mm/vfs: revalidate page->mapping in do_generic_file_read()
[linux-2.6.git] / mm / filemap.c
1 /*
2  *      linux/mm/filemap.c
3  *
4  * Copyright (C) 1994-1999  Linus Torvalds
5  */
6
7 /*
8  * This file handles the generic file mmap semantics used by
9  * most "normal" filesystems (but you don't /have/ to use this:
10  * the NFS filesystem used to do this differently, for example)
11  */
12 #include <linux/module.h>
13 #include <linux/compiler.h>
14 #include <linux/fs.h>
15 #include <linux/uaccess.h>
16 #include <linux/aio.h>
17 #include <linux/capability.h>
18 #include <linux/kernel_stat.h>
19 #include <linux/gfp.h>
20 #include <linux/mm.h>
21 #include <linux/swap.h>
22 #include <linux/mman.h>
23 #include <linux/pagemap.h>
24 #include <linux/file.h>
25 #include <linux/uio.h>
26 #include <linux/hash.h>
27 #include <linux/writeback.h>
28 #include <linux/backing-dev.h>
29 #include <linux/pagevec.h>
30 #include <linux/blkdev.h>
31 #include <linux/security.h>
32 #include <linux/syscalls.h>
33 #include <linux/cpuset.h>
34 #include <linux/hardirq.h> /* for BUG_ON(!in_atomic()) only */
35 #include <linux/memcontrol.h>
36 #include <linux/mm_inline.h> /* for page_is_file_cache() */
37 #include "internal.h"
38
39 /*
40  * FIXME: remove all knowledge of the buffer layer from the core VM
41  */
42 #include <linux/buffer_head.h> /* for try_to_free_buffers */
43
44 #include <asm/mman.h>
45
46 /*
47  * Shared mappings implemented 30.11.1994. It's not fully working yet,
48  * though.
49  *
50  * Shared mappings now work. 15.8.1995  Bruno.
51  *
52  * finished 'unifying' the page and buffer cache and SMP-threaded the
53  * page-cache, 21.05.1999, Ingo Molnar <mingo@redhat.com>
54  *
55  * SMP-threaded pagemap-LRU 1999, Andrea Arcangeli <andrea@suse.de>
56  */
57
58 /*
59  * Lock ordering:
60  *
61  *  ->i_mmap_lock               (truncate_pagecache)
62  *    ->private_lock            (__free_pte->__set_page_dirty_buffers)
63  *      ->swap_lock             (exclusive_swap_page, others)
64  *        ->mapping->tree_lock
65  *
66  *  ->i_mutex
67  *    ->i_mmap_lock             (truncate->unmap_mapping_range)
68  *
69  *  ->mmap_sem
70  *    ->i_mmap_lock
71  *      ->page_table_lock or pte_lock   (various, mainly in memory.c)
72  *        ->mapping->tree_lock  (arch-dependent flush_dcache_mmap_lock)
73  *
74  *  ->mmap_sem
75  *    ->lock_page               (access_process_vm)
76  *
77  *  ->i_mutex                   (generic_file_buffered_write)
78  *    ->mmap_sem                (fault_in_pages_readable->do_page_fault)
79  *
80  *  ->i_mutex
81  *    ->i_alloc_sem             (various)
82  *
83  *  ->inode_lock
84  *    ->sb_lock                 (fs/fs-writeback.c)
85  *    ->mapping->tree_lock      (__sync_single_inode)
86  *
87  *  ->i_mmap_lock
88  *    ->anon_vma.lock           (vma_adjust)
89  *
90  *  ->anon_vma.lock
91  *    ->page_table_lock or pte_lock     (anon_vma_prepare and various)
92  *
93  *  ->page_table_lock or pte_lock
94  *    ->swap_lock               (try_to_unmap_one)
95  *    ->private_lock            (try_to_unmap_one)
96  *    ->tree_lock               (try_to_unmap_one)
97  *    ->zone.lru_lock           (follow_page->mark_page_accessed)
98  *    ->zone.lru_lock           (check_pte_range->isolate_lru_page)
99  *    ->private_lock            (page_remove_rmap->set_page_dirty)
100  *    ->tree_lock               (page_remove_rmap->set_page_dirty)
101  *    ->inode_lock              (page_remove_rmap->set_page_dirty)
102  *    ->inode_lock              (zap_pte_range->set_page_dirty)
103  *    ->private_lock            (zap_pte_range->__set_page_dirty_buffers)
104  *
105  *  ->task->proc_lock
106  *    ->dcache_lock             (proc_pid_lookup)
107  *
108  *  (code doesn't rely on that order, so you could switch it around)
109  *  ->tasklist_lock             (memory_failure, collect_procs_ao)
110  *    ->i_mmap_lock
111  */
112
113 /*
114  * Remove a page from the page cache and free it. Caller has to make
115  * sure the page is locked and that nobody else uses it - or that usage
116  * is safe.  The caller must hold the mapping's tree_lock.
117  */
118 void __remove_from_page_cache(struct page *page)
119 {
120         struct address_space *mapping = page->mapping;
121
122         radix_tree_delete(&mapping->page_tree, page->index);
123         page->mapping = NULL;
124         mapping->nrpages--;
125         __dec_zone_page_state(page, NR_FILE_PAGES);
126         if (PageSwapBacked(page))
127                 __dec_zone_page_state(page, NR_SHMEM);
128         BUG_ON(page_mapped(page));
129
130         /*
131          * Some filesystems seem to re-dirty the page even after
132          * the VM has canceled the dirty bit (eg ext3 journaling).
133          *
134          * Fix it up by doing a final dirty accounting check after
135          * having removed the page entirely.
136          */
137         if (PageDirty(page) && mapping_cap_account_dirty(mapping)) {
138                 dec_zone_page_state(page, NR_FILE_DIRTY);
139                 dec_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
140         }
141 }
142
143 void remove_from_page_cache(struct page *page)
144 {
145         struct address_space *mapping = page->mapping;
146
147         BUG_ON(!PageLocked(page));
148
149         spin_lock_irq(&mapping->tree_lock);
150         __remove_from_page_cache(page);
151         spin_unlock_irq(&mapping->tree_lock);
152         mem_cgroup_uncharge_cache_page(page);
153 }
154 EXPORT_SYMBOL(remove_from_page_cache);
155
156 static int sync_page(void *word)
157 {
158         struct address_space *mapping;
159         struct page *page;
160
161         page = container_of((unsigned long *)word, struct page, flags);
162
163         /*
164          * page_mapping() is being called without PG_locked held.
165          * Some knowledge of the state and use of the page is used to
166          * reduce the requirements down to a memory barrier.
167          * The danger here is of a stale page_mapping() return value
168          * indicating a struct address_space different from the one it's
169          * associated with when it is associated with one.
170          * After smp_mb(), it's either the correct page_mapping() for
171          * the page, or an old page_mapping() and the page's own
172          * page_mapping() has gone NULL.
173          * The ->sync_page() address_space operation must tolerate
174          * page_mapping() going NULL. By an amazing coincidence,
175          * this comes about because none of the users of the page
176          * in the ->sync_page() methods make essential use of the
177          * page_mapping(), merely passing the page down to the backing
178          * device's unplug functions when it's non-NULL, which in turn
179          * ignore it for all cases but swap, where only page_private(page) is
180          * of interest. When page_mapping() does go NULL, the entire
181          * call stack gracefully ignores the page and returns.
182          * -- wli
183          */
184         smp_mb();
185         mapping = page_mapping(page);
186         if (mapping && mapping->a_ops && mapping->a_ops->sync_page)
187                 mapping->a_ops->sync_page(page);
188         io_schedule();
189         return 0;
190 }
191
192 static int sync_page_killable(void *word)
193 {
194         sync_page(word);
195         return fatal_signal_pending(current) ? -EINTR : 0;
196 }
197
198 /**
199  * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
200  * @mapping:    address space structure to write
201  * @start:      offset in bytes where the range starts
202  * @end:        offset in bytes where the range ends (inclusive)
203  * @sync_mode:  enable synchronous operation
204  *
205  * Start writeback against all of a mapping's dirty pages that lie
206  * within the byte offsets <start, end> inclusive.
207  *
208  * If sync_mode is WB_SYNC_ALL then this is a "data integrity" operation, as
209  * opposed to a regular memory cleansing writeback.  The difference between
210  * these two operations is that if a dirty page/buffer is encountered, it must
211  * be waited upon, and not just skipped over.
212  */
213 int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
214                                 loff_t end, int sync_mode)
215 {
216         int ret;
217         struct writeback_control wbc = {
218                 .sync_mode = sync_mode,
219                 .nr_to_write = LONG_MAX,
220                 .range_start = start,
221                 .range_end = end,
222         };
223
224         if (!mapping_cap_writeback_dirty(mapping))
225                 return 0;
226
227         ret = do_writepages(mapping, &wbc);
228         return ret;
229 }
230
231 static inline int __filemap_fdatawrite(struct address_space *mapping,
232         int sync_mode)
233 {
234         return __filemap_fdatawrite_range(mapping, 0, LLONG_MAX, sync_mode);
235 }
236
237 int filemap_fdatawrite(struct address_space *mapping)
238 {
239         return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
240 }
241 EXPORT_SYMBOL(filemap_fdatawrite);
242
243 int filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
244                                 loff_t end)
245 {
246         return __filemap_fdatawrite_range(mapping, start, end, WB_SYNC_ALL);
247 }
248 EXPORT_SYMBOL(filemap_fdatawrite_range);
249
250 /**
251  * filemap_flush - mostly a non-blocking flush
252  * @mapping:    target address_space
253  *
254  * This is a mostly non-blocking flush.  Not suitable for data-integrity
255  * purposes - I/O may not be started against all dirty pages.
256  */
257 int filemap_flush(struct address_space *mapping)
258 {
259         return __filemap_fdatawrite(mapping, WB_SYNC_NONE);
260 }
261 EXPORT_SYMBOL(filemap_flush);
262
263 /**
264  * filemap_fdatawait_range - wait for writeback to complete
265  * @mapping:            address space structure to wait for
266  * @start_byte:         offset in bytes where the range starts
267  * @end_byte:           offset in bytes where the range ends (inclusive)
268  *
269  * Walk the list of under-writeback pages of the given address space
270  * in the given range and wait for all of them.
271  */
272 int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
273                             loff_t end_byte)
274 {
275         pgoff_t index = start_byte >> PAGE_CACHE_SHIFT;
276         pgoff_t end = end_byte >> PAGE_CACHE_SHIFT;
277         struct pagevec pvec;
278         int nr_pages;
279         int ret = 0;
280
281         if (end_byte < start_byte)
282                 return 0;
283
284         pagevec_init(&pvec, 0);
285         while ((index <= end) &&
286                         (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
287                         PAGECACHE_TAG_WRITEBACK,
288                         min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1)) != 0) {
289                 unsigned i;
290
291                 for (i = 0; i < nr_pages; i++) {
292                         struct page *page = pvec.pages[i];
293
294                         /* until radix tree lookup accepts end_index */
295                         if (page->index > end)
296                                 continue;
297
298                         wait_on_page_writeback(page);
299                         if (PageError(page))
300                                 ret = -EIO;
301                 }
302                 pagevec_release(&pvec);
303                 cond_resched();
304         }
305
306         /* Check for outstanding write errors */
307         if (test_and_clear_bit(AS_ENOSPC, &mapping->flags))
308                 ret = -ENOSPC;
309         if (test_and_clear_bit(AS_EIO, &mapping->flags))
310                 ret = -EIO;
311
312         return ret;
313 }
314 EXPORT_SYMBOL(filemap_fdatawait_range);
315
316 /**
317  * filemap_fdatawait - wait for all under-writeback pages to complete
318  * @mapping: address space structure to wait for
319  *
320  * Walk the list of under-writeback pages of the given address space
321  * and wait for all of them.
322  */
323 int filemap_fdatawait(struct address_space *mapping)
324 {
325         loff_t i_size = i_size_read(mapping->host);
326
327         if (i_size == 0)
328                 return 0;
329
330         return filemap_fdatawait_range(mapping, 0, i_size - 1);
331 }
332 EXPORT_SYMBOL(filemap_fdatawait);
333
334 int filemap_write_and_wait(struct address_space *mapping)
335 {
336         int err = 0;
337
338         if (mapping->nrpages) {
339                 err = filemap_fdatawrite(mapping);
340                 /*
341                  * Even if the above returned error, the pages may be
342                  * written partially (e.g. -ENOSPC), so we wait for it.
343                  * But the -EIO is special case, it may indicate the worst
344                  * thing (e.g. bug) happened, so we avoid waiting for it.
345                  */
346                 if (err != -EIO) {
347                         int err2 = filemap_fdatawait(mapping);
348                         if (!err)
349                                 err = err2;
350                 }
351         }
352         return err;
353 }
354 EXPORT_SYMBOL(filemap_write_and_wait);
355
356 /**
357  * filemap_write_and_wait_range - write out & wait on a file range
358  * @mapping:    the address_space for the pages
359  * @lstart:     offset in bytes where the range starts
360  * @lend:       offset in bytes where the range ends (inclusive)
361  *
362  * Write out and wait upon file offsets lstart->lend, inclusive.
363  *
364  * Note that `lend' is inclusive (describes the last byte to be written) so
365  * that this function can be used to write to the very end-of-file (end = -1).
366  */
367 int filemap_write_and_wait_range(struct address_space *mapping,
368                                  loff_t lstart, loff_t lend)
369 {
370         int err = 0;
371
372         if (mapping->nrpages) {
373                 err = __filemap_fdatawrite_range(mapping, lstart, lend,
374                                                  WB_SYNC_ALL);
375                 /* See comment of filemap_write_and_wait() */
376                 if (err != -EIO) {
377                         int err2 = filemap_fdatawait_range(mapping,
378                                                 lstart, lend);
379                         if (!err)
380                                 err = err2;
381                 }
382         }
383         return err;
384 }
385 EXPORT_SYMBOL(filemap_write_and_wait_range);
386
387 /**
388  * add_to_page_cache_locked - add a locked page to the pagecache
389  * @page:       page to add
390  * @mapping:    the page's address_space
391  * @offset:     page index
392  * @gfp_mask:   page allocation mode
393  *
394  * This function is used to add a page to the pagecache. It must be locked.
395  * This function does not add the page to the LRU.  The caller must do that.
396  */
397 int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
398                 pgoff_t offset, gfp_t gfp_mask)
399 {
400         int error;
401
402         VM_BUG_ON(!PageLocked(page));
403
404         error = mem_cgroup_cache_charge(page, current->mm,
405                                         gfp_mask & GFP_RECLAIM_MASK);
406         if (error)
407                 goto out;
408
409         error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
410         if (error == 0) {
411                 page_cache_get(page);
412                 page->mapping = mapping;
413                 page->index = offset;
414
415                 spin_lock_irq(&mapping->tree_lock);
416                 error = radix_tree_insert(&mapping->page_tree, offset, page);
417                 if (likely(!error)) {
418                         mapping->nrpages++;
419                         __inc_zone_page_state(page, NR_FILE_PAGES);
420                         if (PageSwapBacked(page))
421                                 __inc_zone_page_state(page, NR_SHMEM);
422                         spin_unlock_irq(&mapping->tree_lock);
423                 } else {
424                         page->mapping = NULL;
425                         spin_unlock_irq(&mapping->tree_lock);
426                         mem_cgroup_uncharge_cache_page(page);
427                         page_cache_release(page);
428                 }
429                 radix_tree_preload_end();
430         } else
431                 mem_cgroup_uncharge_cache_page(page);
432 out:
433         return error;
434 }
435 EXPORT_SYMBOL(add_to_page_cache_locked);
436
437 int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
438                                 pgoff_t offset, gfp_t gfp_mask)
439 {
440         int ret;
441
442         /*
443          * Splice_read and readahead add shmem/tmpfs pages into the page cache
444          * before shmem_readpage has a chance to mark them as SwapBacked: they
445          * need to go on the anon lru below, and mem_cgroup_cache_charge
446          * (called in add_to_page_cache) needs to know where they're going too.
447          */
448         if (mapping_cap_swap_backed(mapping))
449                 SetPageSwapBacked(page);
450
451         ret = add_to_page_cache(page, mapping, offset, gfp_mask);
452         if (ret == 0) {
453                 if (page_is_file_cache(page))
454                         lru_cache_add_file(page);
455                 else
456                         lru_cache_add_anon(page);
457         }
458         return ret;
459 }
460 EXPORT_SYMBOL_GPL(add_to_page_cache_lru);
461
462 #ifdef CONFIG_NUMA
463 struct page *__page_cache_alloc(gfp_t gfp)
464 {
465         int n;
466         struct page *page;
467
468         if (cpuset_do_page_mem_spread()) {
469                 get_mems_allowed();
470                 n = cpuset_mem_spread_node();
471                 page = alloc_pages_exact_node(n, gfp, 0);
472                 put_mems_allowed();
473                 return page;
474         }
475         return alloc_pages(gfp, 0);
476 }
477 EXPORT_SYMBOL(__page_cache_alloc);
478 #endif
479
480 static int __sleep_on_page_lock(void *word)
481 {
482         io_schedule();
483         return 0;
484 }
485
486 /*
487  * In order to wait for pages to become available there must be
488  * waitqueues associated with pages. By using a hash table of
489  * waitqueues where the bucket discipline is to maintain all
490  * waiters on the same queue and wake all when any of the pages
491  * become available, and for the woken contexts to check to be
492  * sure the appropriate page became available, this saves space
493  * at a cost of "thundering herd" phenomena during rare hash
494  * collisions.
495  */
496 static wait_queue_head_t *page_waitqueue(struct page *page)
497 {
498         const struct zone *zone = page_zone(page);
499
500         return &zone->wait_table[hash_ptr(page, zone->wait_table_bits)];
501 }
502
503 static inline void wake_up_page(struct page *page, int bit)
504 {
505         __wake_up_bit(page_waitqueue(page), &page->flags, bit);
506 }
507
508 void wait_on_page_bit(struct page *page, int bit_nr)
509 {
510         DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
511
512         if (test_bit(bit_nr, &page->flags))
513                 __wait_on_bit(page_waitqueue(page), &wait, sync_page,
514                                                         TASK_UNINTERRUPTIBLE);
515 }
516 EXPORT_SYMBOL(wait_on_page_bit);
517
518 /**
519  * add_page_wait_queue - Add an arbitrary waiter to a page's wait queue
520  * @page: Page defining the wait queue of interest
521  * @waiter: Waiter to add to the queue
522  *
523  * Add an arbitrary @waiter to the wait queue for the nominated @page.
524  */
525 void add_page_wait_queue(struct page *page, wait_queue_t *waiter)
526 {
527         wait_queue_head_t *q = page_waitqueue(page);
528         unsigned long flags;
529
530         spin_lock_irqsave(&q->lock, flags);
531         __add_wait_queue(q, waiter);
532         spin_unlock_irqrestore(&q->lock, flags);
533 }
534 EXPORT_SYMBOL_GPL(add_page_wait_queue);
535
536 /**
537  * unlock_page - unlock a locked page
538  * @page: the page
539  *
540  * Unlocks the page and wakes up sleepers in ___wait_on_page_locked().
541  * Also wakes sleepers in wait_on_page_writeback() because the wakeup
542  * mechananism between PageLocked pages and PageWriteback pages is shared.
543  * But that's OK - sleepers in wait_on_page_writeback() just go back to sleep.
544  *
545  * The mb is necessary to enforce ordering between the clear_bit and the read
546  * of the waitqueue (to avoid SMP races with a parallel wait_on_page_locked()).
547  */
548 void unlock_page(struct page *page)
549 {
550         VM_BUG_ON(!PageLocked(page));
551         clear_bit_unlock(PG_locked, &page->flags);
552         smp_mb__after_clear_bit();
553         wake_up_page(page, PG_locked);
554 }
555 EXPORT_SYMBOL(unlock_page);
556
557 /**
558  * end_page_writeback - end writeback against a page
559  * @page: the page
560  */
561 void end_page_writeback(struct page *page)
562 {
563         if (TestClearPageReclaim(page))
564                 rotate_reclaimable_page(page);
565
566         if (!test_clear_page_writeback(page))
567                 BUG();
568
569         smp_mb__after_clear_bit();
570         wake_up_page(page, PG_writeback);
571 }
572 EXPORT_SYMBOL(end_page_writeback);
573
574 /**
575  * __lock_page - get a lock on the page, assuming we need to sleep to get it
576  * @page: the page to lock
577  *
578  * Ugly. Running sync_page() in state TASK_UNINTERRUPTIBLE is scary.  If some
579  * random driver's requestfn sets TASK_RUNNING, we could busywait.  However
580  * chances are that on the second loop, the block layer's plug list is empty,
581  * so sync_page() will then return in state TASK_UNINTERRUPTIBLE.
582  */
583 void __lock_page(struct page *page)
584 {
585         DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
586
587         __wait_on_bit_lock(page_waitqueue(page), &wait, sync_page,
588                                                         TASK_UNINTERRUPTIBLE);
589 }
590 EXPORT_SYMBOL(__lock_page);
591
592 int __lock_page_killable(struct page *page)
593 {
594         DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
595
596         return __wait_on_bit_lock(page_waitqueue(page), &wait,
597                                         sync_page_killable, TASK_KILLABLE);
598 }
599 EXPORT_SYMBOL_GPL(__lock_page_killable);
600
601 /**
602  * __lock_page_nosync - get a lock on the page, without calling sync_page()
603  * @page: the page to lock
604  *
605  * Variant of lock_page that does not require the caller to hold a reference
606  * on the page's mapping.
607  */
608 void __lock_page_nosync(struct page *page)
609 {
610         DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
611         __wait_on_bit_lock(page_waitqueue(page), &wait, __sleep_on_page_lock,
612                                                         TASK_UNINTERRUPTIBLE);
613 }
614
615 int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
616                          unsigned int flags)
617 {
618         if (!(flags & FAULT_FLAG_ALLOW_RETRY)) {
619                 __lock_page(page);
620                 return 1;
621         } else {
622                 up_read(&mm->mmap_sem);
623                 wait_on_page_locked(page);
624                 return 0;
625         }
626 }
627
628 /**
629  * find_get_page - find and get a page reference
630  * @mapping: the address_space to search
631  * @offset: the page index
632  *
633  * Is there a pagecache struct page at the given (mapping, offset) tuple?
634  * If yes, increment its refcount and return it; if no, return NULL.
635  */
636 struct page *find_get_page(struct address_space *mapping, pgoff_t offset)
637 {
638         void **pagep;
639         struct page *page;
640
641         rcu_read_lock();
642 repeat:
643         page = NULL;
644         pagep = radix_tree_lookup_slot(&mapping->page_tree, offset);
645         if (pagep) {
646                 page = radix_tree_deref_slot(pagep);
647                 if (unlikely(!page || page == RADIX_TREE_RETRY))
648                         goto repeat;
649
650                 if (!page_cache_get_speculative(page))
651                         goto repeat;
652
653                 /*
654                  * Has the page moved?
655                  * This is part of the lockless pagecache protocol. See
656                  * include/linux/pagemap.h for details.
657                  */
658                 if (unlikely(page != *pagep)) {
659                         page_cache_release(page);
660                         goto repeat;
661                 }
662         }
663         rcu_read_unlock();
664
665         return page;
666 }
667 EXPORT_SYMBOL(find_get_page);
668
669 /**
670  * find_lock_page - locate, pin and lock a pagecache page
671  * @mapping: the address_space to search
672  * @offset: the page index
673  *
674  * Locates the desired pagecache page, locks it, increments its reference
675  * count and returns its address.
676  *
677  * Returns zero if the page was not present. find_lock_page() may sleep.
678  */
679 struct page *find_lock_page(struct address_space *mapping, pgoff_t offset)
680 {
681         struct page *page;
682
683 repeat:
684         page = find_get_page(mapping, offset);
685         if (page) {
686                 lock_page(page);
687                 /* Has the page been truncated? */
688                 if (unlikely(page->mapping != mapping)) {
689                         unlock_page(page);
690                         page_cache_release(page);
691                         goto repeat;
692                 }
693                 VM_BUG_ON(page->index != offset);
694         }
695         return page;
696 }
697 EXPORT_SYMBOL(find_lock_page);
698
699 /**
700  * find_or_create_page - locate or add a pagecache page
701  * @mapping: the page's address_space
702  * @index: the page's index into the mapping
703  * @gfp_mask: page allocation mode
704  *
705  * Locates a page in the pagecache.  If the page is not present, a new page
706  * is allocated using @gfp_mask and is added to the pagecache and to the VM's
707  * LRU list.  The returned page is locked and has its reference count
708  * incremented.
709  *
710  * find_or_create_page() may sleep, even if @gfp_flags specifies an atomic
711  * allocation!
712  *
713  * find_or_create_page() returns the desired page's address, or zero on
714  * memory exhaustion.
715  */
716 struct page *find_or_create_page(struct address_space *mapping,
717                 pgoff_t index, gfp_t gfp_mask)
718 {
719         struct page *page;
720         int err;
721 repeat:
722         page = find_lock_page(mapping, index);
723         if (!page) {
724                 page = __page_cache_alloc(gfp_mask);
725                 if (!page)
726                         return NULL;
727                 /*
728                  * We want a regular kernel memory (not highmem or DMA etc)
729                  * allocation for the radix tree nodes, but we need to honour
730                  * the context-specific requirements the caller has asked for.
731                  * GFP_RECLAIM_MASK collects those requirements.
732                  */
733                 err = add_to_page_cache_lru(page, mapping, index,
734                         (gfp_mask & GFP_RECLAIM_MASK));
735                 if (unlikely(err)) {
736                         page_cache_release(page);
737                         page = NULL;
738                         if (err == -EEXIST)
739                                 goto repeat;
740                 }
741         }
742         return page;
743 }
744 EXPORT_SYMBOL(find_or_create_page);
745
746 /**
747  * find_get_pages - gang pagecache lookup
748  * @mapping:    The address_space to search
749  * @start:      The starting page index
750  * @nr_pages:   The maximum number of pages
751  * @pages:      Where the resulting pages are placed
752  *
753  * find_get_pages() will search for and return a group of up to
754  * @nr_pages pages in the mapping.  The pages are placed at @pages.
755  * find_get_pages() takes a reference against the returned pages.
756  *
757  * The search returns a group of mapping-contiguous pages with ascending
758  * indexes.  There may be holes in the indices due to not-present pages.
759  *
760  * find_get_pages() returns the number of pages which were found.
761  */
762 unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
763                             unsigned int nr_pages, struct page **pages)
764 {
765         unsigned int i;
766         unsigned int ret;
767         unsigned int nr_found;
768
769         rcu_read_lock();
770 restart:
771         nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
772                                 (void ***)pages, start, nr_pages);
773         ret = 0;
774         for (i = 0; i < nr_found; i++) {
775                 struct page *page;
776 repeat:
777                 page = radix_tree_deref_slot((void **)pages[i]);
778                 if (unlikely(!page))
779                         continue;
780                 /*
781                  * this can only trigger if nr_found == 1, making livelock
782                  * a non issue.
783                  */
784                 if (unlikely(page == RADIX_TREE_RETRY))
785                         goto restart;
786
787                 if (!page_cache_get_speculative(page))
788                         goto repeat;
789
790                 /* Has the page moved? */
791                 if (unlikely(page != *((void **)pages[i]))) {
792                         page_cache_release(page);
793                         goto repeat;
794                 }
795
796                 pages[ret] = page;
797                 ret++;
798         }
799         rcu_read_unlock();
800         return ret;
801 }
802
803 /**
804  * find_get_pages_contig - gang contiguous pagecache lookup
805  * @mapping:    The address_space to search
806  * @index:      The starting page index
807  * @nr_pages:   The maximum number of pages
808  * @pages:      Where the resulting pages are placed
809  *
810  * find_get_pages_contig() works exactly like find_get_pages(), except
811  * that the returned number of pages are guaranteed to be contiguous.
812  *
813  * find_get_pages_contig() returns the number of pages which were found.
814  */
815 unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
816                                unsigned int nr_pages, struct page **pages)
817 {
818         unsigned int i;
819         unsigned int ret;
820         unsigned int nr_found;
821
822         rcu_read_lock();
823 restart:
824         nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
825                                 (void ***)pages, index, nr_pages);
826         ret = 0;
827         for (i = 0; i < nr_found; i++) {
828                 struct page *page;
829 repeat:
830                 page = radix_tree_deref_slot((void **)pages[i]);
831                 if (unlikely(!page))
832                         continue;
833                 /*
834                  * this can only trigger if nr_found == 1, making livelock
835                  * a non issue.
836                  */
837                 if (unlikely(page == RADIX_TREE_RETRY))
838                         goto restart;
839
840                 if (page->mapping == NULL || page->index != index)
841                         break;
842
843                 if (!page_cache_get_speculative(page))
844                         goto repeat;
845
846                 /* Has the page moved? */
847                 if (unlikely(page != *((void **)pages[i]))) {
848                         page_cache_release(page);
849                         goto repeat;
850                 }
851
852                 pages[ret] = page;
853                 ret++;
854                 index++;
855         }
856         rcu_read_unlock();
857         return ret;
858 }
859 EXPORT_SYMBOL(find_get_pages_contig);
860
861 /**
862  * find_get_pages_tag - find and return pages that match @tag
863  * @mapping:    the address_space to search
864  * @index:      the starting page index
865  * @tag:        the tag index
866  * @nr_pages:   the maximum number of pages
867  * @pages:      where the resulting pages are placed
868  *
869  * Like find_get_pages, except we only return pages which are tagged with
870  * @tag.   We update @index to index the next page for the traversal.
871  */
872 unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
873                         int tag, unsigned int nr_pages, struct page **pages)
874 {
875         unsigned int i;
876         unsigned int ret;
877         unsigned int nr_found;
878
879         rcu_read_lock();
880 restart:
881         nr_found = radix_tree_gang_lookup_tag_slot(&mapping->page_tree,
882                                 (void ***)pages, *index, nr_pages, tag);
883         ret = 0;
884         for (i = 0; i < nr_found; i++) {
885                 struct page *page;
886 repeat:
887                 page = radix_tree_deref_slot((void **)pages[i]);
888                 if (unlikely(!page))
889                         continue;
890                 /*
891                  * this can only trigger if nr_found == 1, making livelock
892                  * a non issue.
893                  */
894                 if (unlikely(page == RADIX_TREE_RETRY))
895                         goto restart;
896
897                 if (!page_cache_get_speculative(page))
898                         goto repeat;
899
900                 /* Has the page moved? */
901                 if (unlikely(page != *((void **)pages[i]))) {
902                         page_cache_release(page);
903                         goto repeat;
904                 }
905
906                 pages[ret] = page;
907                 ret++;
908         }
909         rcu_read_unlock();
910
911         if (ret)
912                 *index = pages[ret - 1]->index + 1;
913
914         return ret;
915 }
916 EXPORT_SYMBOL(find_get_pages_tag);
917
918 /**
919  * grab_cache_page_nowait - returns locked page at given index in given cache
920  * @mapping: target address_space
921  * @index: the page index
922  *
923  * Same as grab_cache_page(), but do not wait if the page is unavailable.
924  * This is intended for speculative data generators, where the data can
925  * be regenerated if the page couldn't be grabbed.  This routine should
926  * be safe to call while holding the lock for another page.
927  *
928  * Clear __GFP_FS when allocating the page to avoid recursion into the fs
929  * and deadlock against the caller's locked page.
930  */
931 struct page *
932 grab_cache_page_nowait(struct address_space *mapping, pgoff_t index)
933 {
934         struct page *page = find_get_page(mapping, index);
935
936         if (page) {
937                 if (trylock_page(page))
938                         return page;
939                 page_cache_release(page);
940                 return NULL;
941         }
942         page = __page_cache_alloc(mapping_gfp_mask(mapping) & ~__GFP_FS);
943         if (page && add_to_page_cache_lru(page, mapping, index, GFP_NOFS)) {
944                 page_cache_release(page);
945                 page = NULL;
946         }
947         return page;
948 }
949 EXPORT_SYMBOL(grab_cache_page_nowait);
950
951 /*
952  * CD/DVDs are error prone. When a medium error occurs, the driver may fail
953  * a _large_ part of the i/o request. Imagine the worst scenario:
954  *
955  *      ---R__________________________________________B__________
956  *         ^ reading here                             ^ bad block(assume 4k)
957  *
958  * read(R) => miss => readahead(R...B) => media error => frustrating retries
959  * => failing the whole request => read(R) => read(R+1) =>
960  * readahead(R+1...B+1) => bang => read(R+2) => read(R+3) =>
961  * readahead(R+3...B+2) => bang => read(R+3) => read(R+4) =>
962  * readahead(R+4...B+3) => bang => read(R+4) => read(R+5) => ......
963  *
964  * It is going insane. Fix it by quickly scaling down the readahead size.
965  */
966 static void shrink_readahead_size_eio(struct file *filp,
967                                         struct file_ra_state *ra)
968 {
969         ra->ra_pages /= 4;
970 }
971
972 /**
973  * do_generic_file_read - generic file read routine
974  * @filp:       the file to read
975  * @ppos:       current file position
976  * @desc:       read_descriptor
977  * @actor:      read method
978  *
979  * This is a generic file read routine, and uses the
980  * mapping->a_ops->readpage() function for the actual low-level stuff.
981  *
982  * This is really ugly. But the goto's actually try to clarify some
983  * of the logic when it comes to error handling etc.
984  */
985 static void do_generic_file_read(struct file *filp, loff_t *ppos,
986                 read_descriptor_t *desc, read_actor_t actor)
987 {
988         struct address_space *mapping = filp->f_mapping;
989         struct inode *inode = mapping->host;
990         struct file_ra_state *ra = &filp->f_ra;
991         pgoff_t index;
992         pgoff_t last_index;
993         pgoff_t prev_index;
994         unsigned long offset;      /* offset into pagecache page */
995         unsigned int prev_offset;
996         int error;
997
998         index = *ppos >> PAGE_CACHE_SHIFT;
999         prev_index = ra->prev_pos >> PAGE_CACHE_SHIFT;
1000         prev_offset = ra->prev_pos & (PAGE_CACHE_SIZE-1);
1001         last_index = (*ppos + desc->count + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;
1002         offset = *ppos & ~PAGE_CACHE_MASK;
1003
1004         for (;;) {
1005                 struct page *page;
1006                 pgoff_t end_index;
1007                 loff_t isize;
1008                 unsigned long nr, ret;
1009
1010                 cond_resched();
1011 find_page:
1012                 page = find_get_page(mapping, index);
1013                 if (!page) {
1014                         page_cache_sync_readahead(mapping,
1015                                         ra, filp,
1016                                         index, last_index - index);
1017                         page = find_get_page(mapping, index);
1018                         if (unlikely(page == NULL))
1019                                 goto no_cached_page;
1020                 }
1021                 if (PageReadahead(page)) {
1022                         page_cache_async_readahead(mapping,
1023                                         ra, filp, page,
1024                                         index, last_index - index);
1025                 }
1026                 if (!PageUptodate(page)) {
1027                         if (inode->i_blkbits == PAGE_CACHE_SHIFT ||
1028                                         !mapping->a_ops->is_partially_uptodate)
1029                                 goto page_not_up_to_date;
1030                         if (!trylock_page(page))
1031                                 goto page_not_up_to_date;
1032                         /* Did it get truncated before we got the lock? */
1033                         if (!page->mapping)
1034                                 goto page_not_up_to_date_locked;
1035                         if (!mapping->a_ops->is_partially_uptodate(page,
1036                                                                 desc, offset))
1037                                 goto page_not_up_to_date_locked;
1038                         unlock_page(page);
1039                 }
1040 page_ok:
1041                 /*
1042                  * i_size must be checked after we know the page is Uptodate.
1043                  *
1044                  * Checking i_size after the check allows us to calculate
1045                  * the correct value for "nr", which means the zero-filled
1046                  * part of the page is not copied back to userspace (unless
1047                  * another truncate extends the file - this is desired though).
1048                  */
1049
1050                 isize = i_size_read(inode);
1051                 end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
1052                 if (unlikely(!isize || index > end_index)) {
1053                         page_cache_release(page);
1054                         goto out;
1055                 }
1056
1057                 /* nr is the maximum number of bytes to copy from this page */
1058                 nr = PAGE_CACHE_SIZE;
1059                 if (index == end_index) {
1060                         nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
1061                         if (nr <= offset) {
1062                                 page_cache_release(page);
1063                                 goto out;
1064                         }
1065                 }
1066                 nr = nr - offset;
1067
1068                 /* If users can be writing to this page using arbitrary
1069                  * virtual addresses, take care about potential aliasing
1070                  * before reading the page on the kernel side.
1071                  */
1072                 if (mapping_writably_mapped(mapping))
1073                         flush_dcache_page(page);
1074
1075                 /*
1076                  * When a sequential read accesses a page several times,
1077                  * only mark it as accessed the first time.
1078                  */
1079                 if (prev_index != index || offset != prev_offset)
1080                         mark_page_accessed(page);
1081                 prev_index = index;
1082
1083                 /*
1084                  * Ok, we have the page, and it's up-to-date, so
1085                  * now we can copy it to user space...
1086                  *
1087                  * The actor routine returns how many bytes were actually used..
1088                  * NOTE! This may not be the same as how much of a user buffer
1089                  * we filled up (we may be padding etc), so we can only update
1090                  * "pos" here (the actor routine has to update the user buffer
1091                  * pointers and the remaining count).
1092                  */
1093                 ret = actor(desc, page, offset, nr);
1094                 offset += ret;
1095                 index += offset >> PAGE_CACHE_SHIFT;
1096                 offset &= ~PAGE_CACHE_MASK;
1097                 prev_offset = offset;
1098
1099                 page_cache_release(page);
1100                 if (ret == nr && desc->count)
1101                         continue;
1102                 goto out;
1103
1104 page_not_up_to_date:
1105                 /* Get exclusive access to the page ... */
1106                 error = lock_page_killable(page);
1107                 if (unlikely(error))
1108                         goto readpage_error;
1109
1110 page_not_up_to_date_locked:
1111                 /* Did it get truncated before we got the lock? */
1112                 if (!page->mapping) {
1113                         unlock_page(page);
1114                         page_cache_release(page);
1115                         continue;
1116                 }
1117
1118                 /* Did somebody else fill it already? */
1119                 if (PageUptodate(page)) {
1120                         unlock_page(page);
1121                         goto page_ok;
1122                 }
1123
1124 readpage:
1125                 /*
1126                  * A previous I/O error may have been due to temporary
1127                  * failures, eg. multipath errors.
1128                  * PG_error will be set again if readpage fails.
1129                  */
1130                 ClearPageError(page);
1131                 /* Start the actual read. The read will unlock the page. */
1132                 error = mapping->a_ops->readpage(filp, page);
1133
1134                 if (unlikely(error)) {
1135                         if (error == AOP_TRUNCATED_PAGE) {
1136                                 page_cache_release(page);
1137                                 goto find_page;
1138                         }
1139                         goto readpage_error;
1140                 }
1141
1142                 if (!PageUptodate(page)) {
1143                         error = lock_page_killable(page);
1144                         if (unlikely(error))
1145                                 goto readpage_error;
1146                         if (!PageUptodate(page)) {
1147                                 if (page->mapping == NULL) {
1148                                         /*
1149                                          * invalidate_mapping_pages got it
1150                                          */
1151                                         unlock_page(page);
1152                                         page_cache_release(page);
1153                                         goto find_page;
1154                                 }
1155                                 unlock_page(page);
1156                                 shrink_readahead_size_eio(filp, ra);
1157                                 error = -EIO;
1158                                 goto readpage_error;
1159                         }
1160                         unlock_page(page);
1161                 }
1162
1163                 goto page_ok;
1164
1165 readpage_error:
1166                 /* UHHUH! A synchronous read error occurred. Report it */
1167                 desc->error = error;
1168                 page_cache_release(page);
1169                 goto out;
1170
1171 no_cached_page:
1172                 /*
1173                  * Ok, it wasn't cached, so we need to create a new
1174                  * page..
1175                  */
1176                 page = page_cache_alloc_cold(mapping);
1177                 if (!page) {
1178                         desc->error = -ENOMEM;
1179                         goto out;
1180                 }
1181                 error = add_to_page_cache_lru(page, mapping,
1182                                                 index, GFP_KERNEL);
1183                 if (error) {
1184                         page_cache_release(page);
1185                         if (error == -EEXIST)
1186                                 goto find_page;
1187                         desc->error = error;
1188                         goto out;
1189                 }
1190                 goto readpage;
1191         }
1192
1193 out:
1194         ra->prev_pos = prev_index;
1195         ra->prev_pos <<= PAGE_CACHE_SHIFT;
1196         ra->prev_pos |= prev_offset;
1197
1198         *ppos = ((loff_t)index << PAGE_CACHE_SHIFT) + offset;
1199         file_accessed(filp);
1200 }
1201
1202 int file_read_actor(read_descriptor_t *desc, struct page *page,
1203                         unsigned long offset, unsigned long size)
1204 {
1205         char *kaddr;
1206         unsigned long left, count = desc->count;
1207
1208         if (size > count)
1209                 size = count;
1210
1211         /*
1212          * Faults on the destination of a read are common, so do it before
1213          * taking the kmap.
1214          */
1215         if (!fault_in_pages_writeable(desc->arg.buf, size)) {
1216                 kaddr = kmap_atomic(page, KM_USER0);
1217                 left = __copy_to_user_inatomic(desc->arg.buf,
1218                                                 kaddr + offset, size);
1219                 kunmap_atomic(kaddr, KM_USER0);
1220                 if (left == 0)
1221                         goto success;
1222         }
1223
1224         /* Do it the slow way */
1225         kaddr = kmap(page);
1226         left = __copy_to_user(desc->arg.buf, kaddr + offset, size);
1227         kunmap(page);
1228
1229         if (left) {
1230                 size -= left;
1231                 desc->error = -EFAULT;
1232         }
1233 success:
1234         desc->count = count - size;
1235         desc->written += size;
1236         desc->arg.buf += size;
1237         return size;
1238 }
1239
1240 /*
1241  * Performs necessary checks before doing a write
1242  * @iov:        io vector request
1243  * @nr_segs:    number of segments in the iovec
1244  * @count:      number of bytes to write
1245  * @access_flags: type of access: %VERIFY_READ or %VERIFY_WRITE
1246  *
1247  * Adjust number of segments and amount of bytes to write (nr_segs should be
1248  * properly initialized first). Returns appropriate error code that caller
1249  * should return or zero in case that write should be allowed.
1250  */
1251 int generic_segment_checks(const struct iovec *iov,
1252                         unsigned long *nr_segs, size_t *count, int access_flags)
1253 {
1254         unsigned long   seg;
1255         size_t cnt = 0;
1256         for (seg = 0; seg < *nr_segs; seg++) {
1257                 const struct iovec *iv = &iov[seg];
1258
1259                 /*
1260                  * If any segment has a negative length, or the cumulative
1261                  * length ever wraps negative then return -EINVAL.
1262                  */
1263                 cnt += iv->iov_len;
1264                 if (unlikely((ssize_t)(cnt|iv->iov_len) < 0))
1265                         return -EINVAL;
1266                 if (access_ok(access_flags, iv->iov_base, iv->iov_len))
1267                         continue;
1268                 if (seg == 0)
1269                         return -EFAULT;
1270                 *nr_segs = seg;
1271                 cnt -= iv->iov_len;     /* This segment is no good */
1272                 break;
1273         }
1274         *count = cnt;
1275         return 0;
1276 }
1277 EXPORT_SYMBOL(generic_segment_checks);
1278
1279 /**
1280  * generic_file_aio_read - generic filesystem read routine
1281  * @iocb:       kernel I/O control block
1282  * @iov:        io vector request
1283  * @nr_segs:    number of segments in the iovec
1284  * @pos:        current file position
1285  *
1286  * This is the "read()" routine for all filesystems
1287  * that can use the page cache directly.
1288  */
1289 ssize_t
1290 generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
1291                 unsigned long nr_segs, loff_t pos)
1292 {
1293         struct file *filp = iocb->ki_filp;
1294         ssize_t retval;
1295         unsigned long seg = 0;
1296         size_t count;
1297         loff_t *ppos = &iocb->ki_pos;
1298
1299         count = 0;
1300         retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
1301         if (retval)
1302                 return retval;
1303
1304         /* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
1305         if (filp->f_flags & O_DIRECT) {
1306                 loff_t size;
1307                 struct address_space *mapping;
1308                 struct inode *inode;
1309
1310                 mapping = filp->f_mapping;
1311                 inode = mapping->host;
1312                 if (!count)
1313                         goto out; /* skip atime */
1314                 size = i_size_read(inode);
1315                 if (pos < size) {
1316                         retval = filemap_write_and_wait_range(mapping, pos,
1317                                         pos + iov_length(iov, nr_segs) - 1);
1318                         if (!retval) {
1319                                 retval = mapping->a_ops->direct_IO(READ, iocb,
1320                                                         iov, pos, nr_segs);
1321                         }
1322                         if (retval > 0) {
1323                                 *ppos = pos + retval;
1324                                 count -= retval;
1325                         }
1326
1327                         /*
1328                          * Btrfs can have a short DIO read if we encounter
1329                          * compressed extents, so if there was an error, or if
1330                          * we've already read everything we wanted to, or if
1331                          * there was a short read because we hit EOF, go ahead
1332                          * and return.  Otherwise fallthrough to buffered io for
1333                          * the rest of the read.
1334                          */
1335                         if (retval < 0 || !count || *ppos >= size) {
1336                                 file_accessed(filp);
1337                                 goto out;
1338                         }
1339                 }
1340         }
1341
1342         count = retval;
1343         for (seg = 0; seg < nr_segs; seg++) {
1344                 read_descriptor_t desc;
1345                 loff_t offset = 0;
1346
1347                 /*
1348                  * If we did a short DIO read we need to skip the section of the
1349                  * iov that we've already read data into.
1350                  */
1351                 if (count) {
1352                         if (count > iov[seg].iov_len) {
1353                                 count -= iov[seg].iov_len;
1354                                 continue;
1355                         }
1356                         offset = count;
1357                         count = 0;
1358                 }
1359
1360                 desc.written = 0;
1361                 desc.arg.buf = iov[seg].iov_base + offset;
1362                 desc.count = iov[seg].iov_len - offset;
1363                 if (desc.count == 0)
1364                         continue;
1365                 desc.error = 0;
1366                 do_generic_file_read(filp, ppos, &desc, file_read_actor);
1367                 retval += desc.written;
1368                 if (desc.error) {
1369                         retval = retval ?: desc.error;
1370                         break;
1371                 }
1372                 if (desc.count > 0)
1373                         break;
1374         }
1375 out:
1376         return retval;
1377 }
1378 EXPORT_SYMBOL(generic_file_aio_read);
1379
1380 static ssize_t
1381 do_readahead(struct address_space *mapping, struct file *filp,
1382              pgoff_t index, unsigned long nr)
1383 {
1384         if (!mapping || !mapping->a_ops || !mapping->a_ops->readpage)
1385                 return -EINVAL;
1386
1387         force_page_cache_readahead(mapping, filp, index, nr);
1388         return 0;
1389 }
1390
1391 SYSCALL_DEFINE(readahead)(int fd, loff_t offset, size_t count)
1392 {
1393         ssize_t ret;
1394         struct file *file;
1395
1396         ret = -EBADF;
1397         file = fget(fd);
1398         if (file) {
1399                 if (file->f_mode & FMODE_READ) {
1400                         struct address_space *mapping = file->f_mapping;
1401                         pgoff_t start = offset >> PAGE_CACHE_SHIFT;
1402                         pgoff_t end = (offset + count - 1) >> PAGE_CACHE_SHIFT;
1403                         unsigned long len = end - start + 1;
1404                         ret = do_readahead(mapping, file, start, len);
1405                 }
1406                 fput(file);
1407         }
1408         return ret;
1409 }
1410 #ifdef CONFIG_HAVE_SYSCALL_WRAPPERS
1411 asmlinkage long SyS_readahead(long fd, loff_t offset, long count)
1412 {
1413         return SYSC_readahead((int) fd, offset, (size_t) count);
1414 }
1415 SYSCALL_ALIAS(sys_readahead, SyS_readahead);
1416 #endif
1417
1418 #ifdef CONFIG_MMU
1419 /**
1420  * page_cache_read - adds requested page to the page cache if not already there
1421  * @file:       file to read
1422  * @offset:     page index
1423  *
1424  * This adds the requested page to the page cache if it isn't already there,
1425  * and schedules an I/O to read in its contents from disk.
1426  */
1427 static int page_cache_read(struct file *file, pgoff_t offset)
1428 {
1429         struct address_space *mapping = file->f_mapping;
1430         struct page *page; 
1431         int ret;
1432
1433         do {
1434                 page = page_cache_alloc_cold(mapping);
1435                 if (!page)
1436                         return -ENOMEM;
1437
1438                 ret = add_to_page_cache_lru(page, mapping, offset, GFP_KERNEL);
1439                 if (ret == 0)
1440                         ret = mapping->a_ops->readpage(file, page);
1441                 else if (ret == -EEXIST)
1442                         ret = 0; /* losing race to add is OK */
1443
1444                 page_cache_release(page);
1445
1446         } while (ret == AOP_TRUNCATED_PAGE);
1447                 
1448         return ret;
1449 }
1450
1451 #define MMAP_LOTSAMISS  (100)
1452
1453 /*
1454  * Synchronous readahead happens when we don't even find
1455  * a page in the page cache at all.
1456  */
1457 static void do_sync_mmap_readahead(struct vm_area_struct *vma,
1458                                    struct file_ra_state *ra,
1459                                    struct file *file,
1460                                    pgoff_t offset)
1461 {
1462         unsigned long ra_pages;
1463         struct address_space *mapping = file->f_mapping;
1464
1465         /* If we don't want any read-ahead, don't bother */
1466         if (VM_RandomReadHint(vma))
1467                 return;
1468
1469         if (VM_SequentialReadHint(vma) ||
1470                         offset - 1 == (ra->prev_pos >> PAGE_CACHE_SHIFT)) {
1471                 page_cache_sync_readahead(mapping, ra, file, offset,
1472                                           ra->ra_pages);
1473                 return;
1474         }
1475
1476         if (ra->mmap_miss < INT_MAX)
1477                 ra->mmap_miss++;
1478
1479         /*
1480          * Do we miss much more than hit in this file? If so,
1481          * stop bothering with read-ahead. It will only hurt.
1482          */
1483         if (ra->mmap_miss > MMAP_LOTSAMISS)
1484                 return;
1485
1486         /*
1487          * mmap read-around
1488          */
1489         ra_pages = max_sane_readahead(ra->ra_pages);
1490         if (ra_pages) {
1491                 ra->start = max_t(long, 0, offset - ra_pages/2);
1492                 ra->size = ra_pages;
1493                 ra->async_size = 0;
1494                 ra_submit(ra, mapping, file);
1495         }
1496 }
1497
1498 /*
1499  * Asynchronous readahead happens when we find the page and PG_readahead,
1500  * so we want to possibly extend the readahead further..
1501  */
1502 static void do_async_mmap_readahead(struct vm_area_struct *vma,
1503                                     struct file_ra_state *ra,
1504                                     struct file *file,
1505                                     struct page *page,
1506                                     pgoff_t offset)
1507 {
1508         struct address_space *mapping = file->f_mapping;
1509
1510         /* If we don't want any read-ahead, don't bother */
1511         if (VM_RandomReadHint(vma))
1512                 return;
1513         if (ra->mmap_miss > 0)
1514                 ra->mmap_miss--;
1515         if (PageReadahead(page))
1516                 page_cache_async_readahead(mapping, ra, file,
1517                                            page, offset, ra->ra_pages);
1518 }
1519
1520 /**
1521  * filemap_fault - read in file data for page fault handling
1522  * @vma:        vma in which the fault was taken
1523  * @vmf:        struct vm_fault containing details of the fault
1524  *
1525  * filemap_fault() is invoked via the vma operations vector for a
1526  * mapped memory region to read in file data during a page fault.
1527  *
1528  * The goto's are kind of ugly, but this streamlines the normal case of having
1529  * it in the page cache, and handles the special cases reasonably without
1530  * having a lot of duplicated code.
1531  */
1532 int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
1533 {
1534         int error;
1535         struct file *file = vma->vm_file;
1536         struct address_space *mapping = file->f_mapping;
1537         struct file_ra_state *ra = &file->f_ra;
1538         struct inode *inode = mapping->host;
1539         pgoff_t offset = vmf->pgoff;
1540         struct page *page;
1541         pgoff_t size;
1542         int ret = 0;
1543
1544         size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
1545         if (offset >= size)
1546                 return VM_FAULT_SIGBUS;
1547
1548         /*
1549          * Do we have something in the page cache already?
1550          */
1551         page = find_get_page(mapping, offset);
1552         if (likely(page)) {
1553                 /*
1554                  * We found the page, so try async readahead before
1555                  * waiting for the lock.
1556                  */
1557                 do_async_mmap_readahead(vma, ra, file, page, offset);
1558         } else {
1559                 /* No page in the page cache at all */
1560                 do_sync_mmap_readahead(vma, ra, file, offset);
1561                 count_vm_event(PGMAJFAULT);
1562                 ret = VM_FAULT_MAJOR;
1563 retry_find:
1564                 page = find_get_page(mapping, offset);
1565                 if (!page)
1566                         goto no_cached_page;
1567         }
1568
1569         if (!lock_page_or_retry(page, vma->vm_mm, vmf->flags)) {
1570                 page_cache_release(page);
1571                 return ret | VM_FAULT_RETRY;
1572         }
1573
1574         /* Did it get truncated? */
1575         if (unlikely(page->mapping != mapping)) {
1576                 unlock_page(page);
1577                 put_page(page);
1578                 goto retry_find;
1579         }
1580         VM_BUG_ON(page->index != offset);
1581
1582         /*
1583          * We have a locked page in the page cache, now we need to check
1584          * that it's up-to-date. If not, it is going to be due to an error.
1585          */
1586         if (unlikely(!PageUptodate(page)))
1587                 goto page_not_uptodate;
1588
1589         /*
1590          * Found the page and have a reference on it.
1591          * We must recheck i_size under page lock.
1592          */
1593         size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
1594         if (unlikely(offset >= size)) {
1595                 unlock_page(page);
1596                 page_cache_release(page);
1597                 return VM_FAULT_SIGBUS;
1598         }
1599
1600         ra->prev_pos = (loff_t)offset << PAGE_CACHE_SHIFT;
1601         vmf->page = page;
1602         return ret | VM_FAULT_LOCKED;
1603
1604 no_cached_page:
1605         /*
1606          * We're only likely to ever get here if MADV_RANDOM is in
1607          * effect.
1608          */
1609         error = page_cache_read(file, offset);
1610
1611         /*
1612          * The page we want has now been added to the page cache.
1613          * In the unlikely event that someone removed it in the
1614          * meantime, we'll just come back here and read it again.
1615          */
1616         if (error >= 0)
1617                 goto retry_find;
1618
1619         /*
1620          * An error return from page_cache_read can result if the
1621          * system is low on memory, or a problem occurs while trying
1622          * to schedule I/O.
1623          */
1624         if (error == -ENOMEM)
1625                 return VM_FAULT_OOM;
1626         return VM_FAULT_SIGBUS;
1627
1628 page_not_uptodate:
1629         /*
1630          * Umm, take care of errors if the page isn't up-to-date.
1631          * Try to re-read it _once_. We do this synchronously,
1632          * because there really aren't any performance issues here
1633          * and we need to check for errors.
1634          */
1635         ClearPageError(page);
1636         error = mapping->a_ops->readpage(file, page);
1637         if (!error) {
1638                 wait_on_page_locked(page);
1639                 if (!PageUptodate(page))
1640                         error = -EIO;
1641         }
1642         page_cache_release(page);
1643
1644         if (!error || error == AOP_TRUNCATED_PAGE)
1645                 goto retry_find;
1646
1647         /* Things didn't work out. Return zero to tell the mm layer so. */
1648         shrink_readahead_size_eio(file, ra);
1649         return VM_FAULT_SIGBUS;
1650 }
1651 EXPORT_SYMBOL(filemap_fault);
1652
1653 const struct vm_operations_struct generic_file_vm_ops = {
1654         .fault          = filemap_fault,
1655 };
1656
1657 /* This is used for a general mmap of a disk file */
1658
1659 int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
1660 {
1661         struct address_space *mapping = file->f_mapping;
1662
1663         if (!mapping->a_ops->readpage)
1664                 return -ENOEXEC;
1665         file_accessed(file);
1666         vma->vm_ops = &generic_file_vm_ops;
1667         vma->vm_flags |= VM_CAN_NONLINEAR;
1668         return 0;
1669 }
1670
1671 /*
1672  * This is for filesystems which do not implement ->writepage.
1673  */
1674 int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
1675 {
1676         if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
1677                 return -EINVAL;
1678         return generic_file_mmap(file, vma);
1679 }
1680 #else
1681 int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
1682 {
1683         return -ENOSYS;
1684 }
1685 int generic_file_readonly_mmap(struct file * file, struct vm_area_struct * vma)
1686 {
1687         return -ENOSYS;
1688 }
1689 #endif /* CONFIG_MMU */
1690
1691 EXPORT_SYMBOL(generic_file_mmap);
1692 EXPORT_SYMBOL(generic_file_readonly_mmap);
1693
1694 static struct page *__read_cache_page(struct address_space *mapping,
1695                                 pgoff_t index,
1696                                 int (*filler)(void *,struct page*),
1697                                 void *data,
1698                                 gfp_t gfp)
1699 {
1700         struct page *page;
1701         int err;
1702 repeat:
1703         page = find_get_page(mapping, index);
1704         if (!page) {
1705                 page = __page_cache_alloc(gfp | __GFP_COLD);
1706                 if (!page)
1707                         return ERR_PTR(-ENOMEM);
1708                 err = add_to_page_cache_lru(page, mapping, index, GFP_KERNEL);
1709                 if (unlikely(err)) {
1710                         page_cache_release(page);
1711                         if (err == -EEXIST)
1712                                 goto repeat;
1713                         /* Presumably ENOMEM for radix tree node */
1714                         return ERR_PTR(err);
1715                 }
1716                 err = filler(data, page);
1717                 if (err < 0) {
1718                         page_cache_release(page);
1719                         page = ERR_PTR(err);
1720                 }
1721         }
1722         return page;
1723 }
1724
1725 static struct page *do_read_cache_page(struct address_space *mapping,
1726                                 pgoff_t index,
1727                                 int (*filler)(void *,struct page*),
1728                                 void *data,
1729                                 gfp_t gfp)
1730
1731 {
1732         struct page *page;
1733         int err;
1734
1735 retry:
1736         page = __read_cache_page(mapping, index, filler, data, gfp);
1737         if (IS_ERR(page))
1738                 return page;
1739         if (PageUptodate(page))
1740                 goto out;
1741
1742         lock_page(page);
1743         if (!page->mapping) {
1744                 unlock_page(page);
1745                 page_cache_release(page);
1746                 goto retry;
1747         }
1748         if (PageUptodate(page)) {
1749                 unlock_page(page);
1750                 goto out;
1751         }
1752         err = filler(data, page);
1753         if (err < 0) {
1754                 page_cache_release(page);
1755                 return ERR_PTR(err);
1756         }
1757 out:
1758         mark_page_accessed(page);
1759         return page;
1760 }
1761
1762 /**
1763  * read_cache_page_async - read into page cache, fill it if needed
1764  * @mapping:    the page's address_space
1765  * @index:      the page index
1766  * @filler:     function to perform the read
1767  * @data:       destination for read data
1768  *
1769  * Same as read_cache_page, but don't wait for page to become unlocked
1770  * after submitting it to the filler.
1771  *
1772  * Read into the page cache. If a page already exists, and PageUptodate() is
1773  * not set, try to fill the page but don't wait for it to become unlocked.
1774  *
1775  * If the page does not get brought uptodate, return -EIO.
1776  */
1777 struct page *read_cache_page_async(struct address_space *mapping,
1778                                 pgoff_t index,
1779                                 int (*filler)(void *,struct page*),
1780                                 void *data)
1781 {
1782         return do_read_cache_page(mapping, index, filler, data, mapping_gfp_mask(mapping));
1783 }
1784 EXPORT_SYMBOL(read_cache_page_async);
1785
1786 static struct page *wait_on_page_read(struct page *page)
1787 {
1788         if (!IS_ERR(page)) {
1789                 wait_on_page_locked(page);
1790                 if (!PageUptodate(page)) {
1791                         page_cache_release(page);
1792                         page = ERR_PTR(-EIO);
1793                 }
1794         }
1795         return page;
1796 }
1797
1798 /**
1799  * read_cache_page_gfp - read into page cache, using specified page allocation flags.
1800  * @mapping:    the page's address_space
1801  * @index:      the page index
1802  * @gfp:        the page allocator flags to use if allocating
1803  *
1804  * This is the same as "read_mapping_page(mapping, index, NULL)", but with
1805  * any new page allocations done using the specified allocation flags. Note
1806  * that the Radix tree operations will still use GFP_KERNEL, so you can't
1807  * expect to do this atomically or anything like that - but you can pass in
1808  * other page requirements.
1809  *
1810  * If the page does not get brought uptodate, return -EIO.
1811  */
1812 struct page *read_cache_page_gfp(struct address_space *mapping,
1813                                 pgoff_t index,
1814                                 gfp_t gfp)
1815 {
1816         filler_t *filler = (filler_t *)mapping->a_ops->readpage;
1817
1818         return wait_on_page_read(do_read_cache_page(mapping, index, filler, NULL, gfp));
1819 }
1820 EXPORT_SYMBOL(read_cache_page_gfp);
1821
1822 /**
1823  * read_cache_page - read into page cache, fill it if needed
1824  * @mapping:    the page's address_space
1825  * @index:      the page index
1826  * @filler:     function to perform the read
1827  * @data:       destination for read data
1828  *
1829  * Read into the page cache. If a page already exists, and PageUptodate() is
1830  * not set, try to fill the page then wait for it to become unlocked.
1831  *
1832  * If the page does not get brought uptodate, return -EIO.
1833  */
1834 struct page *read_cache_page(struct address_space *mapping,
1835                                 pgoff_t index,
1836                                 int (*filler)(void *,struct page*),
1837                                 void *data)
1838 {
1839         return wait_on_page_read(read_cache_page_async(mapping, index, filler, data));
1840 }
1841 EXPORT_SYMBOL(read_cache_page);
1842
1843 /*
1844  * The logic we want is
1845  *
1846  *      if suid or (sgid and xgrp)
1847  *              remove privs
1848  */
1849 int should_remove_suid(struct dentry *dentry)
1850 {
1851         mode_t mode = dentry->d_inode->i_mode;
1852         int kill = 0;
1853
1854         /* suid always must be killed */
1855         if (unlikely(mode & S_ISUID))
1856                 kill = ATTR_KILL_SUID;
1857
1858         /*
1859          * sgid without any exec bits is just a mandatory locking mark; leave
1860          * it alone.  If some exec bits are set, it's a real sgid; kill it.
1861          */
1862         if (unlikely((mode & S_ISGID) && (mode & S_IXGRP)))
1863                 kill |= ATTR_KILL_SGID;
1864
1865         if (unlikely(kill && !capable(CAP_FSETID) && S_ISREG(mode)))
1866                 return kill;
1867
1868         return 0;
1869 }
1870 EXPORT_SYMBOL(should_remove_suid);
1871
1872 static int __remove_suid(struct dentry *dentry, int kill)
1873 {
1874         struct iattr newattrs;
1875
1876         newattrs.ia_valid = ATTR_FORCE | kill;
1877         return notify_change(dentry, &newattrs);
1878 }
1879
1880 int file_remove_suid(struct file *file)
1881 {
1882         struct dentry *dentry = file->f_path.dentry;
1883         int killsuid = should_remove_suid(dentry);
1884         int killpriv = security_inode_need_killpriv(dentry);
1885         int error = 0;
1886
1887         if (killpriv < 0)
1888                 return killpriv;
1889         if (killpriv)
1890                 error = security_inode_killpriv(dentry);
1891         if (!error && killsuid)
1892                 error = __remove_suid(dentry, killsuid);
1893
1894         return error;
1895 }
1896 EXPORT_SYMBOL(file_remove_suid);
1897
1898 static size_t __iovec_copy_from_user_inatomic(char *vaddr,
1899                         const struct iovec *iov, size_t base, size_t bytes)
1900 {
1901         size_t copied = 0, left = 0;
1902
1903         while (bytes) {
1904                 char __user *buf = iov->iov_base + base;
1905                 int copy = min(bytes, iov->iov_len - base);
1906
1907                 base = 0;
1908                 left = __copy_from_user_inatomic(vaddr, buf, copy);
1909                 copied += copy;
1910                 bytes -= copy;
1911                 vaddr += copy;
1912                 iov++;
1913
1914                 if (unlikely(left))
1915                         break;
1916         }
1917         return copied - left;
1918 }
1919
1920 /*
1921  * Copy as much as we can into the page and return the number of bytes which
1922  * were successfully copied.  If a fault is encountered then return the number of
1923  * bytes which were copied.
1924  */
1925 size_t iov_iter_copy_from_user_atomic(struct page *page,
1926                 struct iov_iter *i, unsigned long offset, size_t bytes)
1927 {
1928         char *kaddr;
1929         size_t copied;
1930
1931         BUG_ON(!in_atomic());
1932         kaddr = kmap_atomic(page, KM_USER0);
1933         if (likely(i->nr_segs == 1)) {
1934                 int left;
1935                 char __user *buf = i->iov->iov_base + i->iov_offset;
1936                 left = __copy_from_user_inatomic(kaddr + offset, buf, bytes);
1937                 copied = bytes - left;
1938         } else {
1939                 copied = __iovec_copy_from_user_inatomic(kaddr + offset,
1940                                                 i->iov, i->iov_offset, bytes);
1941         }
1942         kunmap_atomic(kaddr, KM_USER0);
1943
1944         return copied;
1945 }
1946 EXPORT_SYMBOL(iov_iter_copy_from_user_atomic);
1947
1948 /*
1949  * This has the same sideeffects and return value as
1950  * iov_iter_copy_from_user_atomic().
1951  * The difference is that it attempts to resolve faults.
1952  * Page must not be locked.
1953  */
1954 size_t iov_iter_copy_from_user(struct page *page,
1955                 struct iov_iter *i, unsigned long offset, size_t bytes)
1956 {
1957         char *kaddr;
1958         size_t copied;
1959
1960         kaddr = kmap(page);
1961         if (likely(i->nr_segs == 1)) {
1962                 int left;
1963                 char __user *buf = i->iov->iov_base + i->iov_offset;
1964                 left = __copy_from_user(kaddr + offset, buf, bytes);
1965                 copied = bytes - left;
1966         } else {
1967                 copied = __iovec_copy_from_user_inatomic(kaddr + offset,
1968                                                 i->iov, i->iov_offset, bytes);
1969         }
1970         kunmap(page);
1971         return copied;
1972 }
1973 EXPORT_SYMBOL(iov_iter_copy_from_user);
1974
1975 void iov_iter_advance(struct iov_iter *i, size_t bytes)
1976 {
1977         BUG_ON(i->count < bytes);
1978
1979         if (likely(i->nr_segs == 1)) {
1980                 i->iov_offset += bytes;
1981                 i->count -= bytes;
1982         } else {
1983                 const struct iovec *iov = i->iov;
1984                 size_t base = i->iov_offset;
1985
1986                 /*
1987                  * The !iov->iov_len check ensures we skip over unlikely
1988                  * zero-length segments (without overruning the iovec).
1989                  */
1990                 while (bytes || unlikely(i->count && !iov->iov_len)) {
1991                         int copy;
1992
1993                         copy = min(bytes, iov->iov_len - base);
1994                         BUG_ON(!i->count || i->count < copy);
1995                         i->count -= copy;
1996                         bytes -= copy;
1997                         base += copy;
1998                         if (iov->iov_len == base) {
1999                                 iov++;
2000                                 base = 0;
2001                         }
2002                 }
2003                 i->iov = iov;
2004                 i->iov_offset = base;
2005         }
2006 }
2007 EXPORT_SYMBOL(iov_iter_advance);
2008
2009 /*
2010  * Fault in the first iovec of the given iov_iter, to a maximum length
2011  * of bytes. Returns 0 on success, or non-zero if the memory could not be
2012  * accessed (ie. because it is an invalid address).
2013  *
2014  * writev-intensive code may want this to prefault several iovecs -- that
2015  * would be possible (callers must not rely on the fact that _only_ the
2016  * first iovec will be faulted with the current implementation).
2017  */
2018 int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
2019 {
2020         char __user *buf = i->iov->iov_base + i->iov_offset;
2021         bytes = min(bytes, i->iov->iov_len - i->iov_offset);
2022         return fault_in_pages_readable(buf, bytes);
2023 }
2024 EXPORT_SYMBOL(iov_iter_fault_in_readable);
2025
2026 /*
2027  * Return the count of just the current iov_iter segment.
2028  */
2029 size_t iov_iter_single_seg_count(struct iov_iter *i)
2030 {
2031         const struct iovec *iov = i->iov;
2032         if (i->nr_segs == 1)
2033                 return i->count;
2034         else
2035                 return min(i->count, iov->iov_len - i->iov_offset);
2036 }
2037 EXPORT_SYMBOL(iov_iter_single_seg_count);
2038
2039 /*
2040  * Performs necessary checks before doing a write
2041  *
2042  * Can adjust writing position or amount of bytes to write.
2043  * Returns appropriate error code that caller should return or
2044  * zero in case that write should be allowed.
2045  */
2046 inline int generic_write_checks(struct file *file, loff_t *pos, size_t *count, int isblk)
2047 {
2048         struct inode *inode = file->f_mapping->host;
2049         unsigned long limit = rlimit(RLIMIT_FSIZE);
2050
2051         if (unlikely(*pos < 0))
2052                 return -EINVAL;
2053
2054         if (!isblk) {
2055                 /* FIXME: this is for backwards compatibility with 2.4 */
2056                 if (file->f_flags & O_APPEND)
2057                         *pos = i_size_read(inode);
2058
2059                 if (limit != RLIM_INFINITY) {
2060                         if (*pos >= limit) {
2061                                 send_sig(SIGXFSZ, current, 0);
2062                                 return -EFBIG;
2063                         }
2064                         if (*count > limit - (typeof(limit))*pos) {
2065                                 *count = limit - (typeof(limit))*pos;
2066                         }
2067                 }
2068         }
2069
2070         /*
2071          * LFS rule
2072          */
2073         if (unlikely(*pos + *count > MAX_NON_LFS &&
2074                                 !(file->f_flags & O_LARGEFILE))) {
2075                 if (*pos >= MAX_NON_LFS) {
2076                         return -EFBIG;
2077                 }
2078                 if (*count > MAX_NON_LFS - (unsigned long)*pos) {
2079                         *count = MAX_NON_LFS - (unsigned long)*pos;
2080                 }
2081         }
2082
2083         /*
2084          * Are we about to exceed the fs block limit ?
2085          *
2086          * If we have written data it becomes a short write.  If we have
2087          * exceeded without writing data we send a signal and return EFBIG.
2088          * Linus frestrict idea will clean these up nicely..
2089          */
2090         if (likely(!isblk)) {
2091                 if (unlikely(*pos >= inode->i_sb->s_maxbytes)) {
2092                         if (*count || *pos > inode->i_sb->s_maxbytes) {
2093                                 return -EFBIG;
2094                         }
2095                         /* zero-length writes at ->s_maxbytes are OK */
2096                 }
2097
2098                 if (unlikely(*pos + *count > inode->i_sb->s_maxbytes))
2099                         *count = inode->i_sb->s_maxbytes - *pos;
2100         } else {
2101 #ifdef CONFIG_BLOCK
2102                 loff_t isize;
2103                 if (bdev_read_only(I_BDEV(inode)))
2104                         return -EPERM;
2105                 isize = i_size_read(inode);
2106                 if (*pos >= isize) {
2107                         if (*count || *pos > isize)
2108                                 return -ENOSPC;
2109                 }
2110
2111                 if (*pos + *count > isize)
2112                         *count = isize - *pos;
2113 #else
2114                 return -EPERM;
2115 #endif
2116         }
2117         return 0;
2118 }
2119 EXPORT_SYMBOL(generic_write_checks);
2120
2121 int pagecache_write_begin(struct file *file, struct address_space *mapping,
2122                                 loff_t pos, unsigned len, unsigned flags,
2123                                 struct page **pagep, void **fsdata)
2124 {
2125         const struct address_space_operations *aops = mapping->a_ops;
2126
2127         return aops->write_begin(file, mapping, pos, len, flags,
2128                                                         pagep, fsdata);
2129 }
2130 EXPORT_SYMBOL(pagecache_write_begin);
2131
2132 int pagecache_write_end(struct file *file, struct address_space *mapping,
2133                                 loff_t pos, unsigned len, unsigned copied,
2134                                 struct page *page, void *fsdata)
2135 {
2136         const struct address_space_operations *aops = mapping->a_ops;
2137
2138         mark_page_accessed(page);
2139         return aops->write_end(file, mapping, pos, len, copied, page, fsdata);
2140 }
2141 EXPORT_SYMBOL(pagecache_write_end);
2142
2143 ssize_t
2144 generic_file_direct_write(struct kiocb *iocb, const struct iovec *iov,
2145                 unsigned long *nr_segs, loff_t pos, loff_t *ppos,
2146                 size_t count, size_t ocount)
2147 {
2148         struct file     *file = iocb->ki_filp;
2149         struct address_space *mapping = file->f_mapping;
2150         struct inode    *inode = mapping->host;
2151         ssize_t         written;
2152         size_t          write_len;
2153         pgoff_t         end;
2154
2155         if (count != ocount)
2156                 *nr_segs = iov_shorten((struct iovec *)iov, *nr_segs, count);
2157
2158         write_len = iov_length(iov, *nr_segs);
2159         end = (pos + write_len - 1) >> PAGE_CACHE_SHIFT;
2160
2161         written = filemap_write_and_wait_range(mapping, pos, pos + write_len - 1);
2162         if (written)
2163                 goto out;
2164
2165         /*
2166          * After a write we want buffered reads to be sure to go to disk to get
2167          * the new data.  We invalidate clean cached page from the region we're
2168          * about to write.  We do this *before* the write so that we can return
2169          * without clobbering -EIOCBQUEUED from ->direct_IO().
2170          */
2171         if (mapping->nrpages) {
2172                 written = invalidate_inode_pages2_range(mapping,
2173                                         pos >> PAGE_CACHE_SHIFT, end);
2174                 /*
2175                  * If a page can not be invalidated, return 0 to fall back
2176                  * to buffered write.
2177                  */
2178                 if (written) {
2179                         if (written == -EBUSY)
2180                                 return 0;
2181                         goto out;
2182                 }
2183         }
2184
2185         written = mapping->a_ops->direct_IO(WRITE, iocb, iov, pos, *nr_segs);
2186
2187         /*
2188          * Finally, try again to invalidate clean pages which might have been
2189          * cached by non-direct readahead, or faulted in by get_user_pages()
2190          * if the source of the write was an mmap'ed region of the file
2191          * we're writing.  Either one is a pretty crazy thing to do,
2192          * so we don't support it 100%.  If this invalidation
2193          * fails, tough, the write still worked...
2194          */
2195         if (mapping->nrpages) {
2196                 invalidate_inode_pages2_range(mapping,
2197                                               pos >> PAGE_CACHE_SHIFT, end);
2198         }
2199
2200         if (written > 0) {
2201                 pos += written;
2202                 if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
2203                         i_size_write(inode, pos);
2204                         mark_inode_dirty(inode);
2205                 }
2206                 *ppos = pos;
2207         }
2208 out:
2209         return written;
2210 }
2211 EXPORT_SYMBOL(generic_file_direct_write);
2212
2213 /*
2214  * Find or create a page at the given pagecache position. Return the locked
2215  * page. This function is specifically for buffered writes.
2216  */
2217 struct page *grab_cache_page_write_begin(struct address_space *mapping,
2218                                         pgoff_t index, unsigned flags)
2219 {
2220         int status;
2221         struct page *page;
2222         gfp_t gfp_notmask = 0;
2223         if (flags & AOP_FLAG_NOFS)
2224                 gfp_notmask = __GFP_FS;
2225 repeat:
2226         page = find_lock_page(mapping, index);
2227         if (likely(page))
2228                 return page;
2229
2230         page = __page_cache_alloc(mapping_gfp_mask(mapping) & ~gfp_notmask);
2231         if (!page)
2232                 return NULL;
2233         status = add_to_page_cache_lru(page, mapping, index,
2234                                                 GFP_KERNEL & ~gfp_notmask);
2235         if (unlikely(status)) {
2236                 page_cache_release(page);
2237                 if (status == -EEXIST)
2238                         goto repeat;
2239                 return NULL;
2240         }
2241         return page;
2242 }
2243 EXPORT_SYMBOL(grab_cache_page_write_begin);
2244
2245 static ssize_t generic_perform_write(struct file *file,
2246                                 struct iov_iter *i, loff_t pos)
2247 {
2248         struct address_space *mapping = file->f_mapping;
2249         const struct address_space_operations *a_ops = mapping->a_ops;
2250         long status = 0;
2251         ssize_t written = 0;
2252         unsigned int flags = 0;
2253
2254         /*
2255          * Copies from kernel address space cannot fail (NFSD is a big user).
2256          */
2257         if (segment_eq(get_fs(), KERNEL_DS))
2258                 flags |= AOP_FLAG_UNINTERRUPTIBLE;
2259
2260         do {
2261                 struct page *page;
2262                 unsigned long offset;   /* Offset into pagecache page */
2263                 unsigned long bytes;    /* Bytes to write to page */
2264                 size_t copied;          /* Bytes copied from user */
2265                 void *fsdata;
2266
2267                 offset = (pos & (PAGE_CACHE_SIZE - 1));
2268                 bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
2269                                                 iov_iter_count(i));
2270
2271 again:
2272
2273                 /*
2274                  * Bring in the user page that we will copy from _first_.
2275                  * Otherwise there's a nasty deadlock on copying from the
2276                  * same page as we're writing to, without it being marked
2277                  * up-to-date.
2278                  *
2279                  * Not only is this an optimisation, but it is also required
2280                  * to check that the address is actually valid, when atomic
2281                  * usercopies are used, below.
2282                  */
2283                 if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
2284                         status = -EFAULT;
2285                         break;
2286                 }
2287
2288                 status = a_ops->write_begin(file, mapping, pos, bytes, flags,
2289                                                 &page, &fsdata);
2290                 if (unlikely(status))
2291                         break;
2292
2293                 if (mapping_writably_mapped(mapping))
2294                         flush_dcache_page(page);
2295
2296                 pagefault_disable();
2297                 copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
2298                 pagefault_enable();
2299                 flush_dcache_page(page);
2300
2301                 mark_page_accessed(page);
2302                 status = a_ops->write_end(file, mapping, pos, bytes, copied,
2303                                                 page, fsdata);
2304                 if (unlikely(status < 0))
2305                         break;
2306                 copied = status;
2307
2308                 cond_resched();
2309
2310                 iov_iter_advance(i, copied);
2311                 if (unlikely(copied == 0)) {
2312                         /*
2313                          * If we were unable to copy any data at all, we must
2314                          * fall back to a single segment length write.
2315                          *
2316                          * If we didn't fallback here, we could livelock
2317                          * because not all segments in the iov can be copied at
2318                          * once without a pagefault.
2319                          */
2320                         bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
2321                                                 iov_iter_single_seg_count(i));
2322                         goto again;
2323                 }
2324                 pos += copied;
2325                 written += copied;
2326
2327                 balance_dirty_pages_ratelimited(mapping);
2328
2329         } while (iov_iter_count(i));
2330
2331         return written ? written : status;
2332 }
2333
2334 ssize_t
2335 generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
2336                 unsigned long nr_segs, loff_t pos, loff_t *ppos,
2337                 size_t count, ssize_t written)
2338 {
2339         struct file *file = iocb->ki_filp;
2340         ssize_t status;
2341         struct iov_iter i;
2342
2343         iov_iter_init(&i, iov, nr_segs, count, written);
2344         status = generic_perform_write(file, &i, pos);
2345
2346         if (likely(status >= 0)) {
2347                 written += status;
2348                 *ppos = pos + status;
2349         }
2350         
2351         return written ? written : status;
2352 }
2353 EXPORT_SYMBOL(generic_file_buffered_write);
2354
2355 /**
2356  * __generic_file_aio_write - write data to a file
2357  * @iocb:       IO state structure (file, offset, etc.)
2358  * @iov:        vector with data to write
2359  * @nr_segs:    number of segments in the vector
2360  * @ppos:       position where to write
2361  *
2362  * This function does all the work needed for actually writing data to a
2363  * file. It does all basic checks, removes SUID from the file, updates
2364  * modification times and calls proper subroutines depending on whether we
2365  * do direct IO or a standard buffered write.
2366  *
2367  * It expects i_mutex to be grabbed unless we work on a block device or similar
2368  * object which does not need locking at all.
2369  *
2370  * This function does *not* take care of syncing data in case of O_SYNC write.
2371  * A caller has to handle it. This is mainly due to the fact that we want to
2372  * avoid syncing under i_mutex.
2373  */
2374 ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
2375                                  unsigned long nr_segs, loff_t *ppos)
2376 {
2377         struct file *file = iocb->ki_filp;
2378         struct address_space * mapping = file->f_mapping;
2379         size_t ocount;          /* original count */
2380         size_t count;           /* after file limit checks */
2381         struct inode    *inode = mapping->host;
2382         loff_t          pos;
2383         ssize_t         written;
2384         ssize_t         err;
2385
2386         ocount = 0;
2387         err = generic_segment_checks(iov, &nr_segs, &ocount, VERIFY_READ);
2388         if (err)
2389                 return err;
2390
2391         count = ocount;
2392         pos = *ppos;
2393
2394         vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
2395
2396         /* We can write back this queue in page reclaim */
2397         current->backing_dev_info = mapping->backing_dev_info;
2398         written = 0;
2399
2400         err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));
2401         if (err)
2402                 goto out;
2403
2404         if (count == 0)
2405                 goto out;
2406
2407         err = file_remove_suid(file);
2408         if (err)
2409                 goto out;
2410
2411         file_update_time(file);
2412
2413         /* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
2414         if (unlikely(file->f_flags & O_DIRECT)) {
2415                 loff_t endbyte;
2416                 ssize_t written_buffered;
2417
2418                 written = generic_file_direct_write(iocb, iov, &nr_segs, pos,
2419                                                         ppos, count, ocount);
2420                 if (written < 0 || written == count)
2421                         goto out;
2422                 /*
2423                  * direct-io write to a hole: fall through to buffered I/O
2424                  * for completing the rest of the request.
2425                  */
2426                 pos += written;
2427                 count -= written;
2428                 written_buffered = generic_file_buffered_write(iocb, iov,
2429                                                 nr_segs, pos, ppos, count,
2430                                                 written);
2431                 /*
2432                  * If generic_file_buffered_write() retuned a synchronous error
2433                  * then we want to return the number of bytes which were
2434                  * direct-written, or the error code if that was zero.  Note
2435                  * that this differs from normal direct-io semantics, which
2436                  * will return -EFOO even if some bytes were written.
2437                  */
2438                 if (written_buffered < 0) {
2439                         err = written_buffered;
2440                         goto out;
2441                 }
2442
2443                 /*
2444                  * We need to ensure that the page cache pages are written to
2445                  * disk and invalidated to preserve the expected O_DIRECT
2446                  * semantics.
2447                  */
2448                 endbyte = pos + written_buffered - written - 1;
2449                 err = filemap_write_and_wait_range(file->f_mapping, pos, endbyte);
2450                 if (err == 0) {
2451                         written = written_buffered;
2452                         invalidate_mapping_pages(mapping,
2453                                                  pos >> PAGE_CACHE_SHIFT,
2454                                                  endbyte >> PAGE_CACHE_SHIFT);
2455                 } else {
2456                         /*
2457                          * We don't know how much we wrote, so just return
2458                          * the number of bytes which were direct-written
2459                          */
2460                 }
2461         } else {
2462                 written = generic_file_buffered_write(iocb, iov, nr_segs,
2463                                 pos, ppos, count, written);
2464         }
2465 out:
2466         current->backing_dev_info = NULL;
2467         return written ? written : err;
2468 }
2469 EXPORT_SYMBOL(__generic_file_aio_write);
2470
2471 /**
2472  * generic_file_aio_write - write data to a file
2473  * @iocb:       IO state structure
2474  * @iov:        vector with data to write
2475  * @nr_segs:    number of segments in the vector
2476  * @pos:        position in file where to write
2477  *
2478  * This is a wrapper around __generic_file_aio_write() to be used by most
2479  * filesystems. It takes care of syncing the file in case of O_SYNC file
2480  * and acquires i_mutex as needed.
2481  */
2482 ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
2483                 unsigned long nr_segs, loff_t pos)
2484 {
2485         struct file *file = iocb->ki_filp;
2486         struct inode *inode = file->f_mapping->host;
2487         ssize_t ret;
2488
2489         BUG_ON(iocb->ki_pos != pos);
2490
2491         mutex_lock(&inode->i_mutex);
2492         ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
2493         mutex_unlock(&inode->i_mutex);
2494
2495         if (ret > 0 || ret == -EIOCBQUEUED) {
2496                 ssize_t err;
2497
2498                 err = generic_write_sync(file, pos, ret);
2499                 if (err < 0 && ret > 0)
2500                         ret = err;
2501         }
2502         return ret;
2503 }
2504 EXPORT_SYMBOL(generic_file_aio_write);
2505
2506 /**
2507  * try_to_release_page() - release old fs-specific metadata on a page
2508  *
2509  * @page: the page which the kernel is trying to free
2510  * @gfp_mask: memory allocation flags (and I/O mode)
2511  *
2512  * The address_space is to try to release any data against the page
2513  * (presumably at page->private).  If the release was successful, return `1'.
2514  * Otherwise return zero.
2515  *
2516  * This may also be called if PG_fscache is set on a page, indicating that the
2517  * page is known to the local caching routines.
2518  *
2519  * The @gfp_mask argument specifies whether I/O may be performed to release
2520  * this page (__GFP_IO), and whether the call may block (__GFP_WAIT & __GFP_FS).
2521  *
2522  */
2523 int try_to_release_page(struct page *page, gfp_t gfp_mask)
2524 {
2525         struct address_space * const mapping = page->mapping;
2526
2527         BUG_ON(!PageLocked(page));
2528         if (PageWriteback(page))
2529                 return 0;
2530
2531         if (mapping && mapping->a_ops->releasepage)
2532                 return mapping->a_ops->releasepage(page, gfp_mask);
2533         return try_to_free_buffers(page);
2534 }
2535
2536 EXPORT_SYMBOL(try_to_release_page);