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Meta-dependencies,
Nico Schottelius, 2005-05-24
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1. What are Meta-Dependencies?
2. What are the advantages / disadvantages of it?
3. The solutions

1. What are Meta-Dependencies?

A Meta-depedency describes the type of service another service wants, but
not the exact service.

Example:
   remote-services/ssh wants a dns-resolver, it does not care about
   what it is (tinycache, bind, maradns, ...), but that it does
   name caching.


2. What are the advantages / disadvantages of it?

Meta means beeing indirect. Indirect means beeing slow. So, if
cinit would have to care about meta-dependencies, the code would become
much bigger and slower.

On the other hand, one would perhaps like to use meta-dependencies, if
one tests different services with the same functionality or switches
them dependending on the situation (see profile.support).


3. The solutions

As told above, cinit won't care about meta-dependencies and as you'll see
why it does not even need to.

The first solution would be to have a mapping table outside of cinit.
This table could be a file for every meta-dependency and contain the
possibilities:

   dns-resolver:
      remote-services/bind
      local-services/tinydns
      ...

So one would have to call a program, which creates the real cinit
configuration. This is imho not a very elegant solution and could cause
problems, when handling self-written services.

Another possibility is to use symlinks: Create service-directories
for all services beeing installed, but do dependencies in "wants/"
and "needs/" to a symlink (for instance create /etc/cinit/meta
and link to real services in there):

   /etc/cinit/meta/dns-resolver -> ../remote-services/bind/

This way you have the indirection (meta-dependencies) in the filesystem
and cinit does not need any additional code.