Re: [netcf-devel] Arch Linux backend

[David Lutterkort]

Hi Jon,

On Mon, 2009-11-30 at 22:20 +0100, Jon Nordby wrote:
> I'm interesting in writing an Arch Linux backend for netcf. I'd need
> augeas support for the relevant configurations, but what else? What is
> the basic principle, what functions should be implemented etc.? How do
> I approach this?

An Arch Linux backend would be excellent.

The basic idea is that you'd write code that replaces drv_initscripts.c
and add some sort of switch to the autoconf setup that lets you choose
the backend at build time.

We've tried to factor common utility functions out of drv_initscripts.c
into dutil.c and dutil_linux.c - if you find that some of hte
drv_initscripts.c code is useful to you, you should just move it from
that file into one of the util files.

As for how you implement the backend, that's entirely up to you -
strictly speaking, there's no need to use augeas or XSLT for that,
though I found that that simplified the code for the Fedora/RHEL backend
significantly.

For modifying configs, the way drv_initscripts works is that it
transforms back and forth between two trees using XSLT transforms. One
tree is the DOM of the interface XML description (schema is defined in
data/xml/interface.rng), the other is the Augeas tree containing the
config files of interest to network config. The Augeas tree is converted
into an XML DOM in a very simple, straightforward manner, so that an XSL
transform can be applied to it. The data/xml/intscripts-get.xml takes
the interface XML and turns it into Augeas XML,
data/xml/initscripts-put.xml does the reverse transform.

You can find examples of the two XML representations in tests/interface/
and tests/initscripts/ - if you go a similar route for the Arch Linux
backend, you should add a directory tests/archlinux/ or similar and add
files that correspond to the ones in tests/interface/ (and have some
code that tests that one is successfully transformed into the other, see
tests/test-initscripts.c)

David


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