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