Re: [PATCH 2/3] btrfs: extended inode refs

[Jan Schmidt <list.btrfs@jan-o-sch.net>]

Hi Mark,

While reading 3/3 I stumbled across one more thing in this one:

On 05.04.2012 22:09, Mark Fasheh wrote:
> +int btrfs_find_one_extref(struct btrfs_root *root, u64 inode_objectid,
> +			  u64 start_off, struct btrfs_path *path,
> +			  struct btrfs_inode_extref **ret_ref, u64 *found_off)
> +{
> +	int ret, slot;
> +	struct btrfs_key key, found_key;
> +	struct btrfs_inode_extref *ref;
> +	struct extent_buffer *leaf;
> +	struct btrfs_item *item;
> +	unsigned long ptr;
>  
> -/*
> - * There are a few corners where the link count of the file can't
> - * be properly maintained during replay.  So, instead of adding
> - * lots of complexity to the log code, we just scan the backrefs
> - * for any file that has been through replay.
> - *
> - * The scan will update the link count on the inode to reflect the
> - * number of back refs found.  If it goes down to zero, the iput
> - * will free the inode.
> - */
> -static noinline int fixup_inode_link_count(struct btrfs_trans_handle *trans,
> -					   struct btrfs_root *root,
> -					   struct inode *inode)
> +	key.objectid = inode_objectid;
> +	btrfs_set_key_type(&key, BTRFS_INODE_EXTREF_KEY);
> +	key.offset = start_off;
> +
> +	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
> +	if (ret < 0)
> +		goto out;
> +
> +	while (1) {
> +		leaf = path->nodes[0];
> +		slot = path->slots[0];
> +		if (slot >= btrfs_header_nritems(leaf)) {
> +			/*
> +			 * If the item at offset is not found,
> +			 * btrfs_search_slot will point us to the slot
> +			 * where it should be inserted. In our case
> +			 * that will be the slot directly before the
> +			 * next INODE_REF_KEY_V2 item. In the case
> +			 * that we're pointing to the last slot in a
> +			 * leaf, we must move one leaf over.
> +			 */
> +			ret = btrfs_next_leaf(root, path);
> +			if (ret) {
> +				if (ret >= 1)
> +					ret = -ENOENT;
> +				break;
> +			}
> +			continue;
> +		}
> +
> +		item = btrfs_item_nr(leaf, slot);
> +		btrfs_item_key_to_cpu(leaf, &found_key, slot);
> +
> +		/*
> +		 * Check that we're still looking at an extended ref key for
> +		 * this particular objectid. If we have different
> +		 * objectid or type then there are no more to be found
> +		 * in the tree and we can exit.
> +		 */
> +		ret = -ENOENT;
> +		if (found_key.objectid != inode_objectid)
> +			break;
> +		if (btrfs_key_type(&found_key) != BTRFS_INODE_EXTREF_KEY)
> +			break;
> +
> +		ret = 0;
> +		ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
> +		ref = (struct btrfs_inode_extref *)ptr;
> +		*ret_ref = ref;
> +		if (found_off)
> +			*found_off = found_key.offset + 1;
                                                      ^^^
It's evil to call it "found offset" an then return one larger than the
offset found. No caller would ever expect this.

> +		break;
> +	}
> +
> +out:
> +	return ret;
> +}
> +
> +static int count_inode_extrefs(struct btrfs_root *root,
> +			       struct inode *inode, struct btrfs_path *path)
> +{
> +	int ret;
> +	unsigned int nlink = 0;
> +	u64 inode_objectid = btrfs_ino(inode);
> +	u64 offset = 0;
> +	struct btrfs_inode_extref *ref;
> +
> +	while (1) {
> +		ret = btrfs_find_one_extref(root, inode_objectid, offset, path,
> +					    &ref, &offset);
> +		if (ret)
> +			break;
> +
> +		nlink++;
> +		offset++;
		^^^^^^^^
Huh. See? The caller expected to get the offset found from
btrfs_find_one_extref. As it stands you might be missing the very next key.

> +	}
> +
> +	return nlink;
> +}

-Jan