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