SAFE public projects git trees. - safe/jmp/linux-2.6/blob - 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 and fixing the initial implementation
  13  * bugs.
  14  *
  15  * Copyright (C) 2005 Jens Axboe <axboe@suse.de>
  16  * Copyright (C) 2005 Linus Torvalds <torvalds@osdl.org>
  17  *
  18  */
  19 #include <linux/fs.h>
  20 #include <linux/file.h>
  21 #include <linux/pagemap.h>
  22 #include <linux/pipe_fs_i.h>
  23 #include <linux/mm_inline.h>
  24 #include <linux/swap.h>
  25 #include <linux/writeback.h>
  26 #include <linux/buffer_head.h>
  27 #include <linux/module.h>
  28 #include <linux/syscalls.h>
  29
  30 /*
  31  * Passed to the actors
  32  */
  33 struct splice_desc {
  34         unsigned int len, total_len;    /* current and remaining length */
  35         unsigned int flags;             /* splice flags */
  36         struct file *file;              /* file to read/write */
  37         loff_t pos;                     /* file position */
  38 };
  39
  40 /*
  41  * Attempt to steal a page from a pipe buffer. This should perhaps go into
  42  * a vm helper function, it's already simplified quite a bit by the
  43  * addition of remove_mapping(). If success is returned, the caller may
  44  * attempt to reuse this page for another destination.
  45  */
  46 static int page_cache_pipe_buf_steal(struct pipe_inode_info *info,
  47                                      struct pipe_buffer *buf)
  48 {
  49         struct page *page = buf->page;
  50         struct address_space *mapping = page_mapping(page);
  51
  52         WARN_ON(!PageLocked(page));
  53         WARN_ON(!PageUptodate(page));
  54
  55         /*
  56          * At least for ext2 with nobh option, we need to wait on writeback
  57          * completing on this page, since we'll remove it from the pagecache.
  58          * Otherwise truncate wont wait on the page, allowing the disk
  59          * blocks to be reused by someone else before we actually wrote our
  60          * data to them. fs corruption ensues.
  61          */
  62         wait_on_page_writeback(page);
  63
  64         if (PagePrivate(page))
  65                 try_to_release_page(page, mapping_gfp_mask(mapping));
  66
  67         if (!remove_mapping(mapping, page))
  68                 return 1;
  69
  70         buf->flags |= PIPE_BUF_FLAG_STOLEN | PIPE_BUF_FLAG_LRU;
  71         return 0;
  72 }
  73
  74 static void page_cache_pipe_buf_release(struct pipe_inode_info *info,
  75                                         struct pipe_buffer *buf)
  76 {
  77         page_cache_release(buf->page);
  78         buf->page = NULL;
  79         buf->flags &= ~(PIPE_BUF_FLAG_STOLEN | PIPE_BUF_FLAG_LRU);
  80 }
  81
  82 static void *page_cache_pipe_buf_map(struct file *file,
  83                                      struct pipe_inode_info *info,
  84                                      struct pipe_buffer *buf)
  85 {
  86         struct page *page = buf->page;
  87         int err;
  88
  89         if (!PageUptodate(page)) {
  90                 lock_page(page);
  91
  92                 /*
  93                  * Page got truncated/unhashed. This will cause a 0-byte
  94                  * splice, if this is the first page
  95                  */
  96                 if (!page->mapping) {
  97                         err = -ENODATA;
  98                         goto error;
  99                 }
 100
 101                 /*
 102                  * uh oh, read-error from disk
 103                  */
 104                 if (!PageUptodate(page)) {
 105                         err = -EIO;
 106                         goto error;
 107                 }
 108
 109                 /*
 110                  * page is ok afterall, fall through to mapping
 111                  */
 112                 unlock_page(page);
 113         }
 114
 115         return kmap(page);
 116 error:
 117         unlock_page(page);
 118         return ERR_PTR(err);
 119 }
 120
 121 static void page_cache_pipe_buf_unmap(struct pipe_inode_info *info,
 122                                       struct pipe_buffer *buf)
 123 {
 124         kunmap(buf->page);
 125 }
 126
 127 static struct pipe_buf_operations page_cache_pipe_buf_ops = {
 128         .can_merge = 0,
 129         .map = page_cache_pipe_buf_map,
 130         .unmap = page_cache_pipe_buf_unmap,
 131         .release = page_cache_pipe_buf_release,
 132         .steal = page_cache_pipe_buf_steal,
 133 };
 134
 135 /*
 136  * Pipe output worker. This sets up our pipe format with the page cache
 137  * pipe buffer operations. Otherwise very similar to the regular pipe_writev().
 138  */
 139 static ssize_t move_to_pipe(struct inode *inode, struct page **pages,
 140                             int nr_pages, unsigned long offset,
 141                             unsigned long len, unsigned int flags)
 142 {
 143         struct pipe_inode_info *info;
 144         int ret, do_wakeup, i;
 145
 146         ret = 0;
 147         do_wakeup = 0;
 148         i = 0;
 149
 150         mutex_lock(PIPE_MUTEX(*inode));
 151
 152         info = inode->i_pipe;
 153         for (;;) {
 154                 int bufs;
 155
 156                 if (!PIPE_READERS(*inode)) {
 157                         send_sig(SIGPIPE, current, 0);
 158                         if (!ret)
 159                                 ret = -EPIPE;
 160                         break;
 161                 }
 162
 163                 bufs = info->nrbufs;
 164                 if (bufs < PIPE_BUFFERS) {
 165                         int newbuf = (info->curbuf + bufs) & (PIPE_BUFFERS - 1);
 166                         struct pipe_buffer *buf = info->bufs + newbuf;
 167                         struct page *page = pages[i++];
 168                         unsigned long this_len;
 169
 170                         this_len = PAGE_CACHE_SIZE - offset;
 171                         if (this_len > len)
 172                                 this_len = len;
 173
 174                         buf->page = page;
 175                         buf->offset = offset;
 176                         buf->len = this_len;
 177                         buf->ops = &page_cache_pipe_buf_ops;
 178                         info->nrbufs = ++bufs;
 179                         do_wakeup = 1;
 180
 181                         ret += this_len;
 182                         len -= this_len;
 183                         offset = 0;
 184                         if (!--nr_pages)
 185                                 break;
 186                         if (!len)
 187                                 break;
 188                         if (bufs < PIPE_BUFFERS)
 189                                 continue;
 190
 191                         break;
 192                 }
 193
 194                 if (flags & SPLICE_F_NONBLOCK) {
 195                         if (!ret)
 196                                 ret = -EAGAIN;
 197                         break;
 198                 }
 199
 200                 if (signal_pending(current)) {
 201                         if (!ret)
 202                                 ret = -ERESTARTSYS;
 203                         break;
 204                 }
 205
 206                 if (do_wakeup) {
 207                         smp_mb();
 208                         if (waitqueue_active(PIPE_WAIT(*inode)))
 209                                 wake_up_interruptible_sync(PIPE_WAIT(*inode));
 210                         kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO,
 211                                     POLL_IN);
 212                         do_wakeup = 0;
 213                 }
 214
 215                 PIPE_WAITING_WRITERS(*inode)++;
 216                 pipe_wait(inode);
 217                 PIPE_WAITING_WRITERS(*inode)--;
 218         }
 219
 220         mutex_unlock(PIPE_MUTEX(*inode));
 221
 222         if (do_wakeup) {
 223                 smp_mb();
 224                 if (waitqueue_active(PIPE_WAIT(*inode)))
 225                         wake_up_interruptible(PIPE_WAIT(*inode));
 226                 kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO, POLL_IN);
 227         }
 228
 229         while (i < nr_pages)
 230                 page_cache_release(pages[i++]);
 231
 232         return ret;
 233 }
 234
 235 static int __generic_file_splice_read(struct file *in, struct inode *pipe,
 236                                       size_t len, unsigned int flags)
 237 {
 238         struct address_space *mapping = in->f_mapping;
 239         unsigned int offset, nr_pages;
 240         struct page *pages[PIPE_BUFFERS];
 241         struct page *page;
 242         pgoff_t index;
 243         int i;
 244
 245         index = in->f_pos >> PAGE_CACHE_SHIFT;
 246         offset = in->f_pos & ~PAGE_CACHE_MASK;
 247         nr_pages = (len + offset + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 248
 249         if (nr_pages > PIPE_BUFFERS)
 250                 nr_pages = PIPE_BUFFERS;
 251
 252         /*
 253          * initiate read-ahead on this page range. however, don't call into
 254          * read-ahead if this is a non-zero offset (we are likely doing small
 255          * chunk splice and the page is already there) for a single page.
 256          */
 257         if (!offset || nr_pages > 1)
 258                 do_page_cache_readahead(mapping, in, index, nr_pages);
 259
 260         /*
 261          * now fill in the holes
 262          */
 263         for (i = 0; i < nr_pages; i++, index++) {
 264                 /*
 265                  * no page there, look one up / create it
 266                  */
 267                 page = find_or_create_page(mapping, index,
 268                                                    mapping_gfp_mask(mapping));
 269                 if (!page)
 270                         break;
 271
 272                 if (PageUptodate(page))
 273                         unlock_page(page);
 274                 else {
 275                         int error = mapping->a_ops->readpage(in, page);
 276
 277                         if (unlikely(error)) {
 278                                 page_cache_release(page);
 279                                 break;
 280                         }
 281                 }
 282                 pages[i] = page;
 283         }
 284
 285         if (i)
 286                 return move_to_pipe(pipe, pages, i, offset, len, flags);
 287
 288         return 0;
 289 }
 290
 291 /**
 292  * generic_file_splice_read - splice data from file to a pipe
 293  * @in:         file to splice from
 294  * @pipe:       pipe to splice to
 295  * @len:        number of bytes to splice
 296  * @flags:      splice modifier flags
 297  *
 298  * Will read pages from given file and fill them into a pipe.
 299  *
 300  */
 301 ssize_t generic_file_splice_read(struct file *in, struct inode *pipe,
 302                                  size_t len, unsigned int flags)
 303 {
 304         ssize_t spliced;
 305         int ret;
 306
 307         ret = 0;
 308         spliced = 0;
 309         while (len) {
 310                 ret = __generic_file_splice_read(in, pipe, len, flags);
 311
 312                 if (ret <= 0)
 313                         break;
 314
 315                 in->f_pos += ret;
 316                 len -= ret;
 317                 spliced += ret;
 318
 319                 if (!(flags & SPLICE_F_NONBLOCK))
 320                         continue;
 321                 ret = -EAGAIN;
 322                 break;
 323         }
 324
 325         if (spliced)
 326                 return spliced;
 327
 328         return ret;
 329 }
 330
 331 EXPORT_SYMBOL(generic_file_splice_read);
 332
 333 /*
 334  * Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->pos'
 335  * using sendpage().
 336  */
 337 static int pipe_to_sendpage(struct pipe_inode_info *info,
 338                             struct pipe_buffer *buf, struct splice_desc *sd)
 339 {
 340         struct file *file = sd->file;
 341         loff_t pos = sd->pos;
 342         unsigned int offset;
 343         ssize_t ret;
 344         void *ptr;
 345         int more;
 346
 347         /*
 348          * sub-optimal, but we are limited by the pipe ->map. we don't
 349          * need a kmap'ed buffer here, we just want to make sure we
 350          * have the page pinned if the pipe page originates from the
 351          * page cache
 352          */
 353         ptr = buf->ops->map(file, info, buf);
 354         if (IS_ERR(ptr))
 355                 return PTR_ERR(ptr);
 356
 357         offset = pos & ~PAGE_CACHE_MASK;
 358         more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len;
 359
 360         ret = file->f_op->sendpage(file, buf->page, offset, sd->len, &pos,more);
 361
 362         buf->ops->unmap(info, buf);
 363         if (ret == sd->len)
 364                 return 0;
 365
 366         return -EIO;
 367 }
 368
 369 /*
 370  * This is a little more tricky than the file -> pipe splicing. There are
 371  * basically three cases:
 372  *
 373  *      - Destination page already exists in the address space and there
 374  *        are users of it. For that case we have no other option that
 375  *        copying the data. Tough luck.
 376  *      - Destination page already exists in the address space, but there
 377  *        are no users of it. Make sure it's uptodate, then drop it. Fall
 378  *        through to last case.
 379  *      - Destination page does not exist, we can add the pipe page to
 380  *        the page cache and avoid the copy.
 381  *
 382  * If asked to move pages to the output file (SPLICE_F_MOVE is set in
 383  * sd->flags), we attempt to migrate pages from the pipe to the output
 384  * file address space page cache. This is possible if no one else has
 385  * the pipe page referenced outside of the pipe and page cache. If
 386  * SPLICE_F_MOVE isn't set, or we cannot move the page, we simply create
 387  * a new page in the output file page cache and fill/dirty that.
 388  */
 389 static int pipe_to_file(struct pipe_inode_info *info, struct pipe_buffer *buf,
 390                         struct splice_desc *sd)
 391 {
 392         struct file *file = sd->file;
 393         struct address_space *mapping = file->f_mapping;
 394         gfp_t gfp_mask = mapping_gfp_mask(mapping);
 395         unsigned int offset;
 396         struct page *page;
 397         pgoff_t index;
 398         char *src;
 399         int ret;
 400
 401         /*
 402          * make sure the data in this buffer is uptodate
 403          */
 404         src = buf->ops->map(file, info, buf);
 405         if (IS_ERR(src))
 406                 return PTR_ERR(src);
 407
 408         index = sd->pos >> PAGE_CACHE_SHIFT;
 409         offset = sd->pos & ~PAGE_CACHE_MASK;
 410
 411         /*
 412          * reuse buf page, if SPLICE_F_MOVE is set
 413          */
 414         if (sd->flags & SPLICE_F_MOVE) {
 415                 /*
 416                  * If steal succeeds, buf->page is now pruned from the vm
 417                  * side (LRU and page cache) and we can reuse it.
 418                  */
 419                 if (buf->ops->steal(info, buf))
 420                         goto find_page;
 421
 422                 /*
 423                  * this will also set the page locked
 424                  */
 425                 page = buf->page;
 426                 if (add_to_page_cache(page, mapping, index, gfp_mask))
 427                         goto find_page;
 428
 429                 if (!(buf->flags & PIPE_BUF_FLAG_LRU))
 430                         lru_cache_add(page);
 431         } else {
 432 find_page:
 433                 ret = -ENOMEM;
 434                 page = find_or_create_page(mapping, index, gfp_mask);
 435                 if (!page)
 436                         goto out_nomem;
 437
 438                 /*
 439                  * If the page is uptodate, it is also locked. If it isn't
 440                  * uptodate, we can mark it uptodate if we are filling the
 441                  * full page. Otherwise we need to read it in first...
 442                  */
 443                 if (!PageUptodate(page)) {
 444                         if (sd->len < PAGE_CACHE_SIZE) {
 445                                 ret = mapping->a_ops->readpage(file, page);
 446                                 if (unlikely(ret))
 447                                         goto out;
 448
 449                                 lock_page(page);
 450
 451                                 if (!PageUptodate(page)) {
 452                                         /*
 453                                          * page got invalidated, repeat
 454                                          */
 455                                         if (!page->mapping) {
 456                                                 unlock_page(page);
 457                                                 page_cache_release(page);
 458                                                 goto find_page;
 459                                         }
 460                                         ret = -EIO;
 461                                         goto out;
 462                                 }
 463                         } else {
 464                                 WARN_ON(!PageLocked(page));
 465                                 SetPageUptodate(page);
 466                         }
 467                 }
 468         }
 469
 470         ret = mapping->a_ops->prepare_write(file, page, 0, sd->len);
 471         if (ret == AOP_TRUNCATED_PAGE) {
 472                 page_cache_release(page);
 473                 goto find_page;
 474         } else if (ret)
 475                 goto out;
 476
 477         if (!(buf->flags & PIPE_BUF_FLAG_STOLEN)) {
 478                 char *dst = kmap_atomic(page, KM_USER0);
 479
 480                 memcpy(dst + offset, src + buf->offset, sd->len);
 481                 flush_dcache_page(page);
 482                 kunmap_atomic(dst, KM_USER0);
 483         }
 484
 485         ret = mapping->a_ops->commit_write(file, page, 0, sd->len);
 486         if (ret == AOP_TRUNCATED_PAGE) {
 487                 page_cache_release(page);
 488                 goto find_page;
 489         } else if (ret)
 490                 goto out;
 491
 492         mark_page_accessed(page);
 493         balance_dirty_pages_ratelimited(mapping);
 494 out:
 495         if (!(buf->flags & PIPE_BUF_FLAG_STOLEN)) {
 496                 page_cache_release(page);
 497                 unlock_page(page);
 498         }
 499 out_nomem:
 500         buf->ops->unmap(info, buf);
 501         return ret;
 502 }
 503
 504 typedef int (splice_actor)(struct pipe_inode_info *, struct pipe_buffer *,
 505                            struct splice_desc *);
 506
 507 /*
 508  * Pipe input worker. Most of this logic works like a regular pipe, the
 509  * key here is the 'actor' worker passed in that actually moves the data
 510  * to the wanted destination. See pipe_to_file/pipe_to_sendpage above.
 511  */
 512 static ssize_t move_from_pipe(struct inode *inode, struct file *out,
 513                               size_t len, unsigned int flags,
 514                               splice_actor *actor)
 515 {
 516         struct pipe_inode_info *info;
 517         int ret, do_wakeup, err;
 518         struct splice_desc sd;
 519
 520         ret = 0;
 521         do_wakeup = 0;
 522
 523         sd.total_len = len;
 524         sd.flags = flags;
 525         sd.file = out;
 526         sd.pos = out->f_pos;
 527
 528         mutex_lock(PIPE_MUTEX(*inode));
 529
 530         info = inode->i_pipe;
 531         for (;;) {
 532                 int bufs = info->nrbufs;
 533
 534                 if (bufs) {
 535                         int curbuf = info->curbuf;
 536                         struct pipe_buffer *buf = info->bufs + curbuf;
 537                         struct pipe_buf_operations *ops = buf->ops;
 538
 539                         sd.len = buf->len;
 540                         if (sd.len > sd.total_len)
 541                                 sd.len = sd.total_len;
 542
 543                         err = actor(info, buf, &sd);
 544                         if (err) {
 545                                 if (!ret && err != -ENODATA)
 546                                         ret = err;
 547
 548                                 break;
 549                         }
 550
 551                         ret += sd.len;
 552                         buf->offset += sd.len;
 553                         buf->len -= sd.len;
 554                         if (!buf->len) {
 555                                 buf->ops = NULL;
 556                                 ops->release(info, buf);
 557                                 curbuf = (curbuf + 1) & (PIPE_BUFFERS - 1);
 558                                 info->curbuf = curbuf;
 559                                 info->nrbufs = --bufs;
 560                                 do_wakeup = 1;
 561                         }
 562
 563                         sd.pos += sd.len;
 564                         sd.total_len -= sd.len;
 565                         if (!sd.total_len)
 566                                 break;
 567                 }
 568
 569                 if (bufs)
 570                         continue;
 571                 if (!PIPE_WRITERS(*inode))
 572                         break;
 573                 if (!PIPE_WAITING_WRITERS(*inode)) {
 574                         if (ret)
 575                                 break;
 576                 }
 577
 578                 if (flags & SPLICE_F_NONBLOCK) {
 579                         if (!ret)
 580                                 ret = -EAGAIN;
 581                         break;
 582                 }
 583
 584                 if (signal_pending(current)) {
 585                         if (!ret)
 586                                 ret = -ERESTARTSYS;
 587                         break;
 588                 }
 589
 590                 if (do_wakeup) {
 591                         smp_mb();
 592                         if (waitqueue_active(PIPE_WAIT(*inode)))
 593                                 wake_up_interruptible_sync(PIPE_WAIT(*inode));
 594                         kill_fasync(PIPE_FASYNC_WRITERS(*inode),SIGIO,POLL_OUT);
 595                         do_wakeup = 0;
 596                 }
 597
 598                 pipe_wait(inode);
 599         }
 600
 601         mutex_unlock(PIPE_MUTEX(*inode));
 602
 603         if (do_wakeup) {
 604                 smp_mb();
 605                 if (waitqueue_active(PIPE_WAIT(*inode)))
 606                         wake_up_interruptible(PIPE_WAIT(*inode));
 607                 kill_fasync(PIPE_FASYNC_WRITERS(*inode), SIGIO, POLL_OUT);
 608         }
 609
 610         mutex_lock(&out->f_mapping->host->i_mutex);
 611         out->f_pos = sd.pos;
 612         mutex_unlock(&out->f_mapping->host->i_mutex);
 613         return ret;
 614
 615 }
 616
 617 /**
 618  * generic_file_splice_write - splice data from a pipe to a file
 619  * @inode:      pipe inode
 620  * @out:        file to write to
 621  * @len:        number of bytes to splice
 622  * @flags:      splice modifier flags
 623  *
 624  * Will either move or copy pages (determined by @flags options) from
 625  * the given pipe inode to the given file.
 626  *
 627  */
 628 ssize_t generic_file_splice_write(struct inode *inode, struct file *out,
 629                                   size_t len, unsigned int flags)
 630 {
 631         struct address_space *mapping = out->f_mapping;
 632         ssize_t ret = move_from_pipe(inode, out, len, flags, pipe_to_file);
 633
 634         /*
 635          * if file or inode is SYNC and we actually wrote some data, sync it
 636          */
 637         if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(mapping->host))
 638             && ret > 0) {
 639                 struct inode *inode = mapping->host;
 640                 int err;
 641
 642                 mutex_lock(&inode->i_mutex);
 643                 err = generic_osync_inode(mapping->host, mapping,
 644                                                 OSYNC_METADATA|OSYNC_DATA);
 645                 mutex_unlock(&inode->i_mutex);
 646
 647                 if (err)
 648                         ret = err;
 649         }
 650
 651         return ret;
 652 }
 653
 654 EXPORT_SYMBOL(generic_file_splice_write);
 655
 656 /**
 657  * generic_splice_sendpage - splice data from a pipe to a socket
 658  * @inode:      pipe inode
 659  * @out:        socket to write to
 660  * @len:        number of bytes to splice
 661  * @flags:      splice modifier flags
 662  *
 663  * Will send @len bytes from the pipe to a network socket. No data copying
 664  * is involved.
 665  *
 666  */
 667 ssize_t generic_splice_sendpage(struct inode *inode, struct file *out,
 668                                 size_t len, unsigned int flags)
 669 {
 670         return move_from_pipe(inode, out, len, flags, pipe_to_sendpage);
 671 }
 672
 673 EXPORT_SYMBOL(generic_splice_sendpage);
 674
 675 /*
 676  * Attempt to initiate a splice from pipe to file.
 677  */
 678 static long do_splice_from(struct inode *pipe, struct file *out, size_t len,
 679                            unsigned int flags)
 680 {
 681         loff_t pos;
 682         int ret;
 683
 684         if (!out->f_op || !out->f_op->splice_write)
 685                 return -EINVAL;
 686
 687         if (!(out->f_mode & FMODE_WRITE))
 688                 return -EBADF;
 689
 690         pos = out->f_pos;
 691         ret = rw_verify_area(WRITE, out, &pos, len);
 692         if (unlikely(ret < 0))
 693                 return ret;
 694
 695         return out->f_op->splice_write(pipe, out, len, flags);
 696 }
 697
 698 /*
 699  * Attempt to initiate a splice from a file to a pipe.
 700  */
 701 static long do_splice_to(struct file *in, struct inode *pipe, size_t len,
 702                          unsigned int flags)
 703 {
 704         loff_t pos, isize, left;
 705         int ret;
 706
 707         if (!in->f_op || !in->f_op->splice_read)
 708                 return -EINVAL;
 709
 710         if (!(in->f_mode & FMODE_READ))
 711                 return -EBADF;
 712
 713         pos = in->f_pos;
 714         ret = rw_verify_area(READ, in, &pos, len);
 715         if (unlikely(ret < 0))
 716                 return ret;
 717
 718         isize = i_size_read(in->f_mapping->host);
 719         if (unlikely(in->f_pos >= isize))
 720                 return 0;
 721
 722         left = isize - in->f_pos;
 723         if (left < len)
 724                 len = left;
 725
 726         return in->f_op->splice_read(in, pipe, len, flags);
 727 }
 728
 729 /*
 730  * Determine where to splice to/from.
 731  */
 732 static long do_splice(struct file *in, struct file *out, size_t len,
 733                       unsigned int flags)
 734 {
 735         struct inode *pipe;
 736
 737         pipe = in->f_dentry->d_inode;
 738         if (pipe->i_pipe)
 739                 return do_splice_from(pipe, out, len, flags);
 740
 741         pipe = out->f_dentry->d_inode;
 742         if (pipe->i_pipe)
 743                 return do_splice_to(in, pipe, len, flags);
 744
 745         return -EINVAL;
 746 }
 747
 748 asmlinkage long sys_splice(int fdin, int fdout, size_t len, unsigned int flags)
 749 {
 750         long error;
 751         struct file *in, *out;
 752         int fput_in, fput_out;
 753
 754         if (unlikely(!len))
 755                 return 0;
 756
 757         error = -EBADF;
 758         in = fget_light(fdin, &fput_in);
 759         if (in) {
 760                 if (in->f_mode & FMODE_READ) {
 761                         out = fget_light(fdout, &fput_out);
 762                         if (out) {
 763                                 if (out->f_mode & FMODE_WRITE)
 764                                         error = do_splice(in, out, len, flags);
 765                                 fput_light(out, fput_out);
 766                         }
 767                 }
 768
 769                 fput_light(in, fput_in);
 770         }
 771
 772         return error;
 773 }