/*
   * This file is part of UBIFS.
   *
   * Copyright (C) 2006-2008 Nokia Corporation.
   *
   * This program is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 as published by
   * the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
   * more details.
   *
   * You should have received a copy of the GNU General Public License along with
   * this program; if not, write to the Free Software Foundation, Inc., 51
   * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
   *
   * Authors: Artem Bityutskiy (Битюцкий Артём)
   *          Adrian Hunter
   */
  
  /*

   * This file implements VFS file and inode operations for regular files, device

   * nodes and symlinks as well as address space operations.
   *

   * UBIFS uses 2 page flags: @PG_private and @PG_checked. @PG_private is set if
   * the page is dirty and is used for optimization purposes - dirty pages are
   * not budgeted so the flag shows that 'ubifs_write_end()' should not release
   * the budget for this page. The @PG_checked flag is set if full budgeting is
   * required for the page e.g., when it corresponds to a file hole or it is
   * beyond the file size. The budgeting is done in 'ubifs_write_begin()', because
   * it is OK to fail in this function, and the budget is released in
   * 'ubifs_write_end()'. So the @PG_private and @PG_checked flags carry
   * information about how the page was budgeted, to make it possible to release
   * the budget properly.

   *

   * A thing to keep in mind: inode @i_mutex is locked in most VFS operations we
   * implement. However, this is not true for 'ubifs_writepage()', which may be
   * called with @i_mutex unlocked. For example, when pdflush is doing background
   * write-back, it calls 'ubifs_writepage()' with unlocked @i_mutex. At "normal"
   * work-paths the @i_mutex is locked in 'ubifs_writepage()', e.g. in the
   * "sys_write -> alloc_pages -> direct reclaim path". So, in 'ubifs_writepage()'
   * we are only guaranteed that the page is locked.

   *

   * Similarly, @i_mutex is not always locked in 'ubifs_readpage()', e.g., the
   * read-ahead path does not lock it ("sys_read -> generic_file_aio_read ->

   * ondemand_readahead -> readpage"). In case of readahead, @I_SYNC flag is not

   * set as well. However, UBIFS disables readahead.

   */
  
  #include "ubifs.h"
  #include <linux/mount.h>

  #include <linux/namei.h>

  #include <linux/slab.h>

  
  static int read_block(struct inode *inode, void *addr, unsigned int block,
  		      struct ubifs_data_node *dn)
  {
  	struct ubifs_info *c = inode->i_sb->s_fs_info;
  	int err, len, out_len;
  	union ubifs_key key;
  	unsigned int dlen;
  
  	data_key_init(c, &key, inode->i_ino, block);
  	err = ubifs_tnc_lookup(c, &key, dn);
  	if (err) {
  		if (err == -ENOENT)
  			/* Not found, so it must be a hole */
  			memset(addr, 0, UBIFS_BLOCK_SIZE);
  		return err;
  	}

  	ubifs_assert(le64_to_cpu(dn->ch.sqnum) >
  		     ubifs_inode(inode)->creat_sqnum);

  	len = le32_to_cpu(dn->size);
  	if (len <= 0 || len > UBIFS_BLOCK_SIZE)
  		goto dump;
  
  	dlen = le32_to_cpu(dn->ch.len) - UBIFS_DATA_NODE_SZ;
  	out_len = UBIFS_BLOCK_SIZE;
  	err = ubifs_decompress(&dn->data, dlen, addr, &out_len,
  			       le16_to_cpu(dn->compr_type));
  	if (err || len != out_len)
  		goto dump;
  
  	/*
  	 * Data length can be less than a full block, even for blocks that are
  	 * not the last in the file (e.g., as a result of making a hole and
  	 * appending data). Ensure that the remainder is zeroed out.
  	 */
  	if (len < UBIFS_BLOCK_SIZE)
  		memset(addr + len, 0, UBIFS_BLOCK_SIZE - len);
  
  	return 0;
  
  dump:
  	ubifs_err("bad data node (block %u, inode %lu)",
  		  block, inode->i_ino);
  	dbg_dump_node(c, dn);
  	return -EINVAL;
  }
  
  static int do_readpage(struct page *page)
  {
  	void *addr;
  	int err = 0, i;
  	unsigned int block, beyond;
  	struct ubifs_data_node *dn;
  	struct inode *inode = page->mapping->host;
  	loff_t i_size = i_size_read(inode);
  
  	dbg_gen("ino %lu, pg %lu, i_size %lld, flags %#lx",
  		inode->i_ino, page->index, i_size, page->flags);
  	ubifs_assert(!PageChecked(page));
  	ubifs_assert(!PagePrivate(page));
  
  	addr = kmap(page);
  
  	block = page->index << UBIFS_BLOCKS_PER_PAGE_SHIFT;
  	beyond = (i_size + UBIFS_BLOCK_SIZE - 1) >> UBIFS_BLOCK_SHIFT;
  	if (block >= beyond) {
  		/* Reading beyond inode */
  		SetPageChecked(page);
  		memset(addr, 0, PAGE_CACHE_SIZE);
  		goto out;
  	}
  
  	dn = kmalloc(UBIFS_MAX_DATA_NODE_SZ, GFP_NOFS);
  	if (!dn) {
  		err = -ENOMEM;
  		goto error;
  	}
  
  	i = 0;
  	while (1) {
  		int ret;
  
  		if (block >= beyond) {
  			/* Reading beyond inode */
  			err = -ENOENT;
  			memset(addr, 0, UBIFS_BLOCK_SIZE);
  		} else {
  			ret = read_block(inode, addr, block, dn);
  			if (ret) {
  				err = ret;
  				if (err != -ENOENT)
  					break;

  			} else if (block + 1 == beyond) {
  				int dlen = le32_to_cpu(dn->size);
  				int ilen = i_size & (UBIFS_BLOCK_SIZE - 1);
  
  				if (ilen && ilen < dlen)
  					memset(addr + ilen, 0, dlen - ilen);

  			}
  		}
  		if (++i >= UBIFS_BLOCKS_PER_PAGE)
  			break;
  		block += 1;
  		addr += UBIFS_BLOCK_SIZE;
  	}
  	if (err) {
  		if (err == -ENOENT) {
  			/* Not found, so it must be a hole */
  			SetPageChecked(page);
  			dbg_gen("hole");
  			goto out_free;
  		}
  		ubifs_err("cannot read page %lu of inode %lu, error %d",
  			  page->index, inode->i_ino, err);
  		goto error;
  	}
  
  out_free:
  	kfree(dn);
  out:
  	SetPageUptodate(page);
  	ClearPageError(page);
  	flush_dcache_page(page);
  	kunmap(page);
  	return 0;
  
  error:
  	kfree(dn);
  	ClearPageUptodate(page);
  	SetPageError(page);
  	flush_dcache_page(page);
  	kunmap(page);
  	return err;
  }
  
  /**
   * release_new_page_budget - release budget of a new page.
   * @c: UBIFS file-system description object
   *
   * This is a helper function which releases budget corresponding to the budget
   * of one new page of data.
   */
  static void release_new_page_budget(struct ubifs_info *c)
  {
  	struct ubifs_budget_req req = { .recalculate = 1, .new_page = 1 };
  
  	ubifs_release_budget(c, &req);
  }
  
  /**
   * release_existing_page_budget - release budget of an existing page.
   * @c: UBIFS file-system description object
   *
   * This is a helper function which releases budget corresponding to the budget
   * of changing one one page of data which already exists on the flash media.
   */
  static void release_existing_page_budget(struct ubifs_info *c)
  {

  	struct ubifs_budget_req req = { .dd_growth = c->bi.page_budget};

  
  	ubifs_release_budget(c, &req);
  }
  
  static int write_begin_slow(struct address_space *mapping,

  			    loff_t pos, unsigned len, struct page **pagep,
  			    unsigned flags)

  {
  	struct inode *inode = mapping->host;
  	struct ubifs_info *c = inode->i_sb->s_fs_info;
  	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
  	struct ubifs_budget_req req = { .new_page = 1 };
  	int uninitialized_var(err), appending = !!(pos + len > inode->i_size);
  	struct page *page;
  
  	dbg_gen("ino %lu, pos %llu, len %u, i_size %lld",
  		inode->i_ino, pos, len, inode->i_size);
  
  	/*
  	 * At the slow path we have to budget before locking the page, because
  	 * budgeting may force write-back, which would wait on locked pages and
  	 * deadlock if we had the page locked. At this point we do not know
  	 * anything about the page, so assume that this is a new page which is
  	 * written to a hole. This corresponds to largest budget. Later the
  	 * budget will be amended if this is not true.
  	 */
  	if (appending)
  		/* We are appending data, budget for inode change */
  		req.dirtied_ino = 1;
  
  	err = ubifs_budget_space(c, &req);
  	if (unlikely(err))
  		return err;

  	page = grab_cache_page_write_begin(mapping, index, flags);

  	if (unlikely(!page)) {
  		ubifs_release_budget(c, &req);
  		return -ENOMEM;
  	}
  
  	if (!PageUptodate(page)) {

  		if (!(pos & ~PAGE_CACHE_MASK) && len == PAGE_CACHE_SIZE)

  			SetPageChecked(page);
  		else {
  			err = do_readpage(page);
  			if (err) {
  				unlock_page(page);
  				page_cache_release(page);
  				return err;
  			}
  		}
  
  		SetPageUptodate(page);
  		ClearPageError(page);
  	}
  
  	if (PagePrivate(page))
  		/*
  		 * The page is dirty, which means it was budgeted twice:
  		 *   o first time the budget was allocated by the task which
  		 *     made the page dirty and set the PG_private flag;
  		 *   o and then we budgeted for it for the second time at the
  		 *     very beginning of this function.
  		 *
  		 * So what we have to do is to release the page budget we
  		 * allocated.
  		 */
  		release_new_page_budget(c);
  	else if (!PageChecked(page))
  		/*
  		 * We are changing a page which already exists on the media.
  		 * This means that changing the page does not make the amount
  		 * of indexing information larger, and this part of the budget
  		 * which we have already acquired may be released.
  		 */
  		ubifs_convert_page_budget(c);
  
  	if (appending) {
  		struct ubifs_inode *ui = ubifs_inode(inode);
  
  		/*
  		 * 'ubifs_write_end()' is optimized from the fast-path part of
  		 * 'ubifs_write_begin()' and expects the @ui_mutex to be locked
  		 * if data is appended.
  		 */
  		mutex_lock(&ui->ui_mutex);
  		if (ui->dirty)
  			/*
  			 * The inode is dirty already, so we may free the
  			 * budget we allocated.
  			 */
  			ubifs_release_dirty_inode_budget(c, ui);
  	}
  
  	*pagep = page;
  	return 0;
  }
  
  /**
   * allocate_budget - allocate budget for 'ubifs_write_begin()'.
   * @c: UBIFS file-system description object
   * @page: page to allocate budget for
   * @ui: UBIFS inode object the page belongs to
   * @appending: non-zero if the page is appended
   *
   * This is a helper function for 'ubifs_write_begin()' which allocates budget
   * for the operation. The budget is allocated differently depending on whether
   * this is appending, whether the page is dirty or not, and so on. This
   * function leaves the @ui->ui_mutex locked in case of appending. Returns zero
   * in case of success and %-ENOSPC in case of failure.
   */
  static int allocate_budget(struct ubifs_info *c, struct page *page,
  			   struct ubifs_inode *ui, int appending)
  {
  	struct ubifs_budget_req req = { .fast = 1 };
  
  	if (PagePrivate(page)) {
  		if (!appending)
  			/*
  			 * The page is dirty and we are not appending, which
  			 * means no budget is needed at all.
  			 */
  			return 0;
  
  		mutex_lock(&ui->ui_mutex);
  		if (ui->dirty)
  			/*
  			 * The page is dirty and we are appending, so the inode
  			 * has to be marked as dirty. However, it is already
  			 * dirty, so we do not need any budget. We may return,
  			 * but @ui->ui_mutex hast to be left locked because we
  			 * should prevent write-back from flushing the inode
  			 * and freeing the budget. The lock will be released in
  			 * 'ubifs_write_end()'.
  			 */
  			return 0;
  
  		/*
  		 * The page is dirty, we are appending, the inode is clean, so
  		 * we need to budget the inode change.
  		 */
  		req.dirtied_ino = 1;
  	} else {
  		if (PageChecked(page))
  			/*
  			 * The page corresponds to a hole and does not
  			 * exist on the media. So changing it makes
  			 * make the amount of indexing information
  			 * larger, and we have to budget for a new
  			 * page.
  			 */
  			req.new_page = 1;
  		else
  			/*
  			 * Not a hole, the change will not add any new
  			 * indexing information, budget for page
  			 * change.
  			 */
  			req.dirtied_page = 1;
  
  		if (appending) {
  			mutex_lock(&ui->ui_mutex);
  			if (!ui->dirty)
  				/*
  				 * The inode is clean but we will have to mark
  				 * it as dirty because we are appending. This
  				 * needs a budget.
  				 */
  				req.dirtied_ino = 1;
  		}
  	}
  
  	return ubifs_budget_space(c, &req);
  }
  
  /*
   * This function is called when a page of data is going to be written. Since
   * the page of data will not necessarily go to the flash straight away, UBIFS
   * has to reserve space on the media for it, which is done by means of
   * budgeting.
   *
   * This is the hot-path of the file-system and we are trying to optimize it as
   * much as possible. For this reasons it is split on 2 parts - slow and fast.
   *
   * There many budgeting cases:
   *     o a new page is appended - we have to budget for a new page and for
   *       changing the inode; however, if the inode is already dirty, there is
   *       no need to budget for it;
   *     o an existing clean page is changed - we have budget for it; if the page
   *       does not exist on the media (a hole), we have to budget for a new
   *       page; otherwise, we may budget for changing an existing page; the
   *       difference between these cases is that changing an existing page does
   *       not introduce anything new to the FS indexing information, so it does
   *       not grow, and smaller budget is acquired in this case;
   *     o an existing dirty page is changed - no need to budget at all, because
   *       the page budget has been acquired by earlier, when the page has been
   *       marked dirty.
   *
   * UBIFS budgeting sub-system may force write-back if it thinks there is no
   * space to reserve. This imposes some locking restrictions and makes it
   * impossible to take into account the above cases, and makes it impossible to
   * optimize budgeting.
   *
   * The solution for this is that the fast path of 'ubifs_write_begin()' assumes
   * there is a plenty of flash space and the budget will be acquired quickly,
   * without forcing write-back. The slow path does not make this assumption.
   */
  static int ubifs_write_begin(struct file *file, struct address_space *mapping,
  			     loff_t pos, unsigned len, unsigned flags,
  			     struct page **pagep, void **fsdata)
  {
  	struct inode *inode = mapping->host;
  	struct ubifs_info *c = inode->i_sb->s_fs_info;
  	struct ubifs_inode *ui = ubifs_inode(inode);
  	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
  	int uninitialized_var(err), appending = !!(pos + len > inode->i_size);

  	int skipped_read = 0;

  	struct page *page;

  	ubifs_assert(ubifs_inode(inode)->ui_size == inode->i_size);

  	ubifs_assert(!c->ro_media && !c->ro_mount);

  	if (unlikely(c->ro_error))

  		return -EROFS;
  
  	/* Try out the fast-path part first */

  	page = grab_cache_page_write_begin(mapping, index, flags);

  	if (unlikely(!page))
  		return -ENOMEM;
  
  	if (!PageUptodate(page)) {
  		/* The page is not loaded from the flash */

  		if (!(pos & ~PAGE_CACHE_MASK) && len == PAGE_CACHE_SIZE) {

  			/*
  			 * We change whole page so no need to load it. But we

  			 * do not know whether this page exists on the media or
  			 * not, so we assume the latter because it requires
  			 * larger budget. The assumption is that it is better
  			 * to budget a bit more than to read the page from the
  			 * media. Thus, we are setting the @PG_checked flag
  			 * here.

  			 */
  			SetPageChecked(page);

  			skipped_read = 1;
  		} else {

  			err = do_readpage(page);
  			if (err) {
  				unlock_page(page);
  				page_cache_release(page);
  				return err;
  			}
  		}
  
  		SetPageUptodate(page);
  		ClearPageError(page);
  	}
  
  	err = allocate_budget(c, page, ui, appending);
  	if (unlikely(err)) {
  		ubifs_assert(err == -ENOSPC);
  		/*

  		 * If we skipped reading the page because we were going to
  		 * write all of it, then it is not up to date.
  		 */
  		if (skipped_read) {
  			ClearPageChecked(page);
  			ClearPageUptodate(page);
  		}
  		/*

  		 * Budgeting failed which means it would have to force
  		 * write-back but didn't, because we set the @fast flag in the
  		 * request. Write-back cannot be done now, while we have the
  		 * page locked, because it would deadlock. Unlock and free
  		 * everything and fall-back to slow-path.
  		 */
  		if (appending) {
  			ubifs_assert(mutex_is_locked(&ui->ui_mutex));
  			mutex_unlock(&ui->ui_mutex);
  		}
  		unlock_page(page);
  		page_cache_release(page);

  		return write_begin_slow(mapping, pos, len, pagep, flags);

  	}
  
  	/*

  	 * Whee, we acquired budgeting quickly - without involving
  	 * garbage-collection, committing or forcing write-back. We return

  	 * with @ui->ui_mutex locked if we are appending pages, and unlocked
  	 * otherwise. This is an optimization (slightly hacky though).
  	 */
  	*pagep = page;
  	return 0;
  
  }
  
  /**
   * cancel_budget - cancel budget.
   * @c: UBIFS file-system description object
   * @page: page to cancel budget for
   * @ui: UBIFS inode object the page belongs to
   * @appending: non-zero if the page is appended
   *
   * This is a helper function for a page write operation. It unlocks the
   * @ui->ui_mutex in case of appending.
   */
  static void cancel_budget(struct ubifs_info *c, struct page *page,
  			  struct ubifs_inode *ui, int appending)
  {
  	if (appending) {
  		if (!ui->dirty)
  			ubifs_release_dirty_inode_budget(c, ui);
  		mutex_unlock(&ui->ui_mutex);
  	}
  	if (!PagePrivate(page)) {
  		if (PageChecked(page))
  			release_new_page_budget(c);
  		else
  			release_existing_page_budget(c);
  	}
  }
  
  static int ubifs_write_end(struct file *file, struct address_space *mapping,
  			   loff_t pos, unsigned len, unsigned copied,
  			   struct page *page, void *fsdata)
  {
  	struct inode *inode = mapping->host;
  	struct ubifs_inode *ui = ubifs_inode(inode);
  	struct ubifs_info *c = inode->i_sb->s_fs_info;
  	loff_t end_pos = pos + len;
  	int appending = !!(end_pos > inode->i_size);
  
  	dbg_gen("ino %lu, pos %llu, pg %lu, len %u, copied %d, i_size %lld",
  		inode->i_ino, pos, page->index, len, copied, inode->i_size);
  
  	if (unlikely(copied < len && len == PAGE_CACHE_SIZE)) {
  		/*
  		 * VFS copied less data to the page that it intended and
  		 * declared in its '->write_begin()' call via the @len
  		 * argument. If the page was not up-to-date, and @len was
  		 * @PAGE_CACHE_SIZE, the 'ubifs_write_begin()' function did
  		 * not load it from the media (for optimization reasons). This
  		 * means that part of the page contains garbage. So read the
  		 * page now.
  		 */
  		dbg_gen("copied %d instead of %d, read page and repeat",
  			copied, len);
  		cancel_budget(c, page, ui, appending);

  		ClearPageChecked(page);

  
  		/*
  		 * Return 0 to force VFS to repeat the whole operation, or the

  		 * error code if 'do_readpage()' fails.

  		 */
  		copied = do_readpage(page);
  		goto out;
  	}
  
  	if (!PagePrivate(page)) {
  		SetPagePrivate(page);
  		atomic_long_inc(&c->dirty_pg_cnt);
  		__set_page_dirty_nobuffers(page);
  	}
  
  	if (appending) {
  		i_size_write(inode, end_pos);
  		ui->ui_size = end_pos;
  		/*
  		 * Note, we do not set @I_DIRTY_PAGES (which means that the
  		 * inode has dirty pages), this has been done in
  		 * '__set_page_dirty_nobuffers()'.
  		 */
  		__mark_inode_dirty(inode, I_DIRTY_DATASYNC);
  		ubifs_assert(mutex_is_locked(&ui->ui_mutex));
  		mutex_unlock(&ui->ui_mutex);
  	}
  
  out:
  	unlock_page(page);
  	page_cache_release(page);
  	return copied;
  }

  /**
   * populate_page - copy data nodes into a page for bulk-read.
   * @c: UBIFS file-system description object
   * @page: page
   * @bu: bulk-read information
   * @n: next zbranch slot
   *
   * This function returns %0 on success and a negative error code on failure.
   */
  static int populate_page(struct ubifs_info *c, struct page *page,
  			 struct bu_info *bu, int *n)
  {

  	int i = 0, nn = *n, offs = bu->zbranch[0].offs, hole = 0, read = 0;

  	struct inode *inode = page->mapping->host;
  	loff_t i_size = i_size_read(inode);
  	unsigned int page_block;
  	void *addr, *zaddr;
  	pgoff_t end_index;
  
  	dbg_gen("ino %lu, pg %lu, i_size %lld, flags %#lx",
  		inode->i_ino, page->index, i_size, page->flags);
  
  	addr = zaddr = kmap(page);

  	end_index = (i_size - 1) >> PAGE_CACHE_SHIFT;

  	if (!i_size || page->index > end_index) {

  		hole = 1;

  		memset(addr, 0, PAGE_CACHE_SIZE);
  		goto out_hole;
  	}
  
  	page_block = page->index << UBIFS_BLOCKS_PER_PAGE_SHIFT;
  	while (1) {
  		int err, len, out_len, dlen;

  		if (nn >= bu->cnt) {
  			hole = 1;

  			memset(addr, 0, UBIFS_BLOCK_SIZE);

  		} else if (key_block(c, &bu->zbranch[nn].key) == page_block) {

  			struct ubifs_data_node *dn;
  
  			dn = bu->buf + (bu->zbranch[nn].offs - offs);

  			ubifs_assert(le64_to_cpu(dn->ch.sqnum) >

  				     ubifs_inode(inode)->creat_sqnum);
  
  			len = le32_to_cpu(dn->size);
  			if (len <= 0 || len > UBIFS_BLOCK_SIZE)
  				goto out_err;
  
  			dlen = le32_to_cpu(dn->ch.len) - UBIFS_DATA_NODE_SZ;
  			out_len = UBIFS_BLOCK_SIZE;
  			err = ubifs_decompress(&dn->data, dlen, addr, &out_len,
  					       le16_to_cpu(dn->compr_type));
  			if (err || len != out_len)
  				goto out_err;
  
  			if (len < UBIFS_BLOCK_SIZE)
  				memset(addr + len, 0, UBIFS_BLOCK_SIZE - len);
  
  			nn += 1;

  			read = (i << UBIFS_BLOCK_SHIFT) + len;

  		} else if (key_block(c, &bu->zbranch[nn].key) < page_block) {
  			nn += 1;
  			continue;
  		} else {
  			hole = 1;
  			memset(addr, 0, UBIFS_BLOCK_SIZE);

  		}
  		if (++i >= UBIFS_BLOCKS_PER_PAGE)
  			break;
  		addr += UBIFS_BLOCK_SIZE;
  		page_block += 1;
  	}
  
  	if (end_index == page->index) {
  		int len = i_size & (PAGE_CACHE_SIZE - 1);

  		if (len && len < read)

  			memset(zaddr + len, 0, read - len);
  	}
  
  out_hole:
  	if (hole) {
  		SetPageChecked(page);
  		dbg_gen("hole");
  	}
  
  	SetPageUptodate(page);
  	ClearPageError(page);
  	flush_dcache_page(page);
  	kunmap(page);
  	*n = nn;
  	return 0;
  
  out_err:
  	ClearPageUptodate(page);
  	SetPageError(page);
  	flush_dcache_page(page);
  	kunmap(page);
  	ubifs_err("bad data node (block %u, inode %lu)",
  		  page_block, inode->i_ino);
  	return -EINVAL;
  }
  
  /**
   * ubifs_do_bulk_read - do bulk-read.
   * @c: UBIFS file-system description object

   * @bu: bulk-read information
   * @page1: first page to read

   *
   * This function returns %1 if the bulk-read is done, otherwise %0 is returned.
   */

  static int ubifs_do_bulk_read(struct ubifs_info *c, struct bu_info *bu,
  			      struct page *page1)

  {
  	pgoff_t offset = page1->index, end_index;
  	struct address_space *mapping = page1->mapping;
  	struct inode *inode = mapping->host;
  	struct ubifs_inode *ui = ubifs_inode(inode);

  	int err, page_idx, page_cnt, ret = 0, n = 0;

  	int allocate = bu->buf ? 0 : 1;

  	loff_t isize;

  	err = ubifs_tnc_get_bu_keys(c, bu);
  	if (err)
  		goto out_warn;
  
  	if (bu->eof) {
  		/* Turn off bulk-read at the end of the file */
  		ui->read_in_a_row = 1;
  		ui->bulk_read = 0;
  	}
  
  	page_cnt = bu->blk_cnt >> UBIFS_BLOCKS_PER_PAGE_SHIFT;
  	if (!page_cnt) {
  		/*
  		 * This happens when there are multiple blocks per page and the
  		 * blocks for the first page we are looking for, are not
  		 * together. If all the pages were like this, bulk-read would
  		 * reduce performance, so we turn it off for a while.
  		 */

  		goto out_bu_off;

  	}
  
  	if (bu->cnt) {

  		if (allocate) {
  			/*
  			 * Allocate bulk-read buffer depending on how many data
  			 * nodes we are going to read.
  			 */
  			bu->buf_len = bu->zbranch[bu->cnt - 1].offs +
  				      bu->zbranch[bu->cnt - 1].len -
  				      bu->zbranch[0].offs;
  			ubifs_assert(bu->buf_len > 0);
  			ubifs_assert(bu->buf_len <= c->leb_size);
  			bu->buf = kmalloc(bu->buf_len, GFP_NOFS | __GFP_NOWARN);
  			if (!bu->buf)
  				goto out_bu_off;
  		}

  		err = ubifs_tnc_bulk_read(c, bu);
  		if (err)
  			goto out_warn;
  	}
  
  	err = populate_page(c, page1, bu, &n);
  	if (err)
  		goto out_warn;
  
  	unlock_page(page1);
  	ret = 1;
  
  	isize = i_size_read(inode);
  	if (isize == 0)
  		goto out_free;
  	end_index = ((isize - 1) >> PAGE_CACHE_SHIFT);
  
  	for (page_idx = 1; page_idx < page_cnt; page_idx++) {
  		pgoff_t page_offset = offset + page_idx;
  		struct page *page;
  
  		if (page_offset > end_index)
  			break;
  		page = find_or_create_page(mapping, page_offset,
  					   GFP_NOFS | __GFP_COLD);
  		if (!page)
  			break;
  		if (!PageUptodate(page))
  			err = populate_page(c, page, bu, &n);
  		unlock_page(page);
  		page_cache_release(page);
  		if (err)
  			break;
  	}
  
  	ui->last_page_read = offset + page_idx - 1;
  
  out_free:

  	if (allocate)
  		kfree(bu->buf);

  	return ret;
  
  out_warn:
  	ubifs_warn("ignoring error %d and skipping bulk-read", err);
  	goto out_free;

  
  out_bu_off:
  	ui->read_in_a_row = ui->bulk_read = 0;
  	goto out_free;

  }
  
  /**
   * ubifs_bulk_read - determine whether to bulk-read and, if so, do it.
   * @page: page from which to start bulk-read.
   *
   * Some flash media are capable of reading sequentially at faster rates. UBIFS
   * bulk-read facility is designed to take advantage of that, by reading in one
   * go consecutive data nodes that are also located consecutively in the same
   * LEB. This function returns %1 if a bulk-read is done and %0 otherwise.
   */
  static int ubifs_bulk_read(struct page *page)
  {
  	struct inode *inode = page->mapping->host;
  	struct ubifs_info *c = inode->i_sb->s_fs_info;
  	struct ubifs_inode *ui = ubifs_inode(inode);
  	pgoff_t index = page->index, last_page_read = ui->last_page_read;

  	struct bu_info *bu;

  	int err = 0, allocated = 0;

  
  	ui->last_page_read = index;

  	if (!c->bulk_read)
  		return 0;

  	/*

  	 * Bulk-read is protected by @ui->ui_mutex, but it is an optimization,
  	 * so don't bother if we cannot lock the mutex.

  	 */
  	if (!mutex_trylock(&ui->ui_mutex))
  		return 0;

  	if (index != last_page_read + 1) {
  		/* Turn off bulk-read if we stop reading sequentially */
  		ui->read_in_a_row = 1;
  		if (ui->bulk_read)
  			ui->bulk_read = 0;
  		goto out_unlock;
  	}

  	if (!ui->bulk_read) {
  		ui->read_in_a_row += 1;
  		if (ui->read_in_a_row < 3)
  			goto out_unlock;
  		/* Three reads in a row, so switch on bulk-read */
  		ui->bulk_read = 1;
  	}

  	/*
  	 * If possible, try to use pre-allocated bulk-read information, which
  	 * is protected by @c->bu_mutex.
  	 */
  	if (mutex_trylock(&c->bu_mutex))
  		bu = &c->bu;
  	else {
  		bu = kmalloc(sizeof(struct bu_info), GFP_NOFS | __GFP_NOWARN);
  		if (!bu)
  			goto out_unlock;
  
  		bu->buf = NULL;
  		allocated = 1;
  	}

  	bu->buf_len = c->max_bu_buf_len;
  	data_key_init(c, &bu->key, inode->i_ino,
  		      page->index << UBIFS_BLOCKS_PER_PAGE_SHIFT);

  	err = ubifs_do_bulk_read(c, bu, page);

  
  	if (!allocated)
  		mutex_unlock(&c->bu_mutex);
  	else
  		kfree(bu);

  out_unlock:
  	mutex_unlock(&ui->ui_mutex);

  	return err;

  }

  static int ubifs_readpage(struct file *file, struct page *page)
  {

  	if (ubifs_bulk_read(page))
  		return 0;

  	do_readpage(page);
  	unlock_page(page);
  	return 0;
  }
  
  static int do_writepage(struct page *page, int len)
  {
  	int err = 0, i, blen;
  	unsigned int block;
  	void *addr;
  	union ubifs_key key;
  	struct inode *inode = page->mapping->host;
  	struct ubifs_info *c = inode->i_sb->s_fs_info;
  
  #ifdef UBIFS_DEBUG
  	spin_lock(&ui->ui_lock);
  	ubifs_assert(page->index <= ui->synced_i_size << PAGE_CACHE_SIZE);
  	spin_unlock(&ui->ui_lock);
  #endif
  
  	/* Update radix tree tags */
  	set_page_writeback(page);
  
  	addr = kmap(page);
  	block = page->index << UBIFS_BLOCKS_PER_PAGE_SHIFT;
  	i = 0;
  	while (len) {
  		blen = min_t(int, len, UBIFS_BLOCK_SIZE);
  		data_key_init(c, &key, inode->i_ino, block);
  		err = ubifs_jnl_write_data(c, inode, &key, addr, blen);
  		if (err)
  			break;
  		if (++i >= UBIFS_BLOCKS_PER_PAGE)
  			break;
  		block += 1;
  		addr += blen;
  		len -= blen;
  	}
  	if (err) {
  		SetPageError(page);
  		ubifs_err("cannot write page %lu of inode %lu, error %d",
  			  page->index, inode->i_ino, err);
  		ubifs_ro_mode(c, err);
  	}
  
  	ubifs_assert(PagePrivate(page));
  	if (PageChecked(page))
  		release_new_page_budget(c);
  	else
  		release_existing_page_budget(c);
  
  	atomic_long_dec(&c->dirty_pg_cnt);
  	ClearPagePrivate(page);
  	ClearPageChecked(page);
  
  	kunmap(page);
  	unlock_page(page);
  	end_page_writeback(page);
  	return err;
  }
  
  /*
   * When writing-back dirty inodes, VFS first writes-back pages belonging to the
   * inode, then the inode itself. For UBIFS this may cause a problem. Consider a
   * situation when a we have an inode with size 0, then a megabyte of data is
   * appended to the inode, then write-back starts and flushes some amount of the
   * dirty pages, the journal becomes full, commit happens and finishes, and then
   * an unclean reboot happens. When the file system is mounted next time, the
   * inode size would still be 0, but there would be many pages which are beyond
   * the inode size, they would be indexed and consume flash space. Because the
   * journal has been committed, the replay would not be able to detect this
   * situation and correct the inode size. This means UBIFS would have to scan
   * whole index and correct all inode sizes, which is long an unacceptable.
   *
   * To prevent situations like this, UBIFS writes pages back only if they are

   * within the last synchronized inode size, i.e. the size which has been

   * written to the flash media last time. Otherwise, UBIFS forces inode
   * write-back, thus making sure the on-flash inode contains current inode size,
   * and then keeps writing pages back.
   *
   * Some locking issues explanation. 'ubifs_writepage()' first is called with
   * the page locked, and it locks @ui_mutex. However, write-back does take inode
   * @i_mutex, which means other VFS operations may be run on this inode at the
   * same time. And the problematic one is truncation to smaller size, from where

   * we have to call 'truncate_setsize()', which first changes @inode->i_size,
   * then drops the truncated pages. And while dropping the pages, it takes the
   * page lock. This means that 'do_truncation()' cannot call 'truncate_setsize()'
   * with @ui_mutex locked, because it would deadlock with 'ubifs_writepage()'.
   * This means that @inode->i_size is changed while @ui_mutex is unlocked.

   *

   * XXX(truncate): with the new truncate sequence this is not true anymore,
   * and the calls to truncate_setsize can be move around freely.  They should
   * be moved to the very end of the truncate sequence.

   *

   * But in 'ubifs_writepage()' we have to guarantee that we do not write beyond
   * inode size. How do we do this if @inode->i_size may became smaller while we
   * are in the middle of 'ubifs_writepage()'? The UBIFS solution is the
   * @ui->ui_isize "shadow" field which UBIFS uses instead of @inode->i_size
   * internally and updates it under @ui_mutex.
   *
   * Q: why we do not worry that if we race with truncation, we may end up with a
   * situation when the inode is truncated while we are in the middle of
   * 'do_writepage()', so we do write beyond inode size?
   * A: If we are in the middle of 'do_writepage()', truncation would be locked
   * on the page lock and it would not write the truncated inode node to the
   * journal before we have finished.
   */
  static int ubifs_writepage(struct page *page, struct writeback_control *wbc)
  {
  	struct inode *inode = page->mapping->host;
  	struct ubifs_inode *ui = ubifs_inode(inode);
  	loff_t i_size =  i_size_read(inode), synced_i_size;
  	pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
  	int err, len = i_size & (PAGE_CACHE_SIZE - 1);
  	void *kaddr;
  
  	dbg_gen("ino %lu, pg %lu, pg flags %#lx",
  		inode->i_ino, page->index, page->flags);
  	ubifs_assert(PagePrivate(page));
  
  	/* Is the page fully outside @i_size? (truncate in progress) */
  	if (page->index > end_index || (page->index == end_index && !len)) {
  		err = 0;
  		goto out_unlock;
  	}
  
  	spin_lock(&ui->ui_lock);
  	synced_i_size = ui->synced_i_size;
  	spin_unlock(&ui->ui_lock);
  
  	/* Is the page fully inside @i_size? */
  	if (page->index < end_index) {
  		if (page->index >= synced_i_size >> PAGE_CACHE_SHIFT) {

  			err = inode->i_sb->s_op->write_inode(inode, NULL);

  			if (err)
  				goto out_unlock;
  			/*
  			 * The inode has been written, but the write-buffer has
  			 * not been synchronized, so in case of an unclean
  			 * reboot we may end up with some pages beyond inode
  			 * size, but they would be in the journal (because
  			 * commit flushes write buffers) and recovery would deal
  			 * with this.
  			 */
  		}
  		return do_writepage(page, PAGE_CACHE_SIZE);
  	}
  
  	/*
  	 * The page straddles @i_size. It must be zeroed out on each and every
  	 * writepage invocation because it may be mmapped. "A file is mapped
  	 * in multiples of the page size. For a file that is not a multiple of
  	 * the page size, the remaining memory is zeroed when mapped, and
  	 * writes to that region are not written out to the file."
  	 */
  	kaddr = kmap_atomic(page, KM_USER0);
  	memset(kaddr + len, 0, PAGE_CACHE_SIZE - len);
  	flush_dcache_page(page);
  	kunmap_atomic(kaddr, KM_USER0);
  
  	if (i_size > synced_i_size) {

  		err = inode->i_sb->s_op->write_inode(inode, NULL);

  		if (err)
  			goto out_unlock;
  	}
  
  	return do_writepage(page, len);
  
  out_unlock:
  	unlock_page(page);
  	return err;
  }
  
  /**
   * do_attr_changes - change inode attributes.
   * @inode: inode to change attributes for
   * @attr: describes attributes to change
   */
  static void do_attr_changes(struct inode *inode, const struct iattr *attr)
  {
  	if (attr->ia_valid & ATTR_UID)
  		inode->i_uid = attr->ia_uid;
  	if (attr->ia_valid & ATTR_GID)
  		inode->i_gid = attr->ia_gid;
  	if (attr->ia_valid & ATTR_ATIME)
  		inode->i_atime = timespec_trunc(attr->ia_atime,
  						inode->i_sb->s_time_gran);
  	if (attr->ia_valid & ATTR_MTIME)
  		inode->i_mtime = timespec_trunc(attr->ia_mtime,
  						inode->i_sb->s_time_gran);
  	if (attr->ia_valid & ATTR_CTIME)
  		inode->i_ctime = timespec_trunc(attr->ia_ctime,
  						inode->i_sb->s_time_gran);
  	if (attr->ia_valid & ATTR_MODE) {
  		umode_t mode = attr->ia_mode;
  
  		if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
  			mode &= ~S_ISGID;
  		inode->i_mode = mode;
  	}
  }
  
  /**
   * do_truncation - truncate an inode.
   * @c: UBIFS file-system description object
   * @inode: inode to truncate
   * @attr: inode attribute changes description
   *
   * This function implements VFS '->setattr()' call when the inode is truncated
   * to a smaller size. Returns zero in case of success and a negative error code
   * in case of failure.
   */
  static int do_truncation(struct ubifs_info *c, struct inode *inode,
  			 const struct iattr *attr)
  {
  	int err;
  	struct ubifs_budget_req req;
  	loff_t old_size = inode->i_size, new_size = attr->ia_size;

  	int offset = new_size & (UBIFS_BLOCK_SIZE - 1), budgeted = 1;

  	struct ubifs_inode *ui = ubifs_inode(inode);
  
  	dbg_gen("ino %lu, size %lld -> %lld", inode->i_ino, old_size, new_size);
  	memset(&req, 0, sizeof(struct ubifs_budget_req));
  
  	/*
  	 * If this is truncation to a smaller size, and we do not truncate on a
  	 * block boundary, budget for changing one data block, because the last
  	 * block will be re-written.
  	 */
  	if (new_size & (UBIFS_BLOCK_SIZE - 1))
  		req.dirtied_page = 1;
  
  	req.dirtied_ino = 1;
  	/* A funny way to budget for truncation node */
  	req.dirtied_ino_d = UBIFS_TRUN_NODE_SZ;
  	err = ubifs_budget_space(c, &req);

  	if (err) {
  		/*
  		 * Treat truncations to zero as deletion and always allow them,
  		 * just like we do for '->unlink()'.
  		 */
  		if (new_size || err != -ENOSPC)
  			return err;
  		budgeted = 0;
  	}

  	truncate_setsize(inode, new_size);

  
  	if (offset) {
  		pgoff_t index = new_size >> PAGE_CACHE_SHIFT;
  		struct page *page;
  
  		page = find_lock_page(inode->i_mapping, index);
  		if (page) {
  			if (PageDirty(page)) {
  				/*
  				 * 'ubifs_jnl_truncate()' will try to truncate
  				 * the last data node, but it contains
  				 * out-of-date data because the page is dirty.
  				 * Write the page now, so that
  				 * 'ubifs_jnl_truncate()' will see an already
  				 * truncated (and up to date) data node.
  				 */
  				ubifs_assert(PagePrivate(page));
  
  				clear_page_dirty_for_io(page);
  				if (UBIFS_BLOCKS_PER_PAGE_SHIFT)
  					offset = new_size &
  						 (PAGE_CACHE_SIZE - 1);
  				err = do_writepage(page, offset);
  				page_cache_release(page);
  				if (err)
  					goto out_budg;
  				/*
  				 * We could now tell 'ubifs_jnl_truncate()' not
  				 * to read the last block.
  				 */
  			} else {
  				/*
  				 * We could 'kmap()' the page and pass the data
  				 * to 'ubifs_jnl_truncate()' to save it from
  				 * having to read it.
  				 */
  				unlock_page(page);
  				page_cache_release(page);
  			}
  		}
  	}
  
  	mutex_lock(&ui->ui_mutex);
  	ui->ui_size = inode->i_size;
  	/* Truncation changes inode [mc]time */
  	inode->i_mtime = inode->i_ctime = ubifs_current_time(inode);

  	/* Other attributes may be changed at the same time as well */

  	do_attr_changes(inode, attr);

  	err = ubifs_jnl_truncate(c, inode, old_size, new_size);
  	mutex_unlock(&ui->ui_mutex);

  out_budg:

  	if (budgeted)
  		ubifs_release_budget(c, &req);
  	else {

  		c->bi.nospace = c->bi.nospace_rp = 0;

  		smp_wmb();
  	}

  	return err;
  }
  
  /**
   * do_setattr - change inode attributes.
   * @c: UBIFS file-system description object
   * @inode: inode to change attributes for
   * @attr: inode attribute changes description
   *
   * This function implements VFS '->setattr()' call for all cases except
   * truncations to smaller size. Returns zero in case of success and a negative
   * error code in case of failure.
   */
  static int do_setattr(struct ubifs_info *c, struct inode *inode,
  		      const struct iattr *attr)
  {
  	int err, release;
  	loff_t new_size = attr->ia_size;
  	struct ubifs_inode *ui = ubifs_inode(inode);
  	struct ubifs_budget_req req = { .dirtied_ino = 1,

  				.dirtied_ino_d = ALIGN(ui->data_len, 8) };

  
  	err = ubifs_budget_space(c, &req);
  	if (err)
  		return err;
  
  	if (attr->ia_valid & ATTR_SIZE) {
  		dbg_gen("size %lld -> %lld", inode->i_size, new_size);

  		truncate_setsize(inode, new_size);

  	}
  
  	mutex_lock(&ui->ui_mutex);
  	if (attr->ia_valid & ATTR_SIZE) {
  		/* Truncation changes inode [mc]time */
  		inode->i_mtime = inode->i_ctime = ubifs_current_time(inode);

  		/* 'truncate_setsize()' changed @i_size, update @ui_size */

  		ui->ui_size = inode->i_size;
  	}
  
  	do_attr_changes(inode, attr);
  
  	release = ui->dirty;
  	if (attr->ia_valid & ATTR_SIZE)
  		/*
  		 * Inode length changed, so we have to make sure
  		 * @I_DIRTY_DATASYNC is set.
  		 */
  		 __mark_inode_dirty(inode, I_DIRTY_SYNC | I_DIRTY_DATASYNC);
  	else
  		mark_inode_dirty_sync(inode);
  	mutex_unlock(&ui->ui_mutex);
  
  	if (release)
  		ubifs_release_budget(c, &req);
  	if (IS_SYNC(inode))

  		err = inode->i_sb->s_op->write_inode(inode, NULL);

  	return err;

  }
  
  int ubifs_setattr(struct dentry *dentry, struct iattr *attr)
  {
  	int err;
  	struct inode *inode = dentry->d_inode;
  	struct ubifs_info *c = inode->i_sb->s_fs_info;

  	dbg_gen("ino %lu, mode %#x, ia_valid %#x",
  		inode->i_ino, inode->i_mode, attr->ia_valid);

  	err = inode_change_ok(inode, attr);
  	if (err)
  		return err;

  	err = dbg_check_synced_i_size(c, inode);

  	if (err)
  		return err;
  
  	if ((attr->ia_valid & ATTR_SIZE) && attr->ia_size < inode->i_size)
  		/* Truncation to a smaller size */
  		err = do_truncation(c, inode, attr);
  	else
  		err = do_setattr(c, inode, attr);
  
  	return err;
  }
  
  static void ubifs_invalidatepage(struct page *page, unsigned long offset)
  {
  	struct inode *inode = page->mapping->host;
  	struct ubifs_info *c = inode->i_sb->s_fs_info;
  
  	ubifs_assert(PagePrivate(page));
  	if (offset)
  		/* Partial page remains dirty */
  		return;
  
  	if (PageChecked(page))
  		release_new_page_budget(c);
  	else
  		release_existing_page_budget(c);
  
  	atomic_long_dec(&c->dirty_pg_cnt);
  	ClearPagePrivate(page);
  	ClearPageChecked(page);
  }
  
  static void *ubifs_follow_link(struct dentry *dentry, struct nameidata *nd)
  {
  	struct ubifs_inode *ui = ubifs_inode(dentry->d_inode);
  
  	nd_set_link(nd, ui->data);
  	return NULL;
  }

  int ubifs_fsync(struct file *file, loff_t start, loff_t end, int datasync)

  {

  	struct inode *inode = file->f_mapping->host;

  	struct ubifs_info *c = inode->i_sb->s_fs_info;
  	int err;
  
  	dbg_gen("syncing inode %lu", inode->i_ino);

  	if (c->ro_mount)
  		/*
  		 * For some really strange reasons VFS does not filter out
  		 * 'fsync()' for R/O mounted file-systems as per 2.6.39.
  		 */

  		return 0;

  	err = filemap_write_and_wait_range(inode->i_mapping, start, end);
  	if (err)
  		return err;
  	mutex_lock(&inode->i_mutex);
  
  	/* Synchronize the inode unless this is a 'datasync()' call. */

  	if (!datasync || (inode->i_state & I_DIRTY_DATASYNC)) {

  		err = inode->i_sb->s_op->write_inode(inode, NULL);

  		if (err)

  			goto out;

  	}
  
  	/*
  	 * Nodes related to this inode may still sit in a write-buffer. Flush
  	 * them.
  	 */
  	err = ubifs_sync_wbufs_by_inode(c, inode);

  out:
  	mutex_unlock(&inode->i_mutex);
  	return err;

  }
  
  /**
   * mctime_update_needed - check if mtime or ctime update is needed.
   * @inode: the inode to do the check for
   * @now: current time
   *
   * This helper function checks if the inode mtime/ctime should be updated or
   * not. If current values of the time-stamps are within the UBIFS inode time
   * granularity, they are not updated. This is an optimization.
   */
  static inline int mctime_update_needed(const struct inode *inode,
  				       const struct timespec *now)
  {
  	if (!timespec_equal(&inode->i_mtime, now) ||
  	    !timespec_equal(&inode->i_ctime, now))
  		return 1;
  	return 0;
  }
  
  /**
   * update_ctime - update mtime and ctime of an inode.
   * @c: UBIFS file-system description object
   * @inode: inode to update
   *
   * This function updates mtime and ctime of the inode if it is not equivalent to
   * current time. Returns zero in case of success and a negative error code in
   * case of failure.
   */
  static int update_mctime(struct ubifs_info *c, struct inode *inode)
  {
  	struct timespec now = ubifs_current_time(inode);
  	struct ubifs_inode *ui = ubifs_inode(inode);
  
  	if (mctime_update_needed(inode, &now)) {
  		int err, release;
  		struct ubifs_budget_req req = { .dirtied_ino = 1,

  				.dirtied_ino_d = ALIGN(ui->data_len, 8) };

  
  		err = ubifs_budget_space(c, &req);
  		if (err)
  			return err;
  
  		mutex_lock(&ui->ui_mutex);
  		inode->i_mtime = inode->i_ctime = ubifs_current_time(inode);
  		release = ui->dirty;
  		mark_inode_dirty_sync(inode);
  		mutex_unlock(&ui->ui_mutex);
  		if (release)
  			ubifs_release_budget(c, &req);
  	}
  
  	return 0;
  }
  
  static ssize_t ubifs_aio_write(struct kiocb *iocb, const struct iovec *iov,
  			       unsigned long nr_segs, loff_t pos)
  {
  	int err;

  	struct inode *inode = iocb->ki_filp->f_mapping->host;
  	struct ubifs_info *c = inode->i_sb->s_fs_info;
  
  	err = update_mctime(c, inode);
  	if (err)
  		return err;

  	return generic_file_aio_write(iocb, iov, nr_segs, pos);

  }
  
  static int ubifs_set_page_dirty(struct page *page)
  {
  	int ret;
  
  	ret = __set_page_dirty_nobuffers(page);
  	/*
  	 * An attempt to dirty a page without budgeting for it - should not
  	 * happen.
  	 */
  	ubifs_assert(ret == 0);
  	return ret;
  }
  
  static int ubifs_releasepage(struct page *page, gfp_t unused_gfp_flags)
  {
  	/*
  	 * An attempt to release a dirty page without budgeting for it - should
  	 * not happen.
  	 */
  	if (PageWriteback(page))
  		return 0;
  	ubifs_assert(PagePrivate(page));
  	ubifs_assert(0);
  	ClearPagePrivate(page);
  	ClearPageChecked(page);
  	return 1;
  }
  
  /*

   * mmap()d file has taken write protection fault and is being made writable.
   * UBIFS must ensure page is budgeted for.

   */

  static int ubifs_vm_page_mkwrite(struct vm_area_struct *vma,
  				 struct vm_fault *vmf)

  {

  	struct page *page = vmf->page;

  	struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
  	struct ubifs_info *c = inode->i_sb->s_fs_info;
  	struct timespec now = ubifs_current_time(inode);
  	struct ubifs_budget_req req = { .new_page = 1 };
  	int err, update_time;
  
  	dbg_gen("ino %lu, pg %lu, i_size %lld",	inode->i_ino, page->index,
  		i_size_read(inode));

  	ubifs_assert(!c->ro_media && !c->ro_mount);

  	if (unlikely(c->ro_error))

  		return VM_FAULT_SIGBUS; /* -EROFS */

  
  	/*
  	 * We have not locked @page so far so we may budget for changing the
  	 * page. Note, we cannot do this after we locked the page, because
  	 * budgeting may cause write-back which would cause deadlock.
  	 *
  	 * At the moment we do not know whether the page is dirty or not, so we
  	 * assume that it is not and budget for a new page. We could look at
  	 * the @PG_private flag and figure this out, but we may race with write
  	 * back and the page state may change by the time we lock it, so this
  	 * would need additional care. We do not bother with this at the
  	 * moment, although it might be good idea to do. Instead, we allocate
  	 * budget for a new page and amend it later on if the page was in fact
  	 * dirty.
  	 *
  	 * The budgeting-related logic of this function is similar to what we
  	 * do in 'ubifs_write_begin()' and 'ubifs_write_end()'. Glance there
  	 * for more comments.
  	 */
  	update_time = mctime_update_needed(inode, &now);
  	if (update_time)
  		/*
  		 * We have to change inode time stamp which requires extra
  		 * budgeting.
  		 */
  		req.dirtied_ino = 1;
  
  	err = ubifs_budget_space(c, &req);
  	if (unlikely(err)) {
  		if (err == -ENOSPC)
  			ubifs_warn("out of space for mmapped file "
  				   "(inode number %lu)", inode->i_ino);

  		return VM_FAULT_SIGBUS;

  	}
  
  	lock_page(page);
  	if (unlikely(page->mapping != inode->i_mapping ||
  		     page_offset(page) > i_size_read(inode))) {
  		/* Page got truncated out from underneath us */
  		err = -EINVAL;
  		goto out_unlock;
  	}
  
  	if (PagePrivate(page))
  		release_new_page_budget(c);
  	else {
  		if (!PageChecked(page))
  			ubifs_convert_page_budget(c);
  		SetPagePrivate(page);
  		atomic_long_inc(&c->dirty_pg_cnt);
  		__set_page_dirty_nobuffers(page);
  	}
  
  	if (update_time) {
  		int release;
  		struct ubifs_inode *ui = ubifs_inode(inode);
  
  		mutex_lock(&ui->ui_mutex);
  		inode->i_mtime = inode->i_ctime = ubifs_current_time(inode);
  		release = ui->dirty;
  		mark_inode_dirty_sync(inode);
  		mutex_unlock(&ui->ui_mutex);
  		if (release)
  			ubifs_release_dirty_inode_budget(c, ui);
  	}
  
  	unlock_page(page);
  	return 0;
  
  out_unlock:
  	unlock_page(page);
  	ubifs_release_budget(c, &req);

  	if (err)
  		err = VM_FAULT_SIGBUS;

  	return err;
  }

  static const struct vm_operations_struct ubifs_file_vm_ops = {

  	.fault        = filemap_fault,
  	.page_mkwrite = ubifs_vm_page_mkwrite,
  };
  
  static int ubifs_file_mmap(struct file *file, struct vm_area_struct *vma)
  {
  	int err;

  	err = generic_file_mmap(file, vma);
  	if (err)
  		return err;
  	vma->vm_ops = &ubifs_file_vm_ops;
  	return 0;
  }

  const struct address_space_operations ubifs_file_address_operations = {

  	.readpage       = ubifs_readpage,
  	.writepage      = ubifs_writepage,
  	.write_begin    = ubifs_write_begin,
  	.write_end      = ubifs_write_end,
  	.invalidatepage = ubifs_invalidatepage,
  	.set_page_dirty = ubifs_set_page_dirty,
  	.releasepage    = ubifs_releasepage,
  };

  const struct inode_operations ubifs_file_inode_operations = {

  	.setattr     = ubifs_setattr,
  	.getattr     = ubifs_getattr,
  #ifdef CONFIG_UBIFS_FS_XATTR
  	.setxattr    = ubifs_setxattr,
  	.getxattr    = ubifs_getxattr,
  	.listxattr   = ubifs_listxattr,
  	.removexattr = ubifs_removexattr,
  #endif
  };

  const struct inode_operations ubifs_symlink_inode_operations = {

  	.readlink    = generic_readlink,
  	.follow_link = ubifs_follow_link,
  	.setattr     = ubifs_setattr,
  	.getattr     = ubifs_getattr,
  };

  const struct file_operations ubifs_file_operations = {

  	.llseek         = generic_file_llseek,
  	.read           = do_sync_read,
  	.write          = do_sync_write,
  	.aio_read       = generic_file_aio_read,
  	.aio_write      = ubifs_aio_write,
  	.mmap           = ubifs_file_mmap,
  	.fsync          = ubifs_fsync,
  	.unlocked_ioctl = ubifs_ioctl,
  	.splice_read	= generic_file_splice_read,

  	.splice_write	= generic_file_splice_write,

  #ifdef CONFIG_COMPAT
  	.compat_ioctl   = ubifs_compat_ioctl,
  #endif
  };