clixon backend helper

A clixon backend that provides helpful functions for a backend. These are:

• Per-namespace plugins. A plugin may be bound to specific namespaces and is only called for XML items that have the top-level namespaces. That way the plugin doesn't have to parse everything, it just gets what it needs.
• External program helpers. Since clixon drops privileges after it starts, if you need to perform certain operation at privilege you need an external program to do this. (Not yet implmented.)
• python plugins.

Compile and run

NOTE: This requires a version of clixon after 7.3.0. As of writing, that is the latest version, so you will need to pull the end of the clixon git tree at the moment.

Build and install clixon first, or install it from your distro if available. Then run:

    meson setup build
    meson compile -C build
    meson install -C build

This will install the .so in ${prefix}/libexec/clixon_beh.so. It will install a python _clixon_beh.so and clixon_beh.py file into the proper place for python to pick it up. And it will install clixon_beh.h in the include directory. It will install a clixon-beh-config yang file into clixon's yang directory. And that should be all you need.

Note that if you are installing clixon in /usr/local, it will install the python files there, too. Unfortunately, python doesn't work consistently there, it will generally install in /usr/local/lib/python3/..., but python will look in the specific directory for the python version, like /usr/local/lib/python3.12/... so you will need to override the python installation directories. First you need to find them, run:

python -m sysconfig | less

and look for platlib and purelib. Then for setup, run:

meson setup build -Dpython.platlibdir=... -Dpython.purelibdir=...

making the obvious substitutions for .... Then you can compile and install.

Note that if you install in /usr python will look in /usr/lib/python3 so everything works fine in that case.

Examples

Each directory in the examples directory is a stand-alone build

Interfaces

Each of this is an implementation of a full YANG specification.

The C Interface

The C interface for clixon_beh is similar to the one for the clixon proper. The major differences are:

• The module init function is clixon_beh_plugin_init().
• You must call clixon_beh_add_plugin() to register a plugin. You don't return a pointer from the module init function. You can register multiple plugins from the same module.
• You can pass a namespace to clixon_beh_add_plugin(). You will only get called when those namespaces change at the top level, and only with the xml subtrees with thost namespaces (again, top-level). If you pass in NULL for the namespace, you get everything, just like the main clixon API.
• You get a plugin object when you add it. This will be passed in to all your functions. You can store a void * in it to keep data around.
• A transaction is passed around, and you can store a data item in it with clixon_beh_trans_set_data() and retrieve it with clixon_beh_trans_get_data(). Make sure to free it in the end and abort functions!
• Currently the transaction only has the old and new trees, not the added, deleted, and changed trees.

External Program Interface

Not yet implemented.

The Python Interface

See the README.md in the clixon_beh directory for information about the Python interface. For a starter overview, see VADE_MECUM.md in the clixon_beh directory.