fs/cachefiles/rdwr.c

   1 /* Storage object read/write
   2  *
   3  * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public Licence
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the Licence, or (at your option) any later version.
  10  */
  11
  12 #include <linux/mount.h>
  13 #include <linux/slab.h>
  14 #include <linux/file.h>
  15 #include <linux/swap.h>
  16 #include "internal.h"
  17
  18 /*
  19  * detect wake up events generated by the unlocking of pages in which we're
  20  * interested
  21  * - we use this to detect read completion of backing pages
  22  * - the caller holds the waitqueue lock
  23  */
  24 static int cachefiles_read_waiter(wait_queue_t *wait, unsigned mode,
  25                                   int sync, void *_key)
  26 {
  27         struct cachefiles_one_read *monitor =
  28                 container_of(wait, struct cachefiles_one_read, monitor);
  29         struct cachefiles_object *object;
  30         struct wait_bit_key *key = _key;
  31         struct page *page = wait->private;
  32
  33         ASSERT(key);
  34
  35         _enter("{%lu},%u,%d,{%p,%u}",
  36                monitor->netfs_page->index, mode, sync,
  37                key->flags, key->bit_nr);
  38
  39         if (key->flags != &page->flags ||
  40             key->bit_nr != PG_locked)
  41                 return 0;
  42
  43         _debug("--- monitor %p %lx ---", page, page->flags);
  44
  45         if (!PageUptodate(page) && !PageError(page)) {
  46                 /* unlocked, not uptodate and not erronous? */
  47                 _debug("page probably truncated");
  48         }
  49
  50         /* remove from the waitqueue */
  51         list_del(&wait->task_list);
  52
  53         /* move onto the action list and queue for FS-Cache thread pool */
  54         ASSERT(monitor->op);
  55
  56         object = container_of(monitor->op->op.object,
  57                               struct cachefiles_object, fscache);
  58
  59         spin_lock(&object->work_lock);
  60         list_add_tail(&monitor->op_link, &monitor->op->to_do);
  61         spin_unlock(&object->work_lock);
  62
  63         fscache_enqueue_retrieval(monitor->op);
  64         return 0;
  65 }
  66
  67 /*
  68  * handle a probably truncated page
  69  * - check to see if the page is still relevant and reissue the read if
  70  *   possible
  71  * - return -EIO on error, -ENODATA if the page is gone, -EINPROGRESS if we
  72  *   must wait again and 0 if successful
  73  */
  74 static int cachefiles_read_reissue(struct cachefiles_object *object,
  75                                    struct cachefiles_one_read *monitor)
  76 {
  77         struct address_space *bmapping = d_backing_inode(object->backer)->i_mapping;
  78         struct page *backpage = monitor->back_page, *backpage2;
  79         int ret;
  80
  81         _enter("{ino=%lx},{%lx,%lx}",
  82                d_backing_inode(object->backer)->i_ino,
  83                backpage->index, backpage->flags);
  84
  85         /* skip if the page was truncated away completely */
  86         if (backpage->mapping != bmapping) {
  87                 _leave(" = -ENODATA [mapping]");
  88                 return -ENODATA;
  89         }
  90
  91         backpage2 = find_get_page(bmapping, backpage->index);
  92         if (!backpage2) {
  93                 _leave(" = -ENODATA [gone]");
  94                 return -ENODATA;
  95         }
  96
  97         if (backpage != backpage2) {
  98                 put_page(backpage2);
  99                 _leave(" = -ENODATA [different]");
 100                 return -ENODATA;
 101         }
 102
 103         /* the page is still there and we already have a ref on it, so we don't
 104          * need a second */
 105         put_page(backpage2);
 106
 107         INIT_LIST_HEAD(&monitor->op_link);
 108         add_page_wait_queue(backpage, &monitor->monitor);
 109
 110         if (trylock_page(backpage)) {
 111                 ret = -EIO;
 112                 if (PageError(backpage))
 113                         goto unlock_discard;
 114                 ret = 0;
 115                 if (PageUptodate(backpage))
 116                         goto unlock_discard;
 117
 118                 _debug("reissue read");
 119                 ret = bmapping->a_ops->readpage(NULL, backpage);
 120                 if (ret < 0)
 121                         goto unlock_discard;
 122         }
 123
 124         /* but the page may have been read before the monitor was installed, so
 125          * the monitor may miss the event - so we have to ensure that we do get
 126          * one in such a case */
 127         if (trylock_page(backpage)) {
 128                 _debug("jumpstart %p {%lx}", backpage, backpage->flags);
 129                 unlock_page(backpage);
 130         }
 131
 132         /* it'll reappear on the todo list */
 133         _leave(" = -EINPROGRESS");
 134         return -EINPROGRESS;
 135
 136 unlock_discard:
 137         unlock_page(backpage);
 138         spin_lock_irq(&object->work_lock);
 139         list_del(&monitor->op_link);
 140         spin_unlock_irq(&object->work_lock);
 141         _leave(" = %d", ret);
 142         return ret;
 143 }
 144
 145 /*
 146  * copy data from backing pages to netfs pages to complete a read operation
 147  * - driven by FS-Cache's thread pool
 148  */
 149 static void cachefiles_read_copier(struct fscache_operation *_op)
 150 {
 151         struct cachefiles_one_read *monitor;
 152         struct cachefiles_object *object;
 153         struct fscache_retrieval *op;
 154         int error, max;
 155
 156         op = container_of(_op, struct fscache_retrieval, op);
 157         object = container_of(op->op.object,
 158                               struct cachefiles_object, fscache);
 159
 160         _enter("{ino=%lu}", d_backing_inode(object->backer)->i_ino);
 161
 162         max = 8;
 163         spin_lock_irq(&object->work_lock);
 164
 165         while (!list_empty(&op->to_do)) {
 166                 monitor = list_entry(op->to_do.next,
 167                                      struct cachefiles_one_read, op_link);
 168                 list_del(&monitor->op_link);
 169
 170                 spin_unlock_irq(&object->work_lock);
 171
 172                 _debug("- copy {%lu}", monitor->back_page->index);
 173
 174         recheck:
 175                 if (test_bit(FSCACHE_COOKIE_INVALIDATING,
 176                              &object->fscache.cookie->flags)) {
 177                         error = -ESTALE;
 178                 } else if (PageUptodate(monitor->back_page)) {
 179                         copy_highpage(monitor->netfs_page, monitor->back_page);
 180                         fscache_mark_page_cached(monitor->op,
 181                                                  monitor->netfs_page);
 182                         error = 0;
 183                 } else if (!PageError(monitor->back_page)) {
 184                         /* the page has probably been truncated */
 185                         error = cachefiles_read_reissue(object, monitor);
 186                         if (error == -EINPROGRESS)
 187                                 goto next;
 188                         goto recheck;
 189                 } else {
 190                         cachefiles_io_error_obj(
 191                                 object,
 192                                 "Readpage failed on backing file %lx",
 193                                 (unsigned long) monitor->back_page->flags);
 194                         error = -EIO;
 195                 }
 196
 197                 put_page(monitor->back_page);
 198
 199                 fscache_end_io(op, monitor->netfs_page, error);
 200                 put_page(monitor->netfs_page);
 201                 fscache_retrieval_complete(op, 1);
 202                 fscache_put_retrieval(op);
 203                 kfree(monitor);
 204
 205         next:
 206                 /* let the thread pool have some air occasionally */
 207                 max--;
 208                 if (max < 0 || need_resched()) {
 209                         if (!list_empty(&op->to_do))
 210                                 fscache_enqueue_retrieval(op);
 211                         _leave(" [maxed out]");
 212                         return;
 213                 }
 214
 215                 spin_lock_irq(&object->work_lock);
 216         }
 217
 218         spin_unlock_irq(&object->work_lock);
 219         _leave("");
 220 }
 221
 222 /*
 223  * read the corresponding page to the given set from the backing file
 224  * - an uncertain page is simply discarded, to be tried again another time
 225  */
 226 static int cachefiles_read_backing_file_one(struct cachefiles_object *object,
 227                                             struct fscache_retrieval *op,
 228                                             struct page *netpage)
 229 {
 230         struct cachefiles_one_read *monitor;
 231         struct address_space *bmapping;
 232         struct page *newpage, *backpage;
 233         int ret;
 234
 235         _enter("");
 236
 237         _debug("read back %p{%lu,%d}",
 238                netpage, netpage->index, page_count(netpage));
 239
 240         monitor = kzalloc(sizeof(*monitor), cachefiles_gfp);
 241         if (!monitor)
 242                 goto nomem;
 243
 244         monitor->netfs_page = netpage;
 245         monitor->op = fscache_get_retrieval(op);
 246
 247         init_waitqueue_func_entry(&monitor->monitor, cachefiles_read_waiter);
 248
 249         /* attempt to get hold of the backing page */
 250         bmapping = d_backing_inode(object->backer)->i_mapping;
 251         newpage = NULL;
 252
 253         for (;;) {
 254                 backpage = find_get_page(bmapping, netpage->index);
 255                 if (backpage)
 256                         goto backing_page_already_present;
 257
 258                 if (!newpage) {
 259                         newpage = __page_cache_alloc(cachefiles_gfp |
 260                                                      __GFP_COLD);
 261                         if (!newpage)
 262                                 goto nomem_monitor;
 263                 }
 264
 265                 ret = add_to_page_cache_lru(newpage, bmapping,
 266                                             netpage->index, cachefiles_gfp);
 267                 if (ret == 0)
 268                         goto installed_new_backing_page;
 269                 if (ret != -EEXIST)
 270                         goto nomem_page;
 271         }
 272
 273         /* we've installed a new backing page, so now we need to start
 274          * it reading */
 275 installed_new_backing_page:
 276         _debug("- new %p", newpage);
 277
 278         backpage = newpage;
 279         newpage = NULL;
 280
 281 read_backing_page:
 282         ret = bmapping->a_ops->readpage(NULL, backpage);
 283         if (ret < 0)
 284                 goto read_error;
 285
 286         /* set the monitor to transfer the data across */
 287 monitor_backing_page:
 288         _debug("- monitor add");
 289
 290         /* install the monitor */
 291         get_page(monitor->netfs_page);
 292         get_page(backpage);
 293         monitor->back_page = backpage;
 294         monitor->monitor.private = backpage;
 295         add_page_wait_queue(backpage, &monitor->monitor);
 296         monitor = NULL;
 297
 298         /* but the page may have been read before the monitor was installed, so
 299          * the monitor may miss the event - so we have to ensure that we do get
 300          * one in such a case */
 301         if (trylock_page(backpage)) {
 302                 _debug("jumpstart %p {%lx}", backpage, backpage->flags);
 303                 unlock_page(backpage);
 304         }
 305         goto success;
 306
 307         /* if the backing page is already present, it can be in one of
 308          * three states: read in progress, read failed or read okay */
 309 backing_page_already_present:
 310         _debug("- present");
 311
 312         if (newpage) {
 313                 put_page(newpage);
 314                 newpage = NULL;
 315         }
 316
 317         if (PageError(backpage))
 318                 goto io_error;
 319
 320         if (PageUptodate(backpage))
 321                 goto backing_page_already_uptodate;
 322
 323         if (!trylock_page(backpage))
 324                 goto monitor_backing_page;
 325         _debug("read %p {%lx}", backpage, backpage->flags);
 326         goto read_backing_page;
 327
 328         /* the backing page is already up to date, attach the netfs
 329          * page to the pagecache and LRU and copy the data across */
 330 backing_page_already_uptodate:
 331         _debug("- uptodate");
 332
 333         fscache_mark_page_cached(op, netpage);
 334
 335         copy_highpage(netpage, backpage);
 336         fscache_end_io(op, netpage, 0);
 337         fscache_retrieval_complete(op, 1);
 338
 339 success:
 340         _debug("success");
 341         ret = 0;
 342
 343 out:
 344         if (backpage)
 345                 put_page(backpage);
 346         if (monitor) {
 347                 fscache_put_retrieval(monitor->op);
 348                 kfree(monitor);
 349         }
 350         _leave(" = %d", ret);
 351         return ret;
 352
 353 read_error:
 354         _debug("read error %d", ret);
 355         if (ret == -ENOMEM) {
 356                 fscache_retrieval_complete(op, 1);
 357                 goto out;
 358         }
 359 io_error:
 360         cachefiles_io_error_obj(object, "Page read error on backing file");
 361         fscache_retrieval_complete(op, 1);
 362         ret = -ENOBUFS;
 363         goto out;
 364
 365 nomem_page:
 366         put_page(newpage);
 367 nomem_monitor:
 368         fscache_put_retrieval(monitor->op);
 369         kfree(monitor);
 370 nomem:
 371         fscache_retrieval_complete(op, 1);
 372         _leave(" = -ENOMEM");
 373         return -ENOMEM;
 374 }
 375
 376 /*
 377  * read a page from the cache or allocate a block in which to store it
 378  * - cache withdrawal is prevented by the caller
 379  * - returns -EINTR if interrupted
 380  * - returns -ENOMEM if ran out of memory
 381  * - returns -ENOBUFS if no buffers can be made available
 382  * - returns -ENOBUFS if page is beyond EOF
 383  * - if the page is backed by a block in the cache:
 384  *   - a read will be started which will call the callback on completion
 385  *   - 0 will be returned
 386  * - else if the page is unbacked:
 387  *   - the metadata will be retained
 388  *   - -ENODATA will be returned
 389  */
 390 int cachefiles_read_or_alloc_page(struct fscache_retrieval *op,
 391                                   struct page *page,
 392                                   gfp_t gfp)
 393 {
 394         struct cachefiles_object *object;
 395         struct cachefiles_cache *cache;
 396         struct inode *inode;
 397         sector_t block0, block;
 398         unsigned shift;
 399         int ret;
 400
 401         object = container_of(op->op.object,
 402                               struct cachefiles_object, fscache);
 403         cache = container_of(object->fscache.cache,
 404                              struct cachefiles_cache, cache);
 405
 406         _enter("{%p},{%lx},,,", object, page->index);
 407
 408         if (!object->backer)
 409                 goto enobufs;
 410
 411         inode = d_backing_inode(object->backer);
 412         ASSERT(S_ISREG(inode->i_mode));
 413         ASSERT(inode->i_mapping->a_ops->bmap);
 414         ASSERT(inode->i_mapping->a_ops->readpages);
 415
 416         /* calculate the shift required to use bmap */
 417         shift = PAGE_SHIFT - inode->i_sb->s_blocksize_bits;
 418
 419         op->op.flags &= FSCACHE_OP_KEEP_FLAGS;
 420         op->op.flags |= FSCACHE_OP_ASYNC;
 421         op->op.processor = cachefiles_read_copier;
 422
 423         /* we assume the absence or presence of the first block is a good
 424          * enough indication for the page as a whole
 425          * - TODO: don't use bmap() for this as it is _not_ actually good
 426          *   enough for this as it doesn't indicate errors, but it's all we've
 427          *   got for the moment
 428          */
 429         block0 = page->index;
 430         block0 <<= shift;
 431
 432         block = inode->i_mapping->a_ops->bmap(inode->i_mapping, block0);
 433         _debug("%llx -> %llx",
 434                (unsigned long long) block0,
 435                (unsigned long long) block);
 436
 437         if (block) {
 438                 /* submit the apparently valid page to the backing fs to be
 439                  * read from disk */
 440                 ret = cachefiles_read_backing_file_one(object, op, page);
 441         } else if (cachefiles_has_space(cache, 0, 1) == 0) {
 442                 /* there's space in the cache we can use */
 443                 fscache_mark_page_cached(op, page);
 444                 fscache_retrieval_complete(op, 1);
 445                 ret = -ENODATA;
 446         } else {
 447                 goto enobufs;
 448         }
 449
 450         _leave(" = %d", ret);
 451         return ret;
 452
 453 enobufs:
 454         fscache_retrieval_complete(op, 1);
 455         _leave(" = -ENOBUFS");
 456         return -ENOBUFS;
 457 }
 458
 459 /*
 460  * read the corresponding pages to the given set from the backing file
 461  * - any uncertain pages are simply discarded, to be tried again another time
 462  */
 463 static int cachefiles_read_backing_file(struct cachefiles_object *object,
 464                                         struct fscache_retrieval *op,
 465                                         struct list_head *list)
 466 {
 467         struct cachefiles_one_read *monitor = NULL;
 468         struct address_space *bmapping = d_backing_inode(object->backer)->i_mapping;
 469         struct page *newpage = NULL, *netpage, *_n, *backpage = NULL;
 470         int ret = 0;
 471
 472         _enter("");
 473
 474         list_for_each_entry_safe(netpage, _n, list, lru) {
 475                 list_del(&netpage->lru);
 476
 477                 _debug("read back %p{%lu,%d}",
 478                        netpage, netpage->index, page_count(netpage));
 479
 480                 if (!monitor) {
 481                         monitor = kzalloc(sizeof(*monitor), cachefiles_gfp);
 482                         if (!monitor)
 483                                 goto nomem;
 484
 485                         monitor->op = fscache_get_retrieval(op);
 486                         init_waitqueue_func_entry(&monitor->monitor,
 487                                                   cachefiles_read_waiter);
 488                 }
 489
 490                 for (;;) {
 491                         backpage = find_get_page(bmapping, netpage->index);
 492                         if (backpage)
 493                                 goto backing_page_already_present;
 494
 495                         if (!newpage) {
 496                                 newpage = __page_cache_alloc(cachefiles_gfp |
 497                                                              __GFP_COLD);
 498                                 if (!newpage)
 499                                         goto nomem;
 500                         }
 501
 502                         ret = add_to_page_cache_lru(newpage, bmapping,
 503                                                     netpage->index,
 504                                                     cachefiles_gfp);
 505                         if (ret == 0)
 506                                 goto installed_new_backing_page;
 507                         if (ret != -EEXIST)
 508                                 goto nomem;
 509                 }
 510
 511                 /* we've installed a new backing page, so now we need
 512                  * to start it reading */
 513         installed_new_backing_page:
 514                 _debug("- new %p", newpage);
 515
 516                 backpage = newpage;
 517                 newpage = NULL;
 518
 519         reread_backing_page:
 520                 ret = bmapping->a_ops->readpage(NULL, backpage);
 521                 if (ret < 0)
 522                         goto read_error;
 523
 524                 /* add the netfs page to the pagecache and LRU, and set the
 525                  * monitor to transfer the data across */
 526         monitor_backing_page:
 527                 _debug("- monitor add");
 528
 529                 ret = add_to_page_cache_lru(netpage, op->mapping,
 530                                             netpage->index, cachefiles_gfp);
 531                 if (ret < 0) {
 532                         if (ret == -EEXIST) {
 533                                 put_page(netpage);
 534                                 fscache_retrieval_complete(op, 1);
 535                                 continue;
 536                         }
 537                         goto nomem;
 538                 }
 539
 540                 /* install a monitor */
 541                 get_page(netpage);
 542                 monitor->netfs_page = netpage;
 543
 544                 get_page(backpage);
 545                 monitor->back_page = backpage;
 546                 monitor->monitor.private = backpage;
 547                 add_page_wait_queue(backpage, &monitor->monitor);
 548                 monitor = NULL;
 549
 550                 /* but the page may have been read before the monitor was
 551                  * installed, so the monitor may miss the event - so we have to
 552                  * ensure that we do get one in such a case */
 553                 if (trylock_page(backpage)) {
 554                         _debug("2unlock %p {%lx}", backpage, backpage->flags);
 555                         unlock_page(backpage);
 556                 }
 557
 558                 put_page(backpage);
 559                 backpage = NULL;
 560
 561                 put_page(netpage);
 562                 netpage = NULL;
 563                 continue;
 564
 565                 /* if the backing page is already present, it can be in one of
 566                  * three states: read in progress, read failed or read okay */
 567         backing_page_already_present:
 568                 _debug("- present %p", backpage);
 569
 570                 if (PageError(backpage))
 571                         goto io_error;
 572
 573                 if (PageUptodate(backpage))
 574                         goto backing_page_already_uptodate;
 575
 576                 _debug("- not ready %p{%lx}", backpage, backpage->flags);
 577
 578                 if (!trylock_page(backpage))
 579                         goto monitor_backing_page;
 580
 581                 if (PageError(backpage)) {
 582                         _debug("error %lx", backpage->flags);
 583                         unlock_page(backpage);
 584                         goto io_error;
 585                 }
 586
 587                 if (PageUptodate(backpage))
 588                         goto backing_page_already_uptodate_unlock;
 589
 590                 /* we've locked a page that's neither up to date nor erroneous,
 591                  * so we need to attempt to read it again */
 592                 goto reread_backing_page;
 593
 594                 /* the backing page is already up to date, attach the netfs
 595                  * page to the pagecache and LRU and copy the data across */
 596         backing_page_already_uptodate_unlock:
 597                 _debug("uptodate %lx", backpage->flags);
 598                 unlock_page(backpage);
 599         backing_page_already_uptodate:
 600                 _debug("- uptodate");
 601
 602                 ret = add_to_page_cache_lru(netpage, op->mapping,
 603                                             netpage->index, cachefiles_gfp);
 604                 if (ret < 0) {
 605                         if (ret == -EEXIST) {
 606                                 put_page(netpage);
 607                                 fscache_retrieval_complete(op, 1);
 608                                 continue;
 609                         }
 610                         goto nomem;
 611                 }
 612
 613                 copy_highpage(netpage, backpage);
 614
 615                 put_page(backpage);
 616                 backpage = NULL;
 617
 618                 fscache_mark_page_cached(op, netpage);
 619
 620                 /* the netpage is unlocked and marked up to date here */
 621                 fscache_end_io(op, netpage, 0);
 622                 put_page(netpage);
 623                 netpage = NULL;
 624                 fscache_retrieval_complete(op, 1);
 625                 continue;
 626         }
 627
 628         netpage = NULL;
 629
 630         _debug("out");
 631
 632 out:
 633         /* tidy up */
 634         if (newpage)
 635                 put_page(newpage);
 636         if (netpage)
 637                 put_page(netpage);
 638         if (backpage)
 639                 put_page(backpage);
 640         if (monitor) {
 641                 fscache_put_retrieval(op);
 642                 kfree(monitor);
 643         }
 644
 645         list_for_each_entry_safe(netpage, _n, list, lru) {
 646                 list_del(&netpage->lru);
 647                 put_page(netpage);
 648                 fscache_retrieval_complete(op, 1);
 649         }
 650
 651         _leave(" = %d", ret);
 652         return ret;
 653
 654 nomem:
 655         _debug("nomem");
 656         ret = -ENOMEM;
 657         goto record_page_complete;
 658
 659 read_error:
 660         _debug("read error %d", ret);
 661         if (ret == -ENOMEM)
 662                 goto record_page_complete;
 663 io_error:
 664         cachefiles_io_error_obj(object, "Page read error on backing file");
 665         ret = -ENOBUFS;
 666 record_page_complete:
 667         fscache_retrieval_complete(op, 1);
 668         goto out;
 669 }
 670
 671 /*
 672  * read a list of pages from the cache or allocate blocks in which to store
 673  * them
 674  */
 675 int cachefiles_read_or_alloc_pages(struct fscache_retrieval *op,
 676                                    struct list_head *pages,
 677                                    unsigned *nr_pages,
 678                                    gfp_t gfp)
 679 {
 680         struct cachefiles_object *object;
 681         struct cachefiles_cache *cache;
 682         struct list_head backpages;
 683         struct pagevec pagevec;
 684         struct inode *inode;
 685         struct page *page, *_n;
 686         unsigned shift, nrbackpages;
 687         int ret, ret2, space;
 688
 689         object = container_of(op->op.object,
 690                               struct cachefiles_object, fscache);
 691         cache = container_of(object->fscache.cache,
 692                              struct cachefiles_cache, cache);
 693
 694         _enter("{OBJ%x,%d},,%d,,",
 695                object->fscache.debug_id, atomic_read(&op->op.usage),
 696                *nr_pages);
 697
 698         if (!object->backer)
 699                 goto all_enobufs;
 700
 701         space = 1;
 702         if (cachefiles_has_space(cache, 0, *nr_pages) < 0)
 703                 space = 0;
 704
 705         inode = d_backing_inode(object->backer);
 706         ASSERT(S_ISREG(inode->i_mode));
 707         ASSERT(inode->i_mapping->a_ops->bmap);
 708         ASSERT(inode->i_mapping->a_ops->readpages);
 709
 710         /* calculate the shift required to use bmap */
 711         shift = PAGE_SHIFT - inode->i_sb->s_blocksize_bits;
 712
 713         pagevec_init(&pagevec, 0);
 714
 715         op->op.flags &= FSCACHE_OP_KEEP_FLAGS;
 716         op->op.flags |= FSCACHE_OP_ASYNC;
 717         op->op.processor = cachefiles_read_copier;
 718
 719         INIT_LIST_HEAD(&backpages);
 720         nrbackpages = 0;
 721
 722         ret = space ? -ENODATA : -ENOBUFS;
 723         list_for_each_entry_safe(page, _n, pages, lru) {
 724                 sector_t block0, block;
 725
 726                 /* we assume the absence or presence of the first block is a
 727                  * good enough indication for the page as a whole
 728                  * - TODO: don't use bmap() for this as it is _not_ actually
 729                  *   good enough for this as it doesn't indicate errors, but
 730                  *   it's all we've got for the moment
 731                  */
 732                 block0 = page->index;
 733                 block0 <<= shift;
 734
 735                 block = inode->i_mapping->a_ops->bmap(inode->i_mapping,
 736                                                       block0);
 737                 _debug("%llx -> %llx",
 738                        (unsigned long long) block0,
 739                        (unsigned long long) block);
 740
 741                 if (block) {
 742                         /* we have data - add it to the list to give to the
 743                          * backing fs */
 744                         list_move(&page->lru, &backpages);
 745                         (*nr_pages)--;
 746                         nrbackpages++;
 747                 } else if (space && pagevec_add(&pagevec, page) == 0) {
 748                         fscache_mark_pages_cached(op, &pagevec);
 749                         fscache_retrieval_complete(op, 1);
 750                         ret = -ENODATA;
 751                 } else {
 752                         fscache_retrieval_complete(op, 1);
 753                 }
 754         }
 755
 756         if (pagevec_count(&pagevec) > 0)
 757                 fscache_mark_pages_cached(op, &pagevec);
 758
 759         if (list_empty(pages))
 760                 ret = 0;
 761
 762         /* submit the apparently valid pages to the backing fs to be read from
 763          * disk */
 764         if (nrbackpages > 0) {
 765                 ret2 = cachefiles_read_backing_file(object, op, &backpages);
 766                 if (ret2 == -ENOMEM || ret2 == -EINTR)
 767                         ret = ret2;
 768         }
 769
 770         _leave(" = %d [nr=%u%s]",
 771                ret, *nr_pages, list_empty(pages) ? " empty" : "");
 772         return ret;
 773
 774 all_enobufs:
 775         fscache_retrieval_complete(op, *nr_pages);
 776         return -ENOBUFS;
 777 }
 778
 779 /*
 780  * allocate a block in the cache in which to store a page
 781  * - cache withdrawal is prevented by the caller
 782  * - returns -EINTR if interrupted
 783  * - returns -ENOMEM if ran out of memory
 784  * - returns -ENOBUFS if no buffers can be made available
 785  * - returns -ENOBUFS if page is beyond EOF
 786  * - otherwise:
 787  *   - the metadata will be retained
 788  *   - 0 will be returned
 789  */
 790 int cachefiles_allocate_page(struct fscache_retrieval *op,
 791                              struct page *page,
 792                              gfp_t gfp)
 793 {
 794         struct cachefiles_object *object;
 795         struct cachefiles_cache *cache;
 796         int ret;
 797
 798         object = container_of(op->op.object,
 799                               struct cachefiles_object, fscache);
 800         cache = container_of(object->fscache.cache,
 801                              struct cachefiles_cache, cache);
 802
 803         _enter("%p,{%lx},", object, page->index);
 804
 805         ret = cachefiles_has_space(cache, 0, 1);
 806         if (ret == 0)
 807                 fscache_mark_page_cached(op, page);
 808         else
 809                 ret = -ENOBUFS;
 810
 811         fscache_retrieval_complete(op, 1);
 812         _leave(" = %d", ret);
 813         return ret;
 814 }
 815
 816 /*
 817  * allocate blocks in the cache in which to store a set of pages
 818  * - cache withdrawal is prevented by the caller
 819  * - returns -EINTR if interrupted
 820  * - returns -ENOMEM if ran out of memory
 821  * - returns -ENOBUFS if some buffers couldn't be made available
 822  * - returns -ENOBUFS if some pages are beyond EOF
 823  * - otherwise:
 824  *   - -ENODATA will be returned
 825  * - metadata will be retained for any page marked
 826  */
 827 int cachefiles_allocate_pages(struct fscache_retrieval *op,
 828                               struct list_head *pages,
 829                               unsigned *nr_pages,
 830                               gfp_t gfp)
 831 {
 832         struct cachefiles_object *object;
 833         struct cachefiles_cache *cache;
 834         struct pagevec pagevec;
 835         struct page *page;
 836         int ret;
 837
 838         object = container_of(op->op.object,
 839                               struct cachefiles_object, fscache);
 840         cache = container_of(object->fscache.cache,
 841                              struct cachefiles_cache, cache);
 842
 843         _enter("%p,,,%d,", object, *nr_pages);
 844
 845         ret = cachefiles_has_space(cache, 0, *nr_pages);
 846         if (ret == 0) {
 847                 pagevec_init(&pagevec, 0);
 848
 849                 list_for_each_entry(page, pages, lru) {
 850                         if (pagevec_add(&pagevec, page) == 0)
 851                                 fscache_mark_pages_cached(op, &pagevec);
 852                 }
 853
 854                 if (pagevec_count(&pagevec) > 0)
 855                         fscache_mark_pages_cached(op, &pagevec);
 856                 ret = -ENODATA;
 857         } else {
 858                 ret = -ENOBUFS;
 859         }
 860
 861         fscache_retrieval_complete(op, *nr_pages);
 862         _leave(" = %d", ret);
 863         return ret;
 864 }
 865
 866 /*
 867  * request a page be stored in the cache
 868  * - cache withdrawal is prevented by the caller
 869  * - this request may be ignored if there's no cache block available, in which
 870  *   case -ENOBUFS will be returned
 871  * - if the op is in progress, 0 will be returned
 872  */
 873 int cachefiles_write_page(struct fscache_storage *op, struct page *page)
 874 {
 875         struct cachefiles_object *object;
 876         struct cachefiles_cache *cache;
 877         struct file *file;
 878         struct path path;
 879         loff_t pos, eof;
 880         size_t len;
 881         void *data;
 882         int ret = -ENOBUFS;
 883
 884         ASSERT(op != NULL);
 885         ASSERT(page != NULL);
 886
 887         object = container_of(op->op.object,
 888                               struct cachefiles_object, fscache);
 889
 890         _enter("%p,%p{%lx},,,", object, page, page->index);
 891
 892         if (!object->backer) {
 893                 _leave(" = -ENOBUFS");
 894                 return -ENOBUFS;
 895         }
 896
 897         ASSERT(d_is_reg(object->backer));
 898
 899         cache = container_of(object->fscache.cache,
 900                              struct cachefiles_cache, cache);
 901
 902         pos = (loff_t)page->index << PAGE_SHIFT;
 903
 904         /* We mustn't write more data than we have, so we have to beware of a
 905          * partial page at EOF.
 906          */
 907         eof = object->fscache.store_limit_l;
 908         if (pos >= eof)
 909                 goto error;
 910
 911         /* write the page to the backing filesystem and let it store it in its
 912          * own time */
 913         path.mnt = cache->mnt;
 914         path.dentry = object->backer;
 915         file = dentry_open(&path, O_RDWR | O_LARGEFILE, cache->cache_cred);
 916         if (IS_ERR(file)) {
 917                 ret = PTR_ERR(file);
 918                 goto error_2;
 919         }
 920
 921         len = PAGE_SIZE;
 922         if (eof & ~PAGE_MASK) {
 923                 if (eof - pos < PAGE_SIZE) {
 924                         _debug("cut short %llx to %llx",
 925                                pos, eof);
 926                         len = eof - pos;
 927                         ASSERTCMP(pos + len, ==, eof);
 928                 }
 929         }
 930
 931         data = kmap(page);
 932         ret = __kernel_write(file, data, len, &pos);
 933         kunmap(page);
 934         fput(file);
 935         if (ret != len)
 936                 goto error_eio;
 937
 938         _leave(" = 0");
 939         return 0;
 940
 941 error_eio:
 942         ret = -EIO;
 943 error_2:
 944         if (ret == -EIO)
 945                 cachefiles_io_error_obj(object,
 946                                         "Write page to backing file failed");
 947 error:
 948         _leave(" = -ENOBUFS [%d]", ret);
 949         return -ENOBUFS;
 950 }
 951
 952 /*
 953  * detach a backing block from a page
 954  * - cache withdrawal is prevented by the caller
 955  */
 956 void cachefiles_uncache_page(struct fscache_object *_object, struct page *page)
 957 {
 958         struct cachefiles_object *object;
 959         struct cachefiles_cache *cache;
 960
 961         object = container_of(_object, struct cachefiles_object, fscache);
 962         cache = container_of(object->fscache.cache,
 963                              struct cachefiles_cache, cache);
 964
 965         _enter("%p,{%lu}", object, page->index);
 966
 967         spin_unlock(&object->fscache.cookie->lock);
 968 }