Re: [PATCH nf-next v2 1/8] netfilter: nf_tables: Support for subkeys, set with multiple ranged fields

[Stefano Brivio <sbrivio@redhat.com>]

On Mon, 25 Nov 2019 15:30:58 +0100
Pablo Neira Ayuso <pablo@netfilter.org> wrote:

> On Mon, Nov 25, 2019 at 02:26:16PM +0100, Stefano Brivio wrote:
> > On Mon, 25 Nov 2019 10:58:17 +0100
> > Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> >   
> > > On Mon, Nov 25, 2019 at 10:30:35AM +0100, Stefano Brivio wrote:
> > > [...]  
> > > > Another idea could be that we get rid of this flag altogether: if we
> > > > move "subkeys" to set->desc, the ->estimate() functions of rbtree and
> > > > pipapo can check for those and refuse or allow set selection
> > > > accordingly. I have no idea yet if this introduces further complexity
> > > > for nft, because there we would need to decide how to create start/end
> > > > elements depending on the existing set description instead of using a
> > > > single flag. I can give it a try if it makes sense.    
> > > 
> > > nft_set_desc can probably store a boolean 'concat' that is set on if
> > > the NFTA_SET_DESC_SUBKEY attribute is specified. Then, this flag is
> > > not needed and you can just rely on ->estimate() as you describe.  
> > 
> > I could even just check desc->num_subkeys from your patch then, without
> > adding another field to nft_set_desc. Too ugly?  
> 
> OK.
> 
> > > The hashtable will just ignore this description, it does not need the
> > > description even if userspace pass it on since the interval flag is
> > > set on.
> > > 
> > > You just have to update the rbtree to check for desc->concat, if this
> > > is true, then rbtree->estimate() returns false.  
> > 
> > Yes, I think it all makes sense, thanks for detailing the idea. I'll get
> > to this in a few hours.
> >   
> > > BTW, then probably you can rename this attribute to
> > > NFT_SET_DESC_CONCAT?  
> > 
> > It would include sizes, though. What about NFT_SET_DESC_SUBSIZE or
> > NFT_SET_DESC_FIELD_SIZE?  
> 
> You mean this:
> 
>        NFT_SET_DESC_SUBSIZE
>           NFT_SET_DESC_FIELD_SIZE
>           NFT_SET_DESC_FIELD_SIZE
> 
> instead of this:
> 
>         NFT_SET_DESC_CONCAT
>           NFT_LIST_ELEM
>              NFT_SET_DESC_SUBKEY_LEN
>           NFT_LIST_ELEM
>              NFT_SET_DESC_SUBKEY_LEN
> 
> If I described this correctly, your approach is more simple indeed.

Ah, yes, that's what I meant, but that's because I didn't understand
your intention in the first place. :) I see now.

> However, I don't really have specific requirements for the future
> right now. The one below is leaving room to add more subkey fields (to
> describe each subkey if that is ever required). My experience is that
> leaving room to extend netlink in the future is usually a good idea,
> that's all.
> 
> Instead of NFT_LIST_ELEM, something like NFT_SET_DESC_SUBKEY should be
> fine too, ie.
> 
>         NFT_SET_DESC_CONCAT
>           NFT_SET_DESC_SUBKEY
>              NFT_SET_DESC_SUBKEY_LEN
>           NFT_SET_DESC_SUBKEY
>              NFT_SET_DESC_SUBKEY_LEN

Actually:

>         NFT_SET_DESC_CONCAT
>           NFT_LIST_ELEM
>              NFT_SET_DESC_SUBKEY_LEN
>           NFT_LIST_ELEM
>              NFT_SET_DESC_SUBKEY_LEN

sounds better to me. Maybe "SUBKEY" starts looking a bit obscure here:
the "SUB" part is already there, the "KEY" part mostly refers to an
implementation detail. What about:

         NFT_SET_DESC_CONCAT
           NFT_LIST_ELEM
              NFT_SET_DESC_LEN
           NFT_LIST_ELEM
              NFT_SET_DESC_LEN

this?

-- 
Stefano