/*
 * 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 of 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 budgeting purposes - dirty pages should not be
 * budgeted. 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 just 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 the information about how the page
 * was budgeted, to make it possible to release the budget properly.
 *
 * A thing to keep in mind: inode's 'i_mutex' is locked in most VFS operations
 * we implement. However, this is not true for '->writepage()', which might be
 * called with 'i_mutex' unlocked. For example, when pdflush is performing
 * write-back, it calls 'writepage()' with unlocked 'i_mutex', although the
 * inode has 'I_LOCK' flag in this case. At "normal" work-paths 'i_mutex' is
 * locked in '->writepage', e.g. in "sys_write -> alloc_pages -> direct reclaim
 * path'. So, in '->writepage()' we are only guaranteed that the page is
 * locked.
 *
 * Similarly, 'i_mutex' does not have to be locked in readpage(), e.g.,
 * readahead path does not have it locked ("sys_read -> generic_file_aio_read
 * -> ondemand_readahead -> readpage"). In case of readahead, 'I_LOCK' flag is
 * not set as well. However, UBIFS disables readahead.
 *
 * This, for example means that there might be 2 concurrent '->writepage()'
 * calls for the same inode, but different inode dirty pages.
 */

#include "ubifs.h"
#include <linux/mount.h>
#include <linux/namei.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(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;
			}
		}
		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->page_budget};

	ubifs_release_budget(c, &req);
}

static int write_begin_slow(struct address_space *mapping,
			    loff_t pos, unsigned len, struct page **pagep)
{
	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(mapping, index);
	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);
	struct page *page;


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

	if (unlikely(c->ro_media))
		return -EROFS;

	/* Try out the fast-path part first */
	page = __grab_cache_page(mapping, index);
	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
			 * have to set the @PG_checked flag to make the further
			 * code the page is new. This might be not true, but it
			 * is better to budget more that to read the page from
			 * the media.
			 */
			SetPageChecked(page);
		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);
		/*
		 * 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);
	}

	/*
	 * Whee, we aquired budgeting quickly - without involving
	 * garbage-collection, committing or forceing 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);

		/*
		 * Return 0 to force VFS to repeat the whole operation, or the
		 * error code if 'do_readpage()' failes.
		 */
		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;
}

static int ubifs_readpage(struct file *file, struct page *page)
{
	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 last synchronized inode size, i.e. the 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 'vmtruncate()', 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 'vmtruncate()' with
 * @ui_mutex locked, because it would deadlock with 'ubifs_writepage()'. This
 * means that @inode->i_size is changed while @ui_mutex is unlocked.
 *
 * 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, 1);
			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, 1);
		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);
	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)
		return err;

	err = vmtruncate(inode, new_size);
	if (err)
		goto out_budg;

	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);
	/* The 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:
	ubifs_release_budget(c, &req);
	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);
		err = vmtruncate(inode, new_size);
		if (err)
			goto out;
	}

	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);
		/* 'vmtruncate()' 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, 1);
	return err;

out:
	ubifs_release_budget(c, &req);
	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(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, struct dentry *dentry, int datasync)
{
	struct inode *inode = dentry->d_inode;
	struct ubifs_info *c = inode->i_sb->s_fs_info;
	int err;

	dbg_gen("syncing inode %lu", inode->i_ino);

	/*
	 * VFS has already synchronized dirty pages for this inode. 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, 1);
		if (err)
			return err;
	}

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

	return 0;
}

/**
 * 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;
	ssize_t ret;
	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;

	ret = generic_file_aio_write(iocb, iov, nr_segs, pos);
	if (ret < 0)
		return ret;

	if (ret > 0 && (IS_SYNC(inode) || iocb->ki_filp->f_flags & O_SYNC)) {
		err = ubifs_sync_wbufs_by_inode(c, inode);
		if (err)
			return err;
	}

	return ret;
}

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 page *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(!(inode->i_sb->s_flags & MS_RDONLY));

	if (unlikely(c->ro_media))
		return -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 err;
	}

	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);
	return err;
}

static 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;

	/* 'generic_file_mmap()' takes care of NOMMU case */
	err = generic_file_mmap(file, vma);
	if (err)
		return err;
	vma->vm_ops = &ubifs_file_vm_ops;
	return 0;
}

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,
};

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
};

struct inode_operations ubifs_symlink_inode_operations = {
	.readlink    = generic_readlink,
	.follow_link = ubifs_follow_link,
	.setattr     = ubifs_setattr,
	.getattr     = ubifs_getattr,
};

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
};