[radvd-devel-l] RFC: interfaces going up/down during radvd lifetime

[Pekka Savola]

Hi,

A bug report from Simon Oosthoek triggered this issue, and I'd like 
to see if other folks have opinions on this.

Currently if interface doesn't exist when radvd is started, radvd 
doesn't start unless IgnoreIfMissing is defined.  When the interface 
comes up, the user or if{up,down} scripts need to send HUP signal to 
radvd to start using the interface.

Simon's problem was a dynamic wireless interface that's sometimes 
disabled and/or removed.  In such case, radvd didn't automatically 
restart the advertisements when the interface was plugged back in, but 
still kept running.

As a quick fix, I made the behavior more deterministic:
  - if IgnoreIfMissing is not defined, exit immediately if an interface
    becomes inoperational or goes missing.
  - if IgnoreIfMissing is defined, keep radvd alive, waiting for
    HUP signal to restart.

Now, one could argue it'd be nice if this "worked by default", so 
that, for example:
  a) if interface goes missing and comes back, automatically restart
     advertisements
  b) if interface didn't exist when starting up, but IgnoreIfMissing is
     defined, automatically start advertising when the interface starts
     working.
  c) don't print a lot of error messages on missing/non-working
     interfaces if IgnoreIfMissing is defined

I'd like to note that doing the processing checks could take a bit of 
CPU time, especially if you advertise (say) 20 times a second.

Comments?

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings