community features request

[Ondrej Zajicek]

On Wed, Mar 07, 2012 at 03:45:42PM +0400, Oleg wrote:
> So, what's wrong. It works fine, but the code seems some strange:
> 
> 1. If we have empty clist or empty pair set constructions, we can do
>      if ( allowed = [] ) then
>    instead of hack with (0,0) community;

You could have empty pair set (like pair set my_null; my_null = []),
but pair set comparison is not implemented.

> 2. add(C,P) cann't get pair set like delete(C,P) do and

That is because 'delete' is just overloaded, there are two pairs of operations:

add/delete pair

delete/filter pair set.


> 3. we have incompatible types clist and pair set (Why? Why cann't pair set
>    be modifiable?). So we cann't simply do
>      comm = filter(bgp_community, allowed);
>      bgp_community.delete([(51230,*)]);
>      bgp_community.add(comm);
>    instead of tons of lines.

Main reason is that pair sets contain intervals and wild cards and are
represented using balanced trees for efficient matching, their
construction is done in parse-time and not in run-time during matching
so it is faster (and modifying would require re-construction or
rebalancing, which is notrivial), while clist is just a list of pairs.

This is also a reason why set algebra (conjunction. disjunction,
negation) is not implemented for (pair) sets, it have to be done in
parse-time, but current filtering code is based on just run-time
execution.

> function filter_communities(pair set allowed)
> pair set comm;
> pair set def_allowed;
> {
>         def_allowed = [(myas,1000), (myas,1001), (myas,1002)];
>         if ( allowed = [] ) then
>                 allowed = def_allowed;
>         comm = filter(bgp_community, allowed);
>         bgp_community.delete([(myas,*)]);
> 	bgp_community.add(comm);
>         if (( comm = [] ) && ( (myas,1000) ~ allowed )) then
>                 bgp_community.add((myas,1000));
> }
> 
> May be i do something wrong and my code can be simplified?

  The code:
  comm = filter(bgp_community, allowed);
  bgp_community.delete([(myas,*)]);
  bgp_community.add(comm);

  could be done if comm would be clist and adding clist to clist would
  be implemented (which i could add, this is simple).

Another way how to do this is even simpler:

 def_allowed = [(myas,1000), (myas,1001), (myas,1002), (0..myas-1,*), (myas+1..65535,*)];
 bgp_community.filter(def_allowed);
 
 But in that case you have to also add (0..myas-1,*), (myas+1..65535,*)
 to 'allowed' pair set by caller.

-- 
Elen sila lumenn' omentielvo

Ondrej 'SanTiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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