Re: [iptables PATCH v3 04/11] nft-cache: Introduce cache levels

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

Hi Phil,

On Tue, Oct 08, 2019 at 06:14:40PM +0200, Phil Sutter wrote:
> Replace the simple have_cache boolean by a cache level indicator
> defining how complete the cache is. Since have_cache indicated full
> cache (including rules), make code depending on it check for cache level
> NFT_CL_RULES.
> 
> Core cache fetching routine __nft_build_cache() accepts a new level via
> parameter and raises cache completeness to that level.
> 
> Signed-off-by: Phil Sutter <phil@nwl.cc>
> ---
>  iptables/nft-cache.c | 51 +++++++++++++++++++++++++++++++-------------
>  iptables/nft.h       |  9 +++++++-
>  2 files changed, 44 insertions(+), 16 deletions(-)
> 
> diff --git a/iptables/nft-cache.c b/iptables/nft-cache.c
> index 5444419a5cc3b..22a87e94efd76 100644
> --- a/iptables/nft-cache.c
> +++ b/iptables/nft-cache.c
> @@ -224,30 +224,49 @@ static int fetch_rule_cache(struct nft_handle *h)
>  	return 0;
>  }
>  
> -static void __nft_build_cache(struct nft_handle *h)
> +static void __nft_build_cache(struct nft_handle *h, enum nft_cache_level level)
>  {
>  	uint32_t genid_start, genid_stop;
>  
> +	if (level <= h->cache_level)
> +		return;
>  retry:
>  	mnl_genid_get(h, &genid_start);
> -	fetch_table_cache(h);
> -	fetch_chain_cache(h);
> -	fetch_rule_cache(h);
> -	h->have_cache = true;
> -	mnl_genid_get(h, &genid_stop);
>  
> +	switch (h->cache_level) {
> +	case NFT_CL_NONE:
> +		fetch_table_cache(h);
> +		if (level == NFT_CL_TABLES)
> +			break;
> +		/* fall through */
> +	case NFT_CL_TABLES:

If the existing level is TABLES and use wants chains, then you have to
invalidate the existing table cache, then fetch the tables and chains
to make sure cache is consistent. I mean, extending an existing cache
might lead to inconsistencies.

Am I missing anything?

> +		fetch_chain_cache(h);
> +		if (level == NFT_CL_CHAINS)
> +			break;
> +		/* fall through */
> +	case NFT_CL_CHAINS:
> +		fetch_rule_cache(h);
> +		if (level == NFT_CL_RULES)
> +			break;
> +		/* fall through */
> +	case NFT_CL_RULES:
> +		break;
> +	}
> +
> +	mnl_genid_get(h, &genid_stop);
>  	if (genid_start != genid_stop) {
>  		flush_chain_cache(h, NULL);
>  		goto retry;
>  	}
>  
> +	h->cache_level = level;
>  	h->nft_genid = genid_start;
>  }