linux/fs/cachefiles/rdwr.c
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   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 */
  24static int cachefiles_read_waiter(wait_queue_t *wait, unsigned mode,
  25                                  int sync, void *_key)
  26{
  27        struct cachefiles_one_read *monitor =
  28                container_of(wait, struct cachefiles_one_read, monitor);
  29        struct cachefiles_object *object;
  30        struct wait_bit_key *key = _key;
  31        struct page *page = wait->private;
  32
  33        ASSERT(key);
  34
  35        _enter("{%lu},%u,%d,{%p,%u}",
  36               monitor->netfs_page->index, mode, sync,
  37               key->flags, key->bit_nr);
  38
  39        if (key->flags != &page->flags ||
  40            key->bit_nr != PG_locked)
  41                return 0;
  42
  43        _debug("--- monitor %p %lx ---", page, page->flags);
  44
  45        if (!PageUptodate(page) && !PageError(page)) {
  46                /* unlocked, not uptodate and not erronous? */
  47                _debug("page probably truncated");
  48        }
  49
  50        /* remove from the waitqueue */
  51        list_del(&wait->task_list);
  52
  53        /* move onto the action list and queue for FS-Cache thread pool */
  54        ASSERT(monitor->op);
  55
  56        object = container_of(monitor->op->op.object,
  57                              struct cachefiles_object, fscache);
  58
  59        spin_lock(&object->work_lock);
  60        list_add_tail(&monitor->op_link, &monitor->op->to_do);
  61        spin_unlock(&object->work_lock);
  62
  63        fscache_enqueue_retrieval(monitor->op);
  64        return 0;
  65}
  66
  67/*
  68 * handle a probably truncated page
  69 * - check to see if the page is still relevant and reissue the read if
  70 *   possible
  71 * - return -EIO on error, -ENODATA if the page is gone, -EINPROGRESS if we
  72 *   must wait again and 0 if successful
  73 */
  74static 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
 136unlock_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 */
 149static 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 */
 226static int cachefiles_read_backing_file_one(struct cachefiles_object *object,
 227                                            struct fscache_retrieval *op,
 228                                            struct page *netpage)
 229{
 230        struct cachefiles_one_read *monitor;
 231        struct address_space *bmapping;
 232        struct page *newpage, *backpage;
 233        int ret;
 234
 235        _enter("");
 236
 237        _debug("read back %p{%lu,%d}",
 238               netpage, netpage->index, page_count(netpage));
 239
 240        monitor = kzalloc(sizeof(*monitor), cachefiles_gfp);
 241        if (!monitor)
 242                goto nomem;
 243
 244        monitor->netfs_page = netpage;
 245        monitor->op = fscache_get_retrieval(op);
 246
 247        init_waitqueue_func_entry(&monitor->monitor, cachefiles_read_waiter);
 248
 249        /* attempt to get hold of the backing page */
 250        bmapping = d_backing_inode(object->backer)->i_mapping;
 251        newpage = NULL;
 252
 253        for (;;) {
 254                backpage = find_get_page(bmapping, netpage->index);
 255                if (backpage)
 256                        goto backing_page_already_present;
 257
 258                if (!newpage) {
 259                        newpage = __page_cache_alloc(cachefiles_gfp |
 260                                                     __GFP_COLD);
 261                        if (!newpage)
 262                                goto nomem_monitor;
 263                }
 264
 265                ret = add_to_page_cache_lru(newpage, bmapping,
 266                                            netpage->index, cachefiles_gfp);
 267                if (ret == 0)
 268                        goto installed_new_backing_page;
 269                if (ret != -EEXIST)
 270                        goto nomem_page;
 271        }
 272
 273        /* we've installed a new backing page, so now we need to start
 274         * it reading */
 275installed_new_backing_page:
 276        _debug("- new %p", newpage);
 277
 278        backpage = newpage;
 279        newpage = NULL;
 280
 281read_backing_page:
 282        ret = bmapping->a_ops->readpage(NULL, backpage);
 283        if (ret < 0)
 284                goto read_error;
 285
 286        /* set the monitor to transfer the data across */
 287monitor_backing_page:
 288        _debug("- monitor add");
 289
 290        /* install the monitor */
 291        get_page(monitor->netfs_page);
 292        get_page(backpage);
 293        monitor->back_page = backpage;
 294        monitor->monitor.private = backpage;
 295        add_page_wait_queue(backpage, &monitor->monitor);
 296        monitor = NULL;
 297
 298        /* but the page may have been read before the monitor was installed, so
 299         * the monitor may miss the event - so we have to ensure that we do get
 300         * one in such a case */
 301        if (trylock_page(backpage)) {
 302                _debug("jumpstart %p {%lx}", backpage, backpage->flags);
 303                unlock_page(backpage);
 304        }
 305        goto success;
 306
 307        /* if the backing page is already present, it can be in one of
 308         * three states: read in progress, read failed or read okay */
 309backing_page_already_present:
 310        _debug("- present");
 311
 312        if (newpage) {
 313                put_page(newpage);
 314                newpage = NULL;
 315        }
 316
 317        if (PageError(backpage))
 318                goto io_error;
 319
 320        if (PageUptodate(backpage))
 321                goto backing_page_already_uptodate;
 322
 323        if (!trylock_page(backpage))
 324                goto monitor_backing_page;
 325        _debug("read %p {%lx}", backpage, backpage->flags);
 326        goto read_backing_page;
 327
 328        /* the backing page is already up to date, attach the netfs
 329         * page to the pagecache and LRU and copy the data across */
 330backing_page_already_uptodate:
 331        _debug("- uptodate");
 332
 333        fscache_mark_page_cached(op, netpage);
 334
 335        copy_highpage(netpage, backpage);
 336        fscache_end_io(op, netpage, 0);
 337        fscache_retrieval_complete(op, 1);
 338
 339success:
 340        _debug("success");
 341        ret = 0;
 342
 343out:
 344        if (backpage)
 345                put_page(backpage);
 346        if (monitor) {
 347                fscache_put_retrieval(monitor->op);
 348                kfree(monitor);
 349        }
 350        _leave(" = %d", ret);
 351        return ret;
 352
 353read_error:
 354        _debug("read error %d", ret);
 355        if (ret == -ENOMEM) {
 356                fscache_retrieval_complete(op, 1);
 357                goto out;
 358        }
 359io_error:
 360        cachefiles_io_error_obj(object, "Page read error on backing file");
 361        fscache_retrieval_complete(op, 1);
 362        ret = -ENOBUFS;
 363        goto out;
 364
 365nomem_page:
 366        put_page(newpage);
 367nomem_monitor:
 368        fscache_put_retrieval(monitor->op);
 369        kfree(monitor);
 370nomem:
 371        fscache_retrieval_complete(op, 1);
 372        _leave(" = -ENOMEM");
 373        return -ENOMEM;
 374}
 375
 376/*
 377 * read a page from the cache or allocate a block in which to store it
 378 * - cache withdrawal is prevented by the caller
 379 * - returns -EINTR if interrupted
 380 * - returns -ENOMEM if ran out of memory
 381 * - returns -ENOBUFS if no buffers can be made available
 382 * - returns -ENOBUFS if page is beyond EOF
 383 * - if the page is backed by a block in the cache:
 384 *   - a read will be started which will call the callback on completion
 385 *   - 0 will be returned
 386 * - else if the page is unbacked:
 387 *   - the metadata will be retained
 388 *   - -ENODATA will be returned
 389 */
 390int cachefiles_read_or_alloc_page(struct fscache_retrieval *op,
 391                                  struct page *page,
 392                                  gfp_t gfp)
 393{
 394        struct cachefiles_object *object;
 395        struct cachefiles_cache *cache;
 396        struct inode *inode;
 397        sector_t block0, block;
 398        unsigned shift;
 399        int ret;
 400
 401        object = container_of(op->op.object,
 402                              struct cachefiles_object, fscache);
 403        cache = container_of(object->fscache.cache,
 404                             struct cachefiles_cache, cache);
 405
 406        _enter("{%p},{%lx},,,", object, page->index);
 407
 408        if (!object->backer)
 409                goto enobufs;
 410
 411        inode = d_backing_inode(object->backer);
 412        ASSERT(S_ISREG(inode->i_mode));
 413        ASSERT(inode->i_mapping->a_ops->bmap);
 414        ASSERT(inode->i_mapping->a_ops->readpages);
 415
 416        /* calculate the shift required to use bmap */
 417        shift = PAGE_SHIFT - inode->i_sb->s_blocksize_bits;
 418
 419        op->op.flags &= FSCACHE_OP_KEEP_FLAGS;
 420        op->op.flags |= FSCACHE_OP_ASYNC;
 421        op->op.processor = cachefiles_read_copier;
 422
 423        /* we assume the absence or presence of the first block is a good
 424         * enough indication for the page as a whole
 425         * - TODO: don't use bmap() for this as it is _not_ actually good
 426         *   enough for this as it doesn't indicate errors, but it's all we've
 427         *   got for the moment
 428         */
 429        block0 = page->index;
 430        block0 <<= shift;
 431
 432        block = inode->i_mapping->a_ops->bmap(inode->i_mapping, block0);
 433        _debug("%llx -> %llx",
 434               (unsigned long long) block0,
 435               (unsigned long long) block);
 436
 437        if (block) {
 438                /* submit the apparently valid page to the backing fs to be
 439                 * read from disk */
 440                ret = cachefiles_read_backing_file_one(object, op, page);
 441        } else if (cachefiles_has_space(cache, 0, 1) == 0) {
 442                /* there's space in the cache we can use */
 443                fscache_mark_page_cached(op, page);
 444                fscache_retrieval_complete(op, 1);
 445                ret = -ENODATA;
 446        } else {
 447                goto enobufs;
 448        }
 449
 450        _leave(" = %d", ret);
 451        return ret;
 452
 453enobufs:
 454        fscache_retrieval_complete(op, 1);
 455        _leave(" = -ENOBUFS");
 456        return -ENOBUFS;
 457}
 458
 459/*
 460 * read the corresponding pages to the given set from the backing file
 461 * - any uncertain pages are simply discarded, to be tried again another time
 462 */
 463static int cachefiles_read_backing_file(struct cachefiles_object *object,
 464                                        struct fscache_retrieval *op,
 465                                        struct list_head *list)
 466{
 467        struct cachefiles_one_read *monitor = NULL;
 468        struct address_space *bmapping = d_backing_inode(object->backer)->i_mapping;
 469        struct page *newpage = NULL, *netpage, *_n, *backpage = NULL;
 470        int ret = 0;
 471
 472        _enter("");
 473
 474        list_for_each_entry_safe(netpage, _n, list, lru) {
 475                list_del(&netpage->lru);
 476
 477                _debug("read back %p{%lu,%d}",
 478                       netpage, netpage->index, page_count(netpage));
 479
 480                if (!monitor) {
 481                        monitor = kzalloc(sizeof(*monitor), cachefiles_gfp);
 482                        if (!monitor)
 483                                goto nomem;
 484
 485                        monitor->op = fscache_get_retrieval(op);
 486                        init_waitqueue_func_entry(&monitor->monitor,
 487                                                  cachefiles_read_waiter);
 488                }
 489
 490                for (;;) {
 491                        backpage = find_get_page(bmapping, netpage->index);
 492                        if (backpage)
 493                                goto backing_page_already_present;
 494
 495                        if (!newpage) {
 496                                newpage = __page_cache_alloc(cachefiles_gfp |
 497                                                             __GFP_COLD);
 498                                if (!newpage)
 499                                        goto nomem;
 500                        }
 501
 502                        ret = add_to_page_cache_lru(newpage, bmapping,
 503                                                    netpage->index,
 504                                                    cachefiles_gfp);
 505                        if (ret == 0)
 506                                goto installed_new_backing_page;
 507                        if (ret != -EEXIST)
 508                                goto nomem;
 509                }
 510
 511                /* we've installed a new backing page, so now we need
 512                 * to start it reading */
 513        installed_new_backing_page:
 514                _debug("- new %p", newpage);
 515
 516                backpage = newpage;
 517                newpage = NULL;
 518
 519        reread_backing_page:
 520                ret = bmapping->a_ops->readpage(NULL, backpage);
 521                if (ret < 0)
 522                        goto read_error;
 523
 524                /* add the netfs page to the pagecache and LRU, and set the
 525                 * monitor to transfer the data across */
 526        monitor_backing_page:
 527                _debug("- monitor add");
 528
 529                ret = add_to_page_cache_lru(netpage, op->mapping,
 530                                            netpage->index, cachefiles_gfp);
 531                if (ret < 0) {
 532                        if (ret == -EEXIST) {
 533                                put_page(netpage);
 534                                fscache_retrieval_complete(op, 1);
 535                                continue;
 536                        }
 537                        goto nomem;
 538                }
 539
 540                /* install a monitor */
 541                get_page(netpage);
 542                monitor->netfs_page = netpage;
 543
 544                get_page(backpage);
 545                monitor->back_page = backpage;
 546                monitor->monitor.private = backpage;
 547                add_page_wait_queue(backpage, &monitor->monitor);
 548                monitor = NULL;
 549
 550                /* but the page may have been read before the monitor was
 551                 * installed, so the monitor may miss the event - so we have to
 552                 * ensure that we do get one in such a case */
 553                if (trylock_page(backpage)) {
 554                        _debug("2unlock %p {%lx}", backpage, backpage->flags);
 555                        unlock_page(backpage);
 556                }
 557
 558                put_page(backpage);
 559                backpage = NULL;
 560
 561                put_page(netpage);
 562                netpage = NULL;
 563                continue;
 564
 565                /* if the backing page is already present, it can be in one of
 566                 * three states: read in progress, read failed or read okay */
 567        backing_page_already_present:
 568                _debug("- present %p", backpage);
 569
 570                if (PageError(backpage))
 571                        goto io_error;
 572
 573                if (PageUptodate(backpage))
 574                        goto backing_page_already_uptodate;
 575
 576                _debug("- not ready %p{%lx}", backpage, backpage->flags);
 577
 578                if (!trylock_page(backpage))
 579                        goto monitor_backing_page;
 580
 581                if (PageError(backpage)) {
 582                        _debug("error %lx", backpage->flags);
 583                        unlock_page(backpage);
 584                        goto io_error;
 585                }
 586
 587                if (PageUptodate(backpage))
 588                        goto backing_page_already_uptodate_unlock;
 589
 590                /* we've locked a page that's neither up to date nor erroneous,
 591                 * so we need to attempt to read it again */
 592                goto reread_backing_page;
 593
 594                /* the backing page is already up to date, attach the netfs
 595                 * page to the pagecache and LRU and copy the data across */
 596        backing_page_already_uptodate_unlock:
 597                _debug("uptodate %lx", backpage->flags);
 598                unlock_page(backpage);
 599        backing_page_already_uptodate:
 600                _debug("- uptodate");
 601
 602                ret = add_to_page_cache_lru(netpage, op->mapping,
 603                                            netpage->index, cachefiles_gfp);
 604                if (ret < 0) {
 605                        if (ret == -EEXIST) {
 606                                put_page(netpage);
 607                                fscache_retrieval_complete(op, 1);
 608                                continue;
 609                        }
 610                        goto nomem;
 611                }
 612
 613                copy_highpage(netpage, backpage);
 614
 615                put_page(backpage);
 616                backpage = NULL;
 617
 618                fscache_mark_page_cached(op, netpage);
 619
 620                /* the netpage is unlocked and marked up to date here */
 621                fscache_end_io(op, netpage, 0);
 622                put_page(netpage);
 623                netpage = NULL;
 624                fscache_retrieval_complete(op, 1);
 625                continue;
 626        }
 627
 628        netpage = NULL;
 629
 630        _debug("out");
 631
 632out:
 633        /* tidy up */
 634        if (newpage)
 635                put_page(newpage);
 636        if (netpage)
 637                put_page(netpage);
 638        if (backpage)
 639                put_page(backpage);
 640        if (monitor) {
 641                fscache_put_retrieval(op);
 642                kfree(monitor);
 643        }
 644
 645        list_for_each_entry_safe(netpage, _n, list, lru) {
 646                list_del(&netpage->lru);
 647                put_page(netpage);
 648                fscache_retrieval_complete(op, 1);
 649        }
 650
 651        _leave(" = %d", ret);
 652        return ret;
 653
 654nomem:
 655        _debug("nomem");
 656        ret = -ENOMEM;
 657        goto record_page_complete;
 658
 659read_error:
 660        _debug("read error %d", ret);
 661        if (ret == -ENOMEM)
 662                goto record_page_complete;
 663io_error:
 664        cachefiles_io_error_obj(object, "Page read error on backing file");
 665        ret = -ENOBUFS;
 666record_page_complete:
 667        fscache_retrieval_complete(op, 1);
 668        goto out;
 669}
 670
 671/*
 672 * read a list of pages from the cache or allocate blocks in which to store
 673 * them
 674 */
 675int cachefiles_read_or_alloc_pages(struct fscache_retrieval *op,
 676                                   struct list_head *pages,
 677                                   unsigned *nr_pages,
 678                                   gfp_t gfp)
 679{
 680        struct cachefiles_object *object;
 681        struct cachefiles_cache *cache;
 682        struct list_head backpages;
 683        struct pagevec pagevec;
 684        struct inode *inode;
 685        struct page *page, *_n;
 686        unsigned shift, nrbackpages;
 687        int ret, ret2, space;
 688
 689        object = container_of(op->op.object,
 690                              struct cachefiles_object, fscache);
 691        cache = container_of(object->fscache.cache,
 692                             struct cachefiles_cache, cache);
 693
 694        _enter("{OBJ%x,%d},,%d,,",
 695               object->fscache.debug_id, atomic_read(&op->op.usage),
 696               *nr_pages);
 697
 698        if (!object->backer)
 699                goto all_enobufs;
 700
 701        space = 1;
 702        if (cachefiles_has_space(cache, 0, *nr_pages) < 0)
 703                space = 0;
 704
 705        inode = d_backing_inode(object->backer);
 706        ASSERT(S_ISREG(inode->i_mode));
 707        ASSERT(inode->i_mapping->a_ops->bmap);
 708        ASSERT(inode->i_mapping->a_ops->readpages);
 709
 710        /* calculate the shift required to use bmap */
 711        shift = PAGE_SHIFT - inode->i_sb->s_blocksize_bits;
 712
 713        pagevec_init(&pagevec, 0);
 714
 715        op->op.flags &= FSCACHE_OP_KEEP_FLAGS;
 716        op->op.flags |= FSCACHE_OP_ASYNC;
 717        op->op.processor = cachefiles_read_copier;
 718
 719        INIT_LIST_HEAD(&backpages);
 720        nrbackpages = 0;
 721
 722        ret = space ? -ENODATA : -ENOBUFS;
 723        list_for_each_entry_safe(page, _n, pages, lru) {
 724                sector_t block0, block;
 725
 726                /* we assume the absence or presence of the first block is a
 727                 * good enough indication for the page as a whole
 728                 * - TODO: don't use bmap() for this as it is _not_ actually
 729                 *   good enough for this as it doesn't indicate errors, but
 730                 *   it's all we've got for the moment
 731                 */
 732                block0 = page->index;
 733                block0 <<= shift;
 734
 735                block = inode->i_mapping->a_ops->bmap(inode->i_mapping,
 736                                                      block0);
 737                _debug("%llx -> %llx",
 738                       (unsigned long long) block0,
 739                       (unsigned long long) block);
 740
 741                if (block) {
 742                        /* we have data - add it to the list to give to the
 743                         * backing fs */
 744                        list_move(&page->lru, &backpages);
 745                        (*nr_pages)--;
 746                        nrbackpages++;
 747                } else if (space && pagevec_add(&pagevec, page) == 0) {
 748                        fscache_mark_pages_cached(op, &pagevec);
 749                        fscache_retrieval_complete(op, 1);
 750                        ret = -ENODATA;
 751                } else {
 752                        fscache_retrieval_complete(op, 1);
 753                }
 754        }
 755
 756        if (pagevec_count(&pagevec) > 0)
 757                fscache_mark_pages_cached(op, &pagevec);
 758
 759        if (list_empty(pages))
 760                ret = 0;
 761
 762        /* submit the apparently valid pages to the backing fs to be read from
 763         * disk */
 764        if (nrbackpages > 0) {
 765                ret2 = cachefiles_read_backing_file(object, op, &backpages);
 766                if (ret2 == -ENOMEM || ret2 == -EINTR)
 767                        ret = ret2;
 768        }
 769
 770        _leave(" = %d [nr=%u%s]",
 771               ret, *nr_pages, list_empty(pages) ? " empty" : "");
 772        return ret;
 773
 774all_enobufs:
 775        fscache_retrieval_complete(op, *nr_pages);
 776        return -ENOBUFS;
 777}
 778
 779/*
 780 * allocate a block in the cache in which to store a page
 781 * - cache withdrawal is prevented by the caller
 782 * - returns -EINTR if interrupted
 783 * - returns -ENOMEM if ran out of memory
 784 * - returns -ENOBUFS if no buffers can be made available
 785 * - returns -ENOBUFS if page is beyond EOF
 786 * - otherwise:
 787 *   - the metadata will be retained
 788 *   - 0 will be returned
 789 */
 790int cachefiles_allocate_page(struct fscache_retrieval *op,
 791                             struct page *page,
 792                             gfp_t gfp)
 793{
 794        struct cachefiles_object *object;
 795        struct cachefiles_cache *cache;
 796        int ret;
 797
 798        object = container_of(op->op.object,
 799                              struct cachefiles_object, fscache);
 800        cache = container_of(object->fscache.cache,
 801                             struct cachefiles_cache, cache);
 802
 803        _enter("%p,{%lx},", object, page->index);
 804
 805        ret = cachefiles_has_space(cache, 0, 1);
 806        if (ret == 0)
 807                fscache_mark_page_cached(op, page);
 808        else
 809                ret = -ENOBUFS;
 810
 811        fscache_retrieval_complete(op, 1);
 812        _leave(" = %d", ret);
 813        return ret;
 814}
 815
 816/*
 817 * allocate blocks in the cache in which to store a set of pages
 818 * - cache withdrawal is prevented by the caller
 819 * - returns -EINTR if interrupted
 820 * - returns -ENOMEM if ran out of memory
 821 * - returns -ENOBUFS if some buffers couldn't be made available
 822 * - returns -ENOBUFS if some pages are beyond EOF
 823 * - otherwise:
 824 *   - -ENODATA will be returned
 825 * - metadata will be retained for any page marked
 826 */
 827int cachefiles_allocate_pages(struct fscache_retrieval *op,
 828                              struct list_head *pages,
 829                              unsigned *nr_pages,
 830                              gfp_t gfp)
 831{
 832        struct cachefiles_object *object;
 833        struct cachefiles_cache *cache;
 834        struct pagevec pagevec;
 835        struct page *page;
 836        int ret;
 837
 838        object = container_of(op->op.object,
 839                              struct cachefiles_object, fscache);
 840        cache = container_of(object->fscache.cache,
 841                             struct cachefiles_cache, cache);
 842
 843        _enter("%p,,,%d,", object, *nr_pages);
 844
 845        ret = cachefiles_has_space(cache, 0, *nr_pages);
 846        if (ret == 0) {
 847                pagevec_init(&pagevec, 0);
 848
 849                list_for_each_entry(page, pages, lru) {
 850                        if (pagevec_add(&pagevec, page) == 0)
 851                                fscache_mark_pages_cached(op, &pagevec);
 852                }
 853
 854                if (pagevec_count(&pagevec) > 0)
 855                        fscache_mark_pages_cached(op, &pagevec);
 856                ret = -ENODATA;
 857        } else {
 858                ret = -ENOBUFS;
 859        }
 860
 861        fscache_retrieval_complete(op, *nr_pages);
 862        _leave(" = %d", ret);
 863        return ret;
 864}
 865
 866/*
 867 * request a page be stored in the cache
 868 * - cache withdrawal is prevented by the caller
 869 * - this request may be ignored if there's no cache block available, in which
 870 *   case -ENOBUFS will be returned
 871 * - if the op is in progress, 0 will be returned
 872 */
 873int cachefiles_write_page(struct fscache_storage *op, struct page *page)
 874{
 875        struct cachefiles_object *object;
 876        struct cachefiles_cache *cache;
 877        struct file *file;
 878        struct path path;
 879        loff_t pos, eof;
 880        size_t len;
 881        void *data;
 882        int ret = -ENOBUFS;
 883
 884        ASSERT(op != NULL);
 885        ASSERT(page != NULL);
 886
 887        object = container_of(op->op.object,
 888                              struct cachefiles_object, fscache);
 889
 890        _enter("%p,%p{%lx},,,", object, page, page->index);
 891
 892        if (!object->backer) {
 893                _leave(" = -ENOBUFS");
 894                return -ENOBUFS;
 895        }
 896
 897        ASSERT(d_is_reg(object->backer));
 898
 899        cache = container_of(object->fscache.cache,
 900                             struct cachefiles_cache, cache);
 901
 902        pos = (loff_t)page->index << PAGE_SHIFT;
 903
 904        /* We mustn't write more data than we have, so we have to beware of a
 905         * partial page at EOF.
 906         */
 907        eof = object->fscache.store_limit_l;
 908        if (pos >= eof)
 909                goto error;
 910
 911        /* write the page to the backing filesystem and let it store it in its
 912         * own time */
 913        path.mnt = cache->mnt;
 914        path.dentry = object->backer;
 915        file = dentry_open(&path, O_RDWR | O_LARGEFILE, cache->cache_cred);
 916        if (IS_ERR(file)) {
 917                ret = PTR_ERR(file);
 918                goto error_2;
 919        }
 920
 921        len = PAGE_SIZE;
 922        if (eof & ~PAGE_MASK) {
 923                if (eof - pos < PAGE_SIZE) {
 924                        _debug("cut short %llx to %llx",
 925                               pos, eof);
 926                        len = eof - pos;
 927                        ASSERTCMP(pos + len, ==, eof);
 928                }
 929        }
 930
 931        data = kmap(page);
 932        ret = __kernel_write(file, data, len, &pos);
 933        kunmap(page);
 934        fput(file);
 935        if (ret != len)
 936                goto error_eio;
 937
 938        _leave(" = 0");
 939        return 0;
 940
 941error_eio:
 942        ret = -EIO;
 943error_2:
 944        if (ret == -EIO)
 945                cachefiles_io_error_obj(object,
 946                                        "Write page to backing file failed");
 947error:
 948        _leave(" = -ENOBUFS [%d]", ret);
 949        return -ENOBUFS;
 950}
 951
 952/*
 953 * detach a backing block from a page
 954 * - cache withdrawal is prevented by the caller
 955 */
 956void cachefiles_uncache_page(struct fscache_object *_object, struct page *page)
 957{
 958        struct cachefiles_object *object;
 959        struct cachefiles_cache *cache;
 960
 961        object = container_of(_object, struct cachefiles_object, fscache);
 962        cache = container_of(object->fscache.cache,
 963                             struct cachefiles_cache, cache);
 964
 965        _enter("%p,{%lu}", object, page->index);
 966
 967        spin_unlock(&object->fscache.cookie->lock);
 968}
 969