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                                         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 }