configuration files

[Galen Sampson]

Matthew Dillon wrote:
    I personally prefer NOT to use XML for something like this.  I just
    don't see the point... all it does is add reams of API junk that all
    devolve down into accessing some variable or other.
I have 3 bsd machines at home.  I want to be able to manage all of them 
as easy as I manage 1.  The scripts that you wrote for diskless boot is 
a good idea.  It has some drawbacks.  You can only do a full override of 
an entire file.  You mention the ability to do sh programming in 
rc.conf, and this could be used to get around doing a full override but 
that isn't a great option.  I want to be able to have a set of default 
variables for all machines.  I want to then be able to modify only the 
variables I need to override.  If I did this with sh if [ ... ] the 
rc.conf file would get complex and ugly.  Then there is the option to 
put each .conf file in /etc/rc.d/*.  So /etc/rc.d/sendmail.conf for 
instance.  I've looked and I think rcng is set up this way already.  XML 
would solve the problem of setting specific variables in a file, no 
matter what order the variables are listed.  XML also has an import 
statment so you wouldn't need to use cpp to import separate files.

I have tried putting my config files in cvs.  Then I try to merge the 
default file into the machine specific override.  I didn't get it 
working right.  I didn't know about the Infrastructure project 
http://www.infrastructures.org.  The fact that my idea is not unique is 
a good thing.  Maybe they solved some of my problems already.

    The /bin/sh variable=data form is probably as powerful a mechanism as
    we would ever need, especially when combined with autoconf-like mechanisms
    such as, for example, access to the DHCP variable space.  In fact, it
    occurs to me that we could augment 'kenv' to allow setting kernel 
    env variables in addition to retrieving them and use the space to store
    DHCP and/or autoconf variables.  That would be pretty damn cool.  Then
    /etc/rc.conf could be trivially conditionalized.

What are autoconf variables?  Variables obtained automatically I guess 
(not the autoconf build system).  What else provides this besides DHCP?

Regards,
Galen