RFC - per-host configuration of pxe booting

[this mailing list is as good as anyone i guess... feel free
to forward it if you believe there is a more appropriate forum]

The goal of this email is to figure out how to load host-specific
configurations from pxeboot -- maybe as simple as loading
/boot/loader.conf.${hostname} and possibly something slightly more
flexible that allows me to define machine 'classes' (e.g. based on
similar hardware configurations etc.).

I have a trivial suggestion (patches below) to implement the former,
and some ideas for the latter.

At the moment the only host-specific variables available to pxeboot
are: "boot.netif.hwaddr", "boot.netif.ip", and "dhcp.host-name".

"loaddev" is also available but it is not machine-specific.

The list of config files is specified in /boot/defaults/loader.conf
in the "loader_conf_files" variable, and there is no way
to override it from other files.
So we need to change its default value to include the hostname, e.g.

    loader_conf_files="/boot/device.hints /boot/device.hints.${dhcp.host-name} /boot/loader.conf /boot/loader.conf.${dhcp.host-name}"

(pardon the ling line -- forth does not allow line breaks)

Also we need to redefine the function set_conf_files
in /boot/support.4th so that it can expand ${variable}

        : set_conf_files
          conf_files .addr _at_ ?dup if free-memory then
          set_environment_variable
          s" loader_conf_files" getenv
          strdup
          conf_files .len ! conf_files .addr !
        ;

(this is actually a slight simplification of the existing code).

It might be useful to let dhcp pass more parameters to pxeboot
so e.g. we can expand it to a 'machine class' which can be used
for multiple machines. This should be relatively trivial to impelemnt,
but it requires modifications to the pxeboot binary -- no big deal
since this is something centralized.

Comments ?

	cheers
	luigi