Exposing advertisments/offers via dhcpcd-run-hooks

[rmarioe]

I would like to have visibility of all the DHCP servers that offered/advertised a lease in the network to the client through my user defined hook script. It could be handled by adding a reason to run the hooks script (i.e. OFFER/ADVERTISE). Before sending out a PR I would like to know if something like this could be an acceptable enhancement to dhcpcd?

[rsmarples]

dhcpcd currently works on a one to one basis and reacts to the first OFFER/ADVERTISE it gets and then discards the others it receives while it's in the next phase.

What is your use case for this?

[rmarioe]

I want to get configuration data/vendor options of all servers into the hooks environment.

RFC2131 does not mandate this kind of behavior but does allow it:

1. The client receives one or more DHCPOFFER messages from one or more
   servers. The client may choose to wait for multiple responses.
   The client chooses one server from which to request configuration
   parameters, based on the configuration parameters offered in the
   DHCPOFFER messages.

RFC8415:

• Those Advertise messages with the highest server preference value
  SHOULD be preferred over all other Advertise messages. The client
  MAY choose a less preferred server if that server has a better set
  of advertised parameters, such as the available set of IAs, as
  well as the set of other configuration options advertised.

• Within a group of Advertise messages with the same server
  preference value, a client MAY select those servers whose
  Advertise messages advertise information of interest to the
  client.

Having all the info in the environment is enough for me.

If we would go the way of choosing the server in might be trickier.

We could restart the server until the client chooses the correct one in the existing algorithm?
It is first come - first serve currently?

Another way could be for the client to wait for user input on what to choose if the client registered for this hook.