splice: fix infinite loop in generic_file_splice_read()
[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/splice.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 #include <linux/security.h>
32
33 /*
34  * Attempt to steal a page from a pipe buffer. This should perhaps go into
35  * a vm helper function, it's already simplified quite a bit by the
36  * addition of remove_mapping(). If success is returned, the caller may
37  * attempt to reuse this page for another destination.
38  */
39 static int page_cache_pipe_buf_steal(struct pipe_inode_info *pipe,
40                                      struct pipe_buffer *buf)
41 {
42         struct page *page = buf->page;
43         struct address_space *mapping;
44
45         lock_page(page);
46
47         mapping = page_mapping(page);
48         if (mapping) {
49                 WARN_ON(!PageUptodate(page));
50
51                 /*
52                  * At least for ext2 with nobh option, we need to wait on
53                  * writeback completing on this page, since we'll remove it
54                  * from the pagecache.  Otherwise truncate wont wait on the
55                  * page, allowing the disk blocks to be reused by someone else
56                  * before we actually wrote our data to them. fs corruption
57                  * ensues.
58                  */
59                 wait_on_page_writeback(page);
60
61                 if (PagePrivate(page))
62                         try_to_release_page(page, GFP_KERNEL);
63
64                 /*
65                  * If we succeeded in removing the mapping, set LRU flag
66                  * and return good.
67                  */
68                 if (remove_mapping(mapping, page)) {
69                         buf->flags |= PIPE_BUF_FLAG_LRU;
70                         return 0;
71                 }
72         }
73
74         /*
75          * Raced with truncate or failed to remove page from current
76          * address space, unlock and return failure.
77          */
78         unlock_page(page);
79         return 1;
80 }
81
82 static void page_cache_pipe_buf_release(struct pipe_inode_info *pipe,
83                                         struct pipe_buffer *buf)
84 {
85         page_cache_release(buf->page);
86         buf->flags &= ~PIPE_BUF_FLAG_LRU;
87 }
88
89 /*
90  * Check whether the contents of buf is OK to access. Since the content
91  * is a page cache page, IO may be in flight.
92  */
93 static int page_cache_pipe_buf_confirm(struct pipe_inode_info *pipe,
94                                        struct pipe_buffer *buf)
95 {
96         struct page *page = buf->page;
97         int err;
98
99         if (!PageUptodate(page)) {
100                 lock_page(page);
101
102                 /*
103                  * Page got truncated/unhashed. This will cause a 0-byte
104                  * splice, if this is the first page.
105                  */
106                 if (!page->mapping) {
107                         err = -ENODATA;
108                         goto error;
109                 }
110
111                 /*
112                  * Uh oh, read-error from disk.
113                  */
114                 if (!PageUptodate(page)) {
115                         err = -EIO;
116                         goto error;
117                 }
118
119                 /*
120                  * Page is ok afterall, we are done.
121                  */
122                 unlock_page(page);
123         }
124
125         return 0;
126 error:
127         unlock_page(page);
128         return err;
129 }
130
131 static const struct pipe_buf_operations page_cache_pipe_buf_ops = {
132         .can_merge = 0,
133         .map = generic_pipe_buf_map,
134         .unmap = generic_pipe_buf_unmap,
135         .confirm = page_cache_pipe_buf_confirm,
136         .release = page_cache_pipe_buf_release,
137         .steal = page_cache_pipe_buf_steal,
138         .get = generic_pipe_buf_get,
139 };
140
141 static int user_page_pipe_buf_steal(struct pipe_inode_info *pipe,
142                                     struct pipe_buffer *buf)
143 {
144         if (!(buf->flags & PIPE_BUF_FLAG_GIFT))
145                 return 1;
146
147         buf->flags |= PIPE_BUF_FLAG_LRU;
148         return generic_pipe_buf_steal(pipe, buf);
149 }
150
151 static const struct pipe_buf_operations user_page_pipe_buf_ops = {
152         .can_merge = 0,
153         .map = generic_pipe_buf_map,
154         .unmap = generic_pipe_buf_unmap,
155         .confirm = generic_pipe_buf_confirm,
156         .release = page_cache_pipe_buf_release,
157         .steal = user_page_pipe_buf_steal,
158         .get = generic_pipe_buf_get,
159 };
160
161 /**
162  * splice_to_pipe - fill passed data into a pipe
163  * @pipe:       pipe to fill
164  * @spd:        data to fill
165  *
166  * Description:
167  *    @spd contains a map of pages and len/offset tuples, along with
168  *    the struct pipe_buf_operations associated with these pages. This
169  *    function will link that data to the pipe.
170  *
171  */
172 ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
173                        struct splice_pipe_desc *spd)
174 {
175         unsigned int spd_pages = spd->nr_pages;
176         int ret, do_wakeup, page_nr;
177
178         ret = 0;
179         do_wakeup = 0;
180         page_nr = 0;
181
182         if (pipe->inode)
183                 mutex_lock(&pipe->inode->i_mutex);
184
185         for (;;) {
186                 if (!pipe->readers) {
187                         send_sig(SIGPIPE, current, 0);
188                         if (!ret)
189                                 ret = -EPIPE;
190                         break;
191                 }
192
193                 if (pipe->nrbufs < PIPE_BUFFERS) {
194                         int newbuf = (pipe->curbuf + pipe->nrbufs) & (PIPE_BUFFERS - 1);
195                         struct pipe_buffer *buf = pipe->bufs + newbuf;
196
197                         buf->page = spd->pages[page_nr];
198                         buf->offset = spd->partial[page_nr].offset;
199                         buf->len = spd->partial[page_nr].len;
200                         buf->private = spd->partial[page_nr].private;
201                         buf->ops = spd->ops;
202                         if (spd->flags & SPLICE_F_GIFT)
203                                 buf->flags |= PIPE_BUF_FLAG_GIFT;
204
205                         pipe->nrbufs++;
206                         page_nr++;
207                         ret += buf->len;
208
209                         if (pipe->inode)
210                                 do_wakeup = 1;
211
212                         if (!--spd->nr_pages)
213                                 break;
214                         if (pipe->nrbufs < PIPE_BUFFERS)
215                                 continue;
216
217                         break;
218                 }
219
220                 if (spd->flags & SPLICE_F_NONBLOCK) {
221                         if (!ret)
222                                 ret = -EAGAIN;
223                         break;
224                 }
225
226                 if (signal_pending(current)) {
227                         if (!ret)
228                                 ret = -ERESTARTSYS;
229                         break;
230                 }
231
232                 if (do_wakeup) {
233                         smp_mb();
234                         if (waitqueue_active(&pipe->wait))
235                                 wake_up_interruptible_sync(&pipe->wait);
236                         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
237                         do_wakeup = 0;
238                 }
239
240                 pipe->waiting_writers++;
241                 pipe_wait(pipe);
242                 pipe->waiting_writers--;
243         }
244
245         if (pipe->inode) {
246                 mutex_unlock(&pipe->inode->i_mutex);
247
248                 if (do_wakeup) {
249                         smp_mb();
250                         if (waitqueue_active(&pipe->wait))
251                                 wake_up_interruptible(&pipe->wait);
252                         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
253                 }
254         }
255
256         while (page_nr < spd_pages)
257                 spd->spd_release(spd, page_nr++);
258
259         return ret;
260 }
261
262 static void spd_release_page(struct splice_pipe_desc *spd, unsigned int i)
263 {
264         page_cache_release(spd->pages[i]);
265 }
266
267 static int
268 __generic_file_splice_read(struct file *in, loff_t *ppos,
269                            struct pipe_inode_info *pipe, size_t len,
270                            unsigned int flags)
271 {
272         struct address_space *mapping = in->f_mapping;
273         unsigned int loff, nr_pages, req_pages;
274         struct page *pages[PIPE_BUFFERS];
275         struct partial_page partial[PIPE_BUFFERS];
276         struct page *page;
277         pgoff_t index, end_index;
278         loff_t isize;
279         int error, page_nr;
280         struct splice_pipe_desc spd = {
281                 .pages = pages,
282                 .partial = partial,
283                 .flags = flags,
284                 .ops = &page_cache_pipe_buf_ops,
285                 .spd_release = spd_release_page,
286         };
287
288         index = *ppos >> PAGE_CACHE_SHIFT;
289         loff = *ppos & ~PAGE_CACHE_MASK;
290         req_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
291         nr_pages = min(req_pages, (unsigned)PIPE_BUFFERS);
292
293         /*
294          * Lookup the (hopefully) full range of pages we need.
295          */
296         spd.nr_pages = find_get_pages_contig(mapping, index, nr_pages, pages);
297         index += spd.nr_pages;
298
299         /*
300          * If find_get_pages_contig() returned fewer pages than we needed,
301          * readahead/allocate the rest and fill in the holes.
302          */
303         if (spd.nr_pages < nr_pages)
304                 page_cache_sync_readahead(mapping, &in->f_ra, in,
305                                 index, req_pages - spd.nr_pages);
306
307         error = 0;
308         while (spd.nr_pages < nr_pages) {
309                 /*
310                  * Page could be there, find_get_pages_contig() breaks on
311                  * the first hole.
312                  */
313                 page = find_get_page(mapping, index);
314                 if (!page) {
315                         /*
316                          * page didn't exist, allocate one.
317                          */
318                         page = page_cache_alloc_cold(mapping);
319                         if (!page)
320                                 break;
321
322                         error = add_to_page_cache_lru(page, mapping, index,
323                                                 mapping_gfp_mask(mapping));
324                         if (unlikely(error)) {
325                                 page_cache_release(page);
326                                 if (error == -EEXIST)
327                                         continue;
328                                 break;
329                         }
330                         /*
331                          * add_to_page_cache() locks the page, unlock it
332                          * to avoid convoluting the logic below even more.
333                          */
334                         unlock_page(page);
335                 }
336
337                 pages[spd.nr_pages++] = page;
338                 index++;
339         }
340
341         /*
342          * Now loop over the map and see if we need to start IO on any
343          * pages, fill in the partial map, etc.
344          */
345         index = *ppos >> PAGE_CACHE_SHIFT;
346         nr_pages = spd.nr_pages;
347         spd.nr_pages = 0;
348         for (page_nr = 0; page_nr < nr_pages; page_nr++) {
349                 unsigned int this_len;
350
351                 if (!len)
352                         break;
353
354                 /*
355                  * this_len is the max we'll use from this page
356                  */
357                 this_len = min_t(unsigned long, len, PAGE_CACHE_SIZE - loff);
358                 page = pages[page_nr];
359
360                 if (PageReadahead(page))
361                         page_cache_async_readahead(mapping, &in->f_ra, in,
362                                         page, index, req_pages - page_nr);
363
364                 /*
365                  * If the page isn't uptodate, we may need to start io on it
366                  */
367                 if (!PageUptodate(page)) {
368                         /*
369                          * If in nonblock mode then dont block on waiting
370                          * for an in-flight io page
371                          */
372                         if (flags & SPLICE_F_NONBLOCK) {
373                                 if (TestSetPageLocked(page)) {
374                                         error = -EAGAIN;
375                                         break;
376                                 }
377                         } else
378                                 lock_page(page);
379
380                         /*
381                          * page was truncated, stop here. if this isn't the
382                          * first page, we'll just complete what we already
383                          * added
384                          */
385                         if (!page->mapping) {
386                                 unlock_page(page);
387                                 break;
388                         }
389                         /*
390                          * page was already under io and is now done, great
391                          */
392                         if (PageUptodate(page)) {
393                                 unlock_page(page);
394                                 goto fill_it;
395                         }
396
397                         /*
398                          * need to read in the page
399                          */
400                         error = mapping->a_ops->readpage(in, page);
401                         if (unlikely(error)) {
402                                 /*
403                                  * We really should re-lookup the page here,
404                                  * but it complicates things a lot. Instead
405                                  * lets just do what we already stored, and
406                                  * we'll get it the next time we are called.
407                                  */
408                                 if (error == AOP_TRUNCATED_PAGE)
409                                         error = 0;
410
411                                 break;
412                         }
413                 }
414 fill_it:
415                 /*
416                  * i_size must be checked after PageUptodate.
417                  */
418                 isize = i_size_read(mapping->host);
419                 end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
420                 if (unlikely(!isize || index > end_index))
421                         break;
422
423                 /*
424                  * if this is the last page, see if we need to shrink
425                  * the length and stop
426                  */
427                 if (end_index == index) {
428                         unsigned int plen;
429
430                         /*
431                          * max good bytes in this page
432                          */
433                         plen = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
434                         if (plen <= loff)
435                                 break;
436
437                         /*
438                          * force quit after adding this page
439                          */
440                         this_len = min(this_len, plen - loff);
441                         len = this_len;
442                 }
443
444                 partial[page_nr].offset = loff;
445                 partial[page_nr].len = this_len;
446                 len -= this_len;
447                 loff = 0;
448                 spd.nr_pages++;
449                 index++;
450         }
451
452         /*
453          * Release any pages at the end, if we quit early. 'page_nr' is how far
454          * we got, 'nr_pages' is how many pages are in the map.
455          */
456         while (page_nr < nr_pages)
457                 page_cache_release(pages[page_nr++]);
458         in->f_ra.prev_pos = (loff_t)index << PAGE_CACHE_SHIFT;
459
460         if (spd.nr_pages)
461                 return splice_to_pipe(pipe, &spd);
462
463         return error;
464 }
465
466 /**
467  * generic_file_splice_read - splice data from file to a pipe
468  * @in:         file to splice from
469  * @ppos:       position in @in
470  * @pipe:       pipe to splice to
471  * @len:        number of bytes to splice
472  * @flags:      splice modifier flags
473  *
474  * Description:
475  *    Will read pages from given file and fill them into a pipe. Can be
476  *    used as long as the address_space operations for the source implements
477  *    a readpage() hook.
478  *
479  */
480 ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
481                                  struct pipe_inode_info *pipe, size_t len,
482                                  unsigned int flags)
483 {
484         loff_t isize, left;
485         int ret;
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 = __generic_file_splice_read(in, ppos, pipe, len, flags);
496         if (ret > 0)
497                 *ppos += ret;
498
499         return ret;
500 }
501
502 EXPORT_SYMBOL(generic_file_splice_read);
503
504 /*
505  * Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->pos'
506  * using sendpage(). Return the number of bytes sent.
507  */
508 static int pipe_to_sendpage(struct pipe_inode_info *pipe,
509                             struct pipe_buffer *buf, struct splice_desc *sd)
510 {
511         struct file *file = sd->u.file;
512         loff_t pos = sd->pos;
513         int ret, more;
514
515         ret = buf->ops->confirm(pipe, buf);
516         if (!ret) {
517                 more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len;
518
519                 ret = file->f_op->sendpage(file, buf->page, buf->offset,
520                                            sd->len, &pos, more);
521         }
522
523         return ret;
524 }
525
526 /*
527  * This is a little more tricky than the file -> pipe splicing. There are
528  * basically three cases:
529  *
530  *      - Destination page already exists in the address space and there
531  *        are users of it. For that case we have no other option that
532  *        copying the data. Tough luck.
533  *      - Destination page already exists in the address space, but there
534  *        are no users of it. Make sure it's uptodate, then drop it. Fall
535  *        through to last case.
536  *      - Destination page does not exist, we can add the pipe page to
537  *        the page cache and avoid the copy.
538  *
539  * If asked to move pages to the output file (SPLICE_F_MOVE is set in
540  * sd->flags), we attempt to migrate pages from the pipe to the output
541  * file address space page cache. This is possible if no one else has
542  * the pipe page referenced outside of the pipe and page cache. If
543  * SPLICE_F_MOVE isn't set, or we cannot move the page, we simply create
544  * a new page in the output file page cache and fill/dirty that.
545  */
546 static int pipe_to_file(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
547                         struct splice_desc *sd)
548 {
549         struct file *file = sd->u.file;
550         struct address_space *mapping = file->f_mapping;
551         unsigned int offset, this_len;
552         struct page *page;
553         void *fsdata;
554         int ret;
555
556         /*
557          * make sure the data in this buffer is uptodate
558          */
559         ret = buf->ops->confirm(pipe, buf);
560         if (unlikely(ret))
561                 return ret;
562
563         offset = sd->pos & ~PAGE_CACHE_MASK;
564
565         this_len = sd->len;
566         if (this_len + offset > PAGE_CACHE_SIZE)
567                 this_len = PAGE_CACHE_SIZE - offset;
568
569         ret = pagecache_write_begin(file, mapping, sd->pos, this_len,
570                                 AOP_FLAG_UNINTERRUPTIBLE, &page, &fsdata);
571         if (unlikely(ret))
572                 goto out;
573
574         if (buf->page != page) {
575                 /*
576                  * Careful, ->map() uses KM_USER0!
577                  */
578                 char *src = buf->ops->map(pipe, buf, 1);
579                 char *dst = kmap_atomic(page, KM_USER1);
580
581                 memcpy(dst + offset, src + buf->offset, this_len);
582                 flush_dcache_page(page);
583                 kunmap_atomic(dst, KM_USER1);
584                 buf->ops->unmap(pipe, buf, src);
585         }
586         ret = pagecache_write_end(file, mapping, sd->pos, this_len, this_len,
587                                 page, fsdata);
588 out:
589         return ret;
590 }
591
592 /**
593  * __splice_from_pipe - splice data from a pipe to given actor
594  * @pipe:       pipe to splice from
595  * @sd:         information to @actor
596  * @actor:      handler that splices the data
597  *
598  * Description:
599  *    This function does little more than loop over the pipe and call
600  *    @actor to do the actual moving of a single struct pipe_buffer to
601  *    the desired destination. See pipe_to_file, pipe_to_sendpage, or
602  *    pipe_to_user.
603  *
604  */
605 ssize_t __splice_from_pipe(struct pipe_inode_info *pipe, struct splice_desc *sd,
606                            splice_actor *actor)
607 {
608         int ret, do_wakeup, err;
609
610         ret = 0;
611         do_wakeup = 0;
612
613         for (;;) {
614                 if (pipe->nrbufs) {
615                         struct pipe_buffer *buf = pipe->bufs + pipe->curbuf;
616                         const struct pipe_buf_operations *ops = buf->ops;
617
618                         sd->len = buf->len;
619                         if (sd->len > sd->total_len)
620                                 sd->len = sd->total_len;
621
622                         err = actor(pipe, buf, sd);
623                         if (err <= 0) {
624                                 if (!ret && err != -ENODATA)
625                                         ret = err;
626
627                                 break;
628                         }
629
630                         ret += err;
631                         buf->offset += err;
632                         buf->len -= err;
633
634                         sd->len -= err;
635                         sd->pos += err;
636                         sd->total_len -= err;
637                         if (sd->len)
638                                 continue;
639
640                         if (!buf->len) {
641                                 buf->ops = NULL;
642                                 ops->release(pipe, buf);
643                                 pipe->curbuf = (pipe->curbuf + 1) & (PIPE_BUFFERS - 1);
644                                 pipe->nrbufs--;
645                                 if (pipe->inode)
646                                         do_wakeup = 1;
647                         }
648
649                         if (!sd->total_len)
650                                 break;
651                 }
652
653                 if (pipe->nrbufs)
654                         continue;
655                 if (!pipe->writers)
656                         break;
657                 if (!pipe->waiting_writers) {
658                         if (ret)
659                                 break;
660                 }
661
662                 if (sd->flags & SPLICE_F_NONBLOCK) {
663                         if (!ret)
664                                 ret = -EAGAIN;
665                         break;
666                 }
667
668                 if (signal_pending(current)) {
669                         if (!ret)
670                                 ret = -ERESTARTSYS;
671                         break;
672                 }
673
674                 if (do_wakeup) {
675                         smp_mb();
676                         if (waitqueue_active(&pipe->wait))
677                                 wake_up_interruptible_sync(&pipe->wait);
678                         kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
679                         do_wakeup = 0;
680                 }
681
682                 pipe_wait(pipe);
683         }
684
685         if (do_wakeup) {
686                 smp_mb();
687                 if (waitqueue_active(&pipe->wait))
688                         wake_up_interruptible(&pipe->wait);
689                 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
690         }
691
692         return ret;
693 }
694 EXPORT_SYMBOL(__splice_from_pipe);
695
696 /**
697  * splice_from_pipe - splice data from a pipe to a file
698  * @pipe:       pipe to splice from
699  * @out:        file to splice to
700  * @ppos:       position in @out
701  * @len:        how many bytes to splice
702  * @flags:      splice modifier flags
703  * @actor:      handler that splices the data
704  *
705  * Description:
706  *    See __splice_from_pipe. This function locks the input and output inodes,
707  *    otherwise it's identical to __splice_from_pipe().
708  *
709  */
710 ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
711                          loff_t *ppos, size_t len, unsigned int flags,
712                          splice_actor *actor)
713 {
714         ssize_t ret;
715         struct inode *inode = out->f_mapping->host;
716         struct splice_desc sd = {
717                 .total_len = len,
718                 .flags = flags,
719                 .pos = *ppos,
720                 .u.file = out,
721         };
722
723         /*
724          * The actor worker might be calling ->prepare_write and
725          * ->commit_write. Most of the time, these expect i_mutex to
726          * be held. Since this may result in an ABBA deadlock with
727          * pipe->inode, we have to order lock acquiry here.
728          */
729         inode_double_lock(inode, pipe->inode);
730         ret = __splice_from_pipe(pipe, &sd, actor);
731         inode_double_unlock(inode, pipe->inode);
732
733         return ret;
734 }
735
736 /**
737  * generic_file_splice_write_nolock - generic_file_splice_write without mutexes
738  * @pipe:       pipe info
739  * @out:        file to write to
740  * @ppos:       position in @out
741  * @len:        number of bytes to splice
742  * @flags:      splice modifier flags
743  *
744  * Description:
745  *    Will either move or copy pages (determined by @flags options) from
746  *    the given pipe inode to the given file. The caller is responsible
747  *    for acquiring i_mutex on both inodes.
748  *
749  */
750 ssize_t
751 generic_file_splice_write_nolock(struct pipe_inode_info *pipe, struct file *out,
752                                  loff_t *ppos, size_t len, unsigned int flags)
753 {
754         struct address_space *mapping = out->f_mapping;
755         struct inode *inode = mapping->host;
756         struct splice_desc sd = {
757                 .total_len = len,
758                 .flags = flags,
759                 .pos = *ppos,
760                 .u.file = out,
761         };
762         ssize_t ret;
763         int err;
764
765         err = remove_suid(out->f_path.dentry);
766         if (unlikely(err))
767                 return err;
768
769         ret = __splice_from_pipe(pipe, &sd, pipe_to_file);
770         if (ret > 0) {
771                 unsigned long nr_pages;
772
773                 *ppos += ret;
774                 nr_pages = (ret + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
775
776                 /*
777                  * If file or inode is SYNC and we actually wrote some data,
778                  * sync it.
779                  */
780                 if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
781                         err = generic_osync_inode(inode, mapping,
782                                                   OSYNC_METADATA|OSYNC_DATA);
783
784                         if (err)
785                                 ret = err;
786                 }
787                 balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
788         }
789
790         return ret;
791 }
792
793 EXPORT_SYMBOL(generic_file_splice_write_nolock);
794
795 /**
796  * generic_file_splice_write - splice data from a pipe to a file
797  * @pipe:       pipe info
798  * @out:        file to write to
799  * @ppos:       position in @out
800  * @len:        number of bytes to splice
801  * @flags:      splice modifier flags
802  *
803  * Description:
804  *    Will either move or copy pages (determined by @flags options) from
805  *    the given pipe inode to the given file.
806  *
807  */
808 ssize_t
809 generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
810                           loff_t *ppos, size_t len, unsigned int flags)
811 {
812         struct address_space *mapping = out->f_mapping;
813         struct inode *inode = mapping->host;
814         int killsuid, killpriv;
815         ssize_t ret;
816         int err = 0;
817
818         killpriv = security_inode_need_killpriv(out->f_path.dentry);
819         killsuid = should_remove_suid(out->f_path.dentry);
820         if (unlikely(killsuid || killpriv)) {
821                 mutex_lock(&inode->i_mutex);
822                 if (killpriv)
823                         err = security_inode_killpriv(out->f_path.dentry);
824                 if (!err && killsuid)
825                         err = __remove_suid(out->f_path.dentry, killsuid);
826                 mutex_unlock(&inode->i_mutex);
827                 if (err)
828                         return err;
829         }
830
831         ret = splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_file);
832         if (ret > 0) {
833                 unsigned long nr_pages;
834
835                 *ppos += ret;
836                 nr_pages = (ret + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
837
838                 /*
839                  * If file or inode is SYNC and we actually wrote some data,
840                  * sync it.
841                  */
842                 if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
843                         mutex_lock(&inode->i_mutex);
844                         err = generic_osync_inode(inode, mapping,
845                                                   OSYNC_METADATA|OSYNC_DATA);
846                         mutex_unlock(&inode->i_mutex);
847
848                         if (err)
849                                 ret = err;
850                 }
851                 balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
852         }
853
854         return ret;
855 }
856
857 EXPORT_SYMBOL(generic_file_splice_write);
858
859 /**
860  * generic_splice_sendpage - splice data from a pipe to a socket
861  * @pipe:       pipe to splice from
862  * @out:        socket to write to
863  * @ppos:       position in @out
864  * @len:        number of bytes to splice
865  * @flags:      splice modifier flags
866  *
867  * Description:
868  *    Will send @len bytes from the pipe to a network socket. No data copying
869  *    is involved.
870  *
871  */
872 ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe, struct file *out,
873                                 loff_t *ppos, size_t len, unsigned int flags)
874 {
875         return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_sendpage);
876 }
877
878 EXPORT_SYMBOL(generic_splice_sendpage);
879
880 /*
881  * Attempt to initiate a splice from pipe to file.
882  */
883 static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
884                            loff_t *ppos, size_t len, unsigned int flags)
885 {
886         int ret;
887
888         if (unlikely(!out->f_op || !out->f_op->splice_write))
889                 return -EINVAL;
890
891         if (unlikely(!(out->f_mode & FMODE_WRITE)))
892                 return -EBADF;
893
894         ret = rw_verify_area(WRITE, out, ppos, len);
895         if (unlikely(ret < 0))
896                 return ret;
897
898         return out->f_op->splice_write(pipe, out, ppos, len, flags);
899 }
900
901 /*
902  * Attempt to initiate a splice from a file to a pipe.
903  */
904 static long do_splice_to(struct file *in, loff_t *ppos,
905                          struct pipe_inode_info *pipe, size_t len,
906                          unsigned int flags)
907 {
908         int ret;
909
910         if (unlikely(!in->f_op || !in->f_op->splice_read))
911                 return -EINVAL;
912
913         if (unlikely(!(in->f_mode & FMODE_READ)))
914                 return -EBADF;
915
916         ret = rw_verify_area(READ, in, ppos, len);
917         if (unlikely(ret < 0))
918                 return ret;
919
920         return in->f_op->splice_read(in, ppos, pipe, len, flags);
921 }
922
923 /**
924  * splice_direct_to_actor - splices data directly between two non-pipes
925  * @in:         file to splice from
926  * @sd:         actor information on where to splice to
927  * @actor:      handles the data splicing
928  *
929  * Description:
930  *    This is a special case helper to splice directly between two
931  *    points, without requiring an explicit pipe. Internally an allocated
932  *    pipe is cached in the process, and reused during the lifetime of
933  *    that process.
934  *
935  */
936 ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
937                                splice_direct_actor *actor)
938 {
939         struct pipe_inode_info *pipe;
940         long ret, bytes;
941         umode_t i_mode;
942         size_t len;
943         int i, flags;
944
945         /*
946          * We require the input being a regular file, as we don't want to
947          * randomly drop data for eg socket -> socket splicing. Use the
948          * piped splicing for that!
949          */
950         i_mode = in->f_path.dentry->d_inode->i_mode;
951         if (unlikely(!S_ISREG(i_mode) && !S_ISBLK(i_mode)))
952                 return -EINVAL;
953
954         /*
955          * neither in nor out is a pipe, setup an internal pipe attached to
956          * 'out' and transfer the wanted data from 'in' to 'out' through that
957          */
958         pipe = current->splice_pipe;
959         if (unlikely(!pipe)) {
960                 pipe = alloc_pipe_info(NULL);
961                 if (!pipe)
962                         return -ENOMEM;
963
964                 /*
965                  * We don't have an immediate reader, but we'll read the stuff
966                  * out of the pipe right after the splice_to_pipe(). So set
967                  * PIPE_READERS appropriately.
968                  */
969                 pipe->readers = 1;
970
971                 current->splice_pipe = pipe;
972         }
973
974         /*
975          * Do the splice.
976          */
977         ret = 0;
978         bytes = 0;
979         len = sd->total_len;
980         flags = sd->flags;
981
982         /*
983          * Don't block on output, we have to drain the direct pipe.
984          */
985         sd->flags &= ~SPLICE_F_NONBLOCK;
986
987         while (len) {
988                 size_t read_len;
989                 loff_t pos = sd->pos;
990
991                 ret = do_splice_to(in, &pos, pipe, len, flags);
992                 if (unlikely(ret <= 0))
993                         goto out_release;
994
995                 read_len = ret;
996                 sd->total_len = read_len;
997
998                 /*
999                  * NOTE: nonblocking mode only applies to the input. We
1000                  * must not do the output in nonblocking mode as then we
1001                  * could get stuck data in the internal pipe:
1002                  */
1003                 ret = actor(pipe, sd);
1004                 if (unlikely(ret <= 0))
1005                         goto out_release;
1006
1007                 bytes += ret;
1008                 len -= ret;
1009                 sd->pos = pos;
1010
1011                 if (ret < read_len)
1012                         goto out_release;
1013         }
1014
1015 done:
1016         pipe->nrbufs = pipe->curbuf = 0;
1017         file_accessed(in);
1018         return bytes;
1019
1020 out_release:
1021         /*
1022          * If we did an incomplete transfer we must release
1023          * the pipe buffers in question:
1024          */
1025         for (i = 0; i < PIPE_BUFFERS; i++) {
1026                 struct pipe_buffer *buf = pipe->bufs + i;
1027
1028                 if (buf->ops) {
1029                         buf->ops->release(pipe, buf);
1030                         buf->ops = NULL;
1031                 }
1032         }
1033
1034         if (!bytes)
1035                 bytes = ret;
1036
1037         goto done;
1038 }
1039 EXPORT_SYMBOL(splice_direct_to_actor);
1040
1041 static int direct_splice_actor(struct pipe_inode_info *pipe,
1042                                struct splice_desc *sd)
1043 {
1044         struct file *file = sd->u.file;
1045
1046         return do_splice_from(pipe, file, &sd->pos, sd->total_len, sd->flags);
1047 }
1048
1049 /**
1050  * do_splice_direct - splices data directly between two files
1051  * @in:         file to splice from
1052  * @ppos:       input file offset
1053  * @out:        file to splice to
1054  * @len:        number of bytes to splice
1055  * @flags:      splice modifier flags
1056  *
1057  * Description:
1058  *    For use by do_sendfile(). splice can easily emulate sendfile, but
1059  *    doing it in the application would incur an extra system call
1060  *    (splice in + splice out, as compared to just sendfile()). So this helper
1061  *    can splice directly through a process-private pipe.
1062  *
1063  */
1064 long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
1065                       size_t len, unsigned int flags)
1066 {
1067         struct splice_desc sd = {
1068                 .len            = len,
1069                 .total_len      = len,
1070                 .flags          = flags,
1071                 .pos            = *ppos,
1072                 .u.file         = out,
1073         };
1074         long ret;
1075
1076         ret = splice_direct_to_actor(in, &sd, direct_splice_actor);
1077         if (ret > 0)
1078                 *ppos += ret;
1079
1080         return ret;
1081 }
1082
1083 /*
1084  * After the inode slimming patch, i_pipe/i_bdev/i_cdev share the same
1085  * location, so checking ->i_pipe is not enough to verify that this is a
1086  * pipe.
1087  */
1088 static inline struct pipe_inode_info *pipe_info(struct inode *inode)
1089 {
1090         if (S_ISFIFO(inode->i_mode))
1091                 return inode->i_pipe;
1092
1093         return NULL;
1094 }
1095
1096 /*
1097  * Determine where to splice to/from.
1098  */
1099 static long do_splice(struct file *in, loff_t __user *off_in,
1100                       struct file *out, loff_t __user *off_out,
1101                       size_t len, unsigned int flags)
1102 {
1103         struct pipe_inode_info *pipe;
1104         loff_t offset, *off;
1105         long ret;
1106
1107         pipe = pipe_info(in->f_path.dentry->d_inode);
1108         if (pipe) {
1109                 if (off_in)
1110                         return -ESPIPE;
1111                 if (off_out) {
1112                         if (out->f_op->llseek == no_llseek)
1113                                 return -EINVAL;
1114                         if (copy_from_user(&offset, off_out, sizeof(loff_t)))
1115                                 return -EFAULT;
1116                         off = &offset;
1117                 } else
1118                         off = &out->f_pos;
1119
1120                 ret = do_splice_from(pipe, out, off, len, flags);
1121
1122                 if (off_out && copy_to_user(off_out, off, sizeof(loff_t)))
1123                         ret = -EFAULT;
1124
1125                 return ret;
1126         }
1127
1128         pipe = pipe_info(out->f_path.dentry->d_inode);
1129         if (pipe) {
1130                 if (off_out)
1131                         return -ESPIPE;
1132                 if (off_in) {
1133                         if (in->f_op->llseek == no_llseek)
1134                                 return -EINVAL;
1135                         if (copy_from_user(&offset, off_in, sizeof(loff_t)))
1136                                 return -EFAULT;
1137                         off = &offset;
1138                 } else
1139                         off = &in->f_pos;
1140
1141                 ret = do_splice_to(in, off, pipe, len, flags);
1142
1143                 if (off_in && copy_to_user(off_in, off, sizeof(loff_t)))
1144                         ret = -EFAULT;
1145
1146                 return ret;
1147         }
1148
1149         return -EINVAL;
1150 }
1151
1152 /*
1153  * Do a copy-from-user while holding the mmap_semaphore for reading, in a
1154  * manner safe from deadlocking with simultaneous mmap() (grabbing mmap_sem
1155  * for writing) and page faulting on the user memory pointed to by src.
1156  * This assumes that we will very rarely hit the partial != 0 path, or this
1157  * will not be a win.
1158  */
1159 static int copy_from_user_mmap_sem(void *dst, const void __user *src, size_t n)
1160 {
1161         int partial;
1162
1163         if (!access_ok(VERIFY_READ, src, n))
1164                 return -EFAULT;
1165
1166         pagefault_disable();
1167         partial = __copy_from_user_inatomic(dst, src, n);
1168         pagefault_enable();
1169
1170         /*
1171          * Didn't copy everything, drop the mmap_sem and do a faulting copy
1172          */
1173         if (unlikely(partial)) {
1174                 up_read(&current->mm->mmap_sem);
1175                 partial = copy_from_user(dst, src, n);
1176                 down_read(&current->mm->mmap_sem);
1177         }
1178
1179         return partial;
1180 }
1181
1182 /*
1183  * Map an iov into an array of pages and offset/length tupples. With the
1184  * partial_page structure, we can map several non-contiguous ranges into
1185  * our ones pages[] map instead of splitting that operation into pieces.
1186  * Could easily be exported as a generic helper for other users, in which
1187  * case one would probably want to add a 'max_nr_pages' parameter as well.
1188  */
1189 static int get_iovec_page_array(const struct iovec __user *iov,
1190                                 unsigned int nr_vecs, struct page **pages,
1191                                 struct partial_page *partial, int aligned)
1192 {
1193         int buffers = 0, error = 0;
1194
1195         down_read(&current->mm->mmap_sem);
1196
1197         while (nr_vecs) {
1198                 unsigned long off, npages;
1199                 struct iovec entry;
1200                 void __user *base;
1201                 size_t len;
1202                 int i;
1203
1204                 error = -EFAULT;
1205                 if (copy_from_user_mmap_sem(&entry, iov, sizeof(entry)))
1206                         break;
1207
1208                 base = entry.iov_base;
1209                 len = entry.iov_len;
1210
1211                 /*
1212                  * Sanity check this iovec. 0 read succeeds.
1213                  */
1214                 error = 0;
1215                 if (unlikely(!len))
1216                         break;
1217                 error = -EFAULT;
1218                 if (!access_ok(VERIFY_READ, base, len))
1219                         break;
1220
1221                 /*
1222                  * Get this base offset and number of pages, then map
1223                  * in the user pages.
1224                  */
1225                 off = (unsigned long) base & ~PAGE_MASK;
1226
1227                 /*
1228                  * If asked for alignment, the offset must be zero and the
1229                  * length a multiple of the PAGE_SIZE.
1230                  */
1231                 error = -EINVAL;
1232                 if (aligned && (off || len & ~PAGE_MASK))
1233                         break;
1234
1235                 npages = (off + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
1236                 if (npages > PIPE_BUFFERS - buffers)
1237                         npages = PIPE_BUFFERS - buffers;
1238
1239                 error = get_user_pages(current, current->mm,
1240                                        (unsigned long) base, npages, 0, 0,
1241                                        &pages[buffers], NULL);
1242
1243                 if (unlikely(error <= 0))
1244                         break;
1245
1246                 /*
1247                  * Fill this contiguous range into the partial page map.
1248                  */
1249                 for (i = 0; i < error; i++) {
1250                         const int plen = min_t(size_t, len, PAGE_SIZE - off);
1251
1252                         partial[buffers].offset = off;
1253                         partial[buffers].len = plen;
1254
1255                         off = 0;
1256                         len -= plen;
1257                         buffers++;
1258                 }
1259
1260                 /*
1261                  * We didn't complete this iov, stop here since it probably
1262                  * means we have to move some of this into a pipe to
1263                  * be able to continue.
1264                  */
1265                 if (len)
1266                         break;
1267
1268                 /*
1269                  * Don't continue if we mapped fewer pages than we asked for,
1270                  * or if we mapped the max number of pages that we have
1271                  * room for.
1272                  */
1273                 if (error < npages || buffers == PIPE_BUFFERS)
1274                         break;
1275
1276                 nr_vecs--;
1277                 iov++;
1278         }
1279
1280         up_read(&current->mm->mmap_sem);
1281
1282         if (buffers)
1283                 return buffers;
1284
1285         return error;
1286 }
1287
1288 static int pipe_to_user(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
1289                         struct splice_desc *sd)
1290 {
1291         char *src;
1292         int ret;
1293
1294         ret = buf->ops->confirm(pipe, buf);
1295         if (unlikely(ret))
1296                 return ret;
1297
1298         /*
1299          * See if we can use the atomic maps, by prefaulting in the
1300          * pages and doing an atomic copy
1301          */
1302         if (!fault_in_pages_writeable(sd->u.userptr, sd->len)) {
1303                 src = buf->ops->map(pipe, buf, 1);
1304                 ret = __copy_to_user_inatomic(sd->u.userptr, src + buf->offset,
1305                                                         sd->len);
1306                 buf->ops->unmap(pipe, buf, src);
1307                 if (!ret) {
1308                         ret = sd->len;
1309                         goto out;
1310                 }
1311         }
1312
1313         /*
1314          * No dice, use slow non-atomic map and copy
1315          */
1316         src = buf->ops->map(pipe, buf, 0);
1317
1318         ret = sd->len;
1319         if (copy_to_user(sd->u.userptr, src + buf->offset, sd->len))
1320                 ret = -EFAULT;
1321
1322         buf->ops->unmap(pipe, buf, src);
1323 out:
1324         if (ret > 0)
1325                 sd->u.userptr += ret;
1326         return ret;
1327 }
1328
1329 /*
1330  * For lack of a better implementation, implement vmsplice() to userspace
1331  * as a simple copy of the pipes pages to the user iov.
1332  */
1333 static long vmsplice_to_user(struct file *file, const struct iovec __user *iov,
1334                              unsigned long nr_segs, unsigned int flags)
1335 {
1336         struct pipe_inode_info *pipe;
1337         struct splice_desc sd;
1338         ssize_t size;
1339         int error;
1340         long ret;
1341
1342         pipe = pipe_info(file->f_path.dentry->d_inode);
1343         if (!pipe)
1344                 return -EBADF;
1345
1346         if (pipe->inode)
1347                 mutex_lock(&pipe->inode->i_mutex);
1348
1349         error = ret = 0;
1350         while (nr_segs) {
1351                 void __user *base;
1352                 size_t len;
1353
1354                 /*
1355                  * Get user address base and length for this iovec.
1356                  */
1357                 error = get_user(base, &iov->iov_base);
1358                 if (unlikely(error))
1359                         break;
1360                 error = get_user(len, &iov->iov_len);
1361                 if (unlikely(error))
1362                         break;
1363
1364                 /*
1365                  * Sanity check this iovec. 0 read succeeds.
1366                  */
1367                 if (unlikely(!len))
1368                         break;
1369                 if (unlikely(!base)) {
1370                         error = -EFAULT;
1371                         break;
1372                 }
1373
1374                 if (unlikely(!access_ok(VERIFY_WRITE, base, len))) {
1375                         error = -EFAULT;
1376                         break;
1377                 }
1378
1379                 sd.len = 0;
1380                 sd.total_len = len;
1381                 sd.flags = flags;
1382                 sd.u.userptr = base;
1383                 sd.pos = 0;
1384
1385                 size = __splice_from_pipe(pipe, &sd, pipe_to_user);
1386                 if (size < 0) {
1387                         if (!ret)
1388                                 ret = size;
1389
1390                         break;
1391                 }
1392
1393                 ret += size;
1394
1395                 if (size < len)
1396                         break;
1397
1398                 nr_segs--;
1399                 iov++;
1400         }
1401
1402         if (pipe->inode)
1403                 mutex_unlock(&pipe->inode->i_mutex);
1404
1405         if (!ret)
1406                 ret = error;
1407
1408         return ret;
1409 }
1410
1411 /*
1412  * vmsplice splices a user address range into a pipe. It can be thought of
1413  * as splice-from-memory, where the regular splice is splice-from-file (or
1414  * to file). In both cases the output is a pipe, naturally.
1415  */
1416 static long vmsplice_to_pipe(struct file *file, const struct iovec __user *iov,
1417                              unsigned long nr_segs, unsigned int flags)
1418 {
1419         struct pipe_inode_info *pipe;
1420         struct page *pages[PIPE_BUFFERS];
1421         struct partial_page partial[PIPE_BUFFERS];
1422         struct splice_pipe_desc spd = {
1423                 .pages = pages,
1424                 .partial = partial,
1425                 .flags = flags,
1426                 .ops = &user_page_pipe_buf_ops,
1427                 .spd_release = spd_release_page,
1428         };
1429
1430         pipe = pipe_info(file->f_path.dentry->d_inode);
1431         if (!pipe)
1432                 return -EBADF;
1433
1434         spd.nr_pages = get_iovec_page_array(iov, nr_segs, pages, partial,
1435                                             flags & SPLICE_F_GIFT);
1436         if (spd.nr_pages <= 0)
1437                 return spd.nr_pages;
1438
1439         return splice_to_pipe(pipe, &spd);
1440 }
1441
1442 /*
1443  * Note that vmsplice only really supports true splicing _from_ user memory
1444  * to a pipe, not the other way around. Splicing from user memory is a simple
1445  * operation that can be supported without any funky alignment restrictions
1446  * or nasty vm tricks. We simply map in the user memory and fill them into
1447  * a pipe. The reverse isn't quite as easy, though. There are two possible
1448  * solutions for that:
1449  *
1450  *      - memcpy() the data internally, at which point we might as well just
1451  *        do a regular read() on the buffer anyway.
1452  *      - Lots of nasty vm tricks, that are neither fast nor flexible (it
1453  *        has restriction limitations on both ends of the pipe).
1454  *
1455  * Currently we punt and implement it as a normal copy, see pipe_to_user().
1456  *
1457  */
1458 asmlinkage long sys_vmsplice(int fd, const struct iovec __user *iov,
1459                              unsigned long nr_segs, unsigned int flags)
1460 {
1461         struct file *file;
1462         long error;
1463         int fput;
1464
1465         if (unlikely(nr_segs > UIO_MAXIOV))
1466                 return -EINVAL;
1467         else if (unlikely(!nr_segs))
1468                 return 0;
1469
1470         error = -EBADF;
1471         file = fget_light(fd, &fput);
1472         if (file) {
1473                 if (file->f_mode & FMODE_WRITE)
1474                         error = vmsplice_to_pipe(file, iov, nr_segs, flags);
1475                 else if (file->f_mode & FMODE_READ)
1476                         error = vmsplice_to_user(file, iov, nr_segs, flags);
1477
1478                 fput_light(file, fput);
1479         }
1480
1481         return error;
1482 }
1483
1484 asmlinkage long sys_splice(int fd_in, loff_t __user *off_in,
1485                            int fd_out, loff_t __user *off_out,
1486                            size_t len, unsigned int flags)
1487 {
1488         long error;
1489         struct file *in, *out;
1490         int fput_in, fput_out;
1491
1492         if (unlikely(!len))
1493                 return 0;
1494
1495         error = -EBADF;
1496         in = fget_light(fd_in, &fput_in);
1497         if (in) {
1498                 if (in->f_mode & FMODE_READ) {
1499                         out = fget_light(fd_out, &fput_out);
1500                         if (out) {
1501                                 if (out->f_mode & FMODE_WRITE)
1502                                         error = do_splice(in, off_in,
1503                                                           out, off_out,
1504                                                           len, flags);
1505                                 fput_light(out, fput_out);
1506                         }
1507                 }
1508
1509                 fput_light(in, fput_in);
1510         }
1511
1512         return error;
1513 }
1514
1515 /*
1516  * Make sure there's data to read. Wait for input if we can, otherwise
1517  * return an appropriate error.
1518  */
1519 static int link_ipipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
1520 {
1521         int ret;
1522
1523         /*
1524          * Check ->nrbufs without the inode lock first. This function
1525          * is speculative anyways, so missing one is ok.
1526          */
1527         if (pipe->nrbufs)
1528                 return 0;
1529
1530         ret = 0;
1531         mutex_lock(&pipe->inode->i_mutex);
1532
1533         while (!pipe->nrbufs) {
1534                 if (signal_pending(current)) {
1535                         ret = -ERESTARTSYS;
1536                         break;
1537                 }
1538                 if (!pipe->writers)
1539                         break;
1540                 if (!pipe->waiting_writers) {
1541                         if (flags & SPLICE_F_NONBLOCK) {
1542                                 ret = -EAGAIN;
1543                                 break;
1544                         }
1545                 }
1546                 pipe_wait(pipe);
1547         }
1548
1549         mutex_unlock(&pipe->inode->i_mutex);
1550         return ret;
1551 }
1552
1553 /*
1554  * Make sure there's writeable room. Wait for room if we can, otherwise
1555  * return an appropriate error.
1556  */
1557 static int link_opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
1558 {
1559         int ret;
1560
1561         /*
1562          * Check ->nrbufs without the inode lock first. This function
1563          * is speculative anyways, so missing one is ok.
1564          */
1565         if (pipe->nrbufs < PIPE_BUFFERS)
1566                 return 0;
1567
1568         ret = 0;
1569         mutex_lock(&pipe->inode->i_mutex);
1570
1571         while (pipe->nrbufs >= PIPE_BUFFERS) {
1572                 if (!pipe->readers) {
1573                         send_sig(SIGPIPE, current, 0);
1574                         ret = -EPIPE;
1575                         break;
1576                 }
1577                 if (flags & SPLICE_F_NONBLOCK) {
1578                         ret = -EAGAIN;
1579                         break;
1580                 }
1581                 if (signal_pending(current)) {
1582                         ret = -ERESTARTSYS;
1583                         break;
1584                 }
1585                 pipe->waiting_writers++;
1586                 pipe_wait(pipe);
1587                 pipe->waiting_writers--;
1588         }
1589
1590         mutex_unlock(&pipe->inode->i_mutex);
1591         return ret;
1592 }
1593
1594 /*
1595  * Link contents of ipipe to opipe.
1596  */
1597 static int link_pipe(struct pipe_inode_info *ipipe,
1598                      struct pipe_inode_info *opipe,
1599                      size_t len, unsigned int flags)
1600 {
1601         struct pipe_buffer *ibuf, *obuf;
1602         int ret = 0, i = 0, nbuf;
1603
1604         /*
1605          * Potential ABBA deadlock, work around it by ordering lock
1606          * grabbing by inode address. Otherwise two different processes
1607          * could deadlock (one doing tee from A -> B, the other from B -> A).
1608          */
1609         inode_double_lock(ipipe->inode, opipe->inode);
1610
1611         do {
1612                 if (!opipe->readers) {
1613                         send_sig(SIGPIPE, current, 0);
1614                         if (!ret)
1615                                 ret = -EPIPE;
1616                         break;
1617                 }
1618
1619                 /*
1620                  * If we have iterated all input buffers or ran out of
1621                  * output room, break.
1622                  */
1623                 if (i >= ipipe->nrbufs || opipe->nrbufs >= PIPE_BUFFERS)
1624                         break;
1625
1626                 ibuf = ipipe->bufs + ((ipipe->curbuf + i) & (PIPE_BUFFERS - 1));
1627                 nbuf = (opipe->curbuf + opipe->nrbufs) & (PIPE_BUFFERS - 1);
1628
1629                 /*
1630                  * Get a reference to this pipe buffer,
1631                  * so we can copy the contents over.
1632                  */
1633                 ibuf->ops->get(ipipe, ibuf);
1634
1635                 obuf = opipe->bufs + nbuf;
1636                 *obuf = *ibuf;
1637
1638                 /*
1639                  * Don't inherit the gift flag, we need to
1640                  * prevent multiple steals of this page.
1641                  */
1642                 obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
1643
1644                 if (obuf->len > len)
1645                         obuf->len = len;
1646
1647                 opipe->nrbufs++;
1648                 ret += obuf->len;
1649                 len -= obuf->len;
1650                 i++;
1651         } while (len);
1652
1653         /*
1654          * return EAGAIN if we have the potential of some data in the
1655          * future, otherwise just return 0
1656          */
1657         if (!ret && ipipe->waiting_writers && (flags & SPLICE_F_NONBLOCK))
1658                 ret = -EAGAIN;
1659
1660         inode_double_unlock(ipipe->inode, opipe->inode);
1661
1662         /*
1663          * If we put data in the output pipe, wakeup any potential readers.
1664          */
1665         if (ret > 0) {
1666                 smp_mb();
1667                 if (waitqueue_active(&opipe->wait))
1668                         wake_up_interruptible(&opipe->wait);
1669                 kill_fasync(&opipe->fasync_readers, SIGIO, POLL_IN);
1670         }
1671
1672         return ret;
1673 }
1674
1675 /*
1676  * This is a tee(1) implementation that works on pipes. It doesn't copy
1677  * any data, it simply references the 'in' pages on the 'out' pipe.
1678  * The 'flags' used are the SPLICE_F_* variants, currently the only
1679  * applicable one is SPLICE_F_NONBLOCK.
1680  */
1681 static long do_tee(struct file *in, struct file *out, size_t len,
1682                    unsigned int flags)
1683 {
1684         struct pipe_inode_info *ipipe = pipe_info(in->f_path.dentry->d_inode);
1685         struct pipe_inode_info *opipe = pipe_info(out->f_path.dentry->d_inode);
1686         int ret = -EINVAL;
1687
1688         /*
1689          * Duplicate the contents of ipipe to opipe without actually
1690          * copying the data.
1691          */
1692         if (ipipe && opipe && ipipe != opipe) {
1693                 /*
1694                  * Keep going, unless we encounter an error. The ipipe/opipe
1695                  * ordering doesn't really matter.
1696                  */
1697                 ret = link_ipipe_prep(ipipe, flags);
1698                 if (!ret) {
1699                         ret = link_opipe_prep(opipe, flags);
1700                         if (!ret)
1701                                 ret = link_pipe(ipipe, opipe, len, flags);
1702                 }
1703         }
1704
1705         return ret;
1706 }
1707
1708 asmlinkage long sys_tee(int fdin, int fdout, size_t len, unsigned int flags)
1709 {
1710         struct file *in;
1711         int error, fput_in;
1712
1713         if (unlikely(!len))
1714                 return 0;
1715
1716         error = -EBADF;
1717         in = fget_light(fdin, &fput_in);
1718         if (in) {
1719                 if (in->f_mode & FMODE_READ) {
1720                         int fput_out;
1721                         struct file *out = fget_light(fdout, &fput_out);
1722
1723                         if (out) {
1724                                 if (out->f_mode & FMODE_WRITE)
1725                                         error = do_tee(in, out, len, flags);
1726                                 fput_light(out, fput_out);
1727                         }
1728                 }
1729                 fput_light(in, fput_in);
1730         }
1731
1732         return error;
1733 }