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TOMOYO Linux Cross Reference
Linux/mm/filemap.c

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  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/export.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/cleancache.h>
 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_mutex              (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_mutex            (truncate->unmap_mapping_range)
 68  *
 69  *  ->mmap_sem
 70  *    ->i_mmap_mutex
 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  *  bdi->wb.list_lock
 81  *    sb_lock                   (fs/fs-writeback.c)
 82  *    ->mapping->tree_lock      (__sync_single_inode)
 83  *
 84  *  ->i_mmap_mutex
 85  *    ->anon_vma.lock           (vma_adjust)
 86  *
 87  *  ->anon_vma.lock
 88  *    ->page_table_lock or pte_lock     (anon_vma_prepare and various)
 89  *
 90  *  ->page_table_lock or pte_lock
 91  *    ->swap_lock               (try_to_unmap_one)
 92  *    ->private_lock            (try_to_unmap_one)
 93  *    ->tree_lock               (try_to_unmap_one)
 94  *    ->zone.lru_lock           (follow_page->mark_page_accessed)
 95  *    ->zone.lru_lock           (check_pte_range->isolate_lru_page)
 96  *    ->private_lock            (page_remove_rmap->set_page_dirty)
 97  *    ->tree_lock               (page_remove_rmap->set_page_dirty)
 98  *    bdi.wb->list_lock         (page_remove_rmap->set_page_dirty)
 99  *    ->inode->i_lock           (page_remove_rmap->set_page_dirty)
100  *    bdi.wb->list_lock         (zap_pte_range->set_page_dirty)
101  *    ->inode->i_lock           (zap_pte_range->set_page_dirty)
102  *    ->private_lock            (zap_pte_range->__set_page_dirty_buffers)
103  *
104  * ->i_mmap_mutex
105  *   ->tasklist_lock            (memory_failure, collect_procs_ao)
106  */
107 
108 /*
109  * Delete a page from the page cache and free it. Caller has to make
110  * sure the page is locked and that nobody else uses it - or that usage
111  * is safe.  The caller must hold the mapping's tree_lock.
112  */
113 void __delete_from_page_cache(struct page *page)
114 {
115         struct address_space *mapping = page->mapping;
116 
117         /*
118          * if we're uptodate, flush out into the cleancache, otherwise
119          * invalidate any existing cleancache entries.  We can't leave
120          * stale data around in the cleancache once our page is gone
121          */
122         if (PageUptodate(page) && PageMappedToDisk(page))
123                 cleancache_put_page(page);
124         else
125                 cleancache_invalidate_page(mapping, page);
126 
127         radix_tree_delete(&mapping->page_tree, page->index);
128         page->mapping = NULL;
129         /* Leave page->index set: truncation lookup relies upon it */
130         mapping->nrpages--;
131         __dec_zone_page_state(page, NR_FILE_PAGES);
132         if (PageSwapBacked(page))
133                 __dec_zone_page_state(page, NR_SHMEM);
134         BUG_ON(page_mapped(page));
135 
136         /*
137          * Some filesystems seem to re-dirty the page even after
138          * the VM has canceled the dirty bit (eg ext3 journaling).
139          *
140          * Fix it up by doing a final dirty accounting check after
141          * having removed the page entirely.
142          */
143         if (PageDirty(page) && mapping_cap_account_dirty(mapping)) {
144                 dec_zone_page_state(page, NR_FILE_DIRTY);
145                 dec_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
146         }
147 }
148 
149 /**
150  * delete_from_page_cache - delete page from page cache
151  * @page: the page which the kernel is trying to remove from page cache
152  *
153  * This must be called only on pages that have been verified to be in the page
154  * cache and locked.  It will never put the page into the free list, the caller
155  * has a reference on the page.
156  */
157 void delete_from_page_cache(struct page *page)
158 {
159         struct address_space *mapping = page->mapping;
160         void (*freepage)(struct page *);
161 
162         BUG_ON(!PageLocked(page));
163 
164         freepage = mapping->a_ops->freepage;
165         spin_lock_irq(&mapping->tree_lock);
166         __delete_from_page_cache(page);
167         spin_unlock_irq(&mapping->tree_lock);
168         mem_cgroup_uncharge_cache_page(page);
169 
170         if (freepage)
171                 freepage(page);
172         page_cache_release(page);
173 }
174 EXPORT_SYMBOL(delete_from_page_cache);
175 
176 static int sleep_on_page(void *word)
177 {
178         io_schedule();
179         return 0;
180 }
181 
182 static int sleep_on_page_killable(void *word)
183 {
184         sleep_on_page(word);
185         return fatal_signal_pending(current) ? -EINTR : 0;
186 }
187 
188 /**
189  * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
190  * @mapping:    address space structure to write
191  * @start:      offset in bytes where the range starts
192  * @end:        offset in bytes where the range ends (inclusive)
193  * @sync_mode:  enable synchronous operation
194  *
195  * Start writeback against all of a mapping's dirty pages that lie
196  * within the byte offsets <start, end> inclusive.
197  *
198  * If sync_mode is WB_SYNC_ALL then this is a "data integrity" operation, as
199  * opposed to a regular memory cleansing writeback.  The difference between
200  * these two operations is that if a dirty page/buffer is encountered, it must
201  * be waited upon, and not just skipped over.
202  */
203 int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
204                                 loff_t end, int sync_mode)
205 {
206         int ret;
207         struct writeback_control wbc = {
208                 .sync_mode = sync_mode,
209                 .nr_to_write = LONG_MAX,
210                 .range_start = start,
211                 .range_end = end,
212         };
213 
214         if (!mapping_cap_writeback_dirty(mapping))
215                 return 0;
216 
217         ret = do_writepages(mapping, &wbc);
218         return ret;
219 }
220 
221 static inline int __filemap_fdatawrite(struct address_space *mapping,
222         int sync_mode)
223 {
224         return __filemap_fdatawrite_range(mapping, 0, LLONG_MAX, sync_mode);
225 }
226 
227 int filemap_fdatawrite(struct address_space *mapping)
228 {
229         return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
230 }
231 EXPORT_SYMBOL(filemap_fdatawrite);
232 
233 int filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
234                                 loff_t end)
235 {
236         return __filemap_fdatawrite_range(mapping, start, end, WB_SYNC_ALL);
237 }
238 EXPORT_SYMBOL(filemap_fdatawrite_range);
239 
240 /**
241  * filemap_flush - mostly a non-blocking flush
242  * @mapping:    target address_space
243  *
244  * This is a mostly non-blocking flush.  Not suitable for data-integrity
245  * purposes - I/O may not be started against all dirty pages.
246  */
247 int filemap_flush(struct address_space *mapping)
248 {
249         return __filemap_fdatawrite(mapping, WB_SYNC_NONE);
250 }
251 EXPORT_SYMBOL(filemap_flush);
252 
253 /**
254  * filemap_fdatawait_range - wait for writeback to complete
255  * @mapping:            address space structure to wait for
256  * @start_byte:         offset in bytes where the range starts
257  * @end_byte:           offset in bytes where the range ends (inclusive)
258  *
259  * Walk the list of under-writeback pages of the given address space
260  * in the given range and wait for all of them.
261  */
262 int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
263                             loff_t end_byte)
264 {
265         pgoff_t index = start_byte >> PAGE_CACHE_SHIFT;
266         pgoff_t end = end_byte >> PAGE_CACHE_SHIFT;
267         struct pagevec pvec;
268         int nr_pages;
269         int ret = 0;
270 
271         if (end_byte < start_byte)
272                 return 0;
273 
274         pagevec_init(&pvec, 0);
275         while ((index <= end) &&
276                         (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
277                         PAGECACHE_TAG_WRITEBACK,
278                         min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1)) != 0) {
279                 unsigned i;
280 
281                 for (i = 0; i < nr_pages; i++) {
282                         struct page *page = pvec.pages[i];
283 
284                         /* until radix tree lookup accepts end_index */
285                         if (page->index > end)
286                                 continue;
287 
288                         wait_on_page_writeback(page);
289                         if (TestClearPageError(page))
290                                 ret = -EIO;
291                 }
292                 pagevec_release(&pvec);
293                 cond_resched();
294         }
295 
296         /* Check for outstanding write errors */
297         if (test_and_clear_bit(AS_ENOSPC, &mapping->flags))
298                 ret = -ENOSPC;
299         if (test_and_clear_bit(AS_EIO, &mapping->flags))
300                 ret = -EIO;
301 
302         return ret;
303 }
304 EXPORT_SYMBOL(filemap_fdatawait_range);
305 
306 /**
307  * filemap_fdatawait - wait for all under-writeback pages to complete
308  * @mapping: address space structure to wait for
309  *
310  * Walk the list of under-writeback pages of the given address space
311  * and wait for all of them.
312  */
313 int filemap_fdatawait(struct address_space *mapping)
314 {
315         loff_t i_size = i_size_read(mapping->host);
316 
317         if (i_size == 0)
318                 return 0;
319 
320         return filemap_fdatawait_range(mapping, 0, i_size - 1);
321 }
322 EXPORT_SYMBOL(filemap_fdatawait);
323 
324 int filemap_write_and_wait(struct address_space *mapping)
325 {
326         int err = 0;
327 
328         if (mapping->nrpages) {
329                 err = filemap_fdatawrite(mapping);
330                 /*
331                  * Even if the above returned error, the pages may be
332                  * written partially (e.g. -ENOSPC), so we wait for it.
333                  * But the -EIO is special case, it may indicate the worst
334                  * thing (e.g. bug) happened, so we avoid waiting for it.
335                  */
336                 if (err != -EIO) {
337                         int err2 = filemap_fdatawait(mapping);
338                         if (!err)
339                                 err = err2;
340                 }
341         }
342         return err;
343 }
344 EXPORT_SYMBOL(filemap_write_and_wait);
345 
346 /**
347  * filemap_write_and_wait_range - write out & wait on a file range
348  * @mapping:    the address_space for the pages
349  * @lstart:     offset in bytes where the range starts
350  * @lend:       offset in bytes where the range ends (inclusive)
351  *
352  * Write out and wait upon file offsets lstart->lend, inclusive.
353  *
354  * Note that `lend' is inclusive (describes the last byte to be written) so
355  * that this function can be used to write to the very end-of-file (end = -1).
356  */
357 int filemap_write_and_wait_range(struct address_space *mapping,
358                                  loff_t lstart, loff_t lend)
359 {
360         int err = 0;
361 
362         if (mapping->nrpages) {
363                 err = __filemap_fdatawrite_range(mapping, lstart, lend,
364                                                  WB_SYNC_ALL);
365                 /* See comment of filemap_write_and_wait() */
366                 if (err != -EIO) {
367                         int err2 = filemap_fdatawait_range(mapping,
368                                                 lstart, lend);
369                         if (!err)
370                                 err = err2;
371                 }
372         }
373         return err;
374 }
375 EXPORT_SYMBOL(filemap_write_and_wait_range);
376 
377 /**
378  * replace_page_cache_page - replace a pagecache page with a new one
379  * @old:        page to be replaced
380  * @new:        page to replace with
381  * @gfp_mask:   allocation mode
382  *
383  * This function replaces a page in the pagecache with a new one.  On
384  * success it acquires the pagecache reference for the new page and
385  * drops it for the old page.  Both the old and new pages must be
386  * locked.  This function does not add the new page to the LRU, the
387  * caller must do that.
388  *
389  * The remove + add is atomic.  The only way this function can fail is
390  * memory allocation failure.
391  */
392 int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
393 {
394         int error;
395 
396         VM_BUG_ON(!PageLocked(old));
397         VM_BUG_ON(!PageLocked(new));
398         VM_BUG_ON(new->mapping);
399 
400         error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
401         if (!error) {
402                 struct address_space *mapping = old->mapping;
403                 void (*freepage)(struct page *);
404 
405                 pgoff_t offset = old->index;
406                 freepage = mapping->a_ops->freepage;
407 
408                 page_cache_get(new);
409                 new->mapping = mapping;
410                 new->index = offset;
411 
412                 spin_lock_irq(&mapping->tree_lock);
413                 __delete_from_page_cache(old);
414                 error = radix_tree_insert(&mapping->page_tree, offset, new);
415                 BUG_ON(error);
416                 mapping->nrpages++;
417                 __inc_zone_page_state(new, NR_FILE_PAGES);
418                 if (PageSwapBacked(new))
419                         __inc_zone_page_state(new, NR_SHMEM);
420                 spin_unlock_irq(&mapping->tree_lock);
421                 /* mem_cgroup codes must not be called under tree_lock */
422                 mem_cgroup_replace_page_cache(old, new);
423                 radix_tree_preload_end();
424                 if (freepage)
425                         freepage(old);
426                 page_cache_release(old);
427         }
428 
429         return error;
430 }
431 EXPORT_SYMBOL_GPL(replace_page_cache_page);
432 
433 /**
434  * add_to_page_cache_locked - add a locked page to the pagecache
435  * @page:       page to add
436  * @mapping:    the page's address_space
437  * @offset:     page index
438  * @gfp_mask:   page allocation mode
439  *
440  * This function is used to add a page to the pagecache. It must be locked.
441  * This function does not add the page to the LRU.  The caller must do that.
442  */
443 int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
444                 pgoff_t offset, gfp_t gfp_mask)
445 {
446         int error;
447 
448         VM_BUG_ON(!PageLocked(page));
449         VM_BUG_ON(PageSwapBacked(page));
450 
451         error = mem_cgroup_cache_charge(page, current->mm,
452                                         gfp_mask & GFP_RECLAIM_MASK);
453         if (error)
454                 goto out;
455 
456         error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
457         if (error == 0) {
458                 page_cache_get(page);
459                 page->mapping = mapping;
460                 page->index = offset;
461 
462                 spin_lock_irq(&mapping->tree_lock);
463                 error = radix_tree_insert(&mapping->page_tree, offset, page);
464                 if (likely(!error)) {
465                         mapping->nrpages++;
466                         __inc_zone_page_state(page, NR_FILE_PAGES);
467                         spin_unlock_irq(&mapping->tree_lock);
468                 } else {
469                         page->mapping = NULL;
470                         /* Leave page->index set: truncation relies upon it */
471                         spin_unlock_irq(&mapping->tree_lock);
472                         mem_cgroup_uncharge_cache_page(page);
473                         page_cache_release(page);
474                 }
475                 radix_tree_preload_end();
476         } else
477                 mem_cgroup_uncharge_cache_page(page);
478 out:
479         return error;
480 }
481 EXPORT_SYMBOL(add_to_page_cache_locked);
482 
483 int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
484                                 pgoff_t offset, gfp_t gfp_mask)
485 {
486         int ret;
487 
488         ret = add_to_page_cache(page, mapping, offset, gfp_mask);
489         if (ret == 0)
490                 lru_cache_add_file(page);
491         return ret;
492 }
493 EXPORT_SYMBOL_GPL(add_to_page_cache_lru);
494 
495 #ifdef CONFIG_NUMA
496 struct page *__page_cache_alloc(gfp_t gfp)
497 {
498         int n;
499         struct page *page;
500 
501         if (cpuset_do_page_mem_spread()) {
502                 unsigned int cpuset_mems_cookie;
503                 do {
504                         cpuset_mems_cookie = get_mems_allowed();
505                         n = cpuset_mem_spread_node();
506                         page = alloc_pages_exact_node(n, gfp, 0);
507                 } while (!put_mems_allowed(cpuset_mems_cookie) && !page);
508 
509                 return page;
510         }
511         return alloc_pages(gfp, 0);
512 }
513 EXPORT_SYMBOL(__page_cache_alloc);
514 #endif
515 
516 /*
517  * In order to wait for pages to become available there must be
518  * waitqueues associated with pages. By using a hash table of
519  * waitqueues where the bucket discipline is to maintain all
520  * waiters on the same queue and wake all when any of the pages
521  * become available, and for the woken contexts to check to be
522  * sure the appropriate page became available, this saves space
523  * at a cost of "thundering herd" phenomena during rare hash
524  * collisions.
525  */
526 static wait_queue_head_t *page_waitqueue(struct page *page)
527 {
528         const struct zone *zone = page_zone(page);
529 
530         return &zone->wait_table[hash_ptr(page, zone->wait_table_bits)];
531 }
532 
533 static inline void wake_up_page(struct page *page, int bit)
534 {
535         __wake_up_bit(page_waitqueue(page), &page->flags, bit);
536 }
537 
538 void wait_on_page_bit(struct page *page, int bit_nr)
539 {
540         DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
541 
542         if (test_bit(bit_nr, &page->flags))
543                 __wait_on_bit(page_waitqueue(page), &wait, sleep_on_page,
544                                                         TASK_UNINTERRUPTIBLE);
545 }
546 EXPORT_SYMBOL(wait_on_page_bit);
547 
548 int wait_on_page_bit_killable(struct page *page, int bit_nr)
549 {
550         DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
551 
552         if (!test_bit(bit_nr, &page->flags))
553                 return 0;
554 
555         return __wait_on_bit(page_waitqueue(page), &wait,
556                              sleep_on_page_killable, TASK_KILLABLE);
557 }
558 
559 /**
560  * add_page_wait_queue - Add an arbitrary waiter to a page's wait queue
561  * @page: Page defining the wait queue of interest
562  * @waiter: Waiter to add to the queue
563  *
564  * Add an arbitrary @waiter to the wait queue for the nominated @page.
565  */
566 void add_page_wait_queue(struct page *page, wait_queue_t *waiter)
567 {
568         wait_queue_head_t *q = page_waitqueue(page);
569         unsigned long flags;
570 
571         spin_lock_irqsave(&q->lock, flags);
572         __add_wait_queue(q, waiter);
573         spin_unlock_irqrestore(&q->lock, flags);
574 }
575 EXPORT_SYMBOL_GPL(add_page_wait_queue);
576 
577 /**
578  * unlock_page - unlock a locked page
579  * @page: the page
580  *
581  * Unlocks the page and wakes up sleepers in ___wait_on_page_locked().
582  * Also wakes sleepers in wait_on_page_writeback() because the wakeup
583  * mechananism between PageLocked pages and PageWriteback pages is shared.
584  * But that's OK - sleepers in wait_on_page_writeback() just go back to sleep.
585  *
586  * The mb is necessary to enforce ordering between the clear_bit and the read
587  * of the waitqueue (to avoid SMP races with a parallel wait_on_page_locked()).
588  */
589 void unlock_page(struct page *page)
590 {
591         VM_BUG_ON(!PageLocked(page));
592         clear_bit_unlock(PG_locked, &page->flags);
593         smp_mb__after_clear_bit();
594         wake_up_page(page, PG_locked);
595 }
596 EXPORT_SYMBOL(unlock_page);
597 
598 /**
599  * end_page_writeback - end writeback against a page
600  * @page: the page
601  */
602 void end_page_writeback(struct page *page)
603 {
604         if (TestClearPageReclaim(page))
605                 rotate_reclaimable_page(page);
606 
607         if (!test_clear_page_writeback(page))
608                 BUG();
609 
610         smp_mb__after_clear_bit();
611         wake_up_page(page, PG_writeback);
612 }
613 EXPORT_SYMBOL(end_page_writeback);
614 
615 /**
616  * __lock_page - get a lock on the page, assuming we need to sleep to get it
617  * @page: the page to lock
618  */
619 void __lock_page(struct page *page)
620 {
621         DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
622 
623         __wait_on_bit_lock(page_waitqueue(page), &wait, sleep_on_page,
624                                                         TASK_UNINTERRUPTIBLE);
625 }
626 EXPORT_SYMBOL(__lock_page);
627 
628 int __lock_page_killable(struct page *page)
629 {
630         DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
631 
632         return __wait_on_bit_lock(page_waitqueue(page), &wait,
633                                         sleep_on_page_killable, TASK_KILLABLE);
634 }
635 EXPORT_SYMBOL_GPL(__lock_page_killable);
636 
637 int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
638                          unsigned int flags)
639 {
640         if (flags & FAULT_FLAG_ALLOW_RETRY) {
641                 /*
642                  * CAUTION! In this case, mmap_sem is not released
643                  * even though return 0.
644                  */
645                 if (flags & FAULT_FLAG_RETRY_NOWAIT)
646                         return 0;
647 
648                 up_read(&mm->mmap_sem);
649                 if (flags & FAULT_FLAG_KILLABLE)
650                         wait_on_page_locked_killable(page);
651                 else
652                         wait_on_page_locked(page);
653                 return 0;
654         } else {
655                 if (flags & FAULT_FLAG_KILLABLE) {
656                         int ret;
657 
658                         ret = __lock_page_killable(page);
659                         if (ret) {
660                                 up_read(&mm->mmap_sem);
661                                 return 0;
662                         }
663                 } else
664                         __lock_page(page);
665                 return 1;
666         }
667 }
668 
669 /**
670  * find_get_page - find and get a page reference
671  * @mapping: the address_space to search
672  * @offset: the page index
673  *
674  * Is there a pagecache struct page at the given (mapping, offset) tuple?
675  * If yes, increment its refcount and return it; if no, return NULL.
676  */
677 struct page *find_get_page(struct address_space *mapping, pgoff_t offset)
678 {
679         void **pagep;
680         struct page *page;
681 
682         rcu_read_lock();
683 repeat:
684         page = NULL;
685         pagep = radix_tree_lookup_slot(&mapping->page_tree, offset);
686         if (pagep) {
687                 page = radix_tree_deref_slot(pagep);
688                 if (unlikely(!page))
689                         goto out;
690                 if (radix_tree_exception(page)) {
691                         if (radix_tree_deref_retry(page))
692                                 goto repeat;
693                         /*
694                          * Otherwise, shmem/tmpfs must be storing a swap entry
695                          * here as an exceptional entry: so return it without
696                          * attempting to raise page count.
697                          */
698                         goto out;
699                 }
700                 if (!page_cache_get_speculative(page))
701                         goto repeat;
702 
703                 /*
704                  * Has the page moved?
705                  * This is part of the lockless pagecache protocol. See
706                  * include/linux/pagemap.h for details.
707                  */
708                 if (unlikely(page != *pagep)) {
709                         page_cache_release(page);
710                         goto repeat;
711                 }
712         }
713 out:
714         rcu_read_unlock();
715 
716         return page;
717 }
718 EXPORT_SYMBOL(find_get_page);
719 
720 /**
721  * find_lock_page - locate, pin and lock a pagecache page
722  * @mapping: the address_space to search
723  * @offset: the page index
724  *
725  * Locates the desired pagecache page, locks it, increments its reference
726  * count and returns its address.
727  *
728  * Returns zero if the page was not present. find_lock_page() may sleep.
729  */
730 struct page *find_lock_page(struct address_space *mapping, pgoff_t offset)
731 {
732         struct page *page;
733 
734 repeat:
735         page = find_get_page(mapping, offset);
736         if (page && !radix_tree_exception(page)) {
737                 lock_page(page);
738                 /* Has the page been truncated? */
739                 if (unlikely(page->mapping != mapping)) {
740                         unlock_page(page);
741                         page_cache_release(page);
742                         goto repeat;
743                 }
744                 VM_BUG_ON(page->index != offset);
745         }
746         return page;
747 }
748 EXPORT_SYMBOL(find_lock_page);
749 
750 /**
751  * find_or_create_page - locate or add a pagecache page
752  * @mapping: the page's address_space
753  * @index: the page's index into the mapping
754  * @gfp_mask: page allocation mode
755  *
756  * Locates a page in the pagecache.  If the page is not present, a new page
757  * is allocated using @gfp_mask and is added to the pagecache and to the VM's
758  * LRU list.  The returned page is locked and has its reference count
759  * incremented.
760  *
761  * find_or_create_page() may sleep, even if @gfp_flags specifies an atomic
762  * allocation!
763  *
764  * find_or_create_page() returns the desired page's address, or zero on
765  * memory exhaustion.
766  */
767 struct page *find_or_create_page(struct address_space *mapping,
768                 pgoff_t index, gfp_t gfp_mask)
769 {
770         struct page *page;
771         int err;
772 repeat:
773         page = find_lock_page(mapping, index);
774         if (!page) {
775                 page = __page_cache_alloc(gfp_mask);
776                 if (!page)
777                         return NULL;
778                 /*
779                  * We want a regular kernel memory (not highmem or DMA etc)
780                  * allocation for the radix tree nodes, but we need to honour
781                  * the context-specific requirements the caller has asked for.
782                  * GFP_RECLAIM_MASK collects those requirements.
783                  */
784                 err = add_to_page_cache_lru(page, mapping, index,
785                         (gfp_mask & GFP_RECLAIM_MASK));
786                 if (unlikely(err)) {
787                         page_cache_release(page);
788                         page = NULL;
789                         if (err == -EEXIST)
790                                 goto repeat;
791                 }
792         }
793         return page;
794 }
795 EXPORT_SYMBOL(find_or_create_page);
796 
797 /**
798  * find_get_pages - gang pagecache lookup
799  * @mapping:    The address_space to search
800  * @start:      The starting page index
801  * @nr_pages:   The maximum number of pages
802  * @pages:      Where the resulting pages are placed
803  *
804  * find_get_pages() will search for and return a group of up to
805  * @nr_pages pages in the mapping.  The pages are placed at @pages.
806  * find_get_pages() takes a reference against the returned pages.
807  *
808  * The search returns a group of mapping-contiguous pages with ascending
809  * indexes.  There may be holes in the indices due to not-present pages.
810  *
811  * find_get_pages() returns the number of pages which were found.
812  */
813 unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
814                             unsigned int nr_pages, struct page **pages)
815 {
816         struct radix_tree_iter iter;
817         void **slot;
818         unsigned ret = 0;
819 
820         if (unlikely(!nr_pages))
821                 return 0;
822 
823         rcu_read_lock();
824 restart:
825         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
826                 struct page *page;
827 repeat:
828                 page = radix_tree_deref_slot(slot);
829                 if (unlikely(!page))
830                         continue;
831 
832                 if (radix_tree_exception(page)) {
833                         if (radix_tree_deref_retry(page)) {
834                                 /*
835                                  * Transient condition which can only trigger
836                                  * when entry at index 0 moves out of or back
837                                  * to root: none yet gotten, safe to restart.
838                                  */
839                                 WARN_ON(iter.index);
840                                 goto restart;
841                         }
842                         /*
843                          * Otherwise, shmem/tmpfs must be storing a swap entry
844                          * here as an exceptional entry: so skip over it -
845                          * we only reach this from invalidate_mapping_pages().
846                          */
847                         continue;
848                 }
849 
850                 if (!page_cache_get_speculative(page))
851                         goto repeat;
852 
853                 /* Has the page moved? */
854                 if (unlikely(page != *slot)) {
855                         page_cache_release(page);
856                         goto repeat;
857                 }
858 
859                 pages[ret] = page;
860                 if (++ret == nr_pages)
861                         break;
862         }
863 
864         rcu_read_unlock();
865         return ret;
866 }
867 
868 /**
869  * find_get_pages_contig - gang contiguous pagecache lookup
870  * @mapping:    The address_space to search
871  * @index:      The starting page index
872  * @nr_pages:   The maximum number of pages
873  * @pages:      Where the resulting pages are placed
874  *
875  * find_get_pages_contig() works exactly like find_get_pages(), except
876  * that the returned number of pages are guaranteed to be contiguous.
877  *
878  * find_get_pages_contig() returns the number of pages which were found.
879  */
880 unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
881                                unsigned int nr_pages, struct page **pages)
882 {
883         struct radix_tree_iter iter;
884         void **slot;
885         unsigned int ret = 0;
886 
887         if (unlikely(!nr_pages))
888                 return 0;
889 
890         rcu_read_lock();
891 restart:
892         radix_tree_for_each_contig(slot, &mapping->page_tree, &iter, index) {
893                 struct page *page;
894 repeat:
895                 page = radix_tree_deref_slot(slot);
896                 /* The hole, there no reason to continue */
897                 if (unlikely(!page))
898                         break;
899 
900                 if (radix_tree_exception(page)) {
901                         if (radix_tree_deref_retry(page)) {
902                                 /*
903                                  * Transient condition which can only trigger
904                                  * when entry at index 0 moves out of or back
905                                  * to root: none yet gotten, safe to restart.
906                                  */
907                                 goto restart;
908                         }
909                         /*
910                          * Otherwise, shmem/tmpfs must be storing a swap entry
911                          * here as an exceptional entry: so stop looking for
912                          * contiguous pages.
913                          */
914                         break;
915                 }
916 
917                 if (!page_cache_get_speculative(page))
918                         goto repeat;
919 
920                 /* Has the page moved? */
921                 if (unlikely(page != *slot)) {
922                         page_cache_release(page);
923                         goto repeat;
924                 }
925 
926                 /*
927                  * must check mapping and index after taking the ref.
928                  * otherwise we can get both false positives and false
929                  * negatives, which is just confusing to the caller.
930                  */
931                 if (page->mapping == NULL || page->index != iter.index) {
932                         page_cache_release(page);
933                         break;
934                 }
935 
936                 pages[ret] = page;
937                 if (++ret == nr_pages)
938                         break;
939         }
940         rcu_read_unlock();
941         return ret;
942 }
943 EXPORT_SYMBOL(find_get_pages_contig);
944 
945 /**
946  * find_get_pages_tag - find and return pages that match @tag
947  * @mapping:    the address_space to search
948  * @index:      the starting page index
949  * @tag:        the tag index
950  * @nr_pages:   the maximum number of pages
951  * @pages:      where the resulting pages are placed
952  *
953  * Like find_get_pages, except we only return pages which are tagged with
954  * @tag.   We update @index to index the next page for the traversal.
955  */
956 unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
957                         int tag, unsigned int nr_pages, struct page **pages)
958 {
959         struct radix_tree_iter iter;
960         void **slot;
961         unsigned ret = 0;
962 
963         if (unlikely(!nr_pages))
964                 return 0;
965 
966         rcu_read_lock();
967 restart:
968         radix_tree_for_each_tagged(slot, &mapping->page_tree,
969                                    &iter, *index, tag) {
970                 struct page *page;
971 repeat:
972                 page = radix_tree_deref_slot(slot);
973                 if (unlikely(!page))
974                         continue;
975 
976                 if (radix_tree_exception(page)) {
977                         if (radix_tree_deref_retry(page)) {
978                                 /*
979                                  * Transient condition which can only trigger
980                                  * when entry at index 0 moves out of or back
981                                  * to root: none yet gotten, safe to restart.
982                                  */
983                                 goto restart;
984                         }
985                         /*
986                          * This function is never used on a shmem/tmpfs
987                          * mapping, so a swap entry won't be found here.
988                          */
989                         BUG();
990                 }
991 
992                 if (!page_cache_get_speculative(page))
993                         goto repeat;
994 
995                 /* Has the page moved? */
996                 if (unlikely(page != *slot)) {
997                         page_cache_release(page);
998                         goto repeat;
999                 }
1000 
1001                 pages[ret] = page;
1002                 if (++ret == nr_pages)
1003                         break;
1004         }
1005 
1006         rcu_read_unlock();
1007 
1008         if (ret)
1009                 *index = pages[ret - 1]->index + 1;
1010 
1011         return ret;
1012 }
1013 EXPORT_SYMBOL(find_get_pages_tag);
1014 
1015 /**
1016  * grab_cache_page_nowait - returns locked page at given index in given cache
1017  * @mapping: target address_space
1018  * @index: the page index
1019  *
1020  * Same as grab_cache_page(), but do not wait if the page is unavailable.
1021  * This is intended for speculative data generators, where the data can
1022  * be regenerated if the page couldn't be grabbed.  This routine should
1023  * be safe to call while holding the lock for another page.
1024  *
1025  * Clear __GFP_FS when allocating the page to avoid recursion into the fs
1026  * and deadlock against the caller's locked page.
1027  */
1028 struct page *
1029 grab_cache_page_nowait(struct address_space *mapping, pgoff_t index)
1030 {
1031         struct page *page = find_get_page(mapping, index);
1032 
1033         if (page) {
1034                 if (trylock_page(page))
1035                         return page;
1036                 page_cache_release(page);
1037                 return NULL;
1038         }
1039         page = __page_cache_alloc(mapping_gfp_mask(mapping) & ~__GFP_FS);
1040         if (page && add_to_page_cache_lru(page, mapping, index, GFP_NOFS)) {
1041                 page_cache_release(page);
1042                 page = NULL;
1043         }
1044         return page;
1045 }
1046 EXPORT_SYMBOL(grab_cache_page_nowait);
1047 
1048 /*
1049  * CD/DVDs are error prone. When a medium error occurs, the driver may fail
1050  * a _large_ part of the i/o request. Imagine the worst scenario:
1051  *
1052  *      ---R__________________________________________B__________
1053  *         ^ reading here                             ^ bad block(assume 4k)
1054  *
1055  * read(R) => miss => readahead(R...B) => media error => frustrating retries
1056  * => failing the whole request => read(R) => read(R+1) =>
1057  * readahead(R+1...B+1) => bang => read(R+2) => read(R+3) =>
1058  * readahead(R+3...B+2) => bang => read(R+3) => read(R+4) =>
1059  * readahead(R+4...B+3) => bang => read(R+4) => read(R+5) => ......
1060  *
1061  * It is going insane. Fix it by quickly scaling down the readahead size.
1062  */
1063 static void shrink_readahead_size_eio(struct file *filp,
1064                                         struct file_ra_state *ra)
1065 {
1066         ra->ra_pages /= 4;
1067 }
1068 
1069 /**
1070  * do_generic_file_read - generic file read routine
1071  * @filp:       the file to read
1072  * @ppos:       current file position
1073  * @desc:       read_descriptor
1074  * @actor:      read method
1075  *
1076  * This is a generic file read routine, and uses the
1077  * mapping->a_ops->readpage() function for the actual low-level stuff.
1078  *
1079  * This is really ugly. But the goto's actually try to clarify some
1080  * of the logic when it comes to error handling etc.
1081  */
1082 static void do_generic_file_read(struct file *filp, loff_t *ppos,
1083                 read_descriptor_t *desc, read_actor_t actor)
1084 {
1085         struct address_space *mapping = filp->f_mapping;
1086         struct inode *inode = mapping->host;
1087         struct file_ra_state *ra = &filp->f_ra;
1088         pgoff_t index;
1089         pgoff_t last_index;
1090         pgoff_t prev_index;
1091         unsigned long offset;      /* offset into pagecache page */
1092         unsigned int prev_offset;
1093         int error;
1094 
1095         index = *ppos >> PAGE_CACHE_SHIFT;
1096         prev_index = ra->prev_pos >> PAGE_CACHE_SHIFT;
1097         prev_offset = ra->prev_pos & (PAGE_CACHE_SIZE-1);
1098         last_index = (*ppos + desc->count + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;
1099         offset = *ppos & ~PAGE_CACHE_MASK;
1100 
1101         for (;;) {
1102                 struct page *page;
1103                 pgoff_t end_index;
1104                 loff_t isize;
1105                 unsigned long nr, ret;
1106 
1107                 cond_resched();
1108 find_page:
1109                 page = find_get_page(mapping, index);
1110                 if (!page) {
1111                         page_cache_sync_readahead(mapping,
1112                                         ra, filp,
1113                                         index, last_index - index);
1114                         page = find_get_page(mapping, index);
1115                         if (unlikely(page == NULL))
1116                                 goto no_cached_page;
1117                 }
1118                 if (PageReadahead(page)) {
1119                         page_cache_async_readahead(mapping,
1120                                         ra, filp, page,
1121                                         index, last_index - index);
1122                 }
1123                 if (!PageUptodate(page)) {
1124                         if (inode->i_blkbits == PAGE_CACHE_SHIFT ||
1125                                         !mapping->a_ops->is_partially_uptodate)
1126                                 goto page_not_up_to_date;
1127                         if (!trylock_page(page))
1128                                 goto page_not_up_to_date;
1129                         /* Did it get truncated before we got the lock? */
1130                         if (!page->mapping)
1131                                 goto page_not_up_to_date_locked;
1132                         if (!mapping->a_ops->is_partially_uptodate(page,
1133                                                                 desc, offset))
1134                                 goto page_not_up_to_date_locked;
1135                         unlock_page(page);
1136                 }
1137 page_ok:
1138                 /*
1139                  * i_size must be checked after we know the page is Uptodate.
1140                  *
1141                  * Checking i_size after the check allows us to calculate
1142                  * the correct value for "nr", which means the zero-filled
1143                  * part of the page is not copied back to userspace (unless
1144                  * another truncate extends the file - this is desired though).
1145                  */
1146 
1147                 isize = i_size_read(inode);
1148                 end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
1149                 if (unlikely(!isize || index > end_index)) {
1150                         page_cache_release(page);
1151                         goto out;
1152                 }
1153 
1154                 /* nr is the maximum number of bytes to copy from this page */
1155                 nr = PAGE_CACHE_SIZE;
1156                 if (index == end_index) {
1157                         nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
1158                         if (nr <= offset) {
1159                                 page_cache_release(page);
1160                                 goto out;
1161                         }
1162                 }
1163                 nr = nr - offset;
1164 
1165                 /* If users can be writing to this page using arbitrary
1166                  * virtual addresses, take care about potential aliasing
1167                  * before reading the page on the kernel side.
1168                  */
1169                 if (mapping_writably_mapped(mapping))
1170                         flush_dcache_page(page);
1171 
1172                 /*
1173                  * When a sequential read accesses a page several times,
1174                  * only mark it as accessed the first time.
1175                  */
1176                 if (prev_index != index || offset != prev_offset)
1177                         mark_page_accessed(page);
1178                 prev_index = index;
1179 
1180                 /*
1181                  * Ok, we have the page, and it's up-to-date, so
1182                  * now we can copy it to user space...
1183                  *
1184                  * The actor routine returns how many bytes were actually used..
1185                  * NOTE! This may not be the same as how much of a user buffer
1186                  * we filled up (we may be padding etc), so we can only update
1187                  * "pos" here (the actor routine has to update the user buffer
1188                  * pointers and the remaining count).
1189                  */
1190                 ret = actor(desc, page, offset, nr);
1191                 offset += ret;
1192                 index += offset >> PAGE_CACHE_SHIFT;
1193                 offset &= ~PAGE_CACHE_MASK;
1194                 prev_offset = offset;
1195 
1196                 page_cache_release(page);
1197                 if (ret == nr && desc->count)
1198                         continue;
1199                 goto out;
1200 
1201 page_not_up_to_date:
1202                 /* Get exclusive access to the page ... */
1203                 error = lock_page_killable(page);
1204                 if (unlikely(error))
1205                         goto readpage_error;
1206 
1207 page_not_up_to_date_locked:
1208                 /* Did it get truncated before we got the lock? */
1209                 if (!page->mapping) {
1210                         unlock_page(page);
1211                         page_cache_release(page);
1212                         continue;
1213                 }
1214 
1215                 /* Did somebody else fill it already? */
1216                 if (PageUptodate(page)) {
1217                         unlock_page(page);
1218                         goto page_ok;
1219                 }
1220 
1221 readpage:
1222                 /*
1223                  * A previous I/O error may have been due to temporary
1224                  * failures, eg. multipath errors.
1225                  * PG_error will be set again if readpage fails.
1226                  */
1227                 ClearPageError(page);
1228                 /* Start the actual read. The read will unlock the page. */
1229                 error = mapping->a_ops->readpage(filp, page);
1230 
1231                 if (unlikely(error)) {
1232                         if (error == AOP_TRUNCATED_PAGE) {
1233                                 page_cache_release(page);
1234                                 goto find_page;
1235                         }
1236                         goto readpage_error;
1237                 }
1238 
1239                 if (!PageUptodate(page)) {
1240                         error = lock_page_killable(page);
1241                         if (unlikely(error))
1242                                 goto readpage_error;
1243                         if (!PageUptodate(page)) {
1244                                 if (page->mapping == NULL) {
1245                                         /*
1246                                          * invalidate_mapping_pages got it
1247                                          */
1248                                         unlock_page(page);
1249                                         page_cache_release(page);
1250                                         goto find_page;
1251                                 }
1252                                 unlock_page(page);
1253                                 shrink_readahead_size_eio(filp, ra);
1254                                 error = -EIO;
1255                                 goto readpage_error;
1256                         }
1257                         unlock_page(page);
1258                 }
1259 
1260                 goto page_ok;
1261 
1262 readpage_error:
1263                 /* UHHUH! A synchronous read error occurred. Report it */
1264                 desc->error = error;
1265                 page_cache_release(page);
1266                 goto out;
1267 
1268 no_cached_page:
1269                 /*
1270                  * Ok, it wasn't cached, so we need to create a new
1271                  * page..
1272                  */
1273                 page = page_cache_alloc_cold(mapping);
1274                 if (!page) {
1275                         desc->error = -ENOMEM;
1276                         goto out;
1277                 }
1278                 error = add_to_page_cache_lru(page, mapping,
1279                                                 index, GFP_KERNEL);
1280                 if (error) {
1281                         page_cache_release(page);
1282                         if (error == -EEXIST)
1283                                 goto find_page;
1284                         desc->error = error;
1285                         goto out;
1286                 }
1287                 goto readpage;
1288         }
1289 
1290 out:
1291         ra->prev_pos = prev_index;
1292         ra->prev_pos <<= PAGE_CACHE_SHIFT;
1293         ra->prev_pos |= prev_offset;
1294 
1295         *ppos = ((loff_t)index << PAGE_CACHE_SHIFT) + offset;
1296         file_accessed(filp);
1297 }
1298 
1299 int file_read_actor(read_descriptor_t *desc, struct page *page,
1300                         unsigned long offset, unsigned long size)
1301 {
1302         char *kaddr;
1303         unsigned long left, count = desc->count;
1304 
1305         if (size > count)
1306                 size = count;
1307 
1308         /*
1309          * Faults on the destination of a read are common, so do it before
1310          * taking the kmap.
1311          */
1312         if (!fault_in_pages_writeable(desc->arg.buf, size)) {
1313                 kaddr = kmap_atomic(page);
1314                 left = __copy_to_user_inatomic(desc->arg.buf,
1315                                                 kaddr + offset, size);
1316                 kunmap_atomic(kaddr);
1317                 if (left == 0)
1318                         goto success;
1319         }
1320 
1321         /* Do it the slow way */
1322         kaddr = kmap(page);
1323         left = __copy_to_user(desc->arg.buf, kaddr + offset, size);
1324         kunmap(page);
1325 
1326         if (left) {
1327                 size -= left;
1328                 desc->error = -EFAULT;
1329         }
1330 success:
1331         desc->count = count - size;
1332         desc->written += size;
1333         desc->arg.buf += size;
1334         return size;
1335 }
1336 
1337 /*
1338  * Performs necessary checks before doing a write
1339  * @iov:        io vector request
1340  * @nr_segs:    number of segments in the iovec
1341  * @count:      number of bytes to write
1342  * @access_flags: type of access: %VERIFY_READ or %VERIFY_WRITE
1343  *
1344  * Adjust number of segments and amount of bytes to write (nr_segs should be
1345  * properly initialized first). Returns appropriate error code that caller
1346  * should return or zero in case that write should be allowed.
1347  */
1348 int generic_segment_checks(const struct iovec *iov,
1349                         unsigned long *nr_segs, size_t *count, int access_flags)
1350 {
1351         unsigned long   seg;
1352         size_t cnt = 0;
1353         for (seg = 0; seg < *nr_segs; seg++) {
1354                 const struct iovec *iv = &iov[seg];
1355 
1356                 /*
1357                  * If any segment has a negative length, or the cumulative
1358                  * length ever wraps negative then return -EINVAL.
1359                  */
1360                 cnt += iv->iov_len;
1361                 if (unlikely((ssize_t)(cnt|iv->iov_len) < 0))
1362                         return -EINVAL;
1363                 if (access_ok(access_flags, iv->iov_base, iv->iov_len))
1364                         continue;
1365                 if (seg == 0)
1366                         return -EFAULT;
1367                 *nr_segs = seg;
1368                 cnt -= iv->iov_len;     /* This segment is no good */
1369                 break;
1370         }
1371         *count = cnt;
1372         return 0;
1373 }
1374 EXPORT_SYMBOL(generic_segment_checks);
1375 
1376 /**
1377  * generic_file_aio_read - generic filesystem read routine
1378  * @iocb:       kernel I/O control block
1379  * @iov:        io vector request
1380  * @nr_segs:    number of segments in the iovec
1381  * @pos:        current file position
1382  *
1383  * This is the "read()" routine for all filesystems
1384  * that can use the page cache directly.
1385  */
1386 ssize_t
1387 generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
1388                 unsigned long nr_segs, loff_t pos)
1389 {
1390         struct file *filp = iocb->ki_filp;
1391         ssize_t retval;
1392         unsigned long seg = 0;
1393         size_t count;
1394         loff_t *ppos = &iocb->ki_pos;
1395 
1396         count = 0;
1397         retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
1398         if (retval)
1399                 return retval;
1400 
1401         /* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
1402         if (filp->f_flags & O_DIRECT) {
1403                 loff_t size;
1404                 struct address_space *mapping;
1405                 struct inode *inode;
1406 
1407                 mapping = filp->f_mapping;
1408                 inode = mapping->host;
1409                 if (!count)
1410                         goto out; /* skip atime */
1411                 size = i_size_read(inode);
1412                 if (pos < size) {
1413                         retval = filemap_write_and_wait_range(mapping, pos,
1414                                         pos + iov_length(iov, nr_segs) - 1);
1415                         if (!retval) {
1416                                 struct blk_plug plug;
1417 
1418                                 blk_start_plug(&plug);
1419                                 retval = mapping->a_ops->direct_IO(READ, iocb,
1420                                                         iov, pos, nr_segs);
1421                                 blk_finish_plug(&plug);
1422                         }
1423                         if (retval > 0) {
1424                                 *ppos = pos + retval;
1425                                 count -= retval;
1426                         }
1427 
1428                         /*
1429                          * Btrfs can have a short DIO read if we encounter
1430                          * compressed extents, so if there was an error, or if
1431                          * we've already read everything we wanted to, or if
1432                          * there was a short read because we hit EOF, go ahead
1433                          * and return.  Otherwise fallthrough to buffered io for
1434                          * the rest of the read.
1435                          */
1436                         if (retval < 0 || !count || *ppos >= size) {
1437                                 file_accessed(filp);
1438                                 goto out;
1439                         }
1440                 }
1441         }
1442 
1443         count = retval;
1444         for (seg = 0; seg < nr_segs; seg++) {
1445                 read_descriptor_t desc;
1446                 loff_t offset = 0;
1447 
1448                 /*
1449                  * If we did a short DIO read we need to skip the section of the
1450                  * iov that we've already read data into.
1451                  */
1452                 if (count) {
1453                         if (count > iov[seg].iov_len) {
1454                                 count -= iov[seg].iov_len;
1455                                 continue;
1456                         }
1457                         offset = count;
1458                         count = 0;
1459                 }
1460 
1461                 desc.written = 0;
1462                 desc.arg.buf = iov[seg].iov_base + offset;
1463                 desc.count = iov[seg].iov_len - offset;
1464                 if (desc.count == 0)
1465                         continue;
1466                 desc.error = 0;
1467                 do_generic_file_read(filp, ppos, &desc, file_read_actor);
1468                 retval += desc.written;
1469                 if (desc.error) {
1470                         retval = retval ?: desc.error;
1471                         break;
1472                 }
1473                 if (desc.count > 0)
1474                         break;
1475         }
1476 out:
1477         return retval;
1478 }
1479 EXPORT_SYMBOL(generic_file_aio_read);
1480 
1481 static ssize_t
1482 do_readahead(struct address_space *mapping, struct file *filp,
1483              pgoff_t index, unsigned long nr)
1484 {
1485         if (!mapping || !mapping->a_ops || !mapping->a_ops->readpage)
1486                 return -EINVAL;
1487 
1488         force_page_cache_readahead(mapping, filp, index, nr);
1489         return 0;
1490 }
1491 
1492 SYSCALL_DEFINE(readahead)(int fd, loff_t offset, size_t count)
1493 {
1494         ssize_t ret;
1495         struct file *file;
1496 
1497         ret = -EBADF;
1498         file = fget(fd);
1499         if (file) {
1500                 if (file->f_mode & FMODE_READ) {
1501                         struct address_space *mapping = file->f_mapping;
1502                         pgoff_t start = offset >> PAGE_CACHE_SHIFT;
1503                         pgoff_t end = (offset + count - 1) >> PAGE_CACHE_SHIFT;
1504                         unsigned long len = end - start + 1;
1505                         ret = do_readahead(mapping, file, start, len);
1506                 }
1507                 fput(file);
1508         }
1509         return ret;
1510 }
1511 #ifdef CONFIG_HAVE_SYSCALL_WRAPPERS
1512 asmlinkage long SyS_readahead(long fd, loff_t offset, long count)
1513 {
1514         return SYSC_readahead((int) fd, offset, (size_t) count);
1515 }
1516 SYSCALL_ALIAS(sys_readahead, SyS_readahead);
1517 #endif
1518 
1519 #ifdef CONFIG_MMU
1520 /**
1521  * page_cache_read - adds requested page to the page cache if not already there
1522  * @file:       file to read
1523  * @offset:     page index
1524  *
1525  * This adds the requested page to the page cache if it isn't already there,
1526  * and schedules an I/O to read in its contents from disk.
1527  */
1528 static int page_cache_read(struct file *file, pgoff_t offset)
1529 {
1530         struct address_space *mapping = file->f_mapping;
1531         struct page *page; 
1532         int ret;
1533 
1534         do {
1535                 page = page_cache_alloc_cold(mapping);
1536                 if (!page)
1537                         return -ENOMEM;
1538 
1539                 ret = add_to_page_cache_lru(page, mapping, offset, GFP_KERNEL);
1540                 if (ret == 0)
1541                         ret = mapping->a_ops->readpage(file, page);
1542                 else if (ret == -EEXIST)
1543                         ret = 0; /* losing race to add is OK */
1544 
1545                 page_cache_release(page);
1546 
1547         } while (ret == AOP_TRUNCATED_PAGE);
1548                 
1549         return ret;
1550 }
1551 
1552 #define MMAP_LOTSAMISS  (100)
1553 
1554 /*
1555  * Synchronous readahead happens when we don't even find
1556  * a page in the page cache at all.
1557  */
1558 static void do_sync_mmap_readahead(struct vm_area_struct *vma,
1559                                    struct file_ra_state *ra,
1560                                    struct file *file,
1561                                    pgoff_t offset)
1562 {
1563         unsigned long ra_pages;
1564         struct address_space *mapping = file->f_mapping;
1565 
1566         /* If we don't want any read-ahead, don't bother */
1567         if (VM_RandomReadHint(vma))
1568                 return;
1569         if (!ra->ra_pages)
1570                 return;
1571 
1572         if (VM_SequentialReadHint(vma)) {
1573                 page_cache_sync_readahead(mapping, ra, file, offset,
1574                                           ra->ra_pages);
1575                 return;
1576         }
1577 
1578         /* Avoid banging the cache line if not needed */
1579         if (ra->mmap_miss < MMAP_LOTSAMISS * 10)
1580                 ra->mmap_miss++;
1581 
1582         /*
1583          * Do we miss much more than hit in this file? If so,
1584          * stop bothering with read-ahead. It will only hurt.
1585          */
1586         if (ra->mmap_miss > MMAP_LOTSAMISS)
1587                 return;
1588 
1589         /*
1590          * mmap read-around
1591          */
1592         ra_pages = max_sane_readahead(ra->ra_pages);
1593         ra->start = max_t(long, 0, offset - ra_pages / 2);
1594         ra->size = ra_pages;
1595         ra->async_size = ra_pages / 4;
1596         ra_submit(ra, mapping, file);
1597 }
1598 
1599 /*
1600  * Asynchronous readahead happens when we find the page and PG_readahead,
1601  * so we want to possibly extend the readahead further..
1602  */
1603 static void do_async_mmap_readahead(struct vm_area_struct *vma,
1604                                     struct file_ra_state *ra,
1605                                     struct file *file,
1606                                     struct page *page,
1607                                     pgoff_t offset)
1608 {
1609         struct address_space *mapping = file->f_mapping;
1610 
1611         /* If we don't want any read-ahead, don't bother */
1612         if (VM_RandomReadHint(vma))
1613                 return;
1614         if (ra->mmap_miss > 0)
1615                 ra->mmap_miss--;
1616         if (PageReadahead(page))
1617                 page_cache_async_readahead(mapping, ra, file,
1618                                            page, offset, ra->ra_pages);
1619 }
1620 
1621 /**
1622  * filemap_fault - read in file data for page fault handling
1623  * @vma:        vma in which the fault was taken
1624  * @vmf:        struct vm_fault containing details of the fault
1625  *
1626  * filemap_fault() is invoked via the vma operations vector for a
1627  * mapped memory region to read in file data during a page fault.
1628  *
1629  * The goto's are kind of ugly, but this streamlines the normal case of having
1630  * it in the page cache, and handles the special cases reasonably without
1631  * having a lot of duplicated code.
1632  */
1633 int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
1634 {
1635         int error;
1636         struct file *file = vma->vm_file;
1637         struct address_space *mapping = file->f_mapping;
1638         struct file_ra_state *ra = &file->f_ra;
1639         struct inode *inode = mapping->host;
1640         pgoff_t offset = vmf->pgoff;
1641         struct page *page;
1642         pgoff_t size;
1643         int ret = 0;
1644 
1645         size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
1646         if (offset >= size)
1647                 return VM_FAULT_SIGBUS;
1648 
1649         /*
1650          * Do we have something in the page cache already?
1651          */
1652         page = find_get_page(mapping, offset);
1653         if (likely(page)) {
1654                 /*
1655                  * We found the page, so try async readahead before
1656                  * waiting for the lock.
1657                  */
1658                 do_async_mmap_readahead(vma, ra, file, page, offset);
1659         } else {
1660                 /* No page in the page cache at all */
1661                 do_sync_mmap_readahead(vma, ra, file, offset);
1662                 count_vm_event(PGMAJFAULT);
1663                 mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
1664                 ret = VM_FAULT_MAJOR;
1665 retry_find:
1666                 page = find_get_page(mapping, offset);
1667                 if (!page)
1668                         goto no_cached_page;
1669         }
1670 
1671         if (!lock_page_or_retry(page, vma->vm_mm, vmf->flags)) {
1672                 page_cache_release(page);
1673                 return ret | VM_FAULT_RETRY;
1674         }
1675 
1676         /* Did it get truncated? */
1677         if (unlikely(page->mapping != mapping)) {
1678                 unlock_page(page);
1679                 put_page(page);
1680                 goto retry_find;
1681         }
1682         VM_BUG_ON(page->index != offset);
1683 
1684         /*
1685          * We have a locked page in the page cache, now we need to check
1686          * that it's up-to-date. If not, it is going to be due to an error.
1687          */
1688         if (unlikely(!PageUptodate(page)))
1689                 goto page_not_uptodate;
1690 
1691         /*
1692          * Found the page and have a reference on it.
1693          * We must recheck i_size under page lock.
1694          */
1695         size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
1696         if (unlikely(offset >= size)) {
1697                 unlock_page(page);
1698                 page_cache_release(page);
1699                 return VM_FAULT_SIGBUS;
1700         }
1701 
1702         vmf->page = page;
1703         return ret | VM_FAULT_LOCKED;
1704 
1705 no_cached_page:
1706         /*
1707          * We're only likely to ever get here if MADV_RANDOM is in
1708          * effect.
1709          */
1710         error = page_cache_read(file, offset);
1711 
1712         /*
1713          * The page we want has now been added to the page cache.
1714          * In the unlikely event that someone removed it in the
1715          * meantime, we'll just come back here and read it again.
1716          */
1717         if (error >= 0)
1718                 goto retry_find;
1719 
1720         /*
1721          * An error return from page_cache_read can result if the
1722          * system is low on memory, or a problem occurs while trying
1723          * to schedule I/O.
1724          */
1725         if (error == -ENOMEM)
1726                 return VM_FAULT_OOM;
1727         return VM_FAULT_SIGBUS;
1728 
1729 page_not_uptodate:
1730         /*
1731          * Umm, take care of errors if the page isn't up-to-date.
1732          * Try to re-read it _once_. We do this synchronously,
1733          * because there really aren't any performance issues here
1734          * and we need to check for errors.
1735          */
1736         ClearPageError(page);
1737         error = mapping->a_ops->readpage(file, page);
1738         if (!error) {
1739                 wait_on_page_locked(page);
1740                 if (!PageUptodate(page))
1741                         error = -EIO;
1742         }
1743         page_cache_release(page);
1744 
1745         if (!error || error == AOP_TRUNCATED_PAGE)
1746                 goto retry_find;
1747 
1748         /* Things didn't work out. Return zero to tell the mm layer so. */
1749         shrink_readahead_size_eio(file, ra);
1750         return VM_FAULT_SIGBUS;
1751 }
1752 EXPORT_SYMBOL(filemap_fault);
1753 
1754 const struct vm_operations_struct generic_file_vm_ops = {
1755         .fault          = filemap_fault,
1756 };
1757 
1758 /* This is used for a general mmap of a disk file */
1759 
1760 int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
1761 {
1762         struct address_space *mapping = file->f_mapping;
1763 
1764         if (!mapping->a_ops->readpage)
1765                 return -ENOEXEC;
1766         file_accessed(file);
1767         vma->vm_ops = &generic_file_vm_ops;
1768         vma->vm_flags |= VM_CAN_NONLINEAR;
1769         return 0;
1770 }
1771 
1772 /*
1773  * This is for filesystems which do not implement ->writepage.
1774  */
1775 int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
1776 {
1777         if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
1778                 return -EINVAL;
1779         return generic_file_mmap(file, vma);
1780 }
1781 #else
1782 int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
1783 {
1784         return -ENOSYS;
1785 }
1786 int generic_file_readonly_mmap(struct file * file, struct vm_area_struct * vma)
1787 {
1788         return -ENOSYS;
1789 }
1790 #endif /* CONFIG_MMU */
1791 
1792 EXPORT_SYMBOL(generic_file_mmap);
1793 EXPORT_SYMBOL(generic_file_readonly_mmap);
1794 
1795 static struct page *__read_cache_page(struct address_space *mapping,
1796                                 pgoff_t index,
1797                                 int (*filler)(void *, struct page *),
1798                                 void *data,
1799                                 gfp_t gfp)
1800 {
1801         struct page *page;
1802         int err;
1803 repeat:
1804         page = find_get_page(mapping, index);
1805         if (!page) {
1806                 page = __page_cache_alloc(gfp | __GFP_COLD);
1807                 if (!page)
1808                         return ERR_PTR(-ENOMEM);
1809                 err = add_to_page_cache_lru(page, mapping, index, gfp);
1810                 if (unlikely(err)) {
1811                         page_cache_release(page);
1812                         if (err == -EEXIST)
1813                                 goto repeat;
1814                         /* Presumably ENOMEM for radix tree node */
1815                         return ERR_PTR(err);
1816                 }
1817                 err = filler(data, page);
1818                 if (err < 0) {
1819                         page_cache_release(page);
1820                         page = ERR_PTR(err);
1821                 }
1822         }
1823         return page;
1824 }
1825 
1826 static struct page *do_read_cache_page(struct address_space *mapping,
1827                                 pgoff_t index,
1828                                 int (*filler)(void *, struct page *),
1829                                 void *data,
1830                                 gfp_t gfp)
1831 
1832 {
1833         struct page *page;
1834         int err;
1835 
1836 retry:
1837         page = __read_cache_page(mapping, index, filler, data, gfp);
1838         if (IS_ERR(page))
1839                 return page;
1840         if (PageUptodate(page))
1841                 goto out;
1842 
1843         lock_page(page);
1844         if (!page->mapping) {
1845                 unlock_page(page);
1846                 page_cache_release(page);
1847                 goto retry;
1848         }
1849         if (PageUptodate(page)) {
1850                 unlock_page(page);
1851                 goto out;
1852         }
1853         err = filler(data, page);
1854         if (err < 0) {
1855                 page_cache_release(page);
1856                 return ERR_PTR(err);
1857         }
1858 out:
1859         mark_page_accessed(page);
1860         return page;
1861 }
1862 
1863 /**
1864  * read_cache_page_async - read into page cache, fill it if needed
1865  * @mapping:    the page's address_space
1866  * @index:      the page index
1867  * @filler:     function to perform the read
1868  * @data:       first arg to filler(data, page) function, often left as NULL
1869  *
1870  * Same as read_cache_page, but don't wait for page to become unlocked
1871  * after submitting it to the filler.
1872  *
1873  * Read into the page cache. If a page already exists, and PageUptodate() is
1874  * not set, try to fill the page but don't wait for it to become unlocked.
1875  *
1876  * If the page does not get brought uptodate, return -EIO.
1877  */
1878 struct page *read_cache_page_async(struct address_space *mapping,
1879                                 pgoff_t index,
1880                                 int (*filler)(void *, struct page *),
1881                                 void *data)
1882 {
1883         return do_read_cache_page(mapping, index, filler, data, mapping_gfp_mask(mapping));
1884 }
1885 EXPORT_SYMBOL(read_cache_page_async);
1886 
1887 static struct page *wait_on_page_read(struct page *page)
1888 {
1889         if (!IS_ERR(page)) {
1890                 wait_on_page_locked(page);
1891                 if (!PageUptodate(page)) {
1892                         page_cache_release(page);
1893                         page = ERR_PTR(-EIO);
1894                 }
1895         }
1896         return page;
1897 }
1898 
1899 /**
1900  * read_cache_page_gfp - read into page cache, using specified page allocation flags.
1901  * @mapping:    the page's address_space
1902  * @index:      the page index
1903  * @gfp:        the page allocator flags to use if allocating
1904  *
1905  * This is the same as "read_mapping_page(mapping, index, NULL)", but with
1906  * any new page allocations done using the specified allocation flags.
1907  *
1908  * If the page does not get brought uptodate, return -EIO.
1909  */
1910 struct page *read_cache_page_gfp(struct address_space *mapping,
1911                                 pgoff_t index,
1912                                 gfp_t gfp)
1913 {
1914         filler_t *filler = (filler_t *)mapping->a_ops->readpage;
1915 
1916         return wait_on_page_read(do_read_cache_page(mapping, index, filler, NULL, gfp));
1917 }
1918 EXPORT_SYMBOL(read_cache_page_gfp);
1919 
1920 /**
1921  * read_cache_page - read into page cache, fill it if needed
1922  * @mapping:    the page's address_space
1923  * @index:      the page index
1924  * @filler:     function to perform the read
1925  * @data:       first arg to filler(data, page) function, often left as NULL
1926  *
1927  * Read into the page cache. If a page already exists, and PageUptodate() is
1928  * not set, try to fill the page then wait for it to become unlocked.
1929  *
1930  * If the page does not get brought uptodate, return -EIO.
1931  */
1932 struct page *read_cache_page(struct address_space *mapping,
1933                                 pgoff_t index,
1934                                 int (*filler)(void *, struct page *),
1935                                 void *data)
1936 {
1937         return wait_on_page_read(read_cache_page_async(mapping, index, filler, data));
1938 }
1939 EXPORT_SYMBOL(read_cache_page);
1940 
1941 /*
1942  * The logic we want is
1943  *
1944  *      if suid or (sgid and xgrp)
1945  *              remove privs
1946  */
1947 int should_remove_suid(struct dentry *dentry)
1948 {
1949         umode_t mode = dentry->d_inode->i_mode;
1950         int kill = 0;
1951 
1952         /* suid always must be killed */
1953         if (unlikely(mode & S_ISUID))
1954                 kill = ATTR_KILL_SUID;
1955 
1956         /*
1957          * sgid without any exec bits is just a mandatory locking mark; leave
1958          * it alone.  If some exec bits are set, it's a real sgid; kill it.
1959          */
1960         if (unlikely((mode & S_ISGID) && (mode & S_IXGRP)))
1961                 kill |= ATTR_KILL_SGID;
1962 
1963         if (unlikely(kill && !capable(CAP_FSETID) && S_ISREG(mode)))
1964                 return kill;
1965 
1966         return 0;
1967 }
1968 EXPORT_SYMBOL(should_remove_suid);
1969 
1970 static int __remove_suid(struct dentry *dentry, int kill)
1971 {
1972         struct iattr newattrs;
1973 
1974         newattrs.ia_valid = ATTR_FORCE | kill;
1975         return notify_change(dentry, &newattrs);
1976 }
1977 
1978 int file_remove_suid(struct file *file)
1979 {
1980         struct dentry *dentry = file->f_path.dentry;
1981         struct inode *inode = dentry->d_inode;
1982         int killsuid;
1983         int killpriv;
1984         int error = 0;
1985 
1986         /* Fast path for nothing security related */
1987         if (IS_NOSEC(inode))
1988                 return 0;
1989 
1990         killsuid = should_remove_suid(dentry);
1991         killpriv = security_inode_need_killpriv(dentry);
1992 
1993         if (killpriv < 0)
1994                 return killpriv;
1995         if (killpriv)
1996                 error = security_inode_killpriv(dentry);
1997         if (!error && killsuid)
1998                 error = __remove_suid(dentry, killsuid);
1999         if (!error && (inode->i_sb->s_flags & MS_NOSEC))
2000                 inode->i_flags |= S_NOSEC;
2001 
2002         return error;
2003 }
2004 EXPORT_SYMBOL(file_remove_suid);
2005 
2006 static size_t __iovec_copy_from_user_inatomic(char *vaddr,
2007                         const struct iovec *iov, size_t base, size_t bytes)
2008 {
2009         size_t copied = 0, left = 0;
2010 
2011         while (bytes) {
2012                 char __user *buf = iov->iov_base + base;
2013                 int copy = min(bytes, iov->iov_len - base);
2014 
2015                 base = 0;
2016                 left = __copy_from_user_inatomic(vaddr, buf, copy);
2017                 copied += copy;
2018                 bytes -= copy;
2019                 vaddr += copy;
2020                 iov++;
2021 
2022                 if (unlikely(left))
2023                         break;
2024         }
2025         return copied - left;
2026 }
2027 
2028 /*
2029  * Copy as much as we can into the page and return the number of bytes which
2030  * were successfully copied.  If a fault is encountered then return the number of
2031  * bytes which were copied.
2032  */
2033 size_t iov_iter_copy_from_user_atomic(struct page *page,
2034                 struct iov_iter *i, unsigned long offset, size_t bytes)
2035 {
2036         char *kaddr;
2037         size_t copied;
2038 
2039         BUG_ON(!in_atomic());
2040         kaddr = kmap_atomic(page);
2041         if (likely(i->nr_segs == 1)) {
2042                 int left;
2043                 char __user *buf = i->iov->iov_base + i->iov_offset;
2044                 left = __copy_from_user_inatomic(kaddr + offset, buf, bytes);
2045                 copied = bytes - left;
2046         } else {
2047                 copied = __iovec_copy_from_user_inatomic(kaddr + offset,
2048                                                 i->iov, i->iov_offset, bytes);
2049         }
2050         kunmap_atomic(kaddr);
2051 
2052         return copied;
2053 }
2054 EXPORT_SYMBOL(iov_iter_copy_from_user_atomic);
2055 
2056 /*
2057  * This has the same sideeffects and return value as
2058  * iov_iter_copy_from_user_atomic().
2059  * The difference is that it attempts to resolve faults.
2060  * Page must not be locked.
2061  */
2062 size_t iov_iter_copy_from_user(struct page *page,
2063                 struct iov_iter *i, unsigned long offset, size_t bytes)
2064 {
2065         char *kaddr;
2066         size_t copied;
2067 
2068         kaddr = kmap(page);
2069         if (likely(i->nr_segs == 1)) {
2070                 int left;
2071                 char __user *buf = i->iov->iov_base + i->iov_offset;
2072                 left = __copy_from_user(kaddr + offset, buf, bytes);
2073                 copied = bytes - left;
2074         } else {
2075                 copied = __iovec_copy_from_user_inatomic(kaddr + offset,
2076                                                 i->iov, i->iov_offset, bytes);
2077         }
2078         kunmap(page);
2079         return copied;
2080 }
2081 EXPORT_SYMBOL(iov_iter_copy_from_user);
2082 
2083 void iov_iter_advance(struct iov_iter *i, size_t bytes)
2084 {
2085         BUG_ON(i->count < bytes);
2086 
2087         if (likely(i->nr_segs == 1)) {
2088                 i->iov_offset += bytes;
2089                 i->count -= bytes;
2090         } else {
2091                 const struct iovec *iov = i->iov;
2092                 size_t base = i->iov_offset;
2093                 unsigned long nr_segs = i->nr_segs;
2094 
2095                 /*
2096                  * The !iov->iov_len check ensures we skip over unlikely
2097                  * zero-length segments (without overruning the iovec).
2098                  */
2099                 while (bytes || unlikely(i->count && !iov->iov_len)) {
2100                         int copy;
2101 
2102                         copy = min(bytes, iov->iov_len - base);
2103                         BUG_ON(!i->count || i->count < copy);
2104                         i->count -= copy;
2105                         bytes -= copy;
2106                         base += copy;
2107                         if (iov->iov_len == base) {
2108                                 iov++;
2109                                 nr_segs--;
2110                                 base = 0;
2111                         }
2112                 }
2113                 i->iov = iov;
2114                 i->iov_offset = base;
2115                 i->nr_segs = nr_segs;
2116         }
2117 }
2118 EXPORT_SYMBOL(iov_iter_advance);
2119 
2120 /*
2121  * Fault in the first iovec of the given iov_iter, to a maximum length
2122  * of bytes. Returns 0 on success, or non-zero if the memory could not be
2123  * accessed (ie. because it is an invalid address).
2124  *
2125  * writev-intensive code may want this to prefault several iovecs -- that
2126  * would be possible (callers must not rely on the fact that _only_ the
2127  * first iovec will be faulted with the current implementation).
2128  */
2129 int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
2130 {
2131         char __user *buf = i->iov->iov_base + i->iov_offset;
2132         bytes = min(bytes, i->iov->iov_len - i->iov_offset);
2133         return fault_in_pages_readable(buf, bytes);
2134 }
2135 EXPORT_SYMBOL(iov_iter_fault_in_readable);
2136 
2137 /*
2138  * Return the count of just the current iov_iter segment.
2139  */
2140 size_t iov_iter_single_seg_count(struct iov_iter *i)
2141 {
2142         const struct iovec *iov = i->iov;
2143         if (i->nr_segs == 1)
2144                 return i->count;
2145         else
2146                 return min(i->count, iov->iov_len - i->iov_offset);
2147 }
2148 EXPORT_SYMBOL(iov_iter_single_seg_count);
2149 
2150 /*
2151  * Performs necessary checks before doing a write
2152  *
2153  * Can adjust writing position or amount of bytes to write.
2154  * Returns appropriate error code that caller should return or
2155  * zero in case that write should be allowed.
2156  */
2157 inline int generic_write_checks(struct file *file, loff_t *pos, size_t *count, int isblk)
2158 {
2159         struct inode *inode = file->f_mapping->host;
2160         unsigned long limit = rlimit(RLIMIT_FSIZE);
2161 
2162         if (unlikely(*pos < 0))
2163                 return -EINVAL;
2164 
2165         if (!isblk) {
2166                 /* FIXME: this is for backwards compatibility with 2.4 */
2167                 if (file->f_flags & O_APPEND)
2168                         *pos = i_size_read(inode);
2169 
2170                 if (limit != RLIM_INFINITY) {
2171                         if (*pos >= limit) {
2172                                 send_sig(SIGXFSZ, current, 0);
2173                                 return -EFBIG;
2174                         }
2175                         if (*count > limit - (typeof(limit))*pos) {
2176                                 *count = limit - (typeof(limit))*pos;
2177                         }
2178                 }
2179         }
2180 
2181         /*
2182          * LFS rule
2183          */
2184         if (unlikely(*pos + *count > MAX_NON_LFS &&
2185                                 !(file->f_flags & O_LARGEFILE))) {
2186                 if (*pos >= MAX_NON_LFS) {
2187                         return -EFBIG;
2188                 }
2189                 if (*count > MAX_NON_LFS - (unsigned long)*pos) {
2190                         *count = MAX_NON_LFS - (unsigned long)*pos;
2191                 }
2192         }
2193 
2194         /*
2195          * Are we about to exceed the fs block limit ?
2196          *
2197          * If we have written data it becomes a short write.  If we have
2198          * exceeded without writing data we send a signal and return EFBIG.
2199          * Linus frestrict idea will clean these up nicely..
2200          */
2201         if (likely(!isblk)) {
2202                 if (unlikely(*pos >= inode->i_sb->s_maxbytes)) {
2203                         if (*count || *pos > inode->i_sb->s_maxbytes) {
2204                                 return -EFBIG;
2205                         }
2206                         /* zero-length writes at ->s_maxbytes are OK */
2207                 }
2208 
2209                 if (unlikely(*pos + *count > inode->i_sb->s_maxbytes))
2210                         *count = inode->i_sb->s_maxbytes - *pos;
2211         } else {
2212 #ifdef CONFIG_BLOCK
2213                 loff_t isize;
2214                 if (bdev_read_only(I_BDEV(inode)))
2215                         return -EPERM;
2216                 isize = i_size_read(inode);
2217                 if (*pos >= isize) {
2218                         if (*count || *pos > isize)
2219                                 return -ENOSPC;
2220                 }
2221 
2222                 if (*pos + *count > isize)
2223                         *count = isize - *pos;
2224 #else
2225                 return -EPERM;
2226 #endif
2227         }
2228         return 0;
2229 }
2230 EXPORT_SYMBOL(generic_write_checks);
2231 
2232 int pagecache_write_begin(struct file *file, struct address_space *mapping,
2233                                 loff_t pos, unsigned len, unsigned flags,
2234                                 struct page **pagep, void **fsdata)
2235 {
2236         const struct address_space_operations *aops = mapping->a_ops;
2237 
2238         return aops->write_begin(file, mapping, pos, len, flags,
2239                                                         pagep, fsdata);
2240 }
2241 EXPORT_SYMBOL(pagecache_write_begin);
2242 
2243 int pagecache_write_end(struct file *file, struct address_space *mapping,
2244                                 loff_t pos, unsigned len, unsigned copied,
2245                                 struct page *page, void *fsdata)
2246 {
2247         const struct address_space_operations *aops = mapping->a_ops;
2248 
2249         mark_page_accessed(page);
2250         return aops->write_end(file, mapping, pos, len, copied, page, fsdata);
2251 }
2252 EXPORT_SYMBOL(pagecache_write_end);
2253 
2254 ssize_t
2255 generic_file_direct_write(struct kiocb *iocb, const struct iovec *iov,
2256                 unsigned long *nr_segs, loff_t pos, loff_t *ppos,
2257                 size_t count, size_t ocount)
2258 {
2259         struct file     *file = iocb->ki_filp;
2260         struct address_space *mapping = file->f_mapping;
2261         struct inode    *inode = mapping->host;
2262         ssize_t         written;
2263         size_t          write_len;
2264         pgoff_t         end;
2265 
2266         if (count != ocount)
2267                 *nr_segs = iov_shorten((struct iovec *)iov, *nr_segs, count);
2268 
2269         write_len = iov_length(iov, *nr_segs);
2270         end = (pos + write_len - 1) >> PAGE_CACHE_SHIFT;
2271 
2272         written = filemap_write_and_wait_range(mapping, pos, pos + write_len - 1);
2273         if (written)
2274                 goto out;
2275 
2276         /*
2277          * After a write we want buffered reads to be sure to go to disk to get
2278          * the new data.  We invalidate clean cached page from the region we're
2279          * about to write.  We do this *before* the write so that we can return
2280          * without clobbering -EIOCBQUEUED from ->direct_IO().
2281          */
2282         if (mapping->nrpages) {
2283                 written = invalidate_inode_pages2_range(mapping,
2284                                         pos >> PAGE_CACHE_SHIFT, end);
2285                 /*
2286                  * If a page can not be invalidated, return 0 to fall back
2287                  * to buffered write.
2288                  */
2289                 if (written) {
2290                         if (written == -EBUSY)
2291                                 return 0;
2292                         goto out;
2293                 }
2294         }
2295 
2296         written = mapping->a_ops->direct_IO(WRITE, iocb, iov, pos, *nr_segs);
2297 
2298         /*
2299          * Finally, try again to invalidate clean pages which might have been
2300          * cached by non-direct readahead, or faulted in by get_user_pages()
2301          * if the source of the write was an mmap'ed region of the file
2302          * we're writing.  Either one is a pretty crazy thing to do,
2303          * so we don't support it 100%.  If this invalidation
2304          * fails, tough, the write still worked...
2305          */
2306         if (mapping->nrpages) {
2307                 invalidate_inode_pages2_range(mapping,
2308                                               pos >> PAGE_CACHE_SHIFT, end);
2309         }
2310 
2311         if (written > 0) {
2312                 pos += written;
2313                 if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
2314                         i_size_write(inode, pos);
2315                         mark_inode_dirty(inode);
2316                 }
2317                 *ppos = pos;
2318         }
2319 out:
2320         return written;
2321 }
2322 EXPORT_SYMBOL(generic_file_direct_write);
2323 
2324 /*
2325  * Find or create a page at the given pagecache position. Return the locked
2326  * page. This function is specifically for buffered writes.
2327  */
2328 struct page *grab_cache_page_write_begin(struct address_space *mapping,
2329                                         pgoff_t index, unsigned flags)
2330 {
2331         int status;
2332         gfp_t gfp_mask;
2333         struct page *page;
2334         gfp_t gfp_notmask = 0;
2335 
2336         gfp_mask = mapping_gfp_mask(mapping);
2337         if (mapping_cap_account_dirty(mapping))
2338                 gfp_mask |= __GFP_WRITE;
2339         if (flags & AOP_FLAG_NOFS)
2340                 gfp_notmask = __GFP_FS;
2341 repeat:
2342         page = find_lock_page(mapping, index);
2343         if (page)
2344                 goto found;
2345 
2346         page = __page_cache_alloc(gfp_mask & ~gfp_notmask);
2347         if (!page)
2348                 return NULL;
2349         status = add_to_page_cache_lru(page, mapping, index,
2350                                                 GFP_KERNEL & ~gfp_notmask);
2351         if (unlikely(status)) {
2352                 page_cache_release(page);
2353                 if (status == -EEXIST)
2354                         goto repeat;
2355                 return NULL;
2356         }
2357 found:
2358         wait_on_page_writeback(page);
2359         return page;
2360 }
2361 EXPORT_SYMBOL(grab_cache_page_write_begin);
2362 
2363 static ssize_t generic_perform_write(struct file *file,
2364                                 struct iov_iter *i, loff_t pos)
2365 {
2366         struct address_space *mapping = file->f_mapping;
2367         const struct address_space_operations *a_ops = mapping->a_ops;
2368         long status = 0;
2369         ssize_t written = 0;
2370         unsigned int flags = 0;
2371 
2372         /*
2373          * Copies from kernel address space cannot fail (NFSD is a big user).
2374          */
2375         if (segment_eq(get_fs(), KERNEL_DS))
2376                 flags |= AOP_FLAG_UNINTERRUPTIBLE;
2377 
2378         do {
2379                 struct page *page;
2380                 unsigned long offset;   /* Offset into pagecache page */
2381                 unsigned long bytes;    /* Bytes to write to page */
2382                 size_t copied;          /* Bytes copied from user */
2383                 void *fsdata;
2384 
2385                 offset = (pos & (PAGE_CACHE_SIZE - 1));
2386                 bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
2387                                                 iov_iter_count(i));
2388 
2389 again:
2390                 /*
2391                  * Bring in the user page that we will copy from _first_.
2392                  * Otherwise there's a nasty deadlock on copying from the
2393                  * same page as we're writing to, without it being marked
2394                  * up-to-date.
2395                  *
2396                  * Not only is this an optimisation, but it is also required
2397                  * to check that the address is actually valid, when atomic
2398                  * usercopies are used, below.
2399                  */
2400                 if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
2401                         status = -EFAULT;
2402                         break;
2403                 }
2404 
2405                 if (fatal_signal_pending(current)) {
2406                         status = -EINTR;
2407                         break;
2408                 }
2409 
2410                 status = a_ops->write_begin(file, mapping, pos, bytes, flags,
2411                                                 &page, &fsdata);
2412                 if (unlikely(status))
2413                         break;
2414 
2415                 if (mapping_writably_mapped(mapping))
2416                         flush_dcache_page(page);
2417 
2418                 pagefault_disable();
2419                 copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
2420                 pagefault_enable();
2421                 flush_dcache_page(page);
2422 
2423                 mark_page_accessed(page);
2424                 status = a_ops->write_end(file, mapping, pos, bytes, copied,
2425                                                 page, fsdata);
2426                 if (unlikely(status < 0))
2427                         break;
2428                 copied = status;
2429 
2430                 cond_resched();
2431 
2432                 iov_iter_advance(i, copied);
2433                 if (unlikely(copied == 0)) {
2434                         /*
2435                          * If we were unable to copy any data at all, we must
2436                          * fall back to a single segment length write.
2437                          *
2438                          * If we didn't fallback here, we could livelock
2439                          * because not all segments in the iov can be copied at
2440                          * once without a pagefault.
2441                          */
2442                         bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
2443                                                 iov_iter_single_seg_count(i));
2444                         goto again;
2445                 }
2446                 pos += copied;
2447                 written += copied;
2448 
2449                 balance_dirty_pages_ratelimited(mapping);
2450         } while (iov_iter_count(i));
2451 
2452         return written ? written : status;
2453 }
2454 
2455 ssize_t
2456 generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
2457                 unsigned long nr_segs, loff_t pos, loff_t *ppos,
2458                 size_t count, ssize_t written)
2459 {
2460         struct file *file = iocb->ki_filp;
2461         ssize_t status;
2462         struct iov_iter i;
2463 
2464         iov_iter_init(&i, iov, nr_segs, count, written);
2465         status = generic_perform_write(file, &i, pos);
2466 
2467         if (likely(status >= 0)) {
2468                 written += status;
2469                 *ppos = pos + status;
2470         }
2471         
2472         return written ? written : status;
2473 }
2474 EXPORT_SYMBOL(generic_file_buffered_write);
2475 
2476 /**
2477  * __generic_file_aio_write - write data to a file
2478  * @iocb:       IO state structure (file, offset, etc.)
2479  * @iov:        vector with data to write
2480  * @nr_segs:    number of segments in the vector
2481  * @ppos:       position where to write
2482  *
2483  * This function does all the work needed for actually writing data to a
2484  * file. It does all basic checks, removes SUID from the file, updates
2485  * modification times and calls proper subroutines depending on whether we
2486  * do direct IO or a standard buffered write.
2487  *
2488  * It expects i_mutex to be grabbed unless we work on a block device or similar
2489  * object which does not need locking at all.
2490  *
2491  * This function does *not* take care of syncing data in case of O_SYNC write.
2492  * A caller has to handle it. This is mainly due to the fact that we want to
2493  * avoid syncing under i_mutex.
2494  */
2495 ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
2496                                  unsigned long nr_segs, loff_t *ppos)
2497 {
2498         struct file *file = iocb->ki_filp;
2499         struct address_space * mapping = file->f_mapping;
2500         size_t ocount;          /* original count */
2501         size_t count;           /* after file limit checks */
2502         struct inode    *inode = mapping->host;
2503         loff_t          pos;
2504         ssize_t         written;
2505         ssize_t         err;
2506 
2507         ocount = 0;
2508         err = generic_segment_checks(iov, &nr_segs, &ocount, VERIFY_READ);
2509         if (err)
2510                 return err;
2511 
2512         count = ocount;
2513         pos = *ppos;
2514 
2515         vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
2516 
2517         /* We can write back this queue in page reclaim */
2518         current->backing_dev_info = mapping->backing_dev_info;
2519         written = 0;
2520 
2521         err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));
2522         if (err)
2523                 goto out;
2524 
2525         if (count == 0)
2526                 goto out;
2527 
2528         err = file_remove_suid(file);
2529         if (err)
2530                 goto out;
2531 
2532         file_update_time(file);
2533 
2534         /* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
2535         if (unlikely(file->f_flags & O_DIRECT)) {
2536                 loff_t endbyte;
2537                 ssize_t written_buffered;
2538 
2539                 written = generic_file_direct_write(iocb, iov, &nr_segs, pos,
2540                                                         ppos, count, ocount);
2541                 if (written < 0 || written == count)
2542                         goto out;
2543                 /*
2544                  * direct-io write to a hole: fall through to buffered I/O
2545                  * for completing the rest of the request.
2546                  */
2547                 pos += written;
2548                 count -= written;
2549                 written_buffered = generic_file_buffered_write(iocb, iov,
2550                                                 nr_segs, pos, ppos, count,
2551                                                 written);
2552                 /*
2553                  * If generic_file_buffered_write() retuned a synchronous error
2554                  * then we want to return the number of bytes which were
2555                  * direct-written, or the error code if that was zero.  Note
2556                  * that this differs from normal direct-io semantics, which
2557                  * will return -EFOO even if some bytes were written.
2558                  */
2559                 if (written_buffered < 0) {
2560                         err = written_buffered;
2561                         goto out;
2562                 }
2563 
2564                 /*
2565                  * We need to ensure that the page cache pages are written to
2566                  * disk and invalidated to preserve the expected O_DIRECT
2567                  * semantics.
2568                  */
2569                 endbyte = pos + written_buffered - written - 1;
2570                 err = filemap_write_and_wait_range(file->f_mapping, pos, endbyte);
2571                 if (err == 0) {
2572                         written = written_buffered;
2573                         invalidate_mapping_pages(mapping,
2574                                                  pos >> PAGE_CACHE_SHIFT,
2575                                                  endbyte >> PAGE_CACHE_SHIFT);
2576                 } else {
2577                         /*
2578                          * We don't know how much we wrote, so just return
2579                          * the number of bytes which were direct-written
2580                          */
2581                 }
2582         } else {
2583                 written = generic_file_buffered_write(iocb, iov, nr_segs,
2584                                 pos, ppos, count, written);
2585         }
2586 out:
2587         current->backing_dev_info = NULL;
2588         return written ? written : err;
2589 }
2590 EXPORT_SYMBOL(__generic_file_aio_write);
2591 
2592 /**
2593  * generic_file_aio_write - write data to a file
2594  * @iocb:       IO state structure
2595  * @iov:        vector with data to write
2596  * @nr_segs:    number of segments in the vector
2597  * @pos:        position in file where to write
2598  *
2599  * This is a wrapper around __generic_file_aio_write() to be used by most
2600  * filesystems. It takes care of syncing the file in case of O_SYNC file
2601  * and acquires i_mutex as needed.
2602  */
2603 ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
2604                 unsigned long nr_segs, loff_t pos)
2605 {
2606         struct file *file = iocb->ki_filp;
2607         struct inode *inode = file->f_mapping->host;
2608         struct blk_plug plug;
2609         ssize_t ret;
2610 
2611         BUG_ON(iocb->ki_pos != pos);
2612 
2613         mutex_lock(&inode->i_mutex);
2614         blk_start_plug(&plug);
2615         ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
2616         mutex_unlock(&inode->i_mutex);
2617 
2618         if (ret > 0 || ret == -EIOCBQUEUED) {
2619                 ssize_t err;
2620 
2621                 err = generic_write_sync(file, pos, ret);
2622                 if (err < 0 && ret > 0)
2623                         ret = err;
2624         }
2625         blk_finish_plug(&plug);
2626         return ret;
2627 }
2628 EXPORT_SYMBOL(generic_file_aio_write);
2629 
2630 /**
2631  * try_to_release_page() - release old fs-specific metadata on a page
2632  *
2633  * @page: the page which the kernel is trying to free
2634  * @gfp_mask: memory allocation flags (and I/O mode)
2635  *
2636  * The address_space is to try to release any data against the page
2637  * (presumably at page->private).  If the release was successful, return `1'.
2638  * Otherwise return zero.
2639  *
2640  * This may also be called if PG_fscache is set on a page, indicating that the
2641  * page is known to the local caching routines.
2642  *
2643  * The @gfp_mask argument specifies whether I/O may be performed to release
2644  * this page (__GFP_IO), and whether the call may block (__GFP_WAIT & __GFP_FS).
2645  *
2646  */
2647 int try_to_release_page(struct page *page, gfp_t gfp_mask)
2648 {
2649         struct address_space * const mapping = page->mapping;
2650 
2651         BUG_ON(!PageLocked(page));
2652         if (PageWriteback(page))
2653                 return 0;
2654 
2655         if (mapping && mapping->a_ops->releasepage)
2656                 return mapping->a_ops->releasepage(page, gfp_mask);
2657         return try_to_free_buffers(page);
2658 }
2659 
2660 EXPORT_SYMBOL(try_to_release_page);
2661 

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