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/file.h>
  14 #include "internal.h"
  15
  16 /*
  17  * detect wake up events generated by the unlocking of pages in which we're
  18  * interested
  19  * - we use this to detect read completion of backing pages
  20  * - the caller holds the waitqueue lock
  21  */
  22 static int cachefiles_read_waiter(wait_queue_t *wait, unsigned mode,
  23                                   int sync, void *_key)
  24 {
  25         struct cachefiles_one_read *monitor =
  26                 container_of(wait, struct cachefiles_one_read, monitor);
  27         struct cachefiles_object *object;
  28         struct wait_bit_key *key = _key;
  29         struct page *page = wait->private;
  30
  31         ASSERT(key);
  32
  33         _enter("{%lu},%u,%d,{%p,%u}",
  34                monitor->netfs_page->index, mode, sync,
  35                key->flags, key->bit_nr);
  36
  37         if (key->flags != &page->flags ||
  38             key->bit_nr != PG_locked)
  39                 return 0;
  40
  41         _debug("--- monitor %p %lx ---", page, page->flags);
  42
  43         if (!PageUptodate(page) && !PageError(page)) {
  44                 /* unlocked, not uptodate and not erronous? */
  45                 _debug("page probably truncated");
  46         }
  47
  48         /* remove from the waitqueue */
  49         list_del(&wait->task_list);
  50
  51         /* move onto the action list and queue for FS-Cache thread pool */
  52         ASSERT(monitor->op);
  53
  54         object = container_of(monitor->op->op.object,
  55                               struct cachefiles_object, fscache);
  56
  57         spin_lock(&object->work_lock);
  58         list_add_tail(&monitor->op_link, &monitor->op->to_do);
  59         spin_unlock(&object->work_lock);
  60
  61         fscache_enqueue_retrieval(monitor->op);
  62         return 0;
  63 }
  64
  65 /*
  66  * handle a probably truncated page
  67  * - check to see if the page is still relevant and reissue the read if
  68  *   possible
  69  * - return -EIO on error, -ENODATA if the page is gone, -EINPROGRESS if we
  70  *   must wait again and 0 if successful
  71  */
  72 static int cachefiles_read_reissue(struct cachefiles_object *object,
  73                                    struct cachefiles_one_read *monitor)
  74 {
  75         struct address_space *bmapping = object->backer->d_inode->i_mapping;
  76         struct page *backpage = monitor->back_page, *backpage2;
  77         int ret;
  78
  79         kenter("{ino=%lx},{%lx,%lx}",
  80                object->backer->d_inode->i_ino,
  81                backpage->index, backpage->flags);
  82
  83         /* skip if the page was truncated away completely */
  84         if (backpage->mapping != bmapping) {
  85                 kleave(" = -ENODATA [mapping]");
  86                 return -ENODATA;
  87         }
  88
  89         backpage2 = find_get_page(bmapping, backpage->index);
  90         if (!backpage2) {
  91                 kleave(" = -ENODATA [gone]");
  92                 return -ENODATA;
  93         }
  94
  95         if (backpage != backpage2) {
  96                 put_page(backpage2);
  97                 kleave(" = -ENODATA [different]");
  98                 return -ENODATA;
  99         }
 100
 101         /* the page is still there and we already have a ref on it, so we don't
 102          * need a second */
 103         put_page(backpage2);
 104
 105         INIT_LIST_HEAD(&monitor->op_link);
 106         add_page_wait_queue(backpage, &monitor->monitor);
 107
 108         if (trylock_page(backpage)) {
 109                 ret = -EIO;
 110                 if (PageError(backpage))
 111                         goto unlock_discard;
 112                 ret = 0;
 113                 if (PageUptodate(backpage))
 114                         goto unlock_discard;
 115
 116                 kdebug("reissue read");
 117                 ret = bmapping->a_ops->readpage(NULL, backpage);
 118                 if (ret < 0)
 119                         goto unlock_discard;
 120         }
 121
 122         /* but the page may have been read before the monitor was installed, so
 123          * the monitor may miss the event - so we have to ensure that we do get
 124          * one in such a case */
 125         if (trylock_page(backpage)) {
 126                 _debug("jumpstart %p {%lx}", backpage, backpage->flags);
 127                 unlock_page(backpage);
 128         }
 129
 130         /* it'll reappear on the todo list */
 131         kleave(" = -EINPROGRESS");
 132         return -EINPROGRESS;
 133
 134 unlock_discard:
 135         unlock_page(backpage);
 136         spin_lock_irq(&object->work_lock);
 137         list_del(&monitor->op_link);
 138         spin_unlock_irq(&object->work_lock);
 139         kleave(" = %d", ret);
 140         return ret;
 141 }
 142
 143 /*
 144  * copy data from backing pages to netfs pages to complete a read operation
 145  * - driven by FS-Cache's thread pool
 146  */
 147 static void cachefiles_read_copier(struct fscache_operation *_op)
 148 {
 149         struct cachefiles_one_read *monitor;
 150         struct cachefiles_object *object;
 151         struct fscache_retrieval *op;
 152         struct pagevec pagevec;
 153         int error, max;
 154
 155         op = container_of(_op, struct fscache_retrieval, op);
 156         object = container_of(op->op.object,
 157                               struct cachefiles_object, fscache);
 158
 159         _enter("{ino=%lu}", object->backer->d_inode->i_ino);
 160
 161         pagevec_init(&pagevec, 0);
 162
 163         max = 8;
 164         spin_lock_irq(&object->work_lock);
 165
 166         while (!list_empty(&op->to_do)) {
 167                 monitor = list_entry(op->to_do.next,
 168                                      struct cachefiles_one_read, op_link);
 169                 list_del(&monitor->op_link);
 170
 171                 spin_unlock_irq(&object->work_lock);
 172
 173                 _debug("- copy {%lu}", monitor->back_page->index);
 174
 175         recheck:
 176                 if (PageUptodate(monitor->back_page)) {
 177                         copy_highpage(monitor->netfs_page, monitor->back_page);
 178
 179                         pagevec_add(&pagevec, monitor->netfs_page);
 180                         fscache_mark_pages_cached(monitor->op, &pagevec);
 181                         error = 0;
 182                 } else if (!PageError(monitor->back_page)) {
 183                         /* the page has probably been truncated */
 184                         error = cachefiles_read_reissue(object, monitor);
 185                         if (error == -EINPROGRESS)
 186                                 goto next;
 187                         goto recheck;
 188                 } else {
 189                         cachefiles_io_error_obj(
 190                                 object,
 191                                 "Readpage failed on backing file %lx",
 192                                 (unsigned long) monitor->back_page->flags);
 193                         error = -EIO;
 194                 }
 195
 196                 page_cache_release(monitor->back_page);
 197
 198                 fscache_end_io(op, monitor->netfs_page, error);
 199                 page_cache_release(monitor->netfs_page);
 200                 fscache_put_retrieval(op);
 201                 kfree(monitor);
 202
 203         next:
 204                 /* let the thread pool have some air occasionally */
 205                 max--;
 206                 if (max < 0 || need_resched()) {
 207                         if (!list_empty(&op->to_do))
 208                                 fscache_enqueue_retrieval(op);
 209                         _leave(" [maxed out]");
 210                         return;
 211                 }
 212
 213                 spin_lock_irq(&object->work_lock);
 214         }
 215
 216         spin_unlock_irq(&object->work_lock);
 217         _leave("");
 218 }
 219
 220 /*
 221  * read the corresponding page to the given set from the backing file
 222  * - an uncertain page is simply discarded, to be tried again another time
 223  */
 224 static int cachefiles_read_backing_file_one(struct cachefiles_object *object,
 225                                             struct fscache_retrieval *op,
 226                                             struct page *netpage,
 227                                             struct pagevec *pagevec)
 228 {
 229         struct cachefiles_one_read *monitor;
 230         struct address_space *bmapping;
 231         struct page *newpage, *backpage;
 232         int ret;
 233
 234         _enter("");
 235
 236         pagevec_reinit(pagevec);
 237
 238         _debug("read back %p{%lu,%d}",
 239                netpage, netpage->index, page_count(netpage));
 240
 241         monitor = kzalloc(sizeof(*monitor), GFP_KERNEL);
 242         if (!monitor)
 243                 goto nomem;
 244
 245         monitor->netfs_page = netpage;
 246         monitor->op = fscache_get_retrieval(op);
 247
 248         init_waitqueue_func_entry(&monitor->monitor, cachefiles_read_waiter);
 249
 250         /* attempt to get hold of the backing page */
 251         bmapping = object->backer->d_inode->i_mapping;
 252         newpage = NULL;
 253
 254         for (;;) {
 255                 backpage = find_get_page(bmapping, netpage->index);
 256                 if (backpage)
 257                         goto backing_page_already_present;
 258
 259                 if (!newpage) {
 260                         newpage = page_cache_alloc_cold(bmapping);
 261                         if (!newpage)
 262                                 goto nomem_monitor;
 263                 }
 264
 265                 ret = add_to_page_cache(newpage, bmapping,
 266                                         netpage->index, GFP_KERNEL);
 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 add it
 274          * to the LRU list and start it reading */
 275 installed_new_backing_page:
 276         _debug("- new %p", newpage);
 277
 278         backpage = newpage;
 279         newpage = NULL;
 280
 281         page_cache_get(backpage);
 282         pagevec_add(pagevec, backpage);
 283         __pagevec_lru_add_file(pagevec);
 284
 285 read_backing_page:
 286         ret = bmapping->a_ops->readpage(NULL, backpage);
 287         if (ret < 0)
 288                 goto read_error;
 289
 290         /* set the monitor to transfer the data across */
 291 monitor_backing_page:
 292         _debug("- monitor add");
 293
 294         /* install the monitor */
 295         page_cache_get(monitor->netfs_page);
 296         page_cache_get(backpage);
 297         monitor->back_page = backpage;
 298         monitor->monitor.private = backpage;
 299         add_page_wait_queue(backpage, &monitor->monitor);
 300         monitor = NULL;
 301
 302         /* but the page may have been read before the monitor was installed, so
 303          * the monitor may miss the event - so we have to ensure that we do get
 304          * one in such a case */
 305         if (trylock_page(backpage)) {
 306                 _debug("jumpstart %p {%lx}", backpage, backpage->flags);
 307                 unlock_page(backpage);
 308         }
 309         goto success;
 310
 311         /* if the backing page is already present, it can be in one of
 312          * three states: read in progress, read failed or read okay */
 313 backing_page_already_present:
 314         _debug("- present");
 315
 316         if (newpage) {
 317                 page_cache_release(newpage);
 318                 newpage = NULL;
 319         }
 320
 321         if (PageError(backpage))
 322                 goto io_error;
 323
 324         if (PageUptodate(backpage))
 325                 goto backing_page_already_uptodate;
 326
 327         if (!trylock_page(backpage))
 328                 goto monitor_backing_page;
 329         _debug("read %p {%lx}", backpage, backpage->flags);
 330         goto read_backing_page;
 331
 332         /* the backing page is already up to date, attach the netfs
 333          * page to the pagecache and LRU and copy the data across */
 334 backing_page_already_uptodate:
 335         _debug("- uptodate");
 336
 337         pagevec_add(pagevec, netpage);
 338         fscache_mark_pages_cached(op, pagevec);
 339
 340         copy_highpage(netpage, backpage);
 341         fscache_end_io(op, netpage, 0);
 342
 343 success:
 344         _debug("success");
 345         ret = 0;
 346
 347 out:
 348         if (backpage)
 349                 page_cache_release(backpage);
 350         if (monitor) {
 351                 fscache_put_retrieval(monitor->op);
 352                 kfree(monitor);
 353         }
 354         _leave(" = %d", ret);
 355         return ret;
 356
 357 read_error:
 358         _debug("read error %d", ret);
 359         if (ret == -ENOMEM)
 360                 goto out;
 361 io_error:
 362         cachefiles_io_error_obj(object, "Page read error on backing file");
 363         ret = -ENOBUFS;
 364         goto out;
 365
 366 nomem_page:
 367         page_cache_release(newpage);
 368 nomem_monitor:
 369         fscache_put_retrieval(monitor->op);
 370         kfree(monitor);
 371 nomem:
 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 pagevec pagevec;
 397         struct inode *inode;
 398         sector_t block0, block;
 399         unsigned shift;
 400         int ret;
 401
 402         object = container_of(op->op.object,
 403                               struct cachefiles_object, fscache);
 404         cache = container_of(object->fscache.cache,
 405                              struct cachefiles_cache, cache);
 406
 407         _enter("{%p},{%lx},,,", object, page->index);
 408
 409         if (!object->backer)
 410                 return -ENOBUFS;
 411
 412         inode = object->backer->d_inode;
 413         ASSERT(S_ISREG(inode->i_mode));
 414         ASSERT(inode->i_mapping->a_ops->bmap);
 415         ASSERT(inode->i_mapping->a_ops->readpages);
 416
 417         /* calculate the shift required to use bmap */
 418         if (inode->i_sb->s_blocksize > PAGE_SIZE)
 419                 return -ENOBUFS;
 420
 421         shift = PAGE_SHIFT - inode->i_sb->s_blocksize_bits;
 422
 423         op->op.flags &= FSCACHE_OP_KEEP_FLAGS;
 424         op->op.flags |= FSCACHE_OP_FAST;
 425         op->op.processor = cachefiles_read_copier;
 426
 427         pagevec_init(&pagevec, 0);
 428
 429         /* we assume the absence or presence of the first block is a good
 430          * enough indication for the page as a whole
 431          * - TODO: don't use bmap() for this as it is _not_ actually good
 432          *   enough for this as it doesn't indicate errors, but it's all we've
 433          *   got for the moment
 434          */
 435         block0 = page->index;
 436         block0 <<= shift;
 437
 438         block = inode->i_mapping->a_ops->bmap(inode->i_mapping, block0);
 439         _debug("%llx -> %llx",
 440                (unsigned long long) block0,
 441                (unsigned long long) block);
 442
 443         if (block) {
 444                 /* submit the apparently valid page to the backing fs to be
 445                  * read from disk */
 446                 ret = cachefiles_read_backing_file_one(object, op, page,
 447                                                        &pagevec);
 448         } else if (cachefiles_has_space(cache, 0, 1) == 0) {
 449                 /* there's space in the cache we can use */
 450                 pagevec_add(&pagevec, page);
 451                 fscache_mark_pages_cached(op, &pagevec);
 452                 ret = -ENODATA;
 453         } else {
 454                 ret = -ENOBUFS;
 455         }
 456
 457         _leave(" = %d", ret);
 458         return ret;
 459 }
 460
 461 /*
 462  * read the corresponding pages to the given set from the backing file
 463  * - any uncertain pages are simply discarded, to be tried again another time
 464  */
 465 static int cachefiles_read_backing_file(struct cachefiles_object *object,
 466                                         struct fscache_retrieval *op,
 467                                         struct list_head *list,
 468                                         struct pagevec *mark_pvec)
 469 {
 470         struct cachefiles_one_read *monitor = NULL;
 471         struct address_space *bmapping = object->backer->d_inode->i_mapping;
 472         struct pagevec lru_pvec;
 473         struct page *newpage = NULL, *netpage, *_n, *backpage = NULL;
 474         int ret = 0;
 475
 476         _enter("");
 477
 478         pagevec_init(&lru_pvec, 0);
 479
 480         list_for_each_entry_safe(netpage, _n, list, lru) {
 481                 list_del(&netpage->lru);
 482
 483                 _debug("read back %p{%lu,%d}",
 484                        netpage, netpage->index, page_count(netpage));
 485
 486                 if (!monitor) {
 487                         monitor = kzalloc(sizeof(*monitor), GFP_KERNEL);
 488                         if (!monitor)
 489                                 goto nomem;
 490
 491                         monitor->op = fscache_get_retrieval(op);
 492                         init_waitqueue_func_entry(&monitor->monitor,
 493                                                   cachefiles_read_waiter);
 494                 }
 495
 496                 for (;;) {
 497                         backpage = find_get_page(bmapping, netpage->index);
 498                         if (backpage)
 499                                 goto backing_page_already_present;
 500
 501                         if (!newpage) {
 502                                 newpage = page_cache_alloc_cold(bmapping);
 503                                 if (!newpage)
 504                                         goto nomem;
 505                         }
 506
 507                         ret = add_to_page_cache(newpage, bmapping,
 508                                                 netpage->index, GFP_KERNEL);
 509                         if (ret == 0)
 510                                 goto installed_new_backing_page;
 511                         if (ret != -EEXIST)
 512                                 goto nomem;
 513                 }
 514
 515                 /* we've installed a new backing page, so now we need to add it
 516                  * to the LRU list and start it reading */
 517         installed_new_backing_page:
 518                 _debug("- new %p", newpage);
 519
 520                 backpage = newpage;
 521                 newpage = NULL;
 522
 523                 page_cache_get(backpage);
 524                 if (!pagevec_add(&lru_pvec, backpage))
 525                         __pagevec_lru_add_file(&lru_pvec);
 526
 527         reread_backing_page:
 528                 ret = bmapping->a_ops->readpage(NULL, backpage);
 529                 if (ret < 0)
 530                         goto read_error;
 531
 532                 /* add the netfs page to the pagecache and LRU, and set the
 533                  * monitor to transfer the data across */
 534         monitor_backing_page:
 535                 _debug("- monitor add");
 536
 537                 ret = add_to_page_cache(netpage, op->mapping, netpage->index,
 538                                         GFP_KERNEL);
 539                 if (ret < 0) {
 540                         if (ret == -EEXIST) {
 541                                 page_cache_release(netpage);
 542                                 continue;
 543                         }
 544                         goto nomem;
 545                 }
 546
 547                 page_cache_get(netpage);
 548                 if (!pagevec_add(&lru_pvec, netpage))
 549                         __pagevec_lru_add_file(&lru_pvec);
 550
 551                 /* install a monitor */
 552                 page_cache_get(netpage);
 553                 monitor->netfs_page = netpage;
 554
 555                 page_cache_get(backpage);
 556                 monitor->back_page = backpage;
 557                 monitor->monitor.private = backpage;
 558                 add_page_wait_queue(backpage, &monitor->monitor);
 559                 monitor = NULL;
 560
 561                 /* but the page may have been read before the monitor was
 562                  * installed, so the monitor may miss the event - so we have to
 563                  * ensure that we do get one in such a case */
 564                 if (trylock_page(backpage)) {
 565                         _debug("2unlock %p {%lx}", backpage, backpage->flags);
 566                         unlock_page(backpage);
 567                 }
 568
 569                 page_cache_release(backpage);
 570                 backpage = NULL;
 571
 572                 page_cache_release(netpage);
 573                 netpage = NULL;
 574                 continue;
 575
 576                 /* if the backing page is already present, it can be in one of
 577                  * three states: read in progress, read failed or read okay */
 578         backing_page_already_present:
 579                 _debug("- present %p", backpage);
 580
 581                 if (PageError(backpage))
 582                         goto io_error;
 583
 584                 if (PageUptodate(backpage))
 585                         goto backing_page_already_uptodate;
 586
 587                 _debug("- not ready %p{%lx}", backpage, backpage->flags);
 588
 589                 if (!trylock_page(backpage))
 590                         goto monitor_backing_page;
 591
 592                 if (PageError(backpage)) {
 593                         _debug("error %lx", backpage->flags);
 594                         unlock_page(backpage);
 595                         goto io_error;
 596                 }
 597
 598                 if (PageUptodate(backpage))
 599                         goto backing_page_already_uptodate_unlock;
 600
 601                 /* we've locked a page that's neither up to date nor erroneous,
 602                  * so we need to attempt to read it again */
 603                 goto reread_backing_page;
 604
 605                 /* the backing page is already up to date, attach the netfs
 606                  * page to the pagecache and LRU and copy the data across */
 607         backing_page_already_uptodate_unlock:
 608                 _debug("uptodate %lx", backpage->flags);
 609                 unlock_page(backpage);
 610         backing_page_already_uptodate:
 611                 _debug("- uptodate");
 612
 613                 ret = add_to_page_cache(netpage, op->mapping, netpage->index,
 614                                         GFP_KERNEL);
 615                 if (ret < 0) {
 616                         if (ret == -EEXIST) {
 617                                 page_cache_release(netpage);
 618                                 continue;
 619                         }
 620                         goto nomem;
 621                 }
 622
 623                 copy_highpage(netpage, backpage);
 624
 625                 page_cache_release(backpage);
 626                 backpage = NULL;
 627
 628                 if (!pagevec_add(mark_pvec, netpage))
 629                         fscache_mark_pages_cached(op, mark_pvec);
 630
 631                 page_cache_get(netpage);
 632                 if (!pagevec_add(&lru_pvec, netpage))
 633                         __pagevec_lru_add_file(&lru_pvec);
 634
 635                 fscache_end_io(op, netpage, 0);
 636                 page_cache_release(netpage);
 637                 netpage = NULL;
 638                 continue;
 639         }
 640
 641         netpage = NULL;
 642
 643         _debug("out");
 644
 645 out:
 646         /* tidy up */
 647         pagevec_lru_add_file(&lru_pvec);
 648
 649         if (newpage)
 650                 page_cache_release(newpage);
 651         if (netpage)
 652                 page_cache_release(netpage);
 653         if (backpage)
 654                 page_cache_release(backpage);
 655         if (monitor) {
 656                 fscache_put_retrieval(op);
 657                 kfree(monitor);
 658         }
 659
 660         list_for_each_entry_safe(netpage, _n, list, lru) {
 661                 list_del(&netpage->lru);
 662                 page_cache_release(netpage);
 663         }
 664
 665         _leave(" = %d", ret);
 666         return ret;
 667
 668 nomem:
 669         _debug("nomem");
 670         ret = -ENOMEM;
 671         goto out;
 672
 673 read_error:
 674         _debug("read error %d", ret);
 675         if (ret == -ENOMEM)
 676                 goto out;
 677 io_error:
 678         cachefiles_io_error_obj(object, "Page read error on backing file");
 679         ret = -ENOBUFS;
 680         goto out;
 681 }
 682
 683 /*
 684  * read a list of pages from the cache or allocate blocks in which to store
 685  * them
 686  */
 687 int cachefiles_read_or_alloc_pages(struct fscache_retrieval *op,
 688                                    struct list_head *pages,
 689                                    unsigned *nr_pages,
 690                                    gfp_t gfp)
 691 {
 692         struct cachefiles_object *object;
 693         struct cachefiles_cache *cache;
 694         struct list_head backpages;
 695         struct pagevec pagevec;
 696         struct inode *inode;
 697         struct page *page, *_n;
 698         unsigned shift, nrbackpages;
 699         int ret, ret2, space;
 700
 701         object = container_of(op->op.object,
 702                               struct cachefiles_object, fscache);
 703         cache = container_of(object->fscache.cache,
 704                              struct cachefiles_cache, cache);
 705
 706         _enter("{OBJ%x,%d},,%d,,",
 707                object->fscache.debug_id, atomic_read(&op->op.usage),
 708                *nr_pages);
 709
 710         if (!object->backer)
 711                 return -ENOBUFS;
 712
 713         space = 1;
 714         if (cachefiles_has_space(cache, 0, *nr_pages) < 0)
 715                 space = 0;
 716
 717         inode = object->backer->d_inode;
 718         ASSERT(S_ISREG(inode->i_mode));
 719         ASSERT(inode->i_mapping->a_ops->bmap);
 720         ASSERT(inode->i_mapping->a_ops->readpages);
 721
 722         /* calculate the shift required to use bmap */
 723         if (inode->i_sb->s_blocksize > PAGE_SIZE)
 724                 return -ENOBUFS;
 725
 726         shift = PAGE_SHIFT - inode->i_sb->s_blocksize_bits;
 727
 728         pagevec_init(&pagevec, 0);
 729
 730         op->op.flags &= FSCACHE_OP_KEEP_FLAGS;
 731         op->op.flags |= FSCACHE_OP_FAST;
 732         op->op.processor = cachefiles_read_copier;
 733
 734         INIT_LIST_HEAD(&backpages);
 735         nrbackpages = 0;
 736
 737         ret = space ? -ENODATA : -ENOBUFS;
 738         list_for_each_entry_safe(page, _n, pages, lru) {
 739                 sector_t block0, block;
 740
 741                 /* we assume the absence or presence of the first block is a
 742                  * good enough indication for the page as a whole
 743                  * - TODO: don't use bmap() for this as it is _not_ actually
 744                  *   good enough for this as it doesn't indicate errors, but
 745                  *   it's all we've got for the moment
 746                  */
 747                 block0 = page->index;
 748                 block0 <<= shift;
 749
 750                 block = inode->i_mapping->a_ops->bmap(inode->i_mapping,
 751                                                       block0);
 752                 _debug("%llx -> %llx",
 753                        (unsigned long long) block0,
 754                        (unsigned long long) block);
 755
 756                 if (block) {
 757                         /* we have data - add it to the list to give to the
 758                          * backing fs */
 759                         list_move(&page->lru, &backpages);
 760                         (*nr_pages)--;
 761                         nrbackpages++;
 762                 } else if (space && pagevec_add(&pagevec, page) == 0) {
 763                         fscache_mark_pages_cached(op, &pagevec);
 764                         ret = -ENODATA;
 765                 }
 766         }
 767
 768         if (pagevec_count(&pagevec) > 0)
 769                 fscache_mark_pages_cached(op, &pagevec);
 770
 771         if (list_empty(pages))
 772                 ret = 0;
 773
 774         /* submit the apparently valid pages to the backing fs to be read from
 775          * disk */
 776         if (nrbackpages > 0) {
 777                 ret2 = cachefiles_read_backing_file(object, op, &backpages,
 778                                                     &pagevec);
 779                 if (ret2 == -ENOMEM || ret2 == -EINTR)
 780                         ret = ret2;
 781         }
 782
 783         if (pagevec_count(&pagevec) > 0)
 784                 fscache_mark_pages_cached(op, &pagevec);
 785
 786         _leave(" = %d [nr=%u%s]",
 787                ret, *nr_pages, list_empty(pages) ? " empty" : "");
 788         return ret;
 789 }
 790
 791 /*
 792  * allocate a block in the cache in which to store a page
 793  * - cache withdrawal is prevented by the caller
 794  * - returns -EINTR if interrupted
 795  * - returns -ENOMEM if ran out of memory
 796  * - returns -ENOBUFS if no buffers can be made available
 797  * - returns -ENOBUFS if page is beyond EOF
 798  * - otherwise:
 799  *   - the metadata will be retained
 800  *   - 0 will be returned
 801  */
 802 int cachefiles_allocate_page(struct fscache_retrieval *op,
 803                              struct page *page,
 804                              gfp_t gfp)
 805 {
 806         struct cachefiles_object *object;
 807         struct cachefiles_cache *cache;
 808         struct pagevec pagevec;
 809         int ret;
 810
 811         object = container_of(op->op.object,
 812                               struct cachefiles_object, fscache);
 813         cache = container_of(object->fscache.cache,
 814                              struct cachefiles_cache, cache);
 815
 816         _enter("%p,{%lx},", object, page->index);
 817
 818         ret = cachefiles_has_space(cache, 0, 1);
 819         if (ret == 0) {
 820                 pagevec_init(&pagevec, 0);
 821                 pagevec_add(&pagevec, page);
 822                 fscache_mark_pages_cached(op, &pagevec);
 823         } else {
 824                 ret = -ENOBUFS;
 825         }
 826
 827         _leave(" = %d", ret);
 828         return ret;
 829 }
 830
 831 /*
 832  * allocate blocks in the cache in which to store a set of pages
 833  * - cache withdrawal is prevented by the caller
 834  * - returns -EINTR if interrupted
 835  * - returns -ENOMEM if ran out of memory
 836  * - returns -ENOBUFS if some buffers couldn't be made available
 837  * - returns -ENOBUFS if some pages are beyond EOF
 838  * - otherwise:
 839  *   - -ENODATA will be returned
 840  * - metadata will be retained for any page marked
 841  */
 842 int cachefiles_allocate_pages(struct fscache_retrieval *op,
 843                               struct list_head *pages,
 844                               unsigned *nr_pages,
 845                               gfp_t gfp)
 846 {
 847         struct cachefiles_object *object;
 848         struct cachefiles_cache *cache;
 849         struct pagevec pagevec;
 850         struct page *page;
 851         int ret;
 852
 853         object = container_of(op->op.object,
 854                               struct cachefiles_object, fscache);
 855         cache = container_of(object->fscache.cache,
 856                              struct cachefiles_cache, cache);
 857
 858         _enter("%p,,,%d,", object, *nr_pages);
 859
 860         ret = cachefiles_has_space(cache, 0, *nr_pages);
 861         if (ret == 0) {
 862                 pagevec_init(&pagevec, 0);
 863
 864                 list_for_each_entry(page, pages, lru) {
 865                         if (pagevec_add(&pagevec, page) == 0)
 866                                 fscache_mark_pages_cached(op, &pagevec);
 867                 }
 868
 869                 if (pagevec_count(&pagevec) > 0)
 870                         fscache_mark_pages_cached(op, &pagevec);
 871                 ret = -ENODATA;
 872         } else {
 873                 ret = -ENOBUFS;
 874         }
 875
 876         _leave(" = %d", ret);
 877         return ret;
 878 }
 879
 880 /*
 881  * request a page be stored in the cache
 882  * - cache withdrawal is prevented by the caller
 883  * - this request may be ignored if there's no cache block available, in which
 884  *   case -ENOBUFS will be returned
 885  * - if the op is in progress, 0 will be returned
 886  */
 887 int cachefiles_write_page(struct fscache_storage *op, struct page *page)
 888 {
 889         struct cachefiles_object *object;
 890         struct cachefiles_cache *cache;
 891         mm_segment_t old_fs;
 892         struct file *file;
 893         loff_t pos, eof;
 894         size_t len;
 895         void *data;
 896         int ret;
 897
 898         ASSERT(op != NULL);
 899         ASSERT(page != NULL);
 900
 901         object = container_of(op->op.object,
 902                               struct cachefiles_object, fscache);
 903
 904         _enter("%p,%p{%lx},,,", object, page, page->index);
 905
 906         if (!object->backer) {
 907                 _leave(" = -ENOBUFS");
 908                 return -ENOBUFS;
 909         }
 910
 911         ASSERT(S_ISREG(object->backer->d_inode->i_mode));
 912
 913         cache = container_of(object->fscache.cache,
 914                              struct cachefiles_cache, cache);
 915
 916         /* write the page to the backing filesystem and let it store it in its
 917          * own time */
 918         dget(object->backer);
 919         mntget(cache->mnt);
 920         file = dentry_open(object->backer, cache->mnt, O_RDWR,
 921                            cache->cache_cred);
 922         if (IS_ERR(file)) {
 923                 ret = PTR_ERR(file);
 924         } else {
 925                 ret = -EIO;
 926                 if (file->f_op->write) {
 927                         pos = (loff_t) page->index << PAGE_SHIFT;
 928
 929                         /* we mustn't write more data than we have, so we have
 930                          * to beware of a partial page at EOF */
 931                         eof = object->fscache.store_limit_l;
 932                         len = PAGE_SIZE;
 933                         if (eof & ~PAGE_MASK) {
 934                                 ASSERTCMP(pos, <, eof);
 935                                 if (eof - pos < PAGE_SIZE) {
 936                                         _debug("cut short %llx to %llx",
 937                                                pos, eof);
 938                                         len = eof - pos;
 939                                         ASSERTCMP(pos + len, ==, eof);
 940                                 }
 941                         }
 942
 943                         data = kmap(page);
 944                         old_fs = get_fs();
 945                         set_fs(KERNEL_DS);
 946                         ret = file->f_op->write(
 947                                 file, (const void __user *) data, len, &pos);
 948                         set_fs(old_fs);
 949                         kunmap(page);
 950                         if (ret != len)
 951                                 ret = -EIO;
 952                 }
 953                 fput(file);
 954         }
 955
 956         if (ret < 0) {
 957                 if (ret == -EIO)
 958                         cachefiles_io_error_obj(
 959                                 object, "Write page to backing file failed");
 960                 ret = -ENOBUFS;
 961         }
 962
 963         _leave(" = %d", ret);
 964         return ret;
 965 }
 966
 967 /*
 968  * detach a backing block from a page
 969  * - cache withdrawal is prevented by the caller
 970  */
 971 void cachefiles_uncache_page(struct fscache_object *_object, struct page *page)
 972 {
 973         struct cachefiles_object *object;
 974         struct cachefiles_cache *cache;
 975
 976         object = container_of(_object, struct cachefiles_object, fscache);
 977         cache = container_of(object->fscache.cache,
 978                              struct cachefiles_cache, cache);
 979
 980         _enter("%p,{%lu}", object, page->index);
 981
 982         spin_unlock(&object->fscache.cookie->lock);
 983 }