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 }