/* -*- mode: c; c-basic-offset: 8; -*-
   * vim: noexpandtab sw=8 ts=8 sts=0:
   *
   * Copyright (C) 2002, 2004 Oracle.  All rights reserved.
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public
   * License as published by the Free Software Foundation; either
   * version 2 of the License, or (at your option) any later version.
   *
   * 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., 59 Temple Place - Suite 330,
   * Boston, MA 021110-1307, USA.
   */
  
  #include <linux/fs.h>
  #include <linux/slab.h>
  #include <linux/highmem.h>
  #include <linux/pagemap.h>
  #include <asm/byteorder.h>

  #include <linux/swap.h>

  #include <linux/pipe_fs_i.h>

  
  #define MLOG_MASK_PREFIX ML_FILE_IO
  #include <cluster/masklog.h>
  
  #include "ocfs2.h"
  
  #include "alloc.h"
  #include "aops.h"
  #include "dlmglue.h"
  #include "extent_map.h"
  #include "file.h"
  #include "inode.h"
  #include "journal.h"

  #include "suballoc.h"

  #include "super.h"
  #include "symlink.h"
  
  #include "buffer_head_io.h"
  
  static int ocfs2_symlink_get_block(struct inode *inode, sector_t iblock,
  				   struct buffer_head *bh_result, int create)
  {
  	int err = -EIO;
  	int status;
  	struct ocfs2_dinode *fe = NULL;
  	struct buffer_head *bh = NULL;
  	struct buffer_head *buffer_cache_bh = NULL;
  	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
  	void *kaddr;
  
  	mlog_entry("(0x%p, %llu, 0x%p, %d)
  ", inode,
  		   (unsigned long long)iblock, bh_result, create);
  
  	BUG_ON(ocfs2_inode_is_fast_symlink(inode));
  
  	if ((iblock << inode->i_sb->s_blocksize_bits) > PATH_MAX + 1) {
  		mlog(ML_ERROR, "block offset > PATH_MAX: %llu",
  		     (unsigned long long)iblock);
  		goto bail;
  	}
  
  	status = ocfs2_read_block(OCFS2_SB(inode->i_sb),
  				  OCFS2_I(inode)->ip_blkno,
  				  &bh, OCFS2_BH_CACHED, inode);
  	if (status < 0) {
  		mlog_errno(status);
  		goto bail;
  	}
  	fe = (struct ocfs2_dinode *) bh->b_data;
  
  	if (!OCFS2_IS_VALID_DINODE(fe)) {

  		mlog(ML_ERROR, "Invalid dinode #%llu: signature = %.*s
  ",

  		     (unsigned long long)le64_to_cpu(fe->i_blkno), 7,
  		     fe->i_signature);

  		goto bail;
  	}
  
  	if ((u64)iblock >= ocfs2_clusters_to_blocks(inode->i_sb,
  						    le32_to_cpu(fe->i_clusters))) {
  		mlog(ML_ERROR, "block offset is outside the allocated size: "
  		     "%llu
  ", (unsigned long long)iblock);
  		goto bail;
  	}
  
  	/* We don't use the page cache to create symlink data, so if
  	 * need be, copy it over from the buffer cache. */
  	if (!buffer_uptodate(bh_result) && ocfs2_inode_is_new(inode)) {
  		u64 blkno = le64_to_cpu(fe->id2.i_list.l_recs[0].e_blkno) +
  			    iblock;
  		buffer_cache_bh = sb_getblk(osb->sb, blkno);
  		if (!buffer_cache_bh) {
  			mlog(ML_ERROR, "couldn't getblock for symlink!
  ");
  			goto bail;
  		}
  
  		/* we haven't locked out transactions, so a commit
  		 * could've happened. Since we've got a reference on
  		 * the bh, even if it commits while we're doing the
  		 * copy, the data is still good. */
  		if (buffer_jbd(buffer_cache_bh)
  		    && ocfs2_inode_is_new(inode)) {
  			kaddr = kmap_atomic(bh_result->b_page, KM_USER0);
  			if (!kaddr) {
  				mlog(ML_ERROR, "couldn't kmap!
  ");
  				goto bail;
  			}
  			memcpy(kaddr + (bh_result->b_size * iblock),
  			       buffer_cache_bh->b_data,
  			       bh_result->b_size);
  			kunmap_atomic(kaddr, KM_USER0);
  			set_buffer_uptodate(bh_result);
  		}
  		brelse(buffer_cache_bh);
  	}
  
  	map_bh(bh_result, inode->i_sb,
  	       le64_to_cpu(fe->id2.i_list.l_recs[0].e_blkno) + iblock);
  
  	err = 0;
  
  bail:
  	if (bh)
  		brelse(bh);
  
  	mlog_exit(err);
  	return err;
  }
  
  static int ocfs2_get_block(struct inode *inode, sector_t iblock,
  			   struct buffer_head *bh_result, int create)
  {
  	int err = 0;

  	unsigned int ext_flags;

  	u64 p_blkno, past_eof;

  	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);

  
  	mlog_entry("(0x%p, %llu, 0x%p, %d)
  ", inode,
  		   (unsigned long long)iblock, bh_result, create);
  
  	if (OCFS2_I(inode)->ip_flags & OCFS2_INODE_SYSTEM_FILE)
  		mlog(ML_NOTICE, "get_block on system inode 0x%p (%lu)
  ",
  		     inode, inode->i_ino);
  
  	if (S_ISLNK(inode->i_mode)) {
  		/* this always does I/O for some reason. */
  		err = ocfs2_symlink_get_block(inode, iblock, bh_result, create);
  		goto bail;
  	}

  	err = ocfs2_extent_map_get_blocks(inode, iblock, &p_blkno, NULL,
  					  &ext_flags);

  	if (err) {
  		mlog(ML_ERROR, "Error %d from get_blocks(0x%p, %llu, 1, "

  		     "%llu, NULL)
  ", err, inode, (unsigned long long)iblock,
  		     (unsigned long long)p_blkno);

  		goto bail;
  	}

  	/*
  	 * ocfs2 never allocates in this function - the only time we
  	 * need to use BH_New is when we're extending i_size on a file
  	 * system which doesn't support holes, in which case BH_New
  	 * allows block_prepare_write() to zero.
  	 */
  	mlog_bug_on_msg(create && p_blkno == 0 && ocfs2_sparse_alloc(osb),
  			"ino %lu, iblock %llu
  ", inode->i_ino,
  			(unsigned long long)iblock);

  	/* Treat the unwritten extent as a hole for zeroing purposes. */
  	if (p_blkno && !(ext_flags & OCFS2_EXT_UNWRITTEN))

  		map_bh(bh_result, inode->i_sb, p_blkno);
  
  	if (!ocfs2_sparse_alloc(osb)) {
  		if (p_blkno == 0) {
  			err = -EIO;
  			mlog(ML_ERROR,
  			     "iblock = %llu p_blkno = %llu blkno=(%llu)
  ",
  			     (unsigned long long)iblock,
  			     (unsigned long long)p_blkno,
  			     (unsigned long long)OCFS2_I(inode)->ip_blkno);
  			mlog(ML_ERROR, "Size %llu, clusters %u
  ", (unsigned long long)i_size_read(inode), OCFS2_I(inode)->ip_clusters);
  			dump_stack();
  		}

  		past_eof = ocfs2_blocks_for_bytes(inode->i_sb, i_size_read(inode));
  		mlog(0, "Inode %lu, past_eof = %llu
  ", inode->i_ino,
  		     (unsigned long long)past_eof);

  		if (create && (iblock >= past_eof))
  			set_buffer_new(bh_result);
  	}

  
  bail:
  	if (err < 0)
  		err = -EIO;
  
  	mlog_exit(err);
  	return err;
  }
  
  static int ocfs2_readpage(struct file *file, struct page *page)
  {
  	struct inode *inode = page->mapping->host;
  	loff_t start = (loff_t)page->index << PAGE_CACHE_SHIFT;
  	int ret, unlock = 1;
  
  	mlog_entry("(0x%p, %lu)
  ", file, (page ? page->index : 0));

  	ret = ocfs2_meta_lock_with_page(inode, NULL, 0, page);

  	if (ret != 0) {
  		if (ret == AOP_TRUNCATED_PAGE)
  			unlock = 0;
  		mlog_errno(ret);
  		goto out;
  	}

  	if (down_read_trylock(&OCFS2_I(inode)->ip_alloc_sem) == 0) {
  		ret = AOP_TRUNCATED_PAGE;
  		goto out_meta_unlock;
  	}

  
  	/*
  	 * i_size might have just been updated as we grabed the meta lock.  We
  	 * might now be discovering a truncate that hit on another node.
  	 * block_read_full_page->get_block freaks out if it is asked to read
  	 * beyond the end of a file, so we check here.  Callers

  	 * (generic_file_read, vm_ops->fault) are clever enough to check i_size

  	 * and notice that the page they just read isn't needed.
  	 *
  	 * XXX sys_readahead() seems to get that wrong?
  	 */
  	if (start >= i_size_read(inode)) {

  		zero_user_page(page, 0, PAGE_SIZE, KM_USER0);

  		SetPageUptodate(page);
  		ret = 0;
  		goto out_alloc;
  	}
  
  	ret = ocfs2_data_lock_with_page(inode, 0, page);
  	if (ret != 0) {
  		if (ret == AOP_TRUNCATED_PAGE)
  			unlock = 0;
  		mlog_errno(ret);
  		goto out_alloc;
  	}
  
  	ret = block_read_full_page(page, ocfs2_get_block);
  	unlock = 0;
  
  	ocfs2_data_unlock(inode, 0);
  out_alloc:
  	up_read(&OCFS2_I(inode)->ip_alloc_sem);

  out_meta_unlock:

  	ocfs2_meta_unlock(inode, 0);
  out:
  	if (unlock)
  		unlock_page(page);
  	mlog_exit(ret);
  	return ret;
  }
  
  /* Note: Because we don't support holes, our allocation has
   * already happened (allocation writes zeros to the file data)
   * so we don't have to worry about ordered writes in
   * ocfs2_writepage.
   *
   * ->writepage is called during the process of invalidating the page cache
   * during blocked lock processing.  It can't block on any cluster locks
   * to during block mapping.  It's relying on the fact that the block
   * mapping can't have disappeared under the dirty pages that it is
   * being asked to write back.
   */
  static int ocfs2_writepage(struct page *page, struct writeback_control *wbc)
  {
  	int ret;
  
  	mlog_entry("(0x%p)
  ", page);
  
  	ret = block_write_full_page(page, ocfs2_get_block, wbc);
  
  	mlog_exit(ret);
  
  	return ret;
  }

  /*
   * This is called from ocfs2_write_zero_page() which has handled it's
   * own cluster locking and has ensured allocation exists for those
   * blocks to be written.
   */

  int ocfs2_prepare_write_nolock(struct inode *inode, struct page *page,
  			       unsigned from, unsigned to)
  {
  	int ret;
  
  	down_read(&OCFS2_I(inode)->ip_alloc_sem);
  
  	ret = block_prepare_write(page, from, to, ocfs2_get_block);
  
  	up_read(&OCFS2_I(inode)->ip_alloc_sem);
  
  	return ret;
  }

  /* Taken from ext3. We don't necessarily need the full blown
   * functionality yet, but IMHO it's better to cut and paste the whole
   * thing so we can avoid introducing our own bugs (and easily pick up
   * their fixes when they happen) --Mark */

  int walk_page_buffers(	handle_t *handle,
  			struct buffer_head *head,
  			unsigned from,
  			unsigned to,
  			int *partial,
  			int (*fn)(	handle_t *handle,
  					struct buffer_head *bh))

  {
  	struct buffer_head *bh;
  	unsigned block_start, block_end;
  	unsigned blocksize = head->b_size;
  	int err, ret = 0;
  	struct buffer_head *next;
  
  	for (	bh = head, block_start = 0;
  		ret == 0 && (bh != head || !block_start);
  	    	block_start = block_end, bh = next)
  	{
  		next = bh->b_this_page;
  		block_end = block_start + blocksize;
  		if (block_end <= from || block_start >= to) {
  			if (partial && !buffer_uptodate(bh))
  				*partial = 1;
  			continue;
  		}
  		err = (*fn)(handle, bh);
  		if (!ret)
  			ret = err;
  	}
  	return ret;
  }

  handle_t *ocfs2_start_walk_page_trans(struct inode *inode,

  							 struct page *page,
  							 unsigned from,
  							 unsigned to)
  {
  	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);

  	handle_t *handle = NULL;

  	int ret = 0;

  	handle = ocfs2_start_trans(osb, OCFS2_INODE_UPDATE_CREDITS);

  	if (!handle) {
  		ret = -ENOMEM;
  		mlog_errno(ret);
  		goto out;
  	}
  
  	if (ocfs2_should_order_data(inode)) {

  		ret = walk_page_buffers(handle,

  					page_buffers(page),
  					from, to, NULL,
  					ocfs2_journal_dirty_data);
  		if (ret < 0) 
  			mlog_errno(ret);
  	}
  out:
  	if (ret) {
  		if (handle)

  			ocfs2_commit_trans(osb, handle);

  		handle = ERR_PTR(ret);
  	}
  	return handle;
  }

  static sector_t ocfs2_bmap(struct address_space *mapping, sector_t block)
  {
  	sector_t status;
  	u64 p_blkno = 0;
  	int err = 0;
  	struct inode *inode = mapping->host;
  
  	mlog_entry("(block = %llu)
  ", (unsigned long long)block);
  
  	/* We don't need to lock journal system files, since they aren't
  	 * accessed concurrently from multiple nodes.
  	 */
  	if (!INODE_JOURNAL(inode)) {

  		err = ocfs2_meta_lock(inode, NULL, 0);

  		if (err) {
  			if (err != -ENOENT)
  				mlog_errno(err);
  			goto bail;
  		}
  		down_read(&OCFS2_I(inode)->ip_alloc_sem);
  	}

  	err = ocfs2_extent_map_get_blocks(inode, block, &p_blkno, NULL, NULL);

  
  	if (!INODE_JOURNAL(inode)) {
  		up_read(&OCFS2_I(inode)->ip_alloc_sem);
  		ocfs2_meta_unlock(inode, 0);
  	}
  
  	if (err) {
  		mlog(ML_ERROR, "get_blocks() failed, block = %llu
  ",
  		     (unsigned long long)block);
  		mlog_errno(err);
  		goto bail;
  	}
  
  
  bail:
  	status = err ? 0 : p_blkno;
  
  	mlog_exit((int)status);
  
  	return status;
  }
  
  /*
   * TODO: Make this into a generic get_blocks function.
   *
   * From do_direct_io in direct-io.c:
   *  "So what we do is to permit the ->get_blocks function to populate
   *   bh.b_size with the size of IO which is permitted at this offset and
   *   this i_blkbits."
   *
   * This function is called directly from get_more_blocks in direct-io.c.
   *
   * called like this: dio->get_blocks(dio->inode, fs_startblk,
   * 					fs_count, map_bh, dio->rw == WRITE);
   */
  static int ocfs2_direct_IO_get_blocks(struct inode *inode, sector_t iblock,

  				     struct buffer_head *bh_result, int create)
  {
  	int ret;

  	u64 p_blkno, inode_blocks, contig_blocks;

  	unsigned int ext_flags;

  	unsigned char blocksize_bits = inode->i_sb->s_blocksize_bits;

  	unsigned long max_blocks = bh_result->b_size >> inode->i_blkbits;

  	/* This function won't even be called if the request isn't all
  	 * nicely aligned and of the right size, so there's no need
  	 * for us to check any of that. */

  	inode_blocks = ocfs2_blocks_for_bytes(inode->i_sb, i_size_read(inode));

  
  	/*
  	 * Any write past EOF is not allowed because we'd be extending.
  	 */
  	if (create && (iblock + max_blocks) > inode_blocks) {

  		ret = -EIO;
  		goto bail;
  	}

  
  	/* This figures out the size of the next contiguous block, and
  	 * our logical offset */

  	ret = ocfs2_extent_map_get_blocks(inode, iblock, &p_blkno,

  					  &contig_blocks, &ext_flags);

  	if (ret) {
  		mlog(ML_ERROR, "get_blocks() failed iblock=%llu
  ",
  		     (unsigned long long)iblock);
  		ret = -EIO;
  		goto bail;
  	}

  	if (!ocfs2_sparse_alloc(OCFS2_SB(inode->i_sb)) && !p_blkno) {
  		ocfs2_error(inode->i_sb,
  			    "Inode %llu has a hole at block %llu
  ",
  			    (unsigned long long)OCFS2_I(inode)->ip_blkno,
  			    (unsigned long long)iblock);
  		ret = -EROFS;
  		goto bail;
  	}
  
  	/*
  	 * get_more_blocks() expects us to describe a hole by clearing
  	 * the mapped bit on bh_result().

  	 *
  	 * Consider an unwritten extent as a hole.

  	 */

  	if (p_blkno && !(ext_flags & OCFS2_EXT_UNWRITTEN))

  		map_bh(bh_result, inode->i_sb, p_blkno);
  	else {
  		/*
  		 * ocfs2_prepare_inode_for_write() should have caught
  		 * the case where we'd be filling a hole and triggered
  		 * a buffered write instead.
  		 */
  		if (create) {
  			ret = -EIO;
  			mlog_errno(ret);
  			goto bail;
  		}
  
  		clear_buffer_mapped(bh_result);
  	}

  
  	/* make sure we don't map more than max_blocks blocks here as
  	   that's all the kernel will handle at this point. */
  	if (max_blocks < contig_blocks)
  		contig_blocks = max_blocks;
  	bh_result->b_size = contig_blocks << blocksize_bits;
  bail:
  	return ret;
  }
  
  /* 
   * ocfs2_dio_end_io is called by the dio core when a dio is finished.  We're
   * particularly interested in the aio/dio case.  Like the core uses
   * i_alloc_sem, we use the rw_lock DLM lock to protect io on one node from
   * truncation on another.
   */
  static void ocfs2_dio_end_io(struct kiocb *iocb,
  			     loff_t offset,
  			     ssize_t bytes,
  			     void *private)
  {

  	struct inode *inode = iocb->ki_filp->f_path.dentry->d_inode;

  	int level;

  
  	/* this io's submitter should not have unlocked this before we could */
  	BUG_ON(!ocfs2_iocb_is_rw_locked(iocb));

  	ocfs2_iocb_clear_rw_locked(iocb);

  
  	level = ocfs2_iocb_rw_locked_level(iocb);
  	if (!level)
  		up_read(&inode->i_alloc_sem);
  	ocfs2_rw_unlock(inode, level);

  }

  /*
   * ocfs2_invalidatepage() and ocfs2_releasepage() are shamelessly stolen
   * from ext3.  PageChecked() bits have been removed as OCFS2 does not
   * do journalled data.
   */
  static void ocfs2_invalidatepage(struct page *page, unsigned long offset)
  {
  	journal_t *journal = OCFS2_SB(page->mapping->host->i_sb)->journal->j_journal;
  
  	journal_invalidatepage(journal, page, offset);
  }
  
  static int ocfs2_releasepage(struct page *page, gfp_t wait)
  {
  	journal_t *journal = OCFS2_SB(page->mapping->host->i_sb)->journal->j_journal;
  
  	if (!page_has_buffers(page))
  		return 0;
  	return journal_try_to_free_buffers(journal, page, wait);
  }

  static ssize_t ocfs2_direct_IO(int rw,
  			       struct kiocb *iocb,
  			       const struct iovec *iov,
  			       loff_t offset,
  			       unsigned long nr_segs)
  {
  	struct file *file = iocb->ki_filp;

  	struct inode *inode = file->f_path.dentry->d_inode->i_mapping->host;

  	int ret;
  
  	mlog_entry_void();

  	if (!ocfs2_sparse_alloc(OCFS2_SB(inode->i_sb))) {
  		/*
  		 * We get PR data locks even for O_DIRECT.  This
  		 * allows concurrent O_DIRECT I/O but doesn't let
  		 * O_DIRECT with extending and buffered zeroing writes
  		 * race.  If they did race then the buffered zeroing
  		 * could be written back after the O_DIRECT I/O.  It's
  		 * one thing to tell people not to mix buffered and
  		 * O_DIRECT writes, but expecting them to understand
  		 * that file extension is also an implicit buffered
  		 * write is too much.  By getting the PR we force
  		 * writeback of the buffered zeroing before
  		 * proceeding.
  		 */
  		ret = ocfs2_data_lock(inode, 0);
  		if (ret < 0) {
  			mlog_errno(ret);
  			goto out;
  		}
  		ocfs2_data_unlock(inode, 0);

  	}

  	ret = blockdev_direct_IO_no_locking(rw, iocb, inode,
  					    inode->i_sb->s_bdev, iov, offset,
  					    nr_segs, 
  					    ocfs2_direct_IO_get_blocks,
  					    ocfs2_dio_end_io);

  out:

  	mlog_exit(ret);
  	return ret;
  }

  static void ocfs2_figure_cluster_boundaries(struct ocfs2_super *osb,
  					    u32 cpos,
  					    unsigned int *start,
  					    unsigned int *end)
  {
  	unsigned int cluster_start = 0, cluster_end = PAGE_CACHE_SIZE;
  
  	if (unlikely(PAGE_CACHE_SHIFT > osb->s_clustersize_bits)) {
  		unsigned int cpp;
  
  		cpp = 1 << (PAGE_CACHE_SHIFT - osb->s_clustersize_bits);
  
  		cluster_start = cpos % cpp;
  		cluster_start = cluster_start << osb->s_clustersize_bits;
  
  		cluster_end = cluster_start + osb->s_clustersize;
  	}
  
  	BUG_ON(cluster_start > PAGE_SIZE);
  	BUG_ON(cluster_end > PAGE_SIZE);
  
  	if (start)
  		*start = cluster_start;
  	if (end)
  		*end = cluster_end;
  }
  
  /*
   * 'from' and 'to' are the region in the page to avoid zeroing.
   *
   * If pagesize > clustersize, this function will avoid zeroing outside
   * of the cluster boundary.
   *
   * from == to == 0 is code for "zero the entire cluster region"
   */
  static void ocfs2_clear_page_regions(struct page *page,
  				     struct ocfs2_super *osb, u32 cpos,
  				     unsigned from, unsigned to)
  {
  	void *kaddr;
  	unsigned int cluster_start, cluster_end;
  
  	ocfs2_figure_cluster_boundaries(osb, cpos, &cluster_start, &cluster_end);
  
  	kaddr = kmap_atomic(page, KM_USER0);
  
  	if (from || to) {
  		if (from > cluster_start)
  			memset(kaddr + cluster_start, 0, from - cluster_start);
  		if (to < cluster_end)
  			memset(kaddr + to, 0, cluster_end - to);
  	} else {
  		memset(kaddr + cluster_start, 0, cluster_end - cluster_start);
  	}
  
  	kunmap_atomic(kaddr, KM_USER0);
  }
  
  /*
   * Some of this taken from block_prepare_write(). We already have our
   * mapping by now though, and the entire write will be allocating or
   * it won't, so not much need to use BH_New.
   *
   * This will also skip zeroing, which is handled externally.
   */

  int ocfs2_map_page_blocks(struct page *page, u64 *p_blkno,
  			  struct inode *inode, unsigned int from,
  			  unsigned int to, int new)

  {
  	int ret = 0;
  	struct buffer_head *head, *bh, *wait[2], **wait_bh = wait;
  	unsigned int block_end, block_start;
  	unsigned int bsize = 1 << inode->i_blkbits;
  
  	if (!page_has_buffers(page))
  		create_empty_buffers(page, bsize, 0);
  
  	head = page_buffers(page);
  	for (bh = head, block_start = 0; bh != head || !block_start;
  	     bh = bh->b_this_page, block_start += bsize) {
  		block_end = block_start + bsize;

  		clear_buffer_new(bh);

  		/*
  		 * Ignore blocks outside of our i/o range -
  		 * they may belong to unallocated clusters.
  		 */

  		if (block_start >= to || block_end <= from) {

  			if (PageUptodate(page))
  				set_buffer_uptodate(bh);
  			continue;
  		}
  
  		/*
  		 * For an allocating write with cluster size >= page
  		 * size, we always write the entire page.
  		 */

  		if (new)
  			set_buffer_new(bh);

  
  		if (!buffer_mapped(bh)) {
  			map_bh(bh, inode->i_sb, *p_blkno);
  			unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
  		}
  
  		if (PageUptodate(page)) {
  			if (!buffer_uptodate(bh))
  				set_buffer_uptodate(bh);
  		} else if (!buffer_uptodate(bh) && !buffer_delay(bh) &&

  			   !buffer_new(bh) &&
  			   (block_start < from || block_end > to)) {

  			ll_rw_block(READ, 1, &bh);
  			*wait_bh++=bh;
  		}
  
  		*p_blkno = *p_blkno + 1;
  	}
  
  	/*
  	 * If we issued read requests - let them complete.
  	 */
  	while(wait_bh > wait) {
  		wait_on_buffer(*--wait_bh);
  		if (!buffer_uptodate(*wait_bh))
  			ret = -EIO;
  	}
  
  	if (ret == 0 || !new)
  		return ret;
  
  	/*
  	 * If we get -EIO above, zero out any newly allocated blocks
  	 * to avoid exposing stale data.
  	 */
  	bh = head;
  	block_start = 0;
  	do {

  		block_end = block_start + bsize;
  		if (block_end <= from)
  			goto next_bh;
  		if (block_start >= to)
  			break;

  		zero_user_page(page, block_start, bh->b_size, KM_USER0);

  		set_buffer_uptodate(bh);
  		mark_buffer_dirty(bh);
  
  next_bh:
  		block_start = block_end;
  		bh = bh->b_this_page;
  	} while (bh != head);
  
  	return ret;
  }

  #if (PAGE_CACHE_SIZE >= OCFS2_MAX_CLUSTERSIZE)
  #define OCFS2_MAX_CTXT_PAGES	1
  #else
  #define OCFS2_MAX_CTXT_PAGES	(OCFS2_MAX_CLUSTERSIZE / PAGE_CACHE_SIZE)
  #endif
  
  #define OCFS2_MAX_CLUSTERS_PER_PAGE	(PAGE_CACHE_SIZE / OCFS2_MIN_CLUSTERSIZE)

  /*

   * Describe the state of a single cluster to be written to.

   */

  struct ocfs2_write_cluster_desc {
  	u32		c_cpos;
  	u32		c_phys;
  	/*
  	 * Give this a unique field because c_phys eventually gets
  	 * filled.
  	 */
  	unsigned	c_new;

  	unsigned	c_unwritten;

  };

  static inline int ocfs2_should_zero_cluster(struct ocfs2_write_cluster_desc *d)
  {
  	return d->c_new || d->c_unwritten;
  }

  struct ocfs2_write_ctxt {
  	/* Logical cluster position / len of write */
  	u32				w_cpos;
  	u32				w_clen;

  	struct ocfs2_write_cluster_desc	w_desc[OCFS2_MAX_CLUSTERS_PER_PAGE];

  	/*
  	 * This is true if page_size > cluster_size.
  	 *
  	 * It triggers a set of special cases during write which might
  	 * have to deal with allocating writes to partial pages.
  	 */
  	unsigned int			w_large_pages;

  	/*
  	 * Pages involved in this write.
  	 *
  	 * w_target_page is the page being written to by the user.
  	 *
  	 * w_pages is an array of pages which always contains
  	 * w_target_page, and in the case of an allocating write with
  	 * page_size < cluster size, it will contain zero'd and mapped
  	 * pages adjacent to w_target_page which need to be written
  	 * out in so that future reads from that region will get
  	 * zero's.
  	 */
  	struct page			*w_pages[OCFS2_MAX_CTXT_PAGES];
  	unsigned int			w_num_pages;
  	struct page			*w_target_page;

  	/*
  	 * ocfs2_write_end() uses this to know what the real range to
  	 * write in the target should be.
  	 */
  	unsigned int			w_target_from;
  	unsigned int			w_target_to;
  
  	/*
  	 * We could use journal_current_handle() but this is cleaner,
  	 * IMHO -Mark
  	 */
  	handle_t			*w_handle;
  
  	struct buffer_head		*w_di_bh;

  
  	struct ocfs2_cached_dealloc_ctxt w_dealloc;

  };
  
  static void ocfs2_free_write_ctxt(struct ocfs2_write_ctxt *wc)
  {
  	int i;
  
  	for(i = 0; i < wc->w_num_pages; i++) {
  		if (wc->w_pages[i] == NULL)
  			continue;
  
  		unlock_page(wc->w_pages[i]);
  		mark_page_accessed(wc->w_pages[i]);
  		page_cache_release(wc->w_pages[i]);

  	}

  	brelse(wc->w_di_bh);
  	kfree(wc);
  }
  
  static int ocfs2_alloc_write_ctxt(struct ocfs2_write_ctxt **wcp,
  				  struct ocfs2_super *osb, loff_t pos,

  				  unsigned len, struct buffer_head *di_bh)

  {
  	struct ocfs2_write_ctxt *wc;
  
  	wc = kzalloc(sizeof(struct ocfs2_write_ctxt), GFP_NOFS);
  	if (!wc)
  		return -ENOMEM;

  	wc->w_cpos = pos >> osb->s_clustersize_bits;
  	wc->w_clen = ocfs2_clusters_for_bytes(osb->sb, len);

  	get_bh(di_bh);
  	wc->w_di_bh = di_bh;

  	if (unlikely(PAGE_CACHE_SHIFT > osb->s_clustersize_bits))
  		wc->w_large_pages = 1;
  	else
  		wc->w_large_pages = 0;

  	ocfs2_init_dealloc_ctxt(&wc->w_dealloc);

  	*wcp = wc;

  	return 0;

  }
  
  /*

   * If a page has any new buffers, zero them out here, and mark them uptodate
   * and dirty so they'll be written out (in order to prevent uninitialised
   * block data from leaking). And clear the new bit.

   */

  static void ocfs2_zero_new_buffers(struct page *page, unsigned from, unsigned to)

  {

  	unsigned int block_start, block_end;
  	struct buffer_head *head, *bh;

  	BUG_ON(!PageLocked(page));
  	if (!page_has_buffers(page))
  		return;

  	bh = head = page_buffers(page);
  	block_start = 0;
  	do {
  		block_end = block_start + bh->b_size;
  
  		if (buffer_new(bh)) {
  			if (block_end > from && block_start < to) {
  				if (!PageUptodate(page)) {
  					unsigned start, end;

  
  					start = max(from, block_start);
  					end = min(to, block_end);

  					zero_user_page(page, start, end - start, KM_USER0);

  					set_buffer_uptodate(bh);
  				}
  
  				clear_buffer_new(bh);
  				mark_buffer_dirty(bh);
  			}
  		}

  		block_start = block_end;
  		bh = bh->b_this_page;
  	} while (bh != head);
  }
  
  /*
   * Only called when we have a failure during allocating write to write
   * zero's to the newly allocated region.
   */
  static void ocfs2_write_failure(struct inode *inode,
  				struct ocfs2_write_ctxt *wc,
  				loff_t user_pos, unsigned user_len)
  {
  	int i;
  	unsigned from, to;
  	struct page *tmppage;
  
  	ocfs2_zero_new_buffers(wc->w_target_page, user_pos, user_len);

  	if (wc->w_large_pages) {

  		from = wc->w_target_from;
  		to = wc->w_target_to;

  	} else {

  		from = 0;
  		to = PAGE_CACHE_SIZE;

  	}

  	for(i = 0; i < wc->w_num_pages; i++) {
  		tmppage = wc->w_pages[i];

  		if (ocfs2_should_order_data(inode))
  			walk_page_buffers(wc->w_handle, page_buffers(tmppage),
  					  from, to, NULL,
  					  ocfs2_journal_dirty_data);

  		block_commit_write(tmppage, from, to);

  	}

  }

  static int ocfs2_prepare_page_for_write(struct inode *inode, u64 *p_blkno,
  					struct ocfs2_write_ctxt *wc,
  					struct page *page, u32 cpos,
  					loff_t user_pos, unsigned user_len,
  					int new)

  {

  	int ret;
  	unsigned int map_from = 0, map_to = 0;

  	unsigned int cluster_start, cluster_end;

  	unsigned int user_data_from = 0, user_data_to = 0;

  	ocfs2_figure_cluster_boundaries(OCFS2_SB(inode->i_sb), cpos,

  					&cluster_start, &cluster_end);

  	if (page == wc->w_target_page) {
  		map_from = user_pos & (PAGE_CACHE_SIZE - 1);
  		map_to = map_from + user_len;
  
  		if (new)
  			ret = ocfs2_map_page_blocks(page, p_blkno, inode,
  						    cluster_start, cluster_end,
  						    new);
  		else
  			ret = ocfs2_map_page_blocks(page, p_blkno, inode,
  						    map_from, map_to, new);
  		if (ret) {

  			mlog_errno(ret);
  			goto out;
  		}

  		user_data_from = map_from;
  		user_data_to = map_to;

  		if (new) {

  			map_from = cluster_start;
  			map_to = cluster_end;

  		}

  
  		wc->w_target_from = map_from;
  		wc->w_target_to = map_to;

  	} else {
  		/*
  		 * If we haven't allocated the new page yet, we
  		 * shouldn't be writing it out without copying user
  		 * data. This is likely a math error from the caller.
  		 */
  		BUG_ON(!new);

  		map_from = cluster_start;
  		map_to = cluster_end;

  
  		ret = ocfs2_map_page_blocks(page, p_blkno, inode,

  					    cluster_start, cluster_end, new);

  		if (ret) {
  			mlog_errno(ret);
  			goto out;
  		}
  	}
  
  	/*
  	 * Parts of newly allocated pages need to be zero'd.
  	 *
  	 * Above, we have also rewritten 'to' and 'from' - as far as
  	 * the rest of the function is concerned, the entire cluster
  	 * range inside of a page needs to be written.
  	 *
  	 * We can skip this if the page is up to date - it's already
  	 * been zero'd from being read in as a hole.
  	 */
  	if (new && !PageUptodate(page))
  		ocfs2_clear_page_regions(page, OCFS2_SB(inode->i_sb),

  					 cpos, user_data_from, user_data_to);

  
  	flush_dcache_page(page);

  out:

  	return ret;

  }
  
  /*

   * This function will only grab one clusters worth of pages.

   */

  static int ocfs2_grab_pages_for_write(struct address_space *mapping,
  				      struct ocfs2_write_ctxt *wc,

  				      u32 cpos, loff_t user_pos, int new,
  				      struct page *mmap_page)

  {

  	int ret = 0, i;
  	unsigned long start, target_index, index;

  	struct inode *inode = mapping->host;

  	target_index = user_pos >> PAGE_CACHE_SHIFT;

  
  	/*
  	 * Figure out how many pages we'll be manipulating here. For

  	 * non allocating write, we just change the one
  	 * page. Otherwise, we'll need a whole clusters worth.

  	 */

  	if (new) {

  		wc->w_num_pages = ocfs2_pages_per_cluster(inode->i_sb);
  		start = ocfs2_align_clusters_to_page_index(inode->i_sb, cpos);

  	} else {

  		wc->w_num_pages = 1;
  		start = target_index;

  	}

  	for(i = 0; i < wc->w_num_pages; i++) {

  		index = start + i;

  		if (index == target_index && mmap_page) {
  			/*
  			 * ocfs2_pagemkwrite() is a little different
  			 * and wants us to directly use the page
  			 * passed in.
  			 */
  			lock_page(mmap_page);
  
  			if (mmap_page->mapping != mapping) {
  				unlock_page(mmap_page);
  				/*
  				 * Sanity check - the locking in
  				 * ocfs2_pagemkwrite() should ensure
  				 * that this code doesn't trigger.
  				 */
  				ret = -EINVAL;
  				mlog_errno(ret);
  				goto out;
  			}
  
  			page_cache_get(mmap_page);
  			wc->w_pages[i] = mmap_page;
  		} else {
  			wc->w_pages[i] = find_or_create_page(mapping, index,
  							     GFP_NOFS);
  			if (!wc->w_pages[i]) {
  				ret = -ENOMEM;
  				mlog_errno(ret);
  				goto out;
  			}

  		}

  
  		if (index == target_index)
  			wc->w_target_page = wc->w_pages[i];

  	}

  out:
  	return ret;
  }
  
  /*
   * Prepare a single cluster for write one cluster into the file.
   */
  static int ocfs2_write_cluster(struct address_space *mapping,

  			       u32 phys, unsigned int unwritten,
  			       struct ocfs2_alloc_context *data_ac,

  			       struct ocfs2_alloc_context *meta_ac,
  			       struct ocfs2_write_ctxt *wc, u32 cpos,
  			       loff_t user_pos, unsigned user_len)
  {

  	int ret, i, new, should_zero = 0;

  	u64 v_blkno, p_blkno;
  	struct inode *inode = mapping->host;
  
  	new = phys == 0 ? 1 : 0;

  	if (new || unwritten)
  		should_zero = 1;

  
  	if (new) {

  		u32 tmp_pos;

  		/*
  		 * This is safe to call with the page locks - it won't take
  		 * any additional semaphores or cluster locks.
  		 */

  		tmp_pos = cpos;

  		ret = ocfs2_do_extend_allocation(OCFS2_SB(inode->i_sb), inode,

  						 &tmp_pos, 1, 0, wc->w_di_bh,

  						 wc->w_handle, data_ac,
  						 meta_ac, NULL);

  		/*
  		 * This shouldn't happen because we must have already
  		 * calculated the correct meta data allocation required. The
  		 * internal tree allocation code should know how to increase
  		 * transaction credits itself.
  		 *
  		 * If need be, we could handle -EAGAIN for a
  		 * RESTART_TRANS here.
  		 */
  		mlog_bug_on_msg(ret == -EAGAIN,
  				"Inode %llu: EAGAIN return during allocation.
  ",
  				(unsigned long long)OCFS2_I(inode)->ip_blkno);
  		if (ret < 0) {
  			mlog_errno(ret);
  			goto out;
  		}

  	} else if (unwritten) {
  		ret = ocfs2_mark_extent_written(inode, wc->w_di_bh,
  						wc->w_handle, cpos, 1, phys,
  						meta_ac, &wc->w_dealloc);
  		if (ret < 0) {
  			mlog_errno(ret);
  			goto out;
  		}
  	}

  	if (should_zero)

  		v_blkno = ocfs2_clusters_to_blocks(inode->i_sb, cpos);

  	else

  		v_blkno = user_pos >> inode->i_sb->s_blocksize_bits;

  	/*
  	 * The only reason this should fail is due to an inability to
  	 * find the extent added.
  	 */

  	ret = ocfs2_extent_map_get_blocks(inode, v_blkno, &p_blkno, NULL,
  					  NULL);

  	if (ret < 0) {

  		ocfs2_error(inode->i_sb, "Corrupting extend for inode %llu, "
  			    "at logical block %llu",
  			    (unsigned long long)OCFS2_I(inode)->ip_blkno,
  			    (unsigned long long)v_blkno);

  		goto out;
  	}
  
  	BUG_ON(p_blkno == 0);

  	for(i = 0; i < wc->w_num_pages; i++) {
  		int tmpret;

  		tmpret = ocfs2_prepare_page_for_write(inode, &p_blkno, wc,
  						      wc->w_pages[i], cpos,

  						      user_pos, user_len,
  						      should_zero);

  		if (tmpret) {
  			mlog_errno(tmpret);
  			if (ret == 0)
  				tmpret = ret;
  		}

  	}

  	/*
  	 * We only have cleanup to do in case of allocating write.
  	 */
  	if (ret && new)
  		ocfs2_write_failure(inode, wc, user_pos, user_len);

  out:

  	return ret;

  }

  static int ocfs2_write_cluster_by_desc(struct address_space *mapping,
  				       struct ocfs2_alloc_context *data_ac,
  				       struct ocfs2_alloc_context *meta_ac,
  				       struct ocfs2_write_ctxt *wc,
  				       loff_t pos, unsigned len)
  {
  	int ret, i;
  	struct ocfs2_write_cluster_desc *desc;
  
  	for (i = 0; i < wc->w_clen; i++) {
  		desc = &wc->w_desc[i];

  		ret = ocfs2_write_cluster(mapping, desc->c_phys,
  					  desc->c_unwritten, data_ac, meta_ac,
  					  wc, desc->c_cpos, pos, len);

  		if (ret) {
  			mlog_errno(ret);
  			goto out;
  		}
  	}
  
  	ret = 0;
  out:
  	return ret;
  }

  /*
   * ocfs2_write_end() wants to know which parts of the target page it
   * should complete the write on. It's easiest to compute them ahead of
   * time when a more complete view of the write is available.
   */
  static void ocfs2_set_target_boundaries(struct ocfs2_super *osb,
  					struct ocfs2_write_ctxt *wc,
  					loff_t pos, unsigned len, int alloc)

  {

  	struct ocfs2_write_cluster_desc *desc;

  	wc->w_target_from = pos & (PAGE_CACHE_SIZE - 1);
  	wc->w_target_to = wc->w_target_from + len;
  
  	if (alloc == 0)
  		return;
  
  	/*
  	 * Allocating write - we may have different boundaries based
  	 * on page size and cluster size.
  	 *
  	 * NOTE: We can no longer compute one value from the other as
  	 * the actual write length and user provided length may be
  	 * different.
  	 */

  	if (wc->w_large_pages) {
  		/*
  		 * We only care about the 1st and last cluster within

  		 * our range and whether they should be zero'd or not. Either

  		 * value may be extended out to the start/end of a
  		 * newly allocated cluster.
  		 */
  		desc = &wc->w_desc[0];

  		if (ocfs2_should_zero_cluster(desc))

  			ocfs2_figure_cluster_boundaries(osb,
  							desc->c_cpos,
  							&wc->w_target_from,
  							NULL);
  
  		desc = &wc->w_desc[wc->w_clen - 1];

  		if (ocfs2_should_zero_cluster(desc))

  			ocfs2_figure_cluster_boundaries(osb,
  							desc->c_cpos,
  							NULL,
  							&wc->w_target_to);
  	} else {
  		wc->w_target_from = 0;
  		wc->w_target_to = PAGE_CACHE_SIZE;
  	}

  }

  /*
   * Populate each single-cluster write descriptor in the write context
   * with information about the i/o to be done.

   *
   * Returns the number of clusters that will have to be allocated, as
   * well as a worst case estimate of the number of extent records that
   * would have to be created during a write to an unwritten region.

   */
  static int ocfs2_populate_write_desc(struct inode *inode,
  				     struct ocfs2_write_ctxt *wc,

  				     unsigned int *clusters_to_alloc,
  				     unsigned int *extents_to_split)

  {

  	int ret;

  	struct ocfs2_write_cluster_desc *desc;

  	unsigned int num_clusters = 0;

  	unsigned int ext_flags = 0;

  	u32 phys = 0;
  	int i;

  	*clusters_to_alloc = 0;
  	*extents_to_split = 0;

  	for (i = 0; i < wc->w_clen; i++) {
  		desc = &wc->w_desc[i];
  		desc->c_cpos = wc->w_cpos + i;
  
  		if (num_clusters == 0) {

  			/*
  			 * Need to look up the next extent record.
  			 */

  			ret = ocfs2_get_clusters(inode, desc->c_cpos, &phys,

  						 &num_clusters, &ext_flags);

  			if (ret) {
  				mlog_errno(ret);

  				goto out;

  			}

  
  			/*
  			 * Assume worst case - that we're writing in
  			 * the middle of the extent.
  			 *
  			 * We can assume that the write proceeds from
  			 * left to right, in which case the extent
  			 * insert code is smart enough to coalesce the
  			 * next splits into the previous records created.
  			 */
  			if (ext_flags & OCFS2_EXT_UNWRITTEN)
  				*extents_to_split = *extents_to_split + 2;

  		} else if (phys) {
  			/*
  			 * Only increment phys if it doesn't describe
  			 * a hole.
  			 */
  			phys++;
  		}
  
  		desc->c_phys = phys;
  		if (phys == 0) {
  			desc->c_new = 1;

  			*clusters_to_alloc = *clusters_to_alloc + 1;

  		}

  		if (ext_flags & OCFS2_EXT_UNWRITTEN)
  			desc->c_unwritten = 1;

  
  		num_clusters--;

  	}

  	ret = 0;
  out:
  	return ret;
  }
  
  int ocfs2_write_begin_nolock(struct address_space *mapping,
  			     loff_t pos, unsigned len, unsigned flags,
  			     struct page **pagep, void **fsdata,
  			     struct buffer_head *di_bh, struct page *mmap_page)
  {
  	int ret, credits = OCFS2_INODE_UPDATE_CREDITS;

  	unsigned int clusters_to_alloc, extents_to_split;

  	struct ocfs2_write_ctxt *wc;
  	struct inode *inode = mapping->host;
  	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
  	struct ocfs2_dinode *di;
  	struct ocfs2_alloc_context *data_ac = NULL;
  	struct ocfs2_alloc_context *meta_ac = NULL;
  	handle_t *handle;
  
  	ret = ocfs2_alloc_write_ctxt(&wc, osb, pos, len, di_bh);
  	if (ret) {
  		mlog_errno(ret);
  		return ret;
  	}

  	ret = ocfs2_populate_write_desc(inode, wc, &clusters_to_alloc,
  					&extents_to_split);

  	if (ret) {
  		mlog_errno(ret);
  		goto out;
  	}
  
  	di = (struct ocfs2_dinode *)wc->w_di_bh->b_data;

  	/*
  	 * We set w_target_from, w_target_to here so that
  	 * ocfs2_write_end() knows which range in the target page to
  	 * write out. An allocation requires that we write the entire
  	 * cluster range.
  	 */

  	if (clusters_to_alloc || extents_to_split) {

  		/*
  		 * XXX: We are stretching the limits of

  		 * ocfs2_lock_allocators(). It greatly over-estimates

  		 * the work to be done.
  		 */
  		ret = ocfs2_lock_allocators(inode, di, clusters_to_alloc,

  					    extents_to_split, &data_ac, &meta_ac);

  		if (ret) {
  			mlog_errno(ret);

  			goto out;

  		}

  		credits = ocfs2_calc_extend_credits(inode->i_sb, di,
  						    clusters_to_alloc);

  	}

  	ocfs2_set_target_boundaries(osb, wc, pos, len,
  				    clusters_to_alloc + extents_to_split);

  	handle = ocfs2_start_trans(osb, credits);
  	if (IS_ERR(handle)) {
  		ret = PTR_ERR(handle);
  		mlog_errno(ret);

  		goto out;

  	}

  	wc->w_handle = handle;
  
  	/*
  	 * We don't want this to fail in ocfs2_write_end(), so do it
  	 * here.
  	 */
  	ret = ocfs2_journal_access(handle, inode, wc->w_di_bh,
  				   OCFS2_JOURNAL_ACCESS_WRITE);
  	if (ret) {

  		mlog_errno(ret);
  		goto out_commit;
  	}

  	/*
  	 * Fill our page array first. That way we've grabbed enough so
  	 * that we can zero and flush if we error after adding the
  	 * extent.
  	 */
  	ret = ocfs2_grab_pages_for_write(mapping, wc, wc->w_cpos, pos,

  					 clusters_to_alloc + extents_to_split,
  					 mmap_page);

  	if (ret) {
  		mlog_errno(ret);
  		goto out_commit;
  	}

  	ret = ocfs2_write_cluster_by_desc(mapping, data_ac, meta_ac, wc, pos,
  					  len);
  	if (ret) {
  		mlog_errno(ret);
  		goto out_commit;

  	}

  	if (data_ac)
  		ocfs2_free_alloc_context(data_ac);
  	if (meta_ac)
  		ocfs2_free_alloc_context(meta_ac);

  	*pagep = wc->w_target_page;
  	*fsdata = wc;
  	return 0;

  out_commit:
  	ocfs2_commit_trans(osb, handle);

  out:

  	ocfs2_free_write_ctxt(wc);

  	if (data_ac)
  		ocfs2_free_alloc_context(data_ac);
  	if (meta_ac)
  		ocfs2_free_alloc_context(meta_ac);

  	return ret;
  }

  int ocfs2_write_begin(struct file *file, struct address_space *mapping,
  		      loff_t pos, unsigned len, unsigned flags,
  		      struct page **pagep, void **fsdata)
  {
  	int ret;
  	struct buffer_head *di_bh = NULL;
  	struct inode *inode = mapping->host;
  
  	ret = ocfs2_meta_lock(inode, &di_bh, 1);
  	if (ret) {
  		mlog_errno(ret);
  		return ret;
  	}
  
  	/*
  	 * Take alloc sem here to prevent concurrent lookups. That way
  	 * the mapping, zeroing and tree manipulation within
  	 * ocfs2_write() will be safe against ->readpage(). This
  	 * should also serve to lock out allocation from a shared
  	 * writeable region.
  	 */
  	down_write(&OCFS2_I(inode)->ip_alloc_sem);
  
  	ret = ocfs2_data_lock(inode, 1);
  	if (ret) {
  		mlog_errno(ret);
  		goto out_fail;
  	}
  
  	ret = ocfs2_write_begin_nolock(mapping, pos, len, flags, pagep,

  				       fsdata, di_bh, NULL);

  	if (ret) {
  		mlog_errno(ret);
  		goto out_fail_data;
  	}
  
  	brelse(di_bh);
  
  	return 0;
  
  out_fail_data:
  	ocfs2_data_unlock(inode, 1);
  out_fail:
  	up_write(&OCFS2_I(inode)->ip_alloc_sem);
  
  	brelse(di_bh);
  	ocfs2_meta_unlock(inode, 1);
  
  	return ret;
  }

  int ocfs2_write_end_nolock(struct address_space *mapping,
  			   loff_t pos, unsigned len, unsigned copied,
  			   struct page *page, void *fsdata)

  {
  	int i;
  	unsigned from, to, start = pos & (PAGE_CACHE_SIZE - 1);
  	struct inode *inode = mapping->host;
  	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
  	struct ocfs2_write_ctxt *wc = fsdata;
  	struct ocfs2_dinode *di = (struct ocfs2_dinode *)wc->w_di_bh->b_data;
  	handle_t *handle = wc->w_handle;
  	struct page *tmppage;
  
  	if (unlikely(copied < len)) {
  		if (!PageUptodate(wc->w_target_page))
  			copied = 0;
  
  		ocfs2_zero_new_buffers(wc->w_target_page, start+copied,
  				       start+len);
  	}
  	flush_dcache_page(wc->w_target_page);
  
  	for(i = 0; i < wc->w_num_pages; i++) {
  		tmppage = wc->w_pages[i];
  
  		if (tmppage == wc->w_target_page) {
  			from = wc->w_target_from;
  			to = wc->w_target_to;
  
  			BUG_ON(from > PAGE_CACHE_SIZE ||
  			       to > PAGE_CACHE_SIZE ||
  			       to < from);
  		} else {
  			/*
  			 * Pages adjacent to the target (if any) imply
  			 * a hole-filling write in which case we want
  			 * to flush their entire range.
  			 */
  			from = 0;
  			to = PAGE_CACHE_SIZE;
  		}
  
  		if (ocfs2_should_order_data(inode))
  			walk_page_buffers(wc->w_handle, page_buffers(tmppage),
  					  from, to, NULL,
  					  ocfs2_journal_dirty_data);
  
  		block_commit_write(tmppage, from, to);
  	}
  
  	pos += copied;
  	if (pos > inode->i_size) {
  		i_size_write(inode, pos);
  		mark_inode_dirty(inode);
  	}
  	inode->i_blocks = ocfs2_inode_sector_count(inode);
  	di->i_size = cpu_to_le64((u64)i_size_read(inode));
  	inode->i_mtime = inode->i_ctime = CURRENT_TIME;
  	di->i_mtime = di->i_ctime = cpu_to_le64(inode->i_mtime.tv_sec);
  	di->i_mtime_nsec = di->i_ctime_nsec = cpu_to_le32(inode->i_mtime.tv_nsec);

  	ocfs2_journal_dirty(handle, wc->w_di_bh);
  
  	ocfs2_commit_trans(osb, handle);

  	ocfs2_run_deallocs(osb, &wc->w_dealloc);

  	ocfs2_free_write_ctxt(wc);
  
  	return copied;
  }
  
  int ocfs2_write_end(struct file *file, struct address_space *mapping,
  		    loff_t pos, unsigned len, unsigned copied,
  		    struct page *page, void *fsdata)
  {
  	int ret;
  	struct inode *inode = mapping->host;
  
  	ret = ocfs2_write_end_nolock(mapping, pos, len, copied, page, fsdata);

  	ocfs2_data_unlock(inode, 1);
  	up_write(&OCFS2_I(inode)->ip_alloc_sem);
  	ocfs2_meta_unlock(inode, 1);

  	return ret;

  }

  const struct address_space_operations ocfs2_aops = {

  	.readpage	= ocfs2_readpage,
  	.writepage	= ocfs2_writepage,

  	.bmap		= ocfs2_bmap,
  	.sync_page	= block_sync_page,

  	.direct_IO	= ocfs2_direct_IO,
  	.invalidatepage	= ocfs2_invalidatepage,
  	.releasepage	= ocfs2_releasepage,
  	.migratepage	= buffer_migrate_page,

  };