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_entry_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 fscache_retrieval *op = monitor->op;
  31         struct wait_bit_key *key = _key;
  32         struct page *page = wait->private;
  33
  34         ASSERT(key);
  35
  36         _enter("{%lu},%u,%d,{%p,%u}",
  37                monitor->netfs_page->index, mode, sync,
  38                key->flags, key->bit_nr);
  39
  40         if (key->flags != &page->flags ||
  41             key->bit_nr != PG_locked)
  42                 return 0;
  43
  44         _debug("--- monitor %p %lx ---", page, page->flags);
  45
  46         if (!PageUptodate(page) && !PageError(page)) {
  47                 /* unlocked, not uptodate and not erronous? */
  48                 _debug("page probably truncated");
  49         }
  50
  51         /* remove from the waitqueue */
  52         list_del(&wait->entry);
  53
  54         /* move onto the action list and queue for FS-Cache thread pool */
  55         ASSERT(op);
  56
  57         /* We need to temporarily bump the usage count as we don't own a ref
  58          * here otherwise cachefiles_read_copier() may free the op between the
  59          * monitor being enqueued on the op->to_do list and the op getting
  60          * enqueued on the work queue.
  61          */
  62         fscache_get_retrieval(op);
  63
  64         object = container_of(op->op.object, struct cachefiles_object, fscache);
  65         spin_lock(&object->work_lock);
  66         list_add_tail(&monitor->op_link, &op->to_do);
  67         spin_unlock(&object->work_lock);
  68
  69         fscache_enqueue_retrieval(op);
  70         fscache_put_retrieval(op);
  71         return 0;
  72 }
  73
  74 /*
  75  * handle a probably truncated page
  76  * - check to see if the page is still relevant and reissue the read if
  77  *   possible
  78  * - return -EIO on error, -ENODATA if the page is gone, -EINPROGRESS if we
  79  *   must wait again and 0 if successful
  80  */
  81 static int cachefiles_read_reissue(struct cachefiles_object *object,
  82                                    struct cachefiles_one_read *monitor)
  83 {
  84         struct address_space *bmapping = d_backing_inode(object->backer)->i_mapping;
  85         struct page *backpage = monitor->back_page, *backpage2;
  86         int ret;
  87
  88         _enter("{ino=%lx},{%lx,%lx}",
  89                d_backing_inode(object->backer)->i_ino,
  90                backpage->index, backpage->flags);
  91
  92         /* skip if the page was truncated away completely */
  93         if (backpage->mapping != bmapping) {
  94                 _leave(" = -ENODATA [mapping]");
  95                 return -ENODATA;
  96         }
  97
  98         backpage2 = find_get_page(bmapping, backpage->index);
  99         if (!backpage2) {
 100                 _leave(" = -ENODATA [gone]");
 101                 return -ENODATA;
 102         }
 103
 104         if (backpage != backpage2) {
 105                 put_page(backpage2);
 106                 _leave(" = -ENODATA [different]");
 107                 return -ENODATA;
 108         }
 109
 110         /* the page is still there and we already have a ref on it, so we don't
 111          * need a second */
 112         put_page(backpage2);
 113
 114         INIT_LIST_HEAD(&monitor->op_link);
 115         add_page_wait_queue(backpage, &monitor->monitor);
 116
 117         if (trylock_page(backpage)) {
 118                 ret = -EIO;
 119                 if (PageError(backpage))
 120                         goto unlock_discard;
 121                 ret = 0;
 122                 if (PageUptodate(backpage))
 123                         goto unlock_discard;
 124
 125                 _debug("reissue read");
 126                 ret = bmapping->a_ops->readpage(NULL, backpage);
 127                 if (ret < 0)
 128                         goto unlock_discard;
 129         }
 130
 131         /* but the page may have been read before the monitor was installed, so
 132          * the monitor may miss the event - so we have to ensure that we do get
 133          * one in such a case */
 134         if (trylock_page(backpage)) {
 135                 _debug("jumpstart %p {%lx}", backpage, backpage->flags);
 136                 unlock_page(backpage);
 137         }
 138
 139         /* it'll reappear on the todo list */
 140         _leave(" = -EINPROGRESS");
 141         return -EINPROGRESS;
 142
 143 unlock_discard:
 144         unlock_page(backpage);
 145         spin_lock_irq(&object->work_lock);
 146         list_del(&monitor->op_link);
 147         spin_unlock_irq(&object->work_lock);
 148         _leave(" = %d", ret);
 149         return ret;
 150 }
 151
 152 /*
 153  * copy data from backing pages to netfs pages to complete a read operation
 154  * - driven by FS-Cache's thread pool
 155  */
 156 static void cachefiles_read_copier(struct fscache_operation *_op)
 157 {
 158         struct cachefiles_one_read *monitor;
 159         struct cachefiles_object *object;
 160         struct fscache_retrieval *op;
 161         int error, max;
 162
 163         op = container_of(_op, struct fscache_retrieval, op);
 164         object = container_of(op->op.object,
 165                               struct cachefiles_object, fscache);
 166
 167         _enter("{ino=%lu}", d_backing_inode(object->backer)->i_ino);
 168
 169         max = 8;
 170         spin_lock_irq(&object->work_lock);
 171
 172         while (!list_empty(&op->to_do)) {
 173                 monitor = list_entry(op->to_do.next,
 174                                      struct cachefiles_one_read, op_link);
 175                 list_del(&monitor->op_link);
 176
 177                 spin_unlock_irq(&object->work_lock);
 178
 179                 _debug("- copy {%lu}", monitor->back_page->index);
 180
 181         recheck:
 182                 if (test_bit(FSCACHE_COOKIE_INVALIDATING,
 183                              &object->fscache.cookie->flags)) {
 184                         error = -ESTALE;
 185                 } else if (PageUptodate(monitor->back_page)) {
 186                         copy_highpage(monitor->netfs_page, monitor->back_page);
 187                         fscache_mark_page_cached(monitor->op,
 188                                                  monitor->netfs_page);
 189                         error = 0;
 190                 } else if (!PageError(monitor->back_page)) {
 191                         /* the page has probably been truncated */
 192                         error = cachefiles_read_reissue(object, monitor);
 193                         if (error == -EINPROGRESS)
 194                                 goto next;
 195                         goto recheck;
 196                 } else {
 197                         cachefiles_io_error_obj(
 198                                 object,
 199                                 "Readpage failed on backing file %lx",
 200                                 (unsigned long) monitor->back_page->flags);
 201                         error = -EIO;
 202                 }
 203
 204                 put_page(monitor->back_page);
 205
 206                 fscache_end_io(op, monitor->netfs_page, error);
 207                 put_page(monitor->netfs_page);
 208                 fscache_retrieval_complete(op, 1);
 209                 fscache_put_retrieval(op);
 210                 kfree(monitor);
 211
 212         next:
 213                 /* let the thread pool have some air occasionally */
 214                 max--;
 215                 if (max < 0 || need_resched()) {
 216                         if (!list_empty(&op->to_do))
 217                                 fscache_enqueue_retrieval(op);
 218                         _leave(" [maxed out]");
 219                         return;
 220                 }
 221
 222                 spin_lock_irq(&object->work_lock);
 223         }
 224
 225         spin_unlock_irq(&object->work_lock);
 226         _leave("");
 227 }
 228
 229 /*
 230  * read the corresponding page to the given set from the backing file
 231  * - an uncertain page is simply discarded, to be tried again another time
 232  */
 233 static int cachefiles_read_backing_file_one(struct cachefiles_object *object,
 234                                             struct fscache_retrieval *op,
 235                                             struct page *netpage)
 236 {
 237         struct cachefiles_one_read *monitor;
 238         struct address_space *bmapping;
 239         struct page *newpage, *backpage;
 240         int ret;
 241
 242         _enter("");
 243
 244         _debug("read back %p{%lu,%d}",
 245                netpage, netpage->index, page_count(netpage));
 246
 247         monitor = kzalloc(sizeof(*monitor), cachefiles_gfp);
 248         if (!monitor)
 249                 goto nomem;
 250
 251         monitor->netfs_page = netpage;
 252         monitor->op = fscache_get_retrieval(op);
 253
 254         init_waitqueue_func_entry(&monitor->monitor, cachefiles_read_waiter);
 255
 256         /* attempt to get hold of the backing page */
 257         bmapping = d_backing_inode(object->backer)->i_mapping;
 258         newpage = NULL;
 259
 260         for (;;) {
 261                 backpage = find_get_page(bmapping, netpage->index);
 262                 if (backpage)
 263                         goto backing_page_already_present;
 264
 265                 if (!newpage) {
 266                         newpage = __page_cache_alloc(cachefiles_gfp);
 267                         if (!newpage)
 268                                 goto nomem_monitor;
 269                 }
 270
 271                 ret = add_to_page_cache_lru(newpage, bmapping,
 272                                             netpage->index, cachefiles_gfp);
 273                 if (ret == 0)
 274                         goto installed_new_backing_page;
 275                 if (ret != -EEXIST)
 276                         goto nomem_page;
 277         }
 278
 279         /* we've installed a new backing page, so now we need to start
 280          * it reading */
 281 installed_new_backing_page:
 282         _debug("- new %p", newpage);
 283
 284         backpage = newpage;
 285         newpage = NULL;
 286
 287 read_backing_page:
 288         ret = bmapping->a_ops->readpage(NULL, backpage);
 289         if (ret < 0)
 290                 goto read_error;
 291
 292         /* set the monitor to transfer the data across */
 293 monitor_backing_page:
 294         _debug("- monitor add");
 295
 296         /* install the monitor */
 297         get_page(monitor->netfs_page);
 298         get_page(backpage);
 299         monitor->back_page = backpage;
 300         monitor->monitor.private = backpage;
 301         add_page_wait_queue(backpage, &monitor->monitor);
 302         monitor = NULL;
 303
 304         /* but the page may have been read before the monitor was installed, so
 305          * the monitor may miss the event - so we have to ensure that we do get
 306          * one in such a case */
 307         if (trylock_page(backpage)) {
 308                 _debug("jumpstart %p {%lx}", backpage, backpage->flags);
 309                 unlock_page(backpage);
 310         }
 311         goto success;
 312
 313         /* if the backing page is already present, it can be in one of
 314          * three states: read in progress, read failed or read okay */
 315 backing_page_already_present:
 316         _debug("- present");
 317
 318         if (newpage) {
 319                 put_page(newpage);
 320                 newpage = NULL;
 321         }
 322
 323         if (PageError(backpage))
 324                 goto io_error;
 325
 326         if (PageUptodate(backpage))
 327                 goto backing_page_already_uptodate;
 328
 329         if (!trylock_page(backpage))
 330                 goto monitor_backing_page;
 331         _debug("read %p {%lx}", backpage, backpage->flags);
 332         goto read_backing_page;
 333
 334         /* the backing page is already up to date, attach the netfs
 335          * page to the pagecache and LRU and copy the data across */
 336 backing_page_already_uptodate:
 337         _debug("- uptodate");
 338
 339         fscache_mark_page_cached(op, netpage);
 340
 341         copy_highpage(netpage, backpage);
 342         fscache_end_io(op, netpage, 0);
 343         fscache_retrieval_complete(op, 1);
 344
 345 success:
 346         _debug("success");
 347         ret = 0;
 348
 349 out:
 350         if (backpage)
 351                 put_page(backpage);
 352         if (monitor) {
 353                 fscache_put_retrieval(monitor->op);
 354                 kfree(monitor);
 355         }
 356         _leave(" = %d", ret);
 357         return ret;
 358
 359 read_error:
 360         _debug("read error %d", ret);
 361         if (ret == -ENOMEM) {
 362                 fscache_retrieval_complete(op, 1);
 363                 goto out;
 364         }
 365 io_error:
 366         cachefiles_io_error_obj(object, "Page read error on backing file");
 367         fscache_retrieval_complete(op, 1);
 368         ret = -ENOBUFS;
 369         goto out;
 370
 371 nomem_page:
 372         put_page(newpage);
 373 nomem_monitor:
 374         fscache_put_retrieval(monitor->op);
 375         kfree(monitor);
 376 nomem:
 377         fscache_retrieval_complete(op, 1);
 378         _leave(" = -ENOMEM");
 379         return -ENOMEM;
 380 }
 381
 382 /*
 383  * read a page from the cache or allocate a block in which to store it
 384  * - cache withdrawal is prevented by the caller
 385  * - returns -EINTR if interrupted
 386  * - returns -ENOMEM if ran out of memory
 387  * - returns -ENOBUFS if no buffers can be made available
 388  * - returns -ENOBUFS if page is beyond EOF
 389  * - if the page is backed by a block in the cache:
 390  *   - a read will be started which will call the callback on completion
 391  *   - 0 will be returned
 392  * - else if the page is unbacked:
 393  *   - the metadata will be retained
 394  *   - -ENODATA will be returned
 395  */
 396 int cachefiles_read_or_alloc_page(struct fscache_retrieval *op,
 397                                   struct page *page,
 398                                   gfp_t gfp)
 399 {
 400         struct cachefiles_object *object;
 401         struct cachefiles_cache *cache;
 402         struct inode *inode;
 403         sector_t block0, block;
 404         unsigned shift;
 405         int ret;
 406
 407         object = container_of(op->op.object,
 408                               struct cachefiles_object, fscache);
 409         cache = container_of(object->fscache.cache,
 410                              struct cachefiles_cache, cache);
 411
 412         _enter("{%p},{%lx},,,", object, page->index);
 413
 414         if (!object->backer)
 415                 goto enobufs;
 416
 417         inode = d_backing_inode(object->backer);
 418         ASSERT(S_ISREG(inode->i_mode));
 419         ASSERT(inode->i_mapping->a_ops->bmap);
 420         ASSERT(inode->i_mapping->a_ops->readpages);
 421
 422         /* calculate the shift required to use bmap */
 423         shift = PAGE_SHIFT - inode->i_sb->s_blocksize_bits;
 424
 425         op->op.flags &= FSCACHE_OP_KEEP_FLAGS;
 426         op->op.flags |= FSCACHE_OP_ASYNC;
 427         op->op.processor = cachefiles_read_copier;
 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         } else if (cachefiles_has_space(cache, 0, 1) == 0) {
 448                 /* there's space in the cache we can use */
 449                 fscache_mark_page_cached(op, page);
 450                 fscache_retrieval_complete(op, 1);
 451                 ret = -ENODATA;
 452         } else {
 453                 goto enobufs;
 454         }
 455
 456         _leave(" = %d", ret);
 457         return ret;
 458
 459 enobufs:
 460         fscache_retrieval_complete(op, 1);
 461         _leave(" = -ENOBUFS");
 462         return -ENOBUFS;
 463 }
 464
 465 /*
 466  * read the corresponding pages to the given set from the backing file
 467  * - any uncertain pages are simply discarded, to be tried again another time
 468  */
 469 static int cachefiles_read_backing_file(struct cachefiles_object *object,
 470                                         struct fscache_retrieval *op,
 471                                         struct list_head *list)
 472 {
 473         struct cachefiles_one_read *monitor = NULL;
 474         struct address_space *bmapping = d_backing_inode(object->backer)->i_mapping;
 475         struct page *newpage = NULL, *netpage, *_n, *backpage = NULL;
 476         int ret = 0;
 477
 478         _enter("");
 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), cachefiles_gfp);
 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(cachefiles_gfp);
 503                                 if (!newpage)
 504                                         goto nomem;
 505                         }
 506
 507                         ret = add_to_page_cache_lru(newpage, bmapping,
 508                                                     netpage->index,
 509                                                     cachefiles_gfp);
 510                         if (ret == 0)
 511                                 goto installed_new_backing_page;
 512                         if (ret != -EEXIST)
 513                                 goto nomem;
 514                 }
 515
 516                 /* we've installed a new backing page, so now we need
 517                  * to start it reading */
 518         installed_new_backing_page:
 519                 _debug("- new %p", newpage);
 520
 521                 backpage = newpage;
 522                 newpage = NULL;
 523
 524         reread_backing_page:
 525                 ret = bmapping->a_ops->readpage(NULL, backpage);
 526                 if (ret < 0)
 527                         goto read_error;
 528
 529                 /* add the netfs page to the pagecache and LRU, and set the
 530                  * monitor to transfer the data across */
 531         monitor_backing_page:
 532                 _debug("- monitor add");
 533
 534                 ret = add_to_page_cache_lru(netpage, op->mapping,
 535                                             netpage->index, cachefiles_gfp);
 536                 if (ret < 0) {
 537                         if (ret == -EEXIST) {
 538                                 put_page(netpage);
 539                                 fscache_retrieval_complete(op, 1);
 540                                 continue;
 541                         }
 542                         goto nomem;
 543                 }
 544
 545                 /* install a monitor */
 546                 get_page(netpage);
 547                 monitor->netfs_page = netpage;
 548
 549                 get_page(backpage);
 550                 monitor->back_page = backpage;
 551                 monitor->monitor.private = backpage;
 552                 add_page_wait_queue(backpage, &monitor->monitor);
 553                 monitor = NULL;
 554
 555                 /* but the page may have been read before the monitor was
 556                  * installed, so the monitor may miss the event - so we have to
 557                  * ensure that we do get one in such a case */
 558                 if (trylock_page(backpage)) {
 559                         _debug("2unlock %p {%lx}", backpage, backpage->flags);
 560                         unlock_page(backpage);
 561                 }
 562
 563                 put_page(backpage);
 564                 backpage = NULL;
 565
 566                 put_page(netpage);
 567                 netpage = NULL;
 568                 continue;
 569
 570                 /* if the backing page is already present, it can be in one of
 571                  * three states: read in progress, read failed or read okay */
 572         backing_page_already_present:
 573                 _debug("- present %p", backpage);
 574
 575                 if (PageError(backpage))
 576                         goto io_error;
 577
 578                 if (PageUptodate(backpage))
 579                         goto backing_page_already_uptodate;
 580
 581                 _debug("- not ready %p{%lx}", backpage, backpage->flags);
 582
 583                 if (!trylock_page(backpage))
 584                         goto monitor_backing_page;
 585
 586                 if (PageError(backpage)) {
 587                         _debug("error %lx", backpage->flags);
 588                         unlock_page(backpage);
 589                         goto io_error;
 590                 }
 591
 592                 if (PageUptodate(backpage))
 593                         goto backing_page_already_uptodate_unlock;
 594
 595                 /* we've locked a page that's neither up to date nor erroneous,
 596                  * so we need to attempt to read it again */
 597                 goto reread_backing_page;
 598
 599                 /* the backing page is already up to date, attach the netfs
 600                  * page to the pagecache and LRU and copy the data across */
 601         backing_page_already_uptodate_unlock:
 602                 _debug("uptodate %lx", backpage->flags);
 603                 unlock_page(backpage);
 604         backing_page_already_uptodate:
 605                 _debug("- uptodate");
 606
 607                 ret = add_to_page_cache_lru(netpage, op->mapping,
 608                                             netpage->index, cachefiles_gfp);
 609                 if (ret < 0) {
 610                         if (ret == -EEXIST) {
 611                                 put_page(netpage);
 612                                 fscache_retrieval_complete(op, 1);
 613                                 continue;
 614                         }
 615                         goto nomem;
 616                 }
 617
 618                 copy_highpage(netpage, backpage);
 619
 620                 put_page(backpage);
 621                 backpage = NULL;
 622
 623                 fscache_mark_page_cached(op, netpage);
 624
 625                 /* the netpage is unlocked and marked up to date here */
 626                 fscache_end_io(op, netpage, 0);
 627                 put_page(netpage);
 628                 netpage = NULL;
 629                 fscache_retrieval_complete(op, 1);
 630                 continue;
 631         }
 632
 633         netpage = NULL;
 634
 635         _debug("out");
 636
 637 out:
 638         /* tidy up */
 639         if (newpage)
 640                 put_page(newpage);
 641         if (netpage)
 642                 put_page(netpage);
 643         if (backpage)
 644                 put_page(backpage);
 645         if (monitor) {
 646                 fscache_put_retrieval(op);
 647                 kfree(monitor);
 648         }
 649
 650         list_for_each_entry_safe(netpage, _n, list, lru) {
 651                 list_del(&netpage->lru);
 652                 put_page(netpage);
 653                 fscache_retrieval_complete(op, 1);
 654         }
 655
 656         _leave(" = %d", ret);
 657         return ret;
 658
 659 nomem:
 660         _debug("nomem");
 661         ret = -ENOMEM;
 662         goto record_page_complete;
 663
 664 read_error:
 665         _debug("read error %d", ret);
 666         if (ret == -ENOMEM)
 667                 goto record_page_complete;
 668 io_error:
 669         cachefiles_io_error_obj(object, "Page read error on backing file");
 670         ret = -ENOBUFS;
 671 record_page_complete:
 672         fscache_retrieval_complete(op, 1);
 673         goto out;
 674 }
 675
 676 /*
 677  * read a list of pages from the cache or allocate blocks in which to store
 678  * them
 679  */
 680 int cachefiles_read_or_alloc_pages(struct fscache_retrieval *op,
 681                                    struct list_head *pages,
 682                                    unsigned *nr_pages,
 683                                    gfp_t gfp)
 684 {
 685         struct cachefiles_object *object;
 686         struct cachefiles_cache *cache;
 687         struct list_head backpages;
 688         struct pagevec pagevec;
 689         struct inode *inode;
 690         struct page *page, *_n;
 691         unsigned shift, nrbackpages;
 692         int ret, ret2, space;
 693
 694         object = container_of(op->op.object,
 695                               struct cachefiles_object, fscache);
 696         cache = container_of(object->fscache.cache,
 697                              struct cachefiles_cache, cache);
 698
 699         _enter("{OBJ%x,%d},,%d,,",
 700                object->fscache.debug_id, atomic_read(&op->op.usage),
 701                *nr_pages);
 702
 703         if (!object->backer)
 704                 goto all_enobufs;
 705
 706         space = 1;
 707         if (cachefiles_has_space(cache, 0, *nr_pages) < 0)
 708                 space = 0;
 709
 710         inode = d_backing_inode(object->backer);
 711         ASSERT(S_ISREG(inode->i_mode));
 712         ASSERT(inode->i_mapping->a_ops->bmap);
 713         ASSERT(inode->i_mapping->a_ops->readpages);
 714
 715         /* calculate the shift required to use bmap */
 716         shift = PAGE_SHIFT - inode->i_sb->s_blocksize_bits;
 717
 718         pagevec_init(&pagevec);
 719
 720         op->op.flags &= FSCACHE_OP_KEEP_FLAGS;
 721         op->op.flags |= FSCACHE_OP_ASYNC;
 722         op->op.processor = cachefiles_read_copier;
 723
 724         INIT_LIST_HEAD(&backpages);
 725         nrbackpages = 0;
 726
 727         ret = space ? -ENODATA : -ENOBUFS;
 728         list_for_each_entry_safe(page, _n, pages, lru) {
 729                 sector_t block0, block;
 730
 731                 /* we assume the absence or presence of the first block is a
 732                  * good enough indication for the page as a whole
 733                  * - TODO: don't use bmap() for this as it is _not_ actually
 734                  *   good enough for this as it doesn't indicate errors, but
 735                  *   it's all we've got for the moment
 736                  */
 737                 block0 = page->index;
 738                 block0 <<= shift;
 739
 740                 block = inode->i_mapping->a_ops->bmap(inode->i_mapping,
 741                                                       block0);
 742                 _debug("%llx -> %llx",
 743                        (unsigned long long) block0,
 744                        (unsigned long long) block);
 745
 746                 if (block) {
 747                         /* we have data - add it to the list to give to the
 748                          * backing fs */
 749                         list_move(&page->lru, &backpages);
 750                         (*nr_pages)--;
 751                         nrbackpages++;
 752                 } else if (space && pagevec_add(&pagevec, page) == 0) {
 753                         fscache_mark_pages_cached(op, &pagevec);
 754                         fscache_retrieval_complete(op, 1);
 755                         ret = -ENODATA;
 756                 } else {
 757                         fscache_retrieval_complete(op, 1);
 758                 }
 759         }
 760
 761         if (pagevec_count(&pagevec) > 0)
 762                 fscache_mark_pages_cached(op, &pagevec);
 763
 764         if (list_empty(pages))
 765                 ret = 0;
 766
 767         /* submit the apparently valid pages to the backing fs to be read from
 768          * disk */
 769         if (nrbackpages > 0) {
 770                 ret2 = cachefiles_read_backing_file(object, op, &backpages);
 771                 if (ret2 == -ENOMEM || ret2 == -EINTR)
 772                         ret = ret2;
 773         }
 774
 775         _leave(" = %d [nr=%u%s]",
 776                ret, *nr_pages, list_empty(pages) ? " empty" : "");
 777         return ret;
 778
 779 all_enobufs:
 780         fscache_retrieval_complete(op, *nr_pages);
 781         return -ENOBUFS;
 782 }
 783
 784 /*
 785  * allocate a block in the cache in which to store a page
 786  * - cache withdrawal is prevented by the caller
 787  * - returns -EINTR if interrupted
 788  * - returns -ENOMEM if ran out of memory
 789  * - returns -ENOBUFS if no buffers can be made available
 790  * - returns -ENOBUFS if page is beyond EOF
 791  * - otherwise:
 792  *   - the metadata will be retained
 793  *   - 0 will be returned
 794  */
 795 int cachefiles_allocate_page(struct fscache_retrieval *op,
 796                              struct page *page,
 797                              gfp_t gfp)
 798 {
 799         struct cachefiles_object *object;
 800         struct cachefiles_cache *cache;
 801         int ret;
 802
 803         object = container_of(op->op.object,
 804                               struct cachefiles_object, fscache);
 805         cache = container_of(object->fscache.cache,
 806                              struct cachefiles_cache, cache);
 807
 808         _enter("%p,{%lx},", object, page->index);
 809
 810         ret = cachefiles_has_space(cache, 0, 1);
 811         if (ret == 0)
 812                 fscache_mark_page_cached(op, page);
 813         else
 814                 ret = -ENOBUFS;
 815
 816         fscache_retrieval_complete(op, 1);
 817         _leave(" = %d", ret);
 818         return ret;
 819 }
 820
 821 /*
 822  * allocate blocks in the cache in which to store a set of pages
 823  * - cache withdrawal is prevented by the caller
 824  * - returns -EINTR if interrupted
 825  * - returns -ENOMEM if ran out of memory
 826  * - returns -ENOBUFS if some buffers couldn't be made available
 827  * - returns -ENOBUFS if some pages are beyond EOF
 828  * - otherwise:
 829  *   - -ENODATA will be returned
 830  * - metadata will be retained for any page marked
 831  */
 832 int cachefiles_allocate_pages(struct fscache_retrieval *op,
 833                               struct list_head *pages,
 834                               unsigned *nr_pages,
 835                               gfp_t gfp)
 836 {
 837         struct cachefiles_object *object;
 838         struct cachefiles_cache *cache;
 839         struct pagevec pagevec;
 840         struct page *page;
 841         int ret;
 842
 843         object = container_of(op->op.object,
 844                               struct cachefiles_object, fscache);
 845         cache = container_of(object->fscache.cache,
 846                              struct cachefiles_cache, cache);
 847
 848         _enter("%p,,,%d,", object, *nr_pages);
 849
 850         ret = cachefiles_has_space(cache, 0, *nr_pages);
 851         if (ret == 0) {
 852                 pagevec_init(&pagevec);
 853
 854                 list_for_each_entry(page, pages, lru) {
 855                         if (pagevec_add(&pagevec, page) == 0)
 856                                 fscache_mark_pages_cached(op, &pagevec);
 857                 }
 858
 859                 if (pagevec_count(&pagevec) > 0)
 860                         fscache_mark_pages_cached(op, &pagevec);
 861                 ret = -ENODATA;
 862         } else {
 863                 ret = -ENOBUFS;
 864         }
 865
 866         fscache_retrieval_complete(op, *nr_pages);
 867         _leave(" = %d", ret);
 868         return ret;
 869 }
 870
 871 /*
 872  * request a page be stored in the cache
 873  * - cache withdrawal is prevented by the caller
 874  * - this request may be ignored if there's no cache block available, in which
 875  *   case -ENOBUFS will be returned
 876  * - if the op is in progress, 0 will be returned
 877  */
 878 int cachefiles_write_page(struct fscache_storage *op, struct page *page)
 879 {
 880         struct cachefiles_object *object;
 881         struct cachefiles_cache *cache;
 882         struct file *file;
 883         struct path path;
 884         loff_t pos, eof;
 885         size_t len;
 886         void *data;
 887         int ret = -ENOBUFS;
 888
 889         ASSERT(op != NULL);
 890         ASSERT(page != NULL);
 891
 892         object = container_of(op->op.object,
 893                               struct cachefiles_object, fscache);
 894
 895         _enter("%p,%p{%lx},,,", object, page, page->index);
 896
 897         if (!object->backer) {
 898                 _leave(" = -ENOBUFS");
 899                 return -ENOBUFS;
 900         }
 901
 902         ASSERT(d_is_reg(object->backer));
 903
 904         cache = container_of(object->fscache.cache,
 905                              struct cachefiles_cache, cache);
 906
 907         pos = (loff_t)page->index << PAGE_SHIFT;
 908
 909         /* We mustn't write more data than we have, so we have to beware of a
 910          * partial page at EOF.
 911          */
 912         eof = object->fscache.store_limit_l;
 913         if (pos >= eof)
 914                 goto error;
 915
 916         /* write the page to the backing filesystem and let it store it in its
 917          * own time */
 918         path.mnt = cache->mnt;
 919         path.dentry = object->backer;
 920         file = dentry_open(&path, O_RDWR | O_LARGEFILE, cache->cache_cred);
 921         if (IS_ERR(file)) {
 922                 ret = PTR_ERR(file);
 923                 goto error_2;
 924         }
 925
 926         len = PAGE_SIZE;
 927         if (eof & ~PAGE_MASK) {
 928                 if (eof - pos < PAGE_SIZE) {
 929                         _debug("cut short %llx to %llx",
 930                                pos, eof);
 931                         len = eof - pos;
 932                         ASSERTCMP(pos + len, ==, eof);
 933                 }
 934         }
 935
 936         data = kmap(page);
 937         ret = __kernel_write(file, data, len, &pos);
 938         kunmap(page);
 939         fput(file);
 940         if (ret != len)
 941                 goto error_eio;
 942
 943         _leave(" = 0");
 944         return 0;
 945
 946 error_eio:
 947         ret = -EIO;
 948 error_2:
 949         if (ret == -EIO)
 950                 cachefiles_io_error_obj(object,
 951                                         "Write page to backing file failed");
 952 error:
 953         _leave(" = -ENOBUFS [%d]", ret);
 954         return -ENOBUFS;
 955 }
 956
 957 /*
 958  * detach a backing block from a page
 959  * - cache withdrawal is prevented by the caller
 960  */
 961 void cachefiles_uncache_page(struct fscache_object *_object, struct page *page)
 962 {
 963         struct cachefiles_object *object;
 964         struct cachefiles_cache *cache;
 965
 966         object = container_of(_object, struct cachefiles_object, fscache);
 967         cache = container_of(object->fscache.cache,
 968                              struct cachefiles_cache, cache);
 969
 970         _enter("%p,{%lu}", object, page->index);
 971
 972         spin_unlock(&object->fscache.cookie->lock);
 973 }