Merge branch 'printk-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git...
[linux-2.6] / fs / splice.c
1 /*
2  * "splice": joining two ropes together by interweaving their strands.
3  *
4  * This is the "extended pipe" functionality, where a pipe is used as
5  * an arbitrary in-memory buffer. Think of a pipe as a small kernel
6  * buffer that you can use to transfer data from one end to the other.
7  *
8  * The traditional unix read/write is extended with a "splice()" operation
9  * that transfers data buffers to or from a pipe buffer.
10  *
11  * Named by Larry McVoy, original implementation from Linus, extended by
12  * Jens to support splicing to files, network, direct splicing, etc and
13  * fixing lots of bugs.
14  *
15  * Copyright (C) 2005-2006 Jens Axboe <axboe@kernel.dk>
16  * Copyright (C) 2005-2006 Linus Torvalds <torvalds@osdl.org>
17  * Copyright (C) 2006 Ingo Molnar <mingo@elte.hu>
18  *
19  */
20 #include <linux/fs.h>
21 #include <linux/file.h>
22 #include <linux/pagemap.h>
23 #include <linux/splice.h>
24 #include <linux/memcontrol.h>
25 #include <linux/mm_inline.h>
26 #include <linux/swap.h>
27 #include <linux/writeback.h>
28 #include <linux/buffer_head.h>
29 #include <linux/module.h>
30 #include <linux/syscalls.h>
31 #include <linux/uio.h>
32 #include <linux/security.h>
33
34 /*
35  * Attempt to steal a page from a pipe buffer. This should perhaps go into
36  * a vm helper function, it's already simplified quite a bit by the
37  * addition of remove_mapping(). If success is returned, the caller may
38  * attempt to reuse this page for another destination.
39  */
40 static int page_cache_pipe_buf_steal(struct pipe_inode_info *pipe,
41                                      struct pipe_buffer *buf)
42 {
43         struct page *page = buf->page;
44         struct address_space *mapping;
45
46         lock_page(page);
47
48         mapping = page_mapping(page);
49         if (mapping) {
50                 WARN_ON(!PageUptodate(page));
51
52                 /*
53                  * At least for ext2 with nobh option, we need to wait on
54                  * writeback completing on this page, since we'll remove it
55                  * from the pagecache.  Otherwise truncate wont wait on the
56                  * page, allowing the disk blocks to be reused by someone else
57                  * before we actually wrote our data to them. fs corruption
58                  * ensues.
59                  */
60                 wait_on_page_writeback(page);
61
62                 if (page_has_private(page) &&
63                     !try_to_release_page(page, GFP_KERNEL))
64                         goto out_unlock;
65
66                 /*
67                  * If we succeeded in removing the mapping, set LRU flag
68                  * and return good.
69                  */
70                 if (remove_mapping(mapping, page)) {
71                         buf->flags |= PIPE_BUF_FLAG_LRU;
72                         return 0;
73                 }
74         }
75
76         /*
77          * Raced with truncate or failed to remove page from current
78          * address space, unlock and return failure.
79          */
80 out_unlock:
81         unlock_page(page);
82         return 1;
83 }
84
85 static void page_cache_pipe_buf_release(struct pipe_inode_info *pipe,
86                                         struct pipe_buffer *buf)
87 {
88         page_cache_release(buf->page);
89         buf->flags &= ~PIPE_BUF_FLAG_LRU;
90 }
91
92 /*
93  * Check whether the contents of buf is OK to access. Since the content
94  * is a page cache page, IO may be in flight.
95  */
96 static int page_cache_pipe_buf_confirm(struct pipe_inode_info *pipe,
97                                        struct pipe_buffer *buf)
98 {
99         struct page *page = buf->page;
100         int err;
101
102         if (!PageUptodate(page)) {
103                 lock_page(page);
104
105                 /*
106                  * Page got truncated/unhashed. This will cause a 0-byte
107                  * splice, if this is the first page.
108                  */
109                 if (!page->mapping) {
110                         err = -ENODATA;
111                         goto error;
112                 }
113
114                 /*
115                  * Uh oh, read-error from disk.
116                  */
117                 if (!PageUptodate(page)) {
118                         err = -EIO;
119                         goto error;
120                 }
121
122                 /*
123                  * Page is ok afterall, we are done.
124                  */
125                 unlock_page(page);
126         }
127
128         return 0;
129 error:
130         unlock_page(page);
131         return err;
132 }
133
134 static const struct pipe_buf_operations page_cache_pipe_buf_ops = {
135         .can_merge = 0,
136         .map = generic_pipe_buf_map,
137         .unmap = generic_pipe_buf_unmap,
138         .confirm = page_cache_pipe_buf_confirm,
139         .release = page_cache_pipe_buf_release,
140         .steal = page_cache_pipe_buf_steal,
141         .get = generic_pipe_buf_get,
142 };
143
144 static int user_page_pipe_buf_steal(struct pipe_inode_info *pipe,
145                                     struct pipe_buffer *buf)
146 {
147         if (!(buf->flags & PIPE_BUF_FLAG_GIFT))
148                 return 1;
149
150         buf->flags |= PIPE_BUF_FLAG_LRU;
151         return generic_pipe_buf_steal(pipe, buf);
152 }
153
154 static const struct pipe_buf_operations user_page_pipe_buf_ops = {
155         .can_merge = 0,
156         .map = generic_pipe_buf_map,
157         .unmap = generic_pipe_buf_unmap,
158         .confirm = generic_pipe_buf_confirm,
159         .release = page_cache_pipe_buf_release,
160         .steal = user_page_pipe_buf_steal,
161         .get = generic_pipe_buf_get,
162 };
163
164 /**
165  * splice_to_pipe - fill passed data into a pipe
166  * @pipe:       pipe to fill
167  * @spd:        data to fill
168  *
169  * Description:
170  *    @spd contains a map of pages and len/offset tuples, along with
171  *    the struct pipe_buf_operations associated with these pages. This
172  *    function will link that data to the pipe.
173  *
174  */
175 ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
176                        struct splice_pipe_desc *spd)
177 {
178         unsigned int spd_pages = spd->nr_pages;
179         int ret, do_wakeup, page_nr;
180
181         ret = 0;
182         do_wakeup = 0;
183         page_nr = 0;
184
185         pipe_lock(pipe);
186
187         for (;;) {
188                 if (!pipe->readers) {
189                         send_sig(SIGPIPE, current, 0);
190                         if (!ret)
191                                 ret = -EPIPE;
192                         break;
193                 }
194
195                 if (pipe->nrbufs < PIPE_BUFFERS) {
196                         int newbuf = (pipe->curbuf + pipe->nrbufs) & (PIPE_BUFFERS - 1);
197                         struct pipe_buffer *buf = pipe->bufs + newbuf;
198
199                         buf->page = spd->pages[page_nr];
200                         buf->offset = spd->partial[page_nr].offset;
201                         buf->len = spd->partial[page_nr].len;
202                         buf->private = spd->partial[page_nr].private;
203                         buf->ops = spd->ops;
204                         if (spd->flags & SPLICE_F_GIFT)
205                                 buf->flags |= PIPE_BUF_FLAG_GIFT;
206
207                         pipe->nrbufs++;
208                         page_nr++;
209                         ret += buf->len;
210
211                         if (pipe->inode)
212                                 do_wakeup = 1;
213
214                         if (!--spd->nr_pages)
215                                 break;
216                         if (pipe->nrbufs < PIPE_BUFFERS)
217                                 continue;
218
219                         break;
220                 }
221
222                 if (spd->flags & SPLICE_F_NONBLOCK) {
223                         if (!ret)
224                                 ret = -EAGAIN;
225                         break;
226                 }
227
228                 if (signal_pending(current)) {
229                         if (!ret)
230                                 ret = -ERESTARTSYS;
231                         break;
232                 }
233
234                 if (do_wakeup) {
235                         smp_mb();
236                         if (waitqueue_active(&pipe->wait))
237                                 wake_up_interruptible_sync(&pipe->wait);
238                         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
239                         do_wakeup = 0;
240                 }
241
242                 pipe->waiting_writers++;
243                 pipe_wait(pipe);
244                 pipe->waiting_writers--;
245         }
246
247         pipe_unlock(pipe);
248
249         if (do_wakeup) {
250                 smp_mb();
251                 if (waitqueue_active(&pipe->wait))
252                         wake_up_interruptible(&pipe->wait);
253                 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
254         }
255
256         while (page_nr < spd_pages)
257                 spd->spd_release(spd, page_nr++);
258
259         return ret;
260 }
261
262 static void spd_release_page(struct splice_pipe_desc *spd, unsigned int i)
263 {
264         page_cache_release(spd->pages[i]);
265 }
266
267 static int
268 __generic_file_splice_read(struct file *in, loff_t *ppos,
269                            struct pipe_inode_info *pipe, size_t len,
270                            unsigned int flags)
271 {
272         struct address_space *mapping = in->f_mapping;
273         unsigned int loff, nr_pages, req_pages;
274         struct page *pages[PIPE_BUFFERS];
275         struct partial_page partial[PIPE_BUFFERS];
276         struct page *page;
277         pgoff_t index, end_index;
278         loff_t isize;
279         int error, page_nr;
280         struct splice_pipe_desc spd = {
281                 .pages = pages,
282                 .partial = partial,
283                 .flags = flags,
284                 .ops = &page_cache_pipe_buf_ops,
285                 .spd_release = spd_release_page,
286         };
287
288         index = *ppos >> PAGE_CACHE_SHIFT;
289         loff = *ppos & ~PAGE_CACHE_MASK;
290         req_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
291         nr_pages = min(req_pages, (unsigned)PIPE_BUFFERS);
292
293         /*
294          * Lookup the (hopefully) full range of pages we need.
295          */
296         spd.nr_pages = find_get_pages_contig(mapping, index, nr_pages, pages);
297         index += spd.nr_pages;
298
299         /*
300          * If find_get_pages_contig() returned fewer pages than we needed,
301          * readahead/allocate the rest and fill in the holes.
302          */
303         if (spd.nr_pages < nr_pages)
304                 page_cache_sync_readahead(mapping, &in->f_ra, in,
305                                 index, req_pages - spd.nr_pages);
306
307         error = 0;
308         while (spd.nr_pages < nr_pages) {
309                 /*
310                  * Page could be there, find_get_pages_contig() breaks on
311                  * the first hole.
312                  */
313                 page = find_get_page(mapping, index);
314                 if (!page) {
315                         /*
316                          * page didn't exist, allocate one.
317                          */
318                         page = page_cache_alloc_cold(mapping);
319                         if (!page)
320                                 break;
321
322                         error = add_to_page_cache_lru(page, mapping, index,
323                                                 mapping_gfp_mask(mapping));
324                         if (unlikely(error)) {
325                                 page_cache_release(page);
326                                 if (error == -EEXIST)
327                                         continue;
328                                 break;
329                         }
330                         /*
331                          * add_to_page_cache() locks the page, unlock it
332                          * to avoid convoluting the logic below even more.
333                          */
334                         unlock_page(page);
335                 }
336
337                 pages[spd.nr_pages++] = page;
338                 index++;
339         }
340
341         /*
342          * Now loop over the map and see if we need to start IO on any
343          * pages, fill in the partial map, etc.
344          */
345         index = *ppos >> PAGE_CACHE_SHIFT;
346         nr_pages = spd.nr_pages;
347         spd.nr_pages = 0;
348         for (page_nr = 0; page_nr < nr_pages; page_nr++) {
349                 unsigned int this_len;
350
351                 if (!len)
352                         break;
353
354                 /*
355                  * this_len is the max we'll use from this page
356                  */
357                 this_len = min_t(unsigned long, len, PAGE_CACHE_SIZE - loff);
358                 page = pages[page_nr];
359
360                 if (PageReadahead(page))
361                         page_cache_async_readahead(mapping, &in->f_ra, in,
362                                         page, index, req_pages - page_nr);
363
364                 /*
365                  * If the page isn't uptodate, we may need to start io on it
366                  */
367                 if (!PageUptodate(page)) {
368                         /*
369                          * If in nonblock mode then dont block on waiting
370                          * for an in-flight io page
371                          */
372                         if (flags & SPLICE_F_NONBLOCK) {
373                                 if (!trylock_page(page)) {
374                                         error = -EAGAIN;
375                                         break;
376                                 }
377                         } else
378                                 lock_page(page);
379
380                         /*
381                          * Page was truncated, or invalidated by the
382                          * filesystem.  Redo the find/create, but this time the
383                          * page is kept locked, so there's no chance of another
384                          * race with truncate/invalidate.
385                          */
386                         if (!page->mapping) {
387                                 unlock_page(page);
388                                 page = find_or_create_page(mapping, index,
389                                                 mapping_gfp_mask(mapping));
390
391                                 if (!page) {
392                                         error = -ENOMEM;
393                                         break;
394                                 }
395                                 page_cache_release(pages[page_nr]);
396                                 pages[page_nr] = page;
397                         }
398                         /*
399                          * page was already under io and is now done, great
400                          */
401                         if (PageUptodate(page)) {
402                                 unlock_page(page);
403                                 goto fill_it;
404                         }
405
406                         /*
407                          * need to read in the page
408                          */
409                         error = mapping->a_ops->readpage(in, page);
410                         if (unlikely(error)) {
411                                 /*
412                                  * We really should re-lookup the page here,
413                                  * but it complicates things a lot. Instead
414                                  * lets just do what we already stored, and
415                                  * we'll get it the next time we are called.
416                                  */
417                                 if (error == AOP_TRUNCATED_PAGE)
418                                         error = 0;
419
420                                 break;
421                         }
422                 }
423 fill_it:
424                 /*
425                  * i_size must be checked after PageUptodate.
426                  */
427                 isize = i_size_read(mapping->host);
428                 end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
429                 if (unlikely(!isize || index > end_index))
430                         break;
431
432                 /*
433                  * if this is the last page, see if we need to shrink
434                  * the length and stop
435                  */
436                 if (end_index == index) {
437                         unsigned int plen;
438
439                         /*
440                          * max good bytes in this page
441                          */
442                         plen = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
443                         if (plen <= loff)
444                                 break;
445
446                         /*
447                          * force quit after adding this page
448                          */
449                         this_len = min(this_len, plen - loff);
450                         len = this_len;
451                 }
452
453                 partial[page_nr].offset = loff;
454                 partial[page_nr].len = this_len;
455                 len -= this_len;
456                 loff = 0;
457                 spd.nr_pages++;
458                 index++;
459         }
460
461         /*
462          * Release any pages at the end, if we quit early. 'page_nr' is how far
463          * we got, 'nr_pages' is how many pages are in the map.
464          */
465         while (page_nr < nr_pages)
466                 page_cache_release(pages[page_nr++]);
467         in->f_ra.prev_pos = (loff_t)index << PAGE_CACHE_SHIFT;
468
469         if (spd.nr_pages)
470                 return splice_to_pipe(pipe, &spd);
471
472         return error;
473 }
474
475 /**
476  * generic_file_splice_read - splice data from file to a pipe
477  * @in:         file to splice from
478  * @ppos:       position in @in
479  * @pipe:       pipe to splice to
480  * @len:        number of bytes to splice
481  * @flags:      splice modifier flags
482  *
483  * Description:
484  *    Will read pages from given file and fill them into a pipe. Can be
485  *    used as long as the address_space operations for the source implements
486  *    a readpage() hook.
487  *
488  */
489 ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
490                                  struct pipe_inode_info *pipe, size_t len,
491                                  unsigned int flags)
492 {
493         loff_t isize, left;
494         int ret;
495
496         isize = i_size_read(in->f_mapping->host);
497         if (unlikely(*ppos >= isize))
498                 return 0;
499
500         left = isize - *ppos;
501         if (unlikely(left < len))
502                 len = left;
503
504         ret = __generic_file_splice_read(in, ppos, pipe, len, flags);
505         if (ret > 0)
506                 *ppos += ret;
507
508         return ret;
509 }
510
511 EXPORT_SYMBOL(generic_file_splice_read);
512
513 /*
514  * Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->pos'
515  * using sendpage(). Return the number of bytes sent.
516  */
517 static int pipe_to_sendpage(struct pipe_inode_info *pipe,
518                             struct pipe_buffer *buf, struct splice_desc *sd)
519 {
520         struct file *file = sd->u.file;
521         loff_t pos = sd->pos;
522         int ret, more;
523
524         ret = buf->ops->confirm(pipe, buf);
525         if (!ret) {
526                 more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len;
527
528                 ret = file->f_op->sendpage(file, buf->page, buf->offset,
529                                            sd->len, &pos, more);
530         }
531
532         return ret;
533 }
534
535 /*
536  * This is a little more tricky than the file -> pipe splicing. There are
537  * basically three cases:
538  *
539  *      - Destination page already exists in the address space and there
540  *        are users of it. For that case we have no other option that
541  *        copying the data. Tough luck.
542  *      - Destination page already exists in the address space, but there
543  *        are no users of it. Make sure it's uptodate, then drop it. Fall
544  *        through to last case.
545  *      - Destination page does not exist, we can add the pipe page to
546  *        the page cache and avoid the copy.
547  *
548  * If asked to move pages to the output file (SPLICE_F_MOVE is set in
549  * sd->flags), we attempt to migrate pages from the pipe to the output
550  * file address space page cache. This is possible if no one else has
551  * the pipe page referenced outside of the pipe and page cache. If
552  * SPLICE_F_MOVE isn't set, or we cannot move the page, we simply create
553  * a new page in the output file page cache and fill/dirty that.
554  */
555 int pipe_to_file(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
556                  struct splice_desc *sd)
557 {
558         struct file *file = sd->u.file;
559         struct address_space *mapping = file->f_mapping;
560         unsigned int offset, this_len;
561         struct page *page;
562         void *fsdata;
563         int ret;
564
565         /*
566          * make sure the data in this buffer is uptodate
567          */
568         ret = buf->ops->confirm(pipe, buf);
569         if (unlikely(ret))
570                 return ret;
571
572         offset = sd->pos & ~PAGE_CACHE_MASK;
573
574         this_len = sd->len;
575         if (this_len + offset > PAGE_CACHE_SIZE)
576                 this_len = PAGE_CACHE_SIZE - offset;
577
578         ret = pagecache_write_begin(file, mapping, sd->pos, this_len,
579                                 AOP_FLAG_UNINTERRUPTIBLE, &page, &fsdata);
580         if (unlikely(ret))
581                 goto out;
582
583         if (buf->page != page) {
584                 /*
585                  * Careful, ->map() uses KM_USER0!
586                  */
587                 char *src = buf->ops->map(pipe, buf, 1);
588                 char *dst = kmap_atomic(page, KM_USER1);
589
590                 memcpy(dst + offset, src + buf->offset, this_len);
591                 flush_dcache_page(page);
592                 kunmap_atomic(dst, KM_USER1);
593                 buf->ops->unmap(pipe, buf, src);
594         }
595         ret = pagecache_write_end(file, mapping, sd->pos, this_len, this_len,
596                                 page, fsdata);
597 out:
598         return ret;
599 }
600 EXPORT_SYMBOL(pipe_to_file);
601
602 static void wakeup_pipe_writers(struct pipe_inode_info *pipe)
603 {
604         smp_mb();
605         if (waitqueue_active(&pipe->wait))
606                 wake_up_interruptible(&pipe->wait);
607         kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
608 }
609
610 /**
611  * splice_from_pipe_feed - feed available data from a pipe to a file
612  * @pipe:       pipe to splice from
613  * @sd:         information to @actor
614  * @actor:      handler that splices the data
615  *
616  * Description:
617  *    This function loops over the pipe and calls @actor to do the
618  *    actual moving of a single struct pipe_buffer to the desired
619  *    destination.  It returns when there's no more buffers left in
620  *    the pipe or if the requested number of bytes (@sd->total_len)
621  *    have been copied.  It returns a positive number (one) if the
622  *    pipe needs to be filled with more data, zero if the required
623  *    number of bytes have been copied and -errno on error.
624  *
625  *    This, together with splice_from_pipe_{begin,end,next}, may be
626  *    used to implement the functionality of __splice_from_pipe() when
627  *    locking is required around copying the pipe buffers to the
628  *    destination.
629  */
630 int splice_from_pipe_feed(struct pipe_inode_info *pipe, struct splice_desc *sd,
631                           splice_actor *actor)
632 {
633         int ret;
634
635         while (pipe->nrbufs) {
636                 struct pipe_buffer *buf = pipe->bufs + pipe->curbuf;
637                 const struct pipe_buf_operations *ops = buf->ops;
638
639                 sd->len = buf->len;
640                 if (sd->len > sd->total_len)
641                         sd->len = sd->total_len;
642
643                 ret = actor(pipe, buf, sd);
644                 if (ret <= 0) {
645                         if (ret == -ENODATA)
646                                 ret = 0;
647                         return ret;
648                 }
649                 buf->offset += ret;
650                 buf->len -= ret;
651
652                 sd->num_spliced += ret;
653                 sd->len -= ret;
654                 sd->pos += ret;
655                 sd->total_len -= ret;
656
657                 if (!buf->len) {
658                         buf->ops = NULL;
659                         ops->release(pipe, buf);
660                         pipe->curbuf = (pipe->curbuf + 1) & (PIPE_BUFFERS - 1);
661                         pipe->nrbufs--;
662                         if (pipe->inode)
663                                 sd->need_wakeup = true;
664                 }
665
666                 if (!sd->total_len)
667                         return 0;
668         }
669
670         return 1;
671 }
672 EXPORT_SYMBOL(splice_from_pipe_feed);
673
674 /**
675  * splice_from_pipe_next - wait for some data to splice from
676  * @pipe:       pipe to splice from
677  * @sd:         information about the splice operation
678  *
679  * Description:
680  *    This function will wait for some data and return a positive
681  *    value (one) if pipe buffers are available.  It will return zero
682  *    or -errno if no more data needs to be spliced.
683  */
684 int splice_from_pipe_next(struct pipe_inode_info *pipe, struct splice_desc *sd)
685 {
686         while (!pipe->nrbufs) {
687                 if (!pipe->writers)
688                         return 0;
689
690                 if (!pipe->waiting_writers && sd->num_spliced)
691                         return 0;
692
693                 if (sd->flags & SPLICE_F_NONBLOCK)
694                         return -EAGAIN;
695
696                 if (signal_pending(current))
697                         return -ERESTARTSYS;
698
699                 if (sd->need_wakeup) {
700                         wakeup_pipe_writers(pipe);
701                         sd->need_wakeup = false;
702                 }
703
704                 pipe_wait(pipe);
705         }
706
707         return 1;
708 }
709 EXPORT_SYMBOL(splice_from_pipe_next);
710
711 /**
712  * splice_from_pipe_begin - start splicing from pipe
713  * @sd:         information about the splice operation
714  *
715  * Description:
716  *    This function should be called before a loop containing
717  *    splice_from_pipe_next() and splice_from_pipe_feed() to
718  *    initialize the necessary fields of @sd.
719  */
720 void splice_from_pipe_begin(struct splice_desc *sd)
721 {
722         sd->num_spliced = 0;
723         sd->need_wakeup = false;
724 }
725 EXPORT_SYMBOL(splice_from_pipe_begin);
726
727 /**
728  * splice_from_pipe_end - finish splicing from pipe
729  * @pipe:       pipe to splice from
730  * @sd:         information about the splice operation
731  *
732  * Description:
733  *    This function will wake up pipe writers if necessary.  It should
734  *    be called after a loop containing splice_from_pipe_next() and
735  *    splice_from_pipe_feed().
736  */
737 void splice_from_pipe_end(struct pipe_inode_info *pipe, struct splice_desc *sd)
738 {
739         if (sd->need_wakeup)
740                 wakeup_pipe_writers(pipe);
741 }
742 EXPORT_SYMBOL(splice_from_pipe_end);
743
744 /**
745  * __splice_from_pipe - splice data from a pipe to given actor
746  * @pipe:       pipe to splice from
747  * @sd:         information to @actor
748  * @actor:      handler that splices the data
749  *
750  * Description:
751  *    This function does little more than loop over the pipe and call
752  *    @actor to do the actual moving of a single struct pipe_buffer to
753  *    the desired destination. See pipe_to_file, pipe_to_sendpage, or
754  *    pipe_to_user.
755  *
756  */
757 ssize_t __splice_from_pipe(struct pipe_inode_info *pipe, struct splice_desc *sd,
758                            splice_actor *actor)
759 {
760         int ret;
761
762         splice_from_pipe_begin(sd);
763         do {
764                 ret = splice_from_pipe_next(pipe, sd);
765                 if (ret > 0)
766                         ret = splice_from_pipe_feed(pipe, sd, actor);
767         } while (ret > 0);
768         splice_from_pipe_end(pipe, sd);
769
770         return sd->num_spliced ? sd->num_spliced : ret;
771 }
772 EXPORT_SYMBOL(__splice_from_pipe);
773
774 /**
775  * splice_from_pipe - splice data from a pipe to a file
776  * @pipe:       pipe to splice from
777  * @out:        file to splice to
778  * @ppos:       position in @out
779  * @len:        how many bytes to splice
780  * @flags:      splice modifier flags
781  * @actor:      handler that splices the data
782  *
783  * Description:
784  *    See __splice_from_pipe. This function locks the pipe inode,
785  *    otherwise it's identical to __splice_from_pipe().
786  *
787  */
788 ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
789                          loff_t *ppos, size_t len, unsigned int flags,
790                          splice_actor *actor)
791 {
792         ssize_t ret;
793         struct splice_desc sd = {
794                 .total_len = len,
795                 .flags = flags,
796                 .pos = *ppos,
797                 .u.file = out,
798         };
799
800         pipe_lock(pipe);
801         ret = __splice_from_pipe(pipe, &sd, actor);
802         pipe_unlock(pipe);
803
804         return ret;
805 }
806
807 /**
808  * generic_file_splice_write - splice data from a pipe to a file
809  * @pipe:       pipe info
810  * @out:        file to write to
811  * @ppos:       position in @out
812  * @len:        number of bytes to splice
813  * @flags:      splice modifier flags
814  *
815  * Description:
816  *    Will either move or copy pages (determined by @flags options) from
817  *    the given pipe inode to the given file.
818  *
819  */
820 ssize_t
821 generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
822                           loff_t *ppos, size_t len, unsigned int flags)
823 {
824         struct address_space *mapping = out->f_mapping;
825         struct inode *inode = mapping->host;
826         struct splice_desc sd = {
827                 .total_len = len,
828                 .flags = flags,
829                 .pos = *ppos,
830                 .u.file = out,
831         };
832         ssize_t ret;
833
834         pipe_lock(pipe);
835
836         splice_from_pipe_begin(&sd);
837         do {
838                 ret = splice_from_pipe_next(pipe, &sd);
839                 if (ret <= 0)
840                         break;
841
842                 mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
843                 ret = file_remove_suid(out);
844                 if (!ret)
845                         ret = splice_from_pipe_feed(pipe, &sd, pipe_to_file);
846                 mutex_unlock(&inode->i_mutex);
847         } while (ret > 0);
848         splice_from_pipe_end(pipe, &sd);
849
850         pipe_unlock(pipe);
851
852         if (sd.num_spliced)
853                 ret = sd.num_spliced;
854
855         if (ret > 0) {
856                 unsigned long nr_pages;
857
858                 *ppos += ret;
859                 nr_pages = (ret + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
860
861                 /*
862                  * If file or inode is SYNC and we actually wrote some data,
863                  * sync it.
864                  */
865                 if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
866                         int err;
867
868                         mutex_lock(&inode->i_mutex);
869                         err = generic_osync_inode(inode, mapping,
870                                                   OSYNC_METADATA|OSYNC_DATA);
871                         mutex_unlock(&inode->i_mutex);
872
873                         if (err)
874                                 ret = err;
875                 }
876                 balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
877         }
878
879         return ret;
880 }
881
882 EXPORT_SYMBOL(generic_file_splice_write);
883
884 /**
885  * generic_splice_sendpage - splice data from a pipe to a socket
886  * @pipe:       pipe to splice from
887  * @out:        socket to write to
888  * @ppos:       position in @out
889  * @len:        number of bytes to splice
890  * @flags:      splice modifier flags
891  *
892  * Description:
893  *    Will send @len bytes from the pipe to a network socket. No data copying
894  *    is involved.
895  *
896  */
897 ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe, struct file *out,
898                                 loff_t *ppos, size_t len, unsigned int flags)
899 {
900         return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_sendpage);
901 }
902
903 EXPORT_SYMBOL(generic_splice_sendpage);
904
905 /*
906  * Attempt to initiate a splice from pipe to file.
907  */
908 static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
909                            loff_t *ppos, size_t len, unsigned int flags)
910 {
911         int ret;
912
913         if (unlikely(!out->f_op || !out->f_op->splice_write))
914                 return -EINVAL;
915
916         if (unlikely(!(out->f_mode & FMODE_WRITE)))
917                 return -EBADF;
918
919         if (unlikely(out->f_flags & O_APPEND))
920                 return -EINVAL;
921
922         ret = rw_verify_area(WRITE, out, ppos, len);
923         if (unlikely(ret < 0))
924                 return ret;
925
926         return out->f_op->splice_write(pipe, out, ppos, len, flags);
927 }
928
929 /*
930  * Attempt to initiate a splice from a file to a pipe.
931  */
932 static long do_splice_to(struct file *in, loff_t *ppos,
933                          struct pipe_inode_info *pipe, size_t len,
934                          unsigned int flags)
935 {
936         int ret;
937
938         if (unlikely(!in->f_op || !in->f_op->splice_read))
939                 return -EINVAL;
940
941         if (unlikely(!(in->f_mode & FMODE_READ)))
942                 return -EBADF;
943
944         ret = rw_verify_area(READ, in, ppos, len);
945         if (unlikely(ret < 0))
946                 return ret;
947
948         return in->f_op->splice_read(in, ppos, pipe, len, flags);
949 }
950
951 /**
952  * splice_direct_to_actor - splices data directly between two non-pipes
953  * @in:         file to splice from
954  * @sd:         actor information on where to splice to
955  * @actor:      handles the data splicing
956  *
957  * Description:
958  *    This is a special case helper to splice directly between two
959  *    points, without requiring an explicit pipe. Internally an allocated
960  *    pipe is cached in the process, and reused during the lifetime of
961  *    that process.
962  *
963  */
964 ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
965                                splice_direct_actor *actor)
966 {
967         struct pipe_inode_info *pipe;
968         long ret, bytes;
969         umode_t i_mode;
970         size_t len;
971         int i, flags;
972
973         /*
974          * We require the input being a regular file, as we don't want to
975          * randomly drop data for eg socket -> socket splicing. Use the
976          * piped splicing for that!
977          */
978         i_mode = in->f_path.dentry->d_inode->i_mode;
979         if (unlikely(!S_ISREG(i_mode) && !S_ISBLK(i_mode)))
980                 return -EINVAL;
981
982         /*
983          * neither in nor out is a pipe, setup an internal pipe attached to
984          * 'out' and transfer the wanted data from 'in' to 'out' through that
985          */
986         pipe = current->splice_pipe;
987         if (unlikely(!pipe)) {
988                 pipe = alloc_pipe_info(NULL);
989                 if (!pipe)
990                         return -ENOMEM;
991
992                 /*
993                  * We don't have an immediate reader, but we'll read the stuff
994                  * out of the pipe right after the splice_to_pipe(). So set
995                  * PIPE_READERS appropriately.
996                  */
997                 pipe->readers = 1;
998
999                 current->splice_pipe = pipe;
1000         }
1001
1002         /*
1003          * Do the splice.
1004          */
1005         ret = 0;
1006         bytes = 0;
1007         len = sd->total_len;
1008         flags = sd->flags;
1009
1010         /*
1011          * Don't block on output, we have to drain the direct pipe.
1012          */
1013         sd->flags &= ~SPLICE_F_NONBLOCK;
1014
1015         while (len) {
1016                 size_t read_len;
1017                 loff_t pos = sd->pos, prev_pos = pos;
1018
1019                 ret = do_splice_to(in, &pos, pipe, len, flags);
1020                 if (unlikely(ret <= 0))
1021                         goto out_release;
1022
1023                 read_len = ret;
1024                 sd->total_len = read_len;
1025
1026                 /*
1027                  * NOTE: nonblocking mode only applies to the input. We
1028                  * must not do the output in nonblocking mode as then we
1029                  * could get stuck data in the internal pipe:
1030                  */
1031                 ret = actor(pipe, sd);
1032                 if (unlikely(ret <= 0)) {
1033                         sd->pos = prev_pos;
1034                         goto out_release;
1035                 }
1036
1037                 bytes += ret;
1038                 len -= ret;
1039                 sd->pos = pos;
1040
1041                 if (ret < read_len) {
1042                         sd->pos = prev_pos + ret;
1043                         goto out_release;
1044                 }
1045         }
1046
1047 done:
1048         pipe->nrbufs = pipe->curbuf = 0;
1049         file_accessed(in);
1050         return bytes;
1051
1052 out_release:
1053         /*
1054          * If we did an incomplete transfer we must release
1055          * the pipe buffers in question:
1056          */
1057         for (i = 0; i < PIPE_BUFFERS; i++) {
1058                 struct pipe_buffer *buf = pipe->bufs + i;
1059
1060                 if (buf->ops) {
1061                         buf->ops->release(pipe, buf);
1062                         buf->ops = NULL;
1063                 }
1064         }
1065
1066         if (!bytes)
1067                 bytes = ret;
1068
1069         goto done;
1070 }
1071 EXPORT_SYMBOL(splice_direct_to_actor);
1072
1073 static int direct_splice_actor(struct pipe_inode_info *pipe,
1074                                struct splice_desc *sd)
1075 {
1076         struct file *file = sd->u.file;
1077
1078         return do_splice_from(pipe, file, &sd->pos, sd->total_len, sd->flags);
1079 }
1080
1081 /**
1082  * do_splice_direct - splices data directly between two files
1083  * @in:         file to splice from
1084  * @ppos:       input file offset
1085  * @out:        file to splice to
1086  * @len:        number of bytes to splice
1087  * @flags:      splice modifier flags
1088  *
1089  * Description:
1090  *    For use by do_sendfile(). splice can easily emulate sendfile, but
1091  *    doing it in the application would incur an extra system call
1092  *    (splice in + splice out, as compared to just sendfile()). So this helper
1093  *    can splice directly through a process-private pipe.
1094  *
1095  */
1096 long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
1097                       size_t len, unsigned int flags)
1098 {
1099         struct splice_desc sd = {
1100                 .len            = len,
1101                 .total_len      = len,
1102                 .flags          = flags,
1103                 .pos            = *ppos,
1104                 .u.file         = out,
1105         };
1106         long ret;
1107
1108         ret = splice_direct_to_actor(in, &sd, direct_splice_actor);
1109         if (ret > 0)
1110                 *ppos = sd.pos;
1111
1112         return ret;
1113 }
1114
1115 /*
1116  * After the inode slimming patch, i_pipe/i_bdev/i_cdev share the same
1117  * location, so checking ->i_pipe is not enough to verify that this is a
1118  * pipe.
1119  */
1120 static inline struct pipe_inode_info *pipe_info(struct inode *inode)
1121 {
1122         if (S_ISFIFO(inode->i_mode))
1123                 return inode->i_pipe;
1124
1125         return NULL;
1126 }
1127
1128 /*
1129  * Determine where to splice to/from.
1130  */
1131 static long do_splice(struct file *in, loff_t __user *off_in,
1132                       struct file *out, loff_t __user *off_out,
1133                       size_t len, unsigned int flags)
1134 {
1135         struct pipe_inode_info *pipe;
1136         loff_t offset, *off;
1137         long ret;
1138
1139         pipe = pipe_info(in->f_path.dentry->d_inode);
1140         if (pipe) {
1141                 if (off_in)
1142                         return -ESPIPE;
1143                 if (off_out) {
1144                         if (out->f_op->llseek == no_llseek)
1145                                 return -EINVAL;
1146                         if (copy_from_user(&offset, off_out, sizeof(loff_t)))
1147                                 return -EFAULT;
1148                         off = &offset;
1149                 } else
1150                         off = &out->f_pos;
1151
1152                 ret = do_splice_from(pipe, out, off, len, flags);
1153
1154                 if (off_out && copy_to_user(off_out, off, sizeof(loff_t)))
1155                         ret = -EFAULT;
1156
1157                 return ret;
1158         }
1159
1160         pipe = pipe_info(out->f_path.dentry->d_inode);
1161         if (pipe) {
1162                 if (off_out)
1163                         return -ESPIPE;
1164                 if (off_in) {
1165                         if (in->f_op->llseek == no_llseek)
1166                                 return -EINVAL;
1167                         if (copy_from_user(&offset, off_in, sizeof(loff_t)))
1168                                 return -EFAULT;
1169                         off = &offset;
1170                 } else
1171                         off = &in->f_pos;
1172
1173                 ret = do_splice_to(in, off, pipe, len, flags);
1174
1175                 if (off_in && copy_to_user(off_in, off, sizeof(loff_t)))
1176                         ret = -EFAULT;
1177
1178                 return ret;
1179         }
1180
1181         return -EINVAL;
1182 }
1183
1184 /*
1185  * Map an iov into an array of pages and offset/length tupples. With the
1186  * partial_page structure, we can map several non-contiguous ranges into
1187  * our ones pages[] map instead of splitting that operation into pieces.
1188  * Could easily be exported as a generic helper for other users, in which
1189  * case one would probably want to add a 'max_nr_pages' parameter as well.
1190  */
1191 static int get_iovec_page_array(const struct iovec __user *iov,
1192                                 unsigned int nr_vecs, struct page **pages,
1193                                 struct partial_page *partial, int aligned)
1194 {
1195         int buffers = 0, error = 0;
1196
1197         while (nr_vecs) {
1198                 unsigned long off, npages;
1199                 struct iovec entry;
1200                 void __user *base;
1201                 size_t len;
1202                 int i;
1203
1204                 error = -EFAULT;
1205                 if (copy_from_user(&entry, iov, sizeof(entry)))
1206                         break;
1207
1208                 base = entry.iov_base;
1209                 len = entry.iov_len;
1210
1211                 /*
1212                  * Sanity check this iovec. 0 read succeeds.
1213                  */
1214                 error = 0;
1215                 if (unlikely(!len))
1216                         break;
1217                 error = -EFAULT;
1218                 if (!access_ok(VERIFY_READ, base, len))
1219                         break;
1220
1221                 /*
1222                  * Get this base offset and number of pages, then map
1223                  * in the user pages.
1224                  */
1225                 off = (unsigned long) base & ~PAGE_MASK;
1226
1227                 /*
1228                  * If asked for alignment, the offset must be zero and the
1229                  * length a multiple of the PAGE_SIZE.
1230                  */
1231                 error = -EINVAL;
1232                 if (aligned && (off || len & ~PAGE_MASK))
1233                         break;
1234
1235                 npages = (off + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
1236                 if (npages > PIPE_BUFFERS - buffers)
1237                         npages = PIPE_BUFFERS - buffers;
1238
1239                 error = get_user_pages_fast((unsigned long)base, npages,
1240                                         0, &pages[buffers]);
1241
1242                 if (unlikely(error <= 0))
1243                         break;
1244
1245                 /*
1246                  * Fill this contiguous range into the partial page map.
1247                  */
1248                 for (i = 0; i < error; i++) {
1249                         const int plen = min_t(size_t, len, PAGE_SIZE - off);
1250
1251                         partial[buffers].offset = off;
1252                         partial[buffers].len = plen;
1253
1254                         off = 0;
1255                         len -= plen;
1256                         buffers++;
1257                 }
1258
1259                 /*
1260                  * We didn't complete this iov, stop here since it probably
1261                  * means we have to move some of this into a pipe to
1262                  * be able to continue.
1263                  */
1264                 if (len)
1265                         break;
1266
1267                 /*
1268                  * Don't continue if we mapped fewer pages than we asked for,
1269                  * or if we mapped the max number of pages that we have
1270                  * room for.
1271                  */
1272                 if (error < npages || buffers == PIPE_BUFFERS)
1273                         break;
1274
1275                 nr_vecs--;
1276                 iov++;
1277         }
1278
1279         if (buffers)
1280                 return buffers;
1281
1282         return error;
1283 }
1284
1285 static int pipe_to_user(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
1286                         struct splice_desc *sd)
1287 {
1288         char *src;
1289         int ret;
1290
1291         ret = buf->ops->confirm(pipe, buf);
1292         if (unlikely(ret))
1293                 return ret;
1294
1295         /*
1296          * See if we can use the atomic maps, by prefaulting in the
1297          * pages and doing an atomic copy
1298          */
1299         if (!fault_in_pages_writeable(sd->u.userptr, sd->len)) {
1300                 src = buf->ops->map(pipe, buf, 1);
1301                 ret = __copy_to_user_inatomic(sd->u.userptr, src + buf->offset,
1302                                                         sd->len);
1303                 buf->ops->unmap(pipe, buf, src);
1304                 if (!ret) {
1305                         ret = sd->len;
1306                         goto out;
1307                 }
1308         }
1309
1310         /*
1311          * No dice, use slow non-atomic map and copy
1312          */
1313         src = buf->ops->map(pipe, buf, 0);
1314
1315         ret = sd->len;
1316         if (copy_to_user(sd->u.userptr, src + buf->offset, sd->len))
1317                 ret = -EFAULT;
1318
1319         buf->ops->unmap(pipe, buf, src);
1320 out:
1321         if (ret > 0)
1322                 sd->u.userptr += ret;
1323         return ret;
1324 }
1325
1326 /*
1327  * For lack of a better implementation, implement vmsplice() to userspace
1328  * as a simple copy of the pipes pages to the user iov.
1329  */
1330 static long vmsplice_to_user(struct file *file, const struct iovec __user *iov,
1331                              unsigned long nr_segs, unsigned int flags)
1332 {
1333         struct pipe_inode_info *pipe;
1334         struct splice_desc sd;
1335         ssize_t size;
1336         int error;
1337         long ret;
1338
1339         pipe = pipe_info(file->f_path.dentry->d_inode);
1340         if (!pipe)
1341                 return -EBADF;
1342
1343         pipe_lock(pipe);
1344
1345         error = ret = 0;
1346         while (nr_segs) {
1347                 void __user *base;
1348                 size_t len;
1349
1350                 /*
1351                  * Get user address base and length for this iovec.
1352                  */
1353                 error = get_user(base, &iov->iov_base);
1354                 if (unlikely(error))
1355                         break;
1356                 error = get_user(len, &iov->iov_len);
1357                 if (unlikely(error))
1358                         break;
1359
1360                 /*
1361                  * Sanity check this iovec. 0 read succeeds.
1362                  */
1363                 if (unlikely(!len))
1364                         break;
1365                 if (unlikely(!base)) {
1366                         error = -EFAULT;
1367                         break;
1368                 }
1369
1370                 if (unlikely(!access_ok(VERIFY_WRITE, base, len))) {
1371                         error = -EFAULT;
1372                         break;
1373                 }
1374
1375                 sd.len = 0;
1376                 sd.total_len = len;
1377                 sd.flags = flags;
1378                 sd.u.userptr = base;
1379                 sd.pos = 0;
1380
1381                 size = __splice_from_pipe(pipe, &sd, pipe_to_user);
1382                 if (size < 0) {
1383                         if (!ret)
1384                                 ret = size;
1385
1386                         break;
1387                 }
1388
1389                 ret += size;
1390
1391                 if (size < len)
1392                         break;
1393
1394                 nr_segs--;
1395                 iov++;
1396         }
1397
1398         pipe_unlock(pipe);
1399
1400         if (!ret)
1401                 ret = error;
1402
1403         return ret;
1404 }
1405
1406 /*
1407  * vmsplice splices a user address range into a pipe. It can be thought of
1408  * as splice-from-memory, where the regular splice is splice-from-file (or
1409  * to file). In both cases the output is a pipe, naturally.
1410  */
1411 static long vmsplice_to_pipe(struct file *file, const struct iovec __user *iov,
1412                              unsigned long nr_segs, unsigned int flags)
1413 {
1414         struct pipe_inode_info *pipe;
1415         struct page *pages[PIPE_BUFFERS];
1416         struct partial_page partial[PIPE_BUFFERS];
1417         struct splice_pipe_desc spd = {
1418                 .pages = pages,
1419                 .partial = partial,
1420                 .flags = flags,
1421                 .ops = &user_page_pipe_buf_ops,
1422                 .spd_release = spd_release_page,
1423         };
1424
1425         pipe = pipe_info(file->f_path.dentry->d_inode);
1426         if (!pipe)
1427                 return -EBADF;
1428
1429         spd.nr_pages = get_iovec_page_array(iov, nr_segs, pages, partial,
1430                                             flags & SPLICE_F_GIFT);
1431         if (spd.nr_pages <= 0)
1432                 return spd.nr_pages;
1433
1434         return splice_to_pipe(pipe, &spd);
1435 }
1436
1437 /*
1438  * Note that vmsplice only really supports true splicing _from_ user memory
1439  * to a pipe, not the other way around. Splicing from user memory is a simple
1440  * operation that can be supported without any funky alignment restrictions
1441  * or nasty vm tricks. We simply map in the user memory and fill them into
1442  * a pipe. The reverse isn't quite as easy, though. There are two possible
1443  * solutions for that:
1444  *
1445  *      - memcpy() the data internally, at which point we might as well just
1446  *        do a regular read() on the buffer anyway.
1447  *      - Lots of nasty vm tricks, that are neither fast nor flexible (it
1448  *        has restriction limitations on both ends of the pipe).
1449  *
1450  * Currently we punt and implement it as a normal copy, see pipe_to_user().
1451  *
1452  */
1453 SYSCALL_DEFINE4(vmsplice, int, fd, const struct iovec __user *, iov,
1454                 unsigned long, nr_segs, unsigned int, flags)
1455 {
1456         struct file *file;
1457         long error;
1458         int fput;
1459
1460         if (unlikely(nr_segs > UIO_MAXIOV))
1461                 return -EINVAL;
1462         else if (unlikely(!nr_segs))
1463                 return 0;
1464
1465         error = -EBADF;
1466         file = fget_light(fd, &fput);
1467         if (file) {
1468                 if (file->f_mode & FMODE_WRITE)
1469                         error = vmsplice_to_pipe(file, iov, nr_segs, flags);
1470                 else if (file->f_mode & FMODE_READ)
1471                         error = vmsplice_to_user(file, iov, nr_segs, flags);
1472
1473                 fput_light(file, fput);
1474         }
1475
1476         return error;
1477 }
1478
1479 SYSCALL_DEFINE6(splice, int, fd_in, loff_t __user *, off_in,
1480                 int, fd_out, loff_t __user *, off_out,
1481                 size_t, len, unsigned int, flags)
1482 {
1483         long error;
1484         struct file *in, *out;
1485         int fput_in, fput_out;
1486
1487         if (unlikely(!len))
1488                 return 0;
1489
1490         error = -EBADF;
1491         in = fget_light(fd_in, &fput_in);
1492         if (in) {
1493                 if (in->f_mode & FMODE_READ) {
1494                         out = fget_light(fd_out, &fput_out);
1495                         if (out) {
1496                                 if (out->f_mode & FMODE_WRITE)
1497                                         error = do_splice(in, off_in,
1498                                                           out, off_out,
1499                                                           len, flags);
1500                                 fput_light(out, fput_out);
1501                         }
1502                 }
1503
1504                 fput_light(in, fput_in);
1505         }
1506
1507         return error;
1508 }
1509
1510 /*
1511  * Make sure there's data to read. Wait for input if we can, otherwise
1512  * return an appropriate error.
1513  */
1514 static int link_ipipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
1515 {
1516         int ret;
1517
1518         /*
1519          * Check ->nrbufs without the inode lock first. This function
1520          * is speculative anyways, so missing one is ok.
1521          */
1522         if (pipe->nrbufs)
1523                 return 0;
1524
1525         ret = 0;
1526         pipe_lock(pipe);
1527
1528         while (!pipe->nrbufs) {
1529                 if (signal_pending(current)) {
1530                         ret = -ERESTARTSYS;
1531                         break;
1532                 }
1533                 if (!pipe->writers)
1534                         break;
1535                 if (!pipe->waiting_writers) {
1536                         if (flags & SPLICE_F_NONBLOCK) {
1537                                 ret = -EAGAIN;
1538                                 break;
1539                         }
1540                 }
1541                 pipe_wait(pipe);
1542         }
1543
1544         pipe_unlock(pipe);
1545         return ret;
1546 }
1547
1548 /*
1549  * Make sure there's writeable room. Wait for room if we can, otherwise
1550  * return an appropriate error.
1551  */
1552 static int link_opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
1553 {
1554         int ret;
1555
1556         /*
1557          * Check ->nrbufs without the inode lock first. This function
1558          * is speculative anyways, so missing one is ok.
1559          */
1560         if (pipe->nrbufs < PIPE_BUFFERS)
1561                 return 0;
1562
1563         ret = 0;
1564         pipe_lock(pipe);
1565
1566         while (pipe->nrbufs >= PIPE_BUFFERS) {
1567                 if (!pipe->readers) {
1568                         send_sig(SIGPIPE, current, 0);
1569                         ret = -EPIPE;
1570                         break;
1571                 }
1572                 if (flags & SPLICE_F_NONBLOCK) {
1573                         ret = -EAGAIN;
1574                         break;
1575                 }
1576                 if (signal_pending(current)) {
1577                         ret = -ERESTARTSYS;
1578                         break;
1579                 }
1580                 pipe->waiting_writers++;
1581                 pipe_wait(pipe);
1582                 pipe->waiting_writers--;
1583         }
1584
1585         pipe_unlock(pipe);
1586         return ret;
1587 }
1588
1589 /*
1590  * Link contents of ipipe to opipe.
1591  */
1592 static int link_pipe(struct pipe_inode_info *ipipe,
1593                      struct pipe_inode_info *opipe,
1594                      size_t len, unsigned int flags)
1595 {
1596         struct pipe_buffer *ibuf, *obuf;
1597         int ret = 0, i = 0, nbuf;
1598
1599         /*
1600          * Potential ABBA deadlock, work around it by ordering lock
1601          * grabbing by pipe info address. Otherwise two different processes
1602          * could deadlock (one doing tee from A -> B, the other from B -> A).
1603          */
1604         pipe_double_lock(ipipe, opipe);
1605
1606         do {
1607                 if (!opipe->readers) {
1608                         send_sig(SIGPIPE, current, 0);
1609                         if (!ret)
1610                                 ret = -EPIPE;
1611                         break;
1612                 }
1613
1614                 /*
1615                  * If we have iterated all input buffers or ran out of
1616                  * output room, break.
1617                  */
1618                 if (i >= ipipe->nrbufs || opipe->nrbufs >= PIPE_BUFFERS)
1619                         break;
1620
1621                 ibuf = ipipe->bufs + ((ipipe->curbuf + i) & (PIPE_BUFFERS - 1));
1622                 nbuf = (opipe->curbuf + opipe->nrbufs) & (PIPE_BUFFERS - 1);
1623
1624                 /*
1625                  * Get a reference to this pipe buffer,
1626                  * so we can copy the contents over.
1627                  */
1628                 ibuf->ops->get(ipipe, ibuf);
1629
1630                 obuf = opipe->bufs + nbuf;
1631                 *obuf = *ibuf;
1632
1633                 /*
1634                  * Don't inherit the gift flag, we need to
1635                  * prevent multiple steals of this page.
1636                  */
1637                 obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
1638
1639                 if (obuf->len > len)
1640                         obuf->len = len;
1641
1642                 opipe->nrbufs++;
1643                 ret += obuf->len;
1644                 len -= obuf->len;
1645                 i++;
1646         } while (len);
1647
1648         /*
1649          * return EAGAIN if we have the potential of some data in the
1650          * future, otherwise just return 0
1651          */
1652         if (!ret && ipipe->waiting_writers && (flags & SPLICE_F_NONBLOCK))
1653                 ret = -EAGAIN;
1654
1655         pipe_unlock(ipipe);
1656         pipe_unlock(opipe);
1657
1658         /*
1659          * If we put data in the output pipe, wakeup any potential readers.
1660          */
1661         if (ret > 0) {
1662                 smp_mb();
1663                 if (waitqueue_active(&opipe->wait))
1664                         wake_up_interruptible(&opipe->wait);
1665                 kill_fasync(&opipe->fasync_readers, SIGIO, POLL_IN);
1666         }
1667
1668         return ret;
1669 }
1670
1671 /*
1672  * This is a tee(1) implementation that works on pipes. It doesn't copy
1673  * any data, it simply references the 'in' pages on the 'out' pipe.
1674  * The 'flags' used are the SPLICE_F_* variants, currently the only
1675  * applicable one is SPLICE_F_NONBLOCK.
1676  */
1677 static long do_tee(struct file *in, struct file *out, size_t len,
1678                    unsigned int flags)
1679 {
1680         struct pipe_inode_info *ipipe = pipe_info(in->f_path.dentry->d_inode);
1681         struct pipe_inode_info *opipe = pipe_info(out->f_path.dentry->d_inode);
1682         int ret = -EINVAL;
1683
1684         /*
1685          * Duplicate the contents of ipipe to opipe without actually
1686          * copying the data.
1687          */
1688         if (ipipe && opipe && ipipe != opipe) {
1689                 /*
1690                  * Keep going, unless we encounter an error. The ipipe/opipe
1691                  * ordering doesn't really matter.
1692                  */
1693                 ret = link_ipipe_prep(ipipe, flags);
1694                 if (!ret) {
1695                         ret = link_opipe_prep(opipe, flags);
1696                         if (!ret)
1697                                 ret = link_pipe(ipipe, opipe, len, flags);
1698                 }
1699         }
1700
1701         return ret;
1702 }
1703
1704 SYSCALL_DEFINE4(tee, int, fdin, int, fdout, size_t, len, unsigned int, flags)
1705 {
1706         struct file *in;
1707         int error, fput_in;
1708
1709         if (unlikely(!len))
1710                 return 0;
1711
1712         error = -EBADF;
1713         in = fget_light(fdin, &fput_in);
1714         if (in) {
1715                 if (in->f_mode & FMODE_READ) {
1716                         int fput_out;
1717                         struct file *out = fget_light(fdout, &fput_out);
1718
1719                         if (out) {
1720                                 if (out->f_mode & FMODE_WRITE)
1721                                         error = do_tee(in, out, len, flags);
1722                                 fput_light(out, fput_out);
1723                         }
1724                 }
1725                 fput_light(in, fput_in);
1726         }
1727
1728         return error;
1729 }