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