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) && !try_to_release_page(page, GFP_KERNEL))
  62                         goto out_unlock;
  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 out_unlock:
  79         unlock_page(page);
  80         return 1;
  81 }
  82
  83 static void page_cache_pipe_buf_release(struct pipe_inode_info *pipe,
  84                                         struct pipe_buffer *buf)
  85 {
  86         page_cache_release(buf->page);
  87         buf->flags &= ~PIPE_BUF_FLAG_LRU;
  88 }
  89
  90 /*
  91  * Check whether the contents of buf is OK to access. Since the content
  92  * is a page cache page, IO may be in flight.
  93  */
  94 static int page_cache_pipe_buf_confirm(struct pipe_inode_info *pipe,
  95                                        struct pipe_buffer *buf)
  96 {
  97         struct page *page = buf->page;
  98         int err;
  99
 100         if (!PageUptodate(page)) {
 101                 lock_page(page);
 102
 103                 /*
 104                  * Page got truncated/unhashed. This will cause a 0-byte
 105                  * splice, if this is the first page.
 106                  */
 107                 if (!page->mapping) {
 108                         err = -ENODATA;
 109                         goto error;
 110                 }
 111
 112                 /*
 113                  * Uh oh, read-error from disk.
 114                  */
 115                 if (!PageUptodate(page)) {
 116                         err = -EIO;
 117                         goto error;
 118                 }
 119
 120                 /*
 121                  * Page is ok afterall, we are done.
 122                  */
 123                 unlock_page(page);
 124         }
 125
 126         return 0;
 127 error:
 128         unlock_page(page);
 129         return err;
 130 }
 131
 132 static const struct pipe_buf_operations page_cache_pipe_buf_ops = {
 133         .can_merge = 0,
 134         .map = generic_pipe_buf_map,
 135         .unmap = generic_pipe_buf_unmap,
 136         .confirm = page_cache_pipe_buf_confirm,
 137         .release = page_cache_pipe_buf_release,
 138         .steal = page_cache_pipe_buf_steal,
 139         .get = generic_pipe_buf_get,
 140 };
 141
 142 static int user_page_pipe_buf_steal(struct pipe_inode_info *pipe,
 143                                     struct pipe_buffer *buf)
 144 {
 145         if (!(buf->flags & PIPE_BUF_FLAG_GIFT))
 146                 return 1;
 147
 148         buf->flags |= PIPE_BUF_FLAG_LRU;
 149         return generic_pipe_buf_steal(pipe, buf);
 150 }
 151
 152 static const struct pipe_buf_operations user_page_pipe_buf_ops = {
 153         .can_merge = 0,
 154         .map = generic_pipe_buf_map,
 155         .unmap = generic_pipe_buf_unmap,
 156         .confirm = generic_pipe_buf_confirm,
 157         .release = page_cache_pipe_buf_release,
 158         .steal = user_page_pipe_buf_steal,
 159         .get = generic_pipe_buf_get,
 160 };
 161
 162 /**
 163  * splice_to_pipe - fill passed data into a pipe
 164  * @pipe:       pipe to fill
 165  * @spd:        data to fill
 166  *
 167  * Description:
 168  *    @spd contains a map of pages and len/offset tuples, along with
 169  *    the struct pipe_buf_operations associated with these pages. This
 170  *    function will link that data to the pipe.
 171  *
 172  */
 173 ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
 174                        struct splice_pipe_desc *spd)
 175 {
 176         unsigned int spd_pages = spd->nr_pages;
 177         int ret, do_wakeup, page_nr;
 178
 179         ret = 0;
 180         do_wakeup = 0;
 181         page_nr = 0;
 182
 183         if (pipe->inode)
 184                 mutex_lock(&pipe->inode->i_mutex);
 185
 186         for (;;) {
 187                 if (!pipe->readers) {
 188                         send_sig(SIGPIPE, current, 0);
 189                         if (!ret)
 190                                 ret = -EPIPE;
 191                         break;
 192                 }
 193
 194                 if (pipe->nrbufs < PIPE_BUFFERS) {
 195                         int newbuf = (pipe->curbuf + pipe->nrbufs) & (PIPE_BUFFERS - 1);
 196                         struct pipe_buffer *buf = pipe->bufs + newbuf;
 197
 198                         buf->page = spd->pages[page_nr];
 199                         buf->offset = spd->partial[page_nr].offset;
 200                         buf->len = spd->partial[page_nr].len;
 201                         buf->private = spd->partial[page_nr].private;
 202                         buf->ops = spd->ops;
 203                         if (spd->flags & SPLICE_F_GIFT)
 204                                 buf->flags |= PIPE_BUF_FLAG_GIFT;
 205
 206                         pipe->nrbufs++;
 207                         page_nr++;
 208                         ret += buf->len;
 209
 210                         if (pipe->inode)
 211                                 do_wakeup = 1;
 212
 213                         if (!--spd->nr_pages)
 214                                 break;
 215                         if (pipe->nrbufs < PIPE_BUFFERS)
 216                                 continue;
 217
 218                         break;
 219                 }
 220
 221                 if (spd->flags & SPLICE_F_NONBLOCK) {
 222                         if (!ret)
 223                                 ret = -EAGAIN;
 224                         break;
 225                 }
 226
 227                 if (signal_pending(current)) {
 228                         if (!ret)
 229                                 ret = -ERESTARTSYS;
 230                         break;
 231                 }
 232
 233                 if (do_wakeup) {
 234                         smp_mb();
 235                         if (waitqueue_active(&pipe->wait))
 236                                 wake_up_interruptible_sync(&pipe->wait);
 237                         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
 238                         do_wakeup = 0;
 239                 }
 240
 241                 pipe->waiting_writers++;
 242                 pipe_wait(pipe);
 243                 pipe->waiting_writers--;
 244         }
 245
 246         if (pipe->inode) {
 247                 mutex_unlock(&pipe->inode->i_mutex);
 248
 249                 if (do_wakeup) {
 250                         smp_mb();
 251                         if (waitqueue_active(&pipe->wait))
 252                                 wake_up_interruptible(&pipe->wait);
 253                         kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
 254                 }
 255         }
 256
 257         while (page_nr < spd_pages)
 258                 spd->spd_release(spd, page_nr++);
 259
 260         return ret;
 261 }
 262
 263 static void spd_release_page(struct splice_pipe_desc *spd, unsigned int i)
 264 {
 265         page_cache_release(spd->pages[i]);
 266 }
 267
 268 static int
 269 __generic_file_splice_read(struct file *in, loff_t *ppos,
 270                            struct pipe_inode_info *pipe, size_t len,
 271                            unsigned int flags)
 272 {
 273         struct address_space *mapping = in->f_mapping;
 274         unsigned int loff, nr_pages, req_pages;
 275         struct page *pages[PIPE_BUFFERS];
 276         struct partial_page partial[PIPE_BUFFERS];
 277         struct page *page;
 278         pgoff_t index, end_index;
 279         loff_t isize;
 280         int error, page_nr;
 281         struct splice_pipe_desc spd = {
 282                 .pages = pages,
 283                 .partial = partial,
 284                 .flags = flags,
 285                 .ops = &page_cache_pipe_buf_ops,
 286                 .spd_release = spd_release_page,
 287         };
 288
 289         index = *ppos >> PAGE_CACHE_SHIFT;
 290         loff = *ppos & ~PAGE_CACHE_MASK;
 291         req_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 292         nr_pages = min(req_pages, (unsigned)PIPE_BUFFERS);
 293
 294         /*
 295          * Lookup the (hopefully) full range of pages we need.
 296          */
 297         spd.nr_pages = find_get_pages_contig(mapping, index, nr_pages, pages);
 298         index += spd.nr_pages;
 299
 300         /*
 301          * If find_get_pages_contig() returned fewer pages than we needed,
 302          * readahead/allocate the rest and fill in the holes.
 303          */
 304         if (spd.nr_pages < nr_pages)
 305                 page_cache_sync_readahead(mapping, &in->f_ra, in,
 306                                 index, req_pages - spd.nr_pages);
 307
 308         error = 0;
 309         while (spd.nr_pages < nr_pages) {
 310                 /*
 311                  * Page could be there, find_get_pages_contig() breaks on
 312                  * the first hole.
 313                  */
 314                 page = find_get_page(mapping, index);
 315                 if (!page) {
 316                         /*
 317                          * page didn't exist, allocate one.
 318                          */
 319                         page = page_cache_alloc_cold(mapping);
 320                         if (!page)
 321                                 break;
 322
 323                         error = add_to_page_cache_lru(page, mapping, index,
 324                                                 mapping_gfp_mask(mapping));
 325                         if (unlikely(error)) {
 326                                 page_cache_release(page);
 327                                 if (error == -EEXIST)
 328                                         continue;
 329                                 break;
 330                         }
 331                         /*
 332                          * add_to_page_cache() locks the page, unlock it
 333                          * to avoid convoluting the logic below even more.
 334                          */
 335                         unlock_page(page);
 336                 }
 337
 338                 pages[spd.nr_pages++] = page;
 339                 index++;
 340         }
 341
 342         /*
 343          * Now loop over the map and see if we need to start IO on any
 344          * pages, fill in the partial map, etc.
 345          */
 346         index = *ppos >> PAGE_CACHE_SHIFT;
 347         nr_pages = spd.nr_pages;
 348         spd.nr_pages = 0;
 349         for (page_nr = 0; page_nr < nr_pages; page_nr++) {
 350                 unsigned int this_len;
 351
 352                 if (!len)
 353                         break;
 354
 355                 /*
 356                  * this_len is the max we'll use from this page
 357                  */
 358                 this_len = min_t(unsigned long, len, PAGE_CACHE_SIZE - loff);
 359                 page = pages[page_nr];
 360
 361                 if (PageReadahead(page))
 362                         page_cache_async_readahead(mapping, &in->f_ra, in,
 363                                         page, index, req_pages - page_nr);
 364
 365                 /*
 366                  * If the page isn't uptodate, we may need to start io on it
 367                  */
 368                 if (!PageUptodate(page)) {
 369                         /*
 370                          * If in nonblock mode then dont block on waiting
 371                          * for an in-flight io page
 372                          */
 373                         if (flags & SPLICE_F_NONBLOCK) {
 374                                 if (TestSetPageLocked(page)) {
 375                                         error = -EAGAIN;
 376                                         break;
 377                                 }
 378                         } else
 379                                 lock_page(page);
 380
 381                         /*
 382                          * Page was truncated, or invalidated by the
 383                          * filesystem.  Redo the find/create, but this time the
 384                          * page is kept locked, so there's no chance of another
 385                          * race with truncate/invalidate.
 386                          */
 387                         if (!page->mapping) {
 388                                 unlock_page(page);
 389                                 page = find_or_create_page(mapping, index,
 390                                                 mapping_gfp_mask(mapping));
 391
 392                                 if (!page) {
 393                                         error = -ENOMEM;
 394                                         break;
 395                                 }
 396                                 page_cache_release(pages[page_nr]);
 397                                 pages[page_nr] = page;
 398                         }
 399                         /*
 400                          * page was already under io and is now done, great
 401                          */
 402                         if (PageUptodate(page)) {
 403                                 unlock_page(page);
 404                                 goto fill_it;
 405                         }
 406
 407                         /*
 408                          * need to read in the page
 409                          */
 410                         error = mapping->a_ops->readpage(in, page);
 411                         if (unlikely(error)) {
 412                                 /*
 413                                  * We really should re-lookup the page here,
 414                                  * but it complicates things a lot. Instead
 415                                  * lets just do what we already stored, and
 416                                  * we'll get it the next time we are called.
 417                                  */
 418                                 if (error == AOP_TRUNCATED_PAGE)
 419                                         error = 0;
 420
 421                                 break;
 422                         }
 423                 }
 424 fill_it:
 425                 /*
 426                  * i_size must be checked after PageUptodate.
 427                  */
 428                 isize = i_size_read(mapping->host);
 429                 end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
 430                 if (unlikely(!isize || index > end_index))
 431                         break;
 432
 433                 /*
 434                  * if this is the last page, see if we need to shrink
 435                  * the length and stop
 436                  */
 437                 if (end_index == index) {
 438                         unsigned int plen;
 439
 440                         /*
 441                          * max good bytes in this page
 442                          */
 443                         plen = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
 444                         if (plen <= loff)
 445                                 break;
 446
 447                         /*
 448                          * force quit after adding this page
 449                          */
 450                         this_len = min(this_len, plen - loff);
 451                         len = this_len;
 452                 }
 453
 454                 partial[page_nr].offset = loff;
 455                 partial[page_nr].len = this_len;
 456                 len -= this_len;
 457                 loff = 0;
 458                 spd.nr_pages++;
 459                 index++;
 460         }
 461
 462         /*
 463          * Release any pages at the end, if we quit early. 'page_nr' is how far
 464          * we got, 'nr_pages' is how many pages are in the map.
 465          */
 466         while (page_nr < nr_pages)
 467                 page_cache_release(pages[page_nr++]);
 468         in->f_ra.prev_pos = (loff_t)index << PAGE_CACHE_SHIFT;
 469
 470         if (spd.nr_pages)
 471                 return splice_to_pipe(pipe, &spd);
 472
 473         return error;
 474 }
 475
 476 /**
 477  * generic_file_splice_read - splice data from file to a pipe
 478  * @in:         file to splice from
 479  * @ppos:       position in @in
 480  * @pipe:       pipe to splice to
 481  * @len:        number of bytes to splice
 482  * @flags:      splice modifier flags
 483  *
 484  * Description:
 485  *    Will read pages from given file and fill them into a pipe. Can be
 486  *    used as long as the address_space operations for the source implements
 487  *    a readpage() hook.
 488  *
 489  */
 490 ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
 491                                  struct pipe_inode_info *pipe, size_t len,
 492                                  unsigned int flags)
 493 {
 494         loff_t isize, left;
 495         int ret;
 496
 497         isize = i_size_read(in->f_mapping->host);
 498         if (unlikely(*ppos >= isize))
 499                 return 0;
 500
 501         left = isize - *ppos;
 502         if (unlikely(left < len))
 503                 len = left;
 504
 505         ret = __generic_file_splice_read(in, ppos, pipe, len, flags);
 506         if (ret > 0)
 507                 *ppos += ret;
 508
 509         return ret;
 510 }
 511
 512 EXPORT_SYMBOL(generic_file_splice_read);
 513
 514 /*
 515  * Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->pos'
 516  * using sendpage(). Return the number of bytes sent.
 517  */
 518 static int pipe_to_sendpage(struct pipe_inode_info *pipe,
 519                             struct pipe_buffer *buf, struct splice_desc *sd)
 520 {
 521         struct file *file = sd->u.file;
 522         loff_t pos = sd->pos;
 523         int ret, more;
 524
 525         ret = buf->ops->confirm(pipe, buf);
 526         if (!ret) {
 527                 more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len;
 528
 529                 ret = file->f_op->sendpage(file, buf->page, buf->offset,
 530                                            sd->len, &pos, more);
 531         }
 532
 533         return ret;
 534 }
 535
 536 /*
 537  * This is a little more tricky than the file -> pipe splicing. There are
 538  * basically three cases:
 539  *
 540  *      - Destination page already exists in the address space and there
 541  *        are users of it. For that case we have no other option that
 542  *        copying the data. Tough luck.
 543  *      - Destination page already exists in the address space, but there
 544  *        are no users of it. Make sure it's uptodate, then drop it. Fall
 545  *        through to last case.
 546  *      - Destination page does not exist, we can add the pipe page to
 547  *        the page cache and avoid the copy.
 548  *
 549  * If asked to move pages to the output file (SPLICE_F_MOVE is set in
 550  * sd->flags), we attempt to migrate pages from the pipe to the output
 551  * file address space page cache. This is possible if no one else has
 552  * the pipe page referenced outside of the pipe and page cache. If
 553  * SPLICE_F_MOVE isn't set, or we cannot move the page, we simply create
 554  * a new page in the output file page cache and fill/dirty that.
 555  */
 556 static int pipe_to_file(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
 557                         struct splice_desc *sd)
 558 {
 559         struct file *file = sd->u.file;
 560         struct address_space *mapping = file->f_mapping;
 561         unsigned int offset, this_len;
 562         struct page *page;
 563         void *fsdata;
 564         int ret;
 565
 566         /*
 567          * make sure the data in this buffer is uptodate
 568          */
 569         ret = buf->ops->confirm(pipe, buf);
 570         if (unlikely(ret))
 571                 return ret;
 572
 573         offset = sd->pos & ~PAGE_CACHE_MASK;
 574
 575         this_len = sd->len;
 576         if (this_len + offset > PAGE_CACHE_SIZE)
 577                 this_len = PAGE_CACHE_SIZE - offset;
 578
 579         ret = pagecache_write_begin(file, mapping, sd->pos, this_len,
 580                                 AOP_FLAG_UNINTERRUPTIBLE, &page, &fsdata);
 581         if (unlikely(ret))
 582                 goto out;
 583
 584         if (buf->page != page) {
 585                 /*
 586                  * Careful, ->map() uses KM_USER0!
 587                  */
 588                 char *src = buf->ops->map(pipe, buf, 1);
 589                 char *dst = kmap_atomic(page, KM_USER1);
 590
 591                 memcpy(dst + offset, src + buf->offset, this_len);
 592                 flush_dcache_page(page);
 593                 kunmap_atomic(dst, KM_USER1);
 594                 buf->ops->unmap(pipe, buf, src);
 595         }
 596         ret = pagecache_write_end(file, mapping, sd->pos, this_len, this_len,
 597                                 page, fsdata);
 598 out:
 599         return ret;
 600 }
 601
 602 /**
 603  * __splice_from_pipe - splice data from a pipe to given actor
 604  * @pipe:       pipe to splice from
 605  * @sd:         information to @actor
 606  * @actor:      handler that splices the data
 607  *
 608  * Description:
 609  *    This function does little more than loop over the pipe and call
 610  *    @actor to do the actual moving of a single struct pipe_buffer to
 611  *    the desired destination. See pipe_to_file, pipe_to_sendpage, or
 612  *    pipe_to_user.
 613  *
 614  */
 615 ssize_t __splice_from_pipe(struct pipe_inode_info *pipe, struct splice_desc *sd,
 616                            splice_actor *actor)
 617 {
 618         int ret, do_wakeup, err;
 619
 620         ret = 0;
 621         do_wakeup = 0;
 622
 623         for (;;) {
 624                 if (pipe->nrbufs) {
 625                         struct pipe_buffer *buf = pipe->bufs + pipe->curbuf;
 626                         const struct pipe_buf_operations *ops = buf->ops;
 627
 628                         sd->len = buf->len;
 629                         if (sd->len > sd->total_len)
 630                                 sd->len = sd->total_len;
 631
 632                         err = actor(pipe, buf, sd);
 633                         if (err <= 0) {
 634                                 if (!ret && err != -ENODATA)
 635                                         ret = err;
 636
 637                                 break;
 638                         }
 639
 640                         ret += err;
 641                         buf->offset += err;
 642                         buf->len -= err;
 643
 644                         sd->len -= err;
 645                         sd->pos += err;
 646                         sd->total_len -= err;
 647                         if (sd->len)
 648                                 continue;
 649
 650                         if (!buf->len) {
 651                                 buf->ops = NULL;
 652                                 ops->release(pipe, buf);
 653                                 pipe->curbuf = (pipe->curbuf + 1) & (PIPE_BUFFERS - 1);
 654                                 pipe->nrbufs--;
 655                                 if (pipe->inode)
 656                                         do_wakeup = 1;
 657                         }
 658
 659                         if (!sd->total_len)
 660                                 break;
 661                 }
 662
 663                 if (pipe->nrbufs)
 664                         continue;
 665                 if (!pipe->writers)
 666                         break;
 667                 if (!pipe->waiting_writers) {
 668                         if (ret)
 669                                 break;
 670                 }
 671
 672                 if (sd->flags & SPLICE_F_NONBLOCK) {
 673                         if (!ret)
 674                                 ret = -EAGAIN;
 675                         break;
 676                 }
 677
 678                 if (signal_pending(current)) {
 679                         if (!ret)
 680                                 ret = -ERESTARTSYS;
 681                         break;
 682                 }
 683
 684                 if (do_wakeup) {
 685                         smp_mb();
 686                         if (waitqueue_active(&pipe->wait))
 687                                 wake_up_interruptible_sync(&pipe->wait);
 688                         kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
 689                         do_wakeup = 0;
 690                 }
 691
 692                 pipe_wait(pipe);
 693         }
 694
 695         if (do_wakeup) {
 696                 smp_mb();
 697                 if (waitqueue_active(&pipe->wait))
 698                         wake_up_interruptible(&pipe->wait);
 699                 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
 700         }
 701
 702         return ret;
 703 }
 704 EXPORT_SYMBOL(__splice_from_pipe);
 705
 706 /**
 707  * splice_from_pipe - splice data from a pipe to a file
 708  * @pipe:       pipe to splice from
 709  * @out:        file to splice to
 710  * @ppos:       position in @out
 711  * @len:        how many bytes to splice
 712  * @flags:      splice modifier flags
 713  * @actor:      handler that splices the data
 714  *
 715  * Description:
 716  *    See __splice_from_pipe. This function locks the input and output inodes,
 717  *    otherwise it's identical to __splice_from_pipe().
 718  *
 719  */
 720 ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
 721                          loff_t *ppos, size_t len, unsigned int flags,
 722                          splice_actor *actor)
 723 {
 724         ssize_t ret;
 725         struct inode *inode = out->f_mapping->host;
 726         struct splice_desc sd = {
 727                 .total_len = len,
 728                 .flags = flags,
 729                 .pos = *ppos,
 730                 .u.file = out,
 731         };
 732
 733         /*
 734          * The actor worker might be calling ->prepare_write and
 735          * ->commit_write. Most of the time, these expect i_mutex to
 736          * be held. Since this may result in an ABBA deadlock with
 737          * pipe->inode, we have to order lock acquiry here.
 738          */
 739         inode_double_lock(inode, pipe->inode);
 740         ret = __splice_from_pipe(pipe, &sd, actor);
 741         inode_double_unlock(inode, pipe->inode);
 742
 743         return ret;
 744 }
 745
 746 /**
 747  * generic_file_splice_write_nolock - generic_file_splice_write without mutexes
 748  * @pipe:       pipe info
 749  * @out:        file to write to
 750  * @ppos:       position in @out
 751  * @len:        number of bytes to splice
 752  * @flags:      splice modifier flags
 753  *
 754  * Description:
 755  *    Will either move or copy pages (determined by @flags options) from
 756  *    the given pipe inode to the given file. The caller is responsible
 757  *    for acquiring i_mutex on both inodes.
 758  *
 759  */
 760 ssize_t
 761 generic_file_splice_write_nolock(struct pipe_inode_info *pipe, struct file *out,
 762                                  loff_t *ppos, size_t len, unsigned int flags)
 763 {
 764         struct address_space *mapping = out->f_mapping;
 765         struct inode *inode = mapping->host;
 766         struct splice_desc sd = {
 767                 .total_len = len,
 768                 .flags = flags,
 769                 .pos = *ppos,
 770                 .u.file = out,
 771         };
 772         ssize_t ret;
 773         int err;
 774
 775         err = remove_suid(out->f_path.dentry);
 776         if (unlikely(err))
 777                 return err;
 778
 779         ret = __splice_from_pipe(pipe, &sd, pipe_to_file);
 780         if (ret > 0) {
 781                 unsigned long nr_pages;
 782
 783                 *ppos += ret;
 784                 nr_pages = (ret + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 785
 786                 /*
 787                  * If file or inode is SYNC and we actually wrote some data,
 788                  * sync it.
 789                  */
 790                 if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
 791                         err = generic_osync_inode(inode, mapping,
 792                                                   OSYNC_METADATA|OSYNC_DATA);
 793
 794                         if (err)
 795                                 ret = err;
 796                 }
 797                 balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
 798         }
 799
 800         return ret;
 801 }
 802
 803 EXPORT_SYMBOL(generic_file_splice_write_nolock);
 804
 805 /**
 806  * generic_file_splice_write - splice data from a pipe to a file
 807  * @pipe:       pipe info
 808  * @out:        file to write to
 809  * @ppos:       position in @out
 810  * @len:        number of bytes to splice
 811  * @flags:      splice modifier flags
 812  *
 813  * Description:
 814  *    Will either move or copy pages (determined by @flags options) from
 815  *    the given pipe inode to the given file.
 816  *
 817  */
 818 ssize_t
 819 generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 820                           loff_t *ppos, size_t len, unsigned int flags)
 821 {
 822         struct address_space *mapping = out->f_mapping;
 823         struct inode *inode = mapping->host;
 824         struct splice_desc sd = {
 825                 .total_len = len,
 826                 .flags = flags,
 827                 .pos = *ppos,
 828                 .u.file = out,
 829         };
 830         ssize_t ret;
 831
 832         inode_double_lock(inode, pipe->inode);
 833         ret = remove_suid(out->f_path.dentry);
 834         if (likely(!ret))
 835                 ret = __splice_from_pipe(pipe, &sd, pipe_to_file);
 836         inode_double_unlock(inode, pipe->inode);
 837         if (ret > 0) {
 838                 unsigned long nr_pages;
 839
 840                 *ppos += ret;
 841                 nr_pages = (ret + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 842
 843                 /*
 844                  * If file or inode is SYNC and we actually wrote some data,
 845                  * sync it.
 846                  */
 847                 if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
 848                         int err;
 849
 850                         mutex_lock(&inode->i_mutex);
 851                         err = generic_osync_inode(inode, mapping,
 852                                                   OSYNC_METADATA|OSYNC_DATA);
 853                         mutex_unlock(&inode->i_mutex);
 854
 855                         if (err)
 856                                 ret = err;
 857                 }
 858                 balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
 859         }
 860
 861         return ret;
 862 }
 863
 864 EXPORT_SYMBOL(generic_file_splice_write);
 865
 866 /**
 867  * generic_splice_sendpage - splice data from a pipe to a socket
 868  * @pipe:       pipe to splice from
 869  * @out:        socket to write to
 870  * @ppos:       position in @out
 871  * @len:        number of bytes to splice
 872  * @flags:      splice modifier flags
 873  *
 874  * Description:
 875  *    Will send @len bytes from the pipe to a network socket. No data copying
 876  *    is involved.
 877  *
 878  */
 879 ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe, struct file *out,
 880                                 loff_t *ppos, size_t len, unsigned int flags)
 881 {
 882         return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_sendpage);
 883 }
 884
 885 EXPORT_SYMBOL(generic_splice_sendpage);
 886
 887 /*
 888  * Attempt to initiate a splice from pipe to file.
 889  */
 890 static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
 891                            loff_t *ppos, size_t len, unsigned int flags)
 892 {
 893         int ret;
 894
 895         if (unlikely(!out->f_op || !out->f_op->splice_write))
 896                 return -EINVAL;
 897
 898         if (unlikely(!(out->f_mode & FMODE_WRITE)))
 899                 return -EBADF;
 900
 901         ret = rw_verify_area(WRITE, out, ppos, len);
 902         if (unlikely(ret < 0))
 903                 return ret;
 904
 905         return out->f_op->splice_write(pipe, out, ppos, len, flags);
 906 }
 907
 908 /*
 909  * Attempt to initiate a splice from a file to a pipe.
 910  */
 911 static long do_splice_to(struct file *in, loff_t *ppos,
 912                          struct pipe_inode_info *pipe, size_t len,
 913                          unsigned int flags)
 914 {
 915         int ret;
 916
 917         if (unlikely(!in->f_op || !in->f_op->splice_read))
 918                 return -EINVAL;
 919
 920         if (unlikely(!(in->f_mode & FMODE_READ)))
 921                 return -EBADF;
 922
 923         ret = rw_verify_area(READ, in, ppos, len);
 924         if (unlikely(ret < 0))
 925                 return ret;
 926
 927         return in->f_op->splice_read(in, ppos, pipe, len, flags);
 928 }
 929
 930 /**
 931  * splice_direct_to_actor - splices data directly between two non-pipes
 932  * @in:         file to splice from
 933  * @sd:         actor information on where to splice to
 934  * @actor:      handles the data splicing
 935  *
 936  * Description:
 937  *    This is a special case helper to splice directly between two
 938  *    points, without requiring an explicit pipe. Internally an allocated
 939  *    pipe is cached in the process, and reused during the lifetime of
 940  *    that process.
 941  *
 942  */
 943 ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
 944                                splice_direct_actor *actor)
 945 {
 946         struct pipe_inode_info *pipe;
 947         long ret, bytes;
 948         umode_t i_mode;
 949         size_t len;
 950         int i, flags;
 951
 952         /*
 953          * We require the input being a regular file, as we don't want to
 954          * randomly drop data for eg socket -> socket splicing. Use the
 955          * piped splicing for that!
 956          */
 957         i_mode = in->f_path.dentry->d_inode->i_mode;
 958         if (unlikely(!S_ISREG(i_mode) && !S_ISBLK(i_mode)))
 959                 return -EINVAL;
 960
 961         /*
 962          * neither in nor out is a pipe, setup an internal pipe attached to
 963          * 'out' and transfer the wanted data from 'in' to 'out' through that
 964          */
 965         pipe = current->splice_pipe;
 966         if (unlikely(!pipe)) {
 967                 pipe = alloc_pipe_info(NULL);
 968                 if (!pipe)
 969                         return -ENOMEM;
 970
 971                 /*
 972                  * We don't have an immediate reader, but we'll read the stuff
 973                  * out of the pipe right after the splice_to_pipe(). So set
 974                  * PIPE_READERS appropriately.
 975                  */
 976                 pipe->readers = 1;
 977
 978                 current->splice_pipe = pipe;
 979         }
 980
 981         /*
 982          * Do the splice.
 983          */
 984         ret = 0;
 985         bytes = 0;
 986         len = sd->total_len;
 987         flags = sd->flags;
 988
 989         /*
 990          * Don't block on output, we have to drain the direct pipe.
 991          */
 992         sd->flags &= ~SPLICE_F_NONBLOCK;
 993
 994         while (len) {
 995                 size_t read_len;
 996                 loff_t pos = sd->pos, prev_pos = pos;
 997
 998                 ret = do_splice_to(in, &pos, pipe, len, flags);
 999                 if (unlikely(ret <= 0))
1000                         goto out_release;
1001
1002                 read_len = ret;
1003                 sd->total_len = read_len;
1004
1005                 /*
1006                  * NOTE: nonblocking mode only applies to the input. We
1007                  * must not do the output in nonblocking mode as then we
1008                  * could get stuck data in the internal pipe:
1009                  */
1010                 ret = actor(pipe, sd);
1011                 if (unlikely(ret <= 0)) {
1012                         sd->pos = prev_pos;
1013                         goto out_release;
1014                 }
1015
1016                 bytes += ret;
1017                 len -= ret;
1018                 sd->pos = pos;
1019
1020                 if (ret < read_len) {
1021                         sd->pos = prev_pos + ret;
1022                         goto out_release;
1023                 }
1024         }
1025
1026 done:
1027         pipe->nrbufs = pipe->curbuf = 0;
1028         file_accessed(in);
1029         return bytes;
1030
1031 out_release:
1032         /*
1033          * If we did an incomplete transfer we must release
1034          * the pipe buffers in question:
1035          */
1036         for (i = 0; i < PIPE_BUFFERS; i++) {
1037                 struct pipe_buffer *buf = pipe->bufs + i;
1038
1039                 if (buf->ops) {
1040                         buf->ops->release(pipe, buf);
1041                         buf->ops = NULL;
1042                 }
1043         }
1044
1045         if (!bytes)
1046                 bytes = ret;
1047
1048         goto done;
1049 }
1050 EXPORT_SYMBOL(splice_direct_to_actor);
1051
1052 static int direct_splice_actor(struct pipe_inode_info *pipe,
1053                                struct splice_desc *sd)
1054 {
1055         struct file *file = sd->u.file;
1056
1057         return do_splice_from(pipe, file, &sd->pos, sd->total_len, sd->flags);
1058 }
1059
1060 /**
1061  * do_splice_direct - splices data directly between two files
1062  * @in:         file to splice from
1063  * @ppos:       input file offset
1064  * @out:        file to splice to
1065  * @len:        number of bytes to splice
1066  * @flags:      splice modifier flags
1067  *
1068  * Description:
1069  *    For use by do_sendfile(). splice can easily emulate sendfile, but
1070  *    doing it in the application would incur an extra system call
1071  *    (splice in + splice out, as compared to just sendfile()). So this helper
1072  *    can splice directly through a process-private pipe.
1073  *
1074  */
1075 long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
1076                       size_t len, unsigned int flags)
1077 {
1078         struct splice_desc sd = {
1079                 .len            = len,
1080                 .total_len      = len,
1081                 .flags          = flags,
1082                 .pos            = *ppos,
1083                 .u.file         = out,
1084         };
1085         long ret;
1086
1087         ret = splice_direct_to_actor(in, &sd, direct_splice_actor);
1088         if (ret > 0)
1089                 *ppos = sd.pos;
1090
1091         return ret;
1092 }
1093
1094 /*
1095  * After the inode slimming patch, i_pipe/i_bdev/i_cdev share the same
1096  * location, so checking ->i_pipe is not enough to verify that this is a
1097  * pipe.
1098  */
1099 static inline struct pipe_inode_info *pipe_info(struct inode *inode)
1100 {
1101         if (S_ISFIFO(inode->i_mode))
1102                 return inode->i_pipe;
1103
1104         return NULL;
1105 }
1106
1107 /*
1108  * Determine where to splice to/from.
1109  */
1110 static long do_splice(struct file *in, loff_t __user *off_in,
1111                       struct file *out, loff_t __user *off_out,
1112                       size_t len, unsigned int flags)
1113 {
1114         struct pipe_inode_info *pipe;
1115         loff_t offset, *off;
1116         long ret;
1117
1118         pipe = pipe_info(in->f_path.dentry->d_inode);
1119         if (pipe) {
1120                 if (off_in)
1121                         return -ESPIPE;
1122                 if (off_out) {
1123                         if (out->f_op->llseek == no_llseek)
1124                                 return -EINVAL;
1125                         if (copy_from_user(&offset, off_out, sizeof(loff_t)))
1126                                 return -EFAULT;
1127                         off = &offset;
1128                 } else
1129                         off = &out->f_pos;
1130
1131                 ret = do_splice_from(pipe, out, off, len, flags);
1132
1133                 if (off_out && copy_to_user(off_out, off, sizeof(loff_t)))
1134                         ret = -EFAULT;
1135
1136                 return ret;
1137         }
1138
1139         pipe = pipe_info(out->f_path.dentry->d_inode);
1140         if (pipe) {
1141                 if (off_out)
1142                         return -ESPIPE;
1143                 if (off_in) {
1144                         if (in->f_op->llseek == no_llseek)
1145                                 return -EINVAL;
1146                         if (copy_from_user(&offset, off_in, sizeof(loff_t)))
1147                                 return -EFAULT;
1148                         off = &offset;
1149                 } else
1150                         off = &in->f_pos;
1151
1152                 ret = do_splice_to(in, off, pipe, len, flags);
1153
1154                 if (off_in && copy_to_user(off_in, off, sizeof(loff_t)))
1155                         ret = -EFAULT;
1156
1157                 return ret;
1158         }
1159
1160         return -EINVAL;
1161 }
1162
1163 /*
1164  * Do a copy-from-user while holding the mmap_semaphore for reading, in a
1165  * manner safe from deadlocking with simultaneous mmap() (grabbing mmap_sem
1166  * for writing) and page faulting on the user memory pointed to by src.
1167  * This assumes that we will very rarely hit the partial != 0 path, or this
1168  * will not be a win.
1169  */
1170 static int copy_from_user_mmap_sem(void *dst, const void __user *src, size_t n)
1171 {
1172         int partial;
1173
1174         if (!access_ok(VERIFY_READ, src, n))
1175                 return -EFAULT;
1176
1177         pagefault_disable();
1178         partial = __copy_from_user_inatomic(dst, src, n);
1179         pagefault_enable();
1180
1181         /*
1182          * Didn't copy everything, drop the mmap_sem and do a faulting copy
1183          */
1184         if (unlikely(partial)) {
1185                 up_read(&current->mm->mmap_sem);
1186                 partial = copy_from_user(dst, src, n);
1187                 down_read(&current->mm->mmap_sem);
1188         }
1189
1190         return partial;
1191 }
1192
1193 /*
1194  * Map an iov into an array of pages and offset/length tupples. With the
1195  * partial_page structure, we can map several non-contiguous ranges into
1196  * our ones pages[] map instead of splitting that operation into pieces.
1197  * Could easily be exported as a generic helper for other users, in which
1198  * case one would probably want to add a 'max_nr_pages' parameter as well.
1199  */
1200 static int get_iovec_page_array(const struct iovec __user *iov,
1201                                 unsigned int nr_vecs, struct page **pages,
1202                                 struct partial_page *partial, int aligned)
1203 {
1204         int buffers = 0, error = 0;
1205
1206         down_read(&current->mm->mmap_sem);
1207
1208         while (nr_vecs) {
1209                 unsigned long off, npages;
1210                 struct iovec entry;
1211                 void __user *base;
1212                 size_t len;
1213                 int i;
1214
1215                 error = -EFAULT;
1216                 if (copy_from_user_mmap_sem(&entry, iov, sizeof(entry)))
1217                         break;
1218
1219                 base = entry.iov_base;
1220                 len = entry.iov_len;
1221
1222                 /*
1223                  * Sanity check this iovec. 0 read succeeds.
1224                  */
1225                 error = 0;
1226                 if (unlikely(!len))
1227                         break;
1228                 error = -EFAULT;
1229                 if (!access_ok(VERIFY_READ, base, len))
1230                         break;
1231
1232                 /*
1233                  * Get this base offset and number of pages, then map
1234                  * in the user pages.
1235                  */
1236                 off = (unsigned long) base & ~PAGE_MASK;
1237
1238                 /*
1239                  * If asked for alignment, the offset must be zero and the
1240                  * length a multiple of the PAGE_SIZE.
1241                  */
1242                 error = -EINVAL;
1243                 if (aligned && (off || len & ~PAGE_MASK))
1244                         break;
1245
1246                 npages = (off + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
1247                 if (npages > PIPE_BUFFERS - buffers)
1248                         npages = PIPE_BUFFERS - buffers;
1249
1250                 error = get_user_pages(current, current->mm,
1251                                        (unsigned long) base, npages, 0, 0,
1252                                        &pages[buffers], NULL);
1253
1254                 if (unlikely(error <= 0))
1255                         break;
1256
1257                 /*
1258                  * Fill this contiguous range into the partial page map.
1259                  */
1260                 for (i = 0; i < error; i++) {
1261                         const int plen = min_t(size_t, len, PAGE_SIZE - off);
1262
1263                         partial[buffers].offset = off;
1264                         partial[buffers].len = plen;
1265
1266                         off = 0;
1267                         len -= plen;
1268                         buffers++;
1269                 }
1270
1271                 /*
1272                  * We didn't complete this iov, stop here since it probably
1273                  * means we have to move some of this into a pipe to
1274                  * be able to continue.
1275                  */
1276                 if (len)
1277                         break;
1278
1279                 /*
1280                  * Don't continue if we mapped fewer pages than we asked for,
1281                  * or if we mapped the max number of pages that we have
1282                  * room for.
1283                  */
1284                 if (error < npages || buffers == PIPE_BUFFERS)
1285                         break;
1286
1287                 nr_vecs--;
1288                 iov++;
1289         }
1290
1291         up_read(&current->mm->mmap_sem);
1292
1293         if (buffers)
1294                 return buffers;
1295
1296         return error;
1297 }
1298
1299 static int pipe_to_user(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
1300                         struct splice_desc *sd)
1301 {
1302         char *src;
1303         int ret;
1304
1305         ret = buf->ops->confirm(pipe, buf);
1306         if (unlikely(ret))
1307                 return ret;
1308
1309         /*
1310          * See if we can use the atomic maps, by prefaulting in the
1311          * pages and doing an atomic copy
1312          */
1313         if (!fault_in_pages_writeable(sd->u.userptr, sd->len)) {
1314                 src = buf->ops->map(pipe, buf, 1);
1315                 ret = __copy_to_user_inatomic(sd->u.userptr, src + buf->offset,
1316                                                         sd->len);
1317                 buf->ops->unmap(pipe, buf, src);
1318                 if (!ret) {
1319                         ret = sd->len;
1320                         goto out;
1321                 }
1322         }
1323
1324         /*
1325          * No dice, use slow non-atomic map and copy
1326          */
1327         src = buf->ops->map(pipe, buf, 0);
1328
1329         ret = sd->len;
1330         if (copy_to_user(sd->u.userptr, src + buf->offset, sd->len))
1331                 ret = -EFAULT;
1332
1333         buf->ops->unmap(pipe, buf, src);
1334 out:
1335         if (ret > 0)
1336                 sd->u.userptr += ret;
1337         return ret;
1338 }
1339
1340 /*
1341  * For lack of a better implementation, implement vmsplice() to userspace
1342  * as a simple copy of the pipes pages to the user iov.
1343  */
1344 static long vmsplice_to_user(struct file *file, const struct iovec __user *iov,
1345                              unsigned long nr_segs, unsigned int flags)
1346 {
1347         struct pipe_inode_info *pipe;
1348         struct splice_desc sd;
1349         ssize_t size;
1350         int error;
1351         long ret;
1352
1353         pipe = pipe_info(file->f_path.dentry->d_inode);
1354         if (!pipe)
1355                 return -EBADF;
1356
1357         if (pipe->inode)
1358                 mutex_lock(&pipe->inode->i_mutex);
1359
1360         error = ret = 0;
1361         while (nr_segs) {
1362                 void __user *base;
1363                 size_t len;
1364
1365                 /*
1366                  * Get user address base and length for this iovec.
1367                  */
1368                 error = get_user(base, &iov->iov_base);
1369                 if (unlikely(error))
1370                         break;
1371                 error = get_user(len, &iov->iov_len);
1372                 if (unlikely(error))
1373                         break;
1374
1375                 /*
1376                  * Sanity check this iovec. 0 read succeeds.
1377                  */
1378                 if (unlikely(!len))
1379                         break;
1380                 if (unlikely(!base)) {
1381                         error = -EFAULT;
1382                         break;
1383                 }
1384
1385                 if (unlikely(!access_ok(VERIFY_WRITE, base, len))) {
1386                         error = -EFAULT;
1387                         break;
1388                 }
1389
1390                 sd.len = 0;
1391                 sd.total_len = len;
1392                 sd.flags = flags;
1393                 sd.u.userptr = base;
1394                 sd.pos = 0;
1395
1396                 size = __splice_from_pipe(pipe, &sd, pipe_to_user);
1397                 if (size < 0) {
1398                         if (!ret)
1399                                 ret = size;
1400
1401                         break;
1402                 }
1403
1404                 ret += size;
1405
1406                 if (size < len)
1407                         break;
1408
1409                 nr_segs--;
1410                 iov++;
1411         }
1412
1413         if (pipe->inode)
1414                 mutex_unlock(&pipe->inode->i_mutex);
1415
1416         if (!ret)
1417                 ret = error;
1418
1419         return ret;
1420 }
1421
1422 /*
1423  * vmsplice splices a user address range into a pipe. It can be thought of
1424  * as splice-from-memory, where the regular splice is splice-from-file (or
1425  * to file). In both cases the output is a pipe, naturally.
1426  */
1427 static long vmsplice_to_pipe(struct file *file, const struct iovec __user *iov,
1428                              unsigned long nr_segs, unsigned int flags)
1429 {
1430         struct pipe_inode_info *pipe;
1431         struct page *pages[PIPE_BUFFERS];
1432         struct partial_page partial[PIPE_BUFFERS];
1433         struct splice_pipe_desc spd = {
1434                 .pages = pages,
1435                 .partial = partial,
1436                 .flags = flags,
1437                 .ops = &user_page_pipe_buf_ops,
1438                 .spd_release = spd_release_page,
1439         };
1440
1441         pipe = pipe_info(file->f_path.dentry->d_inode);
1442         if (!pipe)
1443                 return -EBADF;
1444
1445         spd.nr_pages = get_iovec_page_array(iov, nr_segs, pages, partial,
1446                                             flags & SPLICE_F_GIFT);
1447         if (spd.nr_pages <= 0)
1448                 return spd.nr_pages;
1449
1450         return splice_to_pipe(pipe, &spd);
1451 }
1452
1453 /*
1454  * Note that vmsplice only really supports true splicing _from_ user memory
1455  * to a pipe, not the other way around. Splicing from user memory is a simple
1456  * operation that can be supported without any funky alignment restrictions
1457  * or nasty vm tricks. We simply map in the user memory and fill them into
1458  * a pipe. The reverse isn't quite as easy, though. There are two possible
1459  * solutions for that:
1460  *
1461  *      - memcpy() the data internally, at which point we might as well just
1462  *        do a regular read() on the buffer anyway.
1463  *      - Lots of nasty vm tricks, that are neither fast nor flexible (it
1464  *        has restriction limitations on both ends of the pipe).
1465  *
1466  * Currently we punt and implement it as a normal copy, see pipe_to_user().
1467  *
1468  */
1469 asmlinkage long sys_vmsplice(int fd, const struct iovec __user *iov,
1470                              unsigned long nr_segs, unsigned int flags)
1471 {
1472         struct file *file;
1473         long error;
1474         int fput;
1475
1476         if (unlikely(nr_segs > UIO_MAXIOV))
1477                 return -EINVAL;
1478         else if (unlikely(!nr_segs))
1479                 return 0;
1480
1481         error = -EBADF;
1482         file = fget_light(fd, &fput);
1483         if (file) {
1484                 if (file->f_mode & FMODE_WRITE)
1485                         error = vmsplice_to_pipe(file, iov, nr_segs, flags);
1486                 else if (file->f_mode & FMODE_READ)
1487                         error = vmsplice_to_user(file, iov, nr_segs, flags);
1488
1489                 fput_light(file, fput);
1490         }
1491
1492         return error;
1493 }
1494
1495 asmlinkage long sys_splice(int fd_in, loff_t __user *off_in,
1496                            int fd_out, loff_t __user *off_out,
1497                            size_t len, unsigned int flags)
1498 {
1499         long error;
1500         struct file *in, *out;
1501         int fput_in, fput_out;
1502
1503         if (unlikely(!len))
1504                 return 0;
1505
1506         error = -EBADF;
1507         in = fget_light(fd_in, &fput_in);
1508         if (in) {
1509                 if (in->f_mode & FMODE_READ) {
1510                         out = fget_light(fd_out, &fput_out);
1511                         if (out) {
1512                                 if (out->f_mode & FMODE_WRITE)
1513                                         error = do_splice(in, off_in,
1514                                                           out, off_out,
1515                                                           len, flags);
1516                                 fput_light(out, fput_out);
1517                         }
1518                 }
1519
1520                 fput_light(in, fput_in);
1521         }
1522
1523         return error;
1524 }
1525
1526 /*
1527  * Make sure there's data to read. Wait for input if we can, otherwise
1528  * return an appropriate error.
1529  */
1530 static int link_ipipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
1531 {
1532         int ret;
1533
1534         /*
1535          * Check ->nrbufs without the inode lock first. This function
1536          * is speculative anyways, so missing one is ok.
1537          */
1538         if (pipe->nrbufs)
1539                 return 0;
1540
1541         ret = 0;
1542         mutex_lock(&pipe->inode->i_mutex);
1543
1544         while (!pipe->nrbufs) {
1545                 if (signal_pending(current)) {
1546                         ret = -ERESTARTSYS;
1547                         break;
1548                 }
1549                 if (!pipe->writers)
1550                         break;
1551                 if (!pipe->waiting_writers) {
1552                         if (flags & SPLICE_F_NONBLOCK) {
1553                                 ret = -EAGAIN;
1554                                 break;
1555                         }
1556                 }
1557                 pipe_wait(pipe);
1558         }
1559
1560         mutex_unlock(&pipe->inode->i_mutex);
1561         return ret;
1562 }
1563
1564 /*
1565  * Make sure there's writeable room. Wait for room if we can, otherwise
1566  * return an appropriate error.
1567  */
1568 static int link_opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
1569 {
1570         int ret;
1571
1572         /*
1573          * Check ->nrbufs without the inode lock first. This function
1574          * is speculative anyways, so missing one is ok.
1575          */
1576         if (pipe->nrbufs < PIPE_BUFFERS)
1577                 return 0;
1578
1579         ret = 0;
1580         mutex_lock(&pipe->inode->i_mutex);
1581
1582         while (pipe->nrbufs >= PIPE_BUFFERS) {
1583                 if (!pipe->readers) {
1584                         send_sig(SIGPIPE, current, 0);
1585                         ret = -EPIPE;
1586                         break;
1587                 }
1588                 if (flags & SPLICE_F_NONBLOCK) {
1589                         ret = -EAGAIN;
1590                         break;
1591                 }
1592                 if (signal_pending(current)) {
1593                         ret = -ERESTARTSYS;
1594                         break;
1595                 }
1596                 pipe->waiting_writers++;
1597                 pipe_wait(pipe);
1598                 pipe->waiting_writers--;
1599         }
1600
1601         mutex_unlock(&pipe->inode->i_mutex);
1602         return ret;
1603 }
1604
1605 /*
1606  * Link contents of ipipe to opipe.
1607  */
1608 static int link_pipe(struct pipe_inode_info *ipipe,
1609                      struct pipe_inode_info *opipe,
1610                      size_t len, unsigned int flags)
1611 {
1612         struct pipe_buffer *ibuf, *obuf;
1613         int ret = 0, i = 0, nbuf;
1614
1615         /*
1616          * Potential ABBA deadlock, work around it by ordering lock
1617          * grabbing by inode address. Otherwise two different processes
1618          * could deadlock (one doing tee from A -> B, the other from B -> A).
1619          */
1620         inode_double_lock(ipipe->inode, opipe->inode);
1621
1622         do {
1623                 if (!opipe->readers) {
1624                         send_sig(SIGPIPE, current, 0);
1625                         if (!ret)
1626                                 ret = -EPIPE;
1627                         break;
1628                 }
1629
1630                 /*
1631                  * If we have iterated all input buffers or ran out of
1632                  * output room, break.
1633                  */
1634                 if (i >= ipipe->nrbufs || opipe->nrbufs >= PIPE_BUFFERS)
1635                         break;
1636
1637                 ibuf = ipipe->bufs + ((ipipe->curbuf + i) & (PIPE_BUFFERS - 1));
1638                 nbuf = (opipe->curbuf + opipe->nrbufs) & (PIPE_BUFFERS - 1);
1639
1640                 /*
1641                  * Get a reference to this pipe buffer,
1642                  * so we can copy the contents over.
1643                  */
1644                 ibuf->ops->get(ipipe, ibuf);
1645
1646                 obuf = opipe->bufs + nbuf;
1647                 *obuf = *ibuf;
1648
1649                 /*
1650                  * Don't inherit the gift flag, we need to
1651                  * prevent multiple steals of this page.
1652                  */
1653                 obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
1654
1655                 if (obuf->len > len)
1656                         obuf->len = len;
1657
1658                 opipe->nrbufs++;
1659                 ret += obuf->len;
1660                 len -= obuf->len;
1661                 i++;
1662         } while (len);
1663
1664         /*
1665          * return EAGAIN if we have the potential of some data in the
1666          * future, otherwise just return 0
1667          */
1668         if (!ret && ipipe->waiting_writers && (flags & SPLICE_F_NONBLOCK))
1669                 ret = -EAGAIN;
1670
1671         inode_double_unlock(ipipe->inode, opipe->inode);
1672
1673         /*
1674          * If we put data in the output pipe, wakeup any potential readers.
1675          */
1676         if (ret > 0) {
1677                 smp_mb();
1678                 if (waitqueue_active(&opipe->wait))
1679                         wake_up_interruptible(&opipe->wait);
1680                 kill_fasync(&opipe->fasync_readers, SIGIO, POLL_IN);
1681         }
1682
1683         return ret;
1684 }
1685
1686 /*
1687  * This is a tee(1) implementation that works on pipes. It doesn't copy
1688  * any data, it simply references the 'in' pages on the 'out' pipe.
1689  * The 'flags' used are the SPLICE_F_* variants, currently the only
1690  * applicable one is SPLICE_F_NONBLOCK.
1691  */
1692 static long do_tee(struct file *in, struct file *out, size_t len,
1693                    unsigned int flags)
1694 {
1695         struct pipe_inode_info *ipipe = pipe_info(in->f_path.dentry->d_inode);
1696         struct pipe_inode_info *opipe = pipe_info(out->f_path.dentry->d_inode);
1697         int ret = -EINVAL;
1698
1699         /*
1700          * Duplicate the contents of ipipe to opipe without actually
1701          * copying the data.
1702          */
1703         if (ipipe && opipe && ipipe != opipe) {
1704                 /*
1705                  * Keep going, unless we encounter an error. The ipipe/opipe
1706                  * ordering doesn't really matter.
1707                  */
1708                 ret = link_ipipe_prep(ipipe, flags);
1709                 if (!ret) {
1710                         ret = link_opipe_prep(opipe, flags);
1711                         if (!ret)
1712                                 ret = link_pipe(ipipe, opipe, len, flags);
1713                 }
1714         }
1715
1716         return ret;
1717 }
1718
1719 asmlinkage long sys_tee(int fdin, int fdout, size_t len, unsigned int flags)
1720 {
1721         struct file *in;
1722         int error, fput_in;
1723
1724         if (unlikely(!len))
1725                 return 0;
1726
1727         error = -EBADF;
1728         in = fget_light(fdin, &fput_in);
1729         if (in) {
1730                 if (in->f_mode & FMODE_READ) {
1731                         int fput_out;
1732                         struct file *out = fget_light(fdout, &fput_out);
1733
1734                         if (out) {
1735                                 if (out->f_mode & FMODE_WRITE)
1736                                         error = do_tee(in, out, len, flags);
1737                                 fput_light(out, fput_out);
1738                         }
1739                 }
1740                 fput_light(in, fput_in);
1741         }
1742
1743         return error;
1744 }