[PATCH] splice(): fix interaction with readahead
[linux-2.6.git] / 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/pipe_fs_i.h>
24 #include <linux/mm_inline.h>
25 #include <linux/swap.h>
26 #include <linux/writeback.h>
27 #include <linux/buffer_head.h>
28 #include <linux/module.h>
29 #include <linux/syscalls.h>
30 #include <linux/uio.h>
31
32 struct partial_page {
33         unsigned int offset;
34         unsigned int len;
35 };
36
37 /*
38  * Passed to splice_to_pipe
39  */
40 struct splice_pipe_desc {
41         struct page **pages;            /* page map */
42         struct partial_page *partial;   /* pages[] may not be contig */
43         int nr_pages;                   /* number of pages in map */
44         unsigned int flags;             /* splice flags */
45         const struct pipe_buf_operations *ops;/* ops associated with output pipe */
46 };
47
48 /*
49  * Attempt to steal a page from a pipe buffer. This should perhaps go into
50  * a vm helper function, it's already simplified quite a bit by the
51  * addition of remove_mapping(). If success is returned, the caller may
52  * attempt to reuse this page for another destination.
53  */
54 static int page_cache_pipe_buf_steal(struct pipe_inode_info *pipe,
55                                      struct pipe_buffer *buf)
56 {
57         struct page *page = buf->page;
58         struct address_space *mapping;
59
60         lock_page(page);
61
62         mapping = page_mapping(page);
63         if (mapping) {
64                 WARN_ON(!PageUptodate(page));
65
66                 /*
67                  * At least for ext2 with nobh option, we need to wait on
68                  * writeback completing on this page, since we'll remove it
69                  * from the pagecache.  Otherwise truncate wont wait on the
70                  * page, allowing the disk blocks to be reused by someone else
71                  * before we actually wrote our data to them. fs corruption
72                  * ensues.
73                  */
74                 wait_on_page_writeback(page);
75
76                 if (PagePrivate(page))
77                         try_to_release_page(page, GFP_KERNEL);
78
79                 /*
80                  * If we succeeded in removing the mapping, set LRU flag
81                  * and return good.
82                  */
83                 if (remove_mapping(mapping, page)) {
84                         buf->flags |= PIPE_BUF_FLAG_LRU;
85                         return 0;
86                 }
87         }
88
89         /*
90          * Raced with truncate or failed to remove page from current
91          * address space, unlock and return failure.
92          */
93         unlock_page(page);
94         return 1;
95 }
96
97 static void page_cache_pipe_buf_release(struct pipe_inode_info *pipe,
98                                         struct pipe_buffer *buf)
99 {
100         page_cache_release(buf->page);
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                 lock_page(page);
112
113                 /*
114                  * Page got truncated/unhashed. This will cause a 0-byte
115                  * splice, if this is the first page.
116                  */
117                 if (!page->mapping) {
118                         err = -ENODATA;
119                         goto error;
120                 }
121
122                 /*
123                  * Uh oh, read-error from disk.
124                  */
125                 if (!PageUptodate(page)) {
126                         err = -EIO;
127                         goto error;
128                 }
129
130                 /*
131                  * Page is ok afterall, we are done.
132                  */
133                 unlock_page(page);
134         }
135
136         return 0;
137 error:
138         unlock_page(page);
139         return err;
140 }
141
142 static const struct pipe_buf_operations page_cache_pipe_buf_ops = {
143         .can_merge = 0,
144         .map = generic_pipe_buf_map,
145         .unmap = generic_pipe_buf_unmap,
146         .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 static int user_page_pipe_buf_steal(struct pipe_inode_info *pipe,
153                                     struct pipe_buffer *buf)
154 {
155         if (!(buf->flags & PIPE_BUF_FLAG_GIFT))
156                 return 1;
157
158         buf->flags |= PIPE_BUF_FLAG_LRU;
159         return generic_pipe_buf_steal(pipe, buf);
160 }
161
162 static const struct pipe_buf_operations user_page_pipe_buf_ops = {
163         .can_merge = 0,
164         .map = generic_pipe_buf_map,
165         .unmap = generic_pipe_buf_unmap,
166         .pin = generic_pipe_buf_pin,
167         .release = page_cache_pipe_buf_release,
168         .steal = user_page_pipe_buf_steal,
169         .get = generic_pipe_buf_get,
170 };
171
172 /*
173  * Pipe output worker. This sets up our pipe format with the page cache
174  * pipe buffer operations. Otherwise very similar to the regular pipe_writev().
175  */
176 static ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
177                               struct splice_pipe_desc *spd)
178 {
179         int ret, do_wakeup, page_nr;
180
181         ret = 0;
182         do_wakeup = 0;
183         page_nr = 0;
184
185         if (pipe->inode)
186                 mutex_lock(&pipe->inode->i_mutex);
187
188         for (;;) {
189                 if (!pipe->readers) {
190                         send_sig(SIGPIPE, current, 0);
191                         if (!ret)
192                                 ret = -EPIPE;
193                         break;
194                 }
195
196                 if (pipe->nrbufs < PIPE_BUFFERS) {
197                         int newbuf = (pipe->curbuf + pipe->nrbufs) & (PIPE_BUFFERS - 1);
198                         struct pipe_buffer *buf = pipe->bufs + newbuf;
199
200                         buf->page = spd->pages[page_nr];
201                         buf->offset = spd->partial[page_nr].offset;
202                         buf->len = spd->partial[page_nr].len;
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         if (pipe->inode)
248                 mutex_unlock(&pipe->inode->i_mutex);
249
250         if (do_wakeup) {
251                 smp_mb();
252                 if (waitqueue_active(&pipe->wait))
253                         wake_up_interruptible(&pipe->wait);
254                 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
255         }
256
257         while (page_nr < spd->nr_pages)
258                 page_cache_release(spd->pages[page_nr++]);
259
260         return ret;
261 }
262
263 static int
264 __generic_file_splice_read(struct file *in, loff_t *ppos,
265                            struct pipe_inode_info *pipe, size_t len,
266                            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         pgoff_t index, end_index;
274         loff_t isize;
275         size_t total_len;
276         int error, page_nr;
277         struct splice_pipe_desc spd = {
278                 .pages = pages,
279                 .partial = partial,
280                 .flags = flags,
281                 .ops = &page_cache_pipe_buf_ops,
282         };
283
284         index = *ppos >> PAGE_CACHE_SHIFT;
285         loff = *ppos & ~PAGE_CACHE_MASK;
286         nr_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
287
288         if (nr_pages > PIPE_BUFFERS)
289                 nr_pages = PIPE_BUFFERS;
290
291         /*
292          * Initiate read-ahead on this page range. however, don't call into
293          * read-ahead if this is a non-zero offset (we are likely doing small
294          * chunk splice and the page is already there) for a single page.
295          */
296         if (!loff || nr_pages > 1)
297                 page_cache_readahead(mapping, &in->f_ra, in, index, nr_pages);
298
299         /*
300          * Now fill in the holes:
301          */
302         error = 0;
303         total_len = 0;
304
305         /*
306          * Lookup the (hopefully) full range of pages we need.
307          */
308         spd.nr_pages = find_get_pages_contig(mapping, index, nr_pages, pages);
309
310         /*
311          * If find_get_pages_contig() returned fewer pages than we needed,
312          * allocate the rest.
313          */
314         index += spd.nr_pages;
315         while (spd.nr_pages < nr_pages) {
316                 /*
317                  * Page could be there, find_get_pages_contig() breaks on
318                  * the first hole.
319                  */
320                 page = find_get_page(mapping, index);
321                 if (!page) {
322                         /*
323                          * Make sure the read-ahead engine is notified
324                          * about this failure.
325                          */
326                         handle_ra_miss(mapping, &in->f_ra, index);
327
328                         /*
329                          * page didn't exist, allocate one.
330                          */
331                         page = page_cache_alloc_cold(mapping);
332                         if (!page)
333                                 break;
334
335                         error = add_to_page_cache_lru(page, mapping, index,
336                                               GFP_KERNEL);
337                         if (unlikely(error)) {
338                                 page_cache_release(page);
339                                 if (error == -EEXIST)
340                                         continue;
341                                 break;
342                         }
343                         /*
344                          * add_to_page_cache() locks the page, unlock it
345                          * to avoid convoluting the logic below even more.
346                          */
347                         unlock_page(page);
348                 }
349
350                 pages[spd.nr_pages++] = page;
351                 index++;
352         }
353
354         /*
355          * Now loop over the map and see if we need to start IO on any
356          * pages, fill in the partial map, etc.
357          */
358         index = *ppos >> PAGE_CACHE_SHIFT;
359         nr_pages = spd.nr_pages;
360         spd.nr_pages = 0;
361         for (page_nr = 0; page_nr < nr_pages; page_nr++) {
362                 unsigned int this_len;
363
364                 if (!len)
365                         break;
366
367                 /*
368                  * this_len is the max we'll use from this page
369                  */
370                 this_len = min_t(unsigned long, len, PAGE_CACHE_SIZE - loff);
371                 page = pages[page_nr];
372
373                 /*
374                  * If the page isn't uptodate, we may need to start io on it
375                  */
376                 if (!PageUptodate(page)) {
377                         /*
378                          * If in nonblock mode then dont block on waiting
379                          * for an in-flight io page
380                          */
381                         if (flags & SPLICE_F_NONBLOCK) {
382                                 if (TestSetPageLocked(page))
383                                         break;
384                         } else
385                                 lock_page(page);
386
387                         /*
388                          * page was truncated, stop here. if this isn't the
389                          * first page, we'll just complete what we already
390                          * added
391                          */
392                         if (!page->mapping) {
393                                 unlock_page(page);
394                                 break;
395                         }
396                         /*
397                          * page was already under io and is now done, great
398                          */
399                         if (PageUptodate(page)) {
400                                 unlock_page(page);
401                                 goto fill_it;
402                         }
403
404                         /*
405                          * need to read in the page
406                          */
407                         error = mapping->a_ops->readpage(in, page);
408                         if (unlikely(error)) {
409                                 /*
410                                  * We really should re-lookup the page here,
411                                  * but it complicates things a lot. Instead
412                                  * lets just do what we already stored, and
413                                  * we'll get it the next time we are called.
414                                  */
415                                 if (error == AOP_TRUNCATED_PAGE)
416                                         error = 0;
417
418                                 break;
419                         }
420
421                         /*
422                          * i_size must be checked after ->readpage().
423                          */
424                         isize = i_size_read(mapping->host);
425                         end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
426                         if (unlikely(!isize || index > end_index))
427                                 break;
428
429                         /*
430                          * if this is the last page, see if we need to shrink
431                          * the length and stop
432                          */
433                         if (end_index == index) {
434                                 loff = PAGE_CACHE_SIZE - (isize & ~PAGE_CACHE_MASK);
435                                 if (total_len + loff > isize)
436                                         break;
437                                 /*
438                                  * force quit after adding this page
439                                  */
440                                 len = this_len;
441                                 this_len = min(this_len, loff);
442                                 loff = 0;
443                         }
444                 }
445 fill_it:
446                 partial[page_nr].offset = loff;
447                 partial[page_nr].len = this_len;
448                 len -= this_len;
449                 total_len += this_len;
450                 loff = 0;
451                 spd.nr_pages++;
452                 index++;
453         }
454
455         /*
456          * Release any pages at the end, if we quit early. 'i' is how far
457          * we got, 'nr_pages' is how many pages are in the map.
458          */
459         while (page_nr < nr_pages)
460                 page_cache_release(pages[page_nr++]);
461
462         if (spd.nr_pages)
463                 return splice_to_pipe(pipe, &spd);
464
465         return error;
466 }
467
468 /**
469  * generic_file_splice_read - splice data from file to a pipe
470  * @in:         file to splice from
471  * @pipe:       pipe to splice to
472  * @len:        number of bytes to splice
473  * @flags:      splice modifier flags
474  *
475  * Will read pages from given file and fill them into a pipe.
476  */
477 ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
478                                  struct pipe_inode_info *pipe, size_t len,
479                                  unsigned int flags)
480 {
481         ssize_t spliced;
482         int ret;
483
484         ret = 0;
485         spliced = 0;
486
487         while (len) {
488                 ret = __generic_file_splice_read(in, ppos, pipe, len, flags);
489
490                 if (ret < 0)
491                         break;
492                 else if (!ret) {
493                         if (spliced)
494                                 break;
495                         if (flags & SPLICE_F_NONBLOCK) {
496                                 ret = -EAGAIN;
497                                 break;
498                         }
499                 }
500
501                 *ppos += ret;
502                 len -= ret;
503                 spliced += ret;
504         }
505
506         if (spliced)
507                 return spliced;
508
509         return ret;
510 }
511
512 EXPORT_SYMBOL(generic_file_splice_read);
513
514 /*
515  * Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->pos'
516  * using sendpage(). Return the number of bytes sent.
517  */
518 static int pipe_to_sendpage(struct pipe_inode_info *pipe,
519                             struct pipe_buffer *buf, struct splice_desc *sd)
520 {
521         struct file *file = sd->file;
522         loff_t pos = sd->pos;
523         int ret, more;
524
525         ret = buf->ops->pin(pipe, buf);
526         if (!ret) {
527                 more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len;
528
529                 ret = file->f_op->sendpage(file, buf->page, buf->offset,
530                                            sd->len, &pos, more);
531         }
532
533         return ret;
534 }
535
536 /*
537  * This is a little more tricky than the file -> pipe splicing. There are
538  * basically three cases:
539  *
540  *      - Destination page already exists in the address space and there
541  *        are users of it. For that case we have no other option that
542  *        copying the data. Tough luck.
543  *      - Destination page already exists in the address space, but there
544  *        are no users of it. Make sure it's uptodate, then drop it. Fall
545  *        through to last case.
546  *      - Destination page does not exist, we can add the pipe page to
547  *        the page cache and avoid the copy.
548  *
549  * If asked to move pages to the output file (SPLICE_F_MOVE is set in
550  * sd->flags), we attempt to migrate pages from the pipe to the output
551  * file address space page cache. This is possible if no one else has
552  * the pipe page referenced outside of the pipe and page cache. If
553  * SPLICE_F_MOVE isn't set, or we cannot move the page, we simply create
554  * a new page in the output file page cache and fill/dirty that.
555  */
556 static int pipe_to_file(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
557                         struct splice_desc *sd)
558 {
559         struct file *file = sd->file;
560         struct address_space *mapping = file->f_mapping;
561         unsigned int offset, this_len;
562         struct page *page;
563         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         if (unlikely(ret))
571                 return ret;
572
573         index = sd->pos >> PAGE_CACHE_SHIFT;
574         offset = sd->pos & ~PAGE_CACHE_MASK;
575
576         this_len = sd->len;
577         if (this_len + offset > PAGE_CACHE_SIZE)
578                 this_len = PAGE_CACHE_SIZE - offset;
579
580 find_page:
581         page = find_lock_page(mapping, index);
582         if (!page) {
583                 ret = -ENOMEM;
584                 page = page_cache_alloc_cold(mapping);
585                 if (unlikely(!page))
586                         goto out_ret;
587
588                 /*
589                  * This will also lock the page
590                  */
591                 ret = add_to_page_cache_lru(page, mapping, index,
592                                             GFP_KERNEL);
593                 if (unlikely(ret))
594                         goto out;
595         }
596
597         ret = mapping->a_ops->prepare_write(file, page, offset, offset+this_len);
598         if (unlikely(ret)) {
599                 loff_t isize = i_size_read(mapping->host);
600
601                 if (ret != AOP_TRUNCATED_PAGE)
602                         unlock_page(page);
603                 page_cache_release(page);
604                 if (ret == AOP_TRUNCATED_PAGE)
605                         goto find_page;
606
607                 /*
608                  * prepare_write() may have instantiated a few blocks
609                  * outside i_size.  Trim these off again.
610                  */
611                 if (sd->pos + this_len > isize)
612                         vmtruncate(mapping->host, isize);
613
614                 goto out_ret;
615         }
616
617         if (buf->page != page) {
618                 /*
619                  * Careful, ->map() uses KM_USER0!
620                  */
621                 char *src = buf->ops->map(pipe, buf, 1);
622                 char *dst = kmap_atomic(page, KM_USER1);
623
624                 memcpy(dst + offset, src + buf->offset, this_len);
625                 flush_dcache_page(page);
626                 kunmap_atomic(dst, KM_USER1);
627                 buf->ops->unmap(pipe, buf, src);
628         }
629
630         ret = mapping->a_ops->commit_write(file, page, offset, offset+this_len);
631         if (ret) {
632                 if (ret == AOP_TRUNCATED_PAGE) {
633                         page_cache_release(page);
634                         goto find_page;
635                 }
636                 if (ret < 0)
637                         goto out;
638                 /*
639                  * Partial write has happened, so 'ret' already initialized by
640                  * number of bytes written, Where is nothing we have to do here.
641                  */
642         } else
643                 ret = this_len;
644         /*
645          * Return the number of bytes written and mark page as
646          * accessed, we are now done!
647          */
648         mark_page_accessed(page);
649         balance_dirty_pages_ratelimited(mapping);
650 out:
651         page_cache_release(page);
652         unlock_page(page);
653 out_ret:
654         return ret;
655 }
656
657 /*
658  * Pipe input worker. Most of this logic works like a regular pipe, the
659  * key here is the 'actor' worker passed in that actually moves the data
660  * to the wanted destination. See pipe_to_file/pipe_to_sendpage above.
661  */
662 ssize_t __splice_from_pipe(struct pipe_inode_info *pipe,
663                            struct file *out, loff_t *ppos, size_t len,
664                            unsigned int flags, splice_actor *actor)
665 {
666         int ret, do_wakeup, err;
667         struct splice_desc sd;
668
669         ret = 0;
670         do_wakeup = 0;
671
672         sd.total_len = len;
673         sd.flags = flags;
674         sd.file = out;
675         sd.pos = *ppos;
676
677         for (;;) {
678                 if (pipe->nrbufs) {
679                         struct pipe_buffer *buf = pipe->bufs + pipe->curbuf;
680                         const struct pipe_buf_operations *ops = buf->ops;
681
682                         sd.len = buf->len;
683                         if (sd.len > sd.total_len)
684                                 sd.len = sd.total_len;
685
686                         err = actor(pipe, buf, &sd);
687                         if (err <= 0) {
688                                 if (!ret && err != -ENODATA)
689                                         ret = err;
690
691                                 break;
692                         }
693
694                         ret += err;
695                         buf->offset += err;
696                         buf->len -= err;
697
698                         sd.len -= err;
699                         sd.pos += err;
700                         sd.total_len -= err;
701                         if (sd.len)
702                                 continue;
703
704                         if (!buf->len) {
705                                 buf->ops = NULL;
706                                 ops->release(pipe, buf);
707                                 pipe->curbuf = (pipe->curbuf + 1) & (PIPE_BUFFERS - 1);
708                                 pipe->nrbufs--;
709                                 if (pipe->inode)
710                                         do_wakeup = 1;
711                         }
712
713                         if (!sd.total_len)
714                                 break;
715                 }
716
717                 if (pipe->nrbufs)
718                         continue;
719                 if (!pipe->writers)
720                         break;
721                 if (!pipe->waiting_writers) {
722                         if (ret)
723                                 break;
724                 }
725
726                 if (flags & SPLICE_F_NONBLOCK) {
727                         if (!ret)
728                                 ret = -EAGAIN;
729                         break;
730                 }
731
732                 if (signal_pending(current)) {
733                         if (!ret)
734                                 ret = -ERESTARTSYS;
735                         break;
736                 }
737
738                 if (do_wakeup) {
739                         smp_mb();
740                         if (waitqueue_active(&pipe->wait))
741                                 wake_up_interruptible_sync(&pipe->wait);
742                         kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
743                         do_wakeup = 0;
744                 }
745
746                 pipe_wait(pipe);
747         }
748
749         if (do_wakeup) {
750                 smp_mb();
751                 if (waitqueue_active(&pipe->wait))
752                         wake_up_interruptible(&pipe->wait);
753                 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
754         }
755
756         return ret;
757 }
758 EXPORT_SYMBOL(__splice_from_pipe);
759
760 ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
761                          loff_t *ppos, size_t len, unsigned int flags,
762                          splice_actor *actor)
763 {
764         ssize_t ret;
765         struct inode *inode = out->f_mapping->host;
766
767         /*
768          * The actor worker might be calling ->prepare_write and
769          * ->commit_write. Most of the time, these expect i_mutex to
770          * be held. Since this may result in an ABBA deadlock with
771          * pipe->inode, we have to order lock acquiry here.
772          */
773         inode_double_lock(inode, pipe->inode);
774         ret = __splice_from_pipe(pipe, out, ppos, len, flags, actor);
775         inode_double_unlock(inode, pipe->inode);
776
777         return ret;
778 }
779
780 /**
781  * generic_file_splice_write_nolock - generic_file_splice_write without mutexes
782  * @pipe:       pipe info
783  * @out:        file to write to
784  * @len:        number of bytes to splice
785  * @flags:      splice modifier flags
786  *
787  * Will either move or copy pages (determined by @flags options) from
788  * the given pipe inode to the given file. The caller is responsible
789  * for acquiring i_mutex on both inodes.
790  *
791  */
792 ssize_t
793 generic_file_splice_write_nolock(struct pipe_inode_info *pipe, struct file *out,
794                                  loff_t *ppos, size_t len, unsigned int flags)
795 {
796         struct address_space *mapping = out->f_mapping;
797         struct inode *inode = mapping->host;
798         ssize_t ret;
799         int err;
800
801         err = remove_suid(out->f_path.dentry);
802         if (unlikely(err))
803                 return err;
804
805         ret = __splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_file);
806         if (ret > 0) {
807                 *ppos += ret;
808
809                 /*
810                  * If file or inode is SYNC and we actually wrote some data,
811                  * sync it.
812                  */
813                 if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
814                         err = generic_osync_inode(inode, mapping,
815                                                   OSYNC_METADATA|OSYNC_DATA);
816
817                         if (err)
818                                 ret = err;
819                 }
820         }
821
822         return ret;
823 }
824
825 EXPORT_SYMBOL(generic_file_splice_write_nolock);
826
827 /**
828  * generic_file_splice_write - splice data from a pipe to a file
829  * @pipe:       pipe info
830  * @out:        file to write to
831  * @len:        number of bytes to splice
832  * @flags:      splice modifier flags
833  *
834  * Will either move or copy pages (determined by @flags options) from
835  * the given pipe inode to the given file.
836  *
837  */
838 ssize_t
839 generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
840                           loff_t *ppos, size_t len, unsigned int flags)
841 {
842         struct address_space *mapping = out->f_mapping;
843         struct inode *inode = mapping->host;
844         ssize_t ret;
845         int err;
846
847         err = should_remove_suid(out->f_path.dentry);
848         if (unlikely(err)) {
849                 mutex_lock(&inode->i_mutex);
850                 err = __remove_suid(out->f_path.dentry, err);
851                 mutex_unlock(&inode->i_mutex);
852                 if (err)
853                         return err;
854         }
855
856         ret = splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_file);
857         if (ret > 0) {
858                 *ppos += ret;
859
860                 /*
861                  * If file or inode is SYNC and we actually wrote some data,
862                  * sync it.
863                  */
864                 if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
865                         mutex_lock(&inode->i_mutex);
866                         err = generic_osync_inode(inode, mapping,
867                                                   OSYNC_METADATA|OSYNC_DATA);
868                         mutex_unlock(&inode->i_mutex);
869
870                         if (err)
871                                 ret = err;
872                 }
873         }
874
875         return ret;
876 }
877
878 EXPORT_SYMBOL(generic_file_splice_write);
879
880 /**
881  * generic_splice_sendpage - splice data from a pipe to a socket
882  * @inode:      pipe inode
883  * @out:        socket to write to
884  * @len:        number of bytes to splice
885  * @flags:      splice modifier flags
886  *
887  * Will send @len bytes from the pipe to a network socket. No data copying
888  * is involved.
889  *
890  */
891 ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe, struct file *out,
892                                 loff_t *ppos, size_t len, unsigned int flags)
893 {
894         return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_sendpage);
895 }
896
897 EXPORT_SYMBOL(generic_splice_sendpage);
898
899 /*
900  * Attempt to initiate a splice from pipe to file.
901  */
902 static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
903                            loff_t *ppos, size_t len, unsigned int flags)
904 {
905         int ret;
906
907         if (unlikely(!out->f_op || !out->f_op->splice_write))
908                 return -EINVAL;
909
910         if (unlikely(!(out->f_mode & FMODE_WRITE)))
911                 return -EBADF;
912
913         ret = rw_verify_area(WRITE, out, ppos, len);
914         if (unlikely(ret < 0))
915                 return ret;
916
917         return out->f_op->splice_write(pipe, out, ppos, len, flags);
918 }
919
920 /*
921  * Attempt to initiate a splice from a file to a pipe.
922  */
923 static long do_splice_to(struct file *in, loff_t *ppos,
924                          struct pipe_inode_info *pipe, size_t len,
925                          unsigned int flags)
926 {
927         loff_t isize, left;
928         int ret;
929
930         if (unlikely(!in->f_op || !in->f_op->splice_read))
931                 return -EINVAL;
932
933         if (unlikely(!(in->f_mode & FMODE_READ)))
934                 return -EBADF;
935
936         ret = rw_verify_area(READ, in, ppos, len);
937         if (unlikely(ret < 0))
938                 return ret;
939
940         isize = i_size_read(in->f_mapping->host);
941         if (unlikely(*ppos >= isize))
942                 return 0;
943         
944         left = isize - *ppos;
945         if (unlikely(left < len))
946                 len = left;
947
948         return in->f_op->splice_read(in, ppos, pipe, len, flags);
949 }
950
951 long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
952                       size_t len, unsigned int flags)
953 {
954         struct pipe_inode_info *pipe;
955         long ret, bytes;
956         loff_t out_off;
957         umode_t i_mode;
958         int i;
959
960         /*
961          * We require the input being a regular file, as we don't want to
962          * randomly drop data for eg socket -> socket splicing. Use the
963          * piped splicing for that!
964          */
965         i_mode = in->f_path.dentry->d_inode->i_mode;
966         if (unlikely(!S_ISREG(i_mode) && !S_ISBLK(i_mode)))
967                 return -EINVAL;
968
969         /*
970          * neither in nor out is a pipe, setup an internal pipe attached to
971          * 'out' and transfer the wanted data from 'in' to 'out' through that
972          */
973         pipe = current->splice_pipe;
974         if (unlikely(!pipe)) {
975                 pipe = alloc_pipe_info(NULL);
976                 if (!pipe)
977                         return -ENOMEM;
978
979                 /*
980                  * We don't have an immediate reader, but we'll read the stuff
981                  * out of the pipe right after the splice_to_pipe(). So set
982                  * PIPE_READERS appropriately.
983                  */
984                 pipe->readers = 1;
985
986                 current->splice_pipe = pipe;
987         }
988
989         /*
990          * Do the splice.
991          */
992         ret = 0;
993         bytes = 0;
994         out_off = 0;
995
996         while (len) {
997                 size_t read_len, max_read_len;
998
999                 /*
1000                  * Do at most PIPE_BUFFERS pages worth of transfer:
1001                  */
1002                 max_read_len = min(len, (size_t)(PIPE_BUFFERS*PAGE_SIZE));
1003
1004                 ret = do_splice_to(in, ppos, pipe, max_read_len, flags);
1005                 if (unlikely(ret < 0))
1006                         goto out_release;
1007
1008                 read_len = ret;
1009
1010                 /*
1011                  * NOTE: nonblocking mode only applies to the input. We
1012                  * must not do the output in nonblocking mode as then we
1013                  * could get stuck data in the internal pipe:
1014                  */
1015                 ret = do_splice_from(pipe, out, &out_off, read_len,
1016                                      flags & ~SPLICE_F_NONBLOCK);
1017                 if (unlikely(ret < 0))
1018                         goto out_release;
1019
1020                 bytes += ret;
1021                 len -= ret;
1022
1023                 /*
1024                  * In nonblocking mode, if we got back a short read then
1025                  * that was due to either an IO error or due to the
1026                  * pagecache entry not being there. In the IO error case
1027                  * the _next_ splice attempt will produce a clean IO error
1028                  * return value (not a short read), so in both cases it's
1029                  * correct to break out of the loop here:
1030                  */
1031                 if ((flags & SPLICE_F_NONBLOCK) && (read_len < max_read_len))
1032                         break;
1033         }
1034
1035         pipe->nrbufs = pipe->curbuf = 0;
1036
1037         return bytes;
1038
1039 out_release:
1040         /*
1041          * If we did an incomplete transfer we must release
1042          * the pipe buffers in question:
1043          */
1044         for (i = 0; i < PIPE_BUFFERS; i++) {
1045                 struct pipe_buffer *buf = pipe->bufs + i;
1046
1047                 if (buf->ops) {
1048                         buf->ops->release(pipe, buf);
1049                         buf->ops = NULL;
1050                 }
1051         }
1052         pipe->nrbufs = pipe->curbuf = 0;
1053
1054         /*
1055          * If we transferred some data, return the number of bytes:
1056          */
1057         if (bytes > 0)
1058                 return bytes;
1059
1060         return ret;
1061 }
1062
1063 EXPORT_SYMBOL(do_splice_direct);
1064
1065 /*
1066  * After the inode slimming patch, i_pipe/i_bdev/i_cdev share the same
1067  * location, so checking ->i_pipe is not enough to verify that this is a
1068  * pipe.
1069  */
1070 static inline struct pipe_inode_info *pipe_info(struct inode *inode)
1071 {
1072         if (S_ISFIFO(inode->i_mode))
1073                 return inode->i_pipe;
1074
1075         return NULL;
1076 }
1077
1078 /*
1079  * Determine where to splice to/from.
1080  */
1081 static long do_splice(struct file *in, loff_t __user *off_in,
1082                       struct file *out, loff_t __user *off_out,
1083                       size_t len, unsigned int flags)
1084 {
1085         struct pipe_inode_info *pipe;
1086         loff_t offset, *off;
1087         long ret;
1088
1089         pipe = pipe_info(in->f_path.dentry->d_inode);
1090         if (pipe) {
1091                 if (off_in)
1092                         return -ESPIPE;
1093                 if (off_out) {
1094                         if (out->f_op->llseek == no_llseek)
1095                                 return -EINVAL;
1096                         if (copy_from_user(&offset, off_out, sizeof(loff_t)))
1097                                 return -EFAULT;
1098                         off = &offset;
1099                 } else
1100                         off = &out->f_pos;
1101
1102                 ret = do_splice_from(pipe, out, off, len, flags);
1103
1104                 if (off_out && copy_to_user(off_out, off, sizeof(loff_t)))
1105                         ret = -EFAULT;
1106
1107                 return ret;
1108         }
1109
1110         pipe = pipe_info(out->f_path.dentry->d_inode);
1111         if (pipe) {
1112                 if (off_out)
1113                         return -ESPIPE;
1114                 if (off_in) {
1115                         if (in->f_op->llseek == no_llseek)
1116                                 return -EINVAL;
1117                         if (copy_from_user(&offset, off_in, sizeof(loff_t)))
1118                                 return -EFAULT;
1119                         off = &offset;
1120                 } else
1121                         off = &in->f_pos;
1122
1123                 ret = do_splice_to(in, off, pipe, len, flags);
1124
1125                 if (off_in && copy_to_user(off_in, off, sizeof(loff_t)))
1126                         ret = -EFAULT;
1127
1128                 return ret;
1129         }
1130
1131         return -EINVAL;
1132 }
1133
1134 /*
1135  * Map an iov into an array of pages and offset/length tupples. With the
1136  * partial_page structure, we can map several non-contiguous ranges into
1137  * our ones pages[] map instead of splitting that operation into pieces.
1138  * Could easily be exported as a generic helper for other users, in which
1139  * case one would probably want to add a 'max_nr_pages' parameter as well.
1140  */
1141 static int get_iovec_page_array(const struct iovec __user *iov,
1142                                 unsigned int nr_vecs, struct page **pages,
1143                                 struct partial_page *partial, int aligned)
1144 {
1145         int buffers = 0, error = 0;
1146
1147         /*
1148          * It's ok to take the mmap_sem for reading, even
1149          * across a "get_user()".
1150          */
1151         down_read(&current->mm->mmap_sem);
1152
1153         while (nr_vecs) {
1154                 unsigned long off, npages;
1155                 void __user *base;
1156                 size_t len;
1157                 int i;
1158
1159                 /*
1160                  * Get user address base and length for this iovec.
1161                  */
1162                 error = get_user(base, &iov->iov_base);
1163                 if (unlikely(error))
1164                         break;
1165                 error = get_user(len, &iov->iov_len);
1166                 if (unlikely(error))
1167                         break;
1168
1169                 /*
1170                  * Sanity check this iovec. 0 read succeeds.
1171                  */
1172                 if (unlikely(!len))
1173                         break;
1174                 error = -EFAULT;
1175                 if (unlikely(!base))
1176                         break;
1177
1178                 /*
1179                  * Get this base offset and number of pages, then map
1180                  * in the user pages.
1181                  */
1182                 off = (unsigned long) base & ~PAGE_MASK;
1183
1184                 /*
1185                  * If asked for alignment, the offset must be zero and the
1186                  * length a multiple of the PAGE_SIZE.
1187                  */
1188                 error = -EINVAL;
1189                 if (aligned && (off || len & ~PAGE_MASK))
1190                         break;
1191
1192                 npages = (off + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
1193                 if (npages > PIPE_BUFFERS - buffers)
1194                         npages = PIPE_BUFFERS - buffers;
1195
1196                 error = get_user_pages(current, current->mm,
1197                                        (unsigned long) base, npages, 0, 0,
1198                                        &pages[buffers], NULL);
1199
1200                 if (unlikely(error <= 0))
1201                         break;
1202
1203                 /*
1204                  * Fill this contiguous range into the partial page map.
1205                  */
1206                 for (i = 0; i < error; i++) {
1207                         const int plen = min_t(size_t, len, PAGE_SIZE - off);
1208
1209                         partial[buffers].offset = off;
1210                         partial[buffers].len = plen;
1211
1212                         off = 0;
1213                         len -= plen;
1214                         buffers++;
1215                 }
1216
1217                 /*
1218                  * We didn't complete this iov, stop here since it probably
1219                  * means we have to move some of this into a pipe to
1220                  * be able to continue.
1221                  */
1222                 if (len)
1223                         break;
1224
1225                 /*
1226                  * Don't continue if we mapped fewer pages than we asked for,
1227                  * or if we mapped the max number of pages that we have
1228                  * room for.
1229                  */
1230                 if (error < npages || buffers == PIPE_BUFFERS)
1231                         break;
1232
1233                 nr_vecs--;
1234                 iov++;
1235         }
1236
1237         up_read(&current->mm->mmap_sem);
1238
1239         if (buffers)
1240                 return buffers;
1241
1242         return error;
1243 }
1244
1245 /*
1246  * vmsplice splices a user address range into a pipe. It can be thought of
1247  * as splice-from-memory, where the regular splice is splice-from-file (or
1248  * to file). In both cases the output is a pipe, naturally.
1249  *
1250  * Note that vmsplice only supports splicing _from_ user memory to a pipe,
1251  * not the other way around. Splicing from user memory is a simple operation
1252  * that can be supported without any funky alignment restrictions or nasty
1253  * vm tricks. We simply map in the user memory and fill them into a pipe.
1254  * The reverse isn't quite as easy, though. There are two possible solutions
1255  * for that:
1256  *
1257  *      - memcpy() the data internally, at which point we might as well just
1258  *        do a regular read() on the buffer anyway.
1259  *      - Lots of nasty vm tricks, that are neither fast nor flexible (it
1260  *        has restriction limitations on both ends of the pipe).
1261  *
1262  * Alas, it isn't here.
1263  *
1264  */
1265 static long do_vmsplice(struct file *file, const struct iovec __user *iov,
1266                         unsigned long nr_segs, unsigned int flags)
1267 {
1268         struct pipe_inode_info *pipe;
1269         struct page *pages[PIPE_BUFFERS];
1270         struct partial_page partial[PIPE_BUFFERS];
1271         struct splice_pipe_desc spd = {
1272                 .pages = pages,
1273                 .partial = partial,
1274                 .flags = flags,
1275                 .ops = &user_page_pipe_buf_ops,
1276         };
1277
1278         pipe = pipe_info(file->f_path.dentry->d_inode);
1279         if (!pipe)
1280                 return -EBADF;
1281         if (unlikely(nr_segs > UIO_MAXIOV))
1282                 return -EINVAL;
1283         else if (unlikely(!nr_segs))
1284                 return 0;
1285
1286         spd.nr_pages = get_iovec_page_array(iov, nr_segs, pages, partial,
1287                                             flags & SPLICE_F_GIFT);
1288         if (spd.nr_pages <= 0)
1289                 return spd.nr_pages;
1290
1291         return splice_to_pipe(pipe, &spd);
1292 }
1293
1294 asmlinkage long sys_vmsplice(int fd, const struct iovec __user *iov,
1295                              unsigned long nr_segs, unsigned int flags)
1296 {
1297         struct file *file;
1298         long error;
1299         int fput;
1300
1301         error = -EBADF;
1302         file = fget_light(fd, &fput);
1303         if (file) {
1304                 if (file->f_mode & FMODE_WRITE)
1305                         error = do_vmsplice(file, iov, nr_segs, flags);
1306
1307                 fput_light(file, fput);
1308         }
1309
1310         return error;
1311 }
1312
1313 asmlinkage long sys_splice(int fd_in, loff_t __user *off_in,
1314                            int fd_out, loff_t __user *off_out,
1315                            size_t len, unsigned int flags)
1316 {
1317         long error;
1318         struct file *in, *out;
1319         int fput_in, fput_out;
1320
1321         if (unlikely(!len))
1322                 return 0;
1323
1324         error = -EBADF;
1325         in = fget_light(fd_in, &fput_in);
1326         if (in) {
1327                 if (in->f_mode & FMODE_READ) {
1328                         out = fget_light(fd_out, &fput_out);
1329                         if (out) {
1330                                 if (out->f_mode & FMODE_WRITE)
1331                                         error = do_splice(in, off_in,
1332                                                           out, off_out,
1333                                                           len, flags);
1334                                 fput_light(out, fput_out);
1335                         }
1336                 }
1337
1338                 fput_light(in, fput_in);
1339         }
1340
1341         return error;
1342 }
1343
1344 /*
1345  * Make sure there's data to read. Wait for input if we can, otherwise
1346  * return an appropriate error.
1347  */
1348 static int link_ipipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
1349 {
1350         int ret;
1351
1352         /*
1353          * Check ->nrbufs without the inode lock first. This function
1354          * is speculative anyways, so missing one is ok.
1355          */
1356         if (pipe->nrbufs)
1357                 return 0;
1358
1359         ret = 0;
1360         mutex_lock(&pipe->inode->i_mutex);
1361
1362         while (!pipe->nrbufs) {
1363                 if (signal_pending(current)) {
1364                         ret = -ERESTARTSYS;
1365                         break;
1366                 }
1367                 if (!pipe->writers)
1368                         break;
1369                 if (!pipe->waiting_writers) {
1370                         if (flags & SPLICE_F_NONBLOCK) {
1371                                 ret = -EAGAIN;
1372                                 break;
1373                         }
1374                 }
1375                 pipe_wait(pipe);
1376         }
1377
1378         mutex_unlock(&pipe->inode->i_mutex);
1379         return ret;
1380 }
1381
1382 /*
1383  * Make sure there's writeable room. Wait for room if we can, otherwise
1384  * return an appropriate error.
1385  */
1386 static int link_opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
1387 {
1388         int ret;
1389
1390         /*
1391          * Check ->nrbufs without the inode lock first. This function
1392          * is speculative anyways, so missing one is ok.
1393          */
1394         if (pipe->nrbufs < PIPE_BUFFERS)
1395                 return 0;
1396
1397         ret = 0;
1398         mutex_lock(&pipe->inode->i_mutex);
1399
1400         while (pipe->nrbufs >= PIPE_BUFFERS) {
1401                 if (!pipe->readers) {
1402                         send_sig(SIGPIPE, current, 0);
1403                         ret = -EPIPE;
1404                         break;
1405                 }
1406                 if (flags & SPLICE_F_NONBLOCK) {
1407                         ret = -EAGAIN;
1408                         break;
1409                 }
1410                 if (signal_pending(current)) {
1411                         ret = -ERESTARTSYS;
1412                         break;
1413                 }
1414                 pipe->waiting_writers++;
1415                 pipe_wait(pipe);
1416                 pipe->waiting_writers--;
1417         }
1418
1419         mutex_unlock(&pipe->inode->i_mutex);
1420         return ret;
1421 }
1422
1423 /*
1424  * Link contents of ipipe to opipe.
1425  */
1426 static int link_pipe(struct pipe_inode_info *ipipe,
1427                      struct pipe_inode_info *opipe,
1428                      size_t len, unsigned int flags)
1429 {
1430         struct pipe_buffer *ibuf, *obuf;
1431         int ret = 0, i = 0, nbuf;
1432
1433         /*
1434          * Potential ABBA deadlock, work around it by ordering lock
1435          * grabbing by inode address. Otherwise two different processes
1436          * could deadlock (one doing tee from A -> B, the other from B -> A).
1437          */
1438         inode_double_lock(ipipe->inode, opipe->inode);
1439
1440         do {
1441                 if (!opipe->readers) {
1442                         send_sig(SIGPIPE, current, 0);
1443                         if (!ret)
1444                                 ret = -EPIPE;
1445                         break;
1446                 }
1447
1448                 /*
1449                  * If we have iterated all input buffers or ran out of
1450                  * output room, break.
1451                  */
1452                 if (i >= ipipe->nrbufs || opipe->nrbufs >= PIPE_BUFFERS)
1453                         break;
1454
1455                 ibuf = ipipe->bufs + ((ipipe->curbuf + i) & (PIPE_BUFFERS - 1));
1456                 nbuf = (opipe->curbuf + opipe->nrbufs) & (PIPE_BUFFERS - 1);
1457
1458                 /*
1459                  * Get a reference to this pipe buffer,
1460                  * so we can copy the contents over.
1461                  */
1462                 ibuf->ops->get(ipipe, ibuf);
1463
1464                 obuf = opipe->bufs + nbuf;
1465                 *obuf = *ibuf;
1466
1467                 /*
1468                  * Don't inherit the gift flag, we need to
1469                  * prevent multiple steals of this page.
1470                  */
1471                 obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
1472
1473                 if (obuf->len > len)
1474                         obuf->len = len;
1475
1476                 opipe->nrbufs++;
1477                 ret += obuf->len;
1478                 len -= obuf->len;
1479                 i++;
1480         } while (len);
1481
1482         inode_double_unlock(ipipe->inode, opipe->inode);
1483
1484         /*
1485          * If we put data in the output pipe, wakeup any potential readers.
1486          */
1487         if (ret > 0) {
1488                 smp_mb();
1489                 if (waitqueue_active(&opipe->wait))
1490                         wake_up_interruptible(&opipe->wait);
1491                 kill_fasync(&opipe->fasync_readers, SIGIO, POLL_IN);
1492         }
1493
1494         return ret;
1495 }
1496
1497 /*
1498  * This is a tee(1) implementation that works on pipes. It doesn't copy
1499  * any data, it simply references the 'in' pages on the 'out' pipe.
1500  * The 'flags' used are the SPLICE_F_* variants, currently the only
1501  * applicable one is SPLICE_F_NONBLOCK.
1502  */
1503 static long do_tee(struct file *in, struct file *out, size_t len,
1504                    unsigned int flags)
1505 {
1506         struct pipe_inode_info *ipipe = pipe_info(in->f_path.dentry->d_inode);
1507         struct pipe_inode_info *opipe = pipe_info(out->f_path.dentry->d_inode);
1508         int ret = -EINVAL;
1509
1510         /*
1511          * Duplicate the contents of ipipe to opipe without actually
1512          * copying the data.
1513          */
1514         if (ipipe && opipe && ipipe != opipe) {
1515                 /*
1516                  * Keep going, unless we encounter an error. The ipipe/opipe
1517                  * ordering doesn't really matter.
1518                  */
1519                 ret = link_ipipe_prep(ipipe, flags);
1520                 if (!ret) {
1521                         ret = link_opipe_prep(opipe, flags);
1522                         if (!ret) {
1523                                 ret = link_pipe(ipipe, opipe, len, flags);
1524                                 if (!ret && (flags & SPLICE_F_NONBLOCK))
1525                                         ret = -EAGAIN;
1526                         }
1527                 }
1528         }
1529
1530         return ret;
1531 }
1532
1533 asmlinkage long sys_tee(int fdin, int fdout, size_t len, unsigned int flags)
1534 {
1535         struct file *in;
1536         int error, fput_in;
1537
1538         if (unlikely(!len))
1539                 return 0;
1540
1541         error = -EBADF;
1542         in = fget_light(fdin, &fput_in);
1543         if (in) {
1544                 if (in->f_mode & FMODE_READ) {
1545                         int fput_out;
1546                         struct file *out = fget_light(fdout, &fput_out);
1547
1548                         if (out) {
1549                                 if (out->f_mode & FMODE_WRITE)
1550                                         error = do_tee(in, out, len, flags);
1551                                 fput_light(out, fput_out);
1552                         }
1553                 }
1554                 fput_light(in, fput_in);
1555         }
1556
1557         return error;
1558 }