splice: abstract out actor data
[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         unsigned int spd_pages = spd->nr_pages;
180         int ret, do_wakeup, page_nr;
181
182         ret = 0;
183         do_wakeup = 0;
184         page_nr = 0;
185
186         if (pipe->inode)
187                 mutex_lock(&pipe->inode->i_mutex);
188
189         for (;;) {
190                 if (!pipe->readers) {
191                         send_sig(SIGPIPE, current, 0);
192                         if (!ret)
193                                 ret = -EPIPE;
194                         break;
195                 }
196
197                 if (pipe->nrbufs < PIPE_BUFFERS) {
198                         int newbuf = (pipe->curbuf + pipe->nrbufs) & (PIPE_BUFFERS - 1);
199                         struct pipe_buffer *buf = pipe->bufs + newbuf;
200
201                         buf->page = spd->pages[page_nr];
202                         buf->offset = spd->partial[page_nr].offset;
203                         buf->len = spd->partial[page_nr].len;
204                         buf->ops = spd->ops;
205                         if (spd->flags & SPLICE_F_GIFT)
206                                 buf->flags |= PIPE_BUF_FLAG_GIFT;
207
208                         pipe->nrbufs++;
209                         page_nr++;
210                         ret += buf->len;
211
212                         if (pipe->inode)
213                                 do_wakeup = 1;
214
215                         if (!--spd->nr_pages)
216                                 break;
217                         if (pipe->nrbufs < PIPE_BUFFERS)
218                                 continue;
219
220                         break;
221                 }
222
223                 if (spd->flags & SPLICE_F_NONBLOCK) {
224                         if (!ret)
225                                 ret = -EAGAIN;
226                         break;
227                 }
228
229                 if (signal_pending(current)) {
230                         if (!ret)
231                                 ret = -ERESTARTSYS;
232                         break;
233                 }
234
235                 if (do_wakeup) {
236                         smp_mb();
237                         if (waitqueue_active(&pipe->wait))
238                                 wake_up_interruptible_sync(&pipe->wait);
239                         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
240                         do_wakeup = 0;
241                 }
242
243                 pipe->waiting_writers++;
244                 pipe_wait(pipe);
245                 pipe->waiting_writers--;
246         }
247
248         if (pipe->inode) {
249                 mutex_unlock(&pipe->inode->i_mutex);
250
251                 if (do_wakeup) {
252                         smp_mb();
253                         if (waitqueue_active(&pipe->wait))
254                                 wake_up_interruptible(&pipe->wait);
255                         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
256                 }
257         }
258
259         while (page_nr < spd_pages)
260                 page_cache_release(spd->pages[page_nr++]);
261
262         return ret;
263 }
264
265 static int
266 __generic_file_splice_read(struct file *in, loff_t *ppos,
267                            struct pipe_inode_info *pipe, size_t len,
268                            unsigned int flags)
269 {
270         struct address_space *mapping = in->f_mapping;
271         unsigned int loff, nr_pages;
272         struct page *pages[PIPE_BUFFERS];
273         struct partial_page partial[PIPE_BUFFERS];
274         struct page *page;
275         pgoff_t index, end_index;
276         loff_t isize;
277         int error, page_nr;
278         struct splice_pipe_desc spd = {
279                 .pages = pages,
280                 .partial = partial,
281                 .flags = flags,
282                 .ops = &page_cache_pipe_buf_ops,
283         };
284
285         index = *ppos >> PAGE_CACHE_SHIFT;
286         loff = *ppos & ~PAGE_CACHE_MASK;
287         nr_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
288
289         if (nr_pages > PIPE_BUFFERS)
290                 nr_pages = PIPE_BUFFERS;
291
292         /*
293          * Don't try to 2nd guess the read-ahead logic, call into
294          * page_cache_readahead() like the page cache reads would do.
295          */
296         page_cache_readahead(mapping, &in->f_ra, in, index, nr_pages);
297
298         /*
299          * Now fill in the holes:
300          */
301         error = 0;
302
303         /*
304          * Lookup the (hopefully) full range of pages we need.
305          */
306         spd.nr_pages = find_get_pages_contig(mapping, index, nr_pages, pages);
307
308         /*
309          * If find_get_pages_contig() returned fewer pages than we needed,
310          * allocate the rest.
311          */
312         index += spd.nr_pages;
313         while (spd.nr_pages < nr_pages) {
314                 /*
315                  * Page could be there, find_get_pages_contig() breaks on
316                  * the first hole.
317                  */
318                 page = find_get_page(mapping, index);
319                 if (!page) {
320                         /*
321                          * Make sure the read-ahead engine is notified
322                          * about this failure.
323                          */
324                         handle_ra_miss(mapping, &in->f_ra, index);
325
326                         /*
327                          * page didn't exist, allocate one.
328                          */
329                         page = page_cache_alloc_cold(mapping);
330                         if (!page)
331                                 break;
332
333                         error = add_to_page_cache_lru(page, mapping, index,
334                                               GFP_KERNEL);
335                         if (unlikely(error)) {
336                                 page_cache_release(page);
337                                 if (error == -EEXIST)
338                                         continue;
339                                 break;
340                         }
341                         /*
342                          * add_to_page_cache() locks the page, unlock it
343                          * to avoid convoluting the logic below even more.
344                          */
345                         unlock_page(page);
346                 }
347
348                 pages[spd.nr_pages++] = page;
349                 index++;
350         }
351
352         /*
353          * Now loop over the map and see if we need to start IO on any
354          * pages, fill in the partial map, etc.
355          */
356         index = *ppos >> PAGE_CACHE_SHIFT;
357         nr_pages = spd.nr_pages;
358         spd.nr_pages = 0;
359         for (page_nr = 0; page_nr < nr_pages; page_nr++) {
360                 unsigned int this_len;
361
362                 if (!len)
363                         break;
364
365                 /*
366                  * this_len is the max we'll use from this page
367                  */
368                 this_len = min_t(unsigned long, len, PAGE_CACHE_SIZE - loff);
369                 page = pages[page_nr];
370
371                 /*
372                  * If the page isn't uptodate, we may need to start io on it
373                  */
374                 if (!PageUptodate(page)) {
375                         /*
376                          * If in nonblock mode then dont block on waiting
377                          * for an in-flight io page
378                          */
379                         if (flags & SPLICE_F_NONBLOCK) {
380                                 if (TestSetPageLocked(page))
381                                         break;
382                         } else
383                                 lock_page(page);
384
385                         /*
386                          * page was truncated, stop here. if this isn't the
387                          * first page, we'll just complete what we already
388                          * added
389                          */
390                         if (!page->mapping) {
391                                 unlock_page(page);
392                                 break;
393                         }
394                         /*
395                          * page was already under io and is now done, great
396                          */
397                         if (PageUptodate(page)) {
398                                 unlock_page(page);
399                                 goto fill_it;
400                         }
401
402                         /*
403                          * need to read in the page
404                          */
405                         error = mapping->a_ops->readpage(in, page);
406                         if (unlikely(error)) {
407                                 /*
408                                  * We really should re-lookup the page here,
409                                  * but it complicates things a lot. Instead
410                                  * lets just do what we already stored, and
411                                  * we'll get it the next time we are called.
412                                  */
413                                 if (error == AOP_TRUNCATED_PAGE)
414                                         error = 0;
415
416                                 break;
417                         }
418                 }
419 fill_it:
420                 /*
421                  * i_size must be checked after PageUptodate.
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                         unsigned int plen;
434
435                         /*
436                          * max good bytes in this page
437                          */
438                         plen = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
439                         if (plen <= loff)
440                                 break;
441
442                         /*
443                          * force quit after adding this page
444                          */
445                         this_len = min(this_len, plen - loff);
446                         len = this_len;
447                 }
448
449                 partial[page_nr].offset = loff;
450                 partial[page_nr].len = this_len;
451                 len -= this_len;
452                 loff = 0;
453                 spd.nr_pages++;
454                 index++;
455         }
456
457         /*
458          * Release any pages at the end, if we quit early. 'page_nr' is how far
459          * we got, 'nr_pages' is how many pages are in the map.
460          */
461         while (page_nr < nr_pages)
462                 page_cache_release(pages[page_nr++]);
463
464         if (spd.nr_pages)
465                 return splice_to_pipe(pipe, &spd);
466
467         return error;
468 }
469
470 /**
471  * generic_file_splice_read - splice data from file to a pipe
472  * @in:         file to splice from
473  * @pipe:       pipe to splice to
474  * @len:        number of bytes to splice
475  * @flags:      splice modifier flags
476  *
477  * Will read pages from given file and fill them into a pipe.
478  */
479 ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
480                                  struct pipe_inode_info *pipe, size_t len,
481                                  unsigned int flags)
482 {
483         ssize_t spliced;
484         int ret;
485         loff_t isize, left;
486
487         isize = i_size_read(in->f_mapping->host);
488         if (unlikely(*ppos >= isize))
489                 return 0;
490
491         left = isize - *ppos;
492         if (unlikely(left < len))
493                 len = left;
494
495         ret = 0;
496         spliced = 0;
497         while (len) {
498                 ret = __generic_file_splice_read(in, ppos, pipe, len, flags);
499
500                 if (ret < 0)
501                         break;
502                 else if (!ret) {
503                         if (spliced)
504                                 break;
505                         if (flags & SPLICE_F_NONBLOCK) {
506                                 ret = -EAGAIN;
507                                 break;
508                         }
509                 }
510
511                 *ppos += ret;
512                 len -= ret;
513                 spliced += ret;
514         }
515
516         if (spliced)
517                 return spliced;
518
519         return ret;
520 }
521
522 EXPORT_SYMBOL(generic_file_splice_read);
523
524 /*
525  * Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->pos'
526  * using sendpage(). Return the number of bytes sent.
527  */
528 static int pipe_to_sendpage(struct pipe_inode_info *pipe,
529                             struct pipe_buffer *buf, struct splice_desc *sd)
530 {
531         struct file *file = sd->file;
532         loff_t pos = sd->pos;
533         int ret, more;
534
535         ret = buf->ops->pin(pipe, buf);
536         if (!ret) {
537                 more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len;
538
539                 ret = file->f_op->sendpage(file, buf->page, buf->offset,
540                                            sd->len, &pos, more);
541         }
542
543         return ret;
544 }
545
546 /*
547  * This is a little more tricky than the file -> pipe splicing. There are
548  * basically three cases:
549  *
550  *      - Destination page already exists in the address space and there
551  *        are users of it. For that case we have no other option that
552  *        copying the data. Tough luck.
553  *      - Destination page already exists in the address space, but there
554  *        are no users of it. Make sure it's uptodate, then drop it. Fall
555  *        through to last case.
556  *      - Destination page does not exist, we can add the pipe page to
557  *        the page cache and avoid the copy.
558  *
559  * If asked to move pages to the output file (SPLICE_F_MOVE is set in
560  * sd->flags), we attempt to migrate pages from the pipe to the output
561  * file address space page cache. This is possible if no one else has
562  * the pipe page referenced outside of the pipe and page cache. If
563  * SPLICE_F_MOVE isn't set, or we cannot move the page, we simply create
564  * a new page in the output file page cache and fill/dirty that.
565  */
566 static int pipe_to_file(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
567                         struct splice_desc *sd)
568 {
569         struct file *file = sd->file;
570         struct address_space *mapping = file->f_mapping;
571         unsigned int offset, this_len;
572         struct page *page;
573         pgoff_t index;
574         int ret;
575
576         /*
577          * make sure the data in this buffer is uptodate
578          */
579         ret = buf->ops->pin(pipe, buf);
580         if (unlikely(ret))
581                 return ret;
582
583         index = sd->pos >> PAGE_CACHE_SHIFT;
584         offset = sd->pos & ~PAGE_CACHE_MASK;
585
586         this_len = sd->len;
587         if (this_len + offset > PAGE_CACHE_SIZE)
588                 this_len = PAGE_CACHE_SIZE - offset;
589
590 find_page:
591         page = find_lock_page(mapping, index);
592         if (!page) {
593                 ret = -ENOMEM;
594                 page = page_cache_alloc_cold(mapping);
595                 if (unlikely(!page))
596                         goto out_ret;
597
598                 /*
599                  * This will also lock the page
600                  */
601                 ret = add_to_page_cache_lru(page, mapping, index,
602                                             GFP_KERNEL);
603                 if (unlikely(ret))
604                         goto out;
605         }
606
607         ret = mapping->a_ops->prepare_write(file, page, offset, offset+this_len);
608         if (unlikely(ret)) {
609                 loff_t isize = i_size_read(mapping->host);
610
611                 if (ret != AOP_TRUNCATED_PAGE)
612                         unlock_page(page);
613                 page_cache_release(page);
614                 if (ret == AOP_TRUNCATED_PAGE)
615                         goto find_page;
616
617                 /*
618                  * prepare_write() may have instantiated a few blocks
619                  * outside i_size.  Trim these off again.
620                  */
621                 if (sd->pos + this_len > isize)
622                         vmtruncate(mapping->host, isize);
623
624                 goto out_ret;
625         }
626
627         if (buf->page != page) {
628                 /*
629                  * Careful, ->map() uses KM_USER0!
630                  */
631                 char *src = buf->ops->map(pipe, buf, 1);
632                 char *dst = kmap_atomic(page, KM_USER1);
633
634                 memcpy(dst + offset, src + buf->offset, this_len);
635                 flush_dcache_page(page);
636                 kunmap_atomic(dst, KM_USER1);
637                 buf->ops->unmap(pipe, buf, src);
638         }
639
640         ret = mapping->a_ops->commit_write(file, page, offset, offset+this_len);
641         if (ret) {
642                 if (ret == AOP_TRUNCATED_PAGE) {
643                         page_cache_release(page);
644                         goto find_page;
645                 }
646                 if (ret < 0)
647                         goto out;
648                 /*
649                  * Partial write has happened, so 'ret' already initialized by
650                  * number of bytes written, Where is nothing we have to do here.
651                  */
652         } else
653                 ret = this_len;
654         /*
655          * Return the number of bytes written and mark page as
656          * accessed, we are now done!
657          */
658         mark_page_accessed(page);
659 out:
660         page_cache_release(page);
661         unlock_page(page);
662 out_ret:
663         return ret;
664 }
665
666 /*
667  * Pipe input worker. Most of this logic works like a regular pipe, the
668  * key here is the 'actor' worker passed in that actually moves the data
669  * to the wanted destination. See pipe_to_file/pipe_to_sendpage above.
670  */
671 ssize_t __splice_from_pipe(struct pipe_inode_info *pipe, struct splice_desc *sd,
672                            splice_actor *actor)
673 {
674         int ret, do_wakeup, err;
675
676         ret = 0;
677         do_wakeup = 0;
678
679         for (;;) {
680                 if (pipe->nrbufs) {
681                         struct pipe_buffer *buf = pipe->bufs + pipe->curbuf;
682                         const struct pipe_buf_operations *ops = buf->ops;
683
684                         sd->len = buf->len;
685                         if (sd->len > sd->total_len)
686                                 sd->len = sd->total_len;
687
688                         err = actor(pipe, buf, sd);
689                         if (err <= 0) {
690                                 if (!ret && err != -ENODATA)
691                                         ret = err;
692
693                                 break;
694                         }
695
696                         ret += err;
697                         buf->offset += err;
698                         buf->len -= err;
699
700                         sd->len -= err;
701                         sd->pos += err;
702                         sd->total_len -= err;
703                         if (sd->len)
704                                 continue;
705
706                         if (!buf->len) {
707                                 buf->ops = NULL;
708                                 ops->release(pipe, buf);
709                                 pipe->curbuf = (pipe->curbuf + 1) & (PIPE_BUFFERS - 1);
710                                 pipe->nrbufs--;
711                                 if (pipe->inode)
712                                         do_wakeup = 1;
713                         }
714
715                         if (!sd->total_len)
716                                 break;
717                 }
718
719                 if (pipe->nrbufs)
720                         continue;
721                 if (!pipe->writers)
722                         break;
723                 if (!pipe->waiting_writers) {
724                         if (ret)
725                                 break;
726                 }
727
728                 if (sd->flags & SPLICE_F_NONBLOCK) {
729                         if (!ret)
730                                 ret = -EAGAIN;
731                         break;
732                 }
733
734                 if (signal_pending(current)) {
735                         if (!ret)
736                                 ret = -ERESTARTSYS;
737                         break;
738                 }
739
740                 if (do_wakeup) {
741                         smp_mb();
742                         if (waitqueue_active(&pipe->wait))
743                                 wake_up_interruptible_sync(&pipe->wait);
744                         kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
745                         do_wakeup = 0;
746                 }
747
748                 pipe_wait(pipe);
749         }
750
751         if (do_wakeup) {
752                 smp_mb();
753                 if (waitqueue_active(&pipe->wait))
754                         wake_up_interruptible(&pipe->wait);
755                 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
756         }
757
758         return ret;
759 }
760 EXPORT_SYMBOL(__splice_from_pipe);
761
762 ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
763                          loff_t *ppos, size_t len, unsigned int flags,
764                          splice_actor *actor)
765 {
766         ssize_t ret;
767         struct inode *inode = out->f_mapping->host;
768         struct splice_desc sd = {
769                 .total_len = len,
770                 .flags = flags,
771                 .pos = *ppos,
772                 .file = out,
773         };
774
775         /*
776          * The actor worker might be calling ->prepare_write and
777          * ->commit_write. Most of the time, these expect i_mutex to
778          * be held. Since this may result in an ABBA deadlock with
779          * pipe->inode, we have to order lock acquiry here.
780          */
781         inode_double_lock(inode, pipe->inode);
782         ret = __splice_from_pipe(pipe, &sd, actor);
783         inode_double_unlock(inode, pipe->inode);
784
785         return ret;
786 }
787
788 /**
789  * generic_file_splice_write_nolock - generic_file_splice_write without mutexes
790  * @pipe:       pipe info
791  * @out:        file to write to
792  * @len:        number of bytes to splice
793  * @flags:      splice modifier flags
794  *
795  * Will either move or copy pages (determined by @flags options) from
796  * the given pipe inode to the given file. The caller is responsible
797  * for acquiring i_mutex on both inodes.
798  *
799  */
800 ssize_t
801 generic_file_splice_write_nolock(struct pipe_inode_info *pipe, struct file *out,
802                                  loff_t *ppos, size_t len, unsigned int flags)
803 {
804         struct address_space *mapping = out->f_mapping;
805         struct inode *inode = mapping->host;
806         struct splice_desc sd = {
807                 .total_len = len,
808                 .flags = flags,
809                 .pos = *ppos,
810                 .file = out,
811         };
812         ssize_t ret;
813         int err;
814
815         err = remove_suid(out->f_path.dentry);
816         if (unlikely(err))
817                 return err;
818
819         ret = __splice_from_pipe(pipe, &sd, pipe_to_file);
820         if (ret > 0) {
821                 unsigned long nr_pages;
822
823                 *ppos += ret;
824                 nr_pages = (ret + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
825
826                 /*
827                  * If file or inode is SYNC and we actually wrote some data,
828                  * sync it.
829                  */
830                 if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
831                         err = generic_osync_inode(inode, mapping,
832                                                   OSYNC_METADATA|OSYNC_DATA);
833
834                         if (err)
835                                 ret = err;
836                 }
837                 balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
838         }
839
840         return ret;
841 }
842
843 EXPORT_SYMBOL(generic_file_splice_write_nolock);
844
845 /**
846  * generic_file_splice_write - splice data from a pipe to a file
847  * @pipe:       pipe info
848  * @out:        file to write to
849  * @len:        number of bytes to splice
850  * @flags:      splice modifier flags
851  *
852  * Will either move or copy pages (determined by @flags options) from
853  * the given pipe inode to the given file.
854  *
855  */
856 ssize_t
857 generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
858                           loff_t *ppos, size_t len, unsigned int flags)
859 {
860         struct address_space *mapping = out->f_mapping;
861         struct inode *inode = mapping->host;
862         ssize_t ret;
863         int err;
864
865         err = should_remove_suid(out->f_path.dentry);
866         if (unlikely(err)) {
867                 mutex_lock(&inode->i_mutex);
868                 err = __remove_suid(out->f_path.dentry, err);
869                 mutex_unlock(&inode->i_mutex);
870                 if (err)
871                         return err;
872         }
873
874         ret = splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_file);
875         if (ret > 0) {
876                 unsigned long nr_pages;
877
878                 *ppos += ret;
879                 nr_pages = (ret + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
880
881                 /*
882                  * If file or inode is SYNC and we actually wrote some data,
883                  * sync it.
884                  */
885                 if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
886                         mutex_lock(&inode->i_mutex);
887                         err = generic_osync_inode(inode, mapping,
888                                                   OSYNC_METADATA|OSYNC_DATA);
889                         mutex_unlock(&inode->i_mutex);
890
891                         if (err)
892                                 ret = err;
893                 }
894                 balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
895         }
896
897         return ret;
898 }
899
900 EXPORT_SYMBOL(generic_file_splice_write);
901
902 /**
903  * generic_splice_sendpage - splice data from a pipe to a socket
904  * @inode:      pipe inode
905  * @out:        socket to write to
906  * @len:        number of bytes to splice
907  * @flags:      splice modifier flags
908  *
909  * Will send @len bytes from the pipe to a network socket. No data copying
910  * is involved.
911  *
912  */
913 ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe, struct file *out,
914                                 loff_t *ppos, size_t len, unsigned int flags)
915 {
916         return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_sendpage);
917 }
918
919 EXPORT_SYMBOL(generic_splice_sendpage);
920
921 /*
922  * Attempt to initiate a splice from pipe to file.
923  */
924 static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
925                            loff_t *ppos, size_t len, unsigned int flags)
926 {
927         int ret;
928
929         if (unlikely(!out->f_op || !out->f_op->splice_write))
930                 return -EINVAL;
931
932         if (unlikely(!(out->f_mode & FMODE_WRITE)))
933                 return -EBADF;
934
935         ret = rw_verify_area(WRITE, out, ppos, len);
936         if (unlikely(ret < 0))
937                 return ret;
938
939         return out->f_op->splice_write(pipe, out, ppos, len, flags);
940 }
941
942 /*
943  * Attempt to initiate a splice from a file to a pipe.
944  */
945 static long do_splice_to(struct file *in, loff_t *ppos,
946                          struct pipe_inode_info *pipe, size_t len,
947                          unsigned int flags)
948 {
949         int ret;
950
951         if (unlikely(!in->f_op || !in->f_op->splice_read))
952                 return -EINVAL;
953
954         if (unlikely(!(in->f_mode & FMODE_READ)))
955                 return -EBADF;
956
957         ret = rw_verify_area(READ, in, ppos, len);
958         if (unlikely(ret < 0))
959                 return ret;
960
961         return in->f_op->splice_read(in, ppos, pipe, len, flags);
962 }
963
964 /*
965  * Splices from an input file to an actor, using a 'direct' pipe.
966  */
967 ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
968                                splice_direct_actor *actor)
969 {
970         struct pipe_inode_info *pipe;
971         long ret, bytes;
972         umode_t i_mode;
973         size_t len;
974         int i, flags;
975
976         /*
977          * We require the input being a regular file, as we don't want to
978          * randomly drop data for eg socket -> socket splicing. Use the
979          * piped splicing for that!
980          */
981         i_mode = in->f_path.dentry->d_inode->i_mode;
982         if (unlikely(!S_ISREG(i_mode) && !S_ISBLK(i_mode)))
983                 return -EINVAL;
984
985         /*
986          * neither in nor out is a pipe, setup an internal pipe attached to
987          * 'out' and transfer the wanted data from 'in' to 'out' through that
988          */
989         pipe = current->splice_pipe;
990         if (unlikely(!pipe)) {
991                 pipe = alloc_pipe_info(NULL);
992                 if (!pipe)
993                         return -ENOMEM;
994
995                 /*
996                  * We don't have an immediate reader, but we'll read the stuff
997                  * out of the pipe right after the splice_to_pipe(). So set
998                  * PIPE_READERS appropriately.
999                  */
1000                 pipe->readers = 1;
1001
1002                 current->splice_pipe = pipe;
1003         }
1004
1005         /*
1006          * Do the splice.
1007          */
1008         ret = 0;
1009         bytes = 0;
1010         len = sd->total_len;
1011         flags = sd->flags;
1012
1013         /*
1014          * Don't block on output, we have to drain the direct pipe.
1015          */
1016         sd->flags &= ~SPLICE_F_NONBLOCK;
1017
1018         while (len) {
1019                 size_t read_len, max_read_len;
1020
1021                 /*
1022                  * Do at most PIPE_BUFFERS pages worth of transfer:
1023                  */
1024                 max_read_len = min(len, (size_t)(PIPE_BUFFERS*PAGE_SIZE));
1025
1026                 ret = do_splice_to(in, &sd->pos, pipe, max_read_len, flags);
1027                 if (unlikely(ret < 0))
1028                         goto out_release;
1029
1030                 read_len = ret;
1031                 sd->total_len = read_len;
1032
1033                 /*
1034                  * NOTE: nonblocking mode only applies to the input. We
1035                  * must not do the output in nonblocking mode as then we
1036                  * could get stuck data in the internal pipe:
1037                  */
1038                 ret = actor(pipe, sd);
1039                 if (unlikely(ret < 0))
1040                         goto out_release;
1041
1042                 bytes += ret;
1043                 len -= ret;
1044
1045                 /*
1046                  * In nonblocking mode, if we got back a short read then
1047                  * that was due to either an IO error or due to the
1048                  * pagecache entry not being there. In the IO error case
1049                  * the _next_ splice attempt will produce a clean IO error
1050                  * return value (not a short read), so in both cases it's
1051                  * correct to break out of the loop here:
1052                  */
1053                 if ((flags & SPLICE_F_NONBLOCK) && (read_len < max_read_len))
1054                         break;
1055         }
1056
1057         pipe->nrbufs = pipe->curbuf = 0;
1058
1059         return bytes;
1060
1061 out_release:
1062         /*
1063          * If we did an incomplete transfer we must release
1064          * the pipe buffers in question:
1065          */
1066         for (i = 0; i < PIPE_BUFFERS; i++) {
1067                 struct pipe_buffer *buf = pipe->bufs + i;
1068
1069                 if (buf->ops) {
1070                         buf->ops->release(pipe, buf);
1071                         buf->ops = NULL;
1072                 }
1073         }
1074         pipe->nrbufs = pipe->curbuf = 0;
1075
1076         /*
1077          * If we transferred some data, return the number of bytes:
1078          */
1079         if (bytes > 0)
1080                 return bytes;
1081
1082         return ret;
1083
1084 }
1085 EXPORT_SYMBOL(splice_direct_to_actor);
1086
1087 static int direct_splice_actor(struct pipe_inode_info *pipe,
1088                                struct splice_desc *sd)
1089 {
1090         struct file *file = sd->file;
1091
1092         return do_splice_from(pipe, file, &sd->pos, sd->total_len, sd->flags);
1093 }
1094
1095 long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
1096                       size_t len, unsigned int flags)
1097 {
1098         struct splice_desc sd = {
1099                 .len            = len,
1100                 .total_len      = len,
1101                 .flags          = flags,
1102                 .pos            = *ppos,
1103                 .file           = out,
1104         };
1105         size_t ret;
1106
1107         ret = splice_direct_to_actor(in, &sd, direct_splice_actor);
1108         *ppos = sd.pos;
1109         return ret;
1110 }
1111
1112 /*
1113  * After the inode slimming patch, i_pipe/i_bdev/i_cdev share the same
1114  * location, so checking ->i_pipe is not enough to verify that this is a
1115  * pipe.
1116  */
1117 static inline struct pipe_inode_info *pipe_info(struct inode *inode)
1118 {
1119         if (S_ISFIFO(inode->i_mode))
1120                 return inode->i_pipe;
1121
1122         return NULL;
1123 }
1124
1125 /*
1126  * Determine where to splice to/from.
1127  */
1128 static long do_splice(struct file *in, loff_t __user *off_in,
1129                       struct file *out, loff_t __user *off_out,
1130                       size_t len, unsigned int flags)
1131 {
1132         struct pipe_inode_info *pipe;
1133         loff_t offset, *off;
1134         long ret;
1135
1136         pipe = pipe_info(in->f_path.dentry->d_inode);
1137         if (pipe) {
1138                 if (off_in)
1139                         return -ESPIPE;
1140                 if (off_out) {
1141                         if (out->f_op->llseek == no_llseek)
1142                                 return -EINVAL;
1143                         if (copy_from_user(&offset, off_out, sizeof(loff_t)))
1144                                 return -EFAULT;
1145                         off = &offset;
1146                 } else
1147                         off = &out->f_pos;
1148
1149                 ret = do_splice_from(pipe, out, off, len, flags);
1150
1151                 if (off_out && copy_to_user(off_out, off, sizeof(loff_t)))
1152                         ret = -EFAULT;
1153
1154                 return ret;
1155         }
1156
1157         pipe = pipe_info(out->f_path.dentry->d_inode);
1158         if (pipe) {
1159                 if (off_out)
1160                         return -ESPIPE;
1161                 if (off_in) {
1162                         if (in->f_op->llseek == no_llseek)
1163                                 return -EINVAL;
1164                         if (copy_from_user(&offset, off_in, sizeof(loff_t)))
1165                                 return -EFAULT;
1166                         off = &offset;
1167                 } else
1168                         off = &in->f_pos;
1169
1170                 ret = do_splice_to(in, off, pipe, len, flags);
1171
1172                 if (off_in && copy_to_user(off_in, off, sizeof(loff_t)))
1173                         ret = -EFAULT;
1174
1175                 return ret;
1176         }
1177
1178         return -EINVAL;
1179 }
1180
1181 /*
1182  * Map an iov into an array of pages and offset/length tupples. With the
1183  * partial_page structure, we can map several non-contiguous ranges into
1184  * our ones pages[] map instead of splitting that operation into pieces.
1185  * Could easily be exported as a generic helper for other users, in which
1186  * case one would probably want to add a 'max_nr_pages' parameter as well.
1187  */
1188 static int get_iovec_page_array(const struct iovec __user *iov,
1189                                 unsigned int nr_vecs, struct page **pages,
1190                                 struct partial_page *partial, int aligned)
1191 {
1192         int buffers = 0, error = 0;
1193
1194         /*
1195          * It's ok to take the mmap_sem for reading, even
1196          * across a "get_user()".
1197          */
1198         down_read(&current->mm->mmap_sem);
1199
1200         while (nr_vecs) {
1201                 unsigned long off, npages;
1202                 void __user *base;
1203                 size_t len;
1204                 int i;
1205
1206                 /*
1207                  * Get user address base and length for this iovec.
1208                  */
1209                 error = get_user(base, &iov->iov_base);
1210                 if (unlikely(error))
1211                         break;
1212                 error = get_user(len, &iov->iov_len);
1213                 if (unlikely(error))
1214                         break;
1215
1216                 /*
1217                  * Sanity check this iovec. 0 read succeeds.
1218                  */
1219                 if (unlikely(!len))
1220                         break;
1221                 error = -EFAULT;
1222                 if (unlikely(!base))
1223                         break;
1224
1225                 /*
1226                  * Get this base offset and number of pages, then map
1227                  * in the user pages.
1228                  */
1229                 off = (unsigned long) base & ~PAGE_MASK;
1230
1231                 /*
1232                  * If asked for alignment, the offset must be zero and the
1233                  * length a multiple of the PAGE_SIZE.
1234                  */
1235                 error = -EINVAL;
1236                 if (aligned && (off || len & ~PAGE_MASK))
1237                         break;
1238
1239                 npages = (off + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
1240                 if (npages > PIPE_BUFFERS - buffers)
1241                         npages = PIPE_BUFFERS - buffers;
1242
1243                 error = get_user_pages(current, current->mm,
1244                                        (unsigned long) base, npages, 0, 0,
1245                                        &pages[buffers], NULL);
1246
1247                 if (unlikely(error <= 0))
1248                         break;
1249
1250                 /*
1251                  * Fill this contiguous range into the partial page map.
1252                  */
1253                 for (i = 0; i < error; i++) {
1254                         const int plen = min_t(size_t, len, PAGE_SIZE - off);
1255
1256                         partial[buffers].offset = off;
1257                         partial[buffers].len = plen;
1258
1259                         off = 0;
1260                         len -= plen;
1261                         buffers++;
1262                 }
1263
1264                 /*
1265                  * We didn't complete this iov, stop here since it probably
1266                  * means we have to move some of this into a pipe to
1267                  * be able to continue.
1268                  */
1269                 if (len)
1270                         break;
1271
1272                 /*
1273                  * Don't continue if we mapped fewer pages than we asked for,
1274                  * or if we mapped the max number of pages that we have
1275                  * room for.
1276                  */
1277                 if (error < npages || buffers == PIPE_BUFFERS)
1278                         break;
1279
1280                 nr_vecs--;
1281                 iov++;
1282         }
1283
1284         up_read(&current->mm->mmap_sem);
1285
1286         if (buffers)
1287                 return buffers;
1288
1289         return error;
1290 }
1291
1292 /*
1293  * vmsplice splices a user address range into a pipe. It can be thought of
1294  * as splice-from-memory, where the regular splice is splice-from-file (or
1295  * to file). In both cases the output is a pipe, naturally.
1296  *
1297  * Note that vmsplice only supports splicing _from_ user memory to a pipe,
1298  * not the other way around. Splicing from user memory is a simple operation
1299  * that can be supported without any funky alignment restrictions or nasty
1300  * vm tricks. We simply map in the user memory and fill them into a pipe.
1301  * The reverse isn't quite as easy, though. There are two possible solutions
1302  * for that:
1303  *
1304  *      - memcpy() the data internally, at which point we might as well just
1305  *        do a regular read() on the buffer anyway.
1306  *      - Lots of nasty vm tricks, that are neither fast nor flexible (it
1307  *        has restriction limitations on both ends of the pipe).
1308  *
1309  * Alas, it isn't here.
1310  *
1311  */
1312 static long do_vmsplice(struct file *file, const struct iovec __user *iov,
1313                         unsigned long nr_segs, unsigned int flags)
1314 {
1315         struct pipe_inode_info *pipe;
1316         struct page *pages[PIPE_BUFFERS];
1317         struct partial_page partial[PIPE_BUFFERS];
1318         struct splice_pipe_desc spd = {
1319                 .pages = pages,
1320                 .partial = partial,
1321                 .flags = flags,
1322                 .ops = &user_page_pipe_buf_ops,
1323         };
1324
1325         pipe = pipe_info(file->f_path.dentry->d_inode);
1326         if (!pipe)
1327                 return -EBADF;
1328         if (unlikely(nr_segs > UIO_MAXIOV))
1329                 return -EINVAL;
1330         else if (unlikely(!nr_segs))
1331                 return 0;
1332
1333         spd.nr_pages = get_iovec_page_array(iov, nr_segs, pages, partial,
1334                                             flags & SPLICE_F_GIFT);
1335         if (spd.nr_pages <= 0)
1336                 return spd.nr_pages;
1337
1338         return splice_to_pipe(pipe, &spd);
1339 }
1340
1341 asmlinkage long sys_vmsplice(int fd, const struct iovec __user *iov,
1342                              unsigned long nr_segs, unsigned int flags)
1343 {
1344         struct file *file;
1345         long error;
1346         int fput;
1347
1348         error = -EBADF;
1349         file = fget_light(fd, &fput);
1350         if (file) {
1351                 if (file->f_mode & FMODE_WRITE)
1352                         error = do_vmsplice(file, iov, nr_segs, flags);
1353
1354                 fput_light(file, fput);
1355         }
1356
1357         return error;
1358 }
1359
1360 asmlinkage long sys_splice(int fd_in, loff_t __user *off_in,
1361                            int fd_out, loff_t __user *off_out,
1362                            size_t len, unsigned int flags)
1363 {
1364         long error;
1365         struct file *in, *out;
1366         int fput_in, fput_out;
1367
1368         if (unlikely(!len))
1369                 return 0;
1370
1371         error = -EBADF;
1372         in = fget_light(fd_in, &fput_in);
1373         if (in) {
1374                 if (in->f_mode & FMODE_READ) {
1375                         out = fget_light(fd_out, &fput_out);
1376                         if (out) {
1377                                 if (out->f_mode & FMODE_WRITE)
1378                                         error = do_splice(in, off_in,
1379                                                           out, off_out,
1380                                                           len, flags);
1381                                 fput_light(out, fput_out);
1382                         }
1383                 }
1384
1385                 fput_light(in, fput_in);
1386         }
1387
1388         return error;
1389 }
1390
1391 /*
1392  * Make sure there's data to read. Wait for input if we can, otherwise
1393  * return an appropriate error.
1394  */
1395 static int link_ipipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
1396 {
1397         int ret;
1398
1399         /*
1400          * Check ->nrbufs without the inode lock first. This function
1401          * is speculative anyways, so missing one is ok.
1402          */
1403         if (pipe->nrbufs)
1404                 return 0;
1405
1406         ret = 0;
1407         mutex_lock(&pipe->inode->i_mutex);
1408
1409         while (!pipe->nrbufs) {
1410                 if (signal_pending(current)) {
1411                         ret = -ERESTARTSYS;
1412                         break;
1413                 }
1414                 if (!pipe->writers)
1415                         break;
1416                 if (!pipe->waiting_writers) {
1417                         if (flags & SPLICE_F_NONBLOCK) {
1418                                 ret = -EAGAIN;
1419                                 break;
1420                         }
1421                 }
1422                 pipe_wait(pipe);
1423         }
1424
1425         mutex_unlock(&pipe->inode->i_mutex);
1426         return ret;
1427 }
1428
1429 /*
1430  * Make sure there's writeable room. Wait for room if we can, otherwise
1431  * return an appropriate error.
1432  */
1433 static int link_opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
1434 {
1435         int ret;
1436
1437         /*
1438          * Check ->nrbufs without the inode lock first. This function
1439          * is speculative anyways, so missing one is ok.
1440          */
1441         if (pipe->nrbufs < PIPE_BUFFERS)
1442                 return 0;
1443
1444         ret = 0;
1445         mutex_lock(&pipe->inode->i_mutex);
1446
1447         while (pipe->nrbufs >= PIPE_BUFFERS) {
1448                 if (!pipe->readers) {
1449                         send_sig(SIGPIPE, current, 0);
1450                         ret = -EPIPE;
1451                         break;
1452                 }
1453                 if (flags & SPLICE_F_NONBLOCK) {
1454                         ret = -EAGAIN;
1455                         break;
1456                 }
1457                 if (signal_pending(current)) {
1458                         ret = -ERESTARTSYS;
1459                         break;
1460                 }
1461                 pipe->waiting_writers++;
1462                 pipe_wait(pipe);
1463                 pipe->waiting_writers--;
1464         }
1465
1466         mutex_unlock(&pipe->inode->i_mutex);
1467         return ret;
1468 }
1469
1470 /*
1471  * Link contents of ipipe to opipe.
1472  */
1473 static int link_pipe(struct pipe_inode_info *ipipe,
1474                      struct pipe_inode_info *opipe,
1475                      size_t len, unsigned int flags)
1476 {
1477         struct pipe_buffer *ibuf, *obuf;
1478         int ret = 0, i = 0, nbuf;
1479
1480         /*
1481          * Potential ABBA deadlock, work around it by ordering lock
1482          * grabbing by inode address. Otherwise two different processes
1483          * could deadlock (one doing tee from A -> B, the other from B -> A).
1484          */
1485         inode_double_lock(ipipe->inode, opipe->inode);
1486
1487         do {
1488                 if (!opipe->readers) {
1489                         send_sig(SIGPIPE, current, 0);
1490                         if (!ret)
1491                                 ret = -EPIPE;
1492                         break;
1493                 }
1494
1495                 /*
1496                  * If we have iterated all input buffers or ran out of
1497                  * output room, break.
1498                  */
1499                 if (i >= ipipe->nrbufs || opipe->nrbufs >= PIPE_BUFFERS)
1500                         break;
1501
1502                 ibuf = ipipe->bufs + ((ipipe->curbuf + i) & (PIPE_BUFFERS - 1));
1503                 nbuf = (opipe->curbuf + opipe->nrbufs) & (PIPE_BUFFERS - 1);
1504
1505                 /*
1506                  * Get a reference to this pipe buffer,
1507                  * so we can copy the contents over.
1508                  */
1509                 ibuf->ops->get(ipipe, ibuf);
1510
1511                 obuf = opipe->bufs + nbuf;
1512                 *obuf = *ibuf;
1513
1514                 /*
1515                  * Don't inherit the gift flag, we need to
1516                  * prevent multiple steals of this page.
1517                  */
1518                 obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
1519
1520                 if (obuf->len > len)
1521                         obuf->len = len;
1522
1523                 opipe->nrbufs++;
1524                 ret += obuf->len;
1525                 len -= obuf->len;
1526                 i++;
1527         } while (len);
1528
1529         inode_double_unlock(ipipe->inode, opipe->inode);
1530
1531         /*
1532          * If we put data in the output pipe, wakeup any potential readers.
1533          */
1534         if (ret > 0) {
1535                 smp_mb();
1536                 if (waitqueue_active(&opipe->wait))
1537                         wake_up_interruptible(&opipe->wait);
1538                 kill_fasync(&opipe->fasync_readers, SIGIO, POLL_IN);
1539         }
1540
1541         return ret;
1542 }
1543
1544 /*
1545  * This is a tee(1) implementation that works on pipes. It doesn't copy
1546  * any data, it simply references the 'in' pages on the 'out' pipe.
1547  * The 'flags' used are the SPLICE_F_* variants, currently the only
1548  * applicable one is SPLICE_F_NONBLOCK.
1549  */
1550 static long do_tee(struct file *in, struct file *out, size_t len,
1551                    unsigned int flags)
1552 {
1553         struct pipe_inode_info *ipipe = pipe_info(in->f_path.dentry->d_inode);
1554         struct pipe_inode_info *opipe = pipe_info(out->f_path.dentry->d_inode);
1555         int ret = -EINVAL;
1556
1557         /*
1558          * Duplicate the contents of ipipe to opipe without actually
1559          * copying the data.
1560          */
1561         if (ipipe && opipe && ipipe != opipe) {
1562                 /*
1563                  * Keep going, unless we encounter an error. The ipipe/opipe
1564                  * ordering doesn't really matter.
1565                  */
1566                 ret = link_ipipe_prep(ipipe, flags);
1567                 if (!ret) {
1568                         ret = link_opipe_prep(opipe, flags);
1569                         if (!ret) {
1570                                 ret = link_pipe(ipipe, opipe, len, flags);
1571                                 if (!ret && (flags & SPLICE_F_NONBLOCK))
1572                                         ret = -EAGAIN;
1573                         }
1574                 }
1575         }
1576
1577         return ret;
1578 }
1579
1580 asmlinkage long sys_tee(int fdin, int fdout, size_t len, unsigned int flags)
1581 {
1582         struct file *in;
1583         int error, fput_in;
1584
1585         if (unlikely(!len))
1586                 return 0;
1587
1588         error = -EBADF;
1589         in = fget_light(fdin, &fput_in);
1590         if (in) {
1591                 if (in->f_mode & FMODE_READ) {
1592                         int fput_out;
1593                         struct file *out = fget_light(fdout, &fput_out);
1594
1595                         if (out) {
1596                                 if (out->f_mode & FMODE_WRITE)
1597                                         error = do_tee(in, out, len, flags);
1598                                 fput_light(out, fput_out);
1599                         }
1600                 }
1601                 fput_light(in, fput_in);
1602         }
1603
1604         return error;
1605 }