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

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