Root/mm/filemap.c

1/*
2 * linux/mm/filemap.c
3 *
4 * Copyright (C) 1994-1999 Linus Torvalds
5 */
6
7/*
8 * This file handles the generic file mmap semantics used by
9 * most "normal" filesystems (but you don't /have/ to use this:
10 * the NFS filesystem used to do this differently, for example)
11 */
12#include <linux/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/cpuset.h>
33#include <linux/hardirq.h> /* for BUG_ON(!in_atomic()) only */
34#include <linux/memcontrol.h>
35#include <linux/cleancache.h>
36#include "internal.h"
37
38#define CREATE_TRACE_POINTS
39#include <trace/events/filemap.h>
40
41/*
42 * FIXME: remove all knowledge of the buffer layer from the core VM
43 */
44#include <linux/buffer_head.h> /* for try_to_free_buffers */
45
46#include <asm/mman.h>
47
48/*
49 * Shared mappings implemented 30.11.1994. It's not fully working yet,
50 * though.
51 *
52 * Shared mappings now work. 15.8.1995 Bruno.
53 *
54 * finished 'unifying' the page and buffer cache and SMP-threaded the
55 * page-cache, 21.05.1999, Ingo Molnar <mingo@redhat.com>
56 *
57 * SMP-threaded pagemap-LRU 1999, Andrea Arcangeli <andrea@suse.de>
58 */
59
60/*
61 * Lock ordering:
62 *
63 * ->i_mmap_mutex (truncate_pagecache)
64 * ->private_lock (__free_pte->__set_page_dirty_buffers)
65 * ->swap_lock (exclusive_swap_page, others)
66 * ->mapping->tree_lock
67 *
68 * ->i_mutex
69 * ->i_mmap_mutex (truncate->unmap_mapping_range)
70 *
71 * ->mmap_sem
72 * ->i_mmap_mutex
73 * ->page_table_lock or pte_lock (various, mainly in memory.c)
74 * ->mapping->tree_lock (arch-dependent flush_dcache_mmap_lock)
75 *
76 * ->mmap_sem
77 * ->lock_page (access_process_vm)
78 *
79 * ->i_mutex (generic_file_buffered_write)
80 * ->mmap_sem (fault_in_pages_readable->do_page_fault)
81 *
82 * bdi->wb.list_lock
83 * sb_lock (fs/fs-writeback.c)
84 * ->mapping->tree_lock (__sync_single_inode)
85 *
86 * ->i_mmap_mutex
87 * ->anon_vma.lock (vma_adjust)
88 *
89 * ->anon_vma.lock
90 * ->page_table_lock or pte_lock (anon_vma_prepare and various)
91 *
92 * ->page_table_lock or pte_lock
93 * ->swap_lock (try_to_unmap_one)
94 * ->private_lock (try_to_unmap_one)
95 * ->tree_lock (try_to_unmap_one)
96 * ->zone.lru_lock (follow_page->mark_page_accessed)
97 * ->zone.lru_lock (check_pte_range->isolate_lru_page)
98 * ->private_lock (page_remove_rmap->set_page_dirty)
99 * ->tree_lock (page_remove_rmap->set_page_dirty)
100 * bdi.wb->list_lock (page_remove_rmap->set_page_dirty)
101 * ->inode->i_lock (page_remove_rmap->set_page_dirty)
102 * bdi.wb->list_lock (zap_pte_range->set_page_dirty)
103 * ->inode->i_lock (zap_pte_range->set_page_dirty)
104 * ->private_lock (zap_pte_range->__set_page_dirty_buffers)
105 *
106 * ->i_mmap_mutex
107 * ->tasklist_lock (memory_failure, collect_procs_ao)
108 */
109
110/*
111 * Delete a page from the page cache and free it. Caller has to make
112 * sure the page is locked and that nobody else uses it - or that usage
113 * is safe. The caller must hold the mapping's tree_lock.
114 */
115void __delete_from_page_cache(struct page *page)
116{
117    struct address_space *mapping = page->mapping;
118
119    trace_mm_filemap_delete_from_page_cache(page);
120    /*
121     * if we're uptodate, flush out into the cleancache, otherwise
122     * invalidate any existing cleancache entries. We can't leave
123     * stale data around in the cleancache once our page is gone
124     */
125    if (PageUptodate(page) && PageMappedToDisk(page))
126        cleancache_put_page(page);
127    else
128        cleancache_invalidate_page(mapping, page);
129
130    radix_tree_delete(&mapping->page_tree, page->index);
131    page->mapping = NULL;
132    /* Leave page->index set: truncation lookup relies upon it */
133    mapping->nrpages--;
134    __dec_zone_page_state(page, NR_FILE_PAGES);
135    if (PageSwapBacked(page))
136        __dec_zone_page_state(page, NR_SHMEM);
137    BUG_ON(page_mapped(page));
138
139    /*
140     * Some filesystems seem to re-dirty the page even after
141     * the VM has canceled the dirty bit (eg ext3 journaling).
142     *
143     * Fix it up by doing a final dirty accounting check after
144     * having removed the page entirely.
145     */
146    if (PageDirty(page) && mapping_cap_account_dirty(mapping)) {
147        dec_zone_page_state(page, NR_FILE_DIRTY);
148        dec_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
149    }
150}
151
152/**
153 * delete_from_page_cache - delete page from page cache
154 * @page: the page which the kernel is trying to remove from page cache
155 *
156 * This must be called only on pages that have been verified to be in the page
157 * cache and locked. It will never put the page into the free list, the caller
158 * has a reference on the page.
159 */
160void delete_from_page_cache(struct page *page)
161{
162    struct address_space *mapping = page->mapping;
163    void (*freepage)(struct page *);
164
165    BUG_ON(!PageLocked(page));
166
167    freepage = mapping->a_ops->freepage;
168    spin_lock_irq(&mapping->tree_lock);
169    __delete_from_page_cache(page);
170    spin_unlock_irq(&mapping->tree_lock);
171    mem_cgroup_uncharge_cache_page(page);
172
173    if (freepage)
174        freepage(page);
175    page_cache_release(page);
176}
177EXPORT_SYMBOL(delete_from_page_cache);
178
179static int sleep_on_page(void *word)
180{
181    io_schedule();
182    return 0;
183}
184
185static int sleep_on_page_killable(void *word)
186{
187    sleep_on_page(word);
188    return fatal_signal_pending(current) ? -EINTR : 0;
189}
190
191static int filemap_check_errors(struct address_space *mapping)
192{
193    int ret = 0;
194    /* Check for outstanding write errors */
195    if (test_and_clear_bit(AS_ENOSPC, &mapping->flags))
196        ret = -ENOSPC;
197    if (test_and_clear_bit(AS_EIO, &mapping->flags))
198        ret = -EIO;
199    return ret;
200}
201
202/**
203 * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
204 * @mapping: address space structure to write
205 * @start: offset in bytes where the range starts
206 * @end: offset in bytes where the range ends (inclusive)
207 * @sync_mode: enable synchronous operation
208 *
209 * Start writeback against all of a mapping's dirty pages that lie
210 * within the byte offsets <start, end> inclusive.
211 *
212 * If sync_mode is WB_SYNC_ALL then this is a "data integrity" operation, as
213 * opposed to a regular memory cleansing writeback. The difference between
214 * these two operations is that if a dirty page/buffer is encountered, it must
215 * be waited upon, and not just skipped over.
216 */
217int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
218                loff_t end, int sync_mode)
219{
220    int ret;
221    struct writeback_control wbc = {
222        .sync_mode = sync_mode,
223        .nr_to_write = LONG_MAX,
224        .range_start = start,
225        .range_end = end,
226    };
227
228    if (!mapping_cap_writeback_dirty(mapping))
229        return 0;
230
231    ret = do_writepages(mapping, &wbc);
232    return ret;
233}
234
235static inline int __filemap_fdatawrite(struct address_space *mapping,
236    int sync_mode)
237{
238    return __filemap_fdatawrite_range(mapping, 0, LLONG_MAX, sync_mode);
239}
240
241int filemap_fdatawrite(struct address_space *mapping)
242{
243    return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
244}
245EXPORT_SYMBOL(filemap_fdatawrite);
246
247int filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
248                loff_t end)
249{
250    return __filemap_fdatawrite_range(mapping, start, end, WB_SYNC_ALL);
251}
252EXPORT_SYMBOL(filemap_fdatawrite_range);
253
254/**
255 * filemap_flush - mostly a non-blocking flush
256 * @mapping: target address_space
257 *
258 * This is a mostly non-blocking flush. Not suitable for data-integrity
259 * purposes - I/O may not be started against all dirty pages.
260 */
261int filemap_flush(struct address_space *mapping)
262{
263    return __filemap_fdatawrite(mapping, WB_SYNC_NONE);
264}
265EXPORT_SYMBOL(filemap_flush);
266
267/**
268 * filemap_fdatawait_range - wait for writeback to complete
269 * @mapping: address space structure to wait for
270 * @start_byte: offset in bytes where the range starts
271 * @end_byte: offset in bytes where the range ends (inclusive)
272 *
273 * Walk the list of under-writeback pages of the given address space
274 * in the given range and wait for all of them.
275 */
276int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
277                loff_t end_byte)
278{
279    pgoff_t index = start_byte >> PAGE_CACHE_SHIFT;
280    pgoff_t end = end_byte >> PAGE_CACHE_SHIFT;
281    struct pagevec pvec;
282    int nr_pages;
283    int ret2, ret = 0;
284
285    if (end_byte < start_byte)
286        goto out;
287
288    pagevec_init(&pvec, 0);
289    while ((index <= end) &&
290            (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
291            PAGECACHE_TAG_WRITEBACK,
292            min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1)) != 0) {
293        unsigned i;
294
295        for (i = 0; i < nr_pages; i++) {
296            struct page *page = pvec.pages[i];
297
298            /* until radix tree lookup accepts end_index */
299            if (page->index > end)
300                continue;
301
302            wait_on_page_writeback(page);
303            if (TestClearPageError(page))
304                ret = -EIO;
305        }
306        pagevec_release(&pvec);
307        cond_resched();
308    }
309out:
310    ret2 = filemap_check_errors(mapping);
311    if (!ret)
312        ret = ret2;
313
314    return ret;
315}
316EXPORT_SYMBOL(filemap_fdatawait_range);
317
318/**
319 * filemap_fdatawait - wait for all under-writeback pages to complete
320 * @mapping: address space structure to wait for
321 *
322 * Walk the list of under-writeback pages of the given address space
323 * and wait for all of them.
324 */
325int filemap_fdatawait(struct address_space *mapping)
326{
327    loff_t i_size = i_size_read(mapping->host);
328
329    if (i_size == 0)
330        return 0;
331
332    return filemap_fdatawait_range(mapping, 0, i_size - 1);
333}
334EXPORT_SYMBOL(filemap_fdatawait);
335
336int filemap_write_and_wait(struct address_space *mapping)
337{
338    int err = 0;
339
340    if (mapping->nrpages) {
341        err = filemap_fdatawrite(mapping);
342        /*
343         * Even if the above returned error, the pages may be
344         * written partially (e.g. -ENOSPC), so we wait for it.
345         * But the -EIO is special case, it may indicate the worst
346         * thing (e.g. bug) happened, so we avoid waiting for it.
347         */
348        if (err != -EIO) {
349            int err2 = filemap_fdatawait(mapping);
350            if (!err)
351                err = err2;
352        }
353    } else {
354        err = filemap_check_errors(mapping);
355    }
356    return err;
357}
358EXPORT_SYMBOL(filemap_write_and_wait);
359
360/**
361 * filemap_write_and_wait_range - write out & wait on a file range
362 * @mapping: the address_space for the pages
363 * @lstart: offset in bytes where the range starts
364 * @lend: offset in bytes where the range ends (inclusive)
365 *
366 * Write out and wait upon file offsets lstart->lend, inclusive.
367 *
368 * Note that `lend' is inclusive (describes the last byte to be written) so
369 * that this function can be used to write to the very end-of-file (end = -1).
370 */
371int filemap_write_and_wait_range(struct address_space *mapping,
372                 loff_t lstart, loff_t lend)
373{
374    int err = 0;
375
376    if (mapping->nrpages) {
377        err = __filemap_fdatawrite_range(mapping, lstart, lend,
378                         WB_SYNC_ALL);
379        /* See comment of filemap_write_and_wait() */
380        if (err != -EIO) {
381            int err2 = filemap_fdatawait_range(mapping,
382                        lstart, lend);
383            if (!err)
384                err = err2;
385        }
386    } else {
387        err = filemap_check_errors(mapping);
388    }
389    return err;
390}
391EXPORT_SYMBOL(filemap_write_and_wait_range);
392
393/**
394 * replace_page_cache_page - replace a pagecache page with a new one
395 * @old: page to be replaced
396 * @new: page to replace with
397 * @gfp_mask: allocation mode
398 *
399 * This function replaces a page in the pagecache with a new one. On
400 * success it acquires the pagecache reference for the new page and
401 * drops it for the old page. Both the old and new pages must be
402 * locked. This function does not add the new page to the LRU, the
403 * caller must do that.
404 *
405 * The remove + add is atomic. The only way this function can fail is
406 * memory allocation failure.
407 */
408int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
409{
410    int error;
411
412    VM_BUG_ON(!PageLocked(old));
413    VM_BUG_ON(!PageLocked(new));
414    VM_BUG_ON(new->mapping);
415
416    error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
417    if (!error) {
418        struct address_space *mapping = old->mapping;
419        void (*freepage)(struct page *);
420
421        pgoff_t offset = old->index;
422        freepage = mapping->a_ops->freepage;
423
424        page_cache_get(new);
425        new->mapping = mapping;
426        new->index = offset;
427
428        spin_lock_irq(&mapping->tree_lock);
429        __delete_from_page_cache(old);
430        error = radix_tree_insert(&mapping->page_tree, offset, new);
431        BUG_ON(error);
432        mapping->nrpages++;
433        __inc_zone_page_state(new, NR_FILE_PAGES);
434        if (PageSwapBacked(new))
435            __inc_zone_page_state(new, NR_SHMEM);
436        spin_unlock_irq(&mapping->tree_lock);
437        /* mem_cgroup codes must not be called under tree_lock */
438        mem_cgroup_replace_page_cache(old, new);
439        radix_tree_preload_end();
440        if (freepage)
441            freepage(old);
442        page_cache_release(old);
443    }
444
445    return error;
446}
447EXPORT_SYMBOL_GPL(replace_page_cache_page);
448
449/**
450 * add_to_page_cache_locked - add a locked page to the pagecache
451 * @page: page to add
452 * @mapping: the page's address_space
453 * @offset: page index
454 * @gfp_mask: page allocation mode
455 *
456 * This function is used to add a page to the pagecache. It must be locked.
457 * This function does not add the page to the LRU. The caller must do that.
458 */
459int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
460        pgoff_t offset, gfp_t gfp_mask)
461{
462    int error;
463
464    VM_BUG_ON(!PageLocked(page));
465    VM_BUG_ON(PageSwapBacked(page));
466
467    error = mem_cgroup_cache_charge(page, current->mm,
468                    gfp_mask & GFP_RECLAIM_MASK);
469    if (error)
470        return error;
471
472    error = radix_tree_maybe_preload(gfp_mask & ~__GFP_HIGHMEM);
473    if (error) {
474        mem_cgroup_uncharge_cache_page(page);
475        return error;
476    }
477
478    page_cache_get(page);
479    page->mapping = mapping;
480    page->index = offset;
481
482    spin_lock_irq(&mapping->tree_lock);
483    error = radix_tree_insert(&mapping->page_tree, offset, page);
484    radix_tree_preload_end();
485    if (unlikely(error))
486        goto err_insert;
487    mapping->nrpages++;
488    __inc_zone_page_state(page, NR_FILE_PAGES);
489    spin_unlock_irq(&mapping->tree_lock);
490    trace_mm_filemap_add_to_page_cache(page);
491    return 0;
492err_insert:
493    page->mapping = NULL;
494    /* Leave page->index set: truncation relies upon it */
495    spin_unlock_irq(&mapping->tree_lock);
496    mem_cgroup_uncharge_cache_page(page);
497    page_cache_release(page);
498    return error;
499}
500EXPORT_SYMBOL(add_to_page_cache_locked);
501
502int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
503                pgoff_t offset, gfp_t gfp_mask)
504{
505    int ret;
506
507    ret = add_to_page_cache(page, mapping, offset, gfp_mask);
508    if (ret == 0)
509        lru_cache_add_file(page);
510    return ret;
511}
512EXPORT_SYMBOL_GPL(add_to_page_cache_lru);
513
514#ifdef CONFIG_NUMA
515struct page *__page_cache_alloc(gfp_t gfp)
516{
517    int n;
518    struct page *page;
519
520    if (cpuset_do_page_mem_spread()) {
521        unsigned int cpuset_mems_cookie;
522        do {
523            cpuset_mems_cookie = get_mems_allowed();
524            n = cpuset_mem_spread_node();
525            page = alloc_pages_exact_node(n, gfp, 0);
526        } while (!put_mems_allowed(cpuset_mems_cookie) && !page);
527
528        return page;
529    }
530    return alloc_pages(gfp, 0);
531}
532EXPORT_SYMBOL(__page_cache_alloc);
533#endif
534
535/*
536 * In order to wait for pages to become available there must be
537 * waitqueues associated with pages. By using a hash table of
538 * waitqueues where the bucket discipline is to maintain all
539 * waiters on the same queue and wake all when any of the pages
540 * become available, and for the woken contexts to check to be
541 * sure the appropriate page became available, this saves space
542 * at a cost of "thundering herd" phenomena during rare hash
543 * collisions.
544 */
545static wait_queue_head_t *page_waitqueue(struct page *page)
546{
547    const struct zone *zone = page_zone(page);
548
549    return &zone->wait_table[hash_ptr(page, zone->wait_table_bits)];
550}
551
552static inline void wake_up_page(struct page *page, int bit)
553{
554    __wake_up_bit(page_waitqueue(page), &page->flags, bit);
555}
556
557void wait_on_page_bit(struct page *page, int bit_nr)
558{
559    DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
560
561    if (test_bit(bit_nr, &page->flags))
562        __wait_on_bit(page_waitqueue(page), &wait, sleep_on_page,
563                            TASK_UNINTERRUPTIBLE);
564}
565EXPORT_SYMBOL(wait_on_page_bit);
566
567int wait_on_page_bit_killable(struct page *page, int bit_nr)
568{
569    DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
570
571    if (!test_bit(bit_nr, &page->flags))
572        return 0;
573
574    return __wait_on_bit(page_waitqueue(page), &wait,
575                 sleep_on_page_killable, TASK_KILLABLE);
576}
577
578/**
579 * add_page_wait_queue - Add an arbitrary waiter to a page's wait queue
580 * @page: Page defining the wait queue of interest
581 * @waiter: Waiter to add to the queue
582 *
583 * Add an arbitrary @waiter to the wait queue for the nominated @page.
584 */
585void add_page_wait_queue(struct page *page, wait_queue_t *waiter)
586{
587    wait_queue_head_t *q = page_waitqueue(page);
588    unsigned long flags;
589
590    spin_lock_irqsave(&q->lock, flags);
591    __add_wait_queue(q, waiter);
592    spin_unlock_irqrestore(&q->lock, flags);
593}
594EXPORT_SYMBOL_GPL(add_page_wait_queue);
595
596/**
597 * unlock_page - unlock a locked page
598 * @page: the page
599 *
600 * Unlocks the page and wakes up sleepers in ___wait_on_page_locked().
601 * Also wakes sleepers in wait_on_page_writeback() because the wakeup
602 * mechananism between PageLocked pages and PageWriteback pages is shared.
603 * But that's OK - sleepers in wait_on_page_writeback() just go back to sleep.
604 *
605 * The mb is necessary to enforce ordering between the clear_bit and the read
606 * of the waitqueue (to avoid SMP races with a parallel wait_on_page_locked()).
607 */
608void unlock_page(struct page *page)
609{
610    VM_BUG_ON(!PageLocked(page));
611    clear_bit_unlock(PG_locked, &page->flags);
612    smp_mb__after_clear_bit();
613    wake_up_page(page, PG_locked);
614}
615EXPORT_SYMBOL(unlock_page);
616
617/**
618 * end_page_writeback - end writeback against a page
619 * @page: the page
620 */
621void end_page_writeback(struct page *page)
622{
623    if (TestClearPageReclaim(page))
624        rotate_reclaimable_page(page);
625
626    if (!test_clear_page_writeback(page))
627        BUG();
628
629    smp_mb__after_clear_bit();
630    wake_up_page(page, PG_writeback);
631}
632EXPORT_SYMBOL(end_page_writeback);
633
634/**
635 * __lock_page - get a lock on the page, assuming we need to sleep to get it
636 * @page: the page to lock
637 */
638void __lock_page(struct page *page)
639{
640    DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
641
642    __wait_on_bit_lock(page_waitqueue(page), &wait, sleep_on_page,
643                            TASK_UNINTERRUPTIBLE);
644}
645EXPORT_SYMBOL(__lock_page);
646
647int __lock_page_killable(struct page *page)
648{
649    DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
650
651    return __wait_on_bit_lock(page_waitqueue(page), &wait,
652                    sleep_on_page_killable, TASK_KILLABLE);
653}
654EXPORT_SYMBOL_GPL(__lock_page_killable);
655
656int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
657             unsigned int flags)
658{
659    if (flags & FAULT_FLAG_ALLOW_RETRY) {
660        /*
661         * CAUTION! In this case, mmap_sem is not released
662         * even though return 0.
663         */
664        if (flags & FAULT_FLAG_RETRY_NOWAIT)
665            return 0;
666
667        up_read(&mm->mmap_sem);
668        if (flags & FAULT_FLAG_KILLABLE)
669            wait_on_page_locked_killable(page);
670        else
671            wait_on_page_locked(page);
672        return 0;
673    } else {
674        if (flags & FAULT_FLAG_KILLABLE) {
675            int ret;
676
677            ret = __lock_page_killable(page);
678            if (ret) {
679                up_read(&mm->mmap_sem);
680                return 0;
681            }
682        } else
683            __lock_page(page);
684        return 1;
685    }
686}
687
688/**
689 * find_get_page - find and get a page reference
690 * @mapping: the address_space to search
691 * @offset: the page index
692 *
693 * Is there a pagecache struct page at the given (mapping, offset) tuple?
694 * If yes, increment its refcount and return it; if no, return NULL.
695 */
696struct page *find_get_page(struct address_space *mapping, pgoff_t offset)
697{
698    void **pagep;
699    struct page *page;
700
701    rcu_read_lock();
702repeat:
703    page = NULL;
704    pagep = radix_tree_lookup_slot(&mapping->page_tree, offset);
705    if (pagep) {
706        page = radix_tree_deref_slot(pagep);
707        if (unlikely(!page))
708            goto out;
709        if (radix_tree_exception(page)) {
710            if (radix_tree_deref_retry(page))
711                goto repeat;
712            /*
713             * Otherwise, shmem/tmpfs must be storing a swap entry
714             * here as an exceptional entry: so return it without
715             * attempting to raise page count.
716             */
717            goto out;
718        }
719        if (!page_cache_get_speculative(page))
720            goto repeat;
721
722        /*
723         * Has the page moved?
724         * This is part of the lockless pagecache protocol. See
725         * include/linux/pagemap.h for details.
726         */
727        if (unlikely(page != *pagep)) {
728            page_cache_release(page);
729            goto repeat;
730        }
731    }
732out:
733    rcu_read_unlock();
734
735    return page;
736}
737EXPORT_SYMBOL(find_get_page);
738
739/**
740 * find_lock_page - locate, pin and lock a pagecache page
741 * @mapping: the address_space to search
742 * @offset: the page index
743 *
744 * Locates the desired pagecache page, locks it, increments its reference
745 * count and returns its address.
746 *
747 * Returns zero if the page was not present. find_lock_page() may sleep.
748 */
749struct page *find_lock_page(struct address_space *mapping, pgoff_t offset)
750{
751    struct page *page;
752
753repeat:
754    page = find_get_page(mapping, offset);
755    if (page && !radix_tree_exception(page)) {
756        lock_page(page);
757        /* Has the page been truncated? */
758        if (unlikely(page->mapping != mapping)) {
759            unlock_page(page);
760            page_cache_release(page);
761            goto repeat;
762        }
763        VM_BUG_ON(page->index != offset);
764    }
765    return page;
766}
767EXPORT_SYMBOL(find_lock_page);
768
769/**
770 * find_or_create_page - locate or add a pagecache page
771 * @mapping: the page's address_space
772 * @index: the page's index into the mapping
773 * @gfp_mask: page allocation mode
774 *
775 * Locates a page in the pagecache. If the page is not present, a new page
776 * is allocated using @gfp_mask and is added to the pagecache and to the VM's
777 * LRU list. The returned page is locked and has its reference count
778 * incremented.
779 *
780 * find_or_create_page() may sleep, even if @gfp_flags specifies an atomic
781 * allocation!
782 *
783 * find_or_create_page() returns the desired page's address, or zero on
784 * memory exhaustion.
785 */
786struct page *find_or_create_page(struct address_space *mapping,
787        pgoff_t index, gfp_t gfp_mask)
788{
789    struct page *page;
790    int err;
791repeat:
792    page = find_lock_page(mapping, index);
793    if (!page) {
794        page = __page_cache_alloc(gfp_mask);
795        if (!page)
796            return NULL;
797        /*
798         * We want a regular kernel memory (not highmem or DMA etc)
799         * allocation for the radix tree nodes, but we need to honour
800         * the context-specific requirements the caller has asked for.
801         * GFP_RECLAIM_MASK collects those requirements.
802         */
803        err = add_to_page_cache_lru(page, mapping, index,
804            (gfp_mask & GFP_RECLAIM_MASK));
805        if (unlikely(err)) {
806            page_cache_release(page);
807            page = NULL;
808            if (err == -EEXIST)
809                goto repeat;
810        }
811    }
812    return page;
813}
814EXPORT_SYMBOL(find_or_create_page);
815
816/**
817 * find_get_pages - gang pagecache lookup
818 * @mapping: The address_space to search
819 * @start: The starting page index
820 * @nr_pages: The maximum number of pages
821 * @pages: Where the resulting pages are placed
822 *
823 * find_get_pages() will search for and return a group of up to
824 * @nr_pages pages in the mapping. The pages are placed at @pages.
825 * find_get_pages() takes a reference against the returned pages.
826 *
827 * The search returns a group of mapping-contiguous pages with ascending
828 * indexes. There may be holes in the indices due to not-present pages.
829 *
830 * find_get_pages() returns the number of pages which were found.
831 */
832unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
833                unsigned int nr_pages, struct page **pages)
834{
835    struct radix_tree_iter iter;
836    void **slot;
837    unsigned ret = 0;
838
839    if (unlikely(!nr_pages))
840        return 0;
841
842    rcu_read_lock();
843restart:
844    radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
845        struct page *page;
846repeat:
847        page = radix_tree_deref_slot(slot);
848        if (unlikely(!page))
849            continue;
850
851        if (radix_tree_exception(page)) {
852            if (radix_tree_deref_retry(page)) {
853                /*
854                 * Transient condition which can only trigger
855                 * when entry at index 0 moves out of or back
856                 * to root: none yet gotten, safe to restart.
857                 */
858                WARN_ON(iter.index);
859                goto restart;
860            }
861            /*
862             * Otherwise, shmem/tmpfs must be storing a swap entry
863             * here as an exceptional entry: so skip over it -
864             * we only reach this from invalidate_mapping_pages().
865             */
866            continue;
867        }
868
869        if (!page_cache_get_speculative(page))
870            goto repeat;
871
872        /* Has the page moved? */
873        if (unlikely(page != *slot)) {
874            page_cache_release(page);
875            goto repeat;
876        }
877
878        pages[ret] = page;
879        if (++ret == nr_pages)
880            break;
881    }
882
883    rcu_read_unlock();
884    return ret;
885}
886
887/**
888 * find_get_pages_contig - gang contiguous pagecache lookup
889 * @mapping: The address_space to search
890 * @index: The starting page index
891 * @nr_pages: The maximum number of pages
892 * @pages: Where the resulting pages are placed
893 *
894 * find_get_pages_contig() works exactly like find_get_pages(), except
895 * that the returned number of pages are guaranteed to be contiguous.
896 *
897 * find_get_pages_contig() returns the number of pages which were found.
898 */
899unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
900                   unsigned int nr_pages, struct page **pages)
901{
902    struct radix_tree_iter iter;
903    void **slot;
904    unsigned int ret = 0;
905
906    if (unlikely(!nr_pages))
907        return 0;
908
909    rcu_read_lock();
910restart:
911    radix_tree_for_each_contig(slot, &mapping->page_tree, &iter, index) {
912        struct page *page;
913repeat:
914        page = radix_tree_deref_slot(slot);
915        /* The hole, there no reason to continue */
916        if (unlikely(!page))
917            break;
918
919        if (radix_tree_exception(page)) {
920            if (radix_tree_deref_retry(page)) {
921                /*
922                 * Transient condition which can only trigger
923                 * when entry at index 0 moves out of or back
924                 * to root: none yet gotten, safe to restart.
925                 */
926                goto restart;
927            }
928            /*
929             * Otherwise, shmem/tmpfs must be storing a swap entry
930             * here as an exceptional entry: so stop looking for
931             * contiguous pages.
932             */
933            break;
934        }
935
936        if (!page_cache_get_speculative(page))
937            goto repeat;
938
939        /* Has the page moved? */
940        if (unlikely(page != *slot)) {
941            page_cache_release(page);
942            goto repeat;
943        }
944
945        /*
946         * must check mapping and index after taking the ref.
947         * otherwise we can get both false positives and false
948         * negatives, which is just confusing to the caller.
949         */
950        if (page->mapping == NULL || page->index != iter.index) {
951            page_cache_release(page);
952            break;
953        }
954
955        pages[ret] = page;
956        if (++ret == nr_pages)
957            break;
958    }
959    rcu_read_unlock();
960    return ret;
961}
962EXPORT_SYMBOL(find_get_pages_contig);
963
964/**
965 * find_get_pages_tag - find and return pages that match @tag
966 * @mapping: the address_space to search
967 * @index: the starting page index
968 * @tag: the tag index
969 * @nr_pages: the maximum number of pages
970 * @pages: where the resulting pages are placed
971 *
972 * Like find_get_pages, except we only return pages which are tagged with
973 * @tag. We update @index to index the next page for the traversal.
974 */
975unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
976            int tag, unsigned int nr_pages, struct page **pages)
977{
978    struct radix_tree_iter iter;
979    void **slot;
980    unsigned ret = 0;
981
982    if (unlikely(!nr_pages))
983        return 0;
984
985    rcu_read_lock();
986restart:
987    radix_tree_for_each_tagged(slot, &mapping->page_tree,
988                   &iter, *index, tag) {
989        struct page *page;
990repeat:
991        page = radix_tree_deref_slot(slot);
992        if (unlikely(!page))
993            continue;
994
995        if (radix_tree_exception(page)) {
996            if (radix_tree_deref_retry(page)) {
997                /*
998                 * Transient condition which can only trigger
999                 * when entry at index 0 moves out of or back
1000                 * to root: none yet gotten, safe to restart.
1001                 */
1002                goto restart;
1003            }
1004            /*
1005             * This function is never used on a shmem/tmpfs
1006             * mapping, so a swap entry won't be found here.
1007             */
1008            BUG();
1009        }
1010
1011        if (!page_cache_get_speculative(page))
1012            goto repeat;
1013
1014        /* Has the page moved? */
1015        if (unlikely(page != *slot)) {
1016            page_cache_release(page);
1017            goto repeat;
1018        }
1019
1020        pages[ret] = page;
1021        if (++ret == nr_pages)
1022            break;
1023    }
1024
1025    rcu_read_unlock();
1026
1027    if (ret)
1028        *index = pages[ret - 1]->index + 1;
1029
1030    return ret;
1031}
1032EXPORT_SYMBOL(find_get_pages_tag);
1033
1034/**
1035 * grab_cache_page_nowait - returns locked page at given index in given cache
1036 * @mapping: target address_space
1037 * @index: the page index
1038 *
1039 * Same as grab_cache_page(), but do not wait if the page is unavailable.
1040 * This is intended for speculative data generators, where the data can
1041 * be regenerated if the page couldn't be grabbed. This routine should
1042 * be safe to call while holding the lock for another page.
1043 *
1044 * Clear __GFP_FS when allocating the page to avoid recursion into the fs
1045 * and deadlock against the caller's locked page.
1046 */
1047struct page *
1048grab_cache_page_nowait(struct address_space *mapping, pgoff_t index)
1049{
1050    struct page *page = find_get_page(mapping, index);
1051
1052    if (page) {
1053        if (trylock_page(page))
1054            return page;
1055        page_cache_release(page);
1056        return NULL;
1057    }
1058    page = __page_cache_alloc(mapping_gfp_mask(mapping) & ~__GFP_FS);
1059    if (page && add_to_page_cache_lru(page, mapping, index, GFP_NOFS)) {
1060        page_cache_release(page);
1061        page = NULL;
1062    }
1063    return page;
1064}
1065EXPORT_SYMBOL(grab_cache_page_nowait);
1066
1067/*
1068 * CD/DVDs are error prone. When a medium error occurs, the driver may fail
1069 * a _large_ part of the i/o request. Imagine the worst scenario:
1070 *
1071 * ---R__________________________________________B__________
1072 * ^ reading here ^ bad block(assume 4k)
1073 *
1074 * read(R) => miss => readahead(R...B) => media error => frustrating retries
1075 * => failing the whole request => read(R) => read(R+1) =>
1076 * readahead(R+1...B+1) => bang => read(R+2) => read(R+3) =>
1077 * readahead(R+3...B+2) => bang => read(R+3) => read(R+4) =>
1078 * readahead(R+4...B+3) => bang => read(R+4) => read(R+5) => ......
1079 *
1080 * It is going insane. Fix it by quickly scaling down the readahead size.
1081 */
1082static void shrink_readahead_size_eio(struct file *filp,
1083                    struct file_ra_state *ra)
1084{
1085    ra->ra_pages /= 4;
1086}
1087
1088/**
1089 * do_generic_file_read - generic file read routine
1090 * @filp: the file to read
1091 * @ppos: current file position
1092 * @desc: read_descriptor
1093 * @actor: read method
1094 *
1095 * This is a generic file read routine, and uses the
1096 * mapping->a_ops->readpage() function for the actual low-level stuff.
1097 *
1098 * This is really ugly. But the goto's actually try to clarify some
1099 * of the logic when it comes to error handling etc.
1100 */
1101static void do_generic_file_read(struct file *filp, loff_t *ppos,
1102        read_descriptor_t *desc, read_actor_t actor)
1103{
1104    struct address_space *mapping = filp->f_mapping;
1105    struct inode *inode = mapping->host;
1106    struct file_ra_state *ra = &filp->f_ra;
1107    pgoff_t index;
1108    pgoff_t last_index;
1109    pgoff_t prev_index;
1110    unsigned long offset; /* offset into pagecache page */
1111    unsigned int prev_offset;
1112    int error;
1113
1114    index = *ppos >> PAGE_CACHE_SHIFT;
1115    prev_index = ra->prev_pos >> PAGE_CACHE_SHIFT;
1116    prev_offset = ra->prev_pos & (PAGE_CACHE_SIZE-1);
1117    last_index = (*ppos + desc->count + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;
1118    offset = *ppos & ~PAGE_CACHE_MASK;
1119
1120    for (;;) {
1121        struct page *page;
1122        pgoff_t end_index;
1123        loff_t isize;
1124        unsigned long nr, ret;
1125
1126        cond_resched();
1127find_page:
1128        page = find_get_page(mapping, index);
1129        if (!page) {
1130            page_cache_sync_readahead(mapping,
1131                    ra, filp,
1132                    index, last_index - index);
1133            page = find_get_page(mapping, index);
1134            if (unlikely(page == NULL))
1135                goto no_cached_page;
1136        }
1137        if (PageReadahead(page)) {
1138            page_cache_async_readahead(mapping,
1139                    ra, filp, page,
1140                    index, last_index - index);
1141        }
1142        if (!PageUptodate(page)) {
1143            if (inode->i_blkbits == PAGE_CACHE_SHIFT ||
1144                    !mapping->a_ops->is_partially_uptodate)
1145                goto page_not_up_to_date;
1146            if (!trylock_page(page))
1147                goto page_not_up_to_date;
1148            /* Did it get truncated before we got the lock? */
1149            if (!page->mapping)
1150                goto page_not_up_to_date_locked;
1151            if (!mapping->a_ops->is_partially_uptodate(page,
1152                                desc, offset))
1153                goto page_not_up_to_date_locked;
1154            unlock_page(page);
1155        }
1156page_ok:
1157        /*
1158         * i_size must be checked after we know the page is Uptodate.
1159         *
1160         * Checking i_size after the check allows us to calculate
1161         * the correct value for "nr", which means the zero-filled
1162         * part of the page is not copied back to userspace (unless
1163         * another truncate extends the file - this is desired though).
1164         */
1165
1166        isize = i_size_read(inode);
1167        end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
1168        if (unlikely(!isize || index > end_index)) {
1169            page_cache_release(page);
1170            goto out;
1171        }
1172
1173        /* nr is the maximum number of bytes to copy from this page */
1174        nr = PAGE_CACHE_SIZE;
1175        if (index == end_index) {
1176            nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
1177            if (nr <= offset) {
1178                page_cache_release(page);
1179                goto out;
1180            }
1181        }
1182        nr = nr - offset;
1183
1184        /* If users can be writing to this page using arbitrary
1185         * virtual addresses, take care about potential aliasing
1186         * before reading the page on the kernel side.
1187         */
1188        if (mapping_writably_mapped(mapping))
1189            flush_dcache_page(page);
1190
1191        /*
1192         * When a sequential read accesses a page several times,
1193         * only mark it as accessed the first time.
1194         */
1195        if (prev_index != index || offset != prev_offset)
1196            mark_page_accessed(page);
1197        prev_index = index;
1198
1199        /*
1200         * Ok, we have the page, and it's up-to-date, so
1201         * now we can copy it to user space...
1202         *
1203         * The actor routine returns how many bytes were actually used..
1204         * NOTE! This may not be the same as how much of a user buffer
1205         * we filled up (we may be padding etc), so we can only update
1206         * "pos" here (the actor routine has to update the user buffer
1207         * pointers and the remaining count).
1208         */
1209        ret = actor(desc, page, offset, nr);
1210        offset += ret;
1211        index += offset >> PAGE_CACHE_SHIFT;
1212        offset &= ~PAGE_CACHE_MASK;
1213        prev_offset = offset;
1214
1215        page_cache_release(page);
1216        if (ret == nr && desc->count)
1217            continue;
1218        goto out;
1219
1220page_not_up_to_date:
1221        /* Get exclusive access to the page ... */
1222        error = lock_page_killable(page);
1223        if (unlikely(error))
1224            goto readpage_error;
1225
1226page_not_up_to_date_locked:
1227        /* Did it get truncated before we got the lock? */
1228        if (!page->mapping) {
1229            unlock_page(page);
1230            page_cache_release(page);
1231            continue;
1232        }
1233
1234        /* Did somebody else fill it already? */
1235        if (PageUptodate(page)) {
1236            unlock_page(page);
1237            goto page_ok;
1238        }
1239
1240readpage:
1241        /*
1242         * A previous I/O error may have been due to temporary
1243         * failures, eg. multipath errors.
1244         * PG_error will be set again if readpage fails.
1245         */
1246        ClearPageError(page);
1247        /* Start the actual read. The read will unlock the page. */
1248        error = mapping->a_ops->readpage(filp, page);
1249
1250        if (unlikely(error)) {
1251            if (error == AOP_TRUNCATED_PAGE) {
1252                page_cache_release(page);
1253                goto find_page;
1254            }
1255            goto readpage_error;
1256        }
1257
1258        if (!PageUptodate(page)) {
1259            error = lock_page_killable(page);
1260            if (unlikely(error))
1261                goto readpage_error;
1262            if (!PageUptodate(page)) {
1263                if (page->mapping == NULL) {
1264                    /*
1265                     * invalidate_mapping_pages got it
1266                     */
1267                    unlock_page(page);
1268                    page_cache_release(page);
1269                    goto find_page;
1270                }
1271                unlock_page(page);
1272                shrink_readahead_size_eio(filp, ra);
1273                error = -EIO;
1274                goto readpage_error;
1275            }
1276            unlock_page(page);
1277        }
1278
1279        goto page_ok;
1280
1281readpage_error:
1282        /* UHHUH! A synchronous read error occurred. Report it */
1283        desc->error = error;
1284        page_cache_release(page);
1285        goto out;
1286
1287no_cached_page:
1288        /*
1289         * Ok, it wasn't cached, so we need to create a new
1290         * page..
1291         */
1292        page = page_cache_alloc_cold(mapping);
1293        if (!page) {
1294            desc->error = -ENOMEM;
1295            goto out;
1296        }
1297        error = add_to_page_cache_lru(page, mapping,
1298                        index, GFP_KERNEL);
1299        if (error) {
1300            page_cache_release(page);
1301            if (error == -EEXIST)
1302                goto find_page;
1303            desc->error = error;
1304            goto out;
1305        }
1306        goto readpage;
1307    }
1308
1309out:
1310    ra->prev_pos = prev_index;
1311    ra->prev_pos <<= PAGE_CACHE_SHIFT;
1312    ra->prev_pos |= prev_offset;
1313
1314    *ppos = ((loff_t)index << PAGE_CACHE_SHIFT) + offset;
1315    file_accessed(filp);
1316}
1317
1318int file_read_actor(read_descriptor_t *desc, struct page *page,
1319            unsigned long offset, unsigned long size)
1320{
1321    char *kaddr;
1322    unsigned long left, count = desc->count;
1323
1324    if (size > count)
1325        size = count;
1326
1327    /*
1328     * Faults on the destination of a read are common, so do it before
1329     * taking the kmap.
1330     */
1331    if (!fault_in_pages_writeable(desc->arg.buf, size)) {
1332        kaddr = kmap_atomic(page);
1333        left = __copy_to_user_inatomic(desc->arg.buf,
1334                        kaddr + offset, size);
1335        kunmap_atomic(kaddr);
1336        if (left == 0)
1337            goto success;
1338    }
1339
1340    /* Do it the slow way */
1341    kaddr = kmap(page);
1342    left = __copy_to_user(desc->arg.buf, kaddr + offset, size);
1343    kunmap(page);
1344
1345    if (left) {
1346        size -= left;
1347        desc->error = -EFAULT;
1348    }
1349success:
1350    desc->count = count - size;
1351    desc->written += size;
1352    desc->arg.buf += size;
1353    return size;
1354}
1355
1356/*
1357 * Performs necessary checks before doing a write
1358 * @iov: io vector request
1359 * @nr_segs: number of segments in the iovec
1360 * @count: number of bytes to write
1361 * @access_flags: type of access: %VERIFY_READ or %VERIFY_WRITE
1362 *
1363 * Adjust number of segments and amount of bytes to write (nr_segs should be
1364 * properly initialized first). Returns appropriate error code that caller
1365 * should return or zero in case that write should be allowed.
1366 */
1367int generic_segment_checks(const struct iovec *iov,
1368            unsigned long *nr_segs, size_t *count, int access_flags)
1369{
1370    unsigned long seg;
1371    size_t cnt = 0;
1372    for (seg = 0; seg < *nr_segs; seg++) {
1373        const struct iovec *iv = &iov[seg];
1374
1375        /*
1376         * If any segment has a negative length, or the cumulative
1377         * length ever wraps negative then return -EINVAL.
1378         */
1379        cnt += iv->iov_len;
1380        if (unlikely((ssize_t)(cnt|iv->iov_len) < 0))
1381            return -EINVAL;
1382        if (access_ok(access_flags, iv->iov_base, iv->iov_len))
1383            continue;
1384        if (seg == 0)
1385            return -EFAULT;
1386        *nr_segs = seg;
1387        cnt -= iv->iov_len; /* This segment is no good */
1388        break;
1389    }
1390    *count = cnt;
1391    return 0;
1392}
1393EXPORT_SYMBOL(generic_segment_checks);
1394
1395/**
1396 * generic_file_aio_read - generic filesystem read routine
1397 * @iocb: kernel I/O control block
1398 * @iov: io vector request
1399 * @nr_segs: number of segments in the iovec
1400 * @pos: current file position
1401 *
1402 * This is the "read()" routine for all filesystems
1403 * that can use the page cache directly.
1404 */
1405ssize_t
1406generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
1407        unsigned long nr_segs, loff_t pos)
1408{
1409    struct file *filp = iocb->ki_filp;
1410    ssize_t retval;
1411    unsigned long seg = 0;
1412    size_t count;
1413    loff_t *ppos = &iocb->ki_pos;
1414
1415    count = 0;
1416    retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
1417    if (retval)
1418        return retval;
1419
1420    /* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
1421    if (filp->f_flags & O_DIRECT) {
1422        loff_t size;
1423        struct address_space *mapping;
1424        struct inode *inode;
1425
1426        mapping = filp->f_mapping;
1427        inode = mapping->host;
1428        if (!count)
1429            goto out; /* skip atime */
1430        size = i_size_read(inode);
1431        if (pos < size) {
1432            retval = filemap_write_and_wait_range(mapping, pos,
1433                    pos + iov_length(iov, nr_segs) - 1);
1434            if (!retval) {
1435                retval = mapping->a_ops->direct_IO(READ, iocb,
1436                            iov, pos, nr_segs);
1437            }
1438            if (retval > 0) {
1439                *ppos = pos + retval;
1440                count -= retval;
1441            }
1442
1443            /*
1444             * Btrfs can have a short DIO read if we encounter
1445             * compressed extents, so if there was an error, or if
1446             * we've already read everything we wanted to, or if
1447             * there was a short read because we hit EOF, go ahead
1448             * and return. Otherwise fallthrough to buffered io for
1449             * the rest of the read.
1450             */
1451            if (retval < 0 || !count || *ppos >= size) {
1452                file_accessed(filp);
1453                goto out;
1454            }
1455        }
1456    }
1457
1458    count = retval;
1459    for (seg = 0; seg < nr_segs; seg++) {
1460        read_descriptor_t desc;
1461        loff_t offset = 0;
1462
1463        /*
1464         * If we did a short DIO read we need to skip the section of the
1465         * iov that we've already read data into.
1466         */
1467        if (count) {
1468            if (count > iov[seg].iov_len) {
1469                count -= iov[seg].iov_len;
1470                continue;
1471            }
1472            offset = count;
1473            count = 0;
1474        }
1475
1476        desc.written = 0;
1477        desc.arg.buf = iov[seg].iov_base + offset;
1478        desc.count = iov[seg].iov_len - offset;
1479        if (desc.count == 0)
1480            continue;
1481        desc.error = 0;
1482        do_generic_file_read(filp, ppos, &desc, file_read_actor);
1483        retval += desc.written;
1484        if (desc.error) {
1485            retval = retval ?: desc.error;
1486            break;
1487        }
1488        if (desc.count > 0)
1489            break;
1490    }
1491out:
1492    return retval;
1493}
1494EXPORT_SYMBOL(generic_file_aio_read);
1495
1496#ifdef CONFIG_MMU
1497/**
1498 * page_cache_read - adds requested page to the page cache if not already there
1499 * @file: file to read
1500 * @offset: page index
1501 *
1502 * This adds the requested page to the page cache if it isn't already there,
1503 * and schedules an I/O to read in its contents from disk.
1504 */
1505static int page_cache_read(struct file *file, pgoff_t offset)
1506{
1507    struct address_space *mapping = file->f_mapping;
1508    struct page *page;
1509    int ret;
1510
1511    do {
1512        page = page_cache_alloc_cold(mapping);
1513        if (!page)
1514            return -ENOMEM;
1515
1516        ret = add_to_page_cache_lru(page, mapping, offset, GFP_KERNEL);
1517        if (ret == 0)
1518            ret = mapping->a_ops->readpage(file, page);
1519        else if (ret == -EEXIST)
1520            ret = 0; /* losing race to add is OK */
1521
1522        page_cache_release(page);
1523
1524    } while (ret == AOP_TRUNCATED_PAGE);
1525        
1526    return ret;
1527}
1528
1529#define MMAP_LOTSAMISS (100)
1530
1531/*
1532 * Synchronous readahead happens when we don't even find
1533 * a page in the page cache at all.
1534 */
1535static void do_sync_mmap_readahead(struct vm_area_struct *vma,
1536                   struct file_ra_state *ra,
1537                   struct file *file,
1538                   pgoff_t offset)
1539{
1540    unsigned long ra_pages;
1541    struct address_space *mapping = file->f_mapping;
1542
1543    /* If we don't want any read-ahead, don't bother */
1544    if (vma->vm_flags & VM_RAND_READ)
1545        return;
1546    if (!ra->ra_pages)
1547        return;
1548
1549    if (vma->vm_flags & VM_SEQ_READ) {
1550        page_cache_sync_readahead(mapping, ra, file, offset,
1551                      ra->ra_pages);
1552        return;
1553    }
1554
1555    /* Avoid banging the cache line if not needed */
1556    if (ra->mmap_miss < MMAP_LOTSAMISS * 10)
1557        ra->mmap_miss++;
1558
1559    /*
1560     * Do we miss much more than hit in this file? If so,
1561     * stop bothering with read-ahead. It will only hurt.
1562     */
1563    if (ra->mmap_miss > MMAP_LOTSAMISS)
1564        return;
1565
1566    /*
1567     * mmap read-around
1568     */
1569    ra_pages = max_sane_readahead(ra->ra_pages);
1570    ra->start = max_t(long, 0, offset - ra_pages / 2);
1571    ra->size = ra_pages;
1572    ra->async_size = ra_pages / 4;
1573    ra_submit(ra, mapping, file);
1574}
1575
1576/*
1577 * Asynchronous readahead happens when we find the page and PG_readahead,
1578 * so we want to possibly extend the readahead further..
1579 */
1580static void do_async_mmap_readahead(struct vm_area_struct *vma,
1581                    struct file_ra_state *ra,
1582                    struct file *file,
1583                    struct page *page,
1584                    pgoff_t offset)
1585{
1586    struct address_space *mapping = file->f_mapping;
1587
1588    /* If we don't want any read-ahead, don't bother */
1589    if (vma->vm_flags & VM_RAND_READ)
1590        return;
1591    if (ra->mmap_miss > 0)
1592        ra->mmap_miss--;
1593    if (PageReadahead(page))
1594        page_cache_async_readahead(mapping, ra, file,
1595                       page, offset, ra->ra_pages);
1596}
1597
1598/**
1599 * filemap_fault - read in file data for page fault handling
1600 * @vma: vma in which the fault was taken
1601 * @vmf: struct vm_fault containing details of the fault
1602 *
1603 * filemap_fault() is invoked via the vma operations vector for a
1604 * mapped memory region to read in file data during a page fault.
1605 *
1606 * The goto's are kind of ugly, but this streamlines the normal case of having
1607 * it in the page cache, and handles the special cases reasonably without
1608 * having a lot of duplicated code.
1609 */
1610int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
1611{
1612    int error;
1613    struct file *file = vma->vm_file;
1614    struct address_space *mapping = file->f_mapping;
1615    struct file_ra_state *ra = &file->f_ra;
1616    struct inode *inode = mapping->host;
1617    pgoff_t offset = vmf->pgoff;
1618    struct page *page;
1619    pgoff_t size;
1620    int ret = 0;
1621
1622    size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
1623    if (offset >= size)
1624        return VM_FAULT_SIGBUS;
1625
1626    /*
1627     * Do we have something in the page cache already?
1628     */
1629    page = find_get_page(mapping, offset);
1630    if (likely(page) && !(vmf->flags & FAULT_FLAG_TRIED)) {
1631        /*
1632         * We found the page, so try async readahead before
1633         * waiting for the lock.
1634         */
1635        do_async_mmap_readahead(vma, ra, file, page, offset);
1636    } else if (!page) {
1637        /* No page in the page cache at all */
1638        do_sync_mmap_readahead(vma, ra, file, offset);
1639        count_vm_event(PGMAJFAULT);
1640        mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
1641        ret = VM_FAULT_MAJOR;
1642retry_find:
1643        page = find_get_page(mapping, offset);
1644        if (!page)
1645            goto no_cached_page;
1646    }
1647
1648    if (!lock_page_or_retry(page, vma->vm_mm, vmf->flags)) {
1649        page_cache_release(page);
1650        return ret | VM_FAULT_RETRY;
1651    }
1652
1653    /* Did it get truncated? */
1654    if (unlikely(page->mapping != mapping)) {
1655        unlock_page(page);
1656        put_page(page);
1657        goto retry_find;
1658    }
1659    VM_BUG_ON(page->index != offset);
1660
1661    /*
1662     * We have a locked page in the page cache, now we need to check
1663     * that it's up-to-date. If not, it is going to be due to an error.
1664     */
1665    if (unlikely(!PageUptodate(page)))
1666        goto page_not_uptodate;
1667
1668    /*
1669     * Found the page and have a reference on it.
1670     * We must recheck i_size under page lock.
1671     */
1672    size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
1673    if (unlikely(offset >= size)) {
1674        unlock_page(page);
1675        page_cache_release(page);
1676        return VM_FAULT_SIGBUS;
1677    }
1678
1679    vmf->page = page;
1680    return ret | VM_FAULT_LOCKED;
1681
1682no_cached_page:
1683    /*
1684     * We're only likely to ever get here if MADV_RANDOM is in
1685     * effect.
1686     */
1687    error = page_cache_read(file, offset);
1688
1689    /*
1690     * The page we want has now been added to the page cache.
1691     * In the unlikely event that someone removed it in the
1692     * meantime, we'll just come back here and read it again.
1693     */
1694    if (error >= 0)
1695        goto retry_find;
1696
1697    /*
1698     * An error return from page_cache_read can result if the
1699     * system is low on memory, or a problem occurs while trying
1700     * to schedule I/O.
1701     */
1702    if (error == -ENOMEM)
1703        return VM_FAULT_OOM;
1704    return VM_FAULT_SIGBUS;
1705
1706page_not_uptodate:
1707    /*
1708     * Umm, take care of errors if the page isn't up-to-date.
1709     * Try to re-read it _once_. We do this synchronously,
1710     * because there really aren't any performance issues here
1711     * and we need to check for errors.
1712     */
1713    ClearPageError(page);
1714    error = mapping->a_ops->readpage(file, page);
1715    if (!error) {
1716        wait_on_page_locked(page);
1717        if (!PageUptodate(page))
1718            error = -EIO;
1719    }
1720    page_cache_release(page);
1721
1722    if (!error || error == AOP_TRUNCATED_PAGE)
1723        goto retry_find;
1724
1725    /* Things didn't work out. Return zero to tell the mm layer so. */
1726    shrink_readahead_size_eio(file, ra);
1727    return VM_FAULT_SIGBUS;
1728}
1729EXPORT_SYMBOL(filemap_fault);
1730
1731int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
1732{
1733    struct page *page = vmf->page;
1734    struct inode *inode = file_inode(vma->vm_file);
1735    int ret = VM_FAULT_LOCKED;
1736
1737    sb_start_pagefault(inode->i_sb);
1738    file_update_time(vma->vm_file);
1739    lock_page(page);
1740    if (page->mapping != inode->i_mapping) {
1741        unlock_page(page);
1742        ret = VM_FAULT_NOPAGE;
1743        goto out;
1744    }
1745    /*
1746     * We mark the page dirty already here so that when freeze is in
1747     * progress, we are guaranteed that writeback during freezing will
1748     * see the dirty page and writeprotect it again.
1749     */
1750    set_page_dirty(page);
1751    wait_for_stable_page(page);
1752out:
1753    sb_end_pagefault(inode->i_sb);
1754    return ret;
1755}
1756EXPORT_SYMBOL(filemap_page_mkwrite);
1757
1758const struct vm_operations_struct generic_file_vm_ops = {
1759    .fault = filemap_fault,
1760    .page_mkwrite = filemap_page_mkwrite,
1761    .remap_pages = generic_file_remap_pages,
1762};
1763
1764/* This is used for a general mmap of a disk file */
1765
1766int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
1767{
1768    struct address_space *mapping = file->f_mapping;
1769
1770    if (!mapping->a_ops->readpage)
1771        return -ENOEXEC;
1772    file_accessed(file);
1773    vma->vm_ops = &generic_file_vm_ops;
1774    return 0;
1775}
1776
1777/*
1778 * This is for filesystems which do not implement ->writepage.
1779 */
1780int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
1781{
1782    if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
1783        return -EINVAL;
1784    return generic_file_mmap(file, vma);
1785}
1786#else
1787int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
1788{
1789    return -ENOSYS;
1790}
1791int generic_file_readonly_mmap(struct file * file, struct vm_area_struct * vma)
1792{
1793    return -ENOSYS;
1794}
1795#endif /* CONFIG_MMU */
1796
1797EXPORT_SYMBOL(generic_file_mmap);
1798EXPORT_SYMBOL(generic_file_readonly_mmap);
1799
1800static struct page *__read_cache_page(struct address_space *mapping,
1801                pgoff_t index,
1802                int (*filler)(void *, struct page *),
1803                void *data,
1804                gfp_t gfp)
1805{
1806    struct page *page;
1807    int err;
1808repeat:
1809    page = find_get_page(mapping, index);
1810    if (!page) {
1811        page = __page_cache_alloc(gfp | __GFP_COLD);
1812        if (!page)
1813            return ERR_PTR(-ENOMEM);
1814        err = add_to_page_cache_lru(page, mapping, index, gfp);
1815        if (unlikely(err)) {
1816            page_cache_release(page);
1817            if (err == -EEXIST)
1818                goto repeat;
1819            /* Presumably ENOMEM for radix tree node */
1820            return ERR_PTR(err);
1821        }
1822        err = filler(data, page);
1823        if (err < 0) {
1824            page_cache_release(page);
1825            page = ERR_PTR(err);
1826        }
1827    }
1828    return page;
1829}
1830
1831static struct page *do_read_cache_page(struct address_space *mapping,
1832                pgoff_t index,
1833                int (*filler)(void *, struct page *),
1834                void *data,
1835                gfp_t gfp)
1836
1837{
1838    struct page *page;
1839    int err;
1840
1841retry:
1842    page = __read_cache_page(mapping, index, filler, data, gfp);
1843    if (IS_ERR(page))
1844        return page;
1845    if (PageUptodate(page))
1846        goto out;
1847
1848    lock_page(page);
1849    if (!page->mapping) {
1850        unlock_page(page);
1851        page_cache_release(page);
1852        goto retry;
1853    }
1854    if (PageUptodate(page)) {
1855        unlock_page(page);
1856        goto out;
1857    }
1858    err = filler(data, page);
1859    if (err < 0) {
1860        page_cache_release(page);
1861        return ERR_PTR(err);
1862    }
1863out:
1864    mark_page_accessed(page);
1865    return page;
1866}
1867
1868/**
1869 * read_cache_page_async - read into page cache, fill it if needed
1870 * @mapping: the page's address_space
1871 * @index: the page index
1872 * @filler: function to perform the read
1873 * @data: first arg to filler(data, page) function, often left as NULL
1874 *
1875 * Same as read_cache_page, but don't wait for page to become unlocked
1876 * after submitting it to the filler.
1877 *
1878 * Read into the page cache. If a page already exists, and PageUptodate() is
1879 * not set, try to fill the page but don't wait for it to become unlocked.
1880 *
1881 * If the page does not get brought uptodate, return -EIO.
1882 */
1883struct page *read_cache_page_async(struct address_space *mapping,
1884                pgoff_t index,
1885                int (*filler)(void *, struct page *),
1886                void *data)
1887{
1888    return do_read_cache_page(mapping, index, filler, data, mapping_gfp_mask(mapping));
1889}
1890EXPORT_SYMBOL(read_cache_page_async);
1891
1892static struct page *wait_on_page_read(struct page *page)
1893{
1894    if (!IS_ERR(page)) {
1895        wait_on_page_locked(page);
1896        if (!PageUptodate(page)) {
1897            page_cache_release(page);
1898            page = ERR_PTR(-EIO);
1899        }
1900    }
1901    return page;
1902}
1903
1904/**
1905 * read_cache_page_gfp - read into page cache, using specified page allocation flags.
1906 * @mapping: the page's address_space
1907 * @index: the page index
1908 * @gfp: the page allocator flags to use if allocating
1909 *
1910 * This is the same as "read_mapping_page(mapping, index, NULL)", but with
1911 * any new page allocations done using the specified allocation flags.
1912 *
1913 * If the page does not get brought uptodate, return -EIO.
1914 */
1915struct page *read_cache_page_gfp(struct address_space *mapping,
1916                pgoff_t index,
1917                gfp_t gfp)
1918{
1919    filler_t *filler = (filler_t *)mapping->a_ops->readpage;
1920
1921    return wait_on_page_read(do_read_cache_page(mapping, index, filler, NULL, gfp));
1922}
1923EXPORT_SYMBOL(read_cache_page_gfp);
1924
1925/**
1926 * read_cache_page - read into page cache, fill it if needed
1927 * @mapping: the page's address_space
1928 * @index: the page index
1929 * @filler: function to perform the read
1930 * @data: first arg to filler(data, page) function, often left as NULL
1931 *
1932 * Read into the page cache. If a page already exists, and PageUptodate() is
1933 * not set, try to fill the page then wait for it to become unlocked.
1934 *
1935 * If the page does not get brought uptodate, return -EIO.
1936 */
1937struct page *read_cache_page(struct address_space *mapping,
1938                pgoff_t index,
1939                int (*filler)(void *, struct page *),
1940                void *data)
1941{
1942    return wait_on_page_read(read_cache_page_async(mapping, index, filler, data));
1943}
1944EXPORT_SYMBOL(read_cache_page);
1945
1946static size_t __iovec_copy_from_user_inatomic(char *vaddr,
1947            const struct iovec *iov, size_t base, size_t bytes)
1948{
1949    size_t copied = 0, left = 0;
1950
1951    while (bytes) {
1952        char __user *buf = iov->iov_base + base;
1953        int copy = min(bytes, iov->iov_len - base);
1954
1955        base = 0;
1956        left = __copy_from_user_inatomic(vaddr, buf, copy);
1957        copied += copy;
1958        bytes -= copy;
1959        vaddr += copy;
1960        iov++;
1961
1962        if (unlikely(left))
1963            break;
1964    }
1965    return copied - left;
1966}
1967
1968/*
1969 * Copy as much as we can into the page and return the number of bytes which
1970 * were successfully copied. If a fault is encountered then return the number of
1971 * bytes which were copied.
1972 */
1973size_t iov_iter_copy_from_user_atomic(struct page *page,
1974        struct iov_iter *i, unsigned long offset, size_t bytes)
1975{
1976    char *kaddr;
1977    size_t copied;
1978
1979    BUG_ON(!in_atomic());
1980    kaddr = kmap_atomic(page);
1981    if (likely(i->nr_segs == 1)) {
1982        int left;
1983        char __user *buf = i->iov->iov_base + i->iov_offset;
1984        left = __copy_from_user_inatomic(kaddr + offset, buf, bytes);
1985        copied = bytes - left;
1986    } else {
1987        copied = __iovec_copy_from_user_inatomic(kaddr + offset,
1988                        i->iov, i->iov_offset, bytes);
1989    }
1990    kunmap_atomic(kaddr);
1991
1992    return copied;
1993}
1994EXPORT_SYMBOL(iov_iter_copy_from_user_atomic);
1995
1996/*
1997 * This has the same sideeffects and return value as
1998 * iov_iter_copy_from_user_atomic().
1999 * The difference is that it attempts to resolve faults.
2000 * Page must not be locked.
2001 */
2002size_t iov_iter_copy_from_user(struct page *page,
2003        struct iov_iter *i, unsigned long offset, size_t bytes)
2004{
2005    char *kaddr;
2006    size_t copied;
2007
2008    kaddr = kmap(page);
2009    if (likely(i->nr_segs == 1)) {
2010        int left;
2011        char __user *buf = i->iov->iov_base + i->iov_offset;
2012        left = __copy_from_user(kaddr + offset, buf, bytes);
2013        copied = bytes - left;
2014    } else {
2015        copied = __iovec_copy_from_user_inatomic(kaddr + offset,
2016                        i->iov, i->iov_offset, bytes);
2017    }
2018    kunmap(page);
2019    return copied;
2020}
2021EXPORT_SYMBOL(iov_iter_copy_from_user);
2022
2023void iov_iter_advance(struct iov_iter *i, size_t bytes)
2024{
2025    BUG_ON(i->count < bytes);
2026
2027    if (likely(i->nr_segs == 1)) {
2028        i->iov_offset += bytes;
2029        i->count -= bytes;
2030    } else {
2031        const struct iovec *iov = i->iov;
2032        size_t base = i->iov_offset;
2033        unsigned long nr_segs = i->nr_segs;
2034
2035        /*
2036         * The !iov->iov_len check ensures we skip over unlikely
2037         * zero-length segments (without overruning the iovec).
2038         */
2039        while (bytes || unlikely(i->count && !iov->iov_len)) {
2040            int copy;
2041
2042            copy = min(bytes, iov->iov_len - base);
2043            BUG_ON(!i->count || i->count < copy);
2044            i->count -= copy;
2045            bytes -= copy;
2046            base += copy;
2047            if (iov->iov_len == base) {
2048                iov++;
2049                nr_segs--;
2050                base = 0;
2051            }
2052        }
2053        i->iov = iov;
2054        i->iov_offset = base;
2055        i->nr_segs = nr_segs;
2056    }
2057}
2058EXPORT_SYMBOL(iov_iter_advance);
2059
2060/*
2061 * Fault in the first iovec of the given iov_iter, to a maximum length
2062 * of bytes. Returns 0 on success, or non-zero if the memory could not be
2063 * accessed (ie. because it is an invalid address).
2064 *
2065 * writev-intensive code may want this to prefault several iovecs -- that
2066 * would be possible (callers must not rely on the fact that _only_ the
2067 * first iovec will be faulted with the current implementation).
2068 */
2069int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
2070{
2071    char __user *buf = i->iov->iov_base + i->iov_offset;
2072    bytes = min(bytes, i->iov->iov_len - i->iov_offset);
2073    return fault_in_pages_readable(buf, bytes);
2074}
2075EXPORT_SYMBOL(iov_iter_fault_in_readable);
2076
2077/*
2078 * Return the count of just the current iov_iter segment.
2079 */
2080size_t iov_iter_single_seg_count(const struct iov_iter *i)
2081{
2082    const struct iovec *iov = i->iov;
2083    if (i->nr_segs == 1)
2084        return i->count;
2085    else
2086        return min(i->count, iov->iov_len - i->iov_offset);
2087}
2088EXPORT_SYMBOL(iov_iter_single_seg_count);
2089
2090/*
2091 * Performs necessary checks before doing a write
2092 *
2093 * Can adjust writing position or amount of bytes to write.
2094 * Returns appropriate error code that caller should return or
2095 * zero in case that write should be allowed.
2096 */
2097inline int generic_write_checks(struct file *file, loff_t *pos, size_t *count, int isblk)
2098{
2099    struct inode *inode = file->f_mapping->host;
2100    unsigned long limit = rlimit(RLIMIT_FSIZE);
2101
2102        if (unlikely(*pos < 0))
2103                return -EINVAL;
2104
2105    if (!isblk) {
2106        /* FIXME: this is for backwards compatibility with 2.4 */
2107        if (file->f_flags & O_APPEND)
2108                        *pos = i_size_read(inode);
2109
2110        if (limit != RLIM_INFINITY) {
2111            if (*pos >= limit) {
2112                send_sig(SIGXFSZ, current, 0);
2113                return -EFBIG;
2114            }
2115            if (*count > limit - (typeof(limit))*pos) {
2116                *count = limit - (typeof(limit))*pos;
2117            }
2118        }
2119    }
2120
2121    /*
2122     * LFS rule
2123     */
2124    if (unlikely(*pos + *count > MAX_NON_LFS &&
2125                !(file->f_flags & O_LARGEFILE))) {
2126        if (*pos >= MAX_NON_LFS) {
2127            return -EFBIG;
2128        }
2129        if (*count > MAX_NON_LFS - (unsigned long)*pos) {
2130            *count = MAX_NON_LFS - (unsigned long)*pos;
2131        }
2132    }
2133
2134    /*
2135     * Are we about to exceed the fs block limit ?
2136     *
2137     * If we have written data it becomes a short write. If we have
2138     * exceeded without writing data we send a signal and return EFBIG.
2139     * Linus frestrict idea will clean these up nicely..
2140     */
2141    if (likely(!isblk)) {
2142        if (unlikely(*pos >= inode->i_sb->s_maxbytes)) {
2143            if (*count || *pos > inode->i_sb->s_maxbytes) {
2144                return -EFBIG;
2145            }
2146            /* zero-length writes at ->s_maxbytes are OK */
2147        }
2148
2149        if (unlikely(*pos + *count > inode->i_sb->s_maxbytes))
2150            *count = inode->i_sb->s_maxbytes - *pos;
2151    } else {
2152#ifdef CONFIG_BLOCK
2153        loff_t isize;
2154        if (bdev_read_only(I_BDEV(inode)))
2155            return -EPERM;
2156        isize = i_size_read(inode);
2157        if (*pos >= isize) {
2158            if (*count || *pos > isize)
2159                return -ENOSPC;
2160        }
2161
2162        if (*pos + *count > isize)
2163            *count = isize - *pos;
2164#else
2165        return -EPERM;
2166#endif
2167    }
2168    return 0;
2169}
2170EXPORT_SYMBOL(generic_write_checks);
2171
2172int pagecache_write_begin(struct file *file, struct address_space *mapping,
2173                loff_t pos, unsigned len, unsigned flags,
2174                struct page **pagep, void **fsdata)
2175{
2176    const struct address_space_operations *aops = mapping->a_ops;
2177
2178    return aops->write_begin(file, mapping, pos, len, flags,
2179                            pagep, fsdata);
2180}
2181EXPORT_SYMBOL(pagecache_write_begin);
2182
2183int pagecache_write_end(struct file *file, struct address_space *mapping,
2184                loff_t pos, unsigned len, unsigned copied,
2185                struct page *page, void *fsdata)
2186{
2187    const struct address_space_operations *aops = mapping->a_ops;
2188
2189    mark_page_accessed(page);
2190    return aops->write_end(file, mapping, pos, len, copied, page, fsdata);
2191}
2192EXPORT_SYMBOL(pagecache_write_end);
2193
2194ssize_t
2195generic_file_direct_write(struct kiocb *iocb, const struct iovec *iov,
2196        unsigned long *nr_segs, loff_t pos, loff_t *ppos,
2197        size_t count, size_t ocount)
2198{
2199    struct file *file = iocb->ki_filp;
2200    struct address_space *mapping = file->f_mapping;
2201    struct inode *inode = mapping->host;
2202    ssize_t written;
2203    size_t write_len;
2204    pgoff_t end;
2205
2206    if (count != ocount)
2207        *nr_segs = iov_shorten((struct iovec *)iov, *nr_segs, count);
2208
2209    write_len = iov_length(iov, *nr_segs);
2210    end = (pos + write_len - 1) >> PAGE_CACHE_SHIFT;
2211
2212    written = filemap_write_and_wait_range(mapping, pos, pos + write_len - 1);
2213    if (written)
2214        goto out;
2215
2216    /*
2217     * After a write we want buffered reads to be sure to go to disk to get
2218     * the new data. We invalidate clean cached page from the region we're
2219     * about to write. We do this *before* the write so that we can return
2220     * without clobbering -EIOCBQUEUED from ->direct_IO().
2221     */
2222    if (mapping->nrpages) {
2223        written = invalidate_inode_pages2_range(mapping,
2224                    pos >> PAGE_CACHE_SHIFT, end);
2225        /*
2226         * If a page can not be invalidated, return 0 to fall back
2227         * to buffered write.
2228         */
2229        if (written) {
2230            if (written == -EBUSY)
2231                return 0;
2232            goto out;
2233        }
2234    }
2235
2236    written = mapping->a_ops->direct_IO(WRITE, iocb, iov, pos, *nr_segs);
2237
2238    /*
2239     * Finally, try again to invalidate clean pages which might have been
2240     * cached by non-direct readahead, or faulted in by get_user_pages()
2241     * if the source of the write was an mmap'ed region of the file
2242     * we're writing. Either one is a pretty crazy thing to do,
2243     * so we don't support it 100%. If this invalidation
2244     * fails, tough, the write still worked...
2245     */
2246    if (mapping->nrpages) {
2247        invalidate_inode_pages2_range(mapping,
2248                          pos >> PAGE_CACHE_SHIFT, end);
2249    }
2250
2251    if (written > 0) {
2252        pos += written;
2253        if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
2254            i_size_write(inode, pos);
2255            mark_inode_dirty(inode);
2256        }
2257        *ppos = pos;
2258    }
2259out:
2260    return written;
2261}
2262EXPORT_SYMBOL(generic_file_direct_write);
2263
2264/*
2265 * Find or create a page at the given pagecache position. Return the locked
2266 * page. This function is specifically for buffered writes.
2267 */
2268struct page *grab_cache_page_write_begin(struct address_space *mapping,
2269                    pgoff_t index, unsigned flags)
2270{
2271    int status;
2272    gfp_t gfp_mask;
2273    struct page *page;
2274    gfp_t gfp_notmask = 0;
2275
2276    gfp_mask = mapping_gfp_mask(mapping);
2277    if (mapping_cap_account_dirty(mapping))
2278        gfp_mask |= __GFP_WRITE;
2279    if (flags & AOP_FLAG_NOFS)
2280        gfp_notmask = __GFP_FS;
2281repeat:
2282    page = find_lock_page(mapping, index);
2283    if (page)
2284        goto found;
2285
2286    page = __page_cache_alloc(gfp_mask & ~gfp_notmask);
2287    if (!page)
2288        return NULL;
2289    status = add_to_page_cache_lru(page, mapping, index,
2290                        GFP_KERNEL & ~gfp_notmask);
2291    if (unlikely(status)) {
2292        page_cache_release(page);
2293        if (status == -EEXIST)
2294            goto repeat;
2295        return NULL;
2296    }
2297found:
2298    wait_for_stable_page(page);
2299    return page;
2300}
2301EXPORT_SYMBOL(grab_cache_page_write_begin);
2302
2303static ssize_t generic_perform_write(struct file *file,
2304                struct iov_iter *i, loff_t pos)
2305{
2306    struct address_space *mapping = file->f_mapping;
2307    const struct address_space_operations *a_ops = mapping->a_ops;
2308    long status = 0;
2309    ssize_t written = 0;
2310    unsigned int flags = 0;
2311
2312    /*
2313     * Copies from kernel address space cannot fail (NFSD is a big user).
2314     */
2315    if (segment_eq(get_fs(), KERNEL_DS))
2316        flags |= AOP_FLAG_UNINTERRUPTIBLE;
2317
2318    do {
2319        struct page *page;
2320        unsigned long offset; /* Offset into pagecache page */
2321        unsigned long bytes; /* Bytes to write to page */
2322        size_t copied; /* Bytes copied from user */
2323        void *fsdata;
2324
2325        offset = (pos & (PAGE_CACHE_SIZE - 1));
2326        bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
2327                        iov_iter_count(i));
2328
2329again:
2330        /*
2331         * Bring in the user page that we will copy from _first_.
2332         * Otherwise there's a nasty deadlock on copying from the
2333         * same page as we're writing to, without it being marked
2334         * up-to-date.
2335         *
2336         * Not only is this an optimisation, but it is also required
2337         * to check that the address is actually valid, when atomic
2338         * usercopies are used, below.
2339         */
2340        if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
2341            status = -EFAULT;
2342            break;
2343        }
2344
2345        status = a_ops->write_begin(file, mapping, pos, bytes, flags,
2346                        &page, &fsdata);
2347        if (unlikely(status))
2348            break;
2349
2350        if (mapping_writably_mapped(mapping))
2351            flush_dcache_page(page);
2352
2353        pagefault_disable();
2354        copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
2355        pagefault_enable();
2356        flush_dcache_page(page);
2357
2358        mark_page_accessed(page);
2359        status = a_ops->write_end(file, mapping, pos, bytes, copied,
2360                        page, fsdata);
2361        if (unlikely(status < 0))
2362            break;
2363        copied = status;
2364
2365        cond_resched();
2366
2367        iov_iter_advance(i, copied);
2368        if (unlikely(copied == 0)) {
2369            /*
2370             * If we were unable to copy any data at all, we must
2371             * fall back to a single segment length write.
2372             *
2373             * If we didn't fallback here, we could livelock
2374             * because not all segments in the iov can be copied at
2375             * once without a pagefault.
2376             */
2377            bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
2378                        iov_iter_single_seg_count(i));
2379            goto again;
2380        }
2381        pos += copied;
2382        written += copied;
2383
2384        balance_dirty_pages_ratelimited(mapping);
2385        if (fatal_signal_pending(current)) {
2386            status = -EINTR;
2387            break;
2388        }
2389    } while (iov_iter_count(i));
2390
2391    return written ? written : status;
2392}
2393
2394ssize_t
2395generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
2396        unsigned long nr_segs, loff_t pos, loff_t *ppos,
2397        size_t count, ssize_t written)
2398{
2399    struct file *file = iocb->ki_filp;
2400    ssize_t status;
2401    struct iov_iter i;
2402
2403    iov_iter_init(&i, iov, nr_segs, count, written);
2404    status = generic_perform_write(file, &i, pos);
2405
2406    if (likely(status >= 0)) {
2407        written += status;
2408        *ppos = pos + status;
2409      }
2410    
2411    return written ? written : status;
2412}
2413EXPORT_SYMBOL(generic_file_buffered_write);
2414
2415/**
2416 * __generic_file_aio_write - write data to a file
2417 * @iocb: IO state structure (file, offset, etc.)
2418 * @iov: vector with data to write
2419 * @nr_segs: number of segments in the vector
2420 * @ppos: position where to write
2421 *
2422 * This function does all the work needed for actually writing data to a
2423 * file. It does all basic checks, removes SUID from the file, updates
2424 * modification times and calls proper subroutines depending on whether we
2425 * do direct IO or a standard buffered write.
2426 *
2427 * It expects i_mutex to be grabbed unless we work on a block device or similar
2428 * object which does not need locking at all.
2429 *
2430 * This function does *not* take care of syncing data in case of O_SYNC write.
2431 * A caller has to handle it. This is mainly due to the fact that we want to
2432 * avoid syncing under i_mutex.
2433 */
2434ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
2435                 unsigned long nr_segs, loff_t *ppos)
2436{
2437    struct file *file = iocb->ki_filp;
2438    struct address_space * mapping = file->f_mapping;
2439    size_t ocount; /* original count */
2440    size_t count; /* after file limit checks */
2441    struct inode *inode = mapping->host;
2442    loff_t pos;
2443    ssize_t written;
2444    ssize_t err;
2445
2446    ocount = 0;
2447    err = generic_segment_checks(iov, &nr_segs, &ocount, VERIFY_READ);
2448    if (err)
2449        return err;
2450
2451    count = ocount;
2452    pos = *ppos;
2453
2454    /* We can write back this queue in page reclaim */
2455    current->backing_dev_info = mapping->backing_dev_info;
2456    written = 0;
2457
2458    err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));
2459    if (err)
2460        goto out;
2461
2462    if (count == 0)
2463        goto out;
2464
2465    err = file_remove_suid(file);
2466    if (err)
2467        goto out;
2468
2469    err = file_update_time(file);
2470    if (err)
2471        goto out;
2472
2473    /* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
2474    if (unlikely(file->f_flags & O_DIRECT)) {
2475        loff_t endbyte;
2476        ssize_t written_buffered;
2477
2478        written = generic_file_direct_write(iocb, iov, &nr_segs, pos,
2479                            ppos, count, ocount);
2480        if (written < 0 || written == count)
2481            goto out;
2482        /*
2483         * direct-io write to a hole: fall through to buffered I/O
2484         * for completing the rest of the request.
2485         */
2486        pos += written;
2487        count -= written;
2488        written_buffered = generic_file_buffered_write(iocb, iov,
2489                        nr_segs, pos, ppos, count,
2490                        written);
2491        /*
2492         * If generic_file_buffered_write() retuned a synchronous error
2493         * then we want to return the number of bytes which were
2494         * direct-written, or the error code if that was zero. Note
2495         * that this differs from normal direct-io semantics, which
2496         * will return -EFOO even if some bytes were written.
2497         */
2498        if (written_buffered < 0) {
2499            err = written_buffered;
2500            goto out;
2501        }
2502
2503        /*
2504         * We need to ensure that the page cache pages are written to
2505         * disk and invalidated to preserve the expected O_DIRECT
2506         * semantics.
2507         */
2508        endbyte = pos + written_buffered - written - 1;
2509        err = filemap_write_and_wait_range(file->f_mapping, pos, endbyte);
2510        if (err == 0) {
2511            written = written_buffered;
2512            invalidate_mapping_pages(mapping,
2513                         pos >> PAGE_CACHE_SHIFT,
2514                         endbyte >> PAGE_CACHE_SHIFT);
2515        } else {
2516            /*
2517             * We don't know how much we wrote, so just return
2518             * the number of bytes which were direct-written
2519             */
2520        }
2521    } else {
2522        written = generic_file_buffered_write(iocb, iov, nr_segs,
2523                pos, ppos, count, written);
2524    }
2525out:
2526    current->backing_dev_info = NULL;
2527    return written ? written : err;
2528}
2529EXPORT_SYMBOL(__generic_file_aio_write);
2530
2531/**
2532 * generic_file_aio_write - write data to a file
2533 * @iocb: IO state structure
2534 * @iov: vector with data to write
2535 * @nr_segs: number of segments in the vector
2536 * @pos: position in file where to write
2537 *
2538 * This is a wrapper around __generic_file_aio_write() to be used by most
2539 * filesystems. It takes care of syncing the file in case of O_SYNC file
2540 * and acquires i_mutex as needed.
2541 */
2542ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
2543        unsigned long nr_segs, loff_t pos)
2544{
2545    struct file *file = iocb->ki_filp;
2546    struct inode *inode = file->f_mapping->host;
2547    ssize_t ret;
2548
2549    BUG_ON(iocb->ki_pos != pos);
2550
2551    mutex_lock(&inode->i_mutex);
2552    ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
2553    mutex_unlock(&inode->i_mutex);
2554
2555    if (ret > 0) {
2556        ssize_t err;
2557
2558        err = generic_write_sync(file, pos, ret);
2559        if (err < 0 && ret > 0)
2560            ret = err;
2561    }
2562    return ret;
2563}
2564EXPORT_SYMBOL(generic_file_aio_write);
2565
2566/**
2567 * try_to_release_page() - release old fs-specific metadata on a page
2568 *
2569 * @page: the page which the kernel is trying to free
2570 * @gfp_mask: memory allocation flags (and I/O mode)
2571 *
2572 * The address_space is to try to release any data against the page
2573 * (presumably at page->private). If the release was successful, return `1'.
2574 * Otherwise return zero.
2575 *
2576 * This may also be called if PG_fscache is set on a page, indicating that the
2577 * page is known to the local caching routines.
2578 *
2579 * The @gfp_mask argument specifies whether I/O may be performed to release
2580 * this page (__GFP_IO), and whether the call may block (__GFP_WAIT & __GFP_FS).
2581 *
2582 */
2583int try_to_release_page(struct page *page, gfp_t gfp_mask)
2584{
2585    struct address_space * const mapping = page->mapping;
2586
2587    BUG_ON(!PageLocked(page));
2588    if (PageWriteback(page))
2589        return 0;
2590
2591    if (mapping && mapping->a_ops->releasepage)
2592        return mapping->a_ops->releasepage(page, gfp_mask);
2593    return try_to_free_buffers(page);
2594}
2595
2596EXPORT_SYMBOL(try_to_release_page);
2597

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