Add the rt linux 4.1.3-rt3 as base

Import the rt linux 4.1.3-rt3 as OPNFV kvm base.

It's from git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git linux-4.1.y-rt and
the base is:

commit 0917f823c59692d751951bf5ea699a2d1e2f26a2
Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date:   Sat Jul 25 12:13:34 2015 +0200

    Prepare v4.1.3-rt3

    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

We lose all the git history this way and it's not good. We
should apply another opnfv project repo in future.

Change-Id: I87543d81c9df70d99c5001fbdf646b202c19f423
Signed-off-by: Yunhong Jiang <yunhong.jiang@intel.com>

1 files changed, 2670 insertions, 0 deletions

diff --git a/kernel/mm/filemap.c b/kernel/mm/filemap.c
new file mode 100644
index 000000000..01cf28476
--- /dev/null
+++ b/kernel/mm/filemap.c
@@ -0,0 +1,2670 @@
+/*
+ *	linux/mm/filemap.c
+ *
+ * Copyright (C) 1994-1999  Linus Torvalds
+ */
+
+/*
+ * This file handles the generic file mmap semantics used by
+ * most "normal" filesystems (but you don't /have/ to use this:
+ * the NFS filesystem used to do this differently, for example)
+ */
+#include <linux/export.h>
+#include <linux/compiler.h>
+#include <linux/fs.h>
+#include <linux/uaccess.h>
+#include <linux/capability.h>
+#include <linux/kernel_stat.h>
+#include <linux/gfp.h>
+#include <linux/mm.h>
+#include <linux/swap.h>
+#include <linux/mman.h>
+#include <linux/pagemap.h>
+#include <linux/file.h>
+#include <linux/uio.h>
+#include <linux/hash.h>
+#include <linux/writeback.h>
+#include <linux/backing-dev.h>
+#include <linux/pagevec.h>
+#include <linux/blkdev.h>
+#include <linux/security.h>
+#include <linux/cpuset.h>
+#include <linux/hardirq.h> /* for BUG_ON(!in_atomic()) only */
+#include <linux/hugetlb.h>
+#include <linux/memcontrol.h>
+#include <linux/cleancache.h>
+#include <linux/rmap.h>
+#include "internal.h"
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/filemap.h>
+
+/*
+ * FIXME: remove all knowledge of the buffer layer from the core VM
+ */
+#include <linux/buffer_head.h> /* for try_to_free_buffers */
+
+#include <asm/mman.h>
+
+/*
+ * Shared mappings implemented 30.11.1994. It's not fully working yet,
+ * though.
+ *
+ * Shared mappings now work. 15.8.1995  Bruno.
+ *
+ * finished 'unifying' the page and buffer cache and SMP-threaded the
+ * page-cache, 21.05.1999, Ingo Molnar <mingo@redhat.com>
+ *
+ * SMP-threaded pagemap-LRU 1999, Andrea Arcangeli <andrea@suse.de>
+ */
+
+/*
+ * Lock ordering:
+ *
+ *  ->i_mmap_rwsem		(truncate_pagecache)
+ *    ->private_lock		(__free_pte->__set_page_dirty_buffers)
+ *      ->swap_lock		(exclusive_swap_page, others)
+ *        ->mapping->tree_lock
+ *
+ *  ->i_mutex
+ *    ->i_mmap_rwsem		(truncate->unmap_mapping_range)
+ *
+ *  ->mmap_sem
+ *    ->i_mmap_rwsem
+ *      ->page_table_lock or pte_lock	(various, mainly in memory.c)
+ *        ->mapping->tree_lock	(arch-dependent flush_dcache_mmap_lock)
+ *
+ *  ->mmap_sem
+ *    ->lock_page		(access_process_vm)
+ *
+ *  ->i_mutex			(generic_perform_write)
+ *    ->mmap_sem		(fault_in_pages_readable->do_page_fault)
+ *
+ *  bdi->wb.list_lock
+ *    sb_lock			(fs/fs-writeback.c)
+ *    ->mapping->tree_lock	(__sync_single_inode)
+ *
+ *  ->i_mmap_rwsem
+ *    ->anon_vma.lock		(vma_adjust)
+ *
+ *  ->anon_vma.lock
+ *    ->page_table_lock or pte_lock	(anon_vma_prepare and various)
+ *
+ *  ->page_table_lock or pte_lock
+ *    ->swap_lock		(try_to_unmap_one)
+ *    ->private_lock		(try_to_unmap_one)
+ *    ->tree_lock		(try_to_unmap_one)
+ *    ->zone.lru_lock		(follow_page->mark_page_accessed)
+ *    ->zone.lru_lock		(check_pte_range->isolate_lru_page)
+ *    ->private_lock		(page_remove_rmap->set_page_dirty)
+ *    ->tree_lock		(page_remove_rmap->set_page_dirty)
+ *    bdi.wb->list_lock		(page_remove_rmap->set_page_dirty)
+ *    ->inode->i_lock		(page_remove_rmap->set_page_dirty)
+ *    bdi.wb->list_lock		(zap_pte_range->set_page_dirty)
+ *    ->inode->i_lock		(zap_pte_range->set_page_dirty)
+ *    ->private_lock		(zap_pte_range->__set_page_dirty_buffers)
+ *
+ * ->i_mmap_rwsem
+ *   ->tasklist_lock            (memory_failure, collect_procs_ao)
+ */
+
+static void page_cache_tree_delete(struct address_space *mapping,
+				   struct page *page, void *shadow)
+{
+	struct radix_tree_node *node;
+	unsigned long index;
+	unsigned int offset;
+	unsigned int tag;
+	void **slot;
+
+	VM_BUG_ON(!PageLocked(page));
+
+	__radix_tree_lookup(&mapping->page_tree, page->index, &node, &slot);
+
+	if (shadow) {
+		mapping->nrshadows++;
+		/*
+		 * Make sure the nrshadows update is committed before
+		 * the nrpages update so that final truncate racing
+		 * with reclaim does not see both counters 0 at the
+		 * same time and miss a shadow entry.
+		 */
+		smp_wmb();
+	}
+	mapping->nrpages--;
+
+	if (!node) {
+		/* Clear direct pointer tags in root node */
+		mapping->page_tree.gfp_mask &= __GFP_BITS_MASK;
+		radix_tree_replace_slot(slot, shadow);
+		return;
+	}
+
+	/* Clear tree tags for the removed page */
+	index = page->index;
+	offset = index & RADIX_TREE_MAP_MASK;
+	for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
+		if (test_bit(offset, node->tags[tag]))
+			radix_tree_tag_clear(&mapping->page_tree, index, tag);
+	}
+
+	/* Delete page, swap shadow entry */
+	radix_tree_replace_slot(slot, shadow);
+	workingset_node_pages_dec(node);
+	if (shadow)
+		workingset_node_shadows_inc(node);
+	else
+		if (__radix_tree_delete_node(&mapping->page_tree, node))
+			return;
+
+	/*
+	 * Track node that only contains shadow entries.
+	 *
+	 * Avoid acquiring the list_lru lock if already tracked.  The
+	 * list_empty() test is safe as node->private_list is
+	 * protected by mapping->tree_lock.
+	 */
+	if (!workingset_node_pages(node) &&
+	    list_empty(&node->private_list)) {
+		node->private_data = mapping;
+		local_lock(workingset_shadow_lock);
+		list_lru_add(&__workingset_shadow_nodes, &node->private_list);
+		local_unlock(workingset_shadow_lock);
+	}
+}
+
+/*
+ * Delete a page from the page cache and free it. Caller has to make
+ * sure the page is locked and that nobody else uses it - or that usage
+ * is safe.  The caller must hold the mapping's tree_lock.
+ */
+void __delete_from_page_cache(struct page *page, void *shadow)
+{
+	struct address_space *mapping = page->mapping;
+
+	trace_mm_filemap_delete_from_page_cache(page);
+	/*
+	 * if we're uptodate, flush out into the cleancache, otherwise
+	 * invalidate any existing cleancache entries.  We can't leave
+	 * stale data around in the cleancache once our page is gone
+	 */
+	if (PageUptodate(page) && PageMappedToDisk(page))
+		cleancache_put_page(page);
+	else
+		cleancache_invalidate_page(mapping, page);
+
+	page_cache_tree_delete(mapping, page, shadow);
+
+	page->mapping = NULL;
+	/* Leave page->index set: truncation lookup relies upon it */
+
+	__dec_zone_page_state(page, NR_FILE_PAGES);
+	if (PageSwapBacked(page))
+		__dec_zone_page_state(page, NR_SHMEM);
+	BUG_ON(page_mapped(page));
+
+	/*
+	 * At this point page must be either written or cleaned by truncate.
+	 * Dirty page here signals a bug and loss of unwritten data.
+	 *
+	 * This fixes dirty accounting after removing the page entirely but
+	 * leaves PageDirty set: it has no effect for truncated page and
+	 * anyway will be cleared before returning page into buddy allocator.
+	 */
+	if (WARN_ON_ONCE(PageDirty(page)))
+		account_page_cleaned(page, mapping);
+}
+
+/**
+ * delete_from_page_cache - delete page from page cache
+ * @page: the page which the kernel is trying to remove from page cache
+ *
+ * This must be called only on pages that have been verified to be in the page
+ * cache and locked.  It will never put the page into the free list, the caller
+ * has a reference on the page.
+ */
+void delete_from_page_cache(struct page *page)
+{
+	struct address_space *mapping = page->mapping;
+	void (*freepage)(struct page *);
+
+	BUG_ON(!PageLocked(page));
+
+	freepage = mapping->a_ops->freepage;
+	spin_lock_irq(&mapping->tree_lock);
+	__delete_from_page_cache(page, NULL);
+	spin_unlock_irq(&mapping->tree_lock);
+
+	if (freepage)
+		freepage(page);
+	page_cache_release(page);
+}
+EXPORT_SYMBOL(delete_from_page_cache);
+
+static int filemap_check_errors(struct address_space *mapping)
+{
+	int ret = 0;
+	/* Check for outstanding write errors */
+	if (test_bit(AS_ENOSPC, &mapping->flags) &&
+	    test_and_clear_bit(AS_ENOSPC, &mapping->flags))
+		ret = -ENOSPC;
+	if (test_bit(AS_EIO, &mapping->flags) &&
+	    test_and_clear_bit(AS_EIO, &mapping->flags))
+		ret = -EIO;
+	return ret;
+}
+
+/**
+ * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
+ * @mapping:	address space structure to write
+ * @start:	offset in bytes where the range starts
+ * @end:	offset in bytes where the range ends (inclusive)
+ * @sync_mode:	enable synchronous operation
+ *
+ * Start writeback against all of a mapping's dirty pages that lie
+ * within the byte offsets <start, end> inclusive.
+ *
+ * If sync_mode is WB_SYNC_ALL then this is a "data integrity" operation, as
+ * opposed to a regular memory cleansing writeback.  The difference between
+ * these two operations is that if a dirty page/buffer is encountered, it must
+ * be waited upon, and not just skipped over.
+ */
+int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
+				loff_t end, int sync_mode)
+{
+	int ret;
+	struct writeback_control wbc = {
+		.sync_mode = sync_mode,
+		.nr_to_write = LONG_MAX,
+		.range_start = start,
+		.range_end = end,
+	};
+
+	if (!mapping_cap_writeback_dirty(mapping))
+		return 0;
+
+	ret = do_writepages(mapping, &wbc);
+	return ret;
+}
+
+static inline int __filemap_fdatawrite(struct address_space *mapping,
+	int sync_mode)
+{
+	return __filemap_fdatawrite_range(mapping, 0, LLONG_MAX, sync_mode);
+}
+
+int filemap_fdatawrite(struct address_space *mapping)
+{
+	return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
+}
+EXPORT_SYMBOL(filemap_fdatawrite);
+
+int filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
+				loff_t end)
+{
+	return __filemap_fdatawrite_range(mapping, start, end, WB_SYNC_ALL);
+}
+EXPORT_SYMBOL(filemap_fdatawrite_range);
+
+/**
+ * filemap_flush - mostly a non-blocking flush
+ * @mapping:	target address_space
+ *
+ * This is a mostly non-blocking flush.  Not suitable for data-integrity
+ * purposes - I/O may not be started against all dirty pages.
+ */
+int filemap_flush(struct address_space *mapping)
+{
+	return __filemap_fdatawrite(mapping, WB_SYNC_NONE);
+}
+EXPORT_SYMBOL(filemap_flush);
+
+/**
+ * filemap_fdatawait_range - wait for writeback to complete
+ * @mapping:		address space structure to wait for
+ * @start_byte:		offset in bytes where the range starts
+ * @end_byte:		offset in bytes where the range ends (inclusive)
+ *
+ * Walk the list of under-writeback pages of the given address space
+ * in the given range and wait for all of them.
+ */
+int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
+			    loff_t end_byte)
+{
+	pgoff_t index = start_byte >> PAGE_CACHE_SHIFT;
+	pgoff_t end = end_byte >> PAGE_CACHE_SHIFT;
+	struct pagevec pvec;
+	int nr_pages;
+	int ret2, ret = 0;
+
+	if (end_byte < start_byte)
+		goto out;
+
+	pagevec_init(&pvec, 0);
+	while ((index <= end) &&
+			(nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
+			PAGECACHE_TAG_WRITEBACK,
+			min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1)) != 0) {
+		unsigned i;
+
+		for (i = 0; i < nr_pages; i++) {
+			struct page *page = pvec.pages[i];
+
+			/* until radix tree lookup accepts end_index */
+			if (page->index > end)
+				continue;
+
+			wait_on_page_writeback(page);
+			if (TestClearPageError(page))
+				ret = -EIO;
+		}
+		pagevec_release(&pvec);
+		cond_resched();
+	}
+out:
+	ret2 = filemap_check_errors(mapping);
+	if (!ret)
+		ret = ret2;
+
+	return ret;
+}
+EXPORT_SYMBOL(filemap_fdatawait_range);
+
+/**
+ * filemap_fdatawait - wait for all under-writeback pages to complete
+ * @mapping: address space structure to wait for
+ *
+ * Walk the list of under-writeback pages of the given address space
+ * and wait for all of them.
+ */
+int filemap_fdatawait(struct address_space *mapping)
+{
+	loff_t i_size = i_size_read(mapping->host);
+
+	if (i_size == 0)
+		return 0;
+
+	return filemap_fdatawait_range(mapping, 0, i_size - 1);
+}
+EXPORT_SYMBOL(filemap_fdatawait);
+
+int filemap_write_and_wait(struct address_space *mapping)
+{
+	int err = 0;
+
+	if (mapping->nrpages) {
+		err = filemap_fdatawrite(mapping);
+		/*
+		 * Even if the above returned error, the pages may be
+		 * written partially (e.g. -ENOSPC), so we wait for it.
+		 * But the -EIO is special case, it may indicate the worst
+		 * thing (e.g. bug) happened, so we avoid waiting for it.
+		 */
+		if (err != -EIO) {
+			int err2 = filemap_fdatawait(mapping);
+			if (!err)
+				err = err2;
+		}
+	} else {
+		err = filemap_check_errors(mapping);
+	}
+	return err;
+}
+EXPORT_SYMBOL(filemap_write_and_wait);
+
+/**
+ * filemap_write_and_wait_range - write out & wait on a file range
+ * @mapping:	the address_space for the pages
+ * @lstart:	offset in bytes where the range starts
+ * @lend:	offset in bytes where the range ends (inclusive)
+ *
+ * Write out and wait upon file offsets lstart->lend, inclusive.
+ *
+ * Note that `lend' is inclusive (describes the last byte to be written) so
+ * that this function can be used to write to the very end-of-file (end = -1).
+ */
+int filemap_write_and_wait_range(struct address_space *mapping,
+				 loff_t lstart, loff_t lend)
+{
+	int err = 0;
+
+	if (mapping->nrpages) {
+		err = __filemap_fdatawrite_range(mapping, lstart, lend,
+						 WB_SYNC_ALL);
+		/* See comment of filemap_write_and_wait() */
+		if (err != -EIO) {
+			int err2 = filemap_fdatawait_range(mapping,
+						lstart, lend);
+			if (!err)
+				err = err2;
+		}
+	} else {
+		err = filemap_check_errors(mapping);
+	}
+	return err;
+}
+EXPORT_SYMBOL(filemap_write_and_wait_range);
+
+/**
+ * replace_page_cache_page - replace a pagecache page with a new one
+ * @old:	page to be replaced
+ * @new:	page to replace with
+ * @gfp_mask:	allocation mode
+ *
+ * This function replaces a page in the pagecache with a new one.  On
+ * success it acquires the pagecache reference for the new page and
+ * drops it for the old page.  Both the old and new pages must be
+ * locked.  This function does not add the new page to the LRU, the
+ * caller must do that.
+ *
+ * The remove + add is atomic.  The only way this function can fail is
+ * memory allocation failure.
+ */
+int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
+{
+	int error;
+
+	VM_BUG_ON_PAGE(!PageLocked(old), old);
+	VM_BUG_ON_PAGE(!PageLocked(new), new);
+	VM_BUG_ON_PAGE(new->mapping, new);
+
+	error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
+	if (!error) {
+		struct address_space *mapping = old->mapping;
+		void (*freepage)(struct page *);
+
+		pgoff_t offset = old->index;
+		freepage = mapping->a_ops->freepage;
+
+		page_cache_get(new);
+		new->mapping = mapping;
+		new->index = offset;
+
+		spin_lock_irq(&mapping->tree_lock);
+		__delete_from_page_cache(old, NULL);
+		error = radix_tree_insert(&mapping->page_tree, offset, new);
+		BUG_ON(error);
+		mapping->nrpages++;
+		__inc_zone_page_state(new, NR_FILE_PAGES);
+		if (PageSwapBacked(new))
+			__inc_zone_page_state(new, NR_SHMEM);
+		spin_unlock_irq(&mapping->tree_lock);
+		mem_cgroup_migrate(old, new, true);
+		radix_tree_preload_end();
+		if (freepage)
+			freepage(old);
+		page_cache_release(old);
+	}
+
+	return error;
+}
+EXPORT_SYMBOL_GPL(replace_page_cache_page);
+
+static int page_cache_tree_insert(struct address_space *mapping,
+				  struct page *page, void **shadowp)
+{
+	struct radix_tree_node *node;
+	void **slot;
+	int error;
+
+	error = __radix_tree_create(&mapping->page_tree, page->index,
+				    &node, &slot);
+	if (error)
+		return error;
+	if (*slot) {
+		void *p;
+
+		p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
+		if (!radix_tree_exceptional_entry(p))
+			return -EEXIST;
+		if (shadowp)
+			*shadowp = p;
+		mapping->nrshadows--;
+		if (node)
+			workingset_node_shadows_dec(node);
+	}
+	radix_tree_replace_slot(slot, page);
+	mapping->nrpages++;
+	if (node) {
+		workingset_node_pages_inc(node);
+		/*
+		 * Don't track node that contains actual pages.
+		 *
+		 * Avoid acquiring the list_lru lock if already
+		 * untracked.  The list_empty() test is safe as
+		 * node->private_list is protected by
+		 * mapping->tree_lock.
+		 */
+		if (!list_empty(&node->private_list)) {
+			local_lock(workingset_shadow_lock);
+			list_lru_del(&__workingset_shadow_nodes,
+				     &node->private_list);
+			local_unlock(workingset_shadow_lock);
+		}
+	}
+	return 0;
+}
+
+static int __add_to_page_cache_locked(struct page *page,
+				      struct address_space *mapping,
+				      pgoff_t offset, gfp_t gfp_mask,
+				      void **shadowp)
+{
+	int huge = PageHuge(page);
+	struct mem_cgroup *memcg;
+	int error;
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE(PageSwapBacked(page), page);
+
+	if (!huge) {
+		error = mem_cgroup_try_charge(page, current->mm,
+					      gfp_mask, &memcg);
+		if (error)
+			return error;
+	}
+
+	error = radix_tree_maybe_preload(gfp_mask & ~__GFP_HIGHMEM);
+	if (error) {
+		if (!huge)
+			mem_cgroup_cancel_charge(page, memcg);
+		return error;
+	}
+
+	page_cache_get(page);
+	page->mapping = mapping;
+	page->index = offset;
+
+	spin_lock_irq(&mapping->tree_lock);
+	error = page_cache_tree_insert(mapping, page, shadowp);
+	radix_tree_preload_end();
+	if (unlikely(error))
+		goto err_insert;
+	__inc_zone_page_state(page, NR_FILE_PAGES);
+	spin_unlock_irq(&mapping->tree_lock);
+	if (!huge)
+		mem_cgroup_commit_charge(page, memcg, false);
+	trace_mm_filemap_add_to_page_cache(page);
+	return 0;
+err_insert:
+	page->mapping = NULL;
+	/* Leave page->index set: truncation relies upon it */
+	spin_unlock_irq(&mapping->tree_lock);
+	if (!huge)
+		mem_cgroup_cancel_charge(page, memcg);
+	page_cache_release(page);
+	return error;
+}
+
+/**
+ * add_to_page_cache_locked - add a locked page to the pagecache
+ * @page:	page to add
+ * @mapping:	the page's address_space
+ * @offset:	page index
+ * @gfp_mask:	page allocation mode
+ *
+ * This function is used to add a page to the pagecache. It must be locked.
+ * This function does not add the page to the LRU.  The caller must do that.
+ */
+int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
+		pgoff_t offset, gfp_t gfp_mask)
+{
+	return __add_to_page_cache_locked(page, mapping, offset,
+					  gfp_mask, NULL);
+}
+EXPORT_SYMBOL(add_to_page_cache_locked);
+
+int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
+				pgoff_t offset, gfp_t gfp_mask)
+{
+	void *shadow = NULL;
+	int ret;
+
+	__set_page_locked(page);
+	ret = __add_to_page_cache_locked(page, mapping, offset,
+					 gfp_mask, &shadow);
+	if (unlikely(ret))
+		__clear_page_locked(page);
+	else {
+		/*
+		 * The page might have been evicted from cache only
+		 * recently, in which case it should be activated like
+		 * any other repeatedly accessed page.
+		 */
+		if (shadow && workingset_refault(shadow)) {
+			SetPageActive(page);
+			workingset_activation(page);
+		} else
+			ClearPageActive(page);
+		lru_cache_add(page);
+	}
+	return ret;
+}
+EXPORT_SYMBOL_GPL(add_to_page_cache_lru);
+
+#ifdef CONFIG_NUMA
+struct page *__page_cache_alloc(gfp_t gfp)
+{
+	int n;
+	struct page *page;
+
+	if (cpuset_do_page_mem_spread()) {
+		unsigned int cpuset_mems_cookie;
+		do {
+			cpuset_mems_cookie = read_mems_allowed_begin();
+			n = cpuset_mem_spread_node();
+			page = alloc_pages_exact_node(n, gfp, 0);
+		} while (!page && read_mems_allowed_retry(cpuset_mems_cookie));
+
+		return page;
+	}
+	return alloc_pages(gfp, 0);
+}
+EXPORT_SYMBOL(__page_cache_alloc);
+#endif
+
+/*
+ * In order to wait for pages to become available there must be
+ * waitqueues associated with pages. By using a hash table of
+ * waitqueues where the bucket discipline is to maintain all
+ * waiters on the same queue and wake all when any of the pages
+ * become available, and for the woken contexts to check to be
+ * sure the appropriate page became available, this saves space
+ * at a cost of "thundering herd" phenomena during rare hash
+ * collisions.
+ */
+wait_queue_head_t *page_waitqueue(struct page *page)
+{
+	const struct zone *zone = page_zone(page);
+
+	return &zone->wait_table[hash_ptr(page, zone->wait_table_bits)];
+}
+EXPORT_SYMBOL(page_waitqueue);
+
+void wait_on_page_bit(struct page *page, int bit_nr)
+{
+	DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
+
+	if (test_bit(bit_nr, &page->flags))
+		__wait_on_bit(page_waitqueue(page), &wait, bit_wait_io,
+							TASK_UNINTERRUPTIBLE);
+}
+EXPORT_SYMBOL(wait_on_page_bit);
+
+int wait_on_page_bit_killable(struct page *page, int bit_nr)
+{
+	DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
+
+	if (!test_bit(bit_nr, &page->flags))
+		return 0;
+
+	return __wait_on_bit(page_waitqueue(page), &wait,
+			     bit_wait_io, TASK_KILLABLE);
+}
+
+int wait_on_page_bit_killable_timeout(struct page *page,
+				       int bit_nr, unsigned long timeout)
+{
+	DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
+
+	wait.key.timeout = jiffies + timeout;
+	if (!test_bit(bit_nr, &page->flags))
+		return 0;
+	return __wait_on_bit(page_waitqueue(page), &wait,
+			     bit_wait_io_timeout, TASK_KILLABLE);
+}
+EXPORT_SYMBOL_GPL(wait_on_page_bit_killable_timeout);
+
+/**
+ * add_page_wait_queue - Add an arbitrary waiter to a page's wait queue
+ * @page: Page defining the wait queue of interest
+ * @waiter: Waiter to add to the queue
+ *
+ * Add an arbitrary @waiter to the wait queue for the nominated @page.
+ */
+void add_page_wait_queue(struct page *page, wait_queue_t *waiter)
+{
+	wait_queue_head_t *q = page_waitqueue(page);
+	unsigned long flags;
+
+	spin_lock_irqsave(&q->lock, flags);
+	__add_wait_queue(q, waiter);
+	spin_unlock_irqrestore(&q->lock, flags);
+}
+EXPORT_SYMBOL_GPL(add_page_wait_queue);
+
+/**
+ * unlock_page - unlock a locked page
+ * @page: the page
+ *
+ * Unlocks the page and wakes up sleepers in ___wait_on_page_locked().
+ * Also wakes sleepers in wait_on_page_writeback() because the wakeup
+ * mechanism between PageLocked pages and PageWriteback pages is shared.
+ * But that's OK - sleepers in wait_on_page_writeback() just go back to sleep.
+ *
+ * The mb is necessary to enforce ordering between the clear_bit and the read
+ * of the waitqueue (to avoid SMP races with a parallel wait_on_page_locked()).
+ */
+void unlock_page(struct page *page)
+{
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	clear_bit_unlock(PG_locked, &page->flags);
+	smp_mb__after_atomic();
+	wake_up_page(page, PG_locked);
+}
+EXPORT_SYMBOL(unlock_page);
+
+/**
+ * end_page_writeback - end writeback against a page
+ * @page: the page
+ */
+void end_page_writeback(struct page *page)
+{
+	/*
+	 * TestClearPageReclaim could be used here but it is an atomic
+	 * operation and overkill in this particular case. Failing to
+	 * shuffle a page marked for immediate reclaim is too mild to
+	 * justify taking an atomic operation penalty at the end of
+	 * ever page writeback.
+	 */
+	if (PageReclaim(page)) {
+		ClearPageReclaim(page);
+		rotate_reclaimable_page(page);
+	}
+
+	if (!test_clear_page_writeback(page))
+		BUG();
+
+	smp_mb__after_atomic();
+	wake_up_page(page, PG_writeback);
+}
+EXPORT_SYMBOL(end_page_writeback);
+
+/*
+ * After completing I/O on a page, call this routine to update the page
+ * flags appropriately
+ */
+void page_endio(struct page *page, int rw, int err)
+{
+	if (rw == READ) {
+		if (!err) {
+			SetPageUptodate(page);
+		} else {
+			ClearPageUptodate(page);
+			SetPageError(page);
+		}
+		unlock_page(page);
+	} else { /* rw == WRITE */
+		if (err) {
+			SetPageError(page);
+			if (page->mapping)
+				mapping_set_error(page->mapping, err);
+		}
+		end_page_writeback(page);
+	}
+}
+EXPORT_SYMBOL_GPL(page_endio);
+
+/**
+ * __lock_page - get a lock on the page, assuming we need to sleep to get it
+ * @page: the page to lock
+ */
+void __lock_page(struct page *page)
+{
+	DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
+
+	__wait_on_bit_lock(page_waitqueue(page), &wait, bit_wait_io,
+							TASK_UNINTERRUPTIBLE);
+}
+EXPORT_SYMBOL(__lock_page);
+
+int __lock_page_killable(struct page *page)
+{
+	DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
+
+	return __wait_on_bit_lock(page_waitqueue(page), &wait,
+					bit_wait_io, TASK_KILLABLE);
+}
+EXPORT_SYMBOL_GPL(__lock_page_killable);
+
+/*
+ * Return values:
+ * 1 - page is locked; mmap_sem is still held.
+ * 0 - page is not locked.
+ *     mmap_sem has been released (up_read()), unless flags had both
+ *     FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_RETRY_NOWAIT set, in
+ *     which case mmap_sem is still held.
+ *
+ * If neither ALLOW_RETRY nor KILLABLE are set, will always return 1
+ * with the page locked and the mmap_sem unperturbed.
+ */
+int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
+			 unsigned int flags)
+{
+	if (flags & FAULT_FLAG_ALLOW_RETRY) {
+		/*
+		 * CAUTION! In this case, mmap_sem is not released
+		 * even though return 0.
+		 */
+		if (flags & FAULT_FLAG_RETRY_NOWAIT)
+			return 0;
+
+		up_read(&mm->mmap_sem);
+		if (flags & FAULT_FLAG_KILLABLE)
+			wait_on_page_locked_killable(page);
+		else
+			wait_on_page_locked(page);
+		return 0;
+	} else {
+		if (flags & FAULT_FLAG_KILLABLE) {
+			int ret;
+
+			ret = __lock_page_killable(page);
+			if (ret) {
+				up_read(&mm->mmap_sem);
+				return 0;
+			}
+		} else
+			__lock_page(page);
+		return 1;
+	}
+}
+
+/**
+ * page_cache_next_hole - find the next hole (not-present entry)
+ * @mapping: mapping
+ * @index: index
+ * @max_scan: maximum range to search
+ *
+ * Search the set [index, min(index+max_scan-1, MAX_INDEX)] for the
+ * lowest indexed hole.
+ *
+ * Returns: the index of the hole if found, otherwise returns an index
+ * outside of the set specified (in which case 'return - index >=
+ * max_scan' will be true). In rare cases of index wrap-around, 0 will
+ * be returned.
+ *
+ * page_cache_next_hole may be called under rcu_read_lock. However,
+ * like radix_tree_gang_lookup, this will not atomically search a
+ * snapshot of the tree at a single point in time. For example, if a
+ * hole is created at index 5, then subsequently a hole is created at
+ * index 10, page_cache_next_hole covering both indexes may return 10
+ * if called under rcu_read_lock.
+ */
+pgoff_t page_cache_next_hole(struct address_space *mapping,
+			     pgoff_t index, unsigned long max_scan)
+{
+	unsigned long i;
+
+	for (i = 0; i < max_scan; i++) {
+		struct page *page;
+
+		page = radix_tree_lookup(&mapping->page_tree, index);
+		if (!page || radix_tree_exceptional_entry(page))
+			break;
+		index++;
+		if (index == 0)
+			break;
+	}
+
+	return index;
+}
+EXPORT_SYMBOL(page_cache_next_hole);
+
+/**
+ * page_cache_prev_hole - find the prev hole (not-present entry)
+ * @mapping: mapping
+ * @index: index
+ * @max_scan: maximum range to search
+ *
+ * Search backwards in the range [max(index-max_scan+1, 0), index] for
+ * the first hole.
+ *
+ * Returns: the index of the hole if found, otherwise returns an index
+ * outside of the set specified (in which case 'index - return >=
+ * max_scan' will be true). In rare cases of wrap-around, ULONG_MAX
+ * will be returned.
+ *
+ * page_cache_prev_hole may be called under rcu_read_lock. However,
+ * like radix_tree_gang_lookup, this will not atomically search a
+ * snapshot of the tree at a single point in time. For example, if a
+ * hole is created at index 10, then subsequently a hole is created at
+ * index 5, page_cache_prev_hole covering both indexes may return 5 if
+ * called under rcu_read_lock.
+ */
+pgoff_t page_cache_prev_hole(struct address_space *mapping,
+			     pgoff_t index, unsigned long max_scan)
+{
+	unsigned long i;
+
+	for (i = 0; i < max_scan; i++) {
+		struct page *page;
+
+		page = radix_tree_lookup(&mapping->page_tree, index);
+		if (!page || radix_tree_exceptional_entry(page))
+			break;
+		index--;
+		if (index == ULONG_MAX)
+			break;
+	}
+
+	return index;
+}
+EXPORT_SYMBOL(page_cache_prev_hole);
+
+/**
+ * find_get_entry - find and get a page cache entry
+ * @mapping: the address_space to search
+ * @offset: the page cache index
+ *
+ * Looks up the page cache slot at @mapping & @offset.  If there is a
+ * page cache page, it is returned with an increased refcount.
+ *
+ * If the slot holds a shadow entry of a previously evicted page, or a
+ * swap entry from shmem/tmpfs, it is returned.
+ *
+ * Otherwise, %NULL is returned.
+ */
+struct page *find_get_entry(struct address_space *mapping, pgoff_t offset)
+{
+	void **pagep;
+	struct page *page;
+
+	rcu_read_lock();
+repeat:
+	page = NULL;
+	pagep = radix_tree_lookup_slot(&mapping->page_tree, offset);
+	if (pagep) {
+		page = radix_tree_deref_slot(pagep);
+		if (unlikely(!page))
+			goto out;
+		if (radix_tree_exception(page)) {
+			if (radix_tree_deref_retry(page))
+				goto repeat;
+			/*
+			 * A shadow entry of a recently evicted page,
+			 * or a swap entry from shmem/tmpfs.  Return
+			 * it without attempting to raise page count.
+			 */
+			goto out;
+		}
+		if (!page_cache_get_speculative(page))
+			goto repeat;
+
+		/*
+		 * Has the page moved?
+		 * This is part of the lockless pagecache protocol. See
+		 * include/linux/pagemap.h for details.
+		 */
+		if (unlikely(page != *pagep)) {
+			page_cache_release(page);
+			goto repeat;
+		}
+	}
+out:
+	rcu_read_unlock();
+
+	return page;
+}
+EXPORT_SYMBOL(find_get_entry);
+
+/**
+ * find_lock_entry - locate, pin and lock a page cache entry
+ * @mapping: the address_space to search
+ * @offset: the page cache index
+ *
+ * Looks up the page cache slot at @mapping & @offset.  If there is a
+ * page cache page, it is returned locked and with an increased
+ * refcount.
+ *
+ * If the slot holds a shadow entry of a previously evicted page, or a
+ * swap entry from shmem/tmpfs, it is returned.
+ *
+ * Otherwise, %NULL is returned.
+ *
+ * find_lock_entry() may sleep.
+ */
+struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset)
+{
+	struct page *page;
+
+repeat:
+	page = find_get_entry(mapping, offset);
+	if (page && !radix_tree_exception(page)) {
+		lock_page(page);
+		/* Has the page been truncated? */
+		if (unlikely(page->mapping != mapping)) {
+			unlock_page(page);
+			page_cache_release(page);
+			goto repeat;
+		}
+		VM_BUG_ON_PAGE(page->index != offset, page);
+	}
+	return page;
+}
+EXPORT_SYMBOL(find_lock_entry);
+
+/**
+ * pagecache_get_page - find and get a page reference
+ * @mapping: the address_space to search
+ * @offset: the page index
+ * @fgp_flags: PCG flags
+ * @gfp_mask: gfp mask to use for the page cache data page allocation
+ *
+ * Looks up the page cache slot at @mapping & @offset.
+ *
+ * PCG flags modify how the page is returned.
+ *
+ * FGP_ACCESSED: the page will be marked accessed
+ * FGP_LOCK: Page is return locked
+ * FGP_CREAT: If page is not present then a new page is allocated using
+ *		@gfp_mask and added to the page cache and the VM's LRU
+ *		list. The page is returned locked and with an increased
+ *		refcount. Otherwise, %NULL is returned.
+ *
+ * If FGP_LOCK or FGP_CREAT are specified then the function may sleep even
+ * if the GFP flags specified for FGP_CREAT are atomic.
+ *
+ * If there is a page cache page, it is returned with an increased refcount.
+ */
+struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
+	int fgp_flags, gfp_t gfp_mask)
+{
+	struct page *page;
+
+repeat:
+	page = find_get_entry(mapping, offset);
+	if (radix_tree_exceptional_entry(page))
+		page = NULL;
+	if (!page)
+		goto no_page;
+
+	if (fgp_flags & FGP_LOCK) {
+		if (fgp_flags & FGP_NOWAIT) {
+			if (!trylock_page(page)) {
+				page_cache_release(page);
+				return NULL;
+			}
+		} else {
+			lock_page(page);
+		}
+
+		/* Has the page been truncated? */
+		if (unlikely(page->mapping != mapping)) {
+			unlock_page(page);
+			page_cache_release(page);
+			goto repeat;
+		}
+		VM_BUG_ON_PAGE(page->index != offset, page);
+	}
+
+	if (page && (fgp_flags & FGP_ACCESSED))
+		mark_page_accessed(page);
+
+no_page:
+	if (!page && (fgp_flags & FGP_CREAT)) {
+		int err;
+		if ((fgp_flags & FGP_WRITE) && mapping_cap_account_dirty(mapping))
+			gfp_mask |= __GFP_WRITE;
+		if (fgp_flags & FGP_NOFS)
+			gfp_mask &= ~__GFP_FS;
+
+		page = __page_cache_alloc(gfp_mask);
+		if (!page)
+			return NULL;
+
+		if (WARN_ON_ONCE(!(fgp_flags & FGP_LOCK)))
+			fgp_flags |= FGP_LOCK;
+
+		/* Init accessed so avoid atomic mark_page_accessed later */
+		if (fgp_flags & FGP_ACCESSED)
+			__SetPageReferenced(page);
+
+		err = add_to_page_cache_lru(page, mapping, offset,
+				gfp_mask & GFP_RECLAIM_MASK);
+		if (unlikely(err)) {
+			page_cache_release(page);
+			page = NULL;
+			if (err == -EEXIST)
+				goto repeat;
+		}
+	}
+
+	return page;
+}
+EXPORT_SYMBOL(pagecache_get_page);
+
+/**
+ * find_get_entries - gang pagecache lookup
+ * @mapping:	The address_space to search
+ * @start:	The starting page cache index
+ * @nr_entries:	The maximum number of entries
+ * @entries:	Where the resulting entries are placed
+ * @indices:	The cache indices corresponding to the entries in @entries
+ *
+ * find_get_entries() will search for and return a group of up to
+ * @nr_entries entries in the mapping.  The entries are placed at
+ * @entries.  find_get_entries() takes a reference against any actual
+ * pages it returns.
+ *
+ * The search returns a group of mapping-contiguous page cache entries
+ * with ascending indexes.  There may be holes in the indices due to
+ * not-present pages.
+ *
+ * Any shadow entries of evicted pages, or swap entries from
+ * shmem/tmpfs, are included in the returned array.
+ *
+ * find_get_entries() returns the number of pages and shadow entries
+ * which were found.
+ */
+unsigned find_get_entries(struct address_space *mapping,
+			  pgoff_t start, unsigned int nr_entries,
+			  struct page **entries, pgoff_t *indices)
+{
+	void **slot;
+	unsigned int ret = 0;
+	struct radix_tree_iter iter;
+
+	if (!nr_entries)
+		return 0;
+
+	rcu_read_lock();
+restart:
+	radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
+		struct page *page;
+repeat:
+		page = radix_tree_deref_slot(slot);
+		if (unlikely(!page))
+			continue;
+		if (radix_tree_exception(page)) {
+			if (radix_tree_deref_retry(page))
+				goto restart;
+			/*
+			 * A shadow entry of a recently evicted page,
+			 * or a swap entry from shmem/tmpfs.  Return
+			 * it without attempting to raise page count.
+			 */
+			goto export;
+		}
+		if (!page_cache_get_speculative(page))
+			goto repeat;
+
+		/* Has the page moved? */
+		if (unlikely(page != *slot)) {
+			page_cache_release(page);
+			goto repeat;
+		}
+export:
+		indices[ret] = iter.index;
+		entries[ret] = page;
+		if (++ret == nr_entries)
+			break;
+	}
+	rcu_read_unlock();
+	return ret;
+}
+
+/**
+ * find_get_pages - gang pagecache lookup
+ * @mapping:	The address_space to search
+ * @start:	The starting page index
+ * @nr_pages:	The maximum number of pages
+ * @pages:	Where the resulting pages are placed
+ *
+ * find_get_pages() will search for and return a group of up to
+ * @nr_pages pages in the mapping.  The pages are placed at @pages.
+ * find_get_pages() takes a reference against the returned pages.
+ *
+ * The search returns a group of mapping-contiguous pages with ascending
+ * indexes.  There may be holes in the indices due to not-present pages.
+ *
+ * find_get_pages() returns the number of pages which were found.
+ */
+unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
+			    unsigned int nr_pages, struct page **pages)
+{
+	struct radix_tree_iter iter;
+	void **slot;
+	unsigned ret = 0;
+
+	if (unlikely(!nr_pages))
+		return 0;
+
+	rcu_read_lock();
+restart:
+	radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
+		struct page *page;
+repeat:
+		page = radix_tree_deref_slot(slot);
+		if (unlikely(!page))
+			continue;
+
+		if (radix_tree_exception(page)) {
+			if (radix_tree_deref_retry(page)) {
+				/*
+				 * Transient condition which can only trigger
+				 * when entry at index 0 moves out of or back
+				 * to root: none yet gotten, safe to restart.
+				 */
+				WARN_ON(iter.index);
+				goto restart;
+			}
+			/*
+			 * A shadow entry of a recently evicted page,
+			 * or a swap entry from shmem/tmpfs.  Skip
+			 * over it.
+			 */
+			continue;
+		}
+
+		if (!page_cache_get_speculative(page))
+			goto repeat;
+
+		/* Has the page moved? */
+		if (unlikely(page != *slot)) {
+			page_cache_release(page);
+			goto repeat;
+		}
+
+		pages[ret] = page;
+		if (++ret == nr_pages)
+			break;
+	}
+
+	rcu_read_unlock();
+	return ret;
+}
+
+/**
+ * find_get_pages_contig - gang contiguous pagecache lookup
+ * @mapping:	The address_space to search
+ * @index:	The starting page index
+ * @nr_pages:	The maximum number of pages
+ * @pages:	Where the resulting pages are placed
+ *
+ * find_get_pages_contig() works exactly like find_get_pages(), except
+ * that the returned number of pages are guaranteed to be contiguous.
+ *
+ * find_get_pages_contig() returns the number of pages which were found.
+ */
+unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
+			       unsigned int nr_pages, struct page **pages)
+{
+	struct radix_tree_iter iter;
+	void **slot;
+	unsigned int ret = 0;
+
+	if (unlikely(!nr_pages))
+		return 0;
+
+	rcu_read_lock();
+restart:
+	radix_tree_for_each_contig(slot, &mapping->page_tree, &iter, index) {
+		struct page *page;
+repeat:
+		page = radix_tree_deref_slot(slot);
+		/* The hole, there no reason to continue */
+		if (unlikely(!page))
+			break;
+
+		if (radix_tree_exception(page)) {
+			if (radix_tree_deref_retry(page)) {
+				/*
+				 * Transient condition which can only trigger
+				 * when entry at index 0 moves out of or back
+				 * to root: none yet gotten, safe to restart.
+				 */
+				goto restart;
+			}
+			/*
+			 * A shadow entry of a recently evicted page,
+			 * or a swap entry from shmem/tmpfs.  Stop
+			 * looking for contiguous pages.
+			 */
+			break;
+		}
+
+		if (!page_cache_get_speculative(page))
+			goto repeat;
+
+		/* Has the page moved? */
+		if (unlikely(page != *slot)) {
+			page_cache_release(page);
+			goto repeat;
+		}
+
+		/*
+		 * must check mapping and index after taking the ref.
+		 * otherwise we can get both false positives and false
+		 * negatives, which is just confusing to the caller.
+		 */
+		if (page->mapping == NULL || page->index != iter.index) {
+			page_cache_release(page);
+			break;
+		}
+
+		pages[ret] = page;
+		if (++ret == nr_pages)
+			break;
+	}
+	rcu_read_unlock();
+	return ret;
+}
+EXPORT_SYMBOL(find_get_pages_contig);
+
+/**
+ * find_get_pages_tag - find and return pages that match @tag
+ * @mapping:	the address_space to search
+ * @index:	the starting page index
+ * @tag:	the tag index
+ * @nr_pages:	the maximum number of pages
+ * @pages:	where the resulting pages are placed
+ *
+ * Like find_get_pages, except we only return pages which are tagged with
+ * @tag.   We update @index to index the next page for the traversal.
+ */
+unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
+			int tag, unsigned int nr_pages, struct page **pages)
+{
+	struct radix_tree_iter iter;
+	void **slot;
+	unsigned ret = 0;
+
+	if (unlikely(!nr_pages))
+		return 0;
+
+	rcu_read_lock();
+restart:
+	radix_tree_for_each_tagged(slot, &mapping->page_tree,
+				   &iter, *index, tag) {
+		struct page *page;
+repeat:
+		page = radix_tree_deref_slot(slot);
+		if (unlikely(!page))
+			continue;
+
+		if (radix_tree_exception(page)) {
+			if (radix_tree_deref_retry(page)) {
+				/*
+				 * Transient condition which can only trigger
+				 * when entry at index 0 moves out of or back
+				 * to root: none yet gotten, safe to restart.
+				 */
+				goto restart;
+			}
+			/*
+			 * A shadow entry of a recently evicted page.
+			 *
+			 * Those entries should never be tagged, but
+			 * this tree walk is lockless and the tags are
+			 * looked up in bulk, one radix tree node at a
+			 * time, so there is a sizable window for page
+			 * reclaim to evict a page we saw tagged.
+			 *
+			 * Skip over it.
+			 */
+			continue;
+		}
+
+		if (!page_cache_get_speculative(page))
+			goto repeat;
+
+		/* Has the page moved? */
+		if (unlikely(page != *slot)) {
+			page_cache_release(page);
+			goto repeat;
+		}
+
+		pages[ret] = page;
+		if (++ret == nr_pages)
+			break;
+	}
+
+	rcu_read_unlock();
+
+	if (ret)
+		*index = pages[ret - 1]->index + 1;
+
+	return ret;
+}
+EXPORT_SYMBOL(find_get_pages_tag);
+
+/*
+ * CD/DVDs are error prone. When a medium error occurs, the driver may fail
+ * a _large_ part of the i/o request. Imagine the worst scenario:
+ *
+ *      ---R__________________________________________B__________
+ *         ^ reading here                             ^ bad block(assume 4k)
+ *
+ * read(R) => miss => readahead(R...B) => media error => frustrating retries
+ * => failing the whole request => read(R) => read(R+1) =>
+ * readahead(R+1...B+1) => bang => read(R+2) => read(R+3) =>
+ * readahead(R+3...B+2) => bang => read(R+3) => read(R+4) =>
+ * readahead(R+4...B+3) => bang => read(R+4) => read(R+5) => ......
+ *
+ * It is going insane. Fix it by quickly scaling down the readahead size.
+ */
+static void shrink_readahead_size_eio(struct file *filp,
+					struct file_ra_state *ra)
+{
+	ra->ra_pages /= 4;
+}
+
+/**
+ * do_generic_file_read - generic file read routine
+ * @filp:	the file to read
+ * @ppos:	current file position
+ * @iter:	data destination
+ * @written:	already copied
+ *
+ * This is a generic file read routine, and uses the
+ * mapping->a_ops->readpage() function for the actual low-level stuff.
+ *
+ * This is really ugly. But the goto's actually try to clarify some
+ * of the logic when it comes to error handling etc.
+ */
+static ssize_t do_generic_file_read(struct file *filp, loff_t *ppos,
+		struct iov_iter *iter, ssize_t written)
+{
+	struct address_space *mapping = filp->f_mapping;
+	struct inode *inode = mapping->host;
+	struct file_ra_state *ra = &filp->f_ra;
+	pgoff_t index;
+	pgoff_t last_index;
+	pgoff_t prev_index;
+	unsigned long offset;      /* offset into pagecache page */
+	unsigned int prev_offset;
+	int error = 0;
+
+	index = *ppos >> PAGE_CACHE_SHIFT;
+	prev_index = ra->prev_pos >> PAGE_CACHE_SHIFT;
+	prev_offset = ra->prev_pos & (PAGE_CACHE_SIZE-1);
+	last_index = (*ppos + iter->count + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;
+	offset = *ppos & ~PAGE_CACHE_MASK;
+
+	for (;;) {
+		struct page *page;
+		pgoff_t end_index;
+		loff_t isize;
+		unsigned long nr, ret;
+
+		cond_resched();
+find_page:
+		page = find_get_page(mapping, index);
+		if (!page) {
+			page_cache_sync_readahead(mapping,
+					ra, filp,
+					index, last_index - index);
+			page = find_get_page(mapping, index);
+			if (unlikely(page == NULL))
+				goto no_cached_page;
+		}
+		if (PageReadahead(page)) {
+			page_cache_async_readahead(mapping,
+					ra, filp, page,
+					index, last_index - index);
+		}
+		if (!PageUptodate(page)) {
+			if (inode->i_blkbits == PAGE_CACHE_SHIFT ||
+					!mapping->a_ops->is_partially_uptodate)
+				goto page_not_up_to_date;
+			if (!trylock_page(page))
+				goto page_not_up_to_date;
+			/* Did it get truncated before we got the lock? */
+			if (!page->mapping)
+				goto page_not_up_to_date_locked;
+			if (!mapping->a_ops->is_partially_uptodate(page,
+							offset, iter->count))
+				goto page_not_up_to_date_locked;
+			unlock_page(page);
+		}
+page_ok:
+		/*
+		 * i_size must be checked after we know the page is Uptodate.
+		 *
+		 * Checking i_size after the check allows us to calculate
+		 * the correct value for "nr", which means the zero-filled
+		 * part of the page is not copied back to userspace (unless
+		 * another truncate extends the file - this is desired though).
+		 */
+
+		isize = i_size_read(inode);
+		end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
+		if (unlikely(!isize || index > end_index)) {
+			page_cache_release(page);
+			goto out;
+		}
+
+		/* nr is the maximum number of bytes to copy from this page */
+		nr = PAGE_CACHE_SIZE;
+		if (index == end_index) {
+			nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
+			if (nr <= offset) {
+				page_cache_release(page);
+				goto out;
+			}
+		}
+		nr = nr - offset;
+
+		/* If users can be writing to this page using arbitrary
+		 * virtual addresses, take care about potential aliasing
+		 * before reading the page on the kernel side.
+		 */
+		if (mapping_writably_mapped(mapping))
+			flush_dcache_page(page);
+
+		/*
+		 * When a sequential read accesses a page several times,
+		 * only mark it as accessed the first time.
+		 */
+		if (prev_index != index || offset != prev_offset)
+			mark_page_accessed(page);
+		prev_index = index;
+
+		/*
+		 * Ok, we have the page, and it's up-to-date, so
+		 * now we can copy it to user space...
+		 */
+
+		ret = copy_page_to_iter(page, offset, nr, iter);
+		offset += ret;
+		index += offset >> PAGE_CACHE_SHIFT;
+		offset &= ~PAGE_CACHE_MASK;
+		prev_offset = offset;
+
+		page_cache_release(page);
+		written += ret;
+		if (!iov_iter_count(iter))
+			goto out;
+		if (ret < nr) {
+			error = -EFAULT;
+			goto out;
+		}
+		continue;
+
+page_not_up_to_date:
+		/* Get exclusive access to the page ... */
+		error = lock_page_killable(page);
+		if (unlikely(error))
+			goto readpage_error;
+
+page_not_up_to_date_locked:
+		/* Did it get truncated before we got the lock? */
+		if (!page->mapping) {
+			unlock_page(page);
+			page_cache_release(page);
+			continue;
+		}
+
+		/* Did somebody else fill it already? */
+		if (PageUptodate(page)) {
+			unlock_page(page);
+			goto page_ok;
+		}
+
+readpage:
+		/*
+		 * A previous I/O error may have been due to temporary
+		 * failures, eg. multipath errors.
+		 * PG_error will be set again if readpage fails.
+		 */
+		ClearPageError(page);
+		/* Start the actual read. The read will unlock the page. */
+		error = mapping->a_ops->readpage(filp, page);
+
+		if (unlikely(error)) {
+			if (error == AOP_TRUNCATED_PAGE) {
+				page_cache_release(page);
+				error = 0;
+				goto find_page;
+			}
+			goto readpage_error;
+		}
+
+		if (!PageUptodate(page)) {
+			error = lock_page_killable(page);
+			if (unlikely(error))
+				goto readpage_error;
+			if (!PageUptodate(page)) {
+				if (page->mapping == NULL) {
+					/*
+					 * invalidate_mapping_pages got it
+					 */
+					unlock_page(page);
+					page_cache_release(page);
+					goto find_page;
+				}
+				unlock_page(page);
+				shrink_readahead_size_eio(filp, ra);
+				error = -EIO;
+				goto readpage_error;
+			}
+			unlock_page(page);
+		}
+
+		goto page_ok;
+
+readpage_error:
+		/* UHHUH! A synchronous read error occurred. Report it */
+		page_cache_release(page);
+		goto out;
+
+no_cached_page:
+		/*
+		 * Ok, it wasn't cached, so we need to create a new
+		 * page..
+		 */
+		page = page_cache_alloc_cold(mapping);
+		if (!page) {
+			error = -ENOMEM;
+			goto out;
+		}
+		error = add_to_page_cache_lru(page, mapping,
+						index, GFP_KERNEL);
+		if (error) {
+			page_cache_release(page);
+			if (error == -EEXIST) {
+				error = 0;
+				goto find_page;
+			}
+			goto out;
+		}
+		goto readpage;
+	}
+
+out:
+	ra->prev_pos = prev_index;
+	ra->prev_pos <<= PAGE_CACHE_SHIFT;
+	ra->prev_pos |= prev_offset;
+
+	*ppos = ((loff_t)index << PAGE_CACHE_SHIFT) + offset;
+	file_accessed(filp);
+	return written ? written : error;
+}
+
+/**
+ * generic_file_read_iter - generic filesystem read routine
+ * @iocb:	kernel I/O control block
+ * @iter:	destination for the data read
+ *
+ * This is the "read_iter()" routine for all filesystems
+ * that can use the page cache directly.
+ */
+ssize_t
+generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+	struct file *file = iocb->ki_filp;
+	ssize_t retval = 0;
+	loff_t *ppos = &iocb->ki_pos;
+	loff_t pos = *ppos;
+
+	if (iocb->ki_flags & IOCB_DIRECT) {
+		struct address_space *mapping = file->f_mapping;
+		struct inode *inode = mapping->host;
+		size_t count = iov_iter_count(iter);
+		loff_t size;
+
+		if (!count)
+			goto out; /* skip atime */
+		size = i_size_read(inode);
+		retval = filemap_write_and_wait_range(mapping, pos,
+					pos + count - 1);
+		if (!retval) {
+			struct iov_iter data = *iter;
+			retval = mapping->a_ops->direct_IO(iocb, &data, pos);
+		}
+
+		if (retval > 0) {
+			*ppos = pos + retval;
+			iov_iter_advance(iter, retval);
+		}
+
+		/*
+		 * Btrfs can have a short DIO read if we encounter
+		 * compressed extents, so if there was an error, or if
+		 * we've already read everything we wanted to, or if
+		 * there was a short read because we hit EOF, go ahead
+		 * and return.  Otherwise fallthrough to buffered io for
+		 * the rest of the read.  Buffered reads will not work for
+		 * DAX files, so don't bother trying.
+		 */
+		if (retval < 0 || !iov_iter_count(iter) || *ppos >= size ||
+		    IS_DAX(inode)) {
+			file_accessed(file);
+			goto out;
+		}
+	}
+
+	retval = do_generic_file_read(file, ppos, iter, retval);
+out:
+	return retval;
+}
+EXPORT_SYMBOL(generic_file_read_iter);
+
+#ifdef CONFIG_MMU
+/**
+ * page_cache_read - adds requested page to the page cache if not already there
+ * @file:	file to read
+ * @offset:	page index
+ *
+ * This adds the requested page to the page cache if it isn't already there,
+ * and schedules an I/O to read in its contents from disk.
+ */
+static int page_cache_read(struct file *file, pgoff_t offset)
+{
+	struct address_space *mapping = file->f_mapping;
+	struct page *page;
+	int ret;
+
+	do {
+		page = page_cache_alloc_cold(mapping);
+		if (!page)
+			return -ENOMEM;
+
+		ret = add_to_page_cache_lru(page, mapping, offset, GFP_KERNEL);
+		if (ret == 0)
+			ret = mapping->a_ops->readpage(file, page);
+		else if (ret == -EEXIST)
+			ret = 0; /* losing race to add is OK */
+
+		page_cache_release(page);
+
+	} while (ret == AOP_TRUNCATED_PAGE);
+
+	return ret;
+}
+
+#define MMAP_LOTSAMISS  (100)
+
+/*
+ * Synchronous readahead happens when we don't even find
+ * a page in the page cache at all.
+ */
+static void do_sync_mmap_readahead(struct vm_area_struct *vma,
+				   struct file_ra_state *ra,
+				   struct file *file,
+				   pgoff_t offset)
+{
+	unsigned long ra_pages;
+	struct address_space *mapping = file->f_mapping;
+
+	/* If we don't want any read-ahead, don't bother */
+	if (vma->vm_flags & VM_RAND_READ)
+		return;
+	if (!ra->ra_pages)
+		return;
+
+	if (vma->vm_flags & VM_SEQ_READ) {
+		page_cache_sync_readahead(mapping, ra, file, offset,
+					  ra->ra_pages);
+		return;
+	}
+
+	/* Avoid banging the cache line if not needed */
+	if (ra->mmap_miss < MMAP_LOTSAMISS * 10)
+		ra->mmap_miss++;
+
+	/*
+	 * Do we miss much more than hit in this file? If so,
+	 * stop bothering with read-ahead. It will only hurt.
+	 */
+	if (ra->mmap_miss > MMAP_LOTSAMISS)
+		return;
+
+	/*
+	 * mmap read-around
+	 */
+	ra_pages = max_sane_readahead(ra->ra_pages);
+	ra->start = max_t(long, 0, offset - ra_pages / 2);
+	ra->size = ra_pages;
+	ra->async_size = ra_pages / 4;
+	ra_submit(ra, mapping, file);
+}
+
+/*
+ * Asynchronous readahead happens when we find the page and PG_readahead,
+ * so we want to possibly extend the readahead further..
+ */
+static void do_async_mmap_readahead(struct vm_area_struct *vma,
+				    struct file_ra_state *ra,
+				    struct file *file,
+				    struct page *page,
+				    pgoff_t offset)
+{
+	struct address_space *mapping = file->f_mapping;
+
+	/* If we don't want any read-ahead, don't bother */
+	if (vma->vm_flags & VM_RAND_READ)
+		return;
+	if (ra->mmap_miss > 0)
+		ra->mmap_miss--;
+	if (PageReadahead(page))
+		page_cache_async_readahead(mapping, ra, file,
+					   page, offset, ra->ra_pages);
+}
+
+/**
+ * filemap_fault - read in file data for page fault handling
+ * @vma:	vma in which the fault was taken
+ * @vmf:	struct vm_fault containing details of the fault
+ *
+ * filemap_fault() is invoked via the vma operations vector for a
+ * mapped memory region to read in file data during a page fault.
+ *
+ * The goto's are kind of ugly, but this streamlines the normal case of having
+ * it in the page cache, and handles the special cases reasonably without
+ * having a lot of duplicated code.
+ *
+ * vma->vm_mm->mmap_sem must be held on entry.
+ *
+ * If our return value has VM_FAULT_RETRY set, it's because
+ * lock_page_or_retry() returned 0.
+ * The mmap_sem has usually been released in this case.
+ * See __lock_page_or_retry() for the exception.
+ *
+ * If our return value does not have VM_FAULT_RETRY set, the mmap_sem
+ * has not been released.
+ *
+ * We never return with VM_FAULT_RETRY and a bit from VM_FAULT_ERROR set.
+ */
+int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+	int error;
+	struct file *file = vma->vm_file;
+	struct address_space *mapping = file->f_mapping;
+	struct file_ra_state *ra = &file->f_ra;
+	struct inode *inode = mapping->host;
+	pgoff_t offset = vmf->pgoff;
+	struct page *page;
+	loff_t size;
+	int ret = 0;
+
+	size = round_up(i_size_read(inode), PAGE_CACHE_SIZE);
+	if (offset >= size >> PAGE_CACHE_SHIFT)
+		return VM_FAULT_SIGBUS;
+
+	/*
+	 * Do we have something in the page cache already?
+	 */
+	page = find_get_page(mapping, offset);
+	if (likely(page) && !(vmf->flags & FAULT_FLAG_TRIED)) {
+		/*
+		 * We found the page, so try async readahead before
+		 * waiting for the lock.
+		 */
+		do_async_mmap_readahead(vma, ra, file, page, offset);
+	} else if (!page) {
+		/* No page in the page cache at all */
+		do_sync_mmap_readahead(vma, ra, file, offset);
+		count_vm_event(PGMAJFAULT);
+		mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
+		ret = VM_FAULT_MAJOR;
+retry_find:
+		page = find_get_page(mapping, offset);
+		if (!page)
+			goto no_cached_page;
+	}
+
+	if (!lock_page_or_retry(page, vma->vm_mm, vmf->flags)) {
+		page_cache_release(page);
+		return ret | VM_FAULT_RETRY;
+	}
+
+	/* Did it get truncated? */
+	if (unlikely(page->mapping != mapping)) {
+		unlock_page(page);
+		put_page(page);
+		goto retry_find;
+	}
+	VM_BUG_ON_PAGE(page->index != offset, page);
+
+	/*
+	 * We have a locked page in the page cache, now we need to check
+	 * that it's up-to-date. If not, it is going to be due to an error.
+	 */
+	if (unlikely(!PageUptodate(page)))
+		goto page_not_uptodate;
+
+	/*
+	 * Found the page and have a reference on it.
+	 * We must recheck i_size under page lock.
+	 */
+	size = round_up(i_size_read(inode), PAGE_CACHE_SIZE);
+	if (unlikely(offset >= size >> PAGE_CACHE_SHIFT)) {
+		unlock_page(page);
+		page_cache_release(page);
+		return VM_FAULT_SIGBUS;
+	}
+
+	vmf->page = page;
+	return ret | VM_FAULT_LOCKED;
+
+no_cached_page:
+	/*
+	 * We're only likely to ever get here if MADV_RANDOM is in
+	 * effect.
+	 */
+	error = page_cache_read(file, offset);
+
+	/*
+	 * The page we want has now been added to the page cache.
+	 * In the unlikely event that someone removed it in the
+	 * meantime, we'll just come back here and read it again.
+	 */
+	if (error >= 0)
+		goto retry_find;
+
+	/*
+	 * An error return from page_cache_read can result if the
+	 * system is low on memory, or a problem occurs while trying
+	 * to schedule I/O.
+	 */
+	if (error == -ENOMEM)
+		return VM_FAULT_OOM;
+	return VM_FAULT_SIGBUS;
+
+page_not_uptodate:
+	/*
+	 * Umm, take care of errors if the page isn't up-to-date.
+	 * Try to re-read it _once_. We do this synchronously,
+	 * because there really aren't any performance issues here
+	 * and we need to check for errors.
+	 */
+	ClearPageError(page);
+	error = mapping->a_ops->readpage(file, page);
+	if (!error) {
+		wait_on_page_locked(page);
+		if (!PageUptodate(page))
+			error = -EIO;
+	}
+	page_cache_release(page);
+
+	if (!error || error == AOP_TRUNCATED_PAGE)
+		goto retry_find;
+
+	/* Things didn't work out. Return zero to tell the mm layer so. */
+	shrink_readahead_size_eio(file, ra);
+	return VM_FAULT_SIGBUS;
+}
+EXPORT_SYMBOL(filemap_fault);
+
+void filemap_map_pages(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+	struct radix_tree_iter iter;
+	void **slot;
+	struct file *file = vma->vm_file;
+	struct address_space *mapping = file->f_mapping;
+	loff_t size;
+	struct page *page;
+	unsigned long address = (unsigned long) vmf->virtual_address;
+	unsigned long addr;
+	pte_t *pte;
+
+	rcu_read_lock();
+	radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, vmf->pgoff) {
+		if (iter.index > vmf->max_pgoff)
+			break;
+repeat:
+		page = radix_tree_deref_slot(slot);
+		if (unlikely(!page))
+			goto next;
+		if (radix_tree_exception(page)) {
+			if (radix_tree_deref_retry(page))
+				break;
+			else
+				goto next;
+		}
+
+		if (!page_cache_get_speculative(page))
+			goto repeat;
+
+		/* Has the page moved? */
+		if (unlikely(page != *slot)) {
+			page_cache_release(page);
+			goto repeat;
+		}
+
+		if (!PageUptodate(page) ||
+				PageReadahead(page) ||
+				PageHWPoison(page))
+			goto skip;
+		if (!trylock_page(page))
+			goto skip;
+
+		if (page->mapping != mapping || !PageUptodate(page))
+			goto unlock;
+
+		size = round_up(i_size_read(mapping->host), PAGE_CACHE_SIZE);
+		if (page->index >= size >> PAGE_CACHE_SHIFT)
+			goto unlock;
+
+		pte = vmf->pte + page->index - vmf->pgoff;
+		if (!pte_none(*pte))
+			goto unlock;
+
+		if (file->f_ra.mmap_miss > 0)
+			file->f_ra.mmap_miss--;
+		addr = address + (page->index - vmf->pgoff) * PAGE_SIZE;
+		do_set_pte(vma, addr, page, pte, false, false);
+		unlock_page(page);
+		goto next;
+unlock:
+		unlock_page(page);
+skip:
+		page_cache_release(page);
+next:
+		if (iter.index == vmf->max_pgoff)
+			break;
+	}
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL(filemap_map_pages);
+
+int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+	struct page *page = vmf->page;
+	struct inode *inode = file_inode(vma->vm_file);
+	int ret = VM_FAULT_LOCKED;
+
+	sb_start_pagefault(inode->i_sb);
+	file_update_time(vma->vm_file);
+	lock_page(page);
+	if (page->mapping != inode->i_mapping) {
+		unlock_page(page);
+		ret = VM_FAULT_NOPAGE;
+		goto out;
+	}
+	/*
+	 * We mark the page dirty already here so that when freeze is in
+	 * progress, we are guaranteed that writeback during freezing will
+	 * see the dirty page and writeprotect it again.
+	 */
+	set_page_dirty(page);
+	wait_for_stable_page(page);
+out:
+	sb_end_pagefault(inode->i_sb);
+	return ret;
+}
+EXPORT_SYMBOL(filemap_page_mkwrite);
+
+const struct vm_operations_struct generic_file_vm_ops = {
+	.fault		= filemap_fault,
+	.map_pages	= filemap_map_pages,
+	.page_mkwrite	= filemap_page_mkwrite,
+};
+
+/* This is used for a general mmap of a disk file */
+
+int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
+{
+	struct address_space *mapping = file->f_mapping;
+
+	if (!mapping->a_ops->readpage)
+		return -ENOEXEC;
+	file_accessed(file);
+	vma->vm_ops = &generic_file_vm_ops;
+	return 0;
+}
+
+/*
+ * This is for filesystems which do not implement ->writepage.
+ */
+int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
+		return -EINVAL;
+	return generic_file_mmap(file, vma);
+}
+#else
+int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
+{
+	return -ENOSYS;
+}
+int generic_file_readonly_mmap(struct file * file, struct vm_area_struct * vma)
+{
+	return -ENOSYS;
+}
+#endif /* CONFIG_MMU */
+
+EXPORT_SYMBOL(generic_file_mmap);
+EXPORT_SYMBOL(generic_file_readonly_mmap);
+
+static struct page *wait_on_page_read(struct page *page)
+{
+	if (!IS_ERR(page)) {
+		wait_on_page_locked(page);
+		if (!PageUptodate(page)) {
+			page_cache_release(page);
+			page = ERR_PTR(-EIO);
+		}
+	}
+	return page;
+}
+
+static struct page *__read_cache_page(struct address_space *mapping,
+				pgoff_t index,
+				int (*filler)(void *, struct page *),
+				void *data,
+				gfp_t gfp)
+{
+	struct page *page;
+	int err;
+repeat:
+	page = find_get_page(mapping, index);
+	if (!page) {
+		page = __page_cache_alloc(gfp | __GFP_COLD);
+		if (!page)
+			return ERR_PTR(-ENOMEM);
+		err = add_to_page_cache_lru(page, mapping, index, gfp);
+		if (unlikely(err)) {
+			page_cache_release(page);
+			if (err == -EEXIST)
+				goto repeat;
+			/* Presumably ENOMEM for radix tree node */
+			return ERR_PTR(err);
+		}
+		err = filler(data, page);
+		if (err < 0) {
+			page_cache_release(page);
+			page = ERR_PTR(err);
+		} else {
+			page = wait_on_page_read(page);
+		}
+	}
+	return page;
+}
+
+static struct page *do_read_cache_page(struct address_space *mapping,
+				pgoff_t index,
+				int (*filler)(void *, struct page *),
+				void *data,
+				gfp_t gfp)
+
+{
+	struct page *page;
+	int err;
+
+retry:
+	page = __read_cache_page(mapping, index, filler, data, gfp);
+	if (IS_ERR(page))
+		return page;
+	if (PageUptodate(page))
+		goto out;
+
+	lock_page(page);
+	if (!page->mapping) {
+		unlock_page(page);
+		page_cache_release(page);
+		goto retry;
+	}
+	if (PageUptodate(page)) {
+		unlock_page(page);
+		goto out;
+	}
+	err = filler(data, page);
+	if (err < 0) {
+		page_cache_release(page);
+		return ERR_PTR(err);
+	} else {
+		page = wait_on_page_read(page);
+		if (IS_ERR(page))
+			return page;
+	}
+out:
+	mark_page_accessed(page);
+	return page;
+}
+
+/**
+ * read_cache_page - read into page cache, fill it if needed
+ * @mapping:	the page's address_space
+ * @index:	the page index
+ * @filler:	function to perform the read
+ * @data:	first arg to filler(data, page) function, often left as NULL
+ *
+ * Read into the page cache. If a page already exists, and PageUptodate() is
+ * not set, try to fill the page and wait for it to become unlocked.
+ *
+ * If the page does not get brought uptodate, return -EIO.
+ */
+struct page *read_cache_page(struct address_space *mapping,
+				pgoff_t index,
+				int (*filler)(void *, struct page *),
+				void *data)
+{
+	return do_read_cache_page(mapping, index, filler, data, mapping_gfp_mask(mapping));
+}
+EXPORT_SYMBOL(read_cache_page);
+
+/**
+ * read_cache_page_gfp - read into page cache, using specified page allocation flags.
+ * @mapping:	the page's address_space
+ * @index:	the page index
+ * @gfp:	the page allocator flags to use if allocating
+ *
+ * This is the same as "read_mapping_page(mapping, index, NULL)", but with
+ * any new page allocations done using the specified allocation flags.
+ *
+ * If the page does not get brought uptodate, return -EIO.
+ */
+struct page *read_cache_page_gfp(struct address_space *mapping,
+				pgoff_t index,
+				gfp_t gfp)
+{
+	filler_t *filler = (filler_t *)mapping->a_ops->readpage;
+
+	return do_read_cache_page(mapping, index, filler, NULL, gfp);
+}
+EXPORT_SYMBOL(read_cache_page_gfp);
+
+/*
+ * Performs necessary checks before doing a write
+ *
+ * Can adjust writing position or amount of bytes to write.
+ * Returns appropriate error code that caller should return or
+ * zero in case that write should be allowed.
+ */
+inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct file *file = iocb->ki_filp;
+	struct inode *inode = file->f_mapping->host;
+	unsigned long limit = rlimit(RLIMIT_FSIZE);
+	loff_t pos;
+
+	if (!iov_iter_count(from))
+		return 0;
+
+	/* FIXME: this is for backwards compatibility with 2.4 */
+	if (iocb->ki_flags & IOCB_APPEND)
+		iocb->ki_pos = i_size_read(inode);
+
+	pos = iocb->ki_pos;
+
+	if (limit != RLIM_INFINITY) {
+		if (iocb->ki_pos >= limit) {
+			send_sig(SIGXFSZ, current, 0);
+			return -EFBIG;
+		}
+		iov_iter_truncate(from, limit - (unsigned long)pos);
+	}
+
+	/*
+	 * LFS rule
+	 */
+	if (unlikely(pos + iov_iter_count(from) > MAX_NON_LFS &&
+				!(file->f_flags & O_LARGEFILE))) {
+		if (pos >= MAX_NON_LFS)
+			return -EFBIG;
+		iov_iter_truncate(from, MAX_NON_LFS - (unsigned long)pos);
+	}
+
+	/*
+	 * Are we about to exceed the fs block limit ?
+	 *
+	 * If we have written data it becomes a short write.  If we have
+	 * exceeded without writing data we send a signal and return EFBIG.
+	 * Linus frestrict idea will clean these up nicely..
+	 */
+	if (unlikely(pos >= inode->i_sb->s_maxbytes))
+		return -EFBIG;
+
+	iov_iter_truncate(from, inode->i_sb->s_maxbytes - pos);
+	return iov_iter_count(from);
+}
+EXPORT_SYMBOL(generic_write_checks);
+
+int pagecache_write_begin(struct file *file, struct address_space *mapping,
+				loff_t pos, unsigned len, unsigned flags,
+				struct page **pagep, void **fsdata)
+{
+	const struct address_space_operations *aops = mapping->a_ops;
+
+	return aops->write_begin(file, mapping, pos, len, flags,
+							pagep, fsdata);
+}
+EXPORT_SYMBOL(pagecache_write_begin);
+
+int pagecache_write_end(struct file *file, struct address_space *mapping,
+				loff_t pos, unsigned len, unsigned copied,
+				struct page *page, void *fsdata)
+{
+	const struct address_space_operations *aops = mapping->a_ops;
+
+	return aops->write_end(file, mapping, pos, len, copied, page, fsdata);
+}
+EXPORT_SYMBOL(pagecache_write_end);
+
+ssize_t
+generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos)
+{
+	struct file	*file = iocb->ki_filp;
+	struct address_space *mapping = file->f_mapping;
+	struct inode	*inode = mapping->host;
+	ssize_t		written;
+	size_t		write_len;
+	pgoff_t		end;
+	struct iov_iter data;
+
+	write_len = iov_iter_count(from);
+	end = (pos + write_len - 1) >> PAGE_CACHE_SHIFT;
+
+	written = filemap_write_and_wait_range(mapping, pos, pos + write_len - 1);
+	if (written)
+		goto out;
+
+	/*
+	 * After a write we want buffered reads to be sure to go to disk to get
+	 * the new data.  We invalidate clean cached page from the region we're
+	 * about to write.  We do this *before* the write so that we can return
+	 * without clobbering -EIOCBQUEUED from ->direct_IO().
+	 */
+	if (mapping->nrpages) {
+		written = invalidate_inode_pages2_range(mapping,
+					pos >> PAGE_CACHE_SHIFT, end);
+		/*
+		 * If a page can not be invalidated, return 0 to fall back
+		 * to buffered write.
+		 */
+		if (written) {
+			if (written == -EBUSY)
+				return 0;
+			goto out;
+		}
+	}
+
+	data = *from;
+	written = mapping->a_ops->direct_IO(iocb, &data, pos);
+
+	/*
+	 * Finally, try again to invalidate clean pages which might have been
+	 * cached by non-direct readahead, or faulted in by get_user_pages()
+	 * if the source of the write was an mmap'ed region of the file
+	 * we're writing.  Either one is a pretty crazy thing to do,
+	 * so we don't support it 100%.  If this invalidation
+	 * fails, tough, the write still worked...
+	 */
+	if (mapping->nrpages) {
+		invalidate_inode_pages2_range(mapping,
+					      pos >> PAGE_CACHE_SHIFT, end);
+	}
+
+	if (written > 0) {
+		pos += written;
+		iov_iter_advance(from, written);
+		if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
+			i_size_write(inode, pos);
+			mark_inode_dirty(inode);
+		}
+		iocb->ki_pos = pos;
+	}
+out:
+	return written;
+}
+EXPORT_SYMBOL(generic_file_direct_write);
+
+/*
+ * Find or create a page at the given pagecache position. Return the locked
+ * page. This function is specifically for buffered writes.
+ */
+struct page *grab_cache_page_write_begin(struct address_space *mapping,
+					pgoff_t index, unsigned flags)
+{
+	struct page *page;
+	int fgp_flags = FGP_LOCK|FGP_ACCESSED|FGP_WRITE|FGP_CREAT;
+
+	if (flags & AOP_FLAG_NOFS)
+		fgp_flags |= FGP_NOFS;
+
+	page = pagecache_get_page(mapping, index, fgp_flags,
+			mapping_gfp_mask(mapping));
+	if (page)
+		wait_for_stable_page(page);
+
+	return page;
+}
+EXPORT_SYMBOL(grab_cache_page_write_begin);
+
+ssize_t generic_perform_write(struct file *file,
+				struct iov_iter *i, loff_t pos)
+{
+	struct address_space *mapping = file->f_mapping;
+	const struct address_space_operations *a_ops = mapping->a_ops;
+	long status = 0;
+	ssize_t written = 0;
+	unsigned int flags = 0;
+
+	/*
+	 * Copies from kernel address space cannot fail (NFSD is a big user).
+	 */
+	if (!iter_is_iovec(i))
+		flags |= AOP_FLAG_UNINTERRUPTIBLE;
+
+	do {
+		struct page *page;
+		unsigned long offset;	/* Offset into pagecache page */
+		unsigned long bytes;	/* Bytes to write to page */
+		size_t copied;		/* Bytes copied from user */
+		void *fsdata;
+
+		offset = (pos & (PAGE_CACHE_SIZE - 1));
+		bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
+						iov_iter_count(i));
+
+again:
+		/*
+		 * Bring in the user page that we will copy from _first_.
+		 * Otherwise there's a nasty deadlock on copying from the
+		 * same page as we're writing to, without it being marked
+		 * up-to-date.
+		 *
+		 * Not only is this an optimisation, but it is also required
+		 * to check that the address is actually valid, when atomic
+		 * usercopies are used, below.
+		 */
+		if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
+			status = -EFAULT;
+			break;
+		}
+
+		status = a_ops->write_begin(file, mapping, pos, bytes, flags,
+						&page, &fsdata);
+		if (unlikely(status < 0))
+			break;
+
+		if (mapping_writably_mapped(mapping))
+			flush_dcache_page(page);
+
+		copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
+		flush_dcache_page(page);
+
+		status = a_ops->write_end(file, mapping, pos, bytes, copied,
+						page, fsdata);
+		if (unlikely(status < 0))
+			break;
+		copied = status;
+
+		cond_resched();
+
+		iov_iter_advance(i, copied);
+		if (unlikely(copied == 0)) {
+			/*
+			 * If we were unable to copy any data at all, we must
+			 * fall back to a single segment length write.
+			 *
+			 * If we didn't fallback here, we could livelock
+			 * because not all segments in the iov can be copied at
+			 * once without a pagefault.
+			 */
+			bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
+						iov_iter_single_seg_count(i));
+			goto again;
+		}
+		pos += copied;
+		written += copied;
+
+		balance_dirty_pages_ratelimited(mapping);
+		if (fatal_signal_pending(current)) {
+			status = -EINTR;
+			break;
+		}
+	} while (iov_iter_count(i));
+
+	return written ? written : status;
+}
+EXPORT_SYMBOL(generic_perform_write);
+
+/**
+ * __generic_file_write_iter - write data to a file
+ * @iocb:	IO state structure (file, offset, etc.)
+ * @from:	iov_iter with data to write
+ *
+ * This function does all the work needed for actually writing data to a
+ * file. It does all basic checks, removes SUID from the file, updates
+ * modification times and calls proper subroutines depending on whether we
+ * do direct IO or a standard buffered write.
+ *
+ * It expects i_mutex to be grabbed unless we work on a block device or similar
+ * object which does not need locking at all.
+ *
+ * This function does *not* take care of syncing data in case of O_SYNC write.
+ * A caller has to handle it. This is mainly due to the fact that we want to
+ * avoid syncing under i_mutex.
+ */
+ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct file *file = iocb->ki_filp;
+	struct address_space * mapping = file->f_mapping;
+	struct inode 	*inode = mapping->host;
+	ssize_t		written = 0;
+	ssize_t		err;
+	ssize_t		status;
+
+	/* We can write back this queue in page reclaim */
+	current->backing_dev_info = inode_to_bdi(inode);
+	err = file_remove_suid(file);
+	if (err)
+		goto out;
+
+	err = file_update_time(file);
+	if (err)
+		goto out;
+
+	if (iocb->ki_flags & IOCB_DIRECT) {
+		loff_t pos, endbyte;
+
+		written = generic_file_direct_write(iocb, from, iocb->ki_pos);
+		/*
+		 * If the write stopped short of completing, fall back to
+		 * buffered writes.  Some filesystems do this for writes to
+		 * holes, for example.  For DAX files, a buffered write will
+		 * not succeed (even if it did, DAX does not handle dirty
+		 * page-cache pages correctly).
+		 */
+		if (written < 0 || !iov_iter_count(from) || IS_DAX(inode))
+			goto out;
+
+		status = generic_perform_write(file, from, pos = iocb->ki_pos);
+		/*
+		 * If generic_perform_write() returned a synchronous error
+		 * then we want to return the number of bytes which were
+		 * direct-written, or the error code if that was zero.  Note
+		 * that this differs from normal direct-io semantics, which
+		 * will return -EFOO even if some bytes were written.
+		 */
+		if (unlikely(status < 0)) {
+			err = status;
+			goto out;
+		}
+		/*
+		 * We need to ensure that the page cache pages are written to
+		 * disk and invalidated to preserve the expected O_DIRECT
+		 * semantics.
+		 */
+		endbyte = pos + status - 1;
+		err = filemap_write_and_wait_range(mapping, pos, endbyte);
+		if (err == 0) {
+			iocb->ki_pos = endbyte + 1;
+			written += status;
+			invalidate_mapping_pages(mapping,
+						 pos >> PAGE_CACHE_SHIFT,
+						 endbyte >> PAGE_CACHE_SHIFT);
+		} else {
+			/*
+			 * We don't know how much we wrote, so just return
+			 * the number of bytes which were direct-written
+			 */
+		}
+	} else {
+		written = generic_perform_write(file, from, iocb->ki_pos);
+		if (likely(written > 0))
+			iocb->ki_pos += written;
+	}
+out:
+	current->backing_dev_info = NULL;
+	return written ? written : err;
+}
+EXPORT_SYMBOL(__generic_file_write_iter);
+
+/**
+ * generic_file_write_iter - write data to a file
+ * @iocb:	IO state structure
+ * @from:	iov_iter with data to write
+ *
+ * This is a wrapper around __generic_file_write_iter() to be used by most
+ * filesystems. It takes care of syncing the file in case of O_SYNC file
+ * and acquires i_mutex as needed.
+ */
+ssize_t generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct file *file = iocb->ki_filp;
+	struct inode *inode = file->f_mapping->host;
+	ssize_t ret;
+
+	mutex_lock(&inode->i_mutex);
+	ret = generic_write_checks(iocb, from);
+	if (ret > 0)
+		ret = __generic_file_write_iter(iocb, from);
+	mutex_unlock(&inode->i_mutex);
+
+	if (ret > 0) {
+		ssize_t err;
+
+		err = generic_write_sync(file, iocb->ki_pos - ret, ret);
+		if (err < 0)
+			ret = err;
+	}
+	return ret;
+}
+EXPORT_SYMBOL(generic_file_write_iter);
+
+/**
+ * try_to_release_page() - release old fs-specific metadata on a page
+ *
+ * @page: the page which the kernel is trying to free
+ * @gfp_mask: memory allocation flags (and I/O mode)
+ *
+ * The address_space is to try to release any data against the page
+ * (presumably at page->private).  If the release was successful, return `1'.
+ * Otherwise return zero.
+ *
+ * This may also be called if PG_fscache is set on a page, indicating that the
+ * page is known to the local caching routines.
+ *
+ * The @gfp_mask argument specifies whether I/O may be performed to release
+ * this page (__GFP_IO), and whether the call may block (__GFP_WAIT & __GFP_FS).
+ *
+ */
+int try_to_release_page(struct page *page, gfp_t gfp_mask)
+{
+	struct address_space * const mapping = page->mapping;
+
+	BUG_ON(!PageLocked(page));
+	if (PageWriteback(page))
+		return 0;
+
+	if (mapping && mapping->a_ops->releasepage)
+		return mapping->a_ops->releasepage(page, gfp_mask);
+	return try_to_free_buffers(page);
+}
+
+EXPORT_SYMBOL(try_to_release_page);