fs/afs/write.c

   1 /* handling of writes to regular files and writing back to the server
   2  *
   3  * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells ([email protected])
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the License, or (at your option) any later version.
  10  */
  11 #include <linux/backing-dev.h>
  12 #include <linux/slab.h>
  13 #include <linux/fs.h>
  14 #include <linux/pagemap.h>
  15 #include <linux/writeback.h>
  16 #include <linux/pagevec.h>
  17 #include "internal.h"
  18
  19 static int afs_write_back_from_locked_page(struct afs_writeback *wb,
  20                                            struct page *page);
  21
  22 /*
  23  * mark a page as having been made dirty and thus needing writeback
  24  */
  25 int afs_set_page_dirty(struct page *page)
  26 {
  27         _enter("");
  28         return __set_page_dirty_nobuffers(page);
  29 }
  30
  31 /*
  32  * unlink a writeback record because its usage has reached zero
  33  * - must be called with the wb->vnode->writeback_lock held
  34  */
  35 static void afs_unlink_writeback(struct afs_writeback *wb)
  36 {
  37         struct afs_writeback *front;
  38         struct afs_vnode *vnode = wb->vnode;
  39
  40         list_del_init(&wb->link);
  41         if (!list_empty(&vnode->writebacks)) {
  42                 /* if an fsync rises to the front of the queue then wake it
  43                  * up */
  44                 front = list_entry(vnode->writebacks.next,
  45                                    struct afs_writeback, link);
  46                 if (front->state == AFS_WBACK_SYNCING) {
  47                         _debug("wake up sync");
  48                         front->state = AFS_WBACK_COMPLETE;
  49                         wake_up(&front->waitq);
  50                 }
  51         }
  52 }
  53
  54 /*
  55  * free a writeback record
  56  */
  57 static void afs_free_writeback(struct afs_writeback *wb)
  58 {
  59         _enter("");
  60         key_put(wb->key);
  61         kfree(wb);
  62 }
  63
  64 /*
  65  * dispose of a reference to a writeback record
  66  */
  67 void afs_put_writeback(struct afs_writeback *wb)
  68 {
  69         struct afs_vnode *vnode = wb->vnode;
  70
  71         _enter("{%d}", wb->usage);
  72
  73         spin_lock(&vnode->writeback_lock);
  74         if (--wb->usage == 0)
  75                 afs_unlink_writeback(wb);
  76         else
  77                 wb = NULL;
  78         spin_unlock(&vnode->writeback_lock);
  79         if (wb)
  80                 afs_free_writeback(wb);
  81 }
  82
  83 /*
  84  * partly or wholly fill a page that's under preparation for writing
  85  */
  86 static int afs_fill_page(struct afs_vnode *vnode, struct key *key,
  87                          loff_t pos, unsigned int len, struct page *page)
  88 {
  89         struct afs_read *req;
  90         int ret;
  91
  92         _enter(",,%llu", (unsigned long long)pos);
  93
  94         req = kzalloc(sizeof(struct afs_read) + sizeof(struct page *),
  95                       GFP_KERNEL);
  96         if (!req)
  97                 return -ENOMEM;
  98
  99         atomic_set(&req->usage, 1);
 100         req->pos = pos;
 101         req->len = len;
 102         req->nr_pages = 1;
 103         req->pages[0] = page;
 104         get_page(page);
 105
 106         ret = afs_vnode_fetch_data(vnode, key, req);
 107         afs_put_read(req);
 108         if (ret < 0) {
 109                 if (ret == -ENOENT) {
 110                         _debug("got NOENT from server"
 111                                " - marking file deleted and stale");
 112                         set_bit(AFS_VNODE_DELETED, &vnode->flags);
 113                         ret = -ESTALE;
 114                 }
 115         }
 116
 117         _leave(" = %d", ret);
 118         return ret;
 119 }
 120
 121 /*
 122  * prepare to perform part of a write to a page
 123  */
 124 int afs_write_begin(struct file *file, struct address_space *mapping,
 125                     loff_t pos, unsigned len, unsigned flags,
 126                     struct page **pagep, void **fsdata)
 127 {
 128         struct afs_writeback *candidate, *wb;
 129         struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
 130         struct page *page;
 131         struct key *key = file->private_data;
 132         unsigned from = pos & (PAGE_SIZE - 1);
 133         unsigned to = from + len;
 134         pgoff_t index = pos >> PAGE_SHIFT;
 135         int ret;
 136
 137         _enter("{%x:%u},{%lx},%u,%u",
 138                vnode->fid.vid, vnode->fid.vnode, index, from, to);
 139
 140         candidate = kzalloc(sizeof(*candidate), GFP_KERNEL);
 141         if (!candidate)
 142                 return -ENOMEM;
 143         candidate->vnode = vnode;
 144         candidate->first = candidate->last = index;
 145         candidate->offset_first = from;
 146         candidate->to_last = to;
 147         INIT_LIST_HEAD(&candidate->link);
 148         candidate->usage = 1;
 149         candidate->state = AFS_WBACK_PENDING;
 150         init_waitqueue_head(&candidate->waitq);
 151
 152         page = grab_cache_page_write_begin(mapping, index, flags);
 153         if (!page) {
 154                 kfree(candidate);
 155                 return -ENOMEM;
 156         }
 157
 158         if (!PageUptodate(page) && len != PAGE_SIZE) {
 159                 ret = afs_fill_page(vnode, key, pos & PAGE_MASK, PAGE_SIZE, page);
 160                 if (ret < 0) {
 161                         unlock_page(page);
 162                         put_page(page);
 163                         kfree(candidate);
 164                         _leave(" = %d [prep]", ret);
 165                         return ret;
 166                 }
 167                 SetPageUptodate(page);
 168         }
 169
 170         /* page won't leak in error case: it eventually gets cleaned off LRU */
 171         *pagep = page;
 172
 173 try_again:
 174         spin_lock(&vnode->writeback_lock);
 175
 176         /* see if this page is already pending a writeback under a suitable key
 177          * - if so we can just join onto that one */
 178         wb = (struct afs_writeback *) page_private(page);
 179         if (wb) {
 180                 if (wb->key == key && wb->state == AFS_WBACK_PENDING)
 181                         goto subsume_in_current_wb;
 182                 goto flush_conflicting_wb;
 183         }
 184
 185         if (index > 0) {
 186                 /* see if we can find an already pending writeback that we can
 187                  * append this page to */
 188                 list_for_each_entry(wb, &vnode->writebacks, link) {
 189                         if (wb->last == index - 1 && wb->key == key &&
 190                             wb->state == AFS_WBACK_PENDING)
 191                                 goto append_to_previous_wb;
 192                 }
 193         }
 194
 195         list_add_tail(&candidate->link, &vnode->writebacks);
 196         candidate->key = key_get(key);
 197         spin_unlock(&vnode->writeback_lock);
 198         SetPagePrivate(page);
 199         set_page_private(page, (unsigned long) candidate);
 200         _leave(" = 0 [new]");
 201         return 0;
 202
 203 subsume_in_current_wb:
 204         _debug("subsume");
 205         ASSERTRANGE(wb->first, <=, index, <=, wb->last);
 206         if (index == wb->first && from < wb->offset_first)
 207                 wb->offset_first = from;
 208         if (index == wb->last && to > wb->to_last)
 209                 wb->to_last = to;
 210         spin_unlock(&vnode->writeback_lock);
 211         kfree(candidate);
 212         _leave(" = 0 [sub]");
 213         return 0;
 214
 215 append_to_previous_wb:
 216         _debug("append into %lx-%lx", wb->first, wb->last);
 217         wb->usage++;
 218         wb->last++;
 219         wb->to_last = to;
 220         spin_unlock(&vnode->writeback_lock);
 221         SetPagePrivate(page);
 222         set_page_private(page, (unsigned long) wb);
 223         kfree(candidate);
 224         _leave(" = 0 [app]");
 225         return 0;
 226
 227         /* the page is currently bound to another context, so if it's dirty we
 228          * need to flush it before we can use the new context */
 229 flush_conflicting_wb:
 230         _debug("flush conflict");
 231         if (wb->state == AFS_WBACK_PENDING)
 232                 wb->state = AFS_WBACK_CONFLICTING;
 233         spin_unlock(&vnode->writeback_lock);
 234         if (clear_page_dirty_for_io(page)) {
 235                 ret = afs_write_back_from_locked_page(wb, page);
 236                 if (ret < 0) {
 237                         afs_put_writeback(candidate);
 238                         _leave(" = %d", ret);
 239                         return ret;
 240                 }
 241         }
 242
 243         /* the page holds a ref on the writeback record */
 244         afs_put_writeback(wb);
 245         set_page_private(page, 0);
 246         ClearPagePrivate(page);
 247         goto try_again;
 248 }
 249
 250 /*
 251  * finalise part of a write to a page
 252  */
 253 int afs_write_end(struct file *file, struct address_space *mapping,
 254                   loff_t pos, unsigned len, unsigned copied,
 255                   struct page *page, void *fsdata)
 256 {
 257         struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
 258         struct key *key = file->private_data;
 259         loff_t i_size, maybe_i_size;
 260         int ret;
 261
 262         _enter("{%x:%u},{%lx}",
 263                vnode->fid.vid, vnode->fid.vnode, page->index);
 264
 265         maybe_i_size = pos + copied;
 266
 267         i_size = i_size_read(&vnode->vfs_inode);
 268         if (maybe_i_size > i_size) {
 269                 spin_lock(&vnode->writeback_lock);
 270                 i_size = i_size_read(&vnode->vfs_inode);
 271                 if (maybe_i_size > i_size)
 272                         i_size_write(&vnode->vfs_inode, maybe_i_size);
 273                 spin_unlock(&vnode->writeback_lock);
 274         }
 275
 276         if (!PageUptodate(page)) {
 277                 if (copied < len) {
 278                         /* Try and load any missing data from the server.  The
 279                          * unmarshalling routine will take care of clearing any
 280                          * bits that are beyond the EOF.
 281                          */
 282                         ret = afs_fill_page(vnode, key, pos + copied,
 283                                             len - copied, page);
 284                         if (ret < 0)
 285                                 return ret;
 286                 }
 287                 SetPageUptodate(page);
 288         }
 289
 290         set_page_dirty(page);
 291         if (PageDirty(page))
 292                 _debug("dirtied");
 293         unlock_page(page);
 294         put_page(page);
 295
 296         return copied;
 297 }
 298
 299 /*
 300  * kill all the pages in the given range
 301  */
 302 static void afs_kill_pages(struct afs_vnode *vnode, bool error,
 303                            pgoff_t first, pgoff_t last)
 304 {
 305         struct pagevec pv;
 306         unsigned count, loop;
 307
 308         _enter("{%x:%u},%lx-%lx",
 309                vnode->fid.vid, vnode->fid.vnode, first, last);
 310
 311         pagevec_init(&pv, 0);
 312
 313         do {
 314                 _debug("kill %lx-%lx", first, last);
 315
 316                 count = last - first + 1;
 317                 if (count > PAGEVEC_SIZE)
 318                         count = PAGEVEC_SIZE;
 319                 pv.nr = find_get_pages_contig(vnode->vfs_inode.i_mapping,
 320                                               first, count, pv.pages);
 321                 ASSERTCMP(pv.nr, ==, count);
 322
 323                 for (loop = 0; loop < count; loop++) {
 324                         struct page *page = pv.pages[loop];
 325                         ClearPageUptodate(page);
 326                         if (error)
 327                                 SetPageError(page);
 328                         if (PageWriteback(page))
 329                                 end_page_writeback(page);
 330                         if (page->index >= first)
 331                                 first = page->index + 1;
 332                 }
 333
 334                 __pagevec_release(&pv);
 335         } while (first < last);
 336
 337         _leave("");
 338 }
 339
 340 /*
 341  * synchronously write back the locked page and any subsequent non-locked dirty
 342  * pages also covered by the same writeback record
 343  */
 344 static int afs_write_back_from_locked_page(struct afs_writeback *wb,
 345                                            struct page *primary_page)
 346 {
 347         struct page *pages[8], *page;
 348         unsigned long count;
 349         unsigned n, offset, to;
 350         pgoff_t start, first, last;
 351         int loop, ret;
 352
 353         _enter(",%lx", primary_page->index);
 354
 355         count = 1;
 356         if (test_set_page_writeback(primary_page))
 357                 BUG();
 358
 359         /* find all consecutive lockable dirty pages, stopping when we find a
 360          * page that is not immediately lockable, is not dirty or is missing,
 361          * or we reach the end of the range */
 362         start = primary_page->index;
 363         if (start >= wb->last)
 364                 goto no_more;
 365         start++;
 366         do {
 367                 _debug("more %lx [%lx]", start, count);
 368                 n = wb->last - start + 1;
 369                 if (n > ARRAY_SIZE(pages))
 370                         n = ARRAY_SIZE(pages);
 371                 n = find_get_pages_contig(wb->vnode->vfs_inode.i_mapping,
 372                                           start, n, pages);
 373                 _debug("fgpc %u", n);
 374                 if (n == 0)
 375                         goto no_more;
 376                 if (pages[0]->index != start) {
 377                         do {
 378                                 put_page(pages[--n]);
 379                         } while (n > 0);
 380                         goto no_more;
 381                 }
 382
 383                 for (loop = 0; loop < n; loop++) {
 384                         page = pages[loop];
 385                         if (page->index > wb->last)
 386                                 break;
 387                         if (!trylock_page(page))
 388                                 break;
 389                         if (!PageDirty(page) ||
 390                             page_private(page) != (unsigned long) wb) {
 391                                 unlock_page(page);
 392                                 break;
 393                         }
 394                         if (!clear_page_dirty_for_io(page))
 395                                 BUG();
 396                         if (test_set_page_writeback(page))
 397                                 BUG();
 398                         unlock_page(page);
 399                         put_page(page);
 400                 }
 401                 count += loop;
 402                 if (loop < n) {
 403                         for (; loop < n; loop++)
 404                                 put_page(pages[loop]);
 405                         goto no_more;
 406                 }
 407
 408                 start += loop;
 409         } while (start <= wb->last && count < 65536);
 410
 411 no_more:
 412         /* we now have a contiguous set of dirty pages, each with writeback set
 413          * and the dirty mark cleared; the first page is locked and must remain
 414          * so, all the rest are unlocked */
 415         first = primary_page->index;
 416         last = first + count - 1;
 417
 418         offset = (first == wb->first) ? wb->offset_first : 0;
 419         to = (last == wb->last) ? wb->to_last : PAGE_SIZE;
 420
 421         _debug("write back %lx[%u..] to %lx[..%u]", first, offset, last, to);
 422
 423         ret = afs_vnode_store_data(wb, first, last, offset, to);
 424         if (ret < 0) {
 425                 switch (ret) {
 426                 case -EDQUOT:
 427                 case -ENOSPC:
 428                         mapping_set_error(wb->vnode->vfs_inode.i_mapping, -ENOSPC);
 429                         break;
 430                 case -EROFS:
 431                 case -EIO:
 432                 case -EREMOTEIO:
 433                 case -EFBIG:
 434                 case -ENOENT:
 435                 case -ENOMEDIUM:
 436                 case -ENXIO:
 437                         afs_kill_pages(wb->vnode, true, first, last);
 438                         mapping_set_error(wb->vnode->vfs_inode.i_mapping, -EIO);
 439                         break;
 440                 case -EACCES:
 441                 case -EPERM:
 442                 case -ENOKEY:
 443                 case -EKEYEXPIRED:
 444                 case -EKEYREJECTED:
 445                 case -EKEYREVOKED:
 446                         afs_kill_pages(wb->vnode, false, first, last);
 447                         break;
 448                 default:
 449                         break;
 450                 }
 451         } else {
 452                 ret = count;
 453         }
 454
 455         _leave(" = %d", ret);
 456         return ret;
 457 }
 458
 459 /*
 460  * write a page back to the server
 461  * - the caller locked the page for us
 462  */
 463 int afs_writepage(struct page *page, struct writeback_control *wbc)
 464 {
 465         struct afs_writeback *wb;
 466         int ret;
 467
 468         _enter("{%lx},", page->index);
 469
 470         wb = (struct afs_writeback *) page_private(page);
 471         ASSERT(wb != NULL);
 472
 473         ret = afs_write_back_from_locked_page(wb, page);
 474         unlock_page(page);
 475         if (ret < 0) {
 476                 _leave(" = %d", ret);
 477                 return 0;
 478         }
 479
 480         wbc->nr_to_write -= ret;
 481
 482         _leave(" = 0");
 483         return 0;
 484 }
 485
 486 /*
 487  * write a region of pages back to the server
 488  */
 489 static int afs_writepages_region(struct address_space *mapping,
 490                                  struct writeback_control *wbc,
 491                                  pgoff_t index, pgoff_t end, pgoff_t *_next)
 492 {
 493         struct afs_writeback *wb;
 494         struct page *page;
 495         int ret, n;
 496
 497         _enter(",,%lx,%lx,", index, end);
 498
 499         do {
 500                 n = find_get_pages_tag(mapping, &index, PAGECACHE_TAG_DIRTY,
 501                                        1, &page);
 502                 if (!n)
 503                         break;
 504
 505                 _debug("wback %lx", page->index);
 506
 507                 if (page->index > end) {
 508                         *_next = index;
 509                         put_page(page);
 510                         _leave(" = 0 [%lx]", *_next);
 511                         return 0;
 512                 }
 513
 514                 /* at this point we hold neither mapping->tree_lock nor lock on
 515                  * the page itself: the page may be truncated or invalidated
 516                  * (changing page->mapping to NULL), or even swizzled back from
 517                  * swapper_space to tmpfs file mapping
 518                  */
 519                 lock_page(page);
 520
 521                 if (page->mapping != mapping || !PageDirty(page)) {
 522                         unlock_page(page);
 523                         put_page(page);
 524                         continue;
 525                 }
 526
 527                 if (PageWriteback(page)) {
 528                         unlock_page(page);
 529                         if (wbc->sync_mode != WB_SYNC_NONE)
 530                                 wait_on_page_writeback(page);
 531                         put_page(page);
 532                         continue;
 533                 }
 534
 535                 wb = (struct afs_writeback *) page_private(page);
 536                 ASSERT(wb != NULL);
 537
 538                 spin_lock(&wb->vnode->writeback_lock);
 539                 wb->state = AFS_WBACK_WRITING;
 540                 spin_unlock(&wb->vnode->writeback_lock);
 541
 542                 if (!clear_page_dirty_for_io(page))
 543                         BUG();
 544                 ret = afs_write_back_from_locked_page(wb, page);
 545                 unlock_page(page);
 546                 put_page(page);
 547                 if (ret < 0) {
 548                         _leave(" = %d", ret);
 549                         return ret;
 550                 }
 551
 552                 wbc->nr_to_write -= ret;
 553
 554                 cond_resched();
 555         } while (index < end && wbc->nr_to_write > 0);
 556
 557         *_next = index;
 558         _leave(" = 0 [%lx]", *_next);
 559         return 0;
 560 }
 561
 562 /*
 563  * write some of the pending data back to the server
 564  */
 565 int afs_writepages(struct address_space *mapping,
 566                    struct writeback_control *wbc)
 567 {
 568         pgoff_t start, end, next;
 569         int ret;
 570
 571         _enter("");
 572
 573         if (wbc->range_cyclic) {
 574                 start = mapping->writeback_index;
 575                 end = -1;
 576                 ret = afs_writepages_region(mapping, wbc, start, end, &next);
 577                 if (start > 0 && wbc->nr_to_write > 0 && ret == 0)
 578                         ret = afs_writepages_region(mapping, wbc, 0, start,
 579                                                     &next);
 580                 mapping->writeback_index = next;
 581         } else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
 582                 end = (pgoff_t)(LLONG_MAX >> PAGE_SHIFT);
 583                 ret = afs_writepages_region(mapping, wbc, 0, end, &next);
 584                 if (wbc->nr_to_write > 0)
 585                         mapping->writeback_index = next;
 586         } else {
 587                 start = wbc->range_start >> PAGE_SHIFT;
 588                 end = wbc->range_end >> PAGE_SHIFT;
 589                 ret = afs_writepages_region(mapping, wbc, start, end, &next);
 590         }
 591
 592         _leave(" = %d", ret);
 593         return ret;
 594 }
 595
 596 /*
 597  * completion of write to server
 598  */
 599 void afs_pages_written_back(struct afs_vnode *vnode, struct afs_call *call)
 600 {
 601         struct afs_writeback *wb = call->wb;
 602         struct pagevec pv;
 603         unsigned count, loop;
 604         pgoff_t first = call->first, last = call->last;
 605         bool free_wb;
 606
 607         _enter("{%x:%u},{%lx-%lx}",
 608                vnode->fid.vid, vnode->fid.vnode, first, last);
 609
 610         ASSERT(wb != NULL);
 611
 612         pagevec_init(&pv, 0);
 613
 614         do {
 615                 _debug("done %lx-%lx", first, last);
 616
 617                 count = last - first + 1;
 618                 if (count > PAGEVEC_SIZE)
 619                         count = PAGEVEC_SIZE;
 620                 pv.nr = find_get_pages_contig(call->mapping, first, count,
 621                                               pv.pages);
 622                 ASSERTCMP(pv.nr, ==, count);
 623
 624                 spin_lock(&vnode->writeback_lock);
 625                 for (loop = 0; loop < count; loop++) {
 626                         struct page *page = pv.pages[loop];
 627                         end_page_writeback(page);
 628                         if (page_private(page) == (unsigned long) wb) {
 629                                 set_page_private(page, 0);
 630                                 ClearPagePrivate(page);
 631                                 wb->usage--;
 632                         }
 633                 }
 634                 free_wb = false;
 635                 if (wb->usage == 0) {
 636                         afs_unlink_writeback(wb);
 637                         free_wb = true;
 638                 }
 639                 spin_unlock(&vnode->writeback_lock);
 640                 first += count;
 641                 if (free_wb) {
 642                         afs_free_writeback(wb);
 643                         wb = NULL;
 644                 }
 645
 646                 __pagevec_release(&pv);
 647         } while (first <= last);
 648
 649         _leave("");
 650 }
 651
 652 /*
 653  * write to an AFS file
 654  */
 655 ssize_t afs_file_write(struct kiocb *iocb, struct iov_iter *from)
 656 {
 657         struct afs_vnode *vnode = AFS_FS_I(file_inode(iocb->ki_filp));
 658         ssize_t result;
 659         size_t count = iov_iter_count(from);
 660
 661         _enter("{%x.%u},{%zu},",
 662                vnode->fid.vid, vnode->fid.vnode, count);
 663
 664         if (IS_SWAPFILE(&vnode->vfs_inode)) {
 665                 printk(KERN_INFO
 666                        "AFS: Attempt to write to active swap file!\n");
 667                 return -EBUSY;
 668         }
 669
 670         if (!count)
 671                 return 0;
 672
 673         result = generic_file_write_iter(iocb, from);
 674
 675         _leave(" = %zd", result);
 676         return result;
 677 }
 678
 679 /*
 680  * flush the vnode to the fileserver
 681  */
 682 int afs_writeback_all(struct afs_vnode *vnode)
 683 {
 684         struct address_space *mapping = vnode->vfs_inode.i_mapping;
 685         struct writeback_control wbc = {
 686                 .sync_mode      = WB_SYNC_ALL,
 687                 .nr_to_write    = LONG_MAX,
 688                 .range_cyclic   = 1,
 689         };
 690         int ret;
 691
 692         _enter("");
 693
 694         ret = mapping->a_ops->writepages(mapping, &wbc);
 695         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 696
 697         _leave(" = %d", ret);
 698         return ret;
 699 }
 700
 701 /*
 702  * flush any dirty pages for this process, and check for write errors.
 703  * - the return status from this call provides a reliable indication of
 704  *   whether any write errors occurred for this process.
 705  */
 706 int afs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 707 {
 708         struct inode *inode = file_inode(file);
 709         struct afs_writeback *wb, *xwb;
 710         struct afs_vnode *vnode = AFS_FS_I(inode);
 711         int ret;
 712
 713         _enter("{%x:%u},{n=%pD},%d",
 714                vnode->fid.vid, vnode->fid.vnode, file,
 715                datasync);
 716
 717         ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
 718         if (ret)
 719                 return ret;
 720         inode_lock(inode);
 721
 722         /* use a writeback record as a marker in the queue - when this reaches
 723          * the front of the queue, all the outstanding writes are either
 724          * completed or rejected */
 725         wb = kzalloc(sizeof(*wb), GFP_KERNEL);
 726         if (!wb) {
 727                 ret = -ENOMEM;
 728                 goto out;
 729         }
 730         wb->vnode = vnode;
 731         wb->first = 0;
 732         wb->last = -1;
 733         wb->offset_first = 0;
 734         wb->to_last = PAGE_SIZE;
 735         wb->usage = 1;
 736         wb->state = AFS_WBACK_SYNCING;
 737         init_waitqueue_head(&wb->waitq);
 738
 739         spin_lock(&vnode->writeback_lock);
 740         list_for_each_entry(xwb, &vnode->writebacks, link) {
 741                 if (xwb->state == AFS_WBACK_PENDING)
 742                         xwb->state = AFS_WBACK_CONFLICTING;
 743         }
 744         list_add_tail(&wb->link, &vnode->writebacks);
 745         spin_unlock(&vnode->writeback_lock);
 746
 747         /* push all the outstanding writebacks to the server */
 748         ret = afs_writeback_all(vnode);
 749         if (ret < 0) {
 750                 afs_put_writeback(wb);
 751                 _leave(" = %d [wb]", ret);
 752                 goto out;
 753         }
 754
 755         /* wait for the preceding writes to actually complete */
 756         ret = wait_event_interruptible(wb->waitq,
 757                                        wb->state == AFS_WBACK_COMPLETE ||
 758                                        vnode->writebacks.next == &wb->link);
 759         afs_put_writeback(wb);
 760         _leave(" = %d", ret);
 761 out:
 762         inode_unlock(inode);
 763         return ret;
 764 }
 765
 766 /*
 767  * Flush out all outstanding writes on a file opened for writing when it is
 768  * closed.
 769  */
 770 int afs_flush(struct file *file, fl_owner_t id)
 771 {
 772         _enter("");
 773
 774         if ((file->f_mode & FMODE_WRITE) == 0)
 775                 return 0;
 776
 777         return vfs_fsync(file, 0);
 778 }
 779
 780 /*
 781  * notification that a previously read-only page is about to become writable
 782  * - if it returns an error, the caller will deliver a bus error signal
 783  */
 784 int afs_page_mkwrite(struct vm_area_struct *vma, struct page *page)
 785 {
 786         struct afs_vnode *vnode = AFS_FS_I(vma->vm_file->f_mapping->host);
 787
 788         _enter("{{%x:%u}},{%lx}",
 789                vnode->fid.vid, vnode->fid.vnode, page->index);
 790
 791         /* wait for the page to be written to the cache before we allow it to
 792          * be modified */
 793 #ifdef CONFIG_AFS_FSCACHE
 794         fscache_wait_on_page_write(vnode->cache, page);
 795 #endif
 796
 797         _leave(" = 0");
 798         return 0;
 799 }