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         if (PageLRU(page)) {
  71                 struct zone *zone = page_zone(page);
  72
  73                 spin_lock_irq(&zone->lru_lock);
  74                 BUG_ON(!PageLRU(page));
  75                 __ClearPageLRU(page);
  76                 del_page_from_lru(zone, page);
  77                 spin_unlock_irq(&zone->lru_lock);
  78         }
  79
  80         return 0;
  81 }
  82
  83 static void page_cache_pipe_buf_release(struct pipe_inode_info *info,
  84                                         struct pipe_buffer *buf)
  85 {
  86         page_cache_release(buf->page);
  87         buf->page = NULL;
  88 }
  89
  90 static void *page_cache_pipe_buf_map(struct file *file,
  91                                      struct pipe_inode_info *info,
  92                                      struct pipe_buffer *buf)
  93 {
  94         struct page *page = buf->page;
  95
  96         lock_page(page);
  97
  98         if (!PageUptodate(page)) {
  99                 unlock_page(page);
 100                 return ERR_PTR(-EIO);
 101         }
 102
 103         if (!page->mapping) {
 104                 unlock_page(page);
 105                 return ERR_PTR(-ENODATA);
 106         }
 107
 108         return kmap(buf->page);
 109 }
 110
 111 static void page_cache_pipe_buf_unmap(struct pipe_inode_info *info,
 112                                       struct pipe_buffer *buf)
 113 {
 114         unlock_page(buf->page);
 115         kunmap(buf->page);
 116 }
 117
 118 static struct pipe_buf_operations page_cache_pipe_buf_ops = {
 119         .can_merge = 0,
 120         .map = page_cache_pipe_buf_map,
 121         .unmap = page_cache_pipe_buf_unmap,
 122         .release = page_cache_pipe_buf_release,
 123         .steal = page_cache_pipe_buf_steal,
 124 };
 125
 126 /*
 127  * Pipe output worker. This sets up our pipe format with the page cache
 128  * pipe buffer operations. Otherwise very similar to the regular pipe_writev().
 129  */
 130 static ssize_t move_to_pipe(struct inode *inode, struct page **pages,
 131                             int nr_pages, unsigned long offset,
 132                             unsigned long len, unsigned int flags)
 133 {
 134         struct pipe_inode_info *info;
 135         int ret, do_wakeup, i;
 136
 137         ret = 0;
 138         do_wakeup = 0;
 139         i = 0;
 140
 141         mutex_lock(PIPE_MUTEX(*inode));
 142
 143         info = inode->i_pipe;
 144         for (;;) {
 145                 int bufs;
 146
 147                 if (!PIPE_READERS(*inode)) {
 148                         send_sig(SIGPIPE, current, 0);
 149                         if (!ret)
 150                                 ret = -EPIPE;
 151                         break;
 152                 }
 153
 154                 bufs = info->nrbufs;
 155                 if (bufs < PIPE_BUFFERS) {
 156                         int newbuf = (info->curbuf + bufs) & (PIPE_BUFFERS - 1);
 157                         struct pipe_buffer *buf = info->bufs + newbuf;
 158                         struct page *page = pages[i++];
 159                         unsigned long this_len;
 160
 161                         this_len = PAGE_CACHE_SIZE - offset;
 162                         if (this_len > len)
 163                                 this_len = len;
 164
 165                         buf->page = page;
 166                         buf->offset = offset;
 167                         buf->len = this_len;
 168                         buf->ops = &page_cache_pipe_buf_ops;
 169                         info->nrbufs = ++bufs;
 170                         do_wakeup = 1;
 171
 172                         ret += this_len;
 173                         len -= this_len;
 174                         offset = 0;
 175                         if (!--nr_pages)
 176                                 break;
 177                         if (!len)
 178                                 break;
 179                         if (bufs < PIPE_BUFFERS)
 180                                 continue;
 181
 182                         break;
 183                 }
 184
 185                 if (flags & SPLICE_F_NONBLOCK) {
 186                         if (!ret)
 187                                 ret = -EAGAIN;
 188                         break;
 189                 }
 190
 191                 if (signal_pending(current)) {
 192                         if (!ret)
 193                                 ret = -ERESTARTSYS;
 194                         break;
 195                 }
 196
 197                 if (do_wakeup) {
 198                         wake_up_interruptible_sync(PIPE_WAIT(*inode));
 199                         kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO,
 200                                     POLL_IN);
 201                         do_wakeup = 0;
 202                 }
 203
 204                 PIPE_WAITING_WRITERS(*inode)++;
 205                 pipe_wait(inode);
 206                 PIPE_WAITING_WRITERS(*inode)--;
 207         }
 208
 209         mutex_unlock(PIPE_MUTEX(*inode));
 210
 211         if (do_wakeup) {
 212                 wake_up_interruptible(PIPE_WAIT(*inode));
 213                 kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO, POLL_IN);
 214         }
 215
 216         while (i < nr_pages)
 217                 page_cache_release(pages[i++]);
 218
 219         return ret;
 220 }
 221
 222 static int __generic_file_splice_read(struct file *in, struct inode *pipe,
 223                                       size_t len, unsigned int flags)
 224 {
 225         struct address_space *mapping = in->f_mapping;
 226         unsigned int offset, nr_pages;
 227         struct page *pages[PIPE_BUFFERS], *shadow[PIPE_BUFFERS];
 228         struct page *page;
 229         pgoff_t index, pidx;
 230         int i, j;
 231
 232         index = in->f_pos >> PAGE_CACHE_SHIFT;
 233         offset = in->f_pos & ~PAGE_CACHE_MASK;
 234         nr_pages = (len + offset + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 235
 236         if (nr_pages > PIPE_BUFFERS)
 237                 nr_pages = PIPE_BUFFERS;
 238
 239         /*
 240          * initiate read-ahead on this page range
 241          */
 242         do_page_cache_readahead(mapping, in, index, nr_pages);
 243
 244         /*
 245          * Get as many pages from the page cache as possible..
 246          * Start IO on the page cache entries we create (we
 247          * can assume that any pre-existing ones we find have
 248          * already had IO started on them).
 249          */
 250         i = find_get_pages(mapping, index, nr_pages, pages);
 251
 252         /*
 253          * common case - we found all pages and they are contiguous,
 254          * kick them off
 255          */
 256         if (i && (pages[i - 1]->index == index + i - 1))
 257                 goto splice_them;
 258
 259         /*
 260          * fill shadow[] with pages at the right locations, so we only
 261          * have to fill holes
 262          */
 263         memset(shadow, 0, nr_pages * sizeof(struct page *));
 264         for (j = 0; j < i; j++)
 265                 shadow[pages[j]->index - index] = pages[j];
 266
 267         /*
 268          * now fill in the holes
 269          */
 270         for (i = 0, pidx = index; i < nr_pages; pidx++, i++) {
 271                 int error;
 272
 273                 if (shadow[i])
 274                         continue;
 275
 276                 /*
 277                  * no page there, look one up / create it
 278                  */
 279                 page = find_or_create_page(mapping, pidx,
 280                                                    mapping_gfp_mask(mapping));
 281                 if (!page)
 282                         break;
 283
 284                 if (PageUptodate(page))
 285                         unlock_page(page);
 286                 else {
 287                         error = mapping->a_ops->readpage(in, page);
 288
 289                         if (unlikely(error)) {
 290                                 page_cache_release(page);
 291                                 break;
 292                         }
 293                 }
 294                 shadow[i] = page;
 295         }
 296
 297         if (!i) {
 298                 for (i = 0; i < nr_pages; i++) {
 299                          if (shadow[i])
 300                                 page_cache_release(shadow[i]);
 301                 }
 302                 return 0;
 303         }
 304
 305         memcpy(pages, shadow, i * sizeof(struct page *));
 306
 307         /*
 308          * Now we splice them into the pipe..
 309          */
 310 splice_them:
 311         return move_to_pipe(pipe, pages, i, offset, len, flags);
 312 }
 313
 314 /**
 315  * generic_file_splice_read - splice data from file to a pipe
 316  * @in:         file to splice from
 317  * @pipe:       pipe to splice to
 318  * @len:        number of bytes to splice
 319  * @flags:      splice modifier flags
 320  *
 321  * Will read pages from given file and fill them into a pipe.
 322  *
 323  */
 324 ssize_t generic_file_splice_read(struct file *in, struct inode *pipe,
 325                                  size_t len, unsigned int flags)
 326 {
 327         ssize_t spliced;
 328         int ret;
 329
 330         ret = 0;
 331         spliced = 0;
 332         while (len) {
 333                 ret = __generic_file_splice_read(in, pipe, len, flags);
 334
 335                 if (ret <= 0)
 336                         break;
 337
 338                 in->f_pos += ret;
 339                 len -= ret;
 340                 spliced += ret;
 341
 342                 if (!(flags & SPLICE_F_NONBLOCK))
 343                         continue;
 344                 ret = -EAGAIN;
 345                 break;
 346         }
 347
 348         if (spliced)
 349                 return spliced;
 350
 351         return ret;
 352 }
 353
 354 EXPORT_SYMBOL(generic_file_splice_read);
 355
 356 /*
 357  * Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->pos'
 358  * using sendpage().
 359  */
 360 static int pipe_to_sendpage(struct pipe_inode_info *info,
 361                             struct pipe_buffer *buf, struct splice_desc *sd)
 362 {
 363         struct file *file = sd->file;
 364         loff_t pos = sd->pos;
 365         unsigned int offset;
 366         ssize_t ret;
 367         void *ptr;
 368         int more;
 369
 370         /*
 371          * sub-optimal, but we are limited by the pipe ->map. we don't
 372          * need a kmap'ed buffer here, we just want to make sure we
 373          * have the page pinned if the pipe page originates from the
 374          * page cache
 375          */
 376         ptr = buf->ops->map(file, info, buf);
 377         if (IS_ERR(ptr))
 378                 return PTR_ERR(ptr);
 379
 380         offset = pos & ~PAGE_CACHE_MASK;
 381         more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len;
 382
 383         ret = file->f_op->sendpage(file, buf->page, offset, sd->len, &pos,more);
 384
 385         buf->ops->unmap(info, buf);
 386         if (ret == sd->len)
 387                 return 0;
 388
 389         return -EIO;
 390 }
 391
 392 /*
 393  * This is a little more tricky than the file -> pipe splicing. There are
 394  * basically three cases:
 395  *
 396  *      - Destination page already exists in the address space and there
 397  *        are users of it. For that case we have no other option that
 398  *        copying the data. Tough luck.
 399  *      - Destination page already exists in the address space, but there
 400  *        are no users of it. Make sure it's uptodate, then drop it. Fall
 401  *        through to last case.
 402  *      - Destination page does not exist, we can add the pipe page to
 403  *        the page cache and avoid the copy.
 404  *
 405  * If asked to move pages to the output file (SPLICE_F_MOVE is set in
 406  * sd->flags), we attempt to migrate pages from the pipe to the output
 407  * file address space page cache. This is possible if no one else has
 408  * the pipe page referenced outside of the pipe and page cache. If
 409  * SPLICE_F_MOVE isn't set, or we cannot move the page, we simply create
 410  * a new page in the output file page cache and fill/dirty that.
 411  */
 412 static int pipe_to_file(struct pipe_inode_info *info, struct pipe_buffer *buf,
 413                         struct splice_desc *sd)
 414 {
 415         struct file *file = sd->file;
 416         struct address_space *mapping = file->f_mapping;
 417         unsigned int offset;
 418         struct page *page;
 419         pgoff_t index;
 420         char *src;
 421         int ret, stolen;
 422
 423         /*
 424          * after this, page will be locked and unmapped
 425          */
 426         src = buf->ops->map(file, info, buf);
 427         if (IS_ERR(src))
 428                 return PTR_ERR(src);
 429
 430         index = sd->pos >> PAGE_CACHE_SHIFT;
 431         offset = sd->pos & ~PAGE_CACHE_MASK;
 432         stolen = 0;
 433
 434         /*
 435          * reuse buf page, if SPLICE_F_MOVE is set
 436          */
 437         if (sd->flags & SPLICE_F_MOVE) {
 438                 /*
 439                  * If steal succeeds, buf->page is now pruned from the vm
 440                  * side (LRU and page cache) and we can reuse it.
 441                  */
 442                 if (buf->ops->steal(info, buf))
 443                         goto find_page;
 444
 445                 page = buf->page;
 446                 stolen = 1;
 447                 if (add_to_page_cache_lru(page, mapping, index,
 448                                                 mapping_gfp_mask(mapping)))
 449                         goto find_page;
 450         } else {
 451 find_page:
 452                 ret = -ENOMEM;
 453                 page = find_or_create_page(mapping, index,
 454                                                 mapping_gfp_mask(mapping));
 455                 if (!page)
 456                         goto out;
 457
 458                 /*
 459                  * If the page is uptodate, it is also locked. If it isn't
 460                  * uptodate, we can mark it uptodate if we are filling the
 461                  * full page. Otherwise we need to read it in first...
 462                  */
 463                 if (!PageUptodate(page)) {
 464                         if (sd->len < PAGE_CACHE_SIZE) {
 465                                 ret = mapping->a_ops->readpage(file, page);
 466                                 if (unlikely(ret))
 467                                         goto out;
 468
 469                                 lock_page(page);
 470
 471                                 if (!PageUptodate(page)) {
 472                                         /*
 473                                          * page got invalidated, repeat
 474                                          */
 475                                         if (!page->mapping) {
 476                                                 unlock_page(page);
 477                                                 page_cache_release(page);
 478                                                 goto find_page;
 479                                         }
 480                                         ret = -EIO;
 481                                         goto out;
 482                                 }
 483                         } else {
 484                                 WARN_ON(!PageLocked(page));
 485                                 SetPageUptodate(page);
 486                         }
 487                 }
 488         }
 489
 490         ret = mapping->a_ops->prepare_write(file, page, 0, sd->len);
 491         if (ret == AOP_TRUNCATED_PAGE) {
 492                 page_cache_release(page);
 493                 goto find_page;
 494         } else if (ret)
 495                 goto out;
 496
 497         if (!stolen) {
 498                 char *dst = kmap_atomic(page, KM_USER0);
 499
 500                 memcpy(dst + offset, src + buf->offset, sd->len);
 501                 flush_dcache_page(page);
 502                 kunmap_atomic(dst, KM_USER0);
 503         }
 504
 505         ret = mapping->a_ops->commit_write(file, page, 0, sd->len);
 506         if (ret == AOP_TRUNCATED_PAGE) {
 507                 page_cache_release(page);
 508                 goto find_page;
 509         } else if (ret)
 510                 goto out;
 511
 512         balance_dirty_pages_ratelimited(mapping);
 513 out:
 514         if (!stolen) {
 515                 page_cache_release(page);
 516                 unlock_page(page);
 517         }
 518         buf->ops->unmap(info, buf);
 519         return ret;
 520 }
 521
 522 typedef int (splice_actor)(struct pipe_inode_info *, struct pipe_buffer *,
 523                            struct splice_desc *);
 524
 525 /*
 526  * Pipe input worker. Most of this logic works like a regular pipe, the
 527  * key here is the 'actor' worker passed in that actually moves the data
 528  * to the wanted destination. See pipe_to_file/pipe_to_sendpage above.
 529  */
 530 static ssize_t move_from_pipe(struct inode *inode, struct file *out,
 531                               size_t len, unsigned int flags,
 532                               splice_actor *actor)
 533 {
 534         struct pipe_inode_info *info;
 535         int ret, do_wakeup, err;
 536         struct splice_desc sd;
 537
 538         ret = 0;
 539         do_wakeup = 0;
 540
 541         sd.total_len = len;
 542         sd.flags = flags;
 543         sd.file = out;
 544         sd.pos = out->f_pos;
 545
 546         mutex_lock(PIPE_MUTEX(*inode));
 547
 548         info = inode->i_pipe;
 549         for (;;) {
 550                 int bufs = info->nrbufs;
 551
 552                 if (bufs) {
 553                         int curbuf = info->curbuf;
 554                         struct pipe_buffer *buf = info->bufs + curbuf;
 555                         struct pipe_buf_operations *ops = buf->ops;
 556
 557                         sd.len = buf->len;
 558                         if (sd.len > sd.total_len)
 559                                 sd.len = sd.total_len;
 560
 561                         err = actor(info, buf, &sd);
 562                         if (err) {
 563                                 if (!ret && err != -ENODATA)
 564                                         ret = err;
 565
 566                                 break;
 567                         }
 568
 569                         ret += sd.len;
 570                         buf->offset += sd.len;
 571                         buf->len -= sd.len;
 572                         if (!buf->len) {
 573                                 buf->ops = NULL;
 574                                 ops->release(info, buf);
 575                                 curbuf = (curbuf + 1) & (PIPE_BUFFERS - 1);
 576                                 info->curbuf = curbuf;
 577                                 info->nrbufs = --bufs;
 578                                 do_wakeup = 1;
 579                         }
 580
 581                         sd.pos += sd.len;
 582                         sd.total_len -= sd.len;
 583                         if (!sd.total_len)
 584                                 break;
 585                 }
 586
 587                 if (bufs)
 588                         continue;
 589                 if (!PIPE_WRITERS(*inode))
 590                         break;
 591                 if (!PIPE_WAITING_WRITERS(*inode)) {
 592                         if (ret)
 593                                 break;
 594                 }
 595
 596                 if (flags & SPLICE_F_NONBLOCK) {
 597                         if (!ret)
 598                                 ret = -EAGAIN;
 599                         break;
 600                 }
 601
 602                 if (signal_pending(current)) {
 603                         if (!ret)
 604                                 ret = -ERESTARTSYS;
 605                         break;
 606                 }
 607
 608                 if (do_wakeup) {
 609                         wake_up_interruptible_sync(PIPE_WAIT(*inode));
 610                         kill_fasync(PIPE_FASYNC_WRITERS(*inode),SIGIO,POLL_OUT);
 611                         do_wakeup = 0;
 612                 }
 613
 614                 pipe_wait(inode);
 615         }
 616
 617         mutex_unlock(PIPE_MUTEX(*inode));
 618
 619         if (do_wakeup) {
 620                 wake_up_interruptible(PIPE_WAIT(*inode));
 621                 kill_fasync(PIPE_FASYNC_WRITERS(*inode), SIGIO, POLL_OUT);
 622         }
 623
 624         mutex_lock(&out->f_mapping->host->i_mutex);
 625         out->f_pos = sd.pos;
 626         mutex_unlock(&out->f_mapping->host->i_mutex);
 627         return ret;
 628
 629 }
 630
 631 /**
 632  * generic_file_splice_write - splice data from a pipe to a file
 633  * @inode:      pipe inode
 634  * @out:        file to write to
 635  * @len:        number of bytes to splice
 636  * @flags:      splice modifier flags
 637  *
 638  * Will either move or copy pages (determined by @flags options) from
 639  * the given pipe inode to the given file.
 640  *
 641  */
 642 ssize_t generic_file_splice_write(struct inode *inode, struct file *out,
 643                                   size_t len, unsigned int flags)
 644 {
 645         struct address_space *mapping = out->f_mapping;
 646         ssize_t ret = move_from_pipe(inode, out, len, flags, pipe_to_file);
 647
 648         /*
 649          * if file or inode is SYNC and we actually wrote some data, sync it
 650          */
 651         if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(mapping->host))
 652             && ret > 0) {
 653                 struct inode *inode = mapping->host;
 654                 int err;
 655
 656                 mutex_lock(&inode->i_mutex);
 657                 err = generic_osync_inode(mapping->host, mapping,
 658                                                 OSYNC_METADATA|OSYNC_DATA);
 659                 mutex_unlock(&inode->i_mutex);
 660
 661                 if (err)
 662                         ret = err;
 663         }
 664
 665         return ret;
 666 }
 667
 668 EXPORT_SYMBOL(generic_file_splice_write);
 669
 670 /**
 671  * generic_splice_sendpage - splice data from a pipe to a socket
 672  * @inode:      pipe inode
 673  * @out:        socket to write to
 674  * @len:        number of bytes to splice
 675  * @flags:      splice modifier flags
 676  *
 677  * Will send @len bytes from the pipe to a network socket. No data copying
 678  * is involved.
 679  *
 680  */
 681 ssize_t generic_splice_sendpage(struct inode *inode, struct file *out,
 682                                 size_t len, unsigned int flags)
 683 {
 684         return move_from_pipe(inode, out, len, flags, pipe_to_sendpage);
 685 }
 686
 687 EXPORT_SYMBOL(generic_splice_sendpage);
 688
 689 /*
 690  * Attempt to initiate a splice from pipe to file.
 691  */
 692 static long do_splice_from(struct inode *pipe, struct file *out, size_t len,
 693                            unsigned int flags)
 694 {
 695         loff_t pos;
 696         int ret;
 697
 698         if (!out->f_op || !out->f_op->splice_write)
 699                 return -EINVAL;
 700
 701         if (!(out->f_mode & FMODE_WRITE))
 702                 return -EBADF;
 703
 704         pos = out->f_pos;
 705         ret = rw_verify_area(WRITE, out, &pos, len);
 706         if (unlikely(ret < 0))
 707                 return ret;
 708
 709         return out->f_op->splice_write(pipe, out, len, flags);
 710 }
 711
 712 /*
 713  * Attempt to initiate a splice from a file to a pipe.
 714  */
 715 static long do_splice_to(struct file *in, struct inode *pipe, size_t len,
 716                          unsigned int flags)
 717 {
 718         loff_t pos, isize, left;
 719         int ret;
 720
 721         if (!in->f_op || !in->f_op->splice_read)
 722                 return -EINVAL;
 723
 724         if (!(in->f_mode & FMODE_READ))
 725                 return -EBADF;
 726
 727         pos = in->f_pos;
 728         ret = rw_verify_area(READ, in, &pos, len);
 729         if (unlikely(ret < 0))
 730                 return ret;
 731
 732         isize = i_size_read(in->f_mapping->host);
 733         if (unlikely(in->f_pos >= isize))
 734                 return 0;
 735
 736         left = isize - in->f_pos;
 737         if (left < len)
 738                 len = left;
 739
 740         return in->f_op->splice_read(in, pipe, len, flags);
 741 }
 742
 743 /*
 744  * Determine where to splice to/from.
 745  */
 746 static long do_splice(struct file *in, struct file *out, size_t len,
 747                       unsigned int flags)
 748 {
 749         struct inode *pipe;
 750
 751         pipe = in->f_dentry->d_inode;
 752         if (pipe->i_pipe)
 753                 return do_splice_from(pipe, out, len, flags);
 754
 755         pipe = out->f_dentry->d_inode;
 756         if (pipe->i_pipe)
 757                 return do_splice_to(in, pipe, len, flags);
 758
 759         return -EINVAL;
 760 }
 761
 762 asmlinkage long sys_splice(int fdin, int fdout, size_t len, unsigned int flags)
 763 {
 764         long error;
 765         struct file *in, *out;
 766         int fput_in, fput_out;
 767
 768         if (unlikely(!len))
 769                 return 0;
 770
 771         error = -EBADF;
 772         in = fget_light(fdin, &fput_in);
 773         if (in) {
 774                 if (in->f_mode & FMODE_READ) {
 775                         out = fget_light(fdout, &fput_out);
 776                         if (out) {
 777                                 if (out->f_mode & FMODE_WRITE)
 778                                         error = do_splice(in, out, len, flags);
 779                                 fput_light(out, fput_out);
 780                         }
 781                 }
 782
 783                 fput_light(in, fput_in);
 784         }
 785
 786         return error;
 787 }