/* Generic part */
  
  typedef struct {
  	block_t	*p;
  	block_t	key;
  	struct buffer_head *bh;
  } Indirect;
  
  static DEFINE_RWLOCK(pointers_lock);
  
  static inline void add_chain(Indirect *p, struct buffer_head *bh, block_t *v)
  {
  	p->key = *(p->p = v);
  	p->bh = bh;
  }
  
  static inline int verify_chain(Indirect *from, Indirect *to)
  {
  	while (from <= to && from->key == *from->p)
  		from++;
  	return (from > to);
  }
  
  static inline block_t *block_end(struct buffer_head *bh)
  {
  	return (block_t *)((char*)bh->b_data + bh->b_size);
  }
  
  static inline Indirect *get_branch(struct inode *inode,
  					int depth,
  					int *offsets,
  					Indirect chain[DEPTH],
  					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, i_data(inode) + *offsets);
  	if (!p->key)
  		goto no_block;
  	while (--depth) {
  		bh = sb_bread(sb, block_to_cpu(p->key));
  		if (!bh)
  			goto failure;
  		read_lock(&pointers_lock);
  		if (!verify_chain(chain, p))
  			goto changed;
  		add_chain(++p, bh, (block_t *)bh->b_data + *++offsets);
  		read_unlock(&pointers_lock);
  		if (!p->key)
  			goto no_block;
  	}
  	return NULL;
  
  changed:
  	read_unlock(&pointers_lock);
  	brelse(bh);
  	*err = -EAGAIN;
  	goto no_block;
  failure:
  	*err = -EIO;
  no_block:
  	return p;
  }
  
  static int alloc_branch(struct inode *inode,
  			     int num,
  			     int *offsets,
  			     Indirect *branch)
  {
  	int n = 0;
  	int i;
  	int parent = minix_new_block(inode);
  
  	branch[0].key = cpu_to_block(parent);
  	if (parent) for (n = 1; n < num; n++) {
  		struct buffer_head *bh;
  		/* Allocate the next block */
  		int nr = minix_new_block(inode);
  		if (!nr)
  			break;
  		branch[n].key = cpu_to_block(nr);
  		bh = sb_getblk(inode->i_sb, parent);
  		lock_buffer(bh);
  		memset(bh->b_data, 0, bh->b_size);
  		branch[n].bh = bh;
  		branch[n].p = (block_t*) bh->b_data + offsets[n];
  		*branch[n].p = branch[n].key;
  		set_buffer_uptodate(bh);
  		unlock_buffer(bh);
  		mark_buffer_dirty_inode(bh, inode);
  		parent = nr;
  	}
  	if (n == num)
  		return 0;
  
  	/* Allocation failed, free what we already allocated */
  	for (i = 1; i < n; i++)
  		bforget(branch[i].bh);
  	for (i = 0; i < n; i++)
  		minix_free_block(inode, block_to_cpu(branch[i].key));
  	return -ENOSPC;
  }
  
  static inline int splice_branch(struct inode *inode,
  				     Indirect chain[DEPTH],
  				     Indirect *where,
  				     int num)
  {
  	int i;
  
  	write_lock(&pointers_lock);
  
  	/* Verify that place we are splicing to is still there and vacant */
  	if (!verify_chain(chain, where-1) || *where->p)
  		goto changed;
  
  	*where->p = where->key;
  
  	write_unlock(&pointers_lock);
  
  	/* We are done with atomic stuff, now do the rest of housekeeping */
  
  	inode->i_ctime = CURRENT_TIME_SEC;
  
  	/* had we spliced it onto indirect block? */
  	if (where->bh)
  		mark_buffer_dirty_inode(where->bh, inode);
  
  	mark_inode_dirty(inode);
  	return 0;
  
  changed:
  	write_unlock(&pointers_lock);
  	for (i = 1; i < num; i++)
  		bforget(where[i].bh);
  	for (i = 0; i < num; i++)
  		minix_free_block(inode, block_to_cpu(where[i].key));
  	return -EAGAIN;
  }
  
  static inline int get_block(struct inode * inode, sector_t block,
  			struct buffer_head *bh, int create)
  {
  	int err = -EIO;
  	int offsets[DEPTH];
  	Indirect chain[DEPTH];
  	Indirect *partial;
  	int left;
  	int depth = block_to_path(inode, block, offsets);
  
  	if (depth == 0)
  		goto out;
  
  reread:
  	partial = get_branch(inode, depth, offsets, chain, &err);
  
  	/* Simplest case - block found, no allocation needed */
  	if (!partial) {
  got_it:
  		map_bh(bh, inode->i_sb, block_to_cpu(chain[depth-1].key));
  		/* Clean up and exit */
  		partial = chain+depth-1; /* the whole chain */
  		goto cleanup;
  	}
  
  	/* Next simple case - plain lookup or failed read of indirect block */
  	if (!create || err == -EIO) {
  cleanup:
  		while (partial > chain) {
  			brelse(partial->bh);
  			partial--;
  		}
  out:
  		return err;
  	}
  
  	/*
  	 * Indirect block might be removed by truncate while we were
  	 * reading it. Handling of that case (forget what we've got and
  	 * reread) is taken out of the main path.
  	 */
  	if (err == -EAGAIN)
  		goto changed;
  
  	left = (chain + depth) - partial;
  	err = alloc_branch(inode, left, offsets+(partial-chain), partial);
  	if (err)
  		goto cleanup;
  
  	if (splice_branch(inode, chain, partial, left) < 0)
  		goto changed;
  
  	set_buffer_new(bh);
  	goto got_it;
  
  changed:
  	while (partial > chain) {
  		brelse(partial->bh);
  		partial--;
  	}
  	goto reread;
  }
  
  static inline int all_zeroes(block_t *p, block_t *q)
  {
  	while (p < q)
  		if (*p++)
  			return 0;
  	return 1;
  }
  
  static Indirect *find_shared(struct inode *inode,
  				int depth,
  				int offsets[DEPTH],
  				Indirect chain[DEPTH],
  				block_t *top)
  {
  	Indirect *partial, *p;
  	int k, err;
  
  	*top = 0;
  	for (k = depth; k > 1 && !offsets[k-1]; k--)
  		;
  	partial = get_branch(inode, k, offsets, chain, &err);
  
  	write_lock(&pointers_lock);
  	if (!partial)
  		partial = chain + k-1;
  	if (!partial->key && *partial->p) {
  		write_unlock(&pointers_lock);
  		goto no_top;
  	}
  	for (p=partial;p>chain && all_zeroes((block_t*)p->bh->b_data,p->p);p--)
  		;
  	if (p == chain + k - 1 && p > chain) {
  		p->p--;
  	} else {
  		*top = *p->p;
  		*p->p = 0;
  	}
  	write_unlock(&pointers_lock);
  
  	while(partial > p)
  	{
  		brelse(partial->bh);
  		partial--;
  	}
  no_top:
  	return partial;
  }
  
  static inline void free_data(struct inode *inode, block_t *p, block_t *q)
  {
  	unsigned long nr;
  
  	for ( ; p < q ; p++) {
  		nr = block_to_cpu(*p);
  		if (nr) {
  			*p = 0;
  			minix_free_block(inode, nr);
  		}
  	}
  }
  
  static void free_branches(struct inode *inode, block_t *p, block_t *q, int depth)
  {
  	struct buffer_head * bh;
  	unsigned long nr;
  
  	if (depth--) {
  		for ( ; p < q ; p++) {
  			nr = block_to_cpu(*p);
  			if (!nr)
  				continue;
  			*p = 0;
  			bh = sb_bread(inode->i_sb, nr);
  			if (!bh)
  				continue;
  			free_branches(inode, (block_t*)bh->b_data,
  				      block_end(bh), depth);
  			bforget(bh);
  			minix_free_block(inode, nr);
  			mark_inode_dirty(inode);
  		}
  	} else
  		free_data(inode, p, q);
  }
  
  static inline void truncate (struct inode * inode)
  {
  	struct super_block *sb = inode->i_sb;
  	block_t *idata = i_data(inode);
  	int offsets[DEPTH];
  	Indirect chain[DEPTH];
  	Indirect *partial;
  	block_t nr = 0;
  	int n;
  	int first_whole;
  	long iblock;
  
  	iblock = (inode->i_size + sb->s_blocksize -1) >> sb->s_blocksize_bits;
  	block_truncate_page(inode->i_mapping, inode->i_size, get_block);
  
  	n = block_to_path(inode, iblock, offsets);
  	if (!n)
  		return;
  
  	if (n == 1) {
  		free_data(inode, idata+offsets[0], idata + DIRECT);
  		first_whole = 0;
  		goto do_indirects;
  	}
  
  	first_whole = offsets[0] + 1 - DIRECT;
  	partial = find_shared(inode, n, offsets, chain, &nr);
  	if (nr) {
  		if (partial == chain)
  			mark_inode_dirty(inode);
  		else
  			mark_buffer_dirty_inode(partial->bh, inode);
  		free_branches(inode, &nr, &nr+1, (chain+n-1) - partial);
  	}
  	/* Clear the ends of indirect blocks on the shared branch */
  	while (partial > chain) {
  		free_branches(inode, partial->p + 1, block_end(partial->bh),
  				(chain+n-1) - partial);
  		mark_buffer_dirty_inode(partial->bh, inode);
  		brelse (partial->bh);
  		partial--;
  	}
  do_indirects:
  	/* Kill the remaining (whole) subtrees */
  	while (first_whole < DEPTH-1) {
  		nr = idata[DIRECT+first_whole];
  		if (nr) {
  			idata[DIRECT+first_whole] = 0;
  			mark_inode_dirty(inode);
  			free_branches(inode, &nr, &nr+1, first_whole+1);
  		}
  		first_whole++;
  	}
  	inode->i_mtime = inode->i_ctime = CURRENT_TIME_SEC;
  	mark_inode_dirty(inode);
  }
  
  static inline unsigned nblocks(loff_t size, struct super_block *sb)
  {
  	int k = sb->s_blocksize_bits - 10;
  	unsigned blocks, res, direct = DIRECT, i = DEPTH;
  	blocks = (size + sb->s_blocksize - 1) >> (BLOCK_SIZE_BITS + k);
  	res = blocks;
  	while (--i && blocks > direct) {
  		blocks -= direct;
  		blocks += sb->s_blocksize/sizeof(block_t) - 1;
  		blocks /= sb->s_blocksize/sizeof(block_t);
  		res += blocks;
  		direct = 1;
  	}
  	return res;
  }