58 lines
1.9 KiB
Text
58 lines
1.9 KiB
Text
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Meta-dependencies,
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Nico Schottelius, 2005-05-24
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1. What are Meta-Dependencies?
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2. What are the advantages / disadvantages of it?
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3. The solutions
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1. What are Meta-Dependencies?
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A Meta-depedency describes the type of service another service wants, but
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not the exact service.
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Example:
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remote-services/ssh wants a dns-resolver, it does not care about
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what it is (tinycache, bind, maradns, ...), but that it does
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name caching.
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2. What are the advantages / disadvantages of it?
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Meta means beeing indirect. Indirect means beeing slow. So, if
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cinit would have to care about meta-dependencies, the code would become
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much bigger and slower.
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On the other hand, one would perhaps like to use meta-dependencies, if
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one tests different services with the same functionality or switches
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them dependending on the situation (see profile.support).
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3. The solutions
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As told above, cinit won't care about meta-dependencies and as you'll see
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why it does not even need to.
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The first solution would be to have a mapping table outside of cinit.
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This table could be a file for every meta-dependency and contain the
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possibilities:
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dns-resolver:
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remote-services/bind
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local-services/tinydns
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...
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So one would have to call a program, which creates the real cinit
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configuration. This is imho not a very elegant solution and could cause
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problems, when handling self-written services.
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Another possibility is to use symlinks: Create service-directories
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for all services beeing installed, but do dependencies in "wants/"
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and "needs/" to a symlink (for instance create /etc/cinit/meta
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and link to real services in there):
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/etc/cinit/meta/dns-resolver -> ../remote-services/bind/
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This way you have the indirection (meta-dependencies) in the filesystem
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and cinit does not need any additional code.
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