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