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, unsigned len, struct page *page)
  88 {
  89         loff_t i_size;
  90         unsigned eof;
  91         int ret;
  92
  93         _enter(",,%llu,%u", (unsigned long long)pos, len);
  94
  95         ASSERTCMP(len, <=, PAGE_CACHE_SIZE);
  96
  97         i_size = i_size_read(&vnode->vfs_inode);
  98         if (pos + len > i_size)
  99                 eof = i_size;
 100         else
 101                 eof = PAGE_CACHE_SIZE;
 102
 103         ret = afs_vnode_fetch_data(vnode, key, 0, eof, page);
 104         if (ret < 0) {
 105                 if (ret == -ENOENT) {
 106                         _debug("got NOENT from server"
 107                                " - marking file deleted and stale");
 108                         set_bit(AFS_VNODE_DELETED, &vnode->flags);
 109                         ret = -ESTALE;
 110                 }
 111         }
 112
 113         _leave(" = %d", ret);
 114         return ret;
 115 }
 116
 117 /*
 118  * prepare to perform part of a write to a page
 119  */
 120 int afs_write_begin(struct file *file, struct address_space *mapping,
 121                     loff_t pos, unsigned len, unsigned flags,
 122                     struct page **pagep, void **fsdata)
 123 {
 124         struct afs_writeback *candidate, *wb;
 125         struct afs_vnode *vnode = AFS_FS_I(file->f_dentry->d_inode);
 126         struct page *page;
 127         struct key *key = file->private_data;
 128         unsigned from = pos & (PAGE_CACHE_SIZE - 1);
 129         unsigned to = from + len;
 130         pgoff_t index = pos >> PAGE_CACHE_SHIFT;
 131         int ret;
 132
 133         _enter("{%x:%u},{%lx},%u,%u",
 134                vnode->fid.vid, vnode->fid.vnode, index, from, to);
 135
 136         candidate = kzalloc(sizeof(*candidate), GFP_KERNEL);
 137         if (!candidate)
 138                 return -ENOMEM;
 139         candidate->vnode = vnode;
 140         candidate->first = candidate->last = index;
 141         candidate->offset_first = from;
 142         candidate->to_last = to;
 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)) {
 156                 _debug("not up to date");
 157                 ret = afs_fill_page(vnode, key, pos, len, page);
 158                 if (ret < 0) {
 159                         kfree(candidate);
 160                         _leave(" = %d [prep]", ret);
 161                         return ret;
 162                 }
 163                 SetPageUptodate(page);
 164         }
 165
 166 try_again:
 167         spin_lock(&vnode->writeback_lock);
 168
 169         /* see if this page is already pending a writeback under a suitable key
 170          * - if so we can just join onto that one */
 171         wb = (struct afs_writeback *) page_private(page);
 172         if (wb) {
 173                 if (wb->key == key && wb->state == AFS_WBACK_PENDING)
 174                         goto subsume_in_current_wb;
 175                 goto flush_conflicting_wb;
 176         }
 177
 178         if (index > 0) {
 179                 /* see if we can find an already pending writeback that we can
 180                  * append this page to */
 181                 list_for_each_entry(wb, &vnode->writebacks, link) {
 182                         if (wb->last == index - 1 && wb->key == key &&
 183                             wb->state == AFS_WBACK_PENDING)
 184                                 goto append_to_previous_wb;
 185                 }
 186         }
 187
 188         list_add_tail(&candidate->link, &vnode->writebacks);
 189         candidate->key = key_get(key);
 190         spin_unlock(&vnode->writeback_lock);
 191         SetPagePrivate(page);
 192         set_page_private(page, (unsigned long) candidate);
 193         _leave(" = 0 [new]");
 194         return 0;
 195
 196 subsume_in_current_wb:
 197         _debug("subsume");
 198         ASSERTRANGE(wb->first, <=, index, <=, wb->last);
 199         if (index == wb->first && from < wb->offset_first)
 200                 wb->offset_first = from;
 201         if (index == wb->last && to > wb->to_last)
 202                 wb->to_last = to;
 203         spin_unlock(&vnode->writeback_lock);
 204         kfree(candidate);
 205         _leave(" = 0 [sub]");
 206         return 0;
 207
 208 append_to_previous_wb:
 209         _debug("append into %lx-%lx", wb->first, wb->last);
 210         wb->usage++;
 211         wb->last++;
 212         wb->to_last = to;
 213         spin_unlock(&vnode->writeback_lock);
 214         SetPagePrivate(page);
 215         set_page_private(page, (unsigned long) wb);
 216         kfree(candidate);
 217         _leave(" = 0 [app]");
 218         return 0;
 219
 220         /* the page is currently bound to another context, so if it's dirty we
 221          * need to flush it before we can use the new context */
 222 flush_conflicting_wb:
 223         _debug("flush conflict");
 224         if (wb->state == AFS_WBACK_PENDING)
 225                 wb->state = AFS_WBACK_CONFLICTING;
 226         spin_unlock(&vnode->writeback_lock);
 227         if (PageDirty(page)) {
 228                 ret = afs_write_back_from_locked_page(wb, page);
 229                 if (ret < 0) {
 230                         afs_put_writeback(candidate);
 231                         _leave(" = %d", ret);
 232                         return ret;
 233                 }
 234         }
 235
 236         /* the page holds a ref on the writeback record */
 237         afs_put_writeback(wb);
 238         set_page_private(page, 0);
 239         ClearPagePrivate(page);
 240         goto try_again;
 241 }
 242
 243 /*
 244  * finalise part of a write to a page
 245  */
 246 int afs_write_end(struct file *file, struct address_space *mapping,
 247                   loff_t pos, unsigned len, unsigned copied,
 248                   struct page *page, void *fsdata)
 249 {
 250         struct afs_vnode *vnode = AFS_FS_I(file->f_dentry->d_inode);
 251         loff_t i_size, maybe_i_size;
 252
 253         _enter("{%x:%u},{%lx}",
 254                vnode->fid.vid, vnode->fid.vnode, page->index);
 255
 256         maybe_i_size = pos + copied;
 257
 258         i_size = i_size_read(&vnode->vfs_inode);
 259         if (maybe_i_size > i_size) {
 260                 spin_lock(&vnode->writeback_lock);
 261                 i_size = i_size_read(&vnode->vfs_inode);
 262                 if (maybe_i_size > i_size)
 263                         i_size_write(&vnode->vfs_inode, maybe_i_size);
 264                 spin_unlock(&vnode->writeback_lock);
 265         }
 266
 267         set_page_dirty(page);
 268         if (PageDirty(page))
 269                 _debug("dirtied");
 270         unlock_page(page);
 271         page_cache_release(page);
 272
 273         return copied;
 274 }
 275
 276 /*
 277  * kill all the pages in the given range
 278  */
 279 static void afs_kill_pages(struct afs_vnode *vnode, bool error,
 280                            pgoff_t first, pgoff_t last)
 281 {
 282         struct pagevec pv;
 283         unsigned count, loop;
 284
 285         _enter("{%x:%u},%lx-%lx",
 286                vnode->fid.vid, vnode->fid.vnode, first, last);
 287
 288         pagevec_init(&pv, 0);
 289
 290         do {
 291                 _debug("kill %lx-%lx", first, last);
 292
 293                 count = last - first + 1;
 294                 if (count > PAGEVEC_SIZE)
 295                         count = PAGEVEC_SIZE;
 296                 pv.nr = find_get_pages_contig(vnode->vfs_inode.i_mapping,
 297                                               first, count, pv.pages);
 298                 ASSERTCMP(pv.nr, ==, count);
 299
 300                 for (loop = 0; loop < count; loop++) {
 301                         ClearPageUptodate(pv.pages[loop]);
 302                         if (error)
 303                                 SetPageError(pv.pages[loop]);
 304                         end_page_writeback(pv.pages[loop]);
 305                 }
 306
 307                 __pagevec_release(&pv);
 308         } while (first < last);
 309
 310         _leave("");
 311 }
 312
 313 /*
 314  * synchronously write back the locked page and any subsequent non-locked dirty
 315  * pages also covered by the same writeback record
 316  */
 317 static int afs_write_back_from_locked_page(struct afs_writeback *wb,
 318                                            struct page *primary_page)
 319 {
 320         struct page *pages[8], *page;
 321         unsigned long count;
 322         unsigned n, offset, to;
 323         pgoff_t start, first, last;
 324         int loop, ret;
 325
 326         _enter(",%lx", primary_page->index);
 327
 328         count = 1;
 329         if (!clear_page_dirty_for_io(primary_page))
 330                 BUG();
 331         if (test_set_page_writeback(primary_page))
 332                 BUG();
 333
 334         /* find all consecutive lockable dirty pages, stopping when we find a
 335          * page that is not immediately lockable, is not dirty or is missing,
 336          * or we reach the end of the range */
 337         start = primary_page->index;
 338         if (start >= wb->last)
 339                 goto no_more;
 340         start++;
 341         do {
 342                 _debug("more %lx [%lx]", start, count);
 343                 n = wb->last - start + 1;
 344                 if (n > ARRAY_SIZE(pages))
 345                         n = ARRAY_SIZE(pages);
 346                 n = find_get_pages_contig(wb->vnode->vfs_inode.i_mapping,
 347                                           start, n, pages);
 348                 _debug("fgpc %u", n);
 349                 if (n == 0)
 350                         goto no_more;
 351                 if (pages[0]->index != start) {
 352                         do {
 353                                 put_page(pages[--n]);
 354                         } while (n > 0);
 355                         goto no_more;
 356                 }
 357
 358                 for (loop = 0; loop < n; loop++) {
 359                         page = pages[loop];
 360                         if (page->index > wb->last)
 361                                 break;
 362                         if (!trylock_page(page))
 363                                 break;
 364                         if (!PageDirty(page) ||
 365                             page_private(page) != (unsigned long) wb) {
 366                                 unlock_page(page);
 367                                 break;
 368                         }
 369                         if (!clear_page_dirty_for_io(page))
 370                                 BUG();
 371                         if (test_set_page_writeback(page))
 372                                 BUG();
 373                         unlock_page(page);
 374                         put_page(page);
 375                 }
 376                 count += loop;
 377                 if (loop < n) {
 378                         for (; loop < n; loop++)
 379                                 put_page(pages[loop]);
 380                         goto no_more;
 381                 }
 382
 383                 start += loop;
 384         } while (start <= wb->last && count < 65536);
 385
 386 no_more:
 387         /* we now have a contiguous set of dirty pages, each with writeback set
 388          * and the dirty mark cleared; the first page is locked and must remain
 389          * so, all the rest are unlocked */
 390         first = primary_page->index;
 391         last = first + count - 1;
 392
 393         offset = (first == wb->first) ? wb->offset_first : 0;
 394         to = (last == wb->last) ? wb->to_last : PAGE_SIZE;
 395
 396         _debug("write back %lx[%u..] to %lx[..%u]", first, offset, last, to);
 397
 398         ret = afs_vnode_store_data(wb, first, last, offset, to);
 399         if (ret < 0) {
 400                 switch (ret) {
 401                 case -EDQUOT:
 402                 case -ENOSPC:
 403                         set_bit(AS_ENOSPC,
 404                                 &wb->vnode->vfs_inode.i_mapping->flags);
 405                         break;
 406                 case -EROFS:
 407                 case -EIO:
 408                 case -EREMOTEIO:
 409                 case -EFBIG:
 410                 case -ENOENT:
 411                 case -ENOMEDIUM:
 412                 case -ENXIO:
 413                         afs_kill_pages(wb->vnode, true, first, last);
 414                         set_bit(AS_EIO, &wb->vnode->vfs_inode.i_mapping->flags);
 415                         break;
 416                 case -EACCES:
 417                 case -EPERM:
 418                 case -ENOKEY:
 419                 case -EKEYEXPIRED:
 420                 case -EKEYREJECTED:
 421                 case -EKEYREVOKED:
 422                         afs_kill_pages(wb->vnode, false, first, last);
 423                         break;
 424                 default:
 425                         break;
 426                 }
 427         } else {
 428                 ret = count;
 429         }
 430
 431         _leave(" = %d", ret);
 432         return ret;
 433 }
 434
 435 /*
 436  * write a page back to the server
 437  * - the caller locked the page for us
 438  */
 439 int afs_writepage(struct page *page, struct writeback_control *wbc)
 440 {
 441         struct backing_dev_info *bdi = page->mapping->backing_dev_info;
 442         struct afs_writeback *wb;
 443         int ret;
 444
 445         _enter("{%lx},", page->index);
 446
 447         wb = (struct afs_writeback *) page_private(page);
 448         ASSERT(wb != NULL);
 449
 450         ret = afs_write_back_from_locked_page(wb, page);
 451         unlock_page(page);
 452         if (ret < 0) {
 453                 _leave(" = %d", ret);
 454                 return 0;
 455         }
 456
 457         wbc->nr_to_write -= ret;
 458         if (wbc->nonblocking && bdi_write_congested(bdi))
 459                 wbc->encountered_congestion = 1;
 460
 461         _leave(" = 0");
 462         return 0;
 463 }
 464
 465 /*
 466  * write a region of pages back to the server
 467  */
 468 static int afs_writepages_region(struct address_space *mapping,
 469                                  struct writeback_control *wbc,
 470                                  pgoff_t index, pgoff_t end, pgoff_t *_next)
 471 {
 472         struct backing_dev_info *bdi = mapping->backing_dev_info;
 473         struct afs_writeback *wb;
 474         struct page *page;
 475         int ret, n;
 476
 477         _enter(",,%lx,%lx,", index, end);
 478
 479         do {
 480                 n = find_get_pages_tag(mapping, &index, PAGECACHE_TAG_DIRTY,
 481                                        1, &page);
 482                 if (!n)
 483                         break;
 484
 485                 _debug("wback %lx", page->index);
 486
 487                 if (page->index > end) {
 488                         *_next = index;
 489                         page_cache_release(page);
 490                         _leave(" = 0 [%lx]", *_next);
 491                         return 0;
 492                 }
 493
 494                 /* at this point we hold neither mapping->tree_lock nor lock on
 495                  * the page itself: the page may be truncated or invalidated
 496                  * (changing page->mapping to NULL), or even swizzled back from
 497                  * swapper_space to tmpfs file mapping
 498                  */
 499                 lock_page(page);
 500
 501                 if (page->mapping != mapping) {
 502                         unlock_page(page);
 503                         page_cache_release(page);
 504                         continue;
 505                 }
 506
 507                 if (wbc->sync_mode != WB_SYNC_NONE)
 508                         wait_on_page_writeback(page);
 509
 510                 if (PageWriteback(page) || !PageDirty(page)) {
 511                         unlock_page(page);
 512                         continue;
 513                 }
 514
 515                 wb = (struct afs_writeback *) page_private(page);
 516                 ASSERT(wb != NULL);
 517
 518                 spin_lock(&wb->vnode->writeback_lock);
 519                 wb->state = AFS_WBACK_WRITING;
 520                 spin_unlock(&wb->vnode->writeback_lock);
 521
 522                 ret = afs_write_back_from_locked_page(wb, page);
 523                 unlock_page(page);
 524                 page_cache_release(page);
 525                 if (ret < 0) {
 526                         _leave(" = %d", ret);
 527                         return ret;
 528                 }
 529
 530                 wbc->nr_to_write -= ret;
 531
 532                 if (wbc->nonblocking && bdi_write_congested(bdi)) {
 533                         wbc->encountered_congestion = 1;
 534                         break;
 535                 }
 536
 537                 cond_resched();
 538         } while (index < end && wbc->nr_to_write > 0);
 539
 540         *_next = index;
 541         _leave(" = 0 [%lx]", *_next);
 542         return 0;
 543 }
 544
 545 /*
 546  * write some of the pending data back to the server
 547  */
 548 int afs_writepages(struct address_space *mapping,
 549                    struct writeback_control *wbc)
 550 {
 551         struct backing_dev_info *bdi = mapping->backing_dev_info;
 552         pgoff_t start, end, next;
 553         int ret;
 554
 555         _enter("");
 556
 557         if (wbc->nonblocking && bdi_write_congested(bdi)) {
 558                 wbc->encountered_congestion = 1;
 559                 _leave(" = 0 [congest]");
 560                 return 0;
 561         }
 562
 563         if (wbc->range_cyclic) {
 564                 start = mapping->writeback_index;
 565                 end = -1;
 566                 ret = afs_writepages_region(mapping, wbc, start, end, &next);
 567                 if (start > 0 && wbc->nr_to_write > 0 && ret == 0 &&
 568                     !(wbc->nonblocking && wbc->encountered_congestion))
 569                         ret = afs_writepages_region(mapping, wbc, 0, start,
 570                                                     &next);
 571                 mapping->writeback_index = next;
 572         } else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
 573                 end = (pgoff_t)(LLONG_MAX >> PAGE_CACHE_SHIFT);
 574                 ret = afs_writepages_region(mapping, wbc, 0, end, &next);
 575                 if (wbc->nr_to_write > 0)
 576                         mapping->writeback_index = next;
 577         } else {
 578                 start = wbc->range_start >> PAGE_CACHE_SHIFT;
 579                 end = wbc->range_end >> PAGE_CACHE_SHIFT;
 580                 ret = afs_writepages_region(mapping, wbc, start, end, &next);
 581         }
 582
 583         _leave(" = %d", ret);
 584         return ret;
 585 }
 586
 587 /*
 588  * completion of write to server
 589  */
 590 void afs_pages_written_back(struct afs_vnode *vnode, struct afs_call *call)
 591 {
 592         struct afs_writeback *wb = call->wb;
 593         struct pagevec pv;
 594         unsigned count, loop;
 595         pgoff_t first = call->first, last = call->last;
 596         bool free_wb;
 597
 598         _enter("{%x:%u},{%lx-%lx}",
 599                vnode->fid.vid, vnode->fid.vnode, first, last);
 600
 601         ASSERT(wb != NULL);
 602
 603         pagevec_init(&pv, 0);
 604
 605         do {
 606                 _debug("done %lx-%lx", first, last);
 607
 608                 count = last - first + 1;
 609                 if (count > PAGEVEC_SIZE)
 610                         count = PAGEVEC_SIZE;
 611                 pv.nr = find_get_pages_contig(call->mapping, first, count,
 612                                               pv.pages);
 613                 ASSERTCMP(pv.nr, ==, count);
 614
 615                 spin_lock(&vnode->writeback_lock);
 616                 for (loop = 0; loop < count; loop++) {
 617                         struct page *page = pv.pages[loop];
 618                         end_page_writeback(page);
 619                         if (page_private(page) == (unsigned long) wb) {
 620                                 set_page_private(page, 0);
 621                                 ClearPagePrivate(page);
 622                                 wb->usage--;
 623                         }
 624                 }
 625                 free_wb = false;
 626                 if (wb->usage == 0) {
 627                         afs_unlink_writeback(wb);
 628                         free_wb = true;
 629                 }
 630                 spin_unlock(&vnode->writeback_lock);
 631                 first += count;
 632                 if (free_wb) {
 633                         afs_free_writeback(wb);
 634                         wb = NULL;
 635                 }
 636
 637                 __pagevec_release(&pv);
 638         } while (first <= last);
 639
 640         _leave("");
 641 }
 642
 643 /*
 644  * write to an AFS file
 645  */
 646 ssize_t afs_file_write(struct kiocb *iocb, const struct iovec *iov,
 647                        unsigned long nr_segs, loff_t pos)
 648 {
 649         struct dentry *dentry = iocb->ki_filp->f_path.dentry;
 650         struct afs_vnode *vnode = AFS_FS_I(dentry->d_inode);
 651         ssize_t result;
 652         size_t count = iov_length(iov, nr_segs);
 653
 654         _enter("{%x.%u},{%zu},%lu,",
 655                vnode->fid.vid, vnode->fid.vnode, count, nr_segs);
 656
 657         if (IS_SWAPFILE(&vnode->vfs_inode)) {
 658                 printk(KERN_INFO
 659                        "AFS: Attempt to write to active swap file!\n");
 660                 return -EBUSY;
 661         }
 662
 663         if (!count)
 664                 return 0;
 665
 666         result = generic_file_aio_write(iocb, iov, nr_segs, pos);
 667         if (IS_ERR_VALUE(result)) {
 668                 _leave(" = %zd", result);
 669                 return result;
 670         }
 671
 672         _leave(" = %zd", result);
 673         return result;
 674 }
 675
 676 /*
 677  * flush the vnode to the fileserver
 678  */
 679 int afs_writeback_all(struct afs_vnode *vnode)
 680 {
 681         struct address_space *mapping = vnode->vfs_inode.i_mapping;
 682         struct writeback_control wbc = {
 683                 .bdi            = mapping->backing_dev_info,
 684                 .sync_mode      = WB_SYNC_ALL,
 685                 .nr_to_write    = LONG_MAX,
 686                 .range_cyclic   = 1,
 687         };
 688         int ret;
 689
 690         _enter("");
 691
 692         ret = mapping->a_ops->writepages(mapping, &wbc);
 693         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 694
 695         _leave(" = %d", ret);
 696         return ret;
 697 }
 698
 699 /*
 700  * flush any dirty pages for this process, and check for write errors.
 701  * - the return status from this call provides a reliable indication of
 702  *   whether any write errors occurred for this process.
 703  */
 704 int afs_fsync(struct file *file, struct dentry *dentry, int datasync)
 705 {
 706         struct afs_writeback *wb, *xwb;
 707         struct afs_vnode *vnode = AFS_FS_I(dentry->d_inode);
 708         int ret;
 709
 710         _enter("{%x:%u},{n=%s},%d",
 711                vnode->fid.vid, vnode->fid.vnode, dentry->d_name.name,
 712                datasync);
 713
 714         /* use a writeback record as a marker in the queue - when this reaches
 715          * the front of the queue, all the outstanding writes are either
 716          * completed or rejected */
 717         wb = kzalloc(sizeof(*wb), GFP_KERNEL);
 718         if (!wb)
 719                 return -ENOMEM;
 720         wb->vnode = vnode;
 721         wb->first = 0;
 722         wb->last = -1;
 723         wb->offset_first = 0;
 724         wb->to_last = PAGE_SIZE;
 725         wb->usage = 1;
 726         wb->state = AFS_WBACK_SYNCING;
 727         init_waitqueue_head(&wb->waitq);
 728
 729         spin_lock(&vnode->writeback_lock);
 730         list_for_each_entry(xwb, &vnode->writebacks, link) {
 731                 if (xwb->state == AFS_WBACK_PENDING)
 732                         xwb->state = AFS_WBACK_CONFLICTING;
 733         }
 734         list_add_tail(&wb->link, &vnode->writebacks);
 735         spin_unlock(&vnode->writeback_lock);
 736
 737         /* push all the outstanding writebacks to the server */
 738         ret = afs_writeback_all(vnode);
 739         if (ret < 0) {
 740                 afs_put_writeback(wb);
 741                 _leave(" = %d [wb]", ret);
 742                 return ret;
 743         }
 744
 745         /* wait for the preceding writes to actually complete */
 746         ret = wait_event_interruptible(wb->waitq,
 747                                        wb->state == AFS_WBACK_COMPLETE ||
 748                                        vnode->writebacks.next == &wb->link);
 749         afs_put_writeback(wb);
 750         _leave(" = %d", ret);
 751         return ret;
 752 }
 753
 754 /*
 755  * notification that a previously read-only page is about to become writable
 756  * - if it returns an error, the caller will deliver a bus error signal
 757  */
 758 int afs_page_mkwrite(struct vm_area_struct *vma, struct page *page)
 759 {
 760         struct afs_vnode *vnode = AFS_FS_I(vma->vm_file->f_mapping->host);
 761
 762         _enter("{{%x:%u}},{%lx}",
 763                vnode->fid.vid, vnode->fid.vnode, page->index);
 764
 765         /* wait for the page to be written to the cache before we allow it to
 766          * be modified */
 767 #ifdef CONFIG_AFS_FSCACHE
 768         fscache_wait_on_page_write(vnode->cache, page);
 769 #endif
 770
 771         _leave(" = 0");
 772         return 0;
 773 }