15690bb1d3b531e65ae9cce255eaf532081667db
[linux-2.6.git] / 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 afs_writeback *wb;
442         int ret;
443
444         _enter("{%lx},", page->index);
445
446         wb = (struct afs_writeback *) page_private(page);
447         ASSERT(wb != NULL);
448
449         ret = afs_write_back_from_locked_page(wb, page);
450         unlock_page(page);
451         if (ret < 0) {
452                 _leave(" = %d", ret);
453                 return 0;
454         }
455
456         wbc->nr_to_write -= ret;
457
458         _leave(" = 0");
459         return 0;
460 }
461
462 /*
463  * write a region of pages back to the server
464  */
465 static int afs_writepages_region(struct address_space *mapping,
466                                  struct writeback_control *wbc,
467                                  pgoff_t index, pgoff_t end, pgoff_t *_next)
468 {
469         struct afs_writeback *wb;
470         struct page *page;
471         int ret, n;
472
473         _enter(",,%lx,%lx,", index, end);
474
475         do {
476                 n = find_get_pages_tag(mapping, &index, PAGECACHE_TAG_DIRTY,
477                                        1, &page);
478                 if (!n)
479                         break;
480
481                 _debug("wback %lx", page->index);
482
483                 if (page->index > end) {
484                         *_next = index;
485                         page_cache_release(page);
486                         _leave(" = 0 [%lx]", *_next);
487                         return 0;
488                 }
489
490                 /* at this point we hold neither mapping->tree_lock nor lock on
491                  * the page itself: the page may be truncated or invalidated
492                  * (changing page->mapping to NULL), or even swizzled back from
493                  * swapper_space to tmpfs file mapping
494                  */
495                 lock_page(page);
496
497                 if (page->mapping != mapping) {
498                         unlock_page(page);
499                         page_cache_release(page);
500                         continue;
501                 }
502
503                 if (wbc->sync_mode != WB_SYNC_NONE)
504                         wait_on_page_writeback(page);
505
506                 if (PageWriteback(page) || !PageDirty(page)) {
507                         unlock_page(page);
508                         continue;
509                 }
510
511                 wb = (struct afs_writeback *) page_private(page);
512                 ASSERT(wb != NULL);
513
514                 spin_lock(&wb->vnode->writeback_lock);
515                 wb->state = AFS_WBACK_WRITING;
516                 spin_unlock(&wb->vnode->writeback_lock);
517
518                 ret = afs_write_back_from_locked_page(wb, page);
519                 unlock_page(page);
520                 page_cache_release(page);
521                 if (ret < 0) {
522                         _leave(" = %d", ret);
523                         return ret;
524                 }
525
526                 wbc->nr_to_write -= ret;
527
528                 cond_resched();
529         } while (index < end && wbc->nr_to_write > 0);
530
531         *_next = index;
532         _leave(" = 0 [%lx]", *_next);
533         return 0;
534 }
535
536 /*
537  * write some of the pending data back to the server
538  */
539 int afs_writepages(struct address_space *mapping,
540                    struct writeback_control *wbc)
541 {
542         pgoff_t start, end, next;
543         int ret;
544
545         _enter("");
546
547         if (wbc->range_cyclic) {
548                 start = mapping->writeback_index;
549                 end = -1;
550                 ret = afs_writepages_region(mapping, wbc, start, end, &next);
551                 if (start > 0 && wbc->nr_to_write > 0 && ret == 0)
552                         ret = afs_writepages_region(mapping, wbc, 0, start,
553                                                     &next);
554                 mapping->writeback_index = next;
555         } else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
556                 end = (pgoff_t)(LLONG_MAX >> PAGE_CACHE_SHIFT);
557                 ret = afs_writepages_region(mapping, wbc, 0, end, &next);
558                 if (wbc->nr_to_write > 0)
559                         mapping->writeback_index = next;
560         } else {
561                 start = wbc->range_start >> PAGE_CACHE_SHIFT;
562                 end = wbc->range_end >> PAGE_CACHE_SHIFT;
563                 ret = afs_writepages_region(mapping, wbc, start, end, &next);
564         }
565
566         _leave(" = %d", ret);
567         return ret;
568 }
569
570 /*
571  * completion of write to server
572  */
573 void afs_pages_written_back(struct afs_vnode *vnode, struct afs_call *call)
574 {
575         struct afs_writeback *wb = call->wb;
576         struct pagevec pv;
577         unsigned count, loop;
578         pgoff_t first = call->first, last = call->last;
579         bool free_wb;
580
581         _enter("{%x:%u},{%lx-%lx}",
582                vnode->fid.vid, vnode->fid.vnode, first, last);
583
584         ASSERT(wb != NULL);
585
586         pagevec_init(&pv, 0);
587
588         do {
589                 _debug("done %lx-%lx", first, last);
590
591                 count = last - first + 1;
592                 if (count > PAGEVEC_SIZE)
593                         count = PAGEVEC_SIZE;
594                 pv.nr = find_get_pages_contig(call->mapping, first, count,
595                                               pv.pages);
596                 ASSERTCMP(pv.nr, ==, count);
597
598                 spin_lock(&vnode->writeback_lock);
599                 for (loop = 0; loop < count; loop++) {
600                         struct page *page = pv.pages[loop];
601                         end_page_writeback(page);
602                         if (page_private(page) == (unsigned long) wb) {
603                                 set_page_private(page, 0);
604                                 ClearPagePrivate(page);
605                                 wb->usage--;
606                         }
607                 }
608                 free_wb = false;
609                 if (wb->usage == 0) {
610                         afs_unlink_writeback(wb);
611                         free_wb = true;
612                 }
613                 spin_unlock(&vnode->writeback_lock);
614                 first += count;
615                 if (free_wb) {
616                         afs_free_writeback(wb);
617                         wb = NULL;
618                 }
619
620                 __pagevec_release(&pv);
621         } while (first <= last);
622
623         _leave("");
624 }
625
626 /*
627  * write to an AFS file
628  */
629 ssize_t afs_file_write(struct kiocb *iocb, const struct iovec *iov,
630                        unsigned long nr_segs, loff_t pos)
631 {
632         struct dentry *dentry = iocb->ki_filp->f_path.dentry;
633         struct afs_vnode *vnode = AFS_FS_I(dentry->d_inode);
634         ssize_t result;
635         size_t count = iov_length(iov, nr_segs);
636
637         _enter("{%x.%u},{%zu},%lu,",
638                vnode->fid.vid, vnode->fid.vnode, count, nr_segs);
639
640         if (IS_SWAPFILE(&vnode->vfs_inode)) {
641                 printk(KERN_INFO
642                        "AFS: Attempt to write to active swap file!\n");
643                 return -EBUSY;
644         }
645
646         if (!count)
647                 return 0;
648
649         result = generic_file_aio_write(iocb, iov, nr_segs, pos);
650         if (IS_ERR_VALUE(result)) {
651                 _leave(" = %zd", result);
652                 return result;
653         }
654
655         _leave(" = %zd", result);
656         return result;
657 }
658
659 /*
660  * flush the vnode to the fileserver
661  */
662 int afs_writeback_all(struct afs_vnode *vnode)
663 {
664         struct address_space *mapping = vnode->vfs_inode.i_mapping;
665         struct writeback_control wbc = {
666                 .sync_mode      = WB_SYNC_ALL,
667                 .nr_to_write    = LONG_MAX,
668                 .range_cyclic   = 1,
669         };
670         int ret;
671
672         _enter("");
673
674         ret = mapping->a_ops->writepages(mapping, &wbc);
675         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
676
677         _leave(" = %d", ret);
678         return ret;
679 }
680
681 /*
682  * flush any dirty pages for this process, and check for write errors.
683  * - the return status from this call provides a reliable indication of
684  *   whether any write errors occurred for this process.
685  */
686 int afs_fsync(struct file *file, int datasync)
687 {
688         struct dentry *dentry = file->f_path.dentry;
689         struct afs_writeback *wb, *xwb;
690         struct afs_vnode *vnode = AFS_FS_I(dentry->d_inode);
691         int ret;
692
693         _enter("{%x:%u},{n=%s},%d",
694                vnode->fid.vid, vnode->fid.vnode, dentry->d_name.name,
695                datasync);
696
697         /* use a writeback record as a marker in the queue - when this reaches
698          * the front of the queue, all the outstanding writes are either
699          * completed or rejected */
700         wb = kzalloc(sizeof(*wb), GFP_KERNEL);
701         if (!wb)
702                 return -ENOMEM;
703         wb->vnode = vnode;
704         wb->first = 0;
705         wb->last = -1;
706         wb->offset_first = 0;
707         wb->to_last = PAGE_SIZE;
708         wb->usage = 1;
709         wb->state = AFS_WBACK_SYNCING;
710         init_waitqueue_head(&wb->waitq);
711
712         spin_lock(&vnode->writeback_lock);
713         list_for_each_entry(xwb, &vnode->writebacks, link) {
714                 if (xwb->state == AFS_WBACK_PENDING)
715                         xwb->state = AFS_WBACK_CONFLICTING;
716         }
717         list_add_tail(&wb->link, &vnode->writebacks);
718         spin_unlock(&vnode->writeback_lock);
719
720         /* push all the outstanding writebacks to the server */
721         ret = afs_writeback_all(vnode);
722         if (ret < 0) {
723                 afs_put_writeback(wb);
724                 _leave(" = %d [wb]", ret);
725                 return ret;
726         }
727
728         /* wait for the preceding writes to actually complete */
729         ret = wait_event_interruptible(wb->waitq,
730                                        wb->state == AFS_WBACK_COMPLETE ||
731                                        vnode->writebacks.next == &wb->link);
732         afs_put_writeback(wb);
733         _leave(" = %d", ret);
734         return ret;
735 }
736
737 /*
738  * notification that a previously read-only page is about to become writable
739  * - if it returns an error, the caller will deliver a bus error signal
740  */
741 int afs_page_mkwrite(struct vm_area_struct *vma, struct page *page)
742 {
743         struct afs_vnode *vnode = AFS_FS_I(vma->vm_file->f_mapping->host);
744
745         _enter("{{%x:%u}},{%lx}",
746                vnode->fid.vid, vnode->fid.vnode, page->index);
747
748         /* wait for the page to be written to the cache before we allow it to
749          * be modified */
750 #ifdef CONFIG_AFS_FSCACHE
751         fscache_wait_on_page_write(vnode->cache, page);
752 #endif
753
754         _leave(" = 0");
755         return 0;
756 }