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 <linux/cleancache.h>
38#include "internal.h"
39
40/*
41 * FIXME: remove all knowledge of the buffer layer from the core VM
42 */
43#include <linux/buffer_head.h> /* for try_to_free_buffers */
44
45#include <asm/mman.h>
46
47/*
48 * Shared mappings implemented 30.11.1994. It's not fully working yet,
49 * though.
50 *
51 * Shared mappings now work. 15.8.1995 Bruno.
52 *
53 * finished 'unifying' the page and buffer cache and SMP-threaded the
54 * page-cache, 21.05.1999, Ingo Molnar <mingo@redhat.com>
55 *
56 * SMP-threaded pagemap-LRU 1999, Andrea Arcangeli <andrea@suse.de>
57 */
58
59/*
60 * Lock ordering:
61 *
62 * ->i_mmap_mutex (truncate_pagecache)
63 * ->private_lock (__free_pte->__set_page_dirty_buffers)
64 * ->swap_lock (exclusive_swap_page, others)
65 * ->mapping->tree_lock
66 *
67 * ->i_mutex
68 * ->i_mmap_mutex (truncate->unmap_mapping_range)
69 *
70 * ->mmap_sem
71 * ->i_mmap_mutex
72 * ->page_table_lock or pte_lock (various, mainly in memory.c)
73 * ->mapping->tree_lock (arch-dependent flush_dcache_mmap_lock)
74 *
75 * ->mmap_sem
76 * ->lock_page (access_process_vm)
77 *
78 * ->i_mutex (generic_file_buffered_write)
79 * ->mmap_sem (fault_in_pages_readable->do_page_fault)
80 *
81 * ->i_mutex
82 * ->i_alloc_sem (various)
83 *
84 * inode_wb_list_lock
85 * sb_lock (fs/fs-writeback.c)
86 * ->mapping->tree_lock (__sync_single_inode)
87 *
88 * ->i_mmap_mutex
89 * ->anon_vma.lock (vma_adjust)
90 *
91 * ->anon_vma.lock
92 * ->page_table_lock or pte_lock (anon_vma_prepare and various)
93 *
94 * ->page_table_lock or pte_lock
95 * ->swap_lock (try_to_unmap_one)
96 * ->private_lock (try_to_unmap_one)
97 * ->tree_lock (try_to_unmap_one)
98 * ->zone.lru_lock (follow_page->mark_page_accessed)
99 * ->zone.lru_lock (check_pte_range->isolate_lru_page)
100 * ->private_lock (page_remove_rmap->set_page_dirty)
101 * ->tree_lock (page_remove_rmap->set_page_dirty)
102 * inode_wb_list_lock (page_remove_rmap->set_page_dirty)
103 * ->inode->i_lock (page_remove_rmap->set_page_dirty)
104 * inode_wb_list_lock (zap_pte_range->set_page_dirty)
105 * ->inode->i_lock (zap_pte_range->set_page_dirty)
106 * ->private_lock (zap_pte_range->__set_page_dirty_buffers)
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_mutex
111 */
112
113/*
114 * Delete 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 __delete_from_page_cache(struct page *page)
119{
120    struct address_space *mapping = page->mapping;
121
122    /*
123     * if we're uptodate, flush out into the cleancache, otherwise
124     * invalidate any existing cleancache entries. We can't leave
125     * stale data around in the cleancache once our page is gone
126     */
127    if (PageUptodate(page) && PageMappedToDisk(page))
128        cleancache_put_page(page);
129    else
130        cleancache_flush_page(mapping, page);
131
132    radix_tree_delete(&mapping->page_tree, page->index);
133    page->mapping = NULL;
134    mapping->nrpages--;
135    __dec_zone_page_state(page, NR_FILE_PAGES);
136    if (PageSwapBacked(page))
137        __dec_zone_page_state(page, NR_SHMEM);
138    BUG_ON(page_mapped(page));
139
140    /*
141     * Some filesystems seem to re-dirty the page even after
142     * the VM has canceled the dirty bit (eg ext3 journaling).
143     *
144     * Fix it up by doing a final dirty accounting check after
145     * having removed the page entirely.
146     */
147    if (PageDirty(page) && mapping_cap_account_dirty(mapping)) {
148        dec_zone_page_state(page, NR_FILE_DIRTY);
149        dec_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
150    }
151}
152
153/**
154 * delete_from_page_cache - delete page from page cache
155 * @page: the page which the kernel is trying to remove from page cache
156 *
157 * This must be called only on pages that have been verified to be in the page
158 * cache and locked. It will never put the page into the free list, the caller
159 * has a reference on the page.
160 */
161void delete_from_page_cache(struct page *page)
162{
163    struct address_space *mapping = page->mapping;
164    void (*freepage)(struct page *);
165
166    BUG_ON(!PageLocked(page));
167
168    freepage = mapping->a_ops->freepage;
169    spin_lock_irq(&mapping->tree_lock);
170    __delete_from_page_cache(page);
171    spin_unlock_irq(&mapping->tree_lock);
172    mem_cgroup_uncharge_cache_page(page);
173
174    if (freepage)
175        freepage(page);
176    page_cache_release(page);
177}
178EXPORT_SYMBOL(delete_from_page_cache);
179
180static int sleep_on_page(void *word)
181{
182    io_schedule();
183    return 0;
184}
185
186static int sleep_on_page_killable(void *word)
187{
188    sleep_on_page(word);
189    return fatal_signal_pending(current) ? -EINTR : 0;
190}
191
192/**
193 * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
194 * @mapping: address space structure to write
195 * @start: offset in bytes where the range starts
196 * @end: offset in bytes where the range ends (inclusive)
197 * @sync_mode: enable synchronous operation
198 *
199 * Start writeback against all of a mapping's dirty pages that lie
200 * within the byte offsets <start, end> inclusive.
201 *
202 * If sync_mode is WB_SYNC_ALL then this is a "data integrity" operation, as
203 * opposed to a regular memory cleansing writeback. The difference between
204 * these two operations is that if a dirty page/buffer is encountered, it must
205 * be waited upon, and not just skipped over.
206 */
207int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
208                loff_t end, int sync_mode)
209{
210    int ret;
211    struct writeback_control wbc = {
212        .sync_mode = sync_mode,
213        .nr_to_write = LONG_MAX,
214        .range_start = start,
215        .range_end = end,
216    };
217
218    if (!mapping_cap_writeback_dirty(mapping))
219        return 0;
220
221    ret = do_writepages(mapping, &wbc);
222    return ret;
223}
224
225static inline int __filemap_fdatawrite(struct address_space *mapping,
226    int sync_mode)
227{
228    return __filemap_fdatawrite_range(mapping, 0, LLONG_MAX, sync_mode);
229}
230
231int filemap_fdatawrite(struct address_space *mapping)
232{
233    return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
234}
235EXPORT_SYMBOL(filemap_fdatawrite);
236
237int filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
238                loff_t end)
239{
240    return __filemap_fdatawrite_range(mapping, start, end, WB_SYNC_ALL);
241}
242EXPORT_SYMBOL(filemap_fdatawrite_range);
243
244/**
245 * filemap_flush - mostly a non-blocking flush
246 * @mapping: target address_space
247 *
248 * This is a mostly non-blocking flush. Not suitable for data-integrity
249 * purposes - I/O may not be started against all dirty pages.
250 */
251int filemap_flush(struct address_space *mapping)
252{
253    return __filemap_fdatawrite(mapping, WB_SYNC_NONE);
254}
255EXPORT_SYMBOL(filemap_flush);
256
257/**
258 * filemap_fdatawait_range - wait for writeback to complete
259 * @mapping: address space structure to wait for
260 * @start_byte: offset in bytes where the range starts
261 * @end_byte: offset in bytes where the range ends (inclusive)
262 *
263 * Walk the list of under-writeback pages of the given address space
264 * in the given range and wait for all of them.
265 */
266int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
267                loff_t end_byte)
268{
269    pgoff_t index = start_byte >> PAGE_CACHE_SHIFT;
270    pgoff_t end = end_byte >> PAGE_CACHE_SHIFT;
271    struct pagevec pvec;
272    int nr_pages;
273    int ret = 0;
274
275    if (end_byte < start_byte)
276        return 0;
277
278    pagevec_init(&pvec, 0);
279    while ((index <= end) &&
280            (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
281            PAGECACHE_TAG_WRITEBACK,
282            min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1)) != 0) {
283        unsigned i;
284
285        for (i = 0; i < nr_pages; i++) {
286            struct page *page = pvec.pages[i];
287
288            /* until radix tree lookup accepts end_index */
289            if (page->index > end)
290                continue;
291
292            wait_on_page_writeback(page);
293            if (TestClearPageError(page))
294                ret = -EIO;
295        }
296        pagevec_release(&pvec);
297        cond_resched();
298    }
299
300    /* Check for outstanding write errors */
301    if (test_and_clear_bit(AS_ENOSPC, &mapping->flags))
302        ret = -ENOSPC;
303    if (test_and_clear_bit(AS_EIO, &mapping->flags))
304        ret = -EIO;
305
306    return ret;
307}
308EXPORT_SYMBOL(filemap_fdatawait_range);
309
310/**
311 * filemap_fdatawait - wait for all under-writeback pages to complete
312 * @mapping: address space structure to wait for
313 *
314 * Walk the list of under-writeback pages of the given address space
315 * and wait for all of them.
316 */
317int filemap_fdatawait(struct address_space *mapping)
318{
319    loff_t i_size = i_size_read(mapping->host);
320
321    if (i_size == 0)
322        return 0;
323
324    return filemap_fdatawait_range(mapping, 0, i_size - 1);
325}
326EXPORT_SYMBOL(filemap_fdatawait);
327
328int filemap_write_and_wait(struct address_space *mapping)
329{
330    int err = 0;
331
332    if (mapping->nrpages) {
333        err = filemap_fdatawrite(mapping);
334        /*
335         * Even if the above returned error, the pages may be
336         * written partially (e.g. -ENOSPC), so we wait for it.
337         * But the -EIO is special case, it may indicate the worst
338         * thing (e.g. bug) happened, so we avoid waiting for it.
339         */
340        if (err != -EIO) {
341            int err2 = filemap_fdatawait(mapping);
342            if (!err)
343                err = err2;
344        }
345    }
346    return err;
347}
348EXPORT_SYMBOL(filemap_write_and_wait);
349
350/**
351 * filemap_write_and_wait_range - write out & wait on a file range
352 * @mapping: the address_space for the pages
353 * @lstart: offset in bytes where the range starts
354 * @lend: offset in bytes where the range ends (inclusive)
355 *
356 * Write out and wait upon file offsets lstart->lend, inclusive.
357 *
358 * Note that `lend' is inclusive (describes the last byte to be written) so
359 * that this function can be used to write to the very end-of-file (end = -1).
360 */
361int filemap_write_and_wait_range(struct address_space *mapping,
362                 loff_t lstart, loff_t lend)
363{
364    int err = 0;
365
366    if (mapping->nrpages) {
367        err = __filemap_fdatawrite_range(mapping, lstart, lend,
368                         WB_SYNC_ALL);
369        /* See comment of filemap_write_and_wait() */
370        if (err != -EIO) {
371            int err2 = filemap_fdatawait_range(mapping,
372                        lstart, lend);
373            if (!err)
374                err = err2;
375        }
376    }
377    return err;
378}
379EXPORT_SYMBOL(filemap_write_and_wait_range);
380
381/**
382 * replace_page_cache_page - replace a pagecache page with a new one
383 * @old: page to be replaced
384 * @new: page to replace with
385 * @gfp_mask: allocation mode
386 *
387 * This function replaces a page in the pagecache with a new one. On
388 * success it acquires the pagecache reference for the new page and
389 * drops it for the old page. Both the old and new pages must be
390 * locked. This function does not add the new page to the LRU, the
391 * caller must do that.
392 *
393 * The remove + add is atomic. The only way this function can fail is
394 * memory allocation failure.
395 */
396int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
397{
398    int error;
399    struct mem_cgroup *memcg = NULL;
400
401    VM_BUG_ON(!PageLocked(old));
402    VM_BUG_ON(!PageLocked(new));
403    VM_BUG_ON(new->mapping);
404
405    /*
406     * This is not page migration, but prepare_migration and
407     * end_migration does enough work for charge replacement.
408     *
409     * In the longer term we probably want a specialized function
410     * for moving the charge from old to new in a more efficient
411     * manner.
412     */
413    error = mem_cgroup_prepare_migration(old, new, &memcg, gfp_mask);
414    if (error)
415        return error;
416
417    error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
418    if (!error) {
419        struct address_space *mapping = old->mapping;
420        void (*freepage)(struct page *);
421
422        pgoff_t offset = old->index;
423        freepage = mapping->a_ops->freepage;
424
425        page_cache_get(new);
426        new->mapping = mapping;
427        new->index = offset;
428
429        spin_lock_irq(&mapping->tree_lock);
430        __delete_from_page_cache(old);
431        error = radix_tree_insert(&mapping->page_tree, offset, new);
432        BUG_ON(error);
433        mapping->nrpages++;
434        __inc_zone_page_state(new, NR_FILE_PAGES);
435        if (PageSwapBacked(new))
436            __inc_zone_page_state(new, NR_SHMEM);
437        spin_unlock_irq(&mapping->tree_lock);
438        radix_tree_preload_end();
439        if (freepage)
440            freepage(old);
441        page_cache_release(old);
442        mem_cgroup_end_migration(memcg, old, new, true);
443    } else {
444        mem_cgroup_end_migration(memcg, old, new, false);
445    }
446
447    return error;
448}
449EXPORT_SYMBOL_GPL(replace_page_cache_page);
450
451/**
452 * add_to_page_cache_locked - add a locked page to the pagecache
453 * @page: page to add
454 * @mapping: the page's address_space
455 * @offset: page index
456 * @gfp_mask: page allocation mode
457 *
458 * This function is used to add a page to the pagecache. It must be locked.
459 * This function does not add the page to the LRU. The caller must do that.
460 */
461int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
462        pgoff_t offset, gfp_t gfp_mask)
463{
464    int error;
465
466    VM_BUG_ON(!PageLocked(page));
467
468    error = mem_cgroup_cache_charge(page, current->mm,
469                    gfp_mask & GFP_RECLAIM_MASK);
470    if (error)
471        goto out;
472
473    error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
474    if (error == 0) {
475        page_cache_get(page);
476        page->mapping = mapping;
477        page->index = offset;
478
479        spin_lock_irq(&mapping->tree_lock);
480        error = radix_tree_insert(&mapping->page_tree, offset, page);
481        if (likely(!error)) {
482            mapping->nrpages++;
483            __inc_zone_page_state(page, NR_FILE_PAGES);
484            if (PageSwapBacked(page))
485                __inc_zone_page_state(page, NR_SHMEM);
486            spin_unlock_irq(&mapping->tree_lock);
487        } else {
488            page->mapping = NULL;
489            spin_unlock_irq(&mapping->tree_lock);
490            mem_cgroup_uncharge_cache_page(page);
491            page_cache_release(page);
492        }
493        radix_tree_preload_end();
494    } else
495        mem_cgroup_uncharge_cache_page(page);
496out:
497    return error;
498}
499EXPORT_SYMBOL(add_to_page_cache_locked);
500
501int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
502                pgoff_t offset, gfp_t gfp_mask)
503{
504    int ret;
505
506    /*
507     * Splice_read and readahead add shmem/tmpfs pages into the page cache
508     * before shmem_readpage has a chance to mark them as SwapBacked: they
509     * need to go on the anon lru below, and mem_cgroup_cache_charge
510     * (called in add_to_page_cache) needs to know where they're going too.
511     */
512    if (mapping_cap_swap_backed(mapping))
513        SetPageSwapBacked(page);
514
515    ret = add_to_page_cache(page, mapping, offset, gfp_mask);
516    if (ret == 0) {
517        if (page_is_file_cache(page))
518            lru_cache_add_file(page);
519        else
520            lru_cache_add_anon(page);
521    }
522    return ret;
523}
524EXPORT_SYMBOL_GPL(add_to_page_cache_lru);
525
526#ifdef CONFIG_NUMA
527struct page *__page_cache_alloc(gfp_t gfp)
528{
529    int n;
530    struct page *page;
531
532    if (cpuset_do_page_mem_spread()) {
533        get_mems_allowed();
534        n = cpuset_mem_spread_node();
535        page = alloc_pages_exact_node(n, gfp, 0);
536        put_mems_allowed();
537        return page;
538    }
539    return alloc_pages(gfp, 0);
540}
541EXPORT_SYMBOL(__page_cache_alloc);
542#endif
543
544/*
545 * In order to wait for pages to become available there must be
546 * waitqueues associated with pages. By using a hash table of
547 * waitqueues where the bucket discipline is to maintain all
548 * waiters on the same queue and wake all when any of the pages
549 * become available, and for the woken contexts to check to be
550 * sure the appropriate page became available, this saves space
551 * at a cost of "thundering herd" phenomena during rare hash
552 * collisions.
553 */
554static wait_queue_head_t *page_waitqueue(struct page *page)
555{
556    const struct zone *zone = page_zone(page);
557
558    return &zone->wait_table[hash_ptr(page, zone->wait_table_bits)];
559}
560
561static inline void wake_up_page(struct page *page, int bit)
562{
563    __wake_up_bit(page_waitqueue(page), &page->flags, bit);
564}
565
566void wait_on_page_bit(struct page *page, int bit_nr)
567{
568    DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
569
570    if (test_bit(bit_nr, &page->flags))
571        __wait_on_bit(page_waitqueue(page), &wait, sleep_on_page,
572                            TASK_UNINTERRUPTIBLE);
573}
574EXPORT_SYMBOL(wait_on_page_bit);
575
576int wait_on_page_bit_killable(struct page *page, int bit_nr)
577{
578    DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
579
580    if (!test_bit(bit_nr, &page->flags))
581        return 0;
582
583    return __wait_on_bit(page_waitqueue(page), &wait,
584                 sleep_on_page_killable, TASK_KILLABLE);
585}
586
587/**
588 * add_page_wait_queue - Add an arbitrary waiter to a page's wait queue
589 * @page: Page defining the wait queue of interest
590 * @waiter: Waiter to add to the queue
591 *
592 * Add an arbitrary @waiter to the wait queue for the nominated @page.
593 */
594void add_page_wait_queue(struct page *page, wait_queue_t *waiter)
595{
596    wait_queue_head_t *q = page_waitqueue(page);
597    unsigned long flags;
598
599    spin_lock_irqsave(&q->lock, flags);
600    __add_wait_queue(q, waiter);
601    spin_unlock_irqrestore(&q->lock, flags);
602}
603EXPORT_SYMBOL_GPL(add_page_wait_queue);
604
605/**
606 * unlock_page - unlock a locked page
607 * @page: the page
608 *
609 * Unlocks the page and wakes up sleepers in ___wait_on_page_locked().
610 * Also wakes sleepers in wait_on_page_writeback() because the wakeup
611 * mechananism between PageLocked pages and PageWriteback pages is shared.
612 * But that's OK - sleepers in wait_on_page_writeback() just go back to sleep.
613 *
614 * The mb is necessary to enforce ordering between the clear_bit and the read
615 * of the waitqueue (to avoid SMP races with a parallel wait_on_page_locked()).
616 */
617void unlock_page(struct page *page)
618{
619    VM_BUG_ON(!PageLocked(page));
620    clear_bit_unlock(PG_locked, &page->flags);
621    smp_mb__after_clear_bit();
622    wake_up_page(page, PG_locked);
623}
624EXPORT_SYMBOL(unlock_page);
625
626/**
627 * end_page_writeback - end writeback against a page
628 * @page: the page
629 */
630void end_page_writeback(struct page *page)
631{
632    if (TestClearPageReclaim(page))
633        rotate_reclaimable_page(page);
634
635    if (!test_clear_page_writeback(page))
636        BUG();
637
638    smp_mb__after_clear_bit();
639    wake_up_page(page, PG_writeback);
640}
641EXPORT_SYMBOL(end_page_writeback);
642
643/**
644 * __lock_page - get a lock on the page, assuming we need to sleep to get it
645 * @page: the page to lock
646 */
647void __lock_page(struct page *page)
648{
649    DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
650
651    __wait_on_bit_lock(page_waitqueue(page), &wait, sleep_on_page,
652                            TASK_UNINTERRUPTIBLE);
653}
654EXPORT_SYMBOL(__lock_page);
655
656int __lock_page_killable(struct page *page)
657{
658    DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
659
660    return __wait_on_bit_lock(page_waitqueue(page), &wait,
661                    sleep_on_page_killable, TASK_KILLABLE);
662}
663EXPORT_SYMBOL_GPL(__lock_page_killable);
664
665int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
666             unsigned int flags)
667{
668    if (flags & FAULT_FLAG_ALLOW_RETRY) {
669        /*
670         * CAUTION! In this case, mmap_sem is not released
671         * even though return 0.
672         */
673        if (flags & FAULT_FLAG_RETRY_NOWAIT)
674            return 0;
675
676        up_read(&mm->mmap_sem);
677        if (flags & FAULT_FLAG_KILLABLE)
678            wait_on_page_locked_killable(page);
679        else
680            wait_on_page_locked(page);
681        return 0;
682    } else {
683        if (flags & FAULT_FLAG_KILLABLE) {
684            int ret;
685
686            ret = __lock_page_killable(page);
687            if (ret) {
688                up_read(&mm->mmap_sem);
689                return 0;
690            }
691        } else
692            __lock_page(page);
693        return 1;
694    }
695}
696
697/**
698 * find_get_page - find and get a page reference
699 * @mapping: the address_space to search
700 * @offset: the page index
701 *
702 * Is there a pagecache struct page at the given (mapping, offset) tuple?
703 * If yes, increment its refcount and return it; if no, return NULL.
704 */
705struct page *find_get_page(struct address_space *mapping, pgoff_t offset)
706{
707    void **pagep;
708    struct page *page;
709
710    rcu_read_lock();
711repeat:
712    page = NULL;
713    pagep = radix_tree_lookup_slot(&mapping->page_tree, offset);
714    if (pagep) {
715        page = radix_tree_deref_slot(pagep);
716        if (unlikely(!page))
717            goto out;
718        if (radix_tree_deref_retry(page))
719            goto repeat;
720
721        if (!page_cache_get_speculative(page))
722            goto repeat;
723
724        /*
725         * Has the page moved?
726         * This is part of the lockless pagecache protocol. See
727         * include/linux/pagemap.h for details.
728         */
729        if (unlikely(page != *pagep)) {
730            page_cache_release(page);
731            goto repeat;
732        }
733    }
734out:
735    rcu_read_unlock();
736
737    return page;
738}
739EXPORT_SYMBOL(find_get_page);
740
741/**
742 * find_lock_page - locate, pin and lock a pagecache page
743 * @mapping: the address_space to search
744 * @offset: the page index
745 *
746 * Locates the desired pagecache page, locks it, increments its reference
747 * count and returns its address.
748 *
749 * Returns zero if the page was not present. find_lock_page() may sleep.
750 */
751struct page *find_lock_page(struct address_space *mapping, pgoff_t offset)
752{
753    struct page *page;
754
755repeat:
756    page = find_get_page(mapping, offset);
757    if (page) {
758        lock_page(page);
759        /* Has the page been truncated? */
760        if (unlikely(page->mapping != mapping)) {
761            unlock_page(page);
762            page_cache_release(page);
763            goto repeat;
764        }
765        VM_BUG_ON(page->index != offset);
766    }
767    return page;
768}
769EXPORT_SYMBOL(find_lock_page);
770
771/**
772 * find_or_create_page - locate or add a pagecache page
773 * @mapping: the page's address_space
774 * @index: the page's index into the mapping
775 * @gfp_mask: page allocation mode
776 *
777 * Locates a page in the pagecache. If the page is not present, a new page
778 * is allocated using @gfp_mask and is added to the pagecache and to the VM's
779 * LRU list. The returned page is locked and has its reference count
780 * incremented.
781 *
782 * find_or_create_page() may sleep, even if @gfp_flags specifies an atomic
783 * allocation!
784 *
785 * find_or_create_page() returns the desired page's address, or zero on
786 * memory exhaustion.
787 */
788struct page *find_or_create_page(struct address_space *mapping,
789        pgoff_t index, gfp_t gfp_mask)
790{
791    struct page *page;
792    int err;
793repeat:
794    page = find_lock_page(mapping, index);
795    if (!page) {
796        page = __page_cache_alloc(gfp_mask);
797        if (!page)
798            return NULL;
799        /*
800         * We want a regular kernel memory (not highmem or DMA etc)
801         * allocation for the radix tree nodes, but we need to honour
802         * the context-specific requirements the caller has asked for.
803         * GFP_RECLAIM_MASK collects those requirements.
804         */
805        err = add_to_page_cache_lru(page, mapping, index,
806            (gfp_mask & GFP_RECLAIM_MASK));
807        if (unlikely(err)) {
808            page_cache_release(page);
809            page = NULL;
810            if (err == -EEXIST)
811                goto repeat;
812        }
813    }
814    return page;
815}
816EXPORT_SYMBOL(find_or_create_page);
817
818/**
819 * find_get_pages - gang pagecache lookup
820 * @mapping: The address_space to search
821 * @start: The starting page index
822 * @nr_pages: The maximum number of pages
823 * @pages: Where the resulting pages are placed
824 *
825 * find_get_pages() will search for and return a group of up to
826 * @nr_pages pages in the mapping. The pages are placed at @pages.
827 * find_get_pages() takes a reference against the returned pages.
828 *
829 * The search returns a group of mapping-contiguous pages with ascending
830 * indexes. There may be holes in the indices due to not-present pages.
831 *
832 * find_get_pages() returns the number of pages which were found.
833 */
834unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
835                unsigned int nr_pages, struct page **pages)
836{
837    unsigned int i;
838    unsigned int ret;
839    unsigned int nr_found;
840
841    rcu_read_lock();
842restart:
843    nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
844                (void ***)pages, start, nr_pages);
845    ret = 0;
846    for (i = 0; i < nr_found; i++) {
847        struct page *page;
848repeat:
849        page = radix_tree_deref_slot((void **)pages[i]);
850        if (unlikely(!page))
851            continue;
852
853        /*
854         * This can only trigger when the entry at index 0 moves out
855         * of or back to the root: none yet gotten, safe to restart.
856         */
857        if (radix_tree_deref_retry(page)) {
858            WARN_ON(start | i);
859            goto restart;
860        }
861
862        if (!page_cache_get_speculative(page))
863            goto repeat;
864
865        /* Has the page moved? */
866        if (unlikely(page != *((void **)pages[i]))) {
867            page_cache_release(page);
868            goto repeat;
869        }
870
871        pages[ret] = page;
872        ret++;
873    }
874
875    /*
876     * If all entries were removed before we could secure them,
877     * try again, because callers stop trying once 0 is returned.
878     */
879    if (unlikely(!ret && nr_found))
880        goto restart;
881    rcu_read_unlock();
882    return ret;
883}
884
885/**
886 * find_get_pages_contig - gang contiguous pagecache lookup
887 * @mapping: The address_space to search
888 * @index: The starting page index
889 * @nr_pages: The maximum number of pages
890 * @pages: Where the resulting pages are placed
891 *
892 * find_get_pages_contig() works exactly like find_get_pages(), except
893 * that the returned number of pages are guaranteed to be contiguous.
894 *
895 * find_get_pages_contig() returns the number of pages which were found.
896 */
897unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
898                   unsigned int nr_pages, struct page **pages)
899{
900    unsigned int i;
901    unsigned int ret;
902    unsigned int nr_found;
903
904    rcu_read_lock();
905restart:
906    nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
907                (void ***)pages, index, nr_pages);
908    ret = 0;
909    for (i = 0; i < nr_found; i++) {
910        struct page *page;
911repeat:
912        page = radix_tree_deref_slot((void **)pages[i]);
913        if (unlikely(!page))
914            continue;
915
916        /*
917         * This can only trigger when the entry at index 0 moves out
918         * of or back to the root: none yet gotten, safe to restart.
919         */
920        if (radix_tree_deref_retry(page))
921            goto restart;
922
923        if (!page_cache_get_speculative(page))
924            goto repeat;
925
926        /* Has the page moved? */
927        if (unlikely(page != *((void **)pages[i]))) {
928            page_cache_release(page);
929            goto repeat;
930        }
931
932        /*
933         * must check mapping and index after taking the ref.
934         * otherwise we can get both false positives and false
935         * negatives, which is just confusing to the caller.
936         */
937        if (page->mapping == NULL || page->index != index) {
938            page_cache_release(page);
939            break;
940        }
941
942        pages[ret] = page;
943        ret++;
944        index++;
945    }
946    rcu_read_unlock();
947    return ret;
948}
949EXPORT_SYMBOL(find_get_pages_contig);
950
951/**
952 * find_get_pages_tag - find and return pages that match @tag
953 * @mapping: the address_space to search
954 * @index: the starting page index
955 * @tag: the tag index
956 * @nr_pages: the maximum number of pages
957 * @pages: where the resulting pages are placed
958 *
959 * Like find_get_pages, except we only return pages which are tagged with
960 * @tag. We update @index to index the next page for the traversal.
961 */
962unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
963            int tag, unsigned int nr_pages, struct page **pages)
964{
965    unsigned int i;
966    unsigned int ret;
967    unsigned int nr_found;
968
969    rcu_read_lock();
970restart:
971    nr_found = radix_tree_gang_lookup_tag_slot(&mapping->page_tree,
972                (void ***)pages, *index, nr_pages, tag);
973    ret = 0;
974    for (i = 0; i < nr_found; i++) {
975        struct page *page;
976repeat:
977        page = radix_tree_deref_slot((void **)pages[i]);
978        if (unlikely(!page))
979            continue;
980
981        /*
982         * This can only trigger when the entry at index 0 moves out
983         * of or back to the root: none yet gotten, safe to restart.
984         */
985        if (radix_tree_deref_retry(page))
986            goto restart;
987
988        if (!page_cache_get_speculative(page))
989            goto repeat;
990
991        /* Has the page moved? */
992        if (unlikely(page != *((void **)pages[i]))) {
993            page_cache_release(page);
994            goto repeat;
995        }
996
997        pages[ret] = page;
998        ret++;
999    }
1000
1001    /*
1002     * If all entries were removed before we could secure them,
1003     * try again, because callers stop trying once 0 is returned.
1004     */
1005    if (unlikely(!ret && nr_found))
1006        goto restart;
1007    rcu_read_unlock();
1008
1009    if (ret)
1010        *index = pages[ret - 1]->index + 1;
1011
1012    return ret;
1013}
1014EXPORT_SYMBOL(find_get_pages_tag);
1015
1016/**
1017 * grab_cache_page_nowait - returns locked page at given index in given cache
1018 * @mapping: target address_space
1019 * @index: the page index
1020 *
1021 * Same as grab_cache_page(), but do not wait if the page is unavailable.
1022 * This is intended for speculative data generators, where the data can
1023 * be regenerated if the page couldn't be grabbed. This routine should
1024 * be safe to call while holding the lock for another page.
1025 *
1026 * Clear __GFP_FS when allocating the page to avoid recursion into the fs
1027 * and deadlock against the caller's locked page.
1028 */
1029struct page *
1030grab_cache_page_nowait(struct address_space *mapping, pgoff_t index)
1031{
1032    struct page *page = find_get_page(mapping, index);
1033
1034    if (page) {
1035        if (trylock_page(page))
1036            return page;
1037        page_cache_release(page);
1038        return NULL;
1039    }
1040    page = __page_cache_alloc(mapping_gfp_mask(mapping) & ~__GFP_FS);
1041    if (page && add_to_page_cache_lru(page, mapping, index, GFP_NOFS)) {
1042        page_cache_release(page);
1043        page = NULL;
1044    }
1045    return page;
1046}
1047EXPORT_SYMBOL(grab_cache_page_nowait);
1048
1049/*
1050 * CD/DVDs are error prone. When a medium error occurs, the driver may fail
1051 * a _large_ part of the i/o request. Imagine the worst scenario:
1052 *
1053 * ---R__________________________________________B__________
1054 * ^ reading here ^ bad block(assume 4k)
1055 *
1056 * read(R) => miss => readahead(R...B) => media error => frustrating retries
1057 * => failing the whole request => read(R) => read(R+1) =>
1058 * readahead(R+1...B+1) => bang => read(R+2) => read(R+3) =>
1059 * readahead(R+3...B+2) => bang => read(R+3) => read(R+4) =>
1060 * readahead(R+4...B+3) => bang => read(R+4) => read(R+5) => ......
1061 *
1062 * It is going insane. Fix it by quickly scaling down the readahead size.
1063 */
1064static void shrink_readahead_size_eio(struct file *filp,
1065                    struct file_ra_state *ra)
1066{
1067    ra->ra_pages /= 4;
1068}
1069
1070/**
1071 * do_generic_file_read - generic file read routine
1072 * @filp: the file to read
1073 * @ppos: current file position
1074 * @desc: read_descriptor
1075 * @actor: read method
1076 *
1077 * This is a generic file read routine, and uses the
1078 * mapping->a_ops->readpage() function for the actual low-level stuff.
1079 *
1080 * This is really ugly. But the goto's actually try to clarify some
1081 * of the logic when it comes to error handling etc.
1082 */
1083static void do_generic_file_read(struct file *filp, loff_t *ppos,
1084        read_descriptor_t *desc, read_actor_t actor)
1085{
1086    struct address_space *mapping = filp->f_mapping;
1087    struct inode *inode = mapping->host;
1088    struct file_ra_state *ra = &filp->f_ra;
1089    pgoff_t index;
1090    pgoff_t last_index;
1091    pgoff_t prev_index;
1092    unsigned long offset; /* offset into pagecache page */
1093    unsigned int prev_offset;
1094    int error;
1095
1096    index = *ppos >> PAGE_CACHE_SHIFT;
1097    prev_index = ra->prev_pos >> PAGE_CACHE_SHIFT;
1098    prev_offset = ra->prev_pos & (PAGE_CACHE_SIZE-1);
1099    last_index = (*ppos + desc->count + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;
1100    offset = *ppos & ~PAGE_CACHE_MASK;
1101
1102    for (;;) {
1103        struct page *page;
1104        pgoff_t end_index;
1105        loff_t isize;
1106        unsigned long nr, ret;
1107
1108        cond_resched();
1109find_page:
1110        page = find_get_page(mapping, index);
1111        if (!page) {
1112            page_cache_sync_readahead(mapping,
1113                    ra, filp,
1114                    index, last_index - index);
1115            page = find_get_page(mapping, index);
1116            if (unlikely(page == NULL))
1117                goto no_cached_page;
1118        }
1119        if (PageReadahead(page)) {
1120            page_cache_async_readahead(mapping,
1121                    ra, filp, page,
1122                    index, last_index - index);
1123        }
1124        if (!PageUptodate(page)) {
1125            if (inode->i_blkbits == PAGE_CACHE_SHIFT ||
1126                    !mapping->a_ops->is_partially_uptodate)
1127                goto page_not_up_to_date;
1128            if (!trylock_page(page))
1129                goto page_not_up_to_date;
1130            /* Did it get truncated before we got the lock? */
1131            if (!page->mapping)
1132                goto page_not_up_to_date_locked;
1133            if (!mapping->a_ops->is_partially_uptodate(page,
1134                                desc, offset))
1135                goto page_not_up_to_date_locked;
1136            unlock_page(page);
1137        }
1138page_ok:
1139        /*
1140         * i_size must be checked after we know the page is Uptodate.
1141         *
1142         * Checking i_size after the check allows us to calculate
1143         * the correct value for "nr", which means the zero-filled
1144         * part of the page is not copied back to userspace (unless
1145         * another truncate extends the file - this is desired though).
1146         */
1147
1148        isize = i_size_read(inode);
1149        end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
1150        if (unlikely(!isize || index > end_index)) {
1151            page_cache_release(page);
1152            goto out;
1153        }
1154
1155        /* nr is the maximum number of bytes to copy from this page */
1156        nr = PAGE_CACHE_SIZE;
1157        if (index == end_index) {
1158            nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
1159            if (nr <= offset) {
1160                page_cache_release(page);
1161                goto out;
1162            }
1163        }
1164        nr = nr - offset;
1165
1166        /* If users can be writing to this page using arbitrary
1167         * virtual addresses, take care about potential aliasing
1168         * before reading the page on the kernel side.
1169         */
1170        if (mapping_writably_mapped(mapping))
1171            flush_dcache_page(page);
1172
1173        /*
1174         * When a sequential read accesses a page several times,
1175         * only mark it as accessed the first time.
1176         */
1177        if (prev_index != index || offset != prev_offset)
1178            mark_page_accessed(page);
1179        prev_index = index;
1180
1181        /*
1182         * Ok, we have the page, and it's up-to-date, so
1183         * now we can copy it to user space...
1184         *
1185         * The actor routine returns how many bytes were actually used..
1186         * NOTE! This may not be the same as how much of a user buffer
1187         * we filled up (we may be padding etc), so we can only update
1188         * "pos" here (the actor routine has to update the user buffer
1189         * pointers and the remaining count).
1190         */
1191        ret = actor(desc, page, offset, nr);
1192        offset += ret;
1193        index += offset >> PAGE_CACHE_SHIFT;
1194        offset &= ~PAGE_CACHE_MASK;
1195        prev_offset = offset;
1196
1197        page_cache_release(page);
1198        if (ret == nr && desc->count)
1199            continue;
1200        goto out;
1201
1202page_not_up_to_date:
1203        /* Get exclusive access to the page ... */
1204        error = lock_page_killable(page);
1205        if (unlikely(error))
1206            goto readpage_error;
1207
1208page_not_up_to_date_locked:
1209        /* Did it get truncated before we got the lock? */
1210        if (!page->mapping) {
1211            unlock_page(page);
1212            page_cache_release(page);
1213            continue;
1214        }
1215
1216        /* Did somebody else fill it already? */
1217        if (PageUptodate(page)) {
1218            unlock_page(page);
1219            goto page_ok;
1220        }
1221
1222readpage:
1223        /*
1224         * A previous I/O error may have been due to temporary
1225         * failures, eg. multipath errors.
1226         * PG_error will be set again if readpage fails.
1227         */
1228        ClearPageError(page);
1229        /* Start the actual read. The read will unlock the page. */
1230        error = mapping->a_ops->readpage(filp, page);
1231
1232        if (unlikely(error)) {
1233            if (error == AOP_TRUNCATED_PAGE) {
1234                page_cache_release(page);
1235                goto find_page;
1236            }
1237            goto readpage_error;
1238        }
1239
1240        if (!PageUptodate(page)) {
1241            error = lock_page_killable(page);
1242            if (unlikely(error))
1243                goto readpage_error;
1244            if (!PageUptodate(page)) {
1245                if (page->mapping == NULL) {
1246                    /*
1247                     * invalidate_mapping_pages got it
1248                     */
1249                    unlock_page(page);
1250                    page_cache_release(page);
1251                    goto find_page;
1252                }
1253                unlock_page(page);
1254                shrink_readahead_size_eio(filp, ra);
1255                error = -EIO;
1256                goto readpage_error;
1257            }
1258            unlock_page(page);
1259        }
1260
1261        goto page_ok;
1262
1263readpage_error:
1264        /* UHHUH! A synchronous read error occurred. Report it */
1265        desc->error = error;
1266        page_cache_release(page);
1267        goto out;
1268
1269no_cached_page:
1270        /*
1271         * Ok, it wasn't cached, so we need to create a new
1272         * page..
1273         */
1274        page = page_cache_alloc_cold(mapping);
1275        if (!page) {
1276            desc->error = -ENOMEM;
1277            goto out;
1278        }
1279        error = add_to_page_cache_lru(page, mapping,
1280                        index, GFP_KERNEL);
1281        if (error) {
1282            page_cache_release(page);
1283            if (error == -EEXIST)
1284                goto find_page;
1285            desc->error = error;
1286            goto out;
1287        }
1288        goto readpage;
1289    }
1290
1291out:
1292    ra->prev_pos = prev_index;
1293    ra->prev_pos <<= PAGE_CACHE_SHIFT;
1294    ra->prev_pos |= prev_offset;
1295
1296    *ppos = ((loff_t)index << PAGE_CACHE_SHIFT) + offset;
1297    file_accessed(filp);
1298}
1299
1300int file_read_actor(read_descriptor_t *desc, struct page *page,
1301            unsigned long offset, unsigned long size)
1302{
1303    char *kaddr;
1304    unsigned long left, count = desc->count;
1305
1306    if (size > count)
1307        size = count;
1308
1309    /*
1310     * Faults on the destination of a read are common, so do it before
1311     * taking the kmap.
1312     */
1313    if (!fault_in_pages_writeable(desc->arg.buf, size)) {
1314        kaddr = kmap_atomic(page, KM_USER0);
1315        left = __copy_to_user_inatomic(desc->arg.buf,
1316                        kaddr + offset, size);
1317        kunmap_atomic(kaddr, KM_USER0);
1318        if (left == 0)
1319            goto success;
1320    }
1321
1322    /* Do it the slow way */
1323    kaddr = kmap(page);
1324    left = __copy_to_user(desc->arg.buf, kaddr + offset, size);
1325    kunmap(page);
1326
1327    if (left) {
1328        size -= left;
1329        desc->error = -EFAULT;
1330    }
1331success:
1332    desc->count = count - size;
1333    desc->written += size;
1334    desc->arg.buf += size;
1335    return size;
1336}
1337
1338/*
1339 * Performs necessary checks before doing a write
1340 * @iov: io vector request
1341 * @nr_segs: number of segments in the iovec
1342 * @count: number of bytes to write
1343 * @access_flags: type of access: %VERIFY_READ or %VERIFY_WRITE
1344 *
1345 * Adjust number of segments and amount of bytes to write (nr_segs should be
1346 * properly initialized first). Returns appropriate error code that caller
1347 * should return or zero in case that write should be allowed.
1348 */
1349int generic_segment_checks(const struct iovec *iov,
1350            unsigned long *nr_segs, size_t *count, int access_flags)
1351{
1352    unsigned long seg;
1353    size_t cnt = 0;
1354    for (seg = 0; seg < *nr_segs; seg++) {
1355        const struct iovec *iv = &iov[seg];
1356
1357        /*
1358         * If any segment has a negative length, or the cumulative
1359         * length ever wraps negative then return -EINVAL.
1360         */
1361        cnt += iv->iov_len;
1362        if (unlikely((ssize_t)(cnt|iv->iov_len) < 0))
1363            return -EINVAL;
1364        if (access_ok(access_flags, iv->iov_base, iv->iov_len))
1365            continue;
1366        if (seg == 0)
1367            return -EFAULT;
1368        *nr_segs = seg;
1369        cnt -= iv->iov_len; /* This segment is no good */
1370        break;
1371    }
1372    *count = cnt;
1373    return 0;
1374}
1375EXPORT_SYMBOL(generic_segment_checks);
1376
1377/**
1378 * generic_file_aio_read - generic filesystem read routine
1379 * @iocb: kernel I/O control block
1380 * @iov: io vector request
1381 * @nr_segs: number of segments in the iovec
1382 * @pos: current file position
1383 *
1384 * This is the "read()" routine for all filesystems
1385 * that can use the page cache directly.
1386 */
1387ssize_t
1388generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
1389        unsigned long nr_segs, loff_t pos)
1390{
1391    struct file *filp = iocb->ki_filp;
1392    ssize_t retval;
1393    unsigned long seg = 0;
1394    size_t count;
1395    loff_t *ppos = &iocb->ki_pos;
1396    struct blk_plug plug;
1397
1398    count = 0;
1399    retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
1400    if (retval)
1401        return retval;
1402
1403    blk_start_plug(&plug);
1404
1405    /* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
1406    if (filp->f_flags & O_DIRECT) {
1407        loff_t size;
1408        struct address_space *mapping;
1409        struct inode *inode;
1410
1411        mapping = filp->f_mapping;
1412        inode = mapping->host;
1413        if (!count)
1414            goto out; /* skip atime */
1415        size = i_size_read(inode);
1416        if (pos < size) {
1417            retval = filemap_write_and_wait_range(mapping, pos,
1418                    pos + iov_length(iov, nr_segs) - 1);
1419            if (!retval) {
1420                retval = mapping->a_ops->direct_IO(READ, iocb,
1421                            iov, pos, nr_segs);
1422            }
1423            if (retval > 0) {
1424                *ppos = pos + retval;
1425                count -= retval;
1426            }
1427
1428            /*
1429             * Btrfs can have a short DIO read if we encounter
1430             * compressed extents, so if there was an error, or if
1431             * we've already read everything we wanted to, or if
1432             * there was a short read because we hit EOF, go ahead
1433             * and return. Otherwise fallthrough to buffered io for
1434             * the rest of the read.
1435             */
1436            if (retval < 0 || !count || *ppos >= size) {
1437                file_accessed(filp);
1438                goto out;
1439            }
1440        }
1441    }
1442
1443    count = retval;
1444    for (seg = 0; seg < nr_segs; seg++) {
1445        read_descriptor_t desc;
1446        loff_t offset = 0;
1447
1448        /*
1449         * If we did a short DIO read we need to skip the section of the
1450         * iov that we've already read data into.
1451         */
1452        if (count) {
1453            if (count > iov[seg].iov_len) {
1454                count -= iov[seg].iov_len;
1455                continue;
1456            }
1457            offset = count;
1458            count = 0;
1459        }
1460
1461        desc.written = 0;
1462        desc.arg.buf = iov[seg].iov_base + offset;
1463        desc.count = iov[seg].iov_len - offset;
1464        if (desc.count == 0)
1465            continue;
1466        desc.error = 0;
1467        do_generic_file_read(filp, ppos, &desc, file_read_actor);
1468        retval += desc.written;
1469        if (desc.error) {
1470            retval = retval ?: desc.error;
1471            break;
1472        }
1473        if (desc.count > 0)
1474            break;
1475    }
1476out:
1477    blk_finish_plug(&plug);
1478    return retval;
1479}
1480EXPORT_SYMBOL(generic_file_aio_read);
1481
1482static ssize_t
1483do_readahead(struct address_space *mapping, struct file *filp,
1484         pgoff_t index, unsigned long nr)
1485{
1486    if (!mapping || !mapping->a_ops || !mapping->a_ops->readpage)
1487        return -EINVAL;
1488
1489    force_page_cache_readahead(mapping, filp, index, nr);
1490    return 0;
1491}
1492
1493SYSCALL_DEFINE(readahead)(int fd, loff_t offset, size_t count)
1494{
1495    ssize_t ret;
1496    struct file *file;
1497
1498    ret = -EBADF;
1499    file = fget(fd);
1500    if (file) {
1501        if (file->f_mode & FMODE_READ) {
1502            struct address_space *mapping = file->f_mapping;
1503            pgoff_t start = offset >> PAGE_CACHE_SHIFT;
1504            pgoff_t end = (offset + count - 1) >> PAGE_CACHE_SHIFT;
1505            unsigned long len = end - start + 1;
1506            ret = do_readahead(mapping, file, start, len);
1507        }
1508        fput(file);
1509    }
1510    return ret;
1511}
1512#ifdef CONFIG_HAVE_SYSCALL_WRAPPERS
1513asmlinkage long SyS_readahead(long fd, loff_t offset, long count)
1514{
1515    return SYSC_readahead((int) fd, offset, (size_t) count);
1516}
1517SYSCALL_ALIAS(sys_readahead, SyS_readahead);
1518#endif
1519
1520#ifdef CONFIG_MMU
1521/**
1522 * page_cache_read - adds requested page to the page cache if not already there
1523 * @file: file to read
1524 * @offset: page index
1525 *
1526 * This adds the requested page to the page cache if it isn't already there,
1527 * and schedules an I/O to read in its contents from disk.
1528 */
1529static int page_cache_read(struct file *file, pgoff_t offset)
1530{
1531    struct address_space *mapping = file->f_mapping;
1532    struct page *page;
1533    int ret;
1534
1535    do {
1536        page = page_cache_alloc_cold(mapping);
1537        if (!page)
1538            return -ENOMEM;
1539
1540        ret = add_to_page_cache_lru(page, mapping, offset, GFP_KERNEL);
1541        if (ret == 0)
1542            ret = mapping->a_ops->readpage(file, page);
1543        else if (ret == -EEXIST)
1544            ret = 0; /* losing race to add is OK */
1545
1546        page_cache_release(page);
1547
1548    } while (ret == AOP_TRUNCATED_PAGE);
1549        
1550    return ret;
1551}
1552
1553#define MMAP_LOTSAMISS (100)
1554
1555/*
1556 * Synchronous readahead happens when we don't even find
1557 * a page in the page cache at all.
1558 */
1559static void do_sync_mmap_readahead(struct vm_area_struct *vma,
1560                   struct file_ra_state *ra,
1561                   struct file *file,
1562                   pgoff_t offset)
1563{
1564    unsigned long ra_pages;
1565    struct address_space *mapping = file->f_mapping;
1566
1567    /* If we don't want any read-ahead, don't bother */
1568    if (VM_RandomReadHint(vma))
1569        return;
1570    if (!ra->ra_pages)
1571        return;
1572
1573    if (VM_SequentialReadHint(vma)) {
1574        page_cache_sync_readahead(mapping, ra, file, offset,
1575                      ra->ra_pages);
1576        return;
1577    }
1578
1579    /* Avoid banging the cache line if not needed */
1580    if (ra->mmap_miss < MMAP_LOTSAMISS * 10)
1581        ra->mmap_miss++;
1582
1583    /*
1584     * Do we miss much more than hit in this file? If so,
1585     * stop bothering with read-ahead. It will only hurt.
1586     */
1587    if (ra->mmap_miss > MMAP_LOTSAMISS)
1588        return;
1589
1590    /*
1591     * mmap read-around
1592     */
1593    ra_pages = max_sane_readahead(ra->ra_pages);
1594    ra->start = max_t(long, 0, offset - ra_pages / 2);
1595    ra->size = ra_pages;
1596    ra->async_size = ra_pages / 4;
1597    ra_submit(ra, mapping, file);
1598}
1599
1600/*
1601 * Asynchronous readahead happens when we find the page and PG_readahead,
1602 * so we want to possibly extend the readahead further..
1603 */
1604static void do_async_mmap_readahead(struct vm_area_struct *vma,
1605                    struct file_ra_state *ra,
1606                    struct file *file,
1607                    struct page *page,
1608                    pgoff_t offset)
1609{
1610    struct address_space *mapping = file->f_mapping;
1611
1612    /* If we don't want any read-ahead, don't bother */
1613    if (VM_RandomReadHint(vma))
1614        return;
1615    if (ra->mmap_miss > 0)
1616        ra->mmap_miss--;
1617    if (PageReadahead(page))
1618        page_cache_async_readahead(mapping, ra, file,
1619                       page, offset, ra->ra_pages);
1620}
1621
1622/**
1623 * filemap_fault - read in file data for page fault handling
1624 * @vma: vma in which the fault was taken
1625 * @vmf: struct vm_fault containing details of the fault
1626 *
1627 * filemap_fault() is invoked via the vma operations vector for a
1628 * mapped memory region to read in file data during a page fault.
1629 *
1630 * The goto's are kind of ugly, but this streamlines the normal case of having
1631 * it in the page cache, and handles the special cases reasonably without
1632 * having a lot of duplicated code.
1633 */
1634int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
1635{
1636    int error;
1637    struct file *file = vma->vm_file;
1638    struct address_space *mapping = file->f_mapping;
1639    struct file_ra_state *ra = &file->f_ra;
1640    struct inode *inode = mapping->host;
1641    pgoff_t offset = vmf->pgoff;
1642    struct page *page;
1643    pgoff_t size;
1644    int ret = 0;
1645
1646    size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
1647    if (offset >= size)
1648        return VM_FAULT_SIGBUS;
1649
1650    /*
1651     * Do we have something in the page cache already?
1652     */
1653    page = find_get_page(mapping, offset);
1654    if (likely(page)) {
1655        /*
1656         * We found the page, so try async readahead before
1657         * waiting for the lock.
1658         */
1659        do_async_mmap_readahead(vma, ra, file, page, offset);
1660    } else {
1661        /* No page in the page cache at all */
1662        do_sync_mmap_readahead(vma, ra, file, offset);
1663        count_vm_event(PGMAJFAULT);
1664        mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
1665        ret = VM_FAULT_MAJOR;
1666retry_find:
1667        page = find_get_page(mapping, offset);
1668        if (!page)
1669            goto no_cached_page;
1670    }
1671
1672    if (!lock_page_or_retry(page, vma->vm_mm, vmf->flags)) {
1673        page_cache_release(page);
1674        return ret | VM_FAULT_RETRY;
1675    }
1676
1677    /* Did it get truncated? */
1678    if (unlikely(page->mapping != mapping)) {
1679        unlock_page(page);
1680        put_page(page);
1681        goto retry_find;
1682    }
1683    VM_BUG_ON(page->index != offset);
1684
1685    /*
1686     * We have a locked page in the page cache, now we need to check
1687     * that it's up-to-date. If not, it is going to be due to an error.
1688     */
1689    if (unlikely(!PageUptodate(page)))
1690        goto page_not_uptodate;
1691
1692    /*
1693     * Found the page and have a reference on it.
1694     * We must recheck i_size under page lock.
1695     */
1696    size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
1697    if (unlikely(offset >= size)) {
1698        unlock_page(page);
1699        page_cache_release(page);
1700        return VM_FAULT_SIGBUS;
1701    }
1702
1703    vmf->page = page;
1704    return ret | VM_FAULT_LOCKED;
1705
1706no_cached_page:
1707    /*
1708     * We're only likely to ever get here if MADV_RANDOM is in
1709     * effect.
1710     */
1711    error = page_cache_read(file, offset);
1712
1713    /*
1714     * The page we want has now been added to the page cache.
1715     * In the unlikely event that someone removed it in the
1716     * meantime, we'll just come back here and read it again.
1717     */
1718    if (error >= 0)
1719        goto retry_find;
1720
1721    /*
1722     * An error return from page_cache_read can result if the
1723     * system is low on memory, or a problem occurs while trying
1724     * to schedule I/O.
1725     */
1726    if (error == -ENOMEM)
1727        return VM_FAULT_OOM;
1728    return VM_FAULT_SIGBUS;
1729
1730page_not_uptodate:
1731    /*
1732     * Umm, take care of errors if the page isn't up-to-date.
1733     * Try to re-read it _once_. We do this synchronously,
1734     * because there really aren't any performance issues here
1735     * and we need to check for errors.
1736     */
1737    ClearPageError(page);
1738    error = mapping->a_ops->readpage(file, page);
1739    if (!error) {
1740        wait_on_page_locked(page);
1741        if (!PageUptodate(page))
1742            error = -EIO;
1743    }
1744    page_cache_release(page);
1745
1746    if (!error || error == AOP_TRUNCATED_PAGE)
1747        goto retry_find;
1748
1749    /* Things didn't work out. Return zero to tell the mm layer so. */
1750    shrink_readahead_size_eio(file, ra);
1751    return VM_FAULT_SIGBUS;
1752}
1753EXPORT_SYMBOL(filemap_fault);
1754
1755const struct vm_operations_struct generic_file_vm_ops = {
1756    .fault = filemap_fault,
1757};
1758
1759/* This is used for a general mmap of a disk file */
1760
1761int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
1762{
1763    struct address_space *mapping = file->f_mapping;
1764
1765    if (!mapping->a_ops->readpage)
1766        return -ENOEXEC;
1767    file_accessed(file);
1768    vma->vm_ops = &generic_file_vm_ops;
1769    vma->vm_flags |= VM_CAN_NONLINEAR;
1770    return 0;
1771}
1772
1773/*
1774 * This is for filesystems which do not implement ->writepage.
1775 */
1776int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
1777{
1778    if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
1779        return -EINVAL;
1780    return generic_file_mmap(file, vma);
1781}
1782#else
1783int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
1784{
1785    return -ENOSYS;
1786}
1787int generic_file_readonly_mmap(struct file * file, struct vm_area_struct * vma)
1788{
1789    return -ENOSYS;
1790}
1791#endif /* CONFIG_MMU */
1792
1793EXPORT_SYMBOL(generic_file_mmap);
1794EXPORT_SYMBOL(generic_file_readonly_mmap);
1795
1796static struct page *__read_cache_page(struct address_space *mapping,
1797                pgoff_t index,
1798                int (*filler)(void *,struct page*),
1799                void *data,
1800                gfp_t gfp)
1801{
1802    struct page *page;
1803    int err;
1804repeat:
1805    page = find_get_page(mapping, index);
1806    if (!page) {
1807        page = __page_cache_alloc(gfp | __GFP_COLD);
1808        if (!page)
1809            return ERR_PTR(-ENOMEM);
1810        err = add_to_page_cache_lru(page, mapping, index, GFP_KERNEL);
1811        if (unlikely(err)) {
1812            page_cache_release(page);
1813            if (err == -EEXIST)
1814                goto repeat;
1815            /* Presumably ENOMEM for radix tree node */
1816            return ERR_PTR(err);
1817        }
1818        err = filler(data, page);
1819        if (err < 0) {
1820            page_cache_release(page);
1821            page = ERR_PTR(err);
1822        }
1823    }
1824    return page;
1825}
1826
1827static struct page *do_read_cache_page(struct address_space *mapping,
1828                pgoff_t index,
1829                int (*filler)(void *,struct page*),
1830                void *data,
1831                gfp_t gfp)
1832
1833{
1834    struct page *page;
1835    int err;
1836
1837retry:
1838    page = __read_cache_page(mapping, index, filler, data, gfp);
1839    if (IS_ERR(page))
1840        return page;
1841    if (PageUptodate(page))
1842        goto out;
1843
1844    lock_page(page);
1845    if (!page->mapping) {
1846        unlock_page(page);
1847        page_cache_release(page);
1848        goto retry;
1849    }
1850    if (PageUptodate(page)) {
1851        unlock_page(page);
1852        goto out;
1853    }
1854    err = filler(data, page);
1855    if (err < 0) {
1856        page_cache_release(page);
1857        return ERR_PTR(err);
1858    }
1859out:
1860    mark_page_accessed(page);
1861    return page;
1862}
1863
1864/**
1865 * read_cache_page_async - read into page cache, fill it if needed
1866 * @mapping: the page's address_space
1867 * @index: the page index
1868 * @filler: function to perform the read
1869 * @data: destination for read data
1870 *
1871 * Same as read_cache_page, but don't wait for page to become unlocked
1872 * after submitting it to the filler.
1873 *
1874 * Read into the page cache. If a page already exists, and PageUptodate() is
1875 * not set, try to fill the page but don't wait for it to become unlocked.
1876 *
1877 * If the page does not get brought uptodate, return -EIO.
1878 */
1879struct page *read_cache_page_async(struct address_space *mapping,
1880                pgoff_t index,
1881                int (*filler)(void *,struct page*),
1882                void *data)
1883{
1884    return do_read_cache_page(mapping, index, filler, data, mapping_gfp_mask(mapping));
1885}
1886EXPORT_SYMBOL(read_cache_page_async);
1887
1888static struct page *wait_on_page_read(struct page *page)
1889{
1890    if (!IS_ERR(page)) {
1891        wait_on_page_locked(page);
1892        if (!PageUptodate(page)) {
1893            page_cache_release(page);
1894            page = ERR_PTR(-EIO);
1895        }
1896    }
1897    return page;
1898}
1899
1900/**
1901 * read_cache_page_gfp - read into page cache, using specified page allocation flags.
1902 * @mapping: the page's address_space
1903 * @index: the page index
1904 * @gfp: the page allocator flags to use if allocating
1905 *
1906 * This is the same as "read_mapping_page(mapping, index, NULL)", but with
1907 * any new page allocations done using the specified allocation flags. Note
1908 * that the Radix tree operations will still use GFP_KERNEL, so you can't
1909 * expect to do this atomically or anything like that - but you can pass in
1910 * other page requirements.
1911 *
1912 * If the page does not get brought uptodate, return -EIO.
1913 */
1914struct page *read_cache_page_gfp(struct address_space *mapping,
1915                pgoff_t index,
1916                gfp_t gfp)
1917{
1918    filler_t *filler = (filler_t *)mapping->a_ops->readpage;
1919
1920    return wait_on_page_read(do_read_cache_page(mapping, index, filler, NULL, gfp));
1921}
1922EXPORT_SYMBOL(read_cache_page_gfp);
1923
1924/**
1925 * read_cache_page - read into page cache, fill it if needed
1926 * @mapping: the page's address_space
1927 * @index: the page index
1928 * @filler: function to perform the read
1929 * @data: destination for read data
1930 *
1931 * Read into the page cache. If a page already exists, and PageUptodate() is
1932 * not set, try to fill the page then wait for it to become unlocked.
1933 *
1934 * If the page does not get brought uptodate, return -EIO.
1935 */
1936struct page *read_cache_page(struct address_space *mapping,
1937                pgoff_t index,
1938                int (*filler)(void *,struct page*),
1939                void *data)
1940{
1941    return wait_on_page_read(read_cache_page_async(mapping, index, filler, data));
1942}
1943EXPORT_SYMBOL(read_cache_page);
1944
1945/*
1946 * The logic we want is
1947 *
1948 * if suid or (sgid and xgrp)
1949 * remove privs
1950 */
1951int should_remove_suid(struct dentry *dentry)
1952{
1953    mode_t mode = dentry->d_inode->i_mode;
1954    int kill = 0;
1955
1956    /* suid always must be killed */
1957    if (unlikely(mode & S_ISUID))
1958        kill = ATTR_KILL_SUID;
1959
1960    /*
1961     * sgid without any exec bits is just a mandatory locking mark; leave
1962     * it alone. If some exec bits are set, it's a real sgid; kill it.
1963     */
1964    if (unlikely((mode & S_ISGID) && (mode & S_IXGRP)))
1965        kill |= ATTR_KILL_SGID;
1966
1967    if (unlikely(kill && !capable(CAP_FSETID) && S_ISREG(mode)))
1968        return kill;
1969
1970    return 0;
1971}
1972EXPORT_SYMBOL(should_remove_suid);
1973
1974static int __remove_suid(struct dentry *dentry, int kill)
1975{
1976    struct iattr newattrs;
1977
1978    newattrs.ia_valid = ATTR_FORCE | kill;
1979    return notify_change(dentry, &newattrs);
1980}
1981
1982int file_remove_suid(struct file *file)
1983{
1984    struct dentry *dentry = file->f_path.dentry;
1985    struct inode *inode = dentry->d_inode;
1986    int killsuid;
1987    int killpriv;
1988    int error = 0;
1989
1990    /* Fast path for nothing security related */
1991    if (IS_NOSEC(inode))
1992        return 0;
1993
1994    killsuid = should_remove_suid(dentry);
1995    killpriv = security_inode_need_killpriv(dentry);
1996
1997    if (killpriv < 0)
1998        return killpriv;
1999    if (killpriv)
2000        error = security_inode_killpriv(dentry);
2001    if (!error && killsuid)
2002        error = __remove_suid(dentry, killsuid);
2003    if (!error && (inode->i_sb->s_flags & MS_NOSEC))
2004        inode->i_flags |= S_NOSEC;
2005
2006    return error;
2007}
2008EXPORT_SYMBOL(file_remove_suid);
2009
2010static size_t __iovec_copy_from_user_inatomic(char *vaddr,
2011            const struct iovec *iov, size_t base, size_t bytes)
2012{
2013    size_t copied = 0, left = 0;
2014
2015    while (bytes) {
2016        char __user *buf = iov->iov_base + base;
2017        int copy = min(bytes, iov->iov_len - base);
2018
2019        base = 0;
2020        left = __copy_from_user_inatomic(vaddr, buf, copy);
2021        copied += copy;
2022        bytes -= copy;
2023        vaddr += copy;
2024        iov++;
2025
2026        if (unlikely(left))
2027            break;
2028    }
2029    return copied - left;
2030}
2031
2032/*
2033 * Copy as much as we can into the page and return the number of bytes which
2034 * were successfully copied. If a fault is encountered then return the number of
2035 * bytes which were copied.
2036 */
2037size_t iov_iter_copy_from_user_atomic(struct page *page,
2038        struct iov_iter *i, unsigned long offset, size_t bytes)
2039{
2040    char *kaddr;
2041    size_t copied;
2042
2043    BUG_ON(!in_atomic());
2044    kaddr = kmap_atomic(page, KM_USER0);
2045    if (likely(i->nr_segs == 1)) {
2046        int left;
2047        char __user *buf = i->iov->iov_base + i->iov_offset;
2048        left = __copy_from_user_inatomic(kaddr + offset, buf, bytes);
2049        copied = bytes - left;
2050    } else {
2051        copied = __iovec_copy_from_user_inatomic(kaddr + offset,
2052                        i->iov, i->iov_offset, bytes);
2053    }
2054    kunmap_atomic(kaddr, KM_USER0);
2055
2056    return copied;
2057}
2058EXPORT_SYMBOL(iov_iter_copy_from_user_atomic);
2059
2060/*
2061 * This has the same sideeffects and return value as
2062 * iov_iter_copy_from_user_atomic().
2063 * The difference is that it attempts to resolve faults.
2064 * Page must not be locked.
2065 */
2066size_t iov_iter_copy_from_user(struct page *page,
2067        struct iov_iter *i, unsigned long offset, size_t bytes)
2068{
2069    char *kaddr;
2070    size_t copied;
2071
2072    kaddr = kmap(page);
2073    if (likely(i->nr_segs == 1)) {
2074        int left;
2075        char __user *buf = i->iov->iov_base + i->iov_offset;
2076        left = __copy_from_user(kaddr + offset, buf, bytes);
2077        copied = bytes - left;
2078    } else {
2079        copied = __iovec_copy_from_user_inatomic(kaddr + offset,
2080                        i->iov, i->iov_offset, bytes);
2081    }
2082    kunmap(page);
2083    return copied;
2084}
2085EXPORT_SYMBOL(iov_iter_copy_from_user);
2086
2087void iov_iter_advance(struct iov_iter *i, size_t bytes)
2088{
2089    BUG_ON(i->count < bytes);
2090
2091    if (likely(i->nr_segs == 1)) {
2092        i->iov_offset += bytes;
2093        i->count -= bytes;
2094    } else {
2095        const struct iovec *iov = i->iov;
2096        size_t base = i->iov_offset;
2097
2098        /*
2099         * The !iov->iov_len check ensures we skip over unlikely
2100         * zero-length segments (without overruning the iovec).
2101         */
2102        while (bytes || unlikely(i->count && !iov->iov_len)) {
2103            int copy;
2104
2105            copy = min(bytes, iov->iov_len - base);
2106            BUG_ON(!i->count || i->count < copy);
2107            i->count -= copy;
2108            bytes -= copy;
2109            base += copy;
2110            if (iov->iov_len == base) {
2111                iov++;
2112                base = 0;
2113            }
2114        }
2115        i->iov = iov;
2116        i->iov_offset = base;
2117    }
2118}
2119EXPORT_SYMBOL(iov_iter_advance);
2120
2121/*
2122 * Fault in the first iovec of the given iov_iter, to a maximum length
2123 * of bytes. Returns 0 on success, or non-zero if the memory could not be
2124 * accessed (ie. because it is an invalid address).
2125 *
2126 * writev-intensive code may want this to prefault several iovecs -- that
2127 * would be possible (callers must not rely on the fact that _only_ the
2128 * first iovec will be faulted with the current implementation).
2129 */
2130int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
2131{
2132    char __user *buf = i->iov->iov_base + i->iov_offset;
2133    bytes = min(bytes, i->iov->iov_len - i->iov_offset);
2134    return fault_in_pages_readable(buf, bytes);
2135}
2136EXPORT_SYMBOL(iov_iter_fault_in_readable);
2137
2138/*
2139 * Return the count of just the current iov_iter segment.
2140 */
2141size_t iov_iter_single_seg_count(struct iov_iter *i)
2142{
2143    const struct iovec *iov = i->iov;
2144    if (i->nr_segs == 1)
2145        return i->count;
2146    else
2147        return min(i->count, iov->iov_len - i->iov_offset);
2148}
2149EXPORT_SYMBOL(iov_iter_single_seg_count);
2150
2151/*
2152 * Performs necessary checks before doing a write
2153 *
2154 * Can adjust writing position or amount of bytes to write.
2155 * Returns appropriate error code that caller should return or
2156 * zero in case that write should be allowed.
2157 */
2158inline int generic_write_checks(struct file *file, loff_t *pos, size_t *count, int isblk)
2159{
2160    struct inode *inode = file->f_mapping->host;
2161    unsigned long limit = rlimit(RLIMIT_FSIZE);
2162
2163        if (unlikely(*pos < 0))
2164                return -EINVAL;
2165
2166    if (!isblk) {
2167        /* FIXME: this is for backwards compatibility with 2.4 */
2168        if (file->f_flags & O_APPEND)
2169                        *pos = i_size_read(inode);
2170
2171        if (limit != RLIM_INFINITY) {
2172            if (*pos >= limit) {
2173                send_sig(SIGXFSZ, current, 0);
2174                return -EFBIG;
2175            }
2176            if (*count > limit - (typeof(limit))*pos) {
2177                *count = limit - (typeof(limit))*pos;
2178            }
2179        }
2180    }
2181
2182    /*
2183     * LFS rule
2184     */
2185    if (unlikely(*pos + *count > MAX_NON_LFS &&
2186                !(file->f_flags & O_LARGEFILE))) {
2187        if (*pos >= MAX_NON_LFS) {
2188            return -EFBIG;
2189        }
2190        if (*count > MAX_NON_LFS - (unsigned long)*pos) {
2191            *count = MAX_NON_LFS - (unsigned long)*pos;
2192        }
2193    }
2194
2195    /*
2196     * Are we about to exceed the fs block limit ?
2197     *
2198     * If we have written data it becomes a short write. If we have
2199     * exceeded without writing data we send a signal and return EFBIG.
2200     * Linus frestrict idea will clean these up nicely..
2201     */
2202    if (likely(!isblk)) {
2203        if (unlikely(*pos >= inode->i_sb->s_maxbytes)) {
2204            if (*count || *pos > inode->i_sb->s_maxbytes) {
2205                return -EFBIG;
2206            }
2207            /* zero-length writes at ->s_maxbytes are OK */
2208        }
2209
2210        if (unlikely(*pos + *count > inode->i_sb->s_maxbytes))
2211            *count = inode->i_sb->s_maxbytes - *pos;
2212    } else {
2213#ifdef CONFIG_BLOCK
2214        loff_t isize;
2215        if (bdev_read_only(I_BDEV(inode)))
2216            return -EPERM;
2217        isize = i_size_read(inode);
2218        if (*pos >= isize) {
2219            if (*count || *pos > isize)
2220                return -ENOSPC;
2221        }
2222
2223        if (*pos + *count > isize)
2224            *count = isize - *pos;
2225#else
2226        return -EPERM;
2227#endif
2228    }
2229    return 0;
2230}
2231EXPORT_SYMBOL(generic_write_checks);
2232
2233int pagecache_write_begin(struct file *file, struct address_space *mapping,
2234                loff_t pos, unsigned len, unsigned flags,
2235                struct page **pagep, void **fsdata)
2236{
2237    const struct address_space_operations *aops = mapping->a_ops;
2238
2239    return aops->write_begin(file, mapping, pos, len, flags,
2240                            pagep, fsdata);
2241}
2242EXPORT_SYMBOL(pagecache_write_begin);
2243
2244int pagecache_write_end(struct file *file, struct address_space *mapping,
2245                loff_t pos, unsigned len, unsigned copied,
2246                struct page *page, void *fsdata)
2247{
2248    const struct address_space_operations *aops = mapping->a_ops;
2249
2250    mark_page_accessed(page);
2251    return aops->write_end(file, mapping, pos, len, copied, page, fsdata);
2252}
2253EXPORT_SYMBOL(pagecache_write_end);
2254
2255ssize_t
2256generic_file_direct_write(struct kiocb *iocb, const struct iovec *iov,
2257        unsigned long *nr_segs, loff_t pos, loff_t *ppos,
2258        size_t count, size_t ocount)
2259{
2260    struct file *file = iocb->ki_filp;
2261    struct address_space *mapping = file->f_mapping;
2262    struct inode *inode = mapping->host;
2263    ssize_t written;
2264    size_t write_len;
2265    pgoff_t end;
2266
2267    if (count != ocount)
2268        *nr_segs = iov_shorten((struct iovec *)iov, *nr_segs, count);
2269
2270    write_len = iov_length(iov, *nr_segs);
2271    end = (pos + write_len - 1) >> PAGE_CACHE_SHIFT;
2272
2273    written = filemap_write_and_wait_range(mapping, pos, pos + write_len - 1);
2274    if (written)
2275        goto out;
2276
2277    /*
2278     * After a write we want buffered reads to be sure to go to disk to get
2279     * the new data. We invalidate clean cached page from the region we're
2280     * about to write. We do this *before* the write so that we can return
2281     * without clobbering -EIOCBQUEUED from ->direct_IO().
2282     */
2283    if (mapping->nrpages) {
2284        written = invalidate_inode_pages2_range(mapping,
2285                    pos >> PAGE_CACHE_SHIFT, end);
2286        /*
2287         * If a page can not be invalidated, return 0 to fall back
2288         * to buffered write.
2289         */
2290        if (written) {
2291            if (written == -EBUSY)
2292                return 0;
2293            goto out;
2294        }
2295    }
2296
2297    written = mapping->a_ops->direct_IO(WRITE, iocb, iov, pos, *nr_segs);
2298
2299    /*
2300     * Finally, try again to invalidate clean pages which might have been
2301     * cached by non-direct readahead, or faulted in by get_user_pages()
2302     * if the source of the write was an mmap'ed region of the file
2303     * we're writing. Either one is a pretty crazy thing to do,
2304     * so we don't support it 100%. If this invalidation
2305     * fails, tough, the write still worked...
2306     */
2307    if (mapping->nrpages) {
2308        invalidate_inode_pages2_range(mapping,
2309                          pos >> PAGE_CACHE_SHIFT, end);
2310    }
2311
2312    if (written > 0) {
2313        pos += written;
2314        if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
2315            i_size_write(inode, pos);
2316            mark_inode_dirty(inode);
2317        }
2318        *ppos = pos;
2319    }
2320out:
2321    return written;
2322}
2323EXPORT_SYMBOL(generic_file_direct_write);
2324
2325/*
2326 * Find or create a page at the given pagecache position. Return the locked
2327 * page. This function is specifically for buffered writes.
2328 */
2329struct page *grab_cache_page_write_begin(struct address_space *mapping,
2330                    pgoff_t index, unsigned flags)
2331{
2332    int status;
2333    struct page *page;
2334    gfp_t gfp_notmask = 0;
2335    if (flags & AOP_FLAG_NOFS)
2336        gfp_notmask = __GFP_FS;
2337repeat:
2338    page = find_lock_page(mapping, index);
2339    if (page)
2340        goto found;
2341
2342    page = __page_cache_alloc(mapping_gfp_mask(mapping) & ~gfp_notmask);
2343    if (!page)
2344        return NULL;
2345    status = add_to_page_cache_lru(page, mapping, index,
2346                        GFP_KERNEL & ~gfp_notmask);
2347    if (unlikely(status)) {
2348        page_cache_release(page);
2349        if (status == -EEXIST)
2350            goto repeat;
2351        return NULL;
2352    }
2353found:
2354    wait_on_page_writeback(page);
2355    return page;
2356}
2357EXPORT_SYMBOL(grab_cache_page_write_begin);
2358
2359static ssize_t generic_perform_write(struct file *file,
2360                struct iov_iter *i, loff_t pos)
2361{
2362    struct address_space *mapping = file->f_mapping;
2363    const struct address_space_operations *a_ops = mapping->a_ops;
2364    long status = 0;
2365    ssize_t written = 0;
2366    unsigned int flags = 0;
2367
2368    /*
2369     * Copies from kernel address space cannot fail (NFSD is a big user).
2370     */
2371    if (segment_eq(get_fs(), KERNEL_DS))
2372        flags |= AOP_FLAG_UNINTERRUPTIBLE;
2373
2374    do {
2375        struct page *page;
2376        unsigned long offset; /* Offset into pagecache page */
2377        unsigned long bytes; /* Bytes to write to page */
2378        size_t copied; /* Bytes copied from user */
2379        void *fsdata;
2380
2381        offset = (pos & (PAGE_CACHE_SIZE - 1));
2382        bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
2383                        iov_iter_count(i));
2384
2385again:
2386
2387        /*
2388         * Bring in the user page that we will copy from _first_.
2389         * Otherwise there's a nasty deadlock on copying from the
2390         * same page as we're writing to, without it being marked
2391         * up-to-date.
2392         *
2393         * Not only is this an optimisation, but it is also required
2394         * to check that the address is actually valid, when atomic
2395         * usercopies are used, below.
2396         */
2397        if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
2398            status = -EFAULT;
2399            break;
2400        }
2401
2402        status = a_ops->write_begin(file, mapping, pos, bytes, flags,
2403                        &page, &fsdata);
2404        if (unlikely(status))
2405            break;
2406
2407        if (mapping_writably_mapped(mapping))
2408            flush_dcache_page(page);
2409
2410        pagefault_disable();
2411        copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
2412        pagefault_enable();
2413        flush_dcache_page(page);
2414
2415        mark_page_accessed(page);
2416        status = a_ops->write_end(file, mapping, pos, bytes, copied,
2417                        page, fsdata);
2418        if (unlikely(status < 0))
2419            break;
2420        copied = status;
2421
2422        cond_resched();
2423
2424        iov_iter_advance(i, copied);
2425        if (unlikely(copied == 0)) {
2426            /*
2427             * If we were unable to copy any data at all, we must
2428             * fall back to a single segment length write.
2429             *
2430             * If we didn't fallback here, we could livelock
2431             * because not all segments in the iov can be copied at
2432             * once without a pagefault.
2433             */
2434            bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
2435                        iov_iter_single_seg_count(i));
2436            goto again;
2437        }
2438        pos += copied;
2439        written += copied;
2440
2441        balance_dirty_pages_ratelimited(mapping);
2442
2443    } while (iov_iter_count(i));
2444
2445    return written ? written : status;
2446}
2447
2448ssize_t
2449generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
2450        unsigned long nr_segs, loff_t pos, loff_t *ppos,
2451        size_t count, ssize_t written)
2452{
2453    struct file *file = iocb->ki_filp;
2454    ssize_t status;
2455    struct iov_iter i;
2456
2457    iov_iter_init(&i, iov, nr_segs, count, written);
2458    status = generic_perform_write(file, &i, pos);
2459
2460    if (likely(status >= 0)) {
2461        written += status;
2462        *ppos = pos + status;
2463      }
2464    
2465    return written ? written : status;
2466}
2467EXPORT_SYMBOL(generic_file_buffered_write);
2468
2469/**
2470 * __generic_file_aio_write - write data to a file
2471 * @iocb: IO state structure (file, offset, etc.)
2472 * @iov: vector with data to write
2473 * @nr_segs: number of segments in the vector
2474 * @ppos: position where to write
2475 *
2476 * This function does all the work needed for actually writing data to a
2477 * file. It does all basic checks, removes SUID from the file, updates
2478 * modification times and calls proper subroutines depending on whether we
2479 * do direct IO or a standard buffered write.
2480 *
2481 * It expects i_mutex to be grabbed unless we work on a block device or similar
2482 * object which does not need locking at all.
2483 *
2484 * This function does *not* take care of syncing data in case of O_SYNC write.
2485 * A caller has to handle it. This is mainly due to the fact that we want to
2486 * avoid syncing under i_mutex.
2487 */
2488ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
2489                 unsigned long nr_segs, loff_t *ppos)
2490{
2491    struct file *file = iocb->ki_filp;
2492    struct address_space * mapping = file->f_mapping;
2493    size_t ocount; /* original count */
2494    size_t count; /* after file limit checks */
2495    struct inode *inode = mapping->host;
2496    loff_t pos;
2497    ssize_t written;
2498    ssize_t err;
2499
2500    ocount = 0;
2501    err = generic_segment_checks(iov, &nr_segs, &ocount, VERIFY_READ);
2502    if (err)
2503        return err;
2504
2505    count = ocount;
2506    pos = *ppos;
2507
2508    vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
2509
2510    /* We can write back this queue in page reclaim */
2511    current->backing_dev_info = mapping->backing_dev_info;
2512    written = 0;
2513
2514    err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));
2515    if (err)
2516        goto out;
2517
2518    if (count == 0)
2519        goto out;
2520
2521    err = file_remove_suid(file);
2522    if (err)
2523        goto out;
2524
2525    file_update_time(file);
2526
2527    /* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
2528    if (unlikely(file->f_flags & O_DIRECT)) {
2529        loff_t endbyte;
2530        ssize_t written_buffered;
2531
2532        written = generic_file_direct_write(iocb, iov, &nr_segs, pos,
2533                            ppos, count, ocount);
2534        if (written < 0 || written == count)
2535            goto out;
2536        /*
2537         * direct-io write to a hole: fall through to buffered I/O
2538         * for completing the rest of the request.
2539         */
2540        pos += written;
2541        count -= written;
2542        written_buffered = generic_file_buffered_write(iocb, iov,
2543                        nr_segs, pos, ppos, count,
2544                        written);
2545        /*
2546         * If generic_file_buffered_write() retuned a synchronous error
2547         * then we want to return the number of bytes which were
2548         * direct-written, or the error code if that was zero. Note
2549         * that this differs from normal direct-io semantics, which
2550         * will return -EFOO even if some bytes were written.
2551         */
2552        if (written_buffered < 0) {
2553            err = written_buffered;
2554            goto out;
2555        }
2556
2557        /*
2558         * We need to ensure that the page cache pages are written to
2559         * disk and invalidated to preserve the expected O_DIRECT
2560         * semantics.
2561         */
2562        endbyte = pos + written_buffered - written - 1;
2563        err = filemap_write_and_wait_range(file->f_mapping, pos, endbyte);
2564        if (err == 0) {
2565            written = written_buffered;
2566            invalidate_mapping_pages(mapping,
2567                         pos >> PAGE_CACHE_SHIFT,
2568                         endbyte >> PAGE_CACHE_SHIFT);
2569        } else {
2570            /*
2571             * We don't know how much we wrote, so just return
2572             * the number of bytes which were direct-written
2573             */
2574        }
2575    } else {
2576        written = generic_file_buffered_write(iocb, iov, nr_segs,
2577                pos, ppos, count, written);
2578    }
2579out:
2580    current->backing_dev_info = NULL;
2581    return written ? written : err;
2582}
2583EXPORT_SYMBOL(__generic_file_aio_write);
2584
2585/**
2586 * generic_file_aio_write - write data to a file
2587 * @iocb: IO state structure
2588 * @iov: vector with data to write
2589 * @nr_segs: number of segments in the vector
2590 * @pos: position in file where to write
2591 *
2592 * This is a wrapper around __generic_file_aio_write() to be used by most
2593 * filesystems. It takes care of syncing the file in case of O_SYNC file
2594 * and acquires i_mutex as needed.
2595 */
2596ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
2597        unsigned long nr_segs, loff_t pos)
2598{
2599    struct file *file = iocb->ki_filp;
2600    struct inode *inode = file->f_mapping->host;
2601    struct blk_plug plug;
2602    ssize_t ret;
2603
2604    BUG_ON(iocb->ki_pos != pos);
2605
2606    mutex_lock(&inode->i_mutex);
2607    blk_start_plug(&plug);
2608    ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
2609    mutex_unlock(&inode->i_mutex);
2610
2611    if (ret > 0 || ret == -EIOCBQUEUED) {
2612        ssize_t err;
2613
2614        err = generic_write_sync(file, pos, ret);
2615        if (err < 0 && ret > 0)
2616            ret = err;
2617    }
2618    blk_finish_plug(&plug);
2619    return ret;
2620}
2621EXPORT_SYMBOL(generic_file_aio_write);
2622
2623/**
2624 * try_to_release_page() - release old fs-specific metadata on a page
2625 *
2626 * @page: the page which the kernel is trying to free
2627 * @gfp_mask: memory allocation flags (and I/O mode)
2628 *
2629 * The address_space is to try to release any data against the page
2630 * (presumably at page->private). If the release was successful, return `1'.
2631 * Otherwise return zero.
2632 *
2633 * This may also be called if PG_fscache is set on a page, indicating that the
2634 * page is known to the local caching routines.
2635 *
2636 * The @gfp_mask argument specifies whether I/O may be performed to release
2637 * this page (__GFP_IO), and whether the call may block (__GFP_WAIT & __GFP_FS).
2638 *
2639 */
2640int try_to_release_page(struct page *page, gfp_t gfp_mask)
2641{
2642    struct address_space * const mapping = page->mapping;
2643
2644    BUG_ON(!PageLocked(page));
2645    if (PageWriteback(page))
2646        return 0;
2647
2648    if (mapping && mapping->a_ops->releasepage)
2649        return mapping->a_ops->releasepage(page, gfp_mask);
2650    return try_to_free_buffers(page);
2651}
2652
2653EXPORT_SYMBOL(try_to_release_page);
2654

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