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Amit K Arora (AKA) writes:

 AKA> +int ext4_ext_check_overlap(struct inode *inode,
 AKA> +					struct ext4_extent *newext,
 AKA> +					unsigned long *block)
 AKA> +{
 AKA> +	struct ext4_ext_path *path;
 AKA> +	unsigned int depth, b1, len1;
 AKA> +	int ret = 0;
 AKA> +
 AKA> +	b1 = le32_to_cpu(newext->ee_block);
 AKA> +	len1 = le16_to_cpu(newext->ee_len);
 AKA> +	path = ext4_ext_find_extent(inode, b1, NULL);
 AKA> +	if (IS_ERR(path)) {
 AKA> +		ret = PTR_ERR(path);
 AKA> +		goto out;
 AKA> +	}
 AKA> +	depth = ext_depth(inode);
 AKA> +	BUG_ON(path[depth].p_ext == NULL && depth != 0);
 AKA> +
 AKA> +	*block = ext4_ext_next_allocated_block(path);
 AKA> +	if (*block == EXT_MAX_BLOCK)
 AKA> +		goto out;
 AKA> +
 AKA> +	if (b1 + len1 > *block)
 AKA> +		ret = 1;
 AKA> +out:
 AKA> +	return ret;
 AKA> +}

I'm also not sure we need ext4_ext_find_extent() here.
there are two possibilities:

1) extent in found path covers block(s) before requested ones
   then ext4_ext_next_allocated_block(path) can be used

2) extent in found path covers block(s) after request ones
   then ee_block from that extent can be used.

thanks, Alex

PS. if I remember the code right .. ;)