Re: [PATCH] monitor: fix printing of range elements in named sets

[Phil Sutter <phil@nwl.cc>]

Hi,

On Thu, Jul 06, 2017 at 04:36:45PM +0200, Arturo Borrero Gonzalez wrote:
> If you add set elements to interval sets, the output is wrong.
> Fix this by caching first element of the range (first event),
> then wait for the second element of the range (second event) to
> print them both at the same time.

As promised, I am preparing my own solution for side-by-side comparison.
Though I'm running into problems and want to use the occasion to discuss
them first:

What I wasn't able to solve yet are half-open ranges, like so:

| nft add set ip t portrange { type inet_service; flags interval; }
| nft add element ip t portrange { 1024-65535 }

In this case there is only a single element with value 1024 which
doesn't have EXPR_F_INTERVAL_END set. Looking at
interval_map_decompose(), this is identified to be a range till the end
of the scope if it's the last element in the set.

In monitor code though, I can't predict whether an interval end element
will come afterwards or not, so I end up caching the element and
everything turns into a mess. I'm pretty sure your solution has the same
problem, could you check that?

Right now, I only see two ways to get this sorted:

1) Change kernel code to always include both start end end of a range in
   a single notification. This would eliminate the need for any caching
   in netlink_events_setelem_cb() altogether!

2) Change monitor code to cache all events until the final NFTA_GEN_ID
   message, then handle all messages at once.

What do you think?

Thanks, Phil