/*
   *  linux/fs/ext3/inode.c
   *
   * Copyright (C) 1992, 1993, 1994, 1995
   * Remy Card (card@masi.ibp.fr)
   * Laboratoire MASI - Institut Blaise Pascal
   * Universite Pierre et Marie Curie (Paris VI)
   *
   *  from
   *
   *  linux/fs/minix/inode.c
   *
   *  Copyright (C) 1991, 1992  Linus Torvalds
   *
   *  Goal-directed block allocation by Stephen Tweedie

   *	(sct@redhat.com), 1993, 1998

   *  Big-endian to little-endian byte-swapping/bitmaps by
   *        David S. Miller (davem@caip.rutgers.edu), 1995
   *  64-bit file support on 64-bit platforms by Jakub Jelinek

   *	(jj@sunsite.ms.mff.cuni.cz)

   *
   *  Assorted race fixes, rewrite of ext3_get_block() by Al Viro, 2000
   */

  #include <linux/fs.h>
  #include <linux/time.h>
  #include <linux/ext3_jbd.h>
  #include <linux/jbd.h>

  #include <linux/highuid.h>
  #include <linux/pagemap.h>
  #include <linux/quotaops.h>
  #include <linux/string.h>
  #include <linux/buffer_head.h>
  #include <linux/writeback.h>
  #include <linux/mpage.h>
  #include <linux/uio.h>

  #include <linux/bio.h>

  #include <linux/fiemap.h>

  #include <linux/namei.h>

  #include <trace/events/ext3.h>

  #include "xattr.h"
  #include "acl.h"
  
  static int ext3_writepage_trans_blocks(struct inode *inode);

  static int ext3_block_truncate_page(struct inode *inode, loff_t from);

  
  /*
   * Test whether an inode is a fast symlink.
   */

  static int ext3_inode_is_fast_symlink(struct inode *inode)

  {
  	int ea_blocks = EXT3_I(inode)->i_file_acl ?
  		(inode->i_sb->s_blocksize >> 9) : 0;

  	return (S_ISLNK(inode->i_mode) && inode->i_blocks - ea_blocks == 0);

  }

  /*
   * The ext3 forget function must perform a revoke if we are freeing data

   * which has been journaled.  Metadata (eg. indirect blocks) must be

   * revoked in all cases.

   *
   * "bh" may be NULL: a metadata block may have been freed from memory
   * but there may still be a record of it in the journal, and that record
   * still needs to be revoked.
   */

  int ext3_forget(handle_t *handle, int is_metadata, struct inode *inode,

  			struct buffer_head *bh, ext3_fsblk_t blocknr)

  {
  	int err;
  
  	might_sleep();

  	trace_ext3_forget(inode, is_metadata, blocknr);

  	BUFFER_TRACE(bh, "enter");
  
  	jbd_debug(4, "forgetting bh %p: is_metadata = %d, mode %o, "
  		  "data mode %lx
  ",
  		  bh, is_metadata, inode->i_mode,
  		  test_opt(inode->i_sb, DATA_FLAGS));
  
  	/* Never use the revoke function if we are doing full data
  	 * journaling: there is no need to, and a V1 superblock won't
  	 * support it.  Otherwise, only skip the revoke on un-journaled
  	 * data blocks. */
  
  	if (test_opt(inode->i_sb, DATA_FLAGS) == EXT3_MOUNT_JOURNAL_DATA ||
  	    (!is_metadata && !ext3_should_journal_data(inode))) {
  		if (bh) {
  			BUFFER_TRACE(bh, "call journal_forget");
  			return ext3_journal_forget(handle, bh);
  		}
  		return 0;
  	}
  
  	/*
  	 * data!=journal && (is_metadata || should_journal_data(inode))
  	 */
  	BUFFER_TRACE(bh, "call ext3_journal_revoke");
  	err = ext3_journal_revoke(handle, blocknr, bh);
  	if (err)

  		ext3_abort(inode->i_sb, __func__,

  			   "error %d when attempting revoke", err);
  	BUFFER_TRACE(bh, "exit");
  	return err;
  }
  
  /*

   * Work out how many blocks we need to proceed with the next chunk of a

   * truncate transaction.
   */

  static unsigned long blocks_for_truncate(struct inode *inode)

  {
  	unsigned long needed;
  
  	needed = inode->i_blocks >> (inode->i_sb->s_blocksize_bits - 9);
  
  	/* Give ourselves just enough room to cope with inodes in which
  	 * i_blocks is corrupt: we've seen disk corruptions in the past
  	 * which resulted in random data in an inode which looked enough
  	 * like a regular file for ext3 to try to delete it.  Things
  	 * will go a bit crazy if that happens, but at least we should
  	 * try not to panic the whole kernel. */
  	if (needed < 2)
  		needed = 2;
  
  	/* But we need to bound the transaction so we don't overflow the
  	 * journal. */

  	if (needed > EXT3_MAX_TRANS_DATA)

  		needed = EXT3_MAX_TRANS_DATA;

  	return EXT3_DATA_TRANS_BLOCKS(inode->i_sb) + needed;

  }

  /*

   * Truncate transactions can be complex and absolutely huge.  So we need to
   * be able to restart the transaction at a conventient checkpoint to make
   * sure we don't overflow the journal.
   *
   * start_transaction gets us a new handle for a truncate transaction,
   * and extend_transaction tries to extend the existing one a bit.  If
   * extend fails, we need to propagate the failure up and restart the

   * transaction in the top-level truncate loop. --sct

   */

  static handle_t *start_transaction(struct inode *inode)

  {
  	handle_t *result;
  
  	result = ext3_journal_start(inode, blocks_for_truncate(inode));
  	if (!IS_ERR(result))
  		return result;
  
  	ext3_std_error(inode->i_sb, PTR_ERR(result));
  	return result;
  }
  
  /*
   * Try to extend this transaction for the purposes of truncation.
   *
   * Returns 0 if we managed to create more room.  If we can't create more
   * room, and the transaction must be restarted we return 1.
   */
  static int try_to_extend_transaction(handle_t *handle, struct inode *inode)
  {
  	if (handle->h_buffer_credits > EXT3_RESERVE_TRANS_BLOCKS)
  		return 0;
  	if (!ext3_journal_extend(handle, blocks_for_truncate(inode)))
  		return 0;
  	return 1;
  }
  
  /*
   * Restart the transaction associated with *handle.  This does a commit,
   * so before we call here everything must be consistently dirtied against
   * this transaction.
   */

  static int truncate_restart_transaction(handle_t *handle, struct inode *inode)

  {

  	int ret;

  	jbd_debug(2, "restarting handle %p
  ", handle);

  	/*
  	 * Drop truncate_mutex to avoid deadlock with ext3_get_blocks_handle
  	 * At this moment, get_block can be called only for blocks inside
  	 * i_size since page cache has been already dropped and writes are
  	 * blocked by i_mutex. So we can safely drop the truncate_mutex.
  	 */
  	mutex_unlock(&EXT3_I(inode)->truncate_mutex);
  	ret = ext3_journal_restart(handle, blocks_for_truncate(inode));
  	mutex_lock(&EXT3_I(inode)->truncate_mutex);
  	return ret;

  }
  
  /*

   * Called at inode eviction from icache

   */

  void ext3_evict_inode (struct inode *inode)

  {

  	struct ext3_inode_info *ei = EXT3_I(inode);

  	struct ext3_block_alloc_info *rsv;

  	handle_t *handle;

  	int want_delete = 0;

  	trace_ext3_evict_inode(inode);

  	if (!inode->i_nlink && !is_bad_inode(inode)) {

  		dquot_initialize(inode);

  		want_delete = 1;
  	}

  	/*
  	 * When journalling data dirty buffers are tracked only in the journal.
  	 * So although mm thinks everything is clean and ready for reaping the
  	 * inode might still have some pages to write in the running
  	 * transaction or waiting to be checkpointed. Thus calling
  	 * journal_invalidatepage() (via truncate_inode_pages()) to discard
  	 * these buffers can cause data loss. Also even if we did not discard
  	 * these buffers, we would have no way to find them after the inode
  	 * is reaped and thus user could see stale data if he tries to read
  	 * them before the transaction is checkpointed. So be careful and
  	 * force everything to disk here... We use ei->i_datasync_tid to
  	 * store the newest transaction containing inode's data.
  	 *
  	 * Note that directories do not have this problem because they don't
  	 * use page cache.

  	 *
  	 * The s_journal check handles the case when ext3_get_journal() fails
  	 * and puts the journal inode.

  	 */
  	if (inode->i_nlink && ext3_should_journal_data(inode) &&

  	    EXT3_SB(inode->i_sb)->s_journal &&

  	    (S_ISLNK(inode->i_mode) || S_ISREG(inode->i_mode))) {
  		tid_t commit_tid = atomic_read(&ei->i_datasync_tid);
  		journal_t *journal = EXT3_SB(inode->i_sb)->s_journal;
  
  		log_start_commit(journal, commit_tid);
  		log_wait_commit(journal, commit_tid);
  		filemap_write_and_wait(&inode->i_data);
  	}

  	truncate_inode_pages(&inode->i_data, 0);

  	ext3_discard_reservation(inode);

  	rsv = ei->i_block_alloc_info;
  	ei->i_block_alloc_info = NULL;

  	if (unlikely(rsv))
  		kfree(rsv);
  
  	if (!want_delete)

  		goto no_delete;
  
  	handle = start_transaction(inode);
  	if (IS_ERR(handle)) {

  		/*
  		 * If we're going to skip the normal cleanup, we still need to
  		 * make sure that the in-core orphan linked list is properly
  		 * cleaned up.
  		 */

  		ext3_orphan_del(NULL, inode);
  		goto no_delete;
  	}
  
  	if (IS_SYNC(inode))
  		handle->h_sync = 1;
  	inode->i_size = 0;
  	if (inode->i_blocks)
  		ext3_truncate(inode);
  	/*

  	 * Kill off the orphan record created when the inode lost the last
  	 * link.  Note that ext3_orphan_del() has to be able to cope with the
  	 * deletion of a non-existent orphan - ext3_truncate() could
  	 * have removed the record.

  	 */
  	ext3_orphan_del(handle, inode);

  	ei->i_dtime = get_seconds();

  	/*

  	 * One subtle ordering requirement: if anything has gone wrong
  	 * (transaction abort, IO errors, whatever), then we can still
  	 * do these next steps (the fs will already have been marked as
  	 * having errors), but we can't free the inode if the mark_dirty

  	 * fails.

  	 */

  	if (ext3_mark_inode_dirty(handle, inode)) {
  		/* If that failed, just dquot_drop() and be done with that */
  		dquot_drop(inode);
  		end_writeback(inode);
  	} else {
  		ext3_xattr_delete_inode(handle, inode);
  		dquot_free_inode(inode);
  		dquot_drop(inode);
  		end_writeback(inode);

  		ext3_free_inode(handle, inode);

  	}

  	ext3_journal_stop(handle);
  	return;
  no_delete:

  	end_writeback(inode);
  	dquot_drop(inode);

  }

  typedef struct {
  	__le32	*p;
  	__le32	key;
  	struct buffer_head *bh;
  } Indirect;
  
  static inline void add_chain(Indirect *p, struct buffer_head *bh, __le32 *v)
  {
  	p->key = *(p->p = v);
  	p->bh = bh;
  }

  static int verify_chain(Indirect *from, Indirect *to)

  {
  	while (from <= to && from->key == *from->p)
  		from++;
  	return (from > to);
  }
  
  /**
   *	ext3_block_to_path - parse the block number into array of offsets
   *	@inode: inode in question (we are only interested in its superblock)
   *	@i_block: block number to be parsed
   *	@offsets: array to store the offsets in
   *      @boundary: set this non-zero if the referred-to block is likely to be
   *             followed (on disk) by an indirect block.
   *
   *	To store the locations of file's data ext3 uses a data structure common
   *	for UNIX filesystems - tree of pointers anchored in the inode, with
   *	data blocks at leaves and indirect blocks in intermediate nodes.
   *	This function translates the block number into path in that tree -
   *	return value is the path length and @offsets[n] is the offset of
   *	pointer to (n+1)th node in the nth one. If @block is out of range
   *	(negative or too large) warning is printed and zero returned.
   *
   *	Note: function doesn't find node addresses, so no IO is needed. All
   *	we need to know is the capacity of indirect blocks (taken from the
   *	inode->i_sb).
   */
  
  /*
   * Portability note: the last comparison (check that we fit into triple
   * indirect block) is spelled differently, because otherwise on an
   * architecture with 32-bit longs and 8Kb pages we might get into trouble
   * if our filesystem had 8Kb blocks. We might use long long, but that would
   * kill us on x86. Oh, well, at least the sign propagation does not matter -
   * i_block would have to be negative in the very beginning, so we would not
   * get there at all.
   */
  
  static int ext3_block_to_path(struct inode *inode,
  			long i_block, int offsets[4], int *boundary)
  {
  	int ptrs = EXT3_ADDR_PER_BLOCK(inode->i_sb);
  	int ptrs_bits = EXT3_ADDR_PER_BLOCK_BITS(inode->i_sb);
  	const long direct_blocks = EXT3_NDIR_BLOCKS,
  		indirect_blocks = ptrs,
  		double_blocks = (1 << (ptrs_bits * 2));
  	int n = 0;
  	int final = 0;
  
  	if (i_block < 0) {
  		ext3_warning (inode->i_sb, "ext3_block_to_path", "block < 0");
  	} else if (i_block < direct_blocks) {
  		offsets[n++] = i_block;
  		final = direct_blocks;
  	} else if ( (i_block -= direct_blocks) < indirect_blocks) {
  		offsets[n++] = EXT3_IND_BLOCK;
  		offsets[n++] = i_block;
  		final = ptrs;
  	} else if ((i_block -= indirect_blocks) < double_blocks) {
  		offsets[n++] = EXT3_DIND_BLOCK;
  		offsets[n++] = i_block >> ptrs_bits;
  		offsets[n++] = i_block & (ptrs - 1);
  		final = ptrs;
  	} else if (((i_block -= double_blocks) >> (ptrs_bits * 2)) < ptrs) {
  		offsets[n++] = EXT3_TIND_BLOCK;
  		offsets[n++] = i_block >> (ptrs_bits * 2);
  		offsets[n++] = (i_block >> ptrs_bits) & (ptrs - 1);
  		offsets[n++] = i_block & (ptrs - 1);
  		final = ptrs;
  	} else {

  		ext3_warning(inode->i_sb, "ext3_block_to_path", "block > big");

  	}
  	if (boundary)

  		*boundary = final - 1 - (i_block & (ptrs - 1));

  	return n;
  }
  
  /**
   *	ext3_get_branch - read the chain of indirect blocks leading to data
   *	@inode: inode in question
   *	@depth: depth of the chain (1 - direct pointer, etc.)
   *	@offsets: offsets of pointers in inode/indirect blocks
   *	@chain: place to store the result
   *	@err: here we store the error value
   *
   *	Function fills the array of triples <key, p, bh> and returns %NULL
   *	if everything went OK or the pointer to the last filled triple
   *	(incomplete one) otherwise. Upon the return chain[i].key contains
   *	the number of (i+1)-th block in the chain (as it is stored in memory,
   *	i.e. little-endian 32-bit), chain[i].p contains the address of that
   *	number (it points into struct inode for i==0 and into the bh->b_data
   *	for i>0) and chain[i].bh points to the buffer_head of i-th indirect
   *	block for i>0 and NULL for i==0. In other words, it holds the block
   *	numbers of the chain, addresses they were taken from (and where we can
   *	verify that chain did not change) and buffer_heads hosting these
   *	numbers.
   *
   *	Function stops when it stumbles upon zero pointer (absent block)
   *		(pointer to last triple returned, *@err == 0)
   *	or when it gets an IO error reading an indirect block
   *		(ditto, *@err == -EIO)
   *	or when it notices that chain had been changed while it was reading
   *		(ditto, *@err == -EAGAIN)
   *	or when it reads all @depth-1 indirect blocks successfully and finds
   *	the whole chain, all way to the data (returns %NULL, *err == 0).
   */
  static Indirect *ext3_get_branch(struct inode *inode, int depth, int *offsets,
  				 Indirect chain[4], int *err)
  {
  	struct super_block *sb = inode->i_sb;
  	Indirect *p = chain;
  	struct buffer_head *bh;
  
  	*err = 0;
  	/* i_data is not going away, no lock needed */
  	add_chain (chain, NULL, EXT3_I(inode)->i_data + *offsets);
  	if (!p->key)
  		goto no_block;
  	while (--depth) {
  		bh = sb_bread(sb, le32_to_cpu(p->key));
  		if (!bh)
  			goto failure;
  		/* Reader: pointers */
  		if (!verify_chain(chain, p))
  			goto changed;
  		add_chain(++p, bh, (__le32*)bh->b_data + *++offsets);
  		/* Reader: end */
  		if (!p->key)
  			goto no_block;
  	}
  	return NULL;
  
  changed:
  	brelse(bh);
  	*err = -EAGAIN;
  	goto no_block;
  failure:
  	*err = -EIO;
  no_block:
  	return p;
  }
  
  /**
   *	ext3_find_near - find a place for allocation with sufficient locality
   *	@inode: owner
   *	@ind: descriptor of indirect block.
   *

   *	This function returns the preferred place for block allocation.

   *	It is used when heuristic for sequential allocation fails.
   *	Rules are:
   *	  + if there is a block to the left of our position - allocate near it.
   *	  + if pointer will live in indirect block - allocate near that block.
   *	  + if pointer will live in inode - allocate in the same

   *	    cylinder group.

   *
   * In the latter case we colour the starting block by the callers PID to
   * prevent it from clashing with concurrent allocations for a different inode
   * in the same block group.   The PID is used here so that functionally related
   * files will be close-by on-disk.
   *
   *	Caller must make sure that @ind is valid and will stay that way.
   */

  static ext3_fsblk_t ext3_find_near(struct inode *inode, Indirect *ind)

  {
  	struct ext3_inode_info *ei = EXT3_I(inode);
  	__le32 *start = ind->bh ? (__le32*) ind->bh->b_data : ei->i_data;
  	__le32 *p;

  	ext3_fsblk_t bg_start;
  	ext3_grpblk_t colour;

  
  	/* Try to find previous block */

  	for (p = ind->p - 1; p >= start; p--) {

  		if (*p)
  			return le32_to_cpu(*p);

  	}

  
  	/* No such thing, so let's try location of indirect block */
  	if (ind->bh)
  		return ind->bh->b_blocknr;
  
  	/*

  	 * It is going to be referred to from the inode itself? OK, just put it
  	 * into the same cylinder group then.

  	 */

  	bg_start = ext3_group_first_block_no(inode->i_sb, ei->i_block_group);

  	colour = (current->pid % 16) *
  			(EXT3_BLOCKS_PER_GROUP(inode->i_sb) / 16);
  	return bg_start + colour;
  }
  
  /**

   *	ext3_find_goal - find a preferred place for allocation.

   *	@inode: owner
   *	@block:  block we want

   *	@partial: pointer to the last triple within a chain

   *

   *	Normally this function find the preferred place for block allocation,

   *	returns it.

   */

  static ext3_fsblk_t ext3_find_goal(struct inode *inode, long block,

  				   Indirect *partial)

  {

  	struct ext3_block_alloc_info *block_i;
  
  	block_i =  EXT3_I(inode)->i_block_alloc_info;

  
  	/*
  	 * try the heuristic for sequential allocation,
  	 * failing that at least try to get decent locality.
  	 */
  	if (block_i && (block == block_i->last_alloc_logical_block + 1)
  		&& (block_i->last_alloc_physical_block != 0)) {

  		return block_i->last_alloc_physical_block + 1;

  	}

  	return ext3_find_near(inode, partial);

  }

  /**

   *	ext3_blks_to_allocate - Look up the block map and count the number

   *	of direct blocks need to be allocated for the given branch.
   *

   *	@branch: chain of indirect blocks

   *	@k: number of blocks need for indirect blocks
   *	@blks: number of data blocks to be mapped.
   *	@blocks_to_boundary:  the offset in the indirect block
   *
   *	return the total number of blocks to be allocate, including the
   *	direct and indirect blocks.
   */

  static int ext3_blks_to_allocate(Indirect *branch, int k, unsigned long blks,

  		int blocks_to_boundary)
  {
  	unsigned long count = 0;
  
  	/*
  	 * Simple case, [t,d]Indirect block(s) has not allocated yet
  	 * then it's clear blocks on that path have not allocated
  	 */
  	if (k > 0) {

  		/* right now we don't handle cross boundary allocation */

  		if (blks < blocks_to_boundary + 1)
  			count += blks;
  		else
  			count += blocks_to_boundary + 1;
  		return count;
  	}
  
  	count++;
  	while (count < blks && count <= blocks_to_boundary &&
  		le32_to_cpu(*(branch[0].p + count)) == 0) {
  		count++;
  	}
  	return count;
  }
  
  /**

   *	ext3_alloc_blocks - multiple allocate blocks needed for a branch
   *	@handle: handle for this transaction
   *	@inode: owner
   *	@goal: preferred place for allocation

   *	@indirect_blks: the number of blocks need to allocate for indirect
   *			blocks

   *	@blks:	number of blocks need to allocated for direct blocks

   *	@new_blocks: on return it will store the new block numbers for
   *	the indirect blocks(if needed) and the first direct block,

   *	@err: here we store the error value
   *
   *	return the number of direct blocks allocated

   */
  static int ext3_alloc_blocks(handle_t *handle, struct inode *inode,

  			ext3_fsblk_t goal, int indirect_blks, int blks,
  			ext3_fsblk_t new_blocks[4], int *err)

  {
  	int target, i;
  	unsigned long count = 0;
  	int index = 0;

  	ext3_fsblk_t current_block = 0;

  	int ret = 0;
  
  	/*
  	 * Here we try to allocate the requested multiple blocks at once,
  	 * on a best-effort basis.
  	 * To build a branch, we should allocate blocks for
  	 * the indirect blocks(if not allocated yet), and at least
  	 * the first direct block of this branch.  That's the
  	 * minimum number of blocks need to allocate(required)
  	 */
  	target = blks + indirect_blks;
  
  	while (1) {
  		count = target;
  		/* allocating blocks for indirect blocks and direct blocks */

  		current_block = ext3_new_blocks(handle,inode,goal,&count,err);

  		if (*err)
  			goto failed_out;
  
  		target -= count;
  		/* allocate blocks for indirect blocks */
  		while (index < indirect_blks && count) {
  			new_blocks[index++] = current_block++;
  			count--;
  		}
  
  		if (count > 0)
  			break;
  	}
  
  	/* save the new block number for the first direct block */
  	new_blocks[index] = current_block;
  
  	/* total number of blocks allocated for direct blocks */
  	ret = count;
  	*err = 0;
  	return ret;
  failed_out:
  	for (i = 0; i <index; i++)
  		ext3_free_blocks(handle, inode, new_blocks[i], 1);
  	return ret;
  }

  
  /**
   *	ext3_alloc_branch - allocate and set up a chain of blocks.

   *	@handle: handle for this transaction

   *	@inode: owner

   *	@indirect_blks: number of allocated indirect blocks
   *	@blks: number of allocated direct blocks

   *	@goal: preferred place for allocation

   *	@offsets: offsets (in the blocks) to store the pointers to next.
   *	@branch: place to store the chain in.
   *

   *	This function allocates blocks, zeroes out all but the last one,

   *	links them into chain and (if we are synchronous) writes them to disk.
   *	In other words, it prepares a branch that can be spliced onto the
   *	inode. It stores the information about that chain in the branch[], in
   *	the same format as ext3_get_branch() would do. We are calling it after
   *	we had read the existing part of chain and partial points to the last
   *	triple of that (one with zero ->key). Upon the exit we have the same

   *	picture as after the successful ext3_get_block(), except that in one

   *	place chain is disconnected - *branch->p is still zero (we did not
   *	set the last link), but branch->key contains the number that should
   *	be placed into *branch->p to fill that gap.
   *
   *	If allocation fails we free all blocks we've allocated (and forget
   *	their buffer_heads) and return the error value the from failed
   *	ext3_alloc_block() (normally -ENOSPC). Otherwise we set the chain
   *	as described above and return 0.
   */

  static int ext3_alloc_branch(handle_t *handle, struct inode *inode,

  			int indirect_blks, int *blks, ext3_fsblk_t goal,

  			int *offsets, Indirect *branch)

  {
  	int blocksize = inode->i_sb->s_blocksize;

  	int i, n = 0;

  	int err = 0;

  	struct buffer_head *bh;
  	int num;

  	ext3_fsblk_t new_blocks[4];
  	ext3_fsblk_t current_block;

  	num = ext3_alloc_blocks(handle, inode, goal, indirect_blks,
  				*blks, new_blocks, &err);
  	if (err)
  		return err;

  	branch[0].key = cpu_to_le32(new_blocks[0]);
  	/*
  	 * metadata blocks and data blocks are allocated.
  	 */
  	for (n = 1; n <= indirect_blks;  n++) {
  		/*
  		 * Get buffer_head for parent block, zero it out
  		 * and set the pointer to new one, then send
  		 * parent to disk.
  		 */
  		bh = sb_getblk(inode->i_sb, new_blocks[n-1]);
  		branch[n].bh = bh;
  		lock_buffer(bh);
  		BUFFER_TRACE(bh, "call get_create_access");
  		err = ext3_journal_get_create_access(handle, bh);
  		if (err) {

  			unlock_buffer(bh);

  			brelse(bh);
  			goto failed;
  		}

  		memset(bh->b_data, 0, blocksize);
  		branch[n].p = (__le32 *) bh->b_data + offsets[n];
  		branch[n].key = cpu_to_le32(new_blocks[n]);
  		*branch[n].p = branch[n].key;
  		if ( n == indirect_blks) {
  			current_block = new_blocks[n];
  			/*
  			 * End of chain, update the last new metablock of
  			 * the chain to point to the new allocated
  			 * data blocks numbers
  			 */
  			for (i=1; i < num; i++)
  				*(branch[n].p + i) = cpu_to_le32(++current_block);

  		}

  		BUFFER_TRACE(bh, "marking uptodate");
  		set_buffer_uptodate(bh);
  		unlock_buffer(bh);

  		BUFFER_TRACE(bh, "call ext3_journal_dirty_metadata");
  		err = ext3_journal_dirty_metadata(handle, bh);
  		if (err)
  			goto failed;
  	}
  	*blks = num;
  	return err;
  failed:

  	/* Allocation failed, free what we already allocated */

  	for (i = 1; i <= n ; i++) {

  		BUFFER_TRACE(branch[i].bh, "call journal_forget");
  		ext3_journal_forget(handle, branch[i].bh);
  	}

  	for (i = 0; i <indirect_blks; i++)
  		ext3_free_blocks(handle, inode, new_blocks[i], 1);
  
  	ext3_free_blocks(handle, inode, new_blocks[i], num);

  	return err;
  }
  
  /**

   * ext3_splice_branch - splice the allocated branch onto inode.

   * @handle: handle for this transaction

   * @inode: owner
   * @block: (logical) number of block we are adding

   * @where: location of missing link
   * @num:   number of indirect blocks we are adding
   * @blks:  number of direct blocks we are adding
   *
   * This function fills the missing link and does all housekeeping needed in
   * inode (->i_blocks, etc.). In case of success we end up with the full
   * chain to new block and return 0.

   */

  static int ext3_splice_branch(handle_t *handle, struct inode *inode,
  			long block, Indirect *where, int num, int blks)

  {
  	int i;
  	int err = 0;

  	struct ext3_block_alloc_info *block_i;

  	ext3_fsblk_t current_block;

  	struct ext3_inode_info *ei = EXT3_I(inode);

  	block_i = ei->i_block_alloc_info;

  	/*
  	 * If we're splicing into a [td]indirect block (as opposed to the
  	 * inode) then we need to get write access to the [td]indirect block
  	 * before the splice.
  	 */
  	if (where->bh) {
  		BUFFER_TRACE(where->bh, "get_write_access");
  		err = ext3_journal_get_write_access(handle, where->bh);
  		if (err)
  			goto err_out;
  	}

  	/* That's it */
  
  	*where->p = where->key;

  
  	/*
  	 * Update the host buffer_head or inode to point to more just allocated
  	 * direct blocks blocks
  	 */

  	if (num == 0 && blks > 1) {

  		current_block = le32_to_cpu(where->key) + 1;

  		for (i = 1; i < blks; i++)
  			*(where->p + i ) = cpu_to_le32(current_block++);
  	}

  
  	/*
  	 * update the most recently allocated logical & physical block
  	 * in i_block_alloc_info, to assist find the proper goal block for next
  	 * allocation
  	 */
  	if (block_i) {

  		block_i->last_alloc_logical_block = block + blks - 1;

  		block_i->last_alloc_physical_block =

  				le32_to_cpu(where[num].key) + blks - 1;

  	}
  
  	/* We are done with atomic stuff, now do the rest of housekeeping */
  
  	inode->i_ctime = CURRENT_TIME_SEC;
  	ext3_mark_inode_dirty(handle, inode);

  	/* ext3_mark_inode_dirty already updated i_sync_tid */
  	atomic_set(&ei->i_datasync_tid, handle->h_transaction->t_tid);

  
  	/* had we spliced it onto indirect block? */
  	if (where->bh) {
  		/*

  		 * If we spliced it onto an indirect block, we haven't

  		 * altered the inode.  Note however that if it is being spliced
  		 * onto an indirect block at the very end of the file (the
  		 * file is growing) then we *will* alter the inode to reflect
  		 * the new i_size.  But that is not done here - it is done in
  		 * generic_commit_write->__mark_inode_dirty->ext3_dirty_inode.
  		 */
  		jbd_debug(5, "splicing indirect only
  ");
  		BUFFER_TRACE(where->bh, "call ext3_journal_dirty_metadata");
  		err = ext3_journal_dirty_metadata(handle, where->bh);

  		if (err)

  			goto err_out;
  	} else {
  		/*
  		 * OK, we spliced it into the inode itself on a direct block.
  		 * Inode was dirtied above.
  		 */
  		jbd_debug(5, "splicing direct
  ");
  	}
  	return err;

  err_out:

  	for (i = 1; i <= num; i++) {

  		BUFFER_TRACE(where[i].bh, "call journal_forget");
  		ext3_journal_forget(handle, where[i].bh);

  		ext3_free_blocks(handle,inode,le32_to_cpu(where[i-1].key),1);

  	}

  	ext3_free_blocks(handle, inode, le32_to_cpu(where[num].key), blks);

  	return err;
  }
  
  /*
   * Allocation strategy is simple: if we have to allocate something, we will
   * have to go the whole way to leaf. So let's do it before attaching anything
   * to tree, set linkage between the newborn blocks, write them if sync is
   * required, recheck the path, free and repeat if check fails, otherwise
   * set the last missing link (that will protect us from any truncate-generated
   * removals - all blocks on the path are immune now) and possibly force the
   * write on the parent block.
   * That has a nice additional property: no special recovery from the failed
   * allocations is needed - we simply release blocks and do not touch anything
   * reachable from inode.
   *

   * `handle' can be NULL if create == 0.

   *
   * The BKL may not be held on entry here.  Be sure to take it early.

   * return > 0, # of blocks mapped or allocated.
   * return = 0, if plain lookup failed.
   * return < 0, error case.

   */

  int ext3_get_blocks_handle(handle_t *handle, struct inode *inode,
  		sector_t iblock, unsigned long maxblocks,
  		struct buffer_head *bh_result,

  		int create)

  {
  	int err = -EIO;
  	int offsets[4];
  	Indirect chain[4];
  	Indirect *partial;

  	ext3_fsblk_t goal;

  	int indirect_blks;

  	int blocks_to_boundary = 0;
  	int depth;

  	struct ext3_inode_info *ei = EXT3_I(inode);

  	int count = 0;

  	ext3_fsblk_t first_block = 0;

  	trace_ext3_get_blocks_enter(inode, iblock, maxblocks, create);

  	J_ASSERT(handle != NULL || create == 0);

  	depth = ext3_block_to_path(inode,iblock,offsets,&blocks_to_boundary);

  
  	if (depth == 0)
  		goto out;

  	partial = ext3_get_branch(inode, depth, offsets, chain, &err);
  
  	/* Simplest case - block found, no allocation needed */
  	if (!partial) {

  		first_block = le32_to_cpu(chain[depth - 1].key);

  		clear_buffer_new(bh_result);

  		count++;
  		/*map more blocks*/
  		while (count < maxblocks && count <= blocks_to_boundary) {

  			ext3_fsblk_t blk;

  			if (!verify_chain(chain, chain + depth - 1)) {

  				/*
  				 * Indirect block might be removed by
  				 * truncate while we were reading it.
  				 * Handling of that case: forget what we've
  				 * got now. Flag the err as EAGAIN, so it
  				 * will reread.
  				 */
  				err = -EAGAIN;
  				count = 0;
  				break;
  			}

  			blk = le32_to_cpu(*(chain[depth-1].p + count));
  
  			if (blk == first_block + count)

  				count++;
  			else
  				break;
  		}
  		if (err != -EAGAIN)
  			goto got_it;

  	}
  
  	/* Next simple case - plain lookup or failed read of indirect block */

  	if (!create || err == -EIO)
  		goto cleanup;

  	/*
  	 * Block out ext3_truncate while we alter the tree
  	 */

  	mutex_lock(&ei->truncate_mutex);

  
  	/*
  	 * If the indirect block is missing while we are reading
  	 * the chain(ext3_get_branch() returns -EAGAIN err), or
  	 * if the chain has been changed after we grab the semaphore,
  	 * (either because another process truncated this branch, or
  	 * another get_block allocated this branch) re-grab the chain to see if
  	 * the request block has been allocated or not.
  	 *
  	 * Since we already block the truncate/other get_block
  	 * at this point, we will have the current copy of the chain when we
  	 * splice the branch into the tree.
  	 */
  	if (err == -EAGAIN || !verify_chain(chain, partial)) {

  		while (partial > chain) {

  			brelse(partial->bh);
  			partial--;
  		}

  		partial = ext3_get_branch(inode, depth, offsets, chain, &err);
  		if (!partial) {

  			count++;

  			mutex_unlock(&ei->truncate_mutex);

  			if (err)
  				goto cleanup;
  			clear_buffer_new(bh_result);
  			goto got_it;
  		}

  	}
  
  	/*

  	 * Okay, we need to do block allocation.  Lazily initialize the block
  	 * allocation info here if necessary
  	*/
  	if (S_ISREG(inode->i_mode) && (!ei->i_block_alloc_info))

  		ext3_init_block_alloc_info(inode);

  	goal = ext3_find_goal(inode, iblock, partial);

  	/* the number of blocks need to allocate for [d,t]indirect blocks */
  	indirect_blks = (chain + depth) - partial - 1;

  
  	/*

  	 * Next look up the indirect map to count the totoal number of
  	 * direct blocks to allocate for this branch.
  	 */
  	count = ext3_blks_to_allocate(partial, indirect_blks,
  					maxblocks, blocks_to_boundary);

  	err = ext3_alloc_branch(handle, inode, indirect_blks, &count, goal,

  				offsets + (partial - chain), partial);

  	/*
  	 * The ext3_splice_branch call will free and forget any buffers

  	 * on the new chain if there is a failure, but that risks using
  	 * up transaction credits, especially for bitmaps where the
  	 * credits cannot be returned.  Can we handle this somehow?  We

  	 * may need to return -EAGAIN upwards in the worst case.  --sct
  	 */

  	if (!err)

  		err = ext3_splice_branch(handle, inode, iblock,
  					partial, indirect_blks, count);

  	mutex_unlock(&ei->truncate_mutex);

  	if (err)
  		goto cleanup;
  
  	set_buffer_new(bh_result);

  got_it:
  	map_bh(bh_result, inode->i_sb, le32_to_cpu(chain[depth-1].key));

  	if (count > blocks_to_boundary)

  		set_buffer_boundary(bh_result);

  	err = count;

  	/* Clean up and exit */
  	partial = chain + depth - 1;	/* the whole chain */
  cleanup:

  	while (partial > chain) {

  		BUFFER_TRACE(partial->bh, "call brelse");

  		brelse(partial->bh);
  		partial--;
  	}

  	BUFFER_TRACE(bh_result, "returned");
  out:

  	trace_ext3_get_blocks_exit(inode, iblock,
  				   depth ? le32_to_cpu(chain[depth-1].key) : 0,
  				   count, err);

  	return err;

  }

  /* Maximum number of blocks we map for direct IO at once. */
  #define DIO_MAX_BLOCKS 4096
  /*
   * Number of credits we need for writing DIO_MAX_BLOCKS:
   * We need sb + group descriptor + bitmap + inode -> 4
   * For B blocks with A block pointers per block we need:
   * 1 (triple ind.) + (B/A/A + 2) (doubly ind.) + (B/A + 2) (indirect).
   * If we plug in 4096 for B and 256 for A (for 1KB block size), we get 25.
   */
  #define DIO_CREDITS 25

  static int ext3_get_block(struct inode *inode, sector_t iblock,
  			struct buffer_head *bh_result, int create)

  {

  	handle_t *handle = ext3_journal_current_handle();

  	int ret = 0, started = 0;

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

  	if (create && !handle) {	/* Direct IO write... */
  		if (max_blocks > DIO_MAX_BLOCKS)
  			max_blocks = DIO_MAX_BLOCKS;
  		handle = ext3_journal_start(inode, DIO_CREDITS +

  				EXT3_MAXQUOTAS_TRANS_BLOCKS(inode->i_sb));

  		if (IS_ERR(handle)) {

  			ret = PTR_ERR(handle);

  			goto out;

  		}

  		started = 1;

  	}

  	ret = ext3_get_blocks_handle(handle, inode, iblock,

  					max_blocks, bh_result, create);

  	if (ret > 0) {
  		bh_result->b_size = (ret << inode->i_blkbits);
  		ret = 0;

  	}

  	if (started)
  		ext3_journal_stop(handle);
  out:

  	return ret;
  }

  int ext3_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
  		u64 start, u64 len)
  {
  	return generic_block_fiemap(inode, fieinfo, start, len,
  				    ext3_get_block);
  }

  /*
   * `handle' can be NULL if create is zero
   */

  struct buffer_head *ext3_getblk(handle_t *handle, struct inode *inode,
  				long block, int create, int *errp)

  {
  	struct buffer_head dummy;
  	int fatal = 0, err;
  
  	J_ASSERT(handle != NULL || create == 0);
  
  	dummy.b_state = 0;
  	dummy.b_blocknr = -1000;
  	buffer_trace_init(&dummy.b_history);

  	err = ext3_get_blocks_handle(handle, inode, block, 1,

  					&dummy, create);

  	/*
  	 * ext3_get_blocks_handle() returns number of blocks
  	 * mapped. 0 in case of a HOLE.
  	 */
  	if (err > 0) {
  		if (err > 1)
  			WARN_ON(1);

  		err = 0;

  	}
  	*errp = err;
  	if (!err && buffer_mapped(&dummy)) {

  		struct buffer_head *bh;
  		bh = sb_getblk(inode->i_sb, dummy.b_blocknr);

  		if (!bh) {
  			*errp = -EIO;
  			goto err;
  		}

  		if (buffer_new(&dummy)) {
  			J_ASSERT(create != 0);

  			J_ASSERT(handle != NULL);

  			/*
  			 * Now that we do not always journal data, we should
  			 * keep in mind whether this should always journal the
  			 * new buffer as metadata.  For now, regular file
  			 * writes use ext3_get_block instead, so it's not a
  			 * problem.
  			 */

  			lock_buffer(bh);
  			BUFFER_TRACE(bh, "call get_create_access");
  			fatal = ext3_journal_get_create_access(handle, bh);
  			if (!fatal && !buffer_uptodate(bh)) {

  				memset(bh->b_data,0,inode->i_sb->s_blocksize);

  				set_buffer_uptodate(bh);
  			}
  			unlock_buffer(bh);
  			BUFFER_TRACE(bh, "call ext3_journal_dirty_metadata");
  			err = ext3_journal_dirty_metadata(handle, bh);
  			if (!fatal)
  				fatal = err;
  		} else {
  			BUFFER_TRACE(bh, "not a new buffer");
  		}
  		if (fatal) {
  			*errp = fatal;
  			brelse(bh);
  			bh = NULL;
  		}
  		return bh;
  	}

  err:

  	return NULL;
  }

  struct buffer_head *ext3_bread(handle_t *handle, struct inode *inode,

  			       int block, int create, int *err)
  {
  	struct buffer_head * bh;
  
  	bh = ext3_getblk(handle, inode, block, create, err);
  	if (!bh)
  		return bh;

  	if (bh_uptodate_or_lock(bh))

  		return bh;

  	get_bh(bh);
  	bh->b_end_io = end_buffer_read_sync;
  	submit_bh(READ | REQ_META | REQ_PRIO, bh);

  	wait_on_buffer(bh);
  	if (buffer_uptodate(bh))
  		return bh;
  	put_bh(bh);
  	*err = -EIO;
  	return NULL;
  }
  
  static 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;
  }
  
  /*
   * To preserve ordering, it is essential that the hole instantiation and
   * the data write be encapsulated in a single transaction.  We cannot
   * close off a transaction and start a new one between the ext3_get_block()
   * and the commit_write().  So doing the journal_start at the start of
   * prepare_write() is the right place.
   *
   * Also, this function can nest inside ext3_writepage() ->
   * block_write_full_page(). In that case, we *know* that ext3_writepage()
   * has generated enough buffer credits to do the whole page.  So we won't
   * block on the journal in that case, which is good, because the caller may
   * be PF_MEMALLOC.
   *
   * By accident, ext3 can be reentered when a transaction is open via
   * quota file writes.  If we were to commit the transaction while thus
   * reentered, there can be a deadlock - we would be holding a quota
   * lock, and the commit would never complete if another thread had a
   * transaction open and was blocking on the quota lock - a ranking
   * violation.
   *
   * So what we do is to rely on the fact that journal_stop/journal_start
   * will _not_ run commit under these circumstances because handle->h_ref
   * is elevated.  We'll still have enough credits for the tiny quotafile

   * write.

   */

  static int do_journal_get_write_access(handle_t *handle,
  					struct buffer_head *bh)

  {

  	int dirty = buffer_dirty(bh);
  	int ret;

  	if (!buffer_mapped(bh) || buffer_freed(bh))
  		return 0;

  	/*
  	 * __block_prepare_write() could have dirtied some buffers. Clean
  	 * the dirty bit as jbd2_journal_get_write_access() could complain
  	 * otherwise about fs integrity issues. Setting of the dirty bit
  	 * by __block_prepare_write() isn't a real problem here as we clear
  	 * the bit before releasing a page lock and thus writeback cannot
  	 * ever write the buffer.
  	 */
  	if (dirty)
  		clear_buffer_dirty(bh);
  	ret = ext3_journal_get_write_access(handle, bh);
  	if (!ret && dirty)
  		ret = ext3_journal_dirty_metadata(handle, bh);
  	return ret;

  }

  /*
   * Truncate blocks that were not used by write. We have to truncate the
   * pagecache as well so that corresponding buffers get properly unmapped.
   */
  static void ext3_truncate_failed_write(struct inode *inode)
  {
  	truncate_inode_pages(inode->i_mapping, inode->i_size);
  	ext3_truncate(inode);
  }

  /*
   * Truncate blocks that were not used by direct IO write. We have to zero out
   * the last file block as well because direct IO might have written to it.
   */
  static void ext3_truncate_failed_direct_write(struct inode *inode)
  {
  	ext3_block_truncate_page(inode, inode->i_size);
  	ext3_truncate(inode);
  }

  static int ext3_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;

  	int ret;

  	handle_t *handle;
  	int retries = 0;

  	struct page *page;
  	pgoff_t index;
  	unsigned from, to;

  	/* Reserve one block more for addition to orphan list in case
  	 * we allocate blocks but write fails for some reason */
  	int needed_blocks = ext3_writepage_trans_blocks(inode) + 1;

  	trace_ext3_write_begin(inode, pos, len, flags);

  	index = pos >> PAGE_CACHE_SHIFT;
  	from = pos & (PAGE_CACHE_SIZE - 1);
  	to = from + len;

  
  retry:

  	page = grab_cache_page_write_begin(mapping, index, flags);

  	if (!page)
  		return -ENOMEM;
  	*pagep = page;

  	handle = ext3_journal_start(inode, needed_blocks);

  	if (IS_ERR(handle)) {

  		unlock_page(page);
  		page_cache_release(page);

  		ret = PTR_ERR(handle);
  		goto out;
  	}

  	ret = __block_write_begin(page, pos, len, ext3_get_block);

  	if (ret)

  		goto write_begin_failed;

  
  	if (ext3_should_journal_data(inode)) {
  		ret = walk_page_buffers(handle, page_buffers(page),
  				from, to, NULL, do_journal_get_write_access);
  	}

  write_begin_failed:
  	if (ret) {

  		/*
  		 * block_write_begin may have instantiated a few blocks
  		 * outside i_size.  Trim these off again. Don't need
  		 * i_size_read because we hold i_mutex.

  		 *
  		 * Add inode to orphan list in case we crash before truncate

  		 * finishes. Do this only if ext3_can_truncate() agrees so
  		 * that orphan processing code is happy.

  		 */

  		if (pos + len > inode->i_size && ext3_can_truncate(inode))

  			ext3_orphan_add(handle, inode);
  		ext3_journal_stop(handle);
  		unlock_page(page);
  		page_cache_release(page);
  		if (pos + len > inode->i_size)

  			ext3_truncate_failed_write(inode);

  	}

  	if (ret == -ENOSPC && ext3_should_retry_alloc(inode->i_sb, &retries))
  		goto retry;

  out:

  	return ret;
  }

  int ext3_journal_dirty_data(handle_t *handle, struct buffer_head *bh)

  {
  	int err = journal_dirty_data(handle, bh);
  	if (err)

  		ext3_journal_abort_handle(__func__, __func__,

  						bh, handle, err);

  	return err;
  }

  /* For ordered writepage and write_end functions */
  static int journal_dirty_data_fn(handle_t *handle, struct buffer_head *bh)
  {
  	/*
  	 * Write could have mapped the buffer but it didn't copy the data in
  	 * yet. So avoid filing such buffer into a transaction.
  	 */
  	if (buffer_mapped(bh) && buffer_uptodate(bh))
  		return ext3_journal_dirty_data(handle, bh);
  	return 0;
  }

  /* For write_end() in data=journal mode */
  static int write_end_fn(handle_t *handle, struct buffer_head *bh)

  {
  	if (!buffer_mapped(bh) || buffer_freed(bh))
  		return 0;
  	set_buffer_uptodate(bh);
  	return ext3_journal_dirty_metadata(handle, bh);
  }
  
  /*

   * This is nasty and subtle: ext3_write_begin() could have allocated blocks
   * for the whole page but later we failed to copy the data in. Update inode
   * size according to what we managed to copy. The rest is going to be
   * truncated in write_end function.

   */

  static void update_file_sizes(struct inode *inode, loff_t pos, unsigned copied)

  {

  	/* What matters to us is i_disksize. We don't write i_size anywhere */
  	if (pos + copied > inode->i_size)
  		i_size_write(inode, pos + copied);
  	if (pos + copied > EXT3_I(inode)->i_disksize) {
  		EXT3_I(inode)->i_disksize = pos + copied;

  		mark_inode_dirty(inode);
  	}

  }
  
  /*

   * We need to pick up the new inode size which generic_commit_write gave us
   * `file' can be NULL - eg, when called from page_symlink().
   *
   * ext3 never places buffers on inode->i_mapping->private_list.  metadata
   * buffers are managed internally.
   */

  static int ext3_ordered_write_end(struct file *file,
  				struct address_space *mapping,
  				loff_t pos, unsigned len, unsigned copied,
  				struct page *page, void *fsdata)

  {
  	handle_t *handle = ext3_journal_current_handle();

  	struct inode *inode = file->f_mapping->host;
  	unsigned from, to;

  	int ret = 0, ret2;

  	trace_ext3_ordered_write_end(inode, pos, len, copied);

  	copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);

  	from = pos & (PAGE_CACHE_SIZE - 1);
  	to = from + copied;

  	ret = walk_page_buffers(handle, page_buffers(page),

  		from, to, NULL, journal_dirty_data_fn);

  	if (ret == 0)
  		update_file_sizes(inode, pos, copied);
  	/*
  	 * There may be allocated blocks outside of i_size because
  	 * we failed to copy some data. Prepare for truncate.
  	 */

  	if (pos + len > inode->i_size && ext3_can_truncate(inode))

  		ext3_orphan_add(handle, inode);

  	ret2 = ext3_journal_stop(handle);
  	if (!ret)
  		ret = ret2;

  	unlock_page(page);
  	page_cache_release(page);

  	if (pos + len > inode->i_size)

  		ext3_truncate_failed_write(inode);

  	return ret ? ret : copied;

  }

  static int ext3_writeback_write_end(struct file *file,
  				struct address_space *mapping,
  				loff_t pos, unsigned len, unsigned copied,
  				struct page *page, void *fsdata)

  {
  	handle_t *handle = ext3_journal_current_handle();

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

  	int ret;

  	trace_ext3_writeback_write_end(inode, pos, len, copied);

  	copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
  	update_file_sizes(inode, pos, copied);
  	/*
  	 * There may be allocated blocks outside of i_size because
  	 * we failed to copy some data. Prepare for truncate.
  	 */

  	if (pos + len > inode->i_size && ext3_can_truncate(inode))

  		ext3_orphan_add(handle, inode);
  	ret = ext3_journal_stop(handle);

  	unlock_page(page);
  	page_cache_release(page);

  	if (pos + len > inode->i_size)

  		ext3_truncate_failed_write(inode);

  	return ret ? ret : copied;

  }

  static int ext3_journalled_write_end(struct file *file,
  				struct address_space *mapping,
  				loff_t pos, unsigned len, unsigned copied,
  				struct page *page, void *fsdata)

  {
  	handle_t *handle = ext3_journal_current_handle();

  	struct inode *inode = mapping->host;

  	struct ext3_inode_info *ei = EXT3_I(inode);

  	int ret = 0, ret2;
  	int partial = 0;

  	unsigned from, to;

  	trace_ext3_journalled_write_end(inode, pos, len, copied);

  	from = pos & (PAGE_CACHE_SIZE - 1);
  	to = from + len;
  
  	if (copied < len) {
  		if (!PageUptodate(page))
  			copied = 0;

  		page_zero_new_buffers(page, from + copied, to);
  		to = from + copied;

  	}

  
  	ret = walk_page_buffers(handle, page_buffers(page), from,

  				to, &partial, write_end_fn);

  	if (!partial)
  		SetPageUptodate(page);

  
  	if (pos + copied > inode->i_size)
  		i_size_write(inode, pos + copied);
  	/*
  	 * There may be allocated blocks outside of i_size because
  	 * we failed to copy some data. Prepare for truncate.
  	 */

  	if (pos + len > inode->i_size && ext3_can_truncate(inode))

  		ext3_orphan_add(handle, inode);

  	ext3_set_inode_state(inode, EXT3_STATE_JDATA);

  	atomic_set(&ei->i_datasync_tid, handle->h_transaction->t_tid);
  	if (inode->i_size > ei->i_disksize) {
  		ei->i_disksize = inode->i_size;

  		ret2 = ext3_mark_inode_dirty(handle, inode);

  		if (!ret)

  			ret = ret2;
  	}

  	ret2 = ext3_journal_stop(handle);
  	if (!ret)
  		ret = ret2;

  	unlock_page(page);
  	page_cache_release(page);

  	if (pos + len > inode->i_size)

  		ext3_truncate_failed_write(inode);

  	return ret ? ret : copied;

  }

  /*

   * bmap() is special.  It gets used by applications such as lilo and by
   * the swapper to find the on-disk block of a specific piece of data.
   *
   * Naturally, this is dangerous if the block concerned is still in the
   * journal.  If somebody makes a swapfile on an ext3 data-journaling
   * filesystem and enables swap, then they may get a nasty shock when the
   * data getting swapped to that swapfile suddenly gets overwritten by
   * the original zero's written out previously to the journal and

   * awaiting writeback in the kernel's buffer cache.

   *
   * So, if we see any bmap calls here on a modified, data-journaled file,

   * take extra steps to flush any blocks which might be in the cache.

   */
  static sector_t ext3_bmap(struct address_space *mapping, sector_t block)
  {
  	struct inode *inode = mapping->host;
  	journal_t *journal;
  	int err;

  	if (ext3_test_inode_state(inode, EXT3_STATE_JDATA)) {

  		/*

  		 * This is a REALLY heavyweight approach, but the use of
  		 * bmap on dirty files is expected to be extremely rare:
  		 * only if we run lilo or swapon on a freshly made file

  		 * do we expect this to happen.

  		 *
  		 * (bmap requires CAP_SYS_RAWIO so this does not
  		 * represent an unprivileged user DOS attack --- we'd be
  		 * in trouble if mortal users could trigger this path at

  		 * will.)

  		 *
  		 * NB. EXT3_STATE_JDATA is not set on files other than
  		 * regular files.  If somebody wants to bmap a directory
  		 * or symlink and gets confused because the buffer
  		 * hasn't yet been flushed to disk, they deserve
  		 * everything they get.
  		 */

  		ext3_clear_inode_state(inode, EXT3_STATE_JDATA);

  		journal = EXT3_JOURNAL(inode);
  		journal_lock_updates(journal);
  		err = journal_flush(journal);
  		journal_unlock_updates(journal);
  
  		if (err)
  			return 0;
  	}
  
  	return generic_block_bmap(mapping,block,ext3_get_block);
  }
  
  static int bget_one(handle_t *handle, struct buffer_head *bh)
  {
  	get_bh(bh);
  	return 0;
  }
  
  static int bput_one(handle_t *handle, struct buffer_head *bh)
  {
  	put_bh(bh);
  	return 0;
  }

  static int buffer_unmapped(handle_t *handle, struct buffer_head *bh)
  {
  	return !buffer_mapped(bh);
  }

  /*
   * Note that we always start a transaction even if we're not journalling
   * data.  This is to preserve ordering: any hole instantiation within
   * __block_write_full_page -> ext3_get_block() should be journalled
   * along with the data so we don't crash and then get metadata which
   * refers to old data.
   *
   * In all journalling modes block_write_full_page() will start the I/O.
   *
   * Problem:
   *
   *	ext3_writepage() -> kmalloc() -> __alloc_pages() -> page_launder() ->
   *		ext3_writepage()
   *
   * Similar for:
   *
   *	ext3_file_write() -> generic_file_write() -> __alloc_pages() -> ...
   *
   * Same applies to ext3_get_block().  We will deadlock on various things like

   * lock_journal and i_truncate_mutex.

   *
   * Setting PF_MEMALLOC here doesn't work - too many internal memory
   * allocations fail.
   *
   * 16May01: If we're reentered then journal_current_handle() will be
   *	    non-zero. We simply *return*.
   *
   * 1 July 2001: @@@ FIXME:
   *   In journalled data mode, a data buffer may be metadata against the
   *   current transaction.  But the same file is part of a shared mapping
   *   and someone does a writepage() on it.
   *
   *   We will move the buffer onto the async_data list, but *after* it has
   *   been dirtied. So there's a small window where we have dirty data on
   *   BJ_Metadata.
   *
   *   Note that this only applies to the last partial page in the file.  The
   *   bit which block_write_full_page() uses prepare/commit for.  (That's
   *   broken code anyway: it's wrong for msync()).
   *
   *   It's a rare case: affects the final partial page, for journalled data
   *   where the file is subject to bith write() and writepage() in the same
   *   transction.  To fix it we'll need a custom block_write_full_page().
   *   We'll probably need that anyway for journalling writepage() output.
   *
   * We don't honour synchronous mounts for writepage().  That would be
   * disastrous.  Any write() or metadata operation will sync the fs for
   * us.
   *
   * AKPM2: if all the page's buffers are mapped to disk and !data=journal,
   * we don't need to open a transaction here.
   */
  static int ext3_ordered_writepage(struct page *page,

  				struct writeback_control *wbc)

  {
  	struct inode *inode = page->mapping->host;
  	struct buffer_head *page_bufs;
  	handle_t *handle = NULL;
  	int ret = 0;
  	int err;
  
  	J_ASSERT(PageLocked(page));

  	/*
  	 * We don't want to warn for emergency remount. The condition is
  	 * ordered to avoid dereferencing inode->i_sb in non-error case to
  	 * avoid slow-downs.
  	 */
  	WARN_ON_ONCE(IS_RDONLY(inode) &&
  		     !(EXT3_SB(inode->i_sb)->s_mount_state & EXT3_ERROR_FS));

  
  	/*
  	 * We give up here if we're reentered, because it might be for a
  	 * different filesystem.
  	 */
  	if (ext3_journal_current_handle())
  		goto out_fail;

  	trace_ext3_ordered_writepage(page);

  	if (!page_has_buffers(page)) {
  		create_empty_buffers(page, inode->i_sb->s_blocksize,
  				(1 << BH_Dirty)|(1 << BH_Uptodate));

  		page_bufs = page_buffers(page);
  	} else {
  		page_bufs = page_buffers(page);
  		if (!walk_page_buffers(NULL, page_bufs, 0, PAGE_CACHE_SIZE,
  				       NULL, buffer_unmapped)) {
  			/* Provide NULL get_block() to catch bugs if buffers
  			 * weren't really mapped */
  			return block_write_full_page(page, NULL, wbc);
  		}

  	}

  	handle = ext3_journal_start(inode, ext3_writepage_trans_blocks(inode));
  
  	if (IS_ERR(handle)) {
  		ret = PTR_ERR(handle);
  		goto out_fail;
  	}

  	walk_page_buffers(handle, page_bufs, 0,
  			PAGE_CACHE_SIZE, NULL, bget_one);
  
  	ret = block_write_full_page(page, ext3_get_block, wbc);
  
  	/*
  	 * The page can become unlocked at any point now, and
  	 * truncate can then come in and change things.  So we
  	 * can't touch *page from now on.  But *page_bufs is
  	 * safe due to elevated refcount.
  	 */
  
  	/*

  	 * And attach them to the current transaction.  But only if

  	 * block_write_full_page() succeeded.  Otherwise they are unmapped,
  	 * and generally junk.
  	 */
  	if (ret == 0) {
  		err = walk_page_buffers(handle, page_bufs, 0, PAGE_CACHE_SIZE,
  					NULL, journal_dirty_data_fn);
  		if (!ret)
  			ret = err;
  	}
  	walk_page_buffers(handle, page_bufs, 0,
  			PAGE_CACHE_SIZE, NULL, bput_one);
  	err = ext3_journal_stop(handle);
  	if (!ret)
  		ret = err;
  	return ret;
  
  out_fail:
  	redirty_page_for_writepage(wbc, page);
  	unlock_page(page);
  	return ret;
  }

  static int ext3_writeback_writepage(struct page *page,
  				struct writeback_control *wbc)
  {
  	struct inode *inode = page->mapping->host;
  	handle_t *handle = NULL;
  	int ret = 0;
  	int err;

  	J_ASSERT(PageLocked(page));

  	/*
  	 * We don't want to warn for emergency remount. The condition is
  	 * ordered to avoid dereferencing inode->i_sb in non-error case to
  	 * avoid slow-downs.
  	 */
  	WARN_ON_ONCE(IS_RDONLY(inode) &&
  		     !(EXT3_SB(inode->i_sb)->s_mount_state & EXT3_ERROR_FS));

  	if (ext3_journal_current_handle())
  		goto out_fail;

  	trace_ext3_writeback_writepage(page);

  	if (page_has_buffers(page)) {
  		if (!walk_page_buffers(NULL, page_buffers(page), 0,
  				      PAGE_CACHE_SIZE, NULL, buffer_unmapped)) {
  			/* Provide NULL get_block() to catch bugs if buffers
  			 * weren't really mapped */
  			return block_write_full_page(page, NULL, wbc);
  		}
  	}

  	handle = ext3_journal_start(inode, ext3_writepage_trans_blocks(inode));
  	if (IS_ERR(handle)) {
  		ret = PTR_ERR(handle);
  		goto out_fail;
  	}

  	ret = block_write_full_page(page, ext3_get_block, wbc);

  
  	err = ext3_journal_stop(handle);
  	if (!ret)
  		ret = err;
  	return ret;
  
  out_fail:
  	redirty_page_for_writepage(wbc, page);
  	unlock_page(page);
  	return ret;
  }
  
  static int ext3_journalled_writepage(struct page *page,
  				struct writeback_control *wbc)
  {
  	struct inode *inode = page->mapping->host;
  	handle_t *handle = NULL;
  	int ret = 0;
  	int err;

  	J_ASSERT(PageLocked(page));

  	/*
  	 * We don't want to warn for emergency remount. The condition is
  	 * ordered to avoid dereferencing inode->i_sb in non-error case to
  	 * avoid slow-downs.
  	 */
  	WARN_ON_ONCE(IS_RDONLY(inode) &&
  		     !(EXT3_SB(inode->i_sb)->s_mount_state & EXT3_ERROR_FS));

  	if (ext3_journal_current_handle())
  		goto no_write;

  	trace_ext3_journalled_writepage(page);

  	handle = ext3_journal_start(inode, ext3_writepage_trans_blocks(inode));
  	if (IS_ERR(handle)) {
  		ret = PTR_ERR(handle);
  		goto no_write;
  	}
  
  	if (!page_has_buffers(page) || PageChecked(page)) {
  		/*
  		 * It's mmapped pagecache.  Add buffers and journal it.  There
  		 * doesn't seem much point in redirtying the page here.
  		 */
  		ClearPageChecked(page);

  		ret = __block_write_begin(page, 0, PAGE_CACHE_SIZE,
  					  ext3_get_block);

  		if (ret != 0) {
  			ext3_journal_stop(handle);

  			goto out_unlock;

  		}

  		ret = walk_page_buffers(handle, page_buffers(page), 0,
  			PAGE_CACHE_SIZE, NULL, do_journal_get_write_access);
  
  		err = walk_page_buffers(handle, page_buffers(page), 0,

  				PAGE_CACHE_SIZE, NULL, write_end_fn);

  		if (ret == 0)
  			ret = err;

  		ext3_set_inode_state(inode, EXT3_STATE_JDATA);

  		atomic_set(&EXT3_I(inode)->i_datasync_tid,
  			   handle->h_transaction->t_tid);

  		unlock_page(page);
  	} else {
  		/*
  		 * It may be a page full of checkpoint-mode buffers.  We don't
  		 * really know unless we go poke around in the buffer_heads.
  		 * But block_write_full_page will do the right thing.
  		 */
  		ret = block_write_full_page(page, ext3_get_block, wbc);
  	}
  	err = ext3_journal_stop(handle);
  	if (!ret)
  		ret = err;
  out:
  	return ret;
  
  no_write:
  	redirty_page_for_writepage(wbc, page);
  out_unlock:
  	unlock_page(page);
  	goto out;
  }
  
  static int ext3_readpage(struct file *file, struct page *page)
  {

  	trace_ext3_readpage(page);

  	return mpage_readpage(page, ext3_get_block);
  }
  
  static int
  ext3_readpages(struct file *file, struct address_space *mapping,
  		struct list_head *pages, unsigned nr_pages)
  {
  	return mpage_readpages(mapping, pages, nr_pages, ext3_get_block);
  }

  static void ext3_invalidatepage(struct page *page, unsigned long offset)

  {
  	journal_t *journal = EXT3_JOURNAL(page->mapping->host);

  	trace_ext3_invalidatepage(page, offset);

  	/*
  	 * If it's a full truncate we just forget about the pending dirtying
  	 */
  	if (offset == 0)
  		ClearPageChecked(page);

  	journal_invalidatepage(journal, page, offset);

  }

  static int ext3_releasepage(struct page *page, gfp_t wait)

  {
  	journal_t *journal = EXT3_JOURNAL(page->mapping->host);

  	trace_ext3_releasepage(page);

  	WARN_ON(PageChecked(page));
  	if (!page_has_buffers(page))
  		return 0;
  	return journal_try_to_free_buffers(journal, page, wait);
  }
  
  /*
   * If the O_DIRECT write will extend the file then add this inode to the
   * orphan list.  So recovery will truncate it back to the original size
   * if the machine crashes during the write.
   *
   * If the O_DIRECT write is intantiating holes inside i_size and the machine

   * crashes then stale disk data _may_ be exposed inside the file. But current
   * VFS code falls back into buffered path in that case so we are safe.

   */
  static ssize_t ext3_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_mapping->host;
  	struct ext3_inode_info *ei = EXT3_I(inode);

  	handle_t *handle;

  	ssize_t ret;
  	int orphan = 0;
  	size_t count = iov_length(iov, nr_segs);

  	int retries = 0;

  	trace_ext3_direct_IO_enter(inode, offset, iov_length(iov, nr_segs), rw);

  	if (rw == WRITE) {
  		loff_t final_size = offset + count;

  		if (final_size > inode->i_size) {

  			/* Credits for sb + inode write */
  			handle = ext3_journal_start(inode, 2);
  			if (IS_ERR(handle)) {
  				ret = PTR_ERR(handle);
  				goto out;
  			}

  			ret = ext3_orphan_add(handle, inode);

  			if (ret) {
  				ext3_journal_stop(handle);
  				goto out;
  			}

  			orphan = 1;
  			ei->i_disksize = inode->i_size;

  			ext3_journal_stop(handle);

  		}
  	}

  retry:

  	ret = blockdev_direct_IO(rw, iocb, inode, iov, offset, nr_segs,
  				 ext3_get_block);

  	/*
  	 * In case of error extending write may have instantiated a few
  	 * blocks outside i_size. Trim these off again.
  	 */
  	if (unlikely((rw & WRITE) && ret < 0)) {
  		loff_t isize = i_size_read(inode);
  		loff_t end = offset + iov_length(iov, nr_segs);
  
  		if (end > isize)

  			ext3_truncate_failed_direct_write(inode);

  	}

  	if (ret == -ENOSPC && ext3_should_retry_alloc(inode->i_sb, &retries))
  		goto retry;

  	if (orphan) {

  		int err;

  		/* Credits for sb + inode write */
  		handle = ext3_journal_start(inode, 2);
  		if (IS_ERR(handle)) {
  			/* This is really bad luck. We've written the data

  			 * but cannot extend i_size. Truncate allocated blocks
  			 * and pretend the write failed... */

  			ext3_truncate_failed_direct_write(inode);

  			ret = PTR_ERR(handle);
  			goto out;
  		}
  		if (inode->i_nlink)

  			ext3_orphan_del(handle, inode);

  		if (ret > 0) {

  			loff_t end = offset + ret;
  			if (end > inode->i_size) {
  				ei->i_disksize = end;
  				i_size_write(inode, end);
  				/*
  				 * We're going to return a positive `ret'
  				 * here due to non-zero-length I/O, so there's
  				 * no way of reporting error returns from
  				 * ext3_mark_inode_dirty() to userspace.  So
  				 * ignore it.
  				 */
  				ext3_mark_inode_dirty(handle, inode);
  			}
  		}
  		err = ext3_journal_stop(handle);
  		if (ret == 0)
  			ret = err;
  	}
  out:

  	trace_ext3_direct_IO_exit(inode, offset,
  				iov_length(iov, nr_segs), rw, ret);

  	return ret;
  }
  
  /*
   * Pages can be marked dirty completely asynchronously from ext3's journalling
   * activity.  By filemap_sync_pte(), try_to_unmap_one(), etc.  We cannot do
   * much here because ->set_page_dirty is called under VFS locks.  The page is
   * not necessarily locked.
   *
   * We cannot just dirty the page and leave attached buffers clean, because the
   * buffers' dirty state is "definitive".  We cannot just set the buffers dirty
   * or jbddirty because all the journalling code will explode.
   *
   * So what we do is to mark the page "pending dirty" and next time writepage
   * is called, propagate that into the buffers appropriately.
   */
  static int ext3_journalled_set_page_dirty(struct page *page)
  {
  	SetPageChecked(page);
  	return __set_page_dirty_nobuffers(page);
  }

  static const struct address_space_operations ext3_ordered_aops = {

  	.readpage		= ext3_readpage,
  	.readpages		= ext3_readpages,
  	.writepage		= ext3_ordered_writepage,

  	.write_begin		= ext3_write_begin,
  	.write_end		= ext3_ordered_write_end,
  	.bmap			= ext3_bmap,
  	.invalidatepage		= ext3_invalidatepage,
  	.releasepage		= ext3_releasepage,
  	.direct_IO		= ext3_direct_IO,
  	.migratepage		= buffer_migrate_page,
  	.is_partially_uptodate  = block_is_partially_uptodate,

  	.error_remove_page	= generic_error_remove_page,

  };

  static const struct address_space_operations ext3_writeback_aops = {

  	.readpage		= ext3_readpage,
  	.readpages		= ext3_readpages,
  	.writepage		= ext3_writeback_writepage,

  	.write_begin		= ext3_write_begin,
  	.write_end		= ext3_writeback_write_end,
  	.bmap			= ext3_bmap,
  	.invalidatepage		= ext3_invalidatepage,
  	.releasepage		= ext3_releasepage,
  	.direct_IO		= ext3_direct_IO,
  	.migratepage		= buffer_migrate_page,
  	.is_partially_uptodate  = block_is_partially_uptodate,

  	.error_remove_page	= generic_error_remove_page,

  };

  static const struct address_space_operations ext3_journalled_aops = {

  	.readpage		= ext3_readpage,
  	.readpages		= ext3_readpages,
  	.writepage		= ext3_journalled_writepage,

  	.write_begin		= ext3_write_begin,
  	.write_end		= ext3_journalled_write_end,
  	.set_page_dirty		= ext3_journalled_set_page_dirty,
  	.bmap			= ext3_bmap,
  	.invalidatepage		= ext3_invalidatepage,
  	.releasepage		= ext3_releasepage,
  	.is_partially_uptodate  = block_is_partially_uptodate,

  	.error_remove_page	= generic_error_remove_page,

  };
  
  void ext3_set_aops(struct inode *inode)
  {
  	if (ext3_should_order_data(inode))
  		inode->i_mapping->a_ops = &ext3_ordered_aops;
  	else if (ext3_should_writeback_data(inode))
  		inode->i_mapping->a_ops = &ext3_writeback_aops;
  	else
  		inode->i_mapping->a_ops = &ext3_journalled_aops;
  }
  
  /*
   * ext3_block_truncate_page() zeroes out a mapping from file offset `from'
   * up to the end of the block which corresponds to `from'.
   * This required during truncate. We need to physically zero the tail end
   * of that block so it doesn't yield old data if the file is later grown.
   */

  static int ext3_block_truncate_page(struct inode *inode, loff_t from)

  {

  	ext3_fsblk_t index = from >> PAGE_CACHE_SHIFT;

  	unsigned offset = from & (PAGE_CACHE_SIZE - 1);

  	unsigned blocksize, iblock, length, pos;

  	struct page *page;
  	handle_t *handle = NULL;

  	struct buffer_head *bh;
  	int err = 0;

  	/* Truncated on block boundary - nothing to do */

  	blocksize = inode->i_sb->s_blocksize;

  	if ((from & (blocksize - 1)) == 0)
  		return 0;
  
  	page = grab_cache_page(inode->i_mapping, index);
  	if (!page)
  		return -ENOMEM;

  	length = blocksize - (offset & (blocksize - 1));
  	iblock = index << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);

  	if (!page_has_buffers(page))
  		create_empty_buffers(page, blocksize, 0);
  
  	/* Find the buffer that contains "offset" */
  	bh = page_buffers(page);
  	pos = blocksize;
  	while (offset >= pos) {
  		bh = bh->b_this_page;
  		iblock++;
  		pos += blocksize;
  	}
  
  	err = 0;
  	if (buffer_freed(bh)) {
  		BUFFER_TRACE(bh, "freed: skip");
  		goto unlock;
  	}
  
  	if (!buffer_mapped(bh)) {
  		BUFFER_TRACE(bh, "unmapped");
  		ext3_get_block(inode, iblock, bh, 0);
  		/* unmapped? It's a hole - nothing to do */
  		if (!buffer_mapped(bh)) {
  			BUFFER_TRACE(bh, "still unmapped");
  			goto unlock;
  		}
  	}
  
  	/* Ok, it's mapped. Make sure it's up-to-date */
  	if (PageUptodate(page))
  		set_buffer_uptodate(bh);

  	if (!bh_uptodate_or_lock(bh)) {
  		err = bh_submit_read(bh);

  		/* Uhhuh. Read error. Complain and punt. */

  		if (err)

  			goto unlock;
  	}

  	/* data=writeback mode doesn't need transaction to zero-out data */
  	if (!ext3_should_writeback_data(inode)) {
  		/* We journal at most one block */
  		handle = ext3_journal_start(inode, 1);
  		if (IS_ERR(handle)) {
  			clear_highpage(page);
  			flush_dcache_page(page);
  			err = PTR_ERR(handle);
  			goto unlock;
  		}
  	}

  	if (ext3_should_journal_data(inode)) {
  		BUFFER_TRACE(bh, "get write access");
  		err = ext3_journal_get_write_access(handle, bh);
  		if (err)

  			goto stop;

  	}

  	zero_user(page, offset, length);

  	BUFFER_TRACE(bh, "zeroed end of block");
  
  	err = 0;
  	if (ext3_should_journal_data(inode)) {
  		err = ext3_journal_dirty_metadata(handle, bh);
  	} else {
  		if (ext3_should_order_data(inode))
  			err = ext3_journal_dirty_data(handle, bh);
  		mark_buffer_dirty(bh);
  	}

  stop:
  	if (handle)
  		ext3_journal_stop(handle);

  
  unlock:
  	unlock_page(page);
  	page_cache_release(page);
  	return err;
  }
  
  /*
   * Probably it should be a library function... search for first non-zero word
   * or memcmp with zero_page, whatever is better for particular architecture.
   * Linus?
   */
  static inline int all_zeroes(__le32 *p, __le32 *q)
  {
  	while (p < q)
  		if (*p++)
  			return 0;
  	return 1;
  }
  
  /**
   *	ext3_find_shared - find the indirect blocks for partial truncation.
   *	@inode:	  inode in question
   *	@depth:	  depth of the affected branch
   *	@offsets: offsets of pointers in that branch (see ext3_block_to_path)
   *	@chain:	  place to store the pointers to partial indirect blocks
   *	@top:	  place to the (detached) top of branch
   *
   *	This is a helper function used by ext3_truncate().
   *
   *	When we do truncate() we may have to clean the ends of several
   *	indirect blocks but leave the blocks themselves alive. Block is

   *	partially truncated if some data below the new i_size is referred

   *	from it (and it is on the path to the first completely truncated
   *	data block, indeed).  We have to free the top of that path along
   *	with everything to the right of the path. Since no allocation
   *	past the truncation point is possible until ext3_truncate()
   *	finishes, we may safely do the latter, but top of branch may
   *	require special attention - pageout below the truncation point
   *	might try to populate it.
   *
   *	We atomically detach the top of branch from the tree, store the
   *	block number of its root in *@top, pointers to buffer_heads of
   *	partially truncated blocks - in @chain[].bh and pointers to
   *	their last elements that should not be removed - in
   *	@chain[].p. Return value is the pointer to last filled element
   *	of @chain.
   *
   *	The work left to caller to do the actual freeing of subtrees:
   *		a) free the subtree starting from *@top
   *		b) free the subtrees whose roots are stored in
   *			(@chain[i].p+1 .. end of @chain[i].bh->b_data)
   *		c) free the subtrees growing from the inode past the @chain[0].
   *			(no partially truncated stuff there).  */

  static Indirect *ext3_find_shared(struct inode *inode, int depth,
  			int offsets[4], Indirect chain[4], __le32 *top)

  {
  	Indirect *partial, *p;
  	int k, err;
  
  	*top = 0;

  	/* Make k index the deepest non-null offset + 1 */

  	for (k = depth; k > 1 && !offsets[k-1]; k--)
  		;
  	partial = ext3_get_branch(inode, k, offsets, chain, &err);
  	/* Writer: pointers */
  	if (!partial)
  		partial = chain + k-1;
  	/*
  	 * If the branch acquired continuation since we've looked at it -
  	 * fine, it should all survive and (new) top doesn't belong to us.
  	 */
  	if (!partial->key && *partial->p)
  		/* Writer: end */
  		goto no_top;
  	for (p=partial; p>chain && all_zeroes((__le32*)p->bh->b_data,p->p); p--)
  		;
  	/*
  	 * OK, we've found the last block that must survive. The rest of our
  	 * branch should be detached before unlocking. However, if that rest
  	 * of branch is all ours and does not grow immediately from the inode
  	 * it's easier to cheat and just decrement partial->p.
  	 */
  	if (p == chain + k - 1 && p > chain) {
  		p->p--;
  	} else {
  		*top = *p->p;
  		/* Nope, don't do this in ext3.  Must leave the tree intact */
  #if 0
  		*p->p = 0;
  #endif
  	}
  	/* Writer: end */

  	while(partial > p) {

  		brelse(partial->bh);
  		partial--;
  	}
  no_top:
  	return partial;
  }
  
  /*
   * Zero a number of block pointers in either an inode or an indirect block.
   * If we restart the transaction we must again get write access to the
   * indirect block for further modification.
   *
   * We release `count' blocks on disk, but (last - first) may be greater
   * than `count' because there can be holes in there.
   */

  static void ext3_clear_blocks(handle_t *handle, struct inode *inode,

  		struct buffer_head *bh, ext3_fsblk_t block_to_free,

  		unsigned long count, __le32 *first, __le32 *last)

  {
  	__le32 *p;
  	if (try_to_extend_transaction(handle, inode)) {
  		if (bh) {
  			BUFFER_TRACE(bh, "call ext3_journal_dirty_metadata");

  			if (ext3_journal_dirty_metadata(handle, bh))
  				return;

  		}
  		ext3_mark_inode_dirty(handle, inode);

  		truncate_restart_transaction(handle, inode);

  		if (bh) {
  			BUFFER_TRACE(bh, "retaking write access");

  			if (ext3_journal_get_write_access(handle, bh))
  				return;

  		}
  	}
  
  	/*
  	 * Any buffers which are on the journal will be in memory. We find
  	 * them on the hash table so journal_revoke() will run journal_forget()
  	 * on them.  We've already detached each block from the file, so
  	 * bforget() in journal_forget() should be safe.
  	 *
  	 * AKPM: turn on bforget in journal_forget()!!!
  	 */
  	for (p = first; p < last; p++) {
  		u32 nr = le32_to_cpu(*p);
  		if (nr) {
  			struct buffer_head *bh;
  
  			*p = 0;
  			bh = sb_find_get_block(inode->i_sb, nr);
  			ext3_forget(handle, 0, inode, bh, nr);
  		}
  	}
  
  	ext3_free_blocks(handle, inode, block_to_free, count);
  }
  
  /**
   * ext3_free_data - free a list of data blocks
   * @handle:	handle for this transaction
   * @inode:	inode we are dealing with
   * @this_bh:	indirect buffer_head which contains *@first and *@last
   * @first:	array of block numbers
   * @last:	points immediately past the end of array
   *

   * We are freeing all blocks referred from that array (numbers are stored as

   * little-endian 32-bit) and updating @inode->i_blocks appropriately.
   *
   * We accumulate contiguous runs of blocks to free.  Conveniently, if these
   * blocks are contiguous then releasing them at one time will only affect one
   * or two bitmap blocks (+ group descriptor(s) and superblock) and we won't
   * actually use a lot of journal space.
   *
   * @this_bh will be %NULL if @first and @last point into the inode's direct
   * block pointers.
   */
  static void ext3_free_data(handle_t *handle, struct inode *inode,
  			   struct buffer_head *this_bh,
  			   __le32 *first, __le32 *last)
  {

  	ext3_fsblk_t block_to_free = 0;    /* Starting block # of a run */

  	unsigned long count = 0;	    /* Number of blocks in the run */

  	__le32 *block_to_free_p = NULL;	    /* Pointer into inode/ind
  					       corresponding to
  					       block_to_free */

  	ext3_fsblk_t nr;		    /* Current block # */

  	__le32 *p;			    /* Pointer into inode/ind
  					       for current block */
  	int err;
  
  	if (this_bh) {				/* For indirect block */
  		BUFFER_TRACE(this_bh, "get_write_access");
  		err = ext3_journal_get_write_access(handle, this_bh);
  		/* Important: if we can't update the indirect pointers
  		 * to the blocks, we can't free them. */
  		if (err)
  			return;
  	}
  
  	for (p = first; p < last; p++) {
  		nr = le32_to_cpu(*p);
  		if (nr) {
  			/* accumulate blocks to free if they're contiguous */
  			if (count == 0) {
  				block_to_free = nr;
  				block_to_free_p = p;
  				count = 1;
  			} else if (nr == block_to_free + count) {
  				count++;
  			} else {

  				ext3_clear_blocks(handle, inode, this_bh,

  						  block_to_free,
  						  count, block_to_free_p, p);
  				block_to_free = nr;
  				block_to_free_p = p;
  				count = 1;
  			}
  		}
  	}
  
  	if (count > 0)
  		ext3_clear_blocks(handle, inode, this_bh, block_to_free,
  				  count, block_to_free_p, p);
  
  	if (this_bh) {
  		BUFFER_TRACE(this_bh, "call ext3_journal_dirty_metadata");

  
  		/*
  		 * The buffer head should have an attached journal head at this
  		 * point. However, if the data is corrupted and an indirect
  		 * block pointed to itself, it would have been detached when
  		 * the block was cleared. Check for this instead of OOPSing.
  		 */
  		if (bh2jh(this_bh))
  			ext3_journal_dirty_metadata(handle, this_bh);
  		else
  			ext3_error(inode->i_sb, "ext3_free_data",
  				   "circular indirect block detected, "
  				   "inode=%lu, block=%llu",
  				   inode->i_ino,
  				   (unsigned long long)this_bh->b_blocknr);

  	}
  }
  
  /**
   *	ext3_free_branches - free an array of branches
   *	@handle: JBD handle for this transaction
   *	@inode:	inode we are dealing with
   *	@parent_bh: the buffer_head which contains *@first and *@last
   *	@first:	array of block numbers
   *	@last:	pointer immediately past the end of array
   *	@depth:	depth of the branches to free
   *

   *	We are freeing all blocks referred from these branches (numbers are

   *	stored as little-endian 32-bit) and updating @inode->i_blocks
   *	appropriately.
   */
  static void ext3_free_branches(handle_t *handle, struct inode *inode,
  			       struct buffer_head *parent_bh,
  			       __le32 *first, __le32 *last, int depth)
  {

  	ext3_fsblk_t nr;

  	__le32 *p;
  
  	if (is_handle_aborted(handle))
  		return;
  
  	if (depth--) {
  		struct buffer_head *bh;
  		int addr_per_block = EXT3_ADDR_PER_BLOCK(inode->i_sb);
  		p = last;
  		while (--p >= first) {
  			nr = le32_to_cpu(*p);
  			if (!nr)
  				continue;		/* A hole */
  
  			/* Go read the buffer for the next level down */
  			bh = sb_bread(inode->i_sb, nr);
  
  			/*
  			 * A read failure? Report error and clear slot
  			 * (should be rare).
  			 */
  			if (!bh) {
  				ext3_error(inode->i_sb, "ext3_free_branches",

  					   "Read failure, inode=%lu, block="E3FSBLK,

  					   inode->i_ino, nr);
  				continue;
  			}
  
  			/* This zaps the entire block.  Bottom up. */
  			BUFFER_TRACE(bh, "free child branches");
  			ext3_free_branches(handle, inode, bh,
  					   (__le32*)bh->b_data,
  					   (__le32*)bh->b_data + addr_per_block,
  					   depth);
  
  			/*

  			 * Everything below this this pointer has been
  			 * released.  Now let this top-of-subtree go.
  			 *
  			 * We want the freeing of this indirect block to be
  			 * atomic in the journal with the updating of the
  			 * bitmap block which owns it.  So make some room in
  			 * the journal.
  			 *
  			 * We zero the parent pointer *after* freeing its
  			 * pointee in the bitmaps, so if extend_transaction()
  			 * for some reason fails to put the bitmap changes and
  			 * the release into the same transaction, recovery
  			 * will merely complain about releasing a free block,
  			 * rather than leaking blocks.
  			 */
  			if (is_handle_aborted(handle))
  				return;
  			if (try_to_extend_transaction(handle, inode)) {
  				ext3_mark_inode_dirty(handle, inode);

  				truncate_restart_transaction(handle, inode);

  			}

  			/*
  			 * We've probably journalled the indirect block several
  			 * times during the truncate.  But it's no longer
  			 * needed and we now drop it from the transaction via
  			 * journal_revoke().
  			 *
  			 * That's easy if it's exclusively part of this
  			 * transaction.  But if it's part of the committing
  			 * transaction then journal_forget() will simply
  			 * brelse() it.  That means that if the underlying
  			 * block is reallocated in ext3_get_block(),
  			 * unmap_underlying_metadata() will find this block
  			 * and will try to get rid of it.  damn, damn. Thus
  			 * we don't allow a block to be reallocated until
  			 * a transaction freeing it has fully committed.
  			 *
  			 * We also have to make sure journal replay after a
  			 * crash does not overwrite non-journaled data blocks
  			 * with old metadata when the block got reallocated for
  			 * data.  Thus we have to store a revoke record for a
  			 * block in the same transaction in which we free the
  			 * block.
  			 */
  			ext3_forget(handle, 1, inode, bh, bh->b_blocknr);

  			ext3_free_blocks(handle, inode, nr, 1);
  
  			if (parent_bh) {
  				/*
  				 * The block which we have just freed is
  				 * pointed to by an indirect block: journal it
  				 */
  				BUFFER_TRACE(parent_bh, "get_write_access");
  				if (!ext3_journal_get_write_access(handle,
  								   parent_bh)){
  					*p = 0;
  					BUFFER_TRACE(parent_bh,
  					"call ext3_journal_dirty_metadata");

  					ext3_journal_dirty_metadata(handle,

  								    parent_bh);
  				}
  			}
  		}
  	} else {
  		/* We have reached the bottom of the tree. */
  		BUFFER_TRACE(parent_bh, "free data blocks");
  		ext3_free_data(handle, inode, parent_bh, first, last);
  	}
  }

  int ext3_can_truncate(struct inode *inode)
  {

  	if (S_ISREG(inode->i_mode))
  		return 1;
  	if (S_ISDIR(inode->i_mode))
  		return 1;
  	if (S_ISLNK(inode->i_mode))
  		return !ext3_inode_is_fast_symlink(inode);
  	return 0;
  }

  /*
   * ext3_truncate()
   *
   * We block out ext3_get_block() block instantiations across the entire
   * transaction, and VFS/VM ensures that ext3_truncate() cannot run
   * simultaneously on behalf of the same inode.
   *

   * As we work through the truncate and commit bits of it to the journal there

   * is one core, guiding principle: the file's tree must always be consistent on
   * disk.  We must be able to restart the truncate after a crash.
   *
   * The file's tree may be transiently inconsistent in memory (although it
   * probably isn't), but whenever we close off and commit a journal transaction,
   * the contents of (the filesystem + the journal) must be consistent and
   * restartable.  It's pretty simple, really: bottom up, right to left (although
   * left-to-right works OK too).
   *
   * Note that at recovery time, journal replay occurs *before* the restart of
   * truncate against the orphan inode list.
   *
   * The committed inode has the new, desired i_size (which is the same as
   * i_disksize in this case).  After a crash, ext3_orphan_cleanup() will see
   * that this inode's truncate did not complete and it will again call
   * ext3_truncate() to have another go.  So there will be instantiated blocks
   * to the right of the truncation point in a crashed ext3 filesystem.  But
   * that's fine - as long as they are linked from the inode, the post-crash
   * ext3_truncate() run will find them and release them.
   */

  void ext3_truncate(struct inode *inode)

  {
  	handle_t *handle;
  	struct ext3_inode_info *ei = EXT3_I(inode);
  	__le32 *i_data = ei->i_data;
  	int addr_per_block = EXT3_ADDR_PER_BLOCK(inode->i_sb);

  	int offsets[4];
  	Indirect chain[4];
  	Indirect *partial;
  	__le32 nr = 0;
  	int n;
  	long last_block;
  	unsigned blocksize = inode->i_sb->s_blocksize;

  	trace_ext3_truncate_enter(inode);

  	if (!ext3_can_truncate(inode))

  		goto out_notrans;