splice: only return -EAGAIN if there's hope of more 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/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                                               GFP_KERNEL);
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                                         break;
375                         } else
376                                 lock_page(page);
377
378                         /*
379                          * page was truncated, stop here. if this isn't the
380                          * first page, we'll just complete what we already
381                          * added
382                          */
383                         if (!page->mapping) {
384                                 unlock_page(page);
385                                 break;
386                         }
387                         /*
388                          * page was already under io and is now done, great
389                          */
390                         if (PageUptodate(page)) {
391                                 unlock_page(page);
392                                 goto fill_it;
393                         }
394
395                         /*
396                          * need to read in the page
397                          */
398                         error = mapping->a_ops->readpage(in, page);
399                         if (unlikely(error)) {
400                                 /*
401                                  * We really should re-lookup the page here,
402                                  * but it complicates things a lot. Instead
403                                  * lets just do what we already stored, and
404                                  * we'll get it the next time we are called.
405                                  */
406                                 if (error == AOP_TRUNCATED_PAGE)
407                                         error = 0;
408
409                                 break;
410                         }
411                 }
412 fill_it:
413                 /*
414                  * i_size must be checked after PageUptodate.
415                  */
416                 isize = i_size_read(mapping->host);
417                 end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
418                 if (unlikely(!isize || index > end_index))
419                         break;
420
421                 /*
422                  * if this is the last page, see if we need to shrink
423                  * the length and stop
424                  */
425                 if (end_index == index) {
426                         unsigned int plen;
427
428                         /*
429                          * max good bytes in this page
430                          */
431                         plen = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
432                         if (plen <= loff)
433                                 break;
434
435                         /*
436                          * force quit after adding this page
437                          */
438                         this_len = min(this_len, plen - loff);
439                         len = this_len;
440                 }
441
442                 partial[page_nr].offset = loff;
443                 partial[page_nr].len = this_len;
444                 len -= this_len;
445                 loff = 0;
446                 spd.nr_pages++;
447                 index++;
448         }
449
450         /*
451          * Release any pages at the end, if we quit early. 'page_nr' is how far
452          * we got, 'nr_pages' is how many pages are in the map.
453          */
454         while (page_nr < nr_pages)
455                 page_cache_release(pages[page_nr++]);
456         in->f_ra.prev_pos = (loff_t)index << PAGE_CACHE_SHIFT;
457
458         if (spd.nr_pages)
459                 return splice_to_pipe(pipe, &spd);
460
461         return error;
462 }
463
464 /**
465  * generic_file_splice_read - splice data from file to a pipe
466  * @in:         file to splice from
467  * @ppos:       position in @in
468  * @pipe:       pipe to splice to
469  * @len:        number of bytes to splice
470  * @flags:      splice modifier flags
471  *
472  * Description:
473  *    Will read pages from given file and fill them into a pipe. Can be
474  *    used as long as the address_space operations for the source implements
475  *    a readpage() hook.
476  *
477  */
478 ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
479                                  struct pipe_inode_info *pipe, size_t len,
480                                  unsigned int flags)
481 {
482         ssize_t spliced;
483         int ret;
484         loff_t isize, left;
485
486         isize = i_size_read(in->f_mapping->host);
487         if (unlikely(*ppos >= isize))
488                 return 0;
489
490         left = isize - *ppos;
491         if (unlikely(left < len))
492                 len = left;
493
494         ret = 0;
495         spliced = 0;
496         while (len && !spliced) {
497                 ret = __generic_file_splice_read(in, ppos, pipe, len, flags);
498
499                 if (ret < 0)
500                         break;
501                 else if (!ret) {
502                         if (spliced)
503                                 break;
504                         if (flags & SPLICE_F_NONBLOCK) {
505                                 ret = -EAGAIN;
506                                 break;
507                         }
508                 }
509
510                 *ppos += ret;
511                 len -= ret;
512                 spliced += ret;
513         }
514
515         if (spliced)
516                 return spliced;
517
518         return ret;
519 }
520
521 EXPORT_SYMBOL(generic_file_splice_read);
522
523 /*
524  * Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->pos'
525  * using sendpage(). Return the number of bytes sent.
526  */
527 static int pipe_to_sendpage(struct pipe_inode_info *pipe,
528                             struct pipe_buffer *buf, struct splice_desc *sd)
529 {
530         struct file *file = sd->u.file;
531         loff_t pos = sd->pos;
532         int ret, more;
533
534         ret = buf->ops->confirm(pipe, buf);
535         if (!ret) {
536                 more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len;
537
538                 ret = file->f_op->sendpage(file, buf->page, buf->offset,
539                                            sd->len, &pos, more);
540         }
541
542         return ret;
543 }
544
545 /*
546  * This is a little more tricky than the file -> pipe splicing. There are
547  * basically three cases:
548  *
549  *      - Destination page already exists in the address space and there
550  *        are users of it. For that case we have no other option that
551  *        copying the data. Tough luck.
552  *      - Destination page already exists in the address space, but there
553  *        are no users of it. Make sure it's uptodate, then drop it. Fall
554  *        through to last case.
555  *      - Destination page does not exist, we can add the pipe page to
556  *        the page cache and avoid the copy.
557  *
558  * If asked to move pages to the output file (SPLICE_F_MOVE is set in
559  * sd->flags), we attempt to migrate pages from the pipe to the output
560  * file address space page cache. This is possible if no one else has
561  * the pipe page referenced outside of the pipe and page cache. If
562  * SPLICE_F_MOVE isn't set, or we cannot move the page, we simply create
563  * a new page in the output file page cache and fill/dirty that.
564  */
565 static int pipe_to_file(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
566                         struct splice_desc *sd)
567 {
568         struct file *file = sd->u.file;
569         struct address_space *mapping = file->f_mapping;
570         unsigned int offset, this_len;
571         struct page *page;
572         void *fsdata;
573         int ret;
574
575         /*
576          * make sure the data in this buffer is uptodate
577          */
578         ret = buf->ops->confirm(pipe, buf);
579         if (unlikely(ret))
580                 return ret;
581
582         offset = sd->pos & ~PAGE_CACHE_MASK;
583
584         this_len = sd->len;
585         if (this_len + offset > PAGE_CACHE_SIZE)
586                 this_len = PAGE_CACHE_SIZE - offset;
587
588         ret = pagecache_write_begin(file, mapping, sd->pos, this_len,
589                                 AOP_FLAG_UNINTERRUPTIBLE, &page, &fsdata);
590         if (unlikely(ret))
591                 goto out;
592
593         if (buf->page != page) {
594                 /*
595                  * Careful, ->map() uses KM_USER0!
596                  */
597                 char *src = buf->ops->map(pipe, buf, 1);
598                 char *dst = kmap_atomic(page, KM_USER1);
599
600                 memcpy(dst + offset, src + buf->offset, this_len);
601                 flush_dcache_page(page);
602                 kunmap_atomic(dst, KM_USER1);
603                 buf->ops->unmap(pipe, buf, src);
604         }
605         ret = pagecache_write_end(file, mapping, sd->pos, this_len, this_len,
606                                 page, fsdata);
607 out:
608         return ret;
609 }
610
611 /**
612  * __splice_from_pipe - splice data from a pipe to given actor
613  * @pipe:       pipe to splice from
614  * @sd:         information to @actor
615  * @actor:      handler that splices the data
616  *
617  * Description:
618  *    This function does little more than loop over the pipe and call
619  *    @actor to do the actual moving of a single struct pipe_buffer to
620  *    the desired destination. See pipe_to_file, pipe_to_sendpage, or
621  *    pipe_to_user.
622  *
623  */
624 ssize_t __splice_from_pipe(struct pipe_inode_info *pipe, struct splice_desc *sd,
625                            splice_actor *actor)
626 {
627         int ret, do_wakeup, err;
628
629         ret = 0;
630         do_wakeup = 0;
631
632         for (;;) {
633                 if (pipe->nrbufs) {
634                         struct pipe_buffer *buf = pipe->bufs + pipe->curbuf;
635                         const struct pipe_buf_operations *ops = buf->ops;
636
637                         sd->len = buf->len;
638                         if (sd->len > sd->total_len)
639                                 sd->len = sd->total_len;
640
641                         err = actor(pipe, buf, sd);
642                         if (err <= 0) {
643                                 if (!ret && err != -ENODATA)
644                                         ret = err;
645
646                                 break;
647                         }
648
649                         ret += err;
650                         buf->offset += err;
651                         buf->len -= err;
652
653                         sd->len -= err;
654                         sd->pos += err;
655                         sd->total_len -= err;
656                         if (sd->len)
657                                 continue;
658
659                         if (!buf->len) {
660                                 buf->ops = NULL;
661                                 ops->release(pipe, buf);
662                                 pipe->curbuf = (pipe->curbuf + 1) & (PIPE_BUFFERS - 1);
663                                 pipe->nrbufs--;
664                                 if (pipe->inode)
665                                         do_wakeup = 1;
666                         }
667
668                         if (!sd->total_len)
669                                 break;
670                 }
671
672                 if (pipe->nrbufs)
673                         continue;
674                 if (!pipe->writers)
675                         break;
676                 if (!pipe->waiting_writers) {
677                         if (ret)
678                                 break;
679                 }
680
681                 if (sd->flags & SPLICE_F_NONBLOCK) {
682                         if (!ret)
683                                 ret = -EAGAIN;
684                         break;
685                 }
686
687                 if (signal_pending(current)) {
688                         if (!ret)
689                                 ret = -ERESTARTSYS;
690                         break;
691                 }
692
693                 if (do_wakeup) {
694                         smp_mb();
695                         if (waitqueue_active(&pipe->wait))
696                                 wake_up_interruptible_sync(&pipe->wait);
697                         kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
698                         do_wakeup = 0;
699                 }
700
701                 pipe_wait(pipe);
702         }
703
704         if (do_wakeup) {
705                 smp_mb();
706                 if (waitqueue_active(&pipe->wait))
707                         wake_up_interruptible(&pipe->wait);
708                 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
709         }
710
711         return ret;
712 }
713 EXPORT_SYMBOL(__splice_from_pipe);
714
715 /**
716  * splice_from_pipe - splice data from a pipe to a file
717  * @pipe:       pipe to splice from
718  * @out:        file to splice to
719  * @ppos:       position in @out
720  * @len:        how many bytes to splice
721  * @flags:      splice modifier flags
722  * @actor:      handler that splices the data
723  *
724  * Description:
725  *    See __splice_from_pipe. This function locks the input and output inodes,
726  *    otherwise it's identical to __splice_from_pipe().
727  *
728  */
729 ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
730                          loff_t *ppos, size_t len, unsigned int flags,
731                          splice_actor *actor)
732 {
733         ssize_t ret;
734         struct inode *inode = out->f_mapping->host;
735         struct splice_desc sd = {
736                 .total_len = len,
737                 .flags = flags,
738                 .pos = *ppos,
739                 .u.file = out,
740         };
741
742         /*
743          * The actor worker might be calling ->prepare_write and
744          * ->commit_write. Most of the time, these expect i_mutex to
745          * be held. Since this may result in an ABBA deadlock with
746          * pipe->inode, we have to order lock acquiry here.
747          */
748         inode_double_lock(inode, pipe->inode);
749         ret = __splice_from_pipe(pipe, &sd, actor);
750         inode_double_unlock(inode, pipe->inode);
751
752         return ret;
753 }
754
755 /**
756  * generic_file_splice_write_nolock - generic_file_splice_write without mutexes
757  * @pipe:       pipe info
758  * @out:        file to write to
759  * @ppos:       position in @out
760  * @len:        number of bytes to splice
761  * @flags:      splice modifier flags
762  *
763  * Description:
764  *    Will either move or copy pages (determined by @flags options) from
765  *    the given pipe inode to the given file. The caller is responsible
766  *    for acquiring i_mutex on both inodes.
767  *
768  */
769 ssize_t
770 generic_file_splice_write_nolock(struct pipe_inode_info *pipe, struct file *out,
771                                  loff_t *ppos, size_t len, unsigned int flags)
772 {
773         struct address_space *mapping = out->f_mapping;
774         struct inode *inode = mapping->host;
775         struct splice_desc sd = {
776                 .total_len = len,
777                 .flags = flags,
778                 .pos = *ppos,
779                 .u.file = out,
780         };
781         ssize_t ret;
782         int err;
783
784         err = remove_suid(out->f_path.dentry);
785         if (unlikely(err))
786                 return err;
787
788         ret = __splice_from_pipe(pipe, &sd, pipe_to_file);
789         if (ret > 0) {
790                 unsigned long nr_pages;
791
792                 *ppos += ret;
793                 nr_pages = (ret + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
794
795                 /*
796                  * If file or inode is SYNC and we actually wrote some data,
797                  * sync it.
798                  */
799                 if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
800                         err = generic_osync_inode(inode, mapping,
801                                                   OSYNC_METADATA|OSYNC_DATA);
802
803                         if (err)
804                                 ret = err;
805                 }
806                 balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
807         }
808
809         return ret;
810 }
811
812 EXPORT_SYMBOL(generic_file_splice_write_nolock);
813
814 /**
815  * generic_file_splice_write - splice data from a pipe to a file
816  * @pipe:       pipe info
817  * @out:        file to write to
818  * @ppos:       position in @out
819  * @len:        number of bytes to splice
820  * @flags:      splice modifier flags
821  *
822  * Description:
823  *    Will either move or copy pages (determined by @flags options) from
824  *    the given pipe inode to the given file.
825  *
826  */
827 ssize_t
828 generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
829                           loff_t *ppos, size_t len, unsigned int flags)
830 {
831         struct address_space *mapping = out->f_mapping;
832         struct inode *inode = mapping->host;
833         int killsuid, killpriv;
834         ssize_t ret;
835         int err = 0;
836
837         killpriv = security_inode_need_killpriv(out->f_path.dentry);
838         killsuid = should_remove_suid(out->f_path.dentry);
839         if (unlikely(killsuid || killpriv)) {
840                 mutex_lock(&inode->i_mutex);
841                 if (killpriv)
842                         err = security_inode_killpriv(out->f_path.dentry);
843                 if (!err && killsuid)
844                         err = __remove_suid(out->f_path.dentry, killsuid);
845                 mutex_unlock(&inode->i_mutex);
846                 if (err)
847                         return err;
848         }
849
850         ret = splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_file);
851         if (ret > 0) {
852                 unsigned long nr_pages;
853
854                 *ppos += ret;
855                 nr_pages = (ret + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
856
857                 /*
858                  * If file or inode is SYNC and we actually wrote some data,
859                  * sync it.
860                  */
861                 if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
862                         mutex_lock(&inode->i_mutex);
863                         err = generic_osync_inode(inode, mapping,
864                                                   OSYNC_METADATA|OSYNC_DATA);
865                         mutex_unlock(&inode->i_mutex);
866
867                         if (err)
868                                 ret = err;
869                 }
870                 balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
871         }
872
873         return ret;
874 }
875
876 EXPORT_SYMBOL(generic_file_splice_write);
877
878 /**
879  * generic_splice_sendpage - splice data from a pipe to a socket
880  * @pipe:       pipe to splice from
881  * @out:        socket to write to
882  * @ppos:       position in @out
883  * @len:        number of bytes to splice
884  * @flags:      splice modifier flags
885  *
886  * Description:
887  *    Will send @len bytes from the pipe to a network socket. No data copying
888  *    is involved.
889  *
890  */
891 ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe, struct file *out,
892                                 loff_t *ppos, size_t len, unsigned int flags)
893 {
894         return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_sendpage);
895 }
896
897 EXPORT_SYMBOL(generic_splice_sendpage);
898
899 /*
900  * Attempt to initiate a splice from pipe to file.
901  */
902 static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
903                            loff_t *ppos, size_t len, unsigned int flags)
904 {
905         int ret;
906
907         if (unlikely(!out->f_op || !out->f_op->splice_write))
908                 return -EINVAL;
909
910         if (unlikely(!(out->f_mode & FMODE_WRITE)))
911                 return -EBADF;
912
913         ret = rw_verify_area(WRITE, out, ppos, len);
914         if (unlikely(ret < 0))
915                 return ret;
916
917         return out->f_op->splice_write(pipe, out, ppos, len, flags);
918 }
919
920 /*
921  * Attempt to initiate a splice from a file to a pipe.
922  */
923 static long do_splice_to(struct file *in, loff_t *ppos,
924                          struct pipe_inode_info *pipe, size_t len,
925                          unsigned int flags)
926 {
927         int ret;
928
929         if (unlikely(!in->f_op || !in->f_op->splice_read))
930                 return -EINVAL;
931
932         if (unlikely(!(in->f_mode & FMODE_READ)))
933                 return -EBADF;
934
935         ret = rw_verify_area(READ, in, ppos, len);
936         if (unlikely(ret < 0))
937                 return ret;
938
939         return in->f_op->splice_read(in, ppos, pipe, len, flags);
940 }
941
942 /**
943  * splice_direct_to_actor - splices data directly between two non-pipes
944  * @in:         file to splice from
945  * @sd:         actor information on where to splice to
946  * @actor:      handles the data splicing
947  *
948  * Description:
949  *    This is a special case helper to splice directly between two
950  *    points, without requiring an explicit pipe. Internally an allocated
951  *    pipe is cached in the process, and reused during the lifetime of
952  *    that process.
953  *
954  */
955 ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
956                                splice_direct_actor *actor)
957 {
958         struct pipe_inode_info *pipe;
959         long ret, bytes;
960         umode_t i_mode;
961         size_t len;
962         int i, flags;
963
964         /*
965          * We require the input being a regular file, as we don't want to
966          * randomly drop data for eg socket -> socket splicing. Use the
967          * piped splicing for that!
968          */
969         i_mode = in->f_path.dentry->d_inode->i_mode;
970         if (unlikely(!S_ISREG(i_mode) && !S_ISBLK(i_mode)))
971                 return -EINVAL;
972
973         /*
974          * neither in nor out is a pipe, setup an internal pipe attached to
975          * 'out' and transfer the wanted data from 'in' to 'out' through that
976          */
977         pipe = current->splice_pipe;
978         if (unlikely(!pipe)) {
979                 pipe = alloc_pipe_info(NULL);
980                 if (!pipe)
981                         return -ENOMEM;
982
983                 /*
984                  * We don't have an immediate reader, but we'll read the stuff
985                  * out of the pipe right after the splice_to_pipe(). So set
986                  * PIPE_READERS appropriately.
987                  */
988                 pipe->readers = 1;
989
990                 current->splice_pipe = pipe;
991         }
992
993         /*
994          * Do the splice.
995          */
996         ret = 0;
997         bytes = 0;
998         len = sd->total_len;
999         flags = sd->flags;
1000
1001         /*
1002          * Don't block on output, we have to drain the direct pipe.
1003          */
1004         sd->flags &= ~SPLICE_F_NONBLOCK;
1005
1006         while (len) {
1007                 size_t read_len;
1008                 loff_t pos = sd->pos;
1009
1010                 ret = do_splice_to(in, &pos, pipe, len, flags);
1011                 if (unlikely(ret <= 0))
1012                         goto out_release;
1013
1014                 read_len = ret;
1015                 sd->total_len = read_len;
1016
1017                 /*
1018                  * NOTE: nonblocking mode only applies to the input. We
1019                  * must not do the output in nonblocking mode as then we
1020                  * could get stuck data in the internal pipe:
1021                  */
1022                 ret = actor(pipe, sd);
1023                 if (unlikely(ret <= 0))
1024                         goto out_release;
1025
1026                 bytes += ret;
1027                 len -= ret;
1028                 sd->pos = pos;
1029
1030                 if (ret < read_len)
1031                         goto out_release;
1032         }
1033
1034 done:
1035         pipe->nrbufs = pipe->curbuf = 0;
1036         file_accessed(in);
1037         return bytes;
1038
1039 out_release:
1040         /*
1041          * If we did an incomplete transfer we must release
1042          * the pipe buffers in question:
1043          */
1044         for (i = 0; i < PIPE_BUFFERS; i++) {
1045                 struct pipe_buffer *buf = pipe->bufs + i;
1046
1047                 if (buf->ops) {
1048                         buf->ops->release(pipe, buf);
1049                         buf->ops = NULL;
1050                 }
1051         }
1052
1053         if (!bytes)
1054                 bytes = ret;
1055
1056         goto done;
1057 }
1058 EXPORT_SYMBOL(splice_direct_to_actor);
1059
1060 static int direct_splice_actor(struct pipe_inode_info *pipe,
1061                                struct splice_desc *sd)
1062 {
1063         struct file *file = sd->u.file;
1064
1065         return do_splice_from(pipe, file, &sd->pos, sd->total_len, sd->flags);
1066 }
1067
1068 /**
1069  * do_splice_direct - splices data directly between two files
1070  * @in:         file to splice from
1071  * @ppos:       input file offset
1072  * @out:        file to splice to
1073  * @len:        number of bytes to splice
1074  * @flags:      splice modifier flags
1075  *
1076  * Description:
1077  *    For use by do_sendfile(). splice can easily emulate sendfile, but
1078  *    doing it in the application would incur an extra system call
1079  *    (splice in + splice out, as compared to just sendfile()). So this helper
1080  *    can splice directly through a process-private pipe.
1081  *
1082  */
1083 long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
1084                       size_t len, unsigned int flags)
1085 {
1086         struct splice_desc sd = {
1087                 .len            = len,
1088                 .total_len      = len,
1089                 .flags          = flags,
1090                 .pos            = *ppos,
1091                 .u.file         = out,
1092         };
1093         long ret;
1094
1095         ret = splice_direct_to_actor(in, &sd, direct_splice_actor);
1096         if (ret > 0)
1097                 *ppos += ret;
1098
1099         return ret;
1100 }
1101
1102 /*
1103  * After the inode slimming patch, i_pipe/i_bdev/i_cdev share the same
1104  * location, so checking ->i_pipe is not enough to verify that this is a
1105  * pipe.
1106  */
1107 static inline struct pipe_inode_info *pipe_info(struct inode *inode)
1108 {
1109         if (S_ISFIFO(inode->i_mode))
1110                 return inode->i_pipe;
1111
1112         return NULL;
1113 }
1114
1115 /*
1116  * Determine where to splice to/from.
1117  */
1118 static long do_splice(struct file *in, loff_t __user *off_in,
1119                       struct file *out, loff_t __user *off_out,
1120                       size_t len, unsigned int flags)
1121 {
1122         struct pipe_inode_info *pipe;
1123         loff_t offset, *off;
1124         long ret;
1125
1126         pipe = pipe_info(in->f_path.dentry->d_inode);
1127         if (pipe) {
1128                 if (off_in)
1129                         return -ESPIPE;
1130                 if (off_out) {
1131                         if (out->f_op->llseek == no_llseek)
1132                                 return -EINVAL;
1133                         if (copy_from_user(&offset, off_out, sizeof(loff_t)))
1134                                 return -EFAULT;
1135                         off = &offset;
1136                 } else
1137                         off = &out->f_pos;
1138
1139                 ret = do_splice_from(pipe, out, off, len, flags);
1140
1141                 if (off_out && copy_to_user(off_out, off, sizeof(loff_t)))
1142                         ret = -EFAULT;
1143
1144                 return ret;
1145         }
1146
1147         pipe = pipe_info(out->f_path.dentry->d_inode);
1148         if (pipe) {
1149                 if (off_out)
1150                         return -ESPIPE;
1151                 if (off_in) {
1152                         if (in->f_op->llseek == no_llseek)
1153                                 return -EINVAL;
1154                         if (copy_from_user(&offset, off_in, sizeof(loff_t)))
1155                                 return -EFAULT;
1156                         off = &offset;
1157                 } else
1158                         off = &in->f_pos;
1159
1160                 ret = do_splice_to(in, off, pipe, len, flags);
1161
1162                 if (off_in && copy_to_user(off_in, off, sizeof(loff_t)))
1163                         ret = -EFAULT;
1164
1165                 return ret;
1166         }
1167
1168         return -EINVAL;
1169 }
1170
1171 /*
1172  * Do a copy-from-user while holding the mmap_semaphore for reading, in a
1173  * manner safe from deadlocking with simultaneous mmap() (grabbing mmap_sem
1174  * for writing) and page faulting on the user memory pointed to by src.
1175  * This assumes that we will very rarely hit the partial != 0 path, or this
1176  * will not be a win.
1177  */
1178 static int copy_from_user_mmap_sem(void *dst, const void __user *src, size_t n)
1179 {
1180         int partial;
1181
1182         if (!access_ok(VERIFY_READ, src, n))
1183                 return -EFAULT;
1184
1185         pagefault_disable();
1186         partial = __copy_from_user_inatomic(dst, src, n);
1187         pagefault_enable();
1188
1189         /*
1190          * Didn't copy everything, drop the mmap_sem and do a faulting copy
1191          */
1192         if (unlikely(partial)) {
1193                 up_read(&current->mm->mmap_sem);
1194                 partial = copy_from_user(dst, src, n);
1195                 down_read(&current->mm->mmap_sem);
1196         }
1197
1198         return partial;
1199 }
1200
1201 /*
1202  * Map an iov into an array of pages and offset/length tupples. With the
1203  * partial_page structure, we can map several non-contiguous ranges into
1204  * our ones pages[] map instead of splitting that operation into pieces.
1205  * Could easily be exported as a generic helper for other users, in which
1206  * case one would probably want to add a 'max_nr_pages' parameter as well.
1207  */
1208 static int get_iovec_page_array(const struct iovec __user *iov,
1209                                 unsigned int nr_vecs, struct page **pages,
1210                                 struct partial_page *partial, int aligned)
1211 {
1212         int buffers = 0, error = 0;
1213
1214         down_read(&current->mm->mmap_sem);
1215
1216         while (nr_vecs) {
1217                 unsigned long off, npages;
1218                 struct iovec entry;
1219                 void __user *base;
1220                 size_t len;
1221                 int i;
1222
1223                 error = -EFAULT;
1224                 if (copy_from_user_mmap_sem(&entry, iov, sizeof(entry)))
1225                         break;
1226
1227                 base = entry.iov_base;
1228                 len = entry.iov_len;
1229
1230                 /*
1231                  * Sanity check this iovec. 0 read succeeds.
1232                  */
1233                 error = 0;
1234                 if (unlikely(!len))
1235                         break;
1236                 error = -EFAULT;
1237                 if (!access_ok(VERIFY_READ, base, len))
1238                         break;
1239
1240                 /*
1241                  * Get this base offset and number of pages, then map
1242                  * in the user pages.
1243                  */
1244                 off = (unsigned long) base & ~PAGE_MASK;
1245
1246                 /*
1247                  * If asked for alignment, the offset must be zero and the
1248                  * length a multiple of the PAGE_SIZE.
1249                  */
1250                 error = -EINVAL;
1251                 if (aligned && (off || len & ~PAGE_MASK))
1252                         break;
1253
1254                 npages = (off + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
1255                 if (npages > PIPE_BUFFERS - buffers)
1256                         npages = PIPE_BUFFERS - buffers;
1257
1258                 error = get_user_pages(current, current->mm,
1259                                        (unsigned long) base, npages, 0, 0,
1260                                        &pages[buffers], NULL);
1261
1262                 if (unlikely(error <= 0))
1263                         break;
1264
1265                 /*
1266                  * Fill this contiguous range into the partial page map.
1267                  */
1268                 for (i = 0; i < error; i++) {
1269                         const int plen = min_t(size_t, len, PAGE_SIZE - off);
1270
1271                         partial[buffers].offset = off;
1272                         partial[buffers].len = plen;
1273
1274                         off = 0;
1275                         len -= plen;
1276                         buffers++;
1277                 }
1278
1279                 /*
1280                  * We didn't complete this iov, stop here since it probably
1281                  * means we have to move some of this into a pipe to
1282                  * be able to continue.
1283                  */
1284                 if (len)
1285                         break;
1286
1287                 /*
1288                  * Don't continue if we mapped fewer pages than we asked for,
1289                  * or if we mapped the max number of pages that we have
1290                  * room for.
1291                  */
1292                 if (error < npages || buffers == PIPE_BUFFERS)
1293                         break;
1294
1295                 nr_vecs--;
1296                 iov++;
1297         }
1298
1299         up_read(&current->mm->mmap_sem);
1300
1301         if (buffers)
1302                 return buffers;
1303
1304         return error;
1305 }
1306
1307 static int pipe_to_user(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
1308                         struct splice_desc *sd)
1309 {
1310         char *src;
1311         int ret;
1312
1313         ret = buf->ops->confirm(pipe, buf);
1314         if (unlikely(ret))
1315                 return ret;
1316
1317         /*
1318          * See if we can use the atomic maps, by prefaulting in the
1319          * pages and doing an atomic copy
1320          */
1321         if (!fault_in_pages_writeable(sd->u.userptr, sd->len)) {
1322                 src = buf->ops->map(pipe, buf, 1);
1323                 ret = __copy_to_user_inatomic(sd->u.userptr, src + buf->offset,
1324                                                         sd->len);
1325                 buf->ops->unmap(pipe, buf, src);
1326                 if (!ret) {
1327                         ret = sd->len;
1328                         goto out;
1329                 }
1330         }
1331
1332         /*
1333          * No dice, use slow non-atomic map and copy
1334          */
1335         src = buf->ops->map(pipe, buf, 0);
1336
1337         ret = sd->len;
1338         if (copy_to_user(sd->u.userptr, src + buf->offset, sd->len))
1339                 ret = -EFAULT;
1340
1341         buf->ops->unmap(pipe, buf, src);
1342 out:
1343         if (ret > 0)
1344                 sd->u.userptr += ret;
1345         return ret;
1346 }
1347
1348 /*
1349  * For lack of a better implementation, implement vmsplice() to userspace
1350  * as a simple copy of the pipes pages to the user iov.
1351  */
1352 static long vmsplice_to_user(struct file *file, const struct iovec __user *iov,
1353                              unsigned long nr_segs, unsigned int flags)
1354 {
1355         struct pipe_inode_info *pipe;
1356         struct splice_desc sd;
1357         ssize_t size;
1358         int error;
1359         long ret;
1360
1361         pipe = pipe_info(file->f_path.dentry->d_inode);
1362         if (!pipe)
1363                 return -EBADF;
1364
1365         if (pipe->inode)
1366                 mutex_lock(&pipe->inode->i_mutex);
1367
1368         error = ret = 0;
1369         while (nr_segs) {
1370                 void __user *base;
1371                 size_t len;
1372
1373                 /*
1374                  * Get user address base and length for this iovec.
1375                  */
1376                 error = get_user(base, &iov->iov_base);
1377                 if (unlikely(error))
1378                         break;
1379                 error = get_user(len, &iov->iov_len);
1380                 if (unlikely(error))
1381                         break;
1382
1383                 /*
1384                  * Sanity check this iovec. 0 read succeeds.
1385                  */
1386                 if (unlikely(!len))
1387                         break;
1388                 if (unlikely(!base)) {
1389                         error = -EFAULT;
1390                         break;
1391                 }
1392
1393                 if (unlikely(!access_ok(VERIFY_WRITE, base, len))) {
1394                         error = -EFAULT;
1395                         break;
1396                 }
1397
1398                 sd.len = 0;
1399                 sd.total_len = len;
1400                 sd.flags = flags;
1401                 sd.u.userptr = base;
1402                 sd.pos = 0;
1403
1404                 size = __splice_from_pipe(pipe, &sd, pipe_to_user);
1405                 if (size < 0) {
1406                         if (!ret)
1407                                 ret = size;
1408
1409                         break;
1410                 }
1411
1412                 ret += size;
1413
1414                 if (size < len)
1415                         break;
1416
1417                 nr_segs--;
1418                 iov++;
1419         }
1420
1421         if (pipe->inode)
1422                 mutex_unlock(&pipe->inode->i_mutex);
1423
1424         if (!ret)
1425                 ret = error;
1426
1427         return ret;
1428 }
1429
1430 /*
1431  * vmsplice splices a user address range into a pipe. It can be thought of
1432  * as splice-from-memory, where the regular splice is splice-from-file (or
1433  * to file). In both cases the output is a pipe, naturally.
1434  */
1435 static long vmsplice_to_pipe(struct file *file, const struct iovec __user *iov,
1436                              unsigned long nr_segs, unsigned int flags)
1437 {
1438         struct pipe_inode_info *pipe;
1439         struct page *pages[PIPE_BUFFERS];
1440         struct partial_page partial[PIPE_BUFFERS];
1441         struct splice_pipe_desc spd = {
1442                 .pages = pages,
1443                 .partial = partial,
1444                 .flags = flags,
1445                 .ops = &user_page_pipe_buf_ops,
1446                 .spd_release = spd_release_page,
1447         };
1448
1449         pipe = pipe_info(file->f_path.dentry->d_inode);
1450         if (!pipe)
1451                 return -EBADF;
1452
1453         spd.nr_pages = get_iovec_page_array(iov, nr_segs, pages, partial,
1454                                             flags & SPLICE_F_GIFT);
1455         if (spd.nr_pages <= 0)
1456                 return spd.nr_pages;
1457
1458         return splice_to_pipe(pipe, &spd);
1459 }
1460
1461 /*
1462  * Note that vmsplice only really supports true splicing _from_ user memory
1463  * to a pipe, not the other way around. Splicing from user memory is a simple
1464  * operation that can be supported without any funky alignment restrictions
1465  * or nasty vm tricks. We simply map in the user memory and fill them into
1466  * a pipe. The reverse isn't quite as easy, though. There are two possible
1467  * solutions for that:
1468  *
1469  *      - memcpy() the data internally, at which point we might as well just
1470  *        do a regular read() on the buffer anyway.
1471  *      - Lots of nasty vm tricks, that are neither fast nor flexible (it
1472  *        has restriction limitations on both ends of the pipe).
1473  *
1474  * Currently we punt and implement it as a normal copy, see pipe_to_user().
1475  *
1476  */
1477 asmlinkage long sys_vmsplice(int fd, const struct iovec __user *iov,
1478                              unsigned long nr_segs, unsigned int flags)
1479 {
1480         struct file *file;
1481         long error;
1482         int fput;
1483
1484         if (unlikely(nr_segs > UIO_MAXIOV))
1485                 return -EINVAL;
1486         else if (unlikely(!nr_segs))
1487                 return 0;
1488
1489         error = -EBADF;
1490         file = fget_light(fd, &fput);
1491         if (file) {
1492                 if (file->f_mode & FMODE_WRITE)
1493                         error = vmsplice_to_pipe(file, iov, nr_segs, flags);
1494                 else if (file->f_mode & FMODE_READ)
1495                         error = vmsplice_to_user(file, iov, nr_segs, flags);
1496
1497                 fput_light(file, fput);
1498         }
1499
1500         return error;
1501 }
1502
1503 asmlinkage long sys_splice(int fd_in, loff_t __user *off_in,
1504                            int fd_out, loff_t __user *off_out,
1505                            size_t len, unsigned int flags)
1506 {
1507         long error;
1508         struct file *in, *out;
1509         int fput_in, fput_out;
1510
1511         if (unlikely(!len))
1512                 return 0;
1513
1514         error = -EBADF;
1515         in = fget_light(fd_in, &fput_in);
1516         if (in) {
1517                 if (in->f_mode & FMODE_READ) {
1518                         out = fget_light(fd_out, &fput_out);
1519                         if (out) {
1520                                 if (out->f_mode & FMODE_WRITE)
1521                                         error = do_splice(in, off_in,
1522                                                           out, off_out,
1523                                                           len, flags);
1524                                 fput_light(out, fput_out);
1525                         }
1526                 }
1527
1528                 fput_light(in, fput_in);
1529         }
1530
1531         return error;
1532 }
1533
1534 /*
1535  * Make sure there's data to read. Wait for input if we can, otherwise
1536  * return an appropriate error.
1537  */
1538 static int link_ipipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
1539 {
1540         int ret;
1541
1542         /*
1543          * Check ->nrbufs without the inode lock first. This function
1544          * is speculative anyways, so missing one is ok.
1545          */
1546         if (pipe->nrbufs)
1547                 return 0;
1548
1549         ret = 0;
1550         mutex_lock(&pipe->inode->i_mutex);
1551
1552         while (!pipe->nrbufs) {
1553                 if (signal_pending(current)) {
1554                         ret = -ERESTARTSYS;
1555                         break;
1556                 }
1557                 if (!pipe->writers)
1558                         break;
1559                 if (!pipe->waiting_writers) {
1560                         if (flags & SPLICE_F_NONBLOCK) {
1561                                 ret = -EAGAIN;
1562                                 break;
1563                         }
1564                 }
1565                 pipe_wait(pipe);
1566         }
1567
1568         mutex_unlock(&pipe->inode->i_mutex);
1569         return ret;
1570 }
1571
1572 /*
1573  * Make sure there's writeable room. Wait for room if we can, otherwise
1574  * return an appropriate error.
1575  */
1576 static int link_opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
1577 {
1578         int ret;
1579
1580         /*
1581          * Check ->nrbufs without the inode lock first. This function
1582          * is speculative anyways, so missing one is ok.
1583          */
1584         if (pipe->nrbufs < PIPE_BUFFERS)
1585                 return 0;
1586
1587         ret = 0;
1588         mutex_lock(&pipe->inode->i_mutex);
1589
1590         while (pipe->nrbufs >= PIPE_BUFFERS) {
1591                 if (!pipe->readers) {
1592                         send_sig(SIGPIPE, current, 0);
1593                         ret = -EPIPE;
1594                         break;
1595                 }
1596                 if (flags & SPLICE_F_NONBLOCK) {
1597                         ret = -EAGAIN;
1598                         break;
1599                 }
1600                 if (signal_pending(current)) {
1601                         ret = -ERESTARTSYS;
1602                         break;
1603                 }
1604                 pipe->waiting_writers++;
1605                 pipe_wait(pipe);
1606                 pipe->waiting_writers--;
1607         }
1608
1609         mutex_unlock(&pipe->inode->i_mutex);
1610         return ret;
1611 }
1612
1613 /*
1614  * Link contents of ipipe to opipe.
1615  */
1616 static int link_pipe(struct pipe_inode_info *ipipe,
1617                      struct pipe_inode_info *opipe,
1618                      size_t len, unsigned int flags)
1619 {
1620         struct pipe_buffer *ibuf, *obuf;
1621         int ret = 0, i = 0, nbuf;
1622
1623         /*
1624          * Potential ABBA deadlock, work around it by ordering lock
1625          * grabbing by inode address. Otherwise two different processes
1626          * could deadlock (one doing tee from A -> B, the other from B -> A).
1627          */
1628         inode_double_lock(ipipe->inode, opipe->inode);
1629
1630         do {
1631                 if (!opipe->readers) {
1632                         send_sig(SIGPIPE, current, 0);
1633                         if (!ret)
1634                                 ret = -EPIPE;
1635                         break;
1636                 }
1637
1638                 /*
1639                  * If we have iterated all input buffers or ran out of
1640                  * output room, break.
1641                  */
1642                 if (i >= ipipe->nrbufs || opipe->nrbufs >= PIPE_BUFFERS)
1643                         break;
1644
1645                 ibuf = ipipe->bufs + ((ipipe->curbuf + i) & (PIPE_BUFFERS - 1));
1646                 nbuf = (opipe->curbuf + opipe->nrbufs) & (PIPE_BUFFERS - 1);
1647
1648                 /*
1649                  * Get a reference to this pipe buffer,
1650                  * so we can copy the contents over.
1651                  */
1652                 ibuf->ops->get(ipipe, ibuf);
1653
1654                 obuf = opipe->bufs + nbuf;
1655                 *obuf = *ibuf;
1656
1657                 /*
1658                  * Don't inherit the gift flag, we need to
1659                  * prevent multiple steals of this page.
1660                  */
1661                 obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
1662
1663                 if (obuf->len > len)
1664                         obuf->len = len;
1665
1666                 opipe->nrbufs++;
1667                 ret += obuf->len;
1668                 len -= obuf->len;
1669                 i++;
1670         } while (len);
1671
1672         /*
1673          * return EAGAIN if we have the potential of some data in the
1674          * future, otherwise just return 0
1675          */
1676         if (!ret && ipipe->waiting_writers && (flags & SPLICE_F_NONBLOCK))
1677                 ret = -EAGAIN;
1678
1679         inode_double_unlock(ipipe->inode, opipe->inode);
1680
1681         /*
1682          * If we put data in the output pipe, wakeup any potential readers.
1683          */
1684         if (ret > 0) {
1685                 smp_mb();
1686                 if (waitqueue_active(&opipe->wait))
1687                         wake_up_interruptible(&opipe->wait);
1688                 kill_fasync(&opipe->fasync_readers, SIGIO, POLL_IN);
1689         }
1690
1691         return ret;
1692 }
1693
1694 /*
1695  * This is a tee(1) implementation that works on pipes. It doesn't copy
1696  * any data, it simply references the 'in' pages on the 'out' pipe.
1697  * The 'flags' used are the SPLICE_F_* variants, currently the only
1698  * applicable one is SPLICE_F_NONBLOCK.
1699  */
1700 static long do_tee(struct file *in, struct file *out, size_t len,
1701                    unsigned int flags)
1702 {
1703         struct pipe_inode_info *ipipe = pipe_info(in->f_path.dentry->d_inode);
1704         struct pipe_inode_info *opipe = pipe_info(out->f_path.dentry->d_inode);
1705         int ret = -EINVAL;
1706
1707         /*
1708          * Duplicate the contents of ipipe to opipe without actually
1709          * copying the data.
1710          */
1711         if (ipipe && opipe && ipipe != opipe) {
1712                 /*
1713                  * Keep going, unless we encounter an error. The ipipe/opipe
1714                  * ordering doesn't really matter.
1715                  */
1716                 ret = link_ipipe_prep(ipipe, flags);
1717                 if (!ret) {
1718                         ret = link_opipe_prep(opipe, flags);
1719                         if (!ret)
1720                                 ret = link_pipe(ipipe, opipe, len, flags);
1721                 }
1722         }
1723
1724         return ret;
1725 }
1726
1727 asmlinkage long sys_tee(int fdin, int fdout, size_t len, unsigned int flags)
1728 {
1729         struct file *in;
1730         int error, fput_in;
1731
1732         if (unlikely(!len))
1733                 return 0;
1734
1735         error = -EBADF;
1736         in = fget_light(fdin, &fput_in);
1737         if (in) {
1738                 if (in->f_mode & FMODE_READ) {
1739                         int fput_out;
1740                         struct file *out = fget_light(fdout, &fput_out);
1741
1742                         if (out) {
1743                                 if (out->f_mode & FMODE_WRITE)
1744                                         error = do_tee(in, out, len, flags);
1745                                 fput_light(out, fput_out);
1746                         }
1747                 }
1748                 fput_light(in, fput_in);
1749         }
1750
1751         return error;
1752 }