ppos, pipe, len, flags);
488

489
		if (ret < 0)
490
			break;
491 492 493 494 495 496 497 498
		else if (!ret) {
			if (spliced)
				break;
			if (flags & SPLICE_F_NONBLOCK) {
				ret = -EAGAIN;
				break;
			}
		}
499

500
		*ppos += ret;
501 502 503 504 505 506 507 508 509 510
		len -= ret;
		spliced += ret;
	}

	if (spliced)
		return spliced;

	return ret;
}

511 512
EXPORT_SYMBOL(generic_file_splice_read);

513
/*
514
 * Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->pos'
J
Jens Axboe 已提交
515
 * using sendpage(). Return the number of bytes sent.
516
 */
517
static int pipe_to_sendpage(struct pipe_inode_info *pipe,
518 519 520 521
			    struct pipe_buffer *buf, struct splice_desc *sd)
{
	struct file *file = sd->file;
	loff_t pos = sd->pos;
522
	int ret, more;
523

524
	ret = buf->ops->pin(pipe, buf);
525 526
	if (!ret) {
		more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len;
527

528 529 530
		ret = file->f_op->sendpage(file, buf->page, buf->offset,
					   sd->len, &pos, more);
	}
531

J
Jens Axboe 已提交
532
	return ret;
533 534 535 536 537 538 539 540 541 542 543 544 545 546 547
}

/*
 * This is a little more tricky than the file -> pipe splicing. There are
 * basically three cases:
 *
 *	- Destination page already exists in the address space and there
 *	  are users of it. For that case we have no other option that
 *	  copying the data. Tough luck.
 *	- Destination page already exists in the address space, but there
 *	  are no users of it. Make sure it's uptodate, then drop it. Fall
 *	  through to last case.
 *	- Destination page does not exist, we can add the pipe page to
 *	  the page cache and avoid the copy.
 *
548 549 550 551 552 553
 * If asked to move pages to the output file (SPLICE_F_MOVE is set in
 * sd->flags), we attempt to migrate pages from the pipe to the output
 * file address space page cache. This is possible if no one else has
 * the pipe page referenced outside of the pipe and page cache. If
 * SPLICE_F_MOVE isn't set, or we cannot move the page, we simply create
 * a new page in the output file page cache and fill/dirty that.
554
 */
555
static int pipe_to_file(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
556 557 558 559
			struct splice_desc *sd)
{
	struct file *file = sd->file;
	struct address_space *mapping = file->f_mapping;
560
	gfp_t gfp_mask = mapping_gfp_mask(mapping);
J
Jens Axboe 已提交
561
	unsigned int offset, this_len;
562 563
	struct page *page;
	pgoff_t index;
564
	int ret;
565 566

	/*
567
	 * make sure the data in this buffer is uptodate
568
	 */
569
	ret = buf->ops->pin(pipe, buf);
570 571
	if (unlikely(ret))
		return ret;
572 573 574 575

	index = sd->pos >> PAGE_CACHE_SHIFT;
	offset = sd->pos & ~PAGE_CACHE_MASK;

J
Jens Axboe 已提交
576 577 578 579
	this_len = sd->len;
	if (this_len + offset > PAGE_CACHE_SIZE)
		this_len = PAGE_CACHE_SIZE - offset;

580
	/*
581 582
	 * Reuse buf page, if SPLICE_F_MOVE is set and we are doing a full
	 * page.
583
	 */
584
	if ((sd->flags & SPLICE_F_MOVE) && this_len == PAGE_CACHE_SIZE) {
585
		/*
J
Jens Axboe 已提交
586 587 588
		 * If steal succeeds, buf->page is now pruned from the
		 * pagecache and we can reuse it. The page will also be
		 * locked on successful return.
589
		 */
590
		if (buf->ops->steal(pipe, buf))
591 592 593
			goto find_page;

		page = buf->page;
594 595
		if (add_to_page_cache(page, mapping, index, gfp_mask)) {
			unlock_page(page);
596
			goto find_page;
597
		}
J
Jens Axboe 已提交
598 599 600 601 602

		page_cache_get(page);

		if (!(buf->flags & PIPE_BUF_FLAG_LRU))
			lru_cache_add(page);
603 604
	} else {
find_page:
605 606 607 608 609 610 611 612 613 614 615 616 617 618 619
		page = find_lock_page(mapping, index);
		if (!page) {
			ret = -ENOMEM;
			page = page_cache_alloc_cold(mapping);
			if (unlikely(!page))
				goto out_nomem;

			/*
			 * This will also lock the page
			 */
			ret = add_to_page_cache_lru(page, mapping, index,
						    gfp_mask);
			if (unlikely(ret))
				goto out;
		}
620 621

		/*
622 623 624 625
		 * We get here with the page locked. If the page is also
		 * uptodate, we don't need to do more. If it isn't, we
		 * may need to bring it in if we are not going to overwrite
		 * the full page.
626 627
		 */
		if (!PageUptodate(page)) {
J
Jens Axboe 已提交
628
			if (this_len < PAGE_CACHE_SIZE) {
629 630 631 632 633 634 635 636
				ret = mapping->a_ops->readpage(file, page);
				if (unlikely(ret))
					goto out;

				lock_page(page);

				if (!PageUptodate(page)) {
					/*
I
Ingo Molnar 已提交
637
					 * Page got invalidated, repeat.
638 639 640 641 642 643 644 645
					 */
					if (!page->mapping) {
						unlock_page(page);
						page_cache_release(page);
						goto find_page;
					}
					ret = -EIO;
					goto out;
646
				}
647
			} else
648
				SetPageUptodate(page);
649 650 651
		}
	}

J
Jens Axboe 已提交
652
	ret = mapping->a_ops->prepare_write(file, page, offset, offset+this_len);
653 654 655 656 657
	if (unlikely(ret)) {
		loff_t isize = i_size_read(mapping->host);

		if (ret != AOP_TRUNCATED_PAGE)
			unlock_page(page);
658
		page_cache_release(page);
659 660 661 662 663 664 665 666 667 668
		if (ret == AOP_TRUNCATED_PAGE)
			goto find_page;

		/*
		 * prepare_write() may have instantiated a few blocks
		 * outside i_size.  Trim these off again.
		 */
		if (sd->pos + this_len > isize)
			vmtruncate(mapping->host, isize);

669
		goto out;
670
	}
671

672
	if (buf->page != page) {
673 674 675
		/*
		 * Careful, ->map() uses KM_USER0!
		 */
676
		char *src = buf->ops->map(pipe, buf, 1);
677
		char *dst = kmap_atomic(page, KM_USER1);
678

J
Jens Axboe 已提交
679
		memcpy(dst + offset, src + buf->offset, this_len);
680
		flush_dcache_page(page);
681
		kunmap_atomic(dst, KM_USER1);
682
		buf->ops->unmap(pipe, buf, src);
683
	}
684

J
Jens Axboe 已提交
685
	ret = mapping->a_ops->commit_write(file, page, offset, offset+this_len);
686 687 688 689 690 691 692 693 694
	if (!ret) {
		/*
		 * Return the number of bytes written and mark page as
		 * accessed, we are now done!
		 */
		ret = this_len;
		mark_page_accessed(page);
		balance_dirty_pages_ratelimited(mapping);
	} else if (ret == AOP_TRUNCATED_PAGE) {
695 696
		page_cache_release(page);
		goto find_page;
697
	}
698
out:
699
	page_cache_release(page);
700
	unlock_page(page);
701
out_nomem:
702 703 704
	return ret;
}

705 706 707 708 709
/*
 * Pipe input worker. Most of this logic works like a regular pipe, the
 * key here is the 'actor' worker passed in that actually moves the data
 * to the wanted destination. See pipe_to_file/pipe_to_sendpage above.
 */
710 711 712
ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
			 loff_t *ppos, size_t len, unsigned int flags,
			 splice_actor *actor)
713 714 715 716 717 718 719 720 721 722
{
	int ret, do_wakeup, err;
	struct splice_desc sd;

	ret = 0;
	do_wakeup = 0;

	sd.total_len = len;
	sd.flags = flags;
	sd.file = out;
723
	sd.pos = *ppos;
724

725 726
	if (pipe->inode)
		mutex_lock(&pipe->inode->i_mutex);
727 728

	for (;;) {
729 730
		if (pipe->nrbufs) {
			struct pipe_buffer *buf = pipe->bufs + pipe->curbuf;
731 732 733 734 735 736
			struct pipe_buf_operations *ops = buf->ops;

			sd.len = buf->len;
			if (sd.len > sd.total_len)
				sd.len = sd.total_len;

737
			err = actor(pipe, buf, &sd);
J
Jens Axboe 已提交
738
			if (err <= 0) {
739 740 741 742 743 744
				if (!ret && err != -ENODATA)
					ret = err;

				break;
			}

J
Jens Axboe 已提交
745 746 747 748 749 750 751 752 753
			ret += err;
			buf->offset += err;
			buf->len -= err;

			sd.len -= err;
			sd.pos += err;
			sd.total_len -= err;
			if (sd.len)
				continue;
I
Ingo Molnar 已提交
754

755 756
			if (!buf->len) {
				buf->ops = NULL;
757
				ops->release(pipe, buf);
758 759 760 761
				pipe->curbuf = (pipe->curbuf + 1) & (PIPE_BUFFERS - 1);
				pipe->nrbufs--;
				if (pipe->inode)
					do_wakeup = 1;
762 763 764 765 766 767
			}

			if (!sd.total_len)
				break;
		}

768
		if (pipe->nrbufs)
769
			continue;
770
		if (!pipe->writers)
771
			break;
772
		if (!pipe->waiting_writers) {
773 774 775 776
			if (ret)
				break;
		}

777 778 779 780 781 782
		if (flags & SPLICE_F_NONBLOCK) {
			if (!ret)
				ret = -EAGAIN;
			break;
		}

783 784 785 786 787 788 789
		if (signal_pending(current)) {
			if (!ret)
				ret = -ERESTARTSYS;
			break;
		}

		if (do_wakeup) {
790
			smp_mb();
791 792 793
			if (waitqueue_active(&pipe->wait))
				wake_up_interruptible_sync(&pipe->wait);
			kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
794 795 796
			do_wakeup = 0;
		}

797
		pipe_wait(pipe);
798 799
	}

800 801
	if (pipe->inode)
		mutex_unlock(&pipe->inode->i_mutex);
802 803

	if (do_wakeup) {
804
		smp_mb();
805 806 807
		if (waitqueue_active(&pipe->wait))
			wake_up_interruptible(&pipe->wait);
		kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
808 809 810 811 812
	}

	return ret;
}

813 814
/**
 * generic_file_splice_write - splice data from a pipe to a file
815
 * @pipe:	pipe info
816 817 818 819 820 821 822 823
 * @out:	file to write to
 * @len:	number of bytes to splice
 * @flags:	splice modifier flags
 *
 * Will either move or copy pages (determined by @flags options) from
 * the given pipe inode to the given file.
 *
 */
824 825
ssize_t
generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
826
			  loff_t *ppos, size_t len, unsigned int flags)
827
{
828
	struct address_space *mapping = out->f_mapping;
829 830
	ssize_t ret;

831
	ret = splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_file);
J
Jens Axboe 已提交
832
	if (ret > 0) {
833 834
		struct inode *inode = mapping->host;

J
Jens Axboe 已提交
835 836 837 838 839 840 841 842 843 844 845 846 847
		*ppos += ret;

		/*
		 * If file or inode is SYNC and we actually wrote some data,
		 * sync it.
		 */
		if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
			int err;

			mutex_lock(&inode->i_mutex);
			err = generic_osync_inode(inode, mapping,
						  OSYNC_METADATA|OSYNC_DATA);
			mutex_unlock(&inode->i_mutex);
848

J
Jens Axboe 已提交
849 850 851
			if (err)
				ret = err;
		}
852 853 854
	}

	return ret;
855 856
}

857 858
EXPORT_SYMBOL(generic_file_splice_write);

859 860 861 862 863 864 865 866 867 868 869
/**
 * generic_splice_sendpage - splice data from a pipe to a socket
 * @inode:	pipe inode
 * @out:	socket to write to
 * @len:	number of bytes to splice
 * @flags:	splice modifier flags
 *
 * Will send @len bytes from the pipe to a network socket. No data copying
 * is involved.
 *
 */
870
ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe, struct file *out,
871
				loff_t *ppos, size_t len, unsigned int flags)
872
{
873
	return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_sendpage);
874 875
}

876
EXPORT_SYMBOL(generic_splice_sendpage);
J
Jeff Garzik 已提交
877

878 879 880
/*
 * Attempt to initiate a splice from pipe to file.
 */
881
static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
882
			   loff_t *ppos, size_t len, unsigned int flags)
883 884 885
{
	int ret;

886
	if (unlikely(!out->f_op || !out->f_op->splice_write))
887 888
		return -EINVAL;

889
	if (unlikely(!(out->f_mode & FMODE_WRITE)))
890 891
		return -EBADF;

892
	ret = rw_verify_area(WRITE, out, ppos, len);
893 894 895
	if (unlikely(ret < 0))
		return ret;

896
	return out->f_op->splice_write(pipe, out, ppos, len, flags);
897 898
}

899 900 901
/*
 * Attempt to initiate a splice from a file to a pipe.
 */
902 903 904
static long do_splice_to(struct file *in, loff_t *ppos,
			 struct pipe_inode_info *pipe, size_t len,
			 unsigned int flags)
905
{
906
	loff_t isize, left;
907 908
	int ret;

909
	if (unlikely(!in->f_op || !in->f_op->splice_read))
910 911
		return -EINVAL;

912
	if (unlikely(!(in->f_mode & FMODE_READ)))
913 914
		return -EBADF;

915
	ret = rw_verify_area(READ, in, ppos, len);
916 917 918 919
	if (unlikely(ret < 0))
		return ret;

	isize = i_size_read(in->f_mapping->host);
920
	if (unlikely(*ppos >= isize))
921 922
		return 0;
	
923
	left = isize - *ppos;
924
	if (unlikely(left < len))
925 926
		len = left;

927
	return in->f_op->splice_read(in, ppos, pipe, len, flags);
928 929
}

930 931
long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
		      size_t len, unsigned int flags)
932 933 934
{
	struct pipe_inode_info *pipe;
	long ret, bytes;
935
	loff_t out_off;
936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952
	umode_t i_mode;
	int i;

	/*
	 * We require the input being a regular file, as we don't want to
	 * randomly drop data for eg socket -> socket splicing. Use the
	 * piped splicing for that!
	 */
	i_mode = in->f_dentry->d_inode->i_mode;
	if (unlikely(!S_ISREG(i_mode) && !S_ISBLK(i_mode)))
		return -EINVAL;

	/*
	 * neither in nor out is a pipe, setup an internal pipe attached to
	 * 'out' and transfer the wanted data from 'in' to 'out' through that
	 */
	pipe = current->splice_pipe;
953
	if (unlikely(!pipe)) {
954 955 956 957 958 959
		pipe = alloc_pipe_info(NULL);
		if (!pipe)
			return -ENOMEM;

		/*
		 * We don't have an immediate reader, but we'll read the stuff
960
		 * out of the pipe right after the splice_to_pipe(). So set
961 962 963 964 965 966 967 968
		 * PIPE_READERS appropriately.
		 */
		pipe->readers = 1;

		current->splice_pipe = pipe;
	}

	/*
I
Ingo Molnar 已提交
969
	 * Do the splice.
970 971 972
	 */
	ret = 0;
	bytes = 0;
973
	out_off = 0;
974 975 976 977 978 979 980 981 982

	while (len) {
		size_t read_len, max_read_len;

		/*
		 * Do at most PIPE_BUFFERS pages worth of transfer:
		 */
		max_read_len = min(len, (size_t)(PIPE_BUFFERS*PAGE_SIZE));

983
		ret = do_splice_to(in, ppos, pipe, max_read_len, flags);
984 985 986 987 988 989 990 991 992 993
		if (unlikely(ret < 0))
			goto out_release;

		read_len = ret;

		/*
		 * NOTE: nonblocking mode only applies to the input. We
		 * must not do the output in nonblocking mode as then we
		 * could get stuck data in the internal pipe:
		 */
994
		ret = do_splice_from(pipe, out, &out_off, read_len,
995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043
				     flags & ~SPLICE_F_NONBLOCK);
		if (unlikely(ret < 0))
			goto out_release;

		bytes += ret;
		len -= ret;

		/*
		 * In nonblocking mode, if we got back a short read then
		 * that was due to either an IO error or due to the
		 * pagecache entry not being there. In the IO error case
		 * the _next_ splice attempt will produce a clean IO error
		 * return value (not a short read), so in both cases it's
		 * correct to break out of the loop here:
		 */
		if ((flags & SPLICE_F_NONBLOCK) && (read_len < max_read_len))
			break;
	}

	pipe->nrbufs = pipe->curbuf = 0;

	return bytes;

out_release:
	/*
	 * If we did an incomplete transfer we must release
	 * the pipe buffers in question:
	 */
	for (i = 0; i < PIPE_BUFFERS; i++) {
		struct pipe_buffer *buf = pipe->bufs + i;

		if (buf->ops) {
			buf->ops->release(pipe, buf);
			buf->ops = NULL;
		}
	}
	pipe->nrbufs = pipe->curbuf = 0;

	/*
	 * If we transferred some data, return the number of bytes:
	 */
	if (bytes > 0)
		return bytes;

	return ret;
}

EXPORT_SYMBOL(do_splice_direct);

1044 1045 1046
/*
 * Determine where to splice to/from.
 */
1047 1048 1049
static long do_splice(struct file *in, loff_t __user *off_in,
		      struct file *out, loff_t __user *off_out,
		      size_t len, unsigned int flags)
1050
{
1051
	struct pipe_inode_info *pipe;
1052
	loff_t offset, *off;
J
Jens Axboe 已提交
1053
	long ret;
1054

1055
	pipe = in->f_dentry->d_inode->i_pipe;
1056 1057 1058
	if (pipe) {
		if (off_in)
			return -ESPIPE;
1059 1060 1061
		if (off_out) {
			if (out->f_op->llseek == no_llseek)
				return -EINVAL;
1062
			if (copy_from_user(&offset, off_out, sizeof(loff_t)))
1063
				return -EFAULT;
1064 1065 1066
			off = &offset;
		} else
			off = &out->f_pos;
1067

J
Jens Axboe 已提交
1068 1069 1070 1071 1072 1073
		ret = do_splice_from(pipe, out, off, len, flags);

		if (off_out && copy_to_user(off_out, off, sizeof(loff_t)))
			ret = -EFAULT;

		return ret;
1074
	}
1075

1076
	pipe = out->f_dentry->d_inode->i_pipe;
1077 1078 1079
	if (pipe) {
		if (off_out)
			return -ESPIPE;
1080 1081 1082
		if (off_in) {
			if (in->f_op->llseek == no_llseek)
				return -EINVAL;
1083
			if (copy_from_user(&offset, off_in, sizeof(loff_t)))
1084
				return -EFAULT;
1085 1086 1087
			off = &offset;
		} else
			off = &in->f_pos;
1088

J
Jens Axboe 已提交
1089 1090 1091 1092 1093 1094
		ret = do_splice_to(in, off, pipe, len, flags);

		if (off_in && copy_to_user(off_in, off, sizeof(loff_t)))
			ret = -EFAULT;

		return ret;
1095
	}
1096 1097 1098 1099

	return -EINVAL;
}

1100 1101 1102 1103 1104 1105 1106 1107 1108
/*
 * Map an iov into an array of pages and offset/length tupples. With the
 * partial_page structure, we can map several non-contiguous ranges into
 * our ones pages[] map instead of splitting that operation into pieces.
 * Could easily be exported as a generic helper for other users, in which
 * case one would probably want to add a 'max_nr_pages' parameter as well.
 */
static int get_iovec_page_array(const struct iovec __user *iov,
				unsigned int nr_vecs, struct page **pages,
1109
				struct partial_page *partial, int aligned)
1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148
{
	int buffers = 0, error = 0;

	/*
	 * It's ok to take the mmap_sem for reading, even
	 * across a "get_user()".
	 */
	down_read(&current->mm->mmap_sem);

	while (nr_vecs) {
		unsigned long off, npages;
		void __user *base;
		size_t len;
		int i;

		/*
		 * Get user address base and length for this iovec.
		 */
		error = get_user(base, &iov->iov_base);
		if (unlikely(error))
			break;
		error = get_user(len, &iov->iov_len);
		if (unlikely(error))
			break;

		/*
		 * Sanity check this iovec. 0 read succeeds.
		 */
		if (unlikely(!len))
			break;
		error = -EFAULT;
		if (unlikely(!base))
			break;

		/*
		 * Get this base offset and number of pages, then map
		 * in the user pages.
		 */
		off = (unsigned long) base & ~PAGE_MASK;
1149 1150 1151 1152 1153 1154 1155 1156 1157

		/*
		 * If asked for alignment, the offset must be zero and the
		 * length a multiple of the PAGE_SIZE.
		 */
		error = -EINVAL;
		if (aligned && (off || len & ~PAGE_MASK))
			break;

1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172
		npages = (off + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
		if (npages > PIPE_BUFFERS - buffers)
			npages = PIPE_BUFFERS - buffers;

		error = get_user_pages(current, current->mm,
				       (unsigned long) base, npages, 0, 0,
				       &pages[buffers], NULL);

		if (unlikely(error <= 0))
			break;

		/*
		 * Fill this contiguous range into the partial page map.
		 */
		for (i = 0; i < error; i++) {
1173
			const int plen = min_t(size_t, len, PAGE_SIZE - off);
1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250

			partial[buffers].offset = off;
			partial[buffers].len = plen;

			off = 0;
			len -= plen;
			buffers++;
		}

		/*
		 * We didn't complete this iov, stop here since it probably
		 * means we have to move some of this into a pipe to
		 * be able to continue.
		 */
		if (len)
			break;

		/*
		 * Don't continue if we mapped fewer pages than we asked for,
		 * or if we mapped the max number of pages that we have
		 * room for.
		 */
		if (error < npages || buffers == PIPE_BUFFERS)
			break;

		nr_vecs--;
		iov++;
	}

	up_read(&current->mm->mmap_sem);

	if (buffers)
		return buffers;

	return error;
}

/*
 * vmsplice splices a user address range into a pipe. It can be thought of
 * as splice-from-memory, where the regular splice is splice-from-file (or
 * to file). In both cases the output is a pipe, naturally.
 *
 * Note that vmsplice only supports splicing _from_ user memory to a pipe,
 * not the other way around. Splicing from user memory is a simple operation
 * that can be supported without any funky alignment restrictions or nasty
 * vm tricks. We simply map in the user memory and fill them into a pipe.
 * The reverse isn't quite as easy, though. There are two possible solutions
 * for that:
 *
 *	- memcpy() the data internally, at which point we might as well just
 *	  do a regular read() on the buffer anyway.
 *	- Lots of nasty vm tricks, that are neither fast nor flexible (it
 *	  has restriction limitations on both ends of the pipe).
 *
 * Alas, it isn't here.
 *
 */
static long do_vmsplice(struct file *file, const struct iovec __user *iov,
			unsigned long nr_segs, unsigned int flags)
{
	struct pipe_inode_info *pipe = file->f_dentry->d_inode->i_pipe;
	struct page *pages[PIPE_BUFFERS];
	struct partial_page partial[PIPE_BUFFERS];
	struct splice_pipe_desc spd = {
		.pages = pages,
		.partial = partial,
		.flags = flags,
		.ops = &user_page_pipe_buf_ops,
	};

	if (unlikely(!pipe))
		return -EBADF;
	if (unlikely(nr_segs > UIO_MAXIOV))
		return -EINVAL;
	else if (unlikely(!nr_segs))
		return 0;

1251 1252
	spd.nr_pages = get_iovec_page_array(iov, nr_segs, pages, partial,
					    flags & SPLICE_F_GIFT);
1253 1254 1255
	if (spd.nr_pages <= 0)
		return spd.nr_pages;

1256
	return splice_to_pipe(pipe, &spd);
1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277
}

asmlinkage long sys_vmsplice(int fd, const struct iovec __user *iov,
			     unsigned long nr_segs, unsigned int flags)
{
	struct file *file;
	long error;
	int fput;

	error = -EBADF;
	file = fget_light(fd, &fput);
	if (file) {
		if (file->f_mode & FMODE_WRITE)
			error = do_vmsplice(file, iov, nr_segs, flags);

		fput_light(file, fput);
	}

	return error;
}

1278 1279 1280
asmlinkage long sys_splice(int fd_in, loff_t __user *off_in,
			   int fd_out, loff_t __user *off_out,
			   size_t len, unsigned int flags)
1281 1282 1283 1284 1285 1286 1287 1288 1289
{
	long error;
	struct file *in, *out;
	int fput_in, fput_out;

	if (unlikely(!len))
		return 0;

	error = -EBADF;
1290
	in = fget_light(fd_in, &fput_in);
1291 1292
	if (in) {
		if (in->f_mode & FMODE_READ) {
1293
			out = fget_light(fd_out, &fput_out);
1294 1295
			if (out) {
				if (out->f_mode & FMODE_WRITE)
1296 1297 1298
					error = do_splice(in, off_in,
							  out, off_out,
							  len, flags);
1299 1300 1301 1302 1303 1304 1305 1306 1307
				fput_light(out, fput_out);
			}
		}

		fput_light(in, fput_in);
	}

	return error;
}
1308 1309 1310 1311 1312 1313 1314 1315 1316

/*
 * Link contents of ipipe to opipe.
 */
static int link_pipe(struct pipe_inode_info *ipipe,
		     struct pipe_inode_info *opipe,
		     size_t len, unsigned int flags)
{
	struct pipe_buffer *ibuf, *obuf;
1317 1318 1319
	int ret, do_wakeup, i, ipipe_first;

	ret = do_wakeup = ipipe_first = 0;
1320 1321 1322 1323 1324 1325 1326

	/*
	 * Potential ABBA deadlock, work around it by ordering lock
	 * grabbing by inode address. Otherwise two different processes
	 * could deadlock (one doing tee from A -> B, the other from B -> A).
	 */
	if (ipipe->inode < opipe->inode) {
1327
		ipipe_first = 1;
1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359
		mutex_lock(&ipipe->inode->i_mutex);
		mutex_lock(&opipe->inode->i_mutex);
	} else {
		mutex_lock(&opipe->inode->i_mutex);
		mutex_lock(&ipipe->inode->i_mutex);
	}

	for (i = 0;; i++) {
		if (!opipe->readers) {
			send_sig(SIGPIPE, current, 0);
			if (!ret)
				ret = -EPIPE;
			break;
		}
		if (ipipe->nrbufs - i) {
			ibuf = ipipe->bufs + ((ipipe->curbuf + i) & (PIPE_BUFFERS - 1));

			/*
			 * If we have room, fill this buffer
			 */
			if (opipe->nrbufs < PIPE_BUFFERS) {
				int nbuf = (opipe->curbuf + opipe->nrbufs) & (PIPE_BUFFERS - 1);

				/*
				 * Get a reference to this pipe buffer,
				 * so we can copy the contents over.
				 */
				ibuf->ops->get(ipipe, ibuf);

				obuf = opipe->bufs + nbuf;
				*obuf = *ibuf;

1360 1361 1362 1363 1364 1365
				/*
				 * Don't inherit the gift flag, we need to
				 * prevent multiple steals of this page.
				 */
				obuf->flags &= ~PIPE_BUF_FLAG_GIFT;

1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381
				if (obuf->len > len)
					obuf->len = len;

				opipe->nrbufs++;
				do_wakeup = 1;
				ret += obuf->len;
				len -= obuf->len;

				if (!len)
					break;
				if (opipe->nrbufs < PIPE_BUFFERS)
					continue;
			}

			/*
			 * We have input available, but no output room.
1382 1383 1384
			 * If we already copied data, return that. If we
			 * need to drop the opipe lock, it must be ordered
			 * last to avoid deadlocks.
1385
			 */
1386
			if ((flags & SPLICE_F_NONBLOCK) || !ipipe_first) {
1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419
				if (!ret)
					ret = -EAGAIN;
				break;
			}
			if (signal_pending(current)) {
				if (!ret)
					ret = -ERESTARTSYS;
				break;
			}
			if (do_wakeup) {
				smp_mb();
				if (waitqueue_active(&opipe->wait))
					wake_up_interruptible(&opipe->wait);
				kill_fasync(&opipe->fasync_readers, SIGIO, POLL_IN);
				do_wakeup = 0;
			}

			opipe->waiting_writers++;
			pipe_wait(opipe);
			opipe->waiting_writers--;
			continue;
		}

		/*
		 * No input buffers, do the usual checks for available
		 * writers and blocking and wait if necessary
		 */
		if (!ipipe->writers)
			break;
		if (!ipipe->waiting_writers) {
			if (ret)
				break;
		}
1420 1421 1422 1423 1424 1425
		/*
		 * pipe_wait() drops the ipipe mutex. To avoid deadlocks
		 * with another process, we can only safely do that if
		 * the ipipe lock is ordered last.
		 */
		if ((flags & SPLICE_F_NONBLOCK) || ipipe_first) {
1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502
			if (!ret)
				ret = -EAGAIN;
			break;
		}
		if (signal_pending(current)) {
			if (!ret)
				ret = -ERESTARTSYS;
			break;
		}

		if (waitqueue_active(&ipipe->wait))
			wake_up_interruptible_sync(&ipipe->wait);
		kill_fasync(&ipipe->fasync_writers, SIGIO, POLL_OUT);

		pipe_wait(ipipe);
	}

	mutex_unlock(&ipipe->inode->i_mutex);
	mutex_unlock(&opipe->inode->i_mutex);

	if (do_wakeup) {
		smp_mb();
		if (waitqueue_active(&opipe->wait))
			wake_up_interruptible(&opipe->wait);
		kill_fasync(&opipe->fasync_readers, SIGIO, POLL_IN);
	}

	return ret;
}

/*
 * This is a tee(1) implementation that works on pipes. It doesn't copy
 * any data, it simply references the 'in' pages on the 'out' pipe.
 * The 'flags' used are the SPLICE_F_* variants, currently the only
 * applicable one is SPLICE_F_NONBLOCK.
 */
static long do_tee(struct file *in, struct file *out, size_t len,
		   unsigned int flags)
{
	struct pipe_inode_info *ipipe = in->f_dentry->d_inode->i_pipe;
	struct pipe_inode_info *opipe = out->f_dentry->d_inode->i_pipe;

	/*
	 * Link ipipe to the two output pipes, consuming as we go along.
	 */
	if (ipipe && opipe)
		return link_pipe(ipipe, opipe, len, flags);

	return -EINVAL;
}

asmlinkage long sys_tee(int fdin, int fdout, size_t len, unsigned int flags)
{
	struct file *in;
	int error, fput_in;

	if (unlikely(!len))
		return 0;

	error = -EBADF;
	in = fget_light(fdin, &fput_in);
	if (in) {
		if (in->f_mode & FMODE_READ) {
			int fput_out;
			struct file *out = fget_light(fdout, &fput_out);

			if (out) {
				if (out->f_mode & FMODE_WRITE)
					error = do_tee(in, out, len, flags);
				fput_light(out, fput_out);
			}
		}
 		fput_light(in, fput_in);
 	}

	return error;
}