[brussels-dev] per-interface tunables in ipadm/ndd

[sowmini.varadhan at sun.com]

Reposting, since my attempts to post this yesterday never showed up:

There have been a lot of discussions about having per-interface
tunables for many of the IP properties, and the frequently raised
question is, "seems like these would be more appopriate as a
tunable-per-interface. Why isn't this so?"

The ipadm/libipadm interfaces are being constructed with the ability to 
set tunables per interface.  But thinking over the issue of ndd
compatibility in the face of per-interface props: the issue is that if
we have a per-interface version of some prop (e.g.,
ip_icmp_err_interval or ip_send_redirects) whose value is different for
different interfaces on the system, then what should '/sbin/ndd -get'
print for that prop?

So we are faced with doing one of the following:

1. remove the support from ndd and support it only in ipadm, essentially
   zero compatibilty.

2. change the output of 'ndd -get /dev/ip <prop>'- instead of printing
   a single int, it will have to print something like (<intf>, <value>)
   pairs. 

   Both #1 and #2 would break existing scripts that made assumptions about
   ndd output. In both cases we'd have to send out EOL notices, etc.
   about the change, if needed

3. provide per-interface prop support in ipadm and leave the "global"
   setting alone (In addition to complicating our kernel tremendously,
   I don't even see how this would work. E.g. if the "prop"
   is some thing like a rate-limit parameter, and the value is different
   for each interface, then what would the global value be?)

4. dont provide per-interface props in ipadm when the prop is already
   there in ndd (not a good solution- this makes ndd Stable through
   some sort of ugly Common Law). Only new props can be tuned per interface.

None of these options is ideal, but #2 seems to make the best of
a bad-deal. Thoughts?

--Sowmini