[PATCH] splice: partial write fix
[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                                 break;
383
384                         lock_page(page);
385
386                         /*
387                          * page was truncated, stop here. if this isn't the
388                          * first page, we'll just complete what we already
389                          * added
390                          */
391                         if (!page->mapping) {
392                                 unlock_page(page);
393                                 break;
394                         }
395                         /*
396                          * page was already under io and is now done, great
397                          */
398                         if (PageUptodate(page)) {
399                                 unlock_page(page);
400                                 goto fill_it;
401                         }
402
403                         /*
404                          * need to read in the page
405                          */
406                         error = mapping->a_ops->readpage(in, page);
407                         if (unlikely(error)) {
408                                 /*
409                                  * We really should re-lookup the page here,
410                                  * but it complicates things a lot. Instead
411                                  * lets just do what we already stored, and
412                                  * we'll get it the next time we are called.
413                                  */
414                                 if (error == AOP_TRUNCATED_PAGE)
415                                         error = 0;
416
417                                 break;
418                         }
419
420                         /*
421                          * i_size must be checked after ->readpage().
422                          */
423                         isize = i_size_read(mapping->host);
424                         end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
425                         if (unlikely(!isize || index > end_index))
426                                 break;
427
428                         /*
429                          * if this is the last page, see if we need to shrink
430                          * the length and stop
431                          */
432                         if (end_index == index) {
433                                 loff = PAGE_CACHE_SIZE - (isize & ~PAGE_CACHE_MASK);
434                                 if (total_len + loff > isize)
435                                         break;
436                                 /*
437                                  * force quit after adding this page
438                                  */
439                                 len = this_len;
440                                 this_len = min(this_len, loff);
441                                 loff = 0;
442                         }
443                 }
444 fill_it:
445                 partial[page_nr].offset = loff;
446                 partial[page_nr].len = this_len;
447                 len -= this_len;
448                 total_len += this_len;
449                 loff = 0;
450                 spd.nr_pages++;
451                 index++;
452         }
453
454         /*
455          * Release any pages at the end, if we quit early. 'i' is how far
456          * we got, 'nr_pages' is how many pages are in the map.
457          */
458         while (page_nr < nr_pages)
459                 page_cache_release(pages[page_nr++]);
460
461         if (spd.nr_pages)
462                 return splice_to_pipe(pipe, &spd);
463
464         return error;
465 }
466
467 /**
468  * generic_file_splice_read - splice data from file to a pipe
469  * @in:         file to splice from
470  * @pipe:       pipe to splice to
471  * @len:        number of bytes to splice
472  * @flags:      splice modifier flags
473  *
474  * Will read pages from given file and fill them into a pipe.
475  */
476 ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
477                                  struct pipe_inode_info *pipe, size_t len,
478                                  unsigned int flags)
479 {
480         ssize_t spliced;
481         int ret;
482
483         ret = 0;
484         spliced = 0;
485
486         while (len) {
487                 ret = __generic_file_splice_read(in, ppos, pipe, len, flags);
488
489                 if (ret < 0)
490                         break;
491                 else if (!ret) {
492                         if (spliced)
493                                 break;
494                         if (flags & SPLICE_F_NONBLOCK) {
495                                 ret = -EAGAIN;
496                                 break;
497                         }
498                 }
499
500                 *ppos += ret;
501                 len -= ret;
502                 spliced += ret;
503         }
504
505         if (spliced)
506                 return spliced;
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->file;
521         loff_t pos = sd->pos;
522         int ret, more;
523
524         ret = buf->ops->pin(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 static int pipe_to_file(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
556                         struct splice_desc *sd)
557 {
558         struct file *file = sd->file;
559         struct address_space *mapping = file->f_mapping;
560         unsigned int offset, this_len;
561         struct page *page;
562         pgoff_t index;
563         int ret;
564
565         /*
566          * make sure the data in this buffer is uptodate
567          */
568         ret = buf->ops->pin(pipe, buf);
569         if (unlikely(ret))
570                 return ret;
571
572         index = sd->pos >> PAGE_CACHE_SHIFT;
573         offset = sd->pos & ~PAGE_CACHE_MASK;
574
575         this_len = sd->len;
576         if (this_len + offset > PAGE_CACHE_SIZE)
577                 this_len = PAGE_CACHE_SIZE - offset;
578
579 find_page:
580         page = find_lock_page(mapping, index);
581         if (!page) {
582                 ret = -ENOMEM;
583                 page = page_cache_alloc_cold(mapping);
584                 if (unlikely(!page))
585                         goto out_ret;
586
587                 /*
588                  * This will also lock the page
589                  */
590                 ret = add_to_page_cache_lru(page, mapping, index,
591                                             GFP_KERNEL);
592                 if (unlikely(ret))
593                         goto out;
594         }
595
596         ret = mapping->a_ops->prepare_write(file, page, offset, offset+this_len);
597         if (unlikely(ret)) {
598                 loff_t isize = i_size_read(mapping->host);
599
600                 if (ret != AOP_TRUNCATED_PAGE)
601                         unlock_page(page);
602                 page_cache_release(page);
603                 if (ret == AOP_TRUNCATED_PAGE)
604                         goto find_page;
605
606                 /*
607                  * prepare_write() may have instantiated a few blocks
608                  * outside i_size.  Trim these off again.
609                  */
610                 if (sd->pos + this_len > isize)
611                         vmtruncate(mapping->host, isize);
612
613                 goto out_ret;
614         }
615
616         if (buf->page != page) {
617                 /*
618                  * Careful, ->map() uses KM_USER0!
619                  */
620                 char *src = buf->ops->map(pipe, buf, 1);
621                 char *dst = kmap_atomic(page, KM_USER1);
622
623                 memcpy(dst + offset, src + buf->offset, this_len);
624                 flush_dcache_page(page);
625                 kunmap_atomic(dst, KM_USER1);
626                 buf->ops->unmap(pipe, buf, src);
627         }
628
629         ret = mapping->a_ops->commit_write(file, page, offset, offset+this_len);
630         if (ret) {
631                 if (ret == AOP_TRUNCATED_PAGE) {
632                         page_cache_release(page);
633                         goto find_page;
634                 }
635                 if (ret < 0)
636                         goto out;
637                 /*
638                  * Partial write has happened, so 'ret' already initialized by
639                  * number of bytes written, Where is nothing we have to do here.
640                  */
641         } else
642                 ret = this_len;
643         /*
644          * Return the number of bytes written and mark page as
645          * accessed, we are now done!
646          */
647         mark_page_accessed(page);
648         balance_dirty_pages_ratelimited(mapping);
649 out:
650         page_cache_release(page);
651         unlock_page(page);
652 out_ret:
653         return ret;
654 }
655
656 /*
657  * Pipe input worker. Most of this logic works like a regular pipe, the
658  * key here is the 'actor' worker passed in that actually moves the data
659  * to the wanted destination. See pipe_to_file/pipe_to_sendpage above.
660  */
661 ssize_t __splice_from_pipe(struct pipe_inode_info *pipe,
662                            struct file *out, loff_t *ppos, size_t len,
663                            unsigned int flags, splice_actor *actor)
664 {
665         int ret, do_wakeup, err;
666         struct splice_desc sd;
667
668         ret = 0;
669         do_wakeup = 0;
670
671         sd.total_len = len;
672         sd.flags = flags;
673         sd.file = out;
674         sd.pos = *ppos;
675
676         for (;;) {
677                 if (pipe->nrbufs) {
678                         struct pipe_buffer *buf = pipe->bufs + pipe->curbuf;
679                         const struct pipe_buf_operations *ops = buf->ops;
680
681                         sd.len = buf->len;
682                         if (sd.len > sd.total_len)
683                                 sd.len = sd.total_len;
684
685                         err = actor(pipe, buf, &sd);
686                         if (err <= 0) {
687                                 if (!ret && err != -ENODATA)
688                                         ret = err;
689
690                                 break;
691                         }
692
693                         ret += err;
694                         buf->offset += err;
695                         buf->len -= err;
696
697                         sd.len -= err;
698                         sd.pos += err;
699                         sd.total_len -= err;
700                         if (sd.len)
701                                 continue;
702
703                         if (!buf->len) {
704                                 buf->ops = NULL;
705                                 ops->release(pipe, buf);
706                                 pipe->curbuf = (pipe->curbuf + 1) & (PIPE_BUFFERS - 1);
707                                 pipe->nrbufs--;
708                                 if (pipe->inode)
709                                         do_wakeup = 1;
710                         }
711
712                         if (!sd.total_len)
713                                 break;
714                 }
715
716                 if (pipe->nrbufs)
717                         continue;
718                 if (!pipe->writers)
719                         break;
720                 if (!pipe->waiting_writers) {
721                         if (ret)
722                                 break;
723                 }
724
725                 if (flags & SPLICE_F_NONBLOCK) {
726                         if (!ret)
727                                 ret = -EAGAIN;
728                         break;
729                 }
730
731                 if (signal_pending(current)) {
732                         if (!ret)
733                                 ret = -ERESTARTSYS;
734                         break;
735                 }
736
737                 if (do_wakeup) {
738                         smp_mb();
739                         if (waitqueue_active(&pipe->wait))
740                                 wake_up_interruptible_sync(&pipe->wait);
741                         kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
742                         do_wakeup = 0;
743                 }
744
745                 pipe_wait(pipe);
746         }
747
748         if (do_wakeup) {
749                 smp_mb();
750                 if (waitqueue_active(&pipe->wait))
751                         wake_up_interruptible(&pipe->wait);
752                 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
753         }
754
755         return ret;
756 }
757 EXPORT_SYMBOL(__splice_from_pipe);
758
759 ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
760                          loff_t *ppos, size_t len, unsigned int flags,
761                          splice_actor *actor)
762 {
763         ssize_t ret;
764         struct inode *inode = out->f_mapping->host;
765
766         /*
767          * The actor worker might be calling ->prepare_write and
768          * ->commit_write. Most of the time, these expect i_mutex to
769          * be held. Since this may result in an ABBA deadlock with
770          * pipe->inode, we have to order lock acquiry here.
771          */
772         inode_double_lock(inode, pipe->inode);
773         ret = __splice_from_pipe(pipe, out, ppos, len, flags, actor);
774         inode_double_unlock(inode, pipe->inode);
775
776         return ret;
777 }
778
779 /**
780  * generic_file_splice_write_nolock - generic_file_splice_write without mutexes
781  * @pipe:       pipe info
782  * @out:        file to write to
783  * @len:        number of bytes to splice
784  * @flags:      splice modifier flags
785  *
786  * Will either move or copy pages (determined by @flags options) from
787  * the given pipe inode to the given file. The caller is responsible
788  * for acquiring i_mutex on both inodes.
789  *
790  */
791 ssize_t
792 generic_file_splice_write_nolock(struct pipe_inode_info *pipe, struct file *out,
793                                  loff_t *ppos, size_t len, unsigned int flags)
794 {
795         struct address_space *mapping = out->f_mapping;
796         struct inode *inode = mapping->host;
797         ssize_t ret;
798         int err;
799
800         err = remove_suid(out->f_path.dentry);
801         if (unlikely(err))
802                 return err;
803
804         ret = __splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_file);
805         if (ret > 0) {
806                 *ppos += ret;
807
808                 /*
809                  * If file or inode is SYNC and we actually wrote some data,
810                  * sync it.
811                  */
812                 if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
813                         err = generic_osync_inode(inode, mapping,
814                                                   OSYNC_METADATA|OSYNC_DATA);
815
816                         if (err)
817                                 ret = err;
818                 }
819         }
820
821         return ret;
822 }
823
824 EXPORT_SYMBOL(generic_file_splice_write_nolock);
825
826 /**
827  * generic_file_splice_write - splice data from a pipe to a file
828  * @pipe:       pipe info
829  * @out:        file to write to
830  * @len:        number of bytes to splice
831  * @flags:      splice modifier flags
832  *
833  * Will either move or copy pages (determined by @flags options) from
834  * the given pipe inode to the given file.
835  *
836  */
837 ssize_t
838 generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
839                           loff_t *ppos, size_t len, unsigned int flags)
840 {
841         struct address_space *mapping = out->f_mapping;
842         struct inode *inode = mapping->host;
843         ssize_t ret;
844         int err;
845
846         err = should_remove_suid(out->f_path.dentry);
847         if (unlikely(err)) {
848                 mutex_lock(&inode->i_mutex);
849                 err = __remove_suid(out->f_path.dentry, err);
850                 mutex_unlock(&inode->i_mutex);
851                 if (err)
852                         return err;
853         }
854
855         ret = splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_file);
856         if (ret > 0) {
857                 *ppos += ret;
858
859                 /*
860                  * If file or inode is SYNC and we actually wrote some data,
861                  * sync it.
862                  */
863                 if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
864                         mutex_lock(&inode->i_mutex);
865                         err = generic_osync_inode(inode, mapping,
866                                                   OSYNC_METADATA|OSYNC_DATA);
867                         mutex_unlock(&inode->i_mutex);
868
869                         if (err)
870                                 ret = err;
871                 }
872         }
873
874         return ret;
875 }
876
877 EXPORT_SYMBOL(generic_file_splice_write);
878
879 /**
880  * generic_splice_sendpage - splice data from a pipe to a socket
881  * @inode:      pipe inode
882  * @out:        socket to write to
883  * @len:        number of bytes to splice
884  * @flags:      splice modifier flags
885  *
886  * Will send @len bytes from the pipe to a network socket. No data copying
887  * is involved.
888  *
889  */
890 ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe, struct file *out,
891                                 loff_t *ppos, size_t len, unsigned int flags)
892 {
893         return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_sendpage);
894 }
895
896 EXPORT_SYMBOL(generic_splice_sendpage);
897
898 /*
899  * Attempt to initiate a splice from pipe to file.
900  */
901 static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
902                            loff_t *ppos, size_t len, unsigned int flags)
903 {
904         int ret;
905
906         if (unlikely(!out->f_op || !out->f_op->splice_write))
907                 return -EINVAL;
908
909         if (unlikely(!(out->f_mode & FMODE_WRITE)))
910                 return -EBADF;
911
912         ret = rw_verify_area(WRITE, out, ppos, len);
913         if (unlikely(ret < 0))
914                 return ret;
915
916         return out->f_op->splice_write(pipe, out, ppos, len, flags);
917 }
918
919 /*
920  * Attempt to initiate a splice from a file to a pipe.
921  */
922 static long do_splice_to(struct file *in, loff_t *ppos,
923                          struct pipe_inode_info *pipe, size_t len,
924                          unsigned int flags)
925 {
926         loff_t isize, left;
927         int ret;
928
929         if (unlikely(!in->f_op || !in->f_op->splice_read))
930                 return -EINVAL;
931
932         if (unlikely(!(in->f_mode & FMODE_READ)))
933                 return -EBADF;
934
935         ret = rw_verify_area(READ, in, ppos, len);
936         if (unlikely(ret < 0))
937                 return ret;
938
939         isize = i_size_read(in->f_mapping->host);
940         if (unlikely(*ppos >= isize))
941                 return 0;
942         
943         left = isize - *ppos;
944         if (unlikely(left < len))
945                 len = left;
946
947         return in->f_op->splice_read(in, ppos, pipe, len, flags);
948 }
949
950 long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
951                       size_t len, unsigned int flags)
952 {
953         struct pipe_inode_info *pipe;
954         long ret, bytes;
955         loff_t out_off;
956         umode_t i_mode;
957         int i;
958
959         /*
960          * We require the input being a regular file, as we don't want to
961          * randomly drop data for eg socket -> socket splicing. Use the
962          * piped splicing for that!
963          */
964         i_mode = in->f_path.dentry->d_inode->i_mode;
965         if (unlikely(!S_ISREG(i_mode) && !S_ISBLK(i_mode)))
966                 return -EINVAL;
967
968         /*
969          * neither in nor out is a pipe, setup an internal pipe attached to
970          * 'out' and transfer the wanted data from 'in' to 'out' through that
971          */
972         pipe = current->splice_pipe;
973         if (unlikely(!pipe)) {
974                 pipe = alloc_pipe_info(NULL);
975                 if (!pipe)
976                         return -ENOMEM;
977
978                 /*
979                  * We don't have an immediate reader, but we'll read the stuff
980                  * out of the pipe right after the splice_to_pipe(). So set
981                  * PIPE_READERS appropriately.
982                  */
983                 pipe->readers = 1;
984
985                 current->splice_pipe = pipe;
986         }
987
988         /*
989          * Do the splice.
990          */
991         ret = 0;
992         bytes = 0;
993         out_off = 0;
994
995         while (len) {
996                 size_t read_len, max_read_len;
997
998                 /*
999                  * Do at most PIPE_BUFFERS pages worth of transfer:
1000                  */
1001                 max_read_len = min(len, (size_t)(PIPE_BUFFERS*PAGE_SIZE));
1002
1003                 ret = do_splice_to(in, ppos, pipe, max_read_len, flags);
1004                 if (unlikely(ret < 0))
1005                         goto out_release;
1006
1007                 read_len = ret;
1008
1009                 /*
1010                  * NOTE: nonblocking mode only applies to the input. We
1011                  * must not do the output in nonblocking mode as then we
1012                  * could get stuck data in the internal pipe:
1013                  */
1014                 ret = do_splice_from(pipe, out, &out_off, read_len,
1015                                      flags & ~SPLICE_F_NONBLOCK);
1016                 if (unlikely(ret < 0))
1017                         goto out_release;
1018
1019                 bytes += ret;
1020                 len -= ret;
1021
1022                 /*
1023                  * In nonblocking mode, if we got back a short read then
1024                  * that was due to either an IO error or due to the
1025                  * pagecache entry not being there. In the IO error case
1026                  * the _next_ splice attempt will produce a clean IO error
1027                  * return value (not a short read), so in both cases it's
1028                  * correct to break out of the loop here:
1029                  */
1030                 if ((flags & SPLICE_F_NONBLOCK) && (read_len < max_read_len))
1031                         break;
1032         }
1033
1034         pipe->nrbufs = pipe->curbuf = 0;
1035
1036         return bytes;
1037
1038 out_release:
1039         /*
1040          * If we did an incomplete transfer we must release
1041          * the pipe buffers in question:
1042          */
1043         for (i = 0; i < PIPE_BUFFERS; i++) {
1044                 struct pipe_buffer *buf = pipe->bufs + i;
1045
1046                 if (buf->ops) {
1047                         buf->ops->release(pipe, buf);
1048                         buf->ops = NULL;
1049                 }
1050         }
1051         pipe->nrbufs = pipe->curbuf = 0;
1052
1053         /*
1054          * If we transferred some data, return the number of bytes:
1055          */
1056         if (bytes > 0)
1057                 return bytes;
1058
1059         return ret;
1060 }
1061
1062 EXPORT_SYMBOL(do_splice_direct);
1063
1064 /*
1065  * After the inode slimming patch, i_pipe/i_bdev/i_cdev share the same
1066  * location, so checking ->i_pipe is not enough to verify that this is a
1067  * pipe.
1068  */
1069 static inline struct pipe_inode_info *pipe_info(struct inode *inode)
1070 {
1071         if (S_ISFIFO(inode->i_mode))
1072                 return inode->i_pipe;
1073
1074         return NULL;
1075 }
1076
1077 /*
1078  * Determine where to splice to/from.
1079  */
1080 static long do_splice(struct file *in, loff_t __user *off_in,
1081                       struct file *out, loff_t __user *off_out,
1082                       size_t len, unsigned int flags)
1083 {
1084         struct pipe_inode_info *pipe;
1085         loff_t offset, *off;
1086         long ret;
1087
1088         pipe = pipe_info(in->f_path.dentry->d_inode);
1089         if (pipe) {
1090                 if (off_in)
1091                         return -ESPIPE;
1092                 if (off_out) {
1093                         if (out->f_op->llseek == no_llseek)
1094                                 return -EINVAL;
1095                         if (copy_from_user(&offset, off_out, sizeof(loff_t)))
1096                                 return -EFAULT;
1097                         off = &offset;
1098                 } else
1099                         off = &out->f_pos;
1100
1101                 ret = do_splice_from(pipe, out, off, len, flags);
1102
1103                 if (off_out && copy_to_user(off_out, off, sizeof(loff_t)))
1104                         ret = -EFAULT;
1105
1106                 return ret;
1107         }
1108
1109         pipe = pipe_info(out->f_path.dentry->d_inode);
1110         if (pipe) {
1111                 if (off_out)
1112                         return -ESPIPE;
1113                 if (off_in) {
1114                         if (in->f_op->llseek == no_llseek)
1115                                 return -EINVAL;
1116                         if (copy_from_user(&offset, off_in, sizeof(loff_t)))
1117                                 return -EFAULT;
1118                         off = &offset;
1119                 } else
1120                         off = &in->f_pos;
1121
1122                 ret = do_splice_to(in, off, pipe, len, flags);
1123
1124                 if (off_in && copy_to_user(off_in, off, sizeof(loff_t)))
1125                         ret = -EFAULT;
1126
1127                 return ret;
1128         }
1129
1130         return -EINVAL;
1131 }
1132
1133 /*
1134  * Map an iov into an array of pages and offset/length tupples. With the
1135  * partial_page structure, we can map several non-contiguous ranges into
1136  * our ones pages[] map instead of splitting that operation into pieces.
1137  * Could easily be exported as a generic helper for other users, in which
1138  * case one would probably want to add a 'max_nr_pages' parameter as well.
1139  */
1140 static int get_iovec_page_array(const struct iovec __user *iov,
1141                                 unsigned int nr_vecs, struct page **pages,
1142                                 struct partial_page *partial, int aligned)
1143 {
1144         int buffers = 0, error = 0;
1145
1146         /*
1147          * It's ok to take the mmap_sem for reading, even
1148          * across a "get_user()".
1149          */
1150         down_read(&current->mm->mmap_sem);
1151
1152         while (nr_vecs) {
1153                 unsigned long off, npages;
1154                 void __user *base;
1155                 size_t len;
1156                 int i;
1157
1158                 /*
1159                  * Get user address base and length for this iovec.
1160                  */
1161                 error = get_user(base, &iov->iov_base);
1162                 if (unlikely(error))
1163                         break;
1164                 error = get_user(len, &iov->iov_len);
1165                 if (unlikely(error))
1166                         break;
1167
1168                 /*
1169                  * Sanity check this iovec. 0 read succeeds.
1170                  */
1171                 if (unlikely(!len))
1172                         break;
1173                 error = -EFAULT;
1174                 if (unlikely(!base))
1175                         break;
1176
1177                 /*
1178                  * Get this base offset and number of pages, then map
1179                  * in the user pages.
1180                  */
1181                 off = (unsigned long) base & ~PAGE_MASK;
1182
1183                 /*
1184                  * If asked for alignment, the offset must be zero and the
1185                  * length a multiple of the PAGE_SIZE.
1186                  */
1187                 error = -EINVAL;
1188                 if (aligned && (off || len & ~PAGE_MASK))
1189                         break;
1190
1191                 npages = (off + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
1192                 if (npages > PIPE_BUFFERS - buffers)
1193                         npages = PIPE_BUFFERS - buffers;
1194
1195                 error = get_user_pages(current, current->mm,
1196                                        (unsigned long) base, npages, 0, 0,
1197                                        &pages[buffers], NULL);
1198
1199                 if (unlikely(error <= 0))
1200                         break;
1201
1202                 /*
1203                  * Fill this contiguous range into the partial page map.
1204                  */
1205                 for (i = 0; i < error; i++) {
1206                         const int plen = min_t(size_t, len, PAGE_SIZE - off);
1207
1208                         partial[buffers].offset = off;
1209                         partial[buffers].len = plen;
1210
1211                         off = 0;
1212                         len -= plen;
1213                         buffers++;
1214                 }
1215
1216                 /*
1217                  * We didn't complete this iov, stop here since it probably
1218                  * means we have to move some of this into a pipe to
1219                  * be able to continue.
1220                  */
1221                 if (len)
1222                         break;
1223
1224                 /*
1225                  * Don't continue if we mapped fewer pages than we asked for,
1226                  * or if we mapped the max number of pages that we have
1227                  * room for.
1228                  */
1229                 if (error < npages || buffers == PIPE_BUFFERS)
1230                         break;
1231
1232                 nr_vecs--;
1233                 iov++;
1234         }
1235
1236         up_read(&current->mm->mmap_sem);
1237
1238         if (buffers)
1239                 return buffers;
1240
1241         return error;
1242 }
1243
1244 /*
1245  * vmsplice splices a user address range into a pipe. It can be thought of
1246  * as splice-from-memory, where the regular splice is splice-from-file (or
1247  * to file). In both cases the output is a pipe, naturally.
1248  *
1249  * Note that vmsplice only supports splicing _from_ user memory to a pipe,
1250  * not the other way around. Splicing from user memory is a simple operation
1251  * that can be supported without any funky alignment restrictions or nasty
1252  * vm tricks. We simply map in the user memory and fill them into a pipe.
1253  * The reverse isn't quite as easy, though. There are two possible solutions
1254  * for that:
1255  *
1256  *      - memcpy() the data internally, at which point we might as well just
1257  *        do a regular read() on the buffer anyway.
1258  *      - Lots of nasty vm tricks, that are neither fast nor flexible (it
1259  *        has restriction limitations on both ends of the pipe).
1260  *
1261  * Alas, it isn't here.
1262  *
1263  */
1264 static long do_vmsplice(struct file *file, const struct iovec __user *iov,
1265                         unsigned long nr_segs, unsigned int flags)
1266 {
1267         struct pipe_inode_info *pipe;
1268         struct page *pages[PIPE_BUFFERS];
1269         struct partial_page partial[PIPE_BUFFERS];
1270         struct splice_pipe_desc spd = {
1271                 .pages = pages,
1272                 .partial = partial,
1273                 .flags = flags,
1274                 .ops = &user_page_pipe_buf_ops,
1275         };
1276
1277         pipe = pipe_info(file->f_path.dentry->d_inode);
1278         if (!pipe)
1279                 return -EBADF;
1280         if (unlikely(nr_segs > UIO_MAXIOV))
1281                 return -EINVAL;
1282         else if (unlikely(!nr_segs))
1283                 return 0;
1284
1285         spd.nr_pages = get_iovec_page_array(iov, nr_segs, pages, partial,
1286                                             flags & SPLICE_F_GIFT);
1287         if (spd.nr_pages <= 0)
1288                 return spd.nr_pages;
1289
1290         return splice_to_pipe(pipe, &spd);
1291 }
1292
1293 asmlinkage long sys_vmsplice(int fd, const struct iovec __user *iov,
1294                              unsigned long nr_segs, unsigned int flags)
1295 {
1296         struct file *file;
1297         long error;
1298         int fput;
1299
1300         error = -EBADF;
1301         file = fget_light(fd, &fput);
1302         if (file) {
1303                 if (file->f_mode & FMODE_WRITE)
1304                         error = do_vmsplice(file, iov, nr_segs, flags);
1305
1306                 fput_light(file, fput);
1307         }
1308
1309         return error;
1310 }
1311
1312 asmlinkage long sys_splice(int fd_in, loff_t __user *off_in,
1313                            int fd_out, loff_t __user *off_out,
1314                            size_t len, unsigned int flags)
1315 {
1316         long error;
1317         struct file *in, *out;
1318         int fput_in, fput_out;
1319
1320         if (unlikely(!len))
1321                 return 0;
1322
1323         error = -EBADF;
1324         in = fget_light(fd_in, &fput_in);
1325         if (in) {
1326                 if (in->f_mode & FMODE_READ) {
1327                         out = fget_light(fd_out, &fput_out);
1328                         if (out) {
1329                                 if (out->f_mode & FMODE_WRITE)
1330                                         error = do_splice(in, off_in,
1331                                                           out, off_out,
1332                                                           len, flags);
1333                                 fput_light(out, fput_out);
1334                         }
1335                 }
1336
1337                 fput_light(in, fput_in);
1338         }
1339
1340         return error;
1341 }
1342
1343 /*
1344  * Make sure there's data to read. Wait for input if we can, otherwise
1345  * return an appropriate error.
1346  */
1347 static int link_ipipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
1348 {
1349         int ret;
1350
1351         /*
1352          * Check ->nrbufs without the inode lock first. This function
1353          * is speculative anyways, so missing one is ok.
1354          */
1355         if (pipe->nrbufs)
1356                 return 0;
1357
1358         ret = 0;
1359         mutex_lock(&pipe->inode->i_mutex);
1360
1361         while (!pipe->nrbufs) {
1362                 if (signal_pending(current)) {
1363                         ret = -ERESTARTSYS;
1364                         break;
1365                 }
1366                 if (!pipe->writers)
1367                         break;
1368                 if (!pipe->waiting_writers) {
1369                         if (flags & SPLICE_F_NONBLOCK) {
1370                                 ret = -EAGAIN;
1371                                 break;
1372                         }
1373                 }
1374                 pipe_wait(pipe);
1375         }
1376
1377         mutex_unlock(&pipe->inode->i_mutex);
1378         return ret;
1379 }
1380
1381 /*
1382  * Make sure there's writeable room. Wait for room if we can, otherwise
1383  * return an appropriate error.
1384  */
1385 static int link_opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
1386 {
1387         int ret;
1388
1389         /*
1390          * Check ->nrbufs without the inode lock first. This function
1391          * is speculative anyways, so missing one is ok.
1392          */
1393         if (pipe->nrbufs < PIPE_BUFFERS)
1394                 return 0;
1395
1396         ret = 0;
1397         mutex_lock(&pipe->inode->i_mutex);
1398
1399         while (pipe->nrbufs >= PIPE_BUFFERS) {
1400                 if (!pipe->readers) {
1401                         send_sig(SIGPIPE, current, 0);
1402                         ret = -EPIPE;
1403                         break;
1404                 }
1405                 if (flags & SPLICE_F_NONBLOCK) {
1406                         ret = -EAGAIN;
1407                         break;
1408                 }
1409                 if (signal_pending(current)) {
1410                         ret = -ERESTARTSYS;
1411                         break;
1412                 }
1413                 pipe->waiting_writers++;
1414                 pipe_wait(pipe);
1415                 pipe->waiting_writers--;
1416         }
1417
1418         mutex_unlock(&pipe->inode->i_mutex);
1419         return ret;
1420 }
1421
1422 /*
1423  * Link contents of ipipe to opipe.
1424  */
1425 static int link_pipe(struct pipe_inode_info *ipipe,
1426                      struct pipe_inode_info *opipe,
1427                      size_t len, unsigned int flags)
1428 {
1429         struct pipe_buffer *ibuf, *obuf;
1430         int ret = 0, i = 0, nbuf;
1431
1432         /*
1433          * Potential ABBA deadlock, work around it by ordering lock
1434          * grabbing by inode address. Otherwise two different processes
1435          * could deadlock (one doing tee from A -> B, the other from B -> A).
1436          */
1437         inode_double_lock(ipipe->inode, opipe->inode);
1438
1439         do {
1440                 if (!opipe->readers) {
1441                         send_sig(SIGPIPE, current, 0);
1442                         if (!ret)
1443                                 ret = -EPIPE;
1444                         break;
1445                 }
1446
1447                 /*
1448                  * If we have iterated all input buffers or ran out of
1449                  * output room, break.
1450                  */
1451                 if (i >= ipipe->nrbufs || opipe->nrbufs >= PIPE_BUFFERS)
1452                         break;
1453
1454                 ibuf = ipipe->bufs + ((ipipe->curbuf + i) & (PIPE_BUFFERS - 1));
1455                 nbuf = (opipe->curbuf + opipe->nrbufs) & (PIPE_BUFFERS - 1);
1456
1457                 /*
1458                  * Get a reference to this pipe buffer,
1459                  * so we can copy the contents over.
1460                  */
1461                 ibuf->ops->get(ipipe, ibuf);
1462
1463                 obuf = opipe->bufs + nbuf;
1464                 *obuf = *ibuf;
1465
1466                 /*
1467                  * Don't inherit the gift flag, we need to
1468                  * prevent multiple steals of this page.
1469                  */
1470                 obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
1471
1472                 if (obuf->len > len)
1473                         obuf->len = len;
1474
1475                 opipe->nrbufs++;
1476                 ret += obuf->len;
1477                 len -= obuf->len;
1478                 i++;
1479         } while (len);
1480
1481         inode_double_unlock(ipipe->inode, opipe->inode);
1482
1483         /*
1484          * If we put data in the output pipe, wakeup any potential readers.
1485          */
1486         if (ret > 0) {
1487                 smp_mb();
1488                 if (waitqueue_active(&opipe->wait))
1489                         wake_up_interruptible(&opipe->wait);
1490                 kill_fasync(&opipe->fasync_readers, SIGIO, POLL_IN);
1491         }
1492
1493         return ret;
1494 }
1495
1496 /*
1497  * This is a tee(1) implementation that works on pipes. It doesn't copy
1498  * any data, it simply references the 'in' pages on the 'out' pipe.
1499  * The 'flags' used are the SPLICE_F_* variants, currently the only
1500  * applicable one is SPLICE_F_NONBLOCK.
1501  */
1502 static long do_tee(struct file *in, struct file *out, size_t len,
1503                    unsigned int flags)
1504 {
1505         struct pipe_inode_info *ipipe = pipe_info(in->f_path.dentry->d_inode);
1506         struct pipe_inode_info *opipe = pipe_info(out->f_path.dentry->d_inode);
1507         int ret = -EINVAL;
1508
1509         /*
1510          * Duplicate the contents of ipipe to opipe without actually
1511          * copying the data.
1512          */
1513         if (ipipe && opipe && ipipe != opipe) {
1514                 /*
1515                  * Keep going, unless we encounter an error. The ipipe/opipe
1516                  * ordering doesn't really matter.
1517                  */
1518                 ret = link_ipipe_prep(ipipe, flags);
1519                 if (!ret) {
1520                         ret = link_opipe_prep(opipe, flags);
1521                         if (!ret) {
1522                                 ret = link_pipe(ipipe, opipe, len, flags);
1523                                 if (!ret && (flags & SPLICE_F_NONBLOCK))
1524                                         ret = -EAGAIN;
1525                         }
1526                 }
1527         }
1528
1529         return ret;
1530 }
1531
1532 asmlinkage long sys_tee(int fdin, int fdout, size_t len, unsigned int flags)
1533 {
1534         struct file *in;
1535         int error, fput_in;
1536
1537         if (unlikely(!len))
1538                 return 0;
1539
1540         error = -EBADF;
1541         in = fget_light(fdin, &fput_in);
1542         if (in) {
1543                 if (in->f_mode & FMODE_READ) {
1544                         int fput_out;
1545                         struct file *out = fget_light(fdout, &fput_out);
1546
1547                         if (out) {
1548                                 if (out->f_mode & FMODE_WRITE)
1549                                         error = do_tee(in, out, len, flags);
1550                                 fput_light(out, fput_out);
1551                         }
1552                 }
1553                 fput_light(in, fput_in);
1554         }
1555
1556         return error;
1557 }