Re: [nft PATCH 4/4] segtree: Refactor ei_insert()

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Thu, Jan 23, 2020 at 03:30:49PM +0100, Phil Sutter wrote:
> With all simplifications in place, reorder the code to streamline it
> further. Apart from making the second call to ei_lookup() conditional,
> debug output is slightly enhanced.
> 
> Signed-off-by: Phil Sutter <phil@nwl.cc>
> ---
>  src/segtree.c | 63 +++++++++++++++++++++++----------------------------
>  1 file changed, 28 insertions(+), 35 deletions(-)
> 
> diff --git a/src/segtree.c b/src/segtree.c
> index 3c0989e76093a..edec9f4ebf174 100644
> --- a/src/segtree.c
> +++ b/src/segtree.c
> @@ -192,48 +192,41 @@ static int ei_insert(struct list_head *msgs, struct seg_tree *tree,
>  {
>  	struct elementary_interval *lei, *rei;
>  
> -	/*
> -	 * Lookup the intervals containing the left and right endpoints.
> -	 */
>  	lei = ei_lookup(tree, new->left);
> -	rei = ei_lookup(tree, new->right);
> -
> -	if (segtree_debug(tree->debug_mask))
> -		pr_gmp_debug("insert: [%Zx %Zx]\n", new->left, new->right);
> -
> -	if (lei != NULL && rei != NULL && lei == rei) {
> -		if (!merge)
> -			goto err;
> -
> -		ei_destroy(new);
> +	if (lei == NULL) {
> +		/* no overlaps, just add the new interval */
> +		if (segtree_debug(tree->debug_mask))
> +			pr_gmp_debug("insert: [%Zx %Zx]\n",
> +				     new->left, new->right);
> +		__ei_insert(tree, new);
>  		return 0;
> -	} else {
> -		if (lei != NULL) {
> -			if (!merge)
> -				goto err;
> -			/*
> -			 * Left endpoint is within lei, adjust it so we have:
> -			 *
> -			 * [lei_left, new_right]
> -			 */
> -			if (segtree_debug(tree->debug_mask)) {
> -				pr_gmp_debug("adjust left [%Zx %Zx]\n",
> -					     lei->left, lei->right);
> -			}
> +	}
>  
> -			mpz_set(lei->right, new->right);
> -			ei_destroy(new);
> -			return 0;
> -		}
> +	if (!merge) {
> +		errno = EEXIST;
> +		return expr_binary_error(msgs, lei->expr, new->expr,
> +					 "conflicting intervals specified");
>  	}

Not your fault, but I think this check is actually useless given that
the overlap check happens before (unless you consider to consolidate
the insertion and the overlap checks in ei_insert).

> -	__ei_insert(tree, new);
> +	/* caller sorted intervals, so rei is either equal to lei or NULL */
> +	rei = ei_lookup(tree, new->right);
> +	if (rei != lei) {

Isn't this always true? I mean rei != lei always stands true?

> +		/*
> +		 * Left endpoint is within lei, adjust it so we have:
> +		 *
> +		 * [lei_left, new_right]
> +		 */
> +		if (segtree_debug(tree->debug_mask))
> +			pr_gmp_debug("adjust right: [%Zx %Zx]\n",
> +				     lei->left, lei->right);
> +		mpz_set(lei->right, new->right);
> +	} else if (segtree_debug(tree->debug_mask)) {
> +		pr_gmp_debug("skip new: [%Zx %Zx] for old: [%Zx %Zx]\n",
> +			     new->left, new->right, lei->left, lei->right);
> +	}
>  
> +	ei_destroy(new);
>  	return 0;
> -err:
> -	errno = EEXIST;
> -	return expr_binary_error(msgs, lei->expr, new->expr,
> -				 "conflicting intervals specified");
>  }
>  
>  /*
> -- 
> 2.24.1
>