collectd's build system

It has been asked how to include a new plugin in the build system. I have to admit that I'm not too firm with autoconf/automake myself, so this is more a "it works for me" than a "this is how it works" description.

In the past, the --enable-plugin argument was used to enable/disable the building of plugins, with the default being "enabled" for all plugins. This was necessary because the "server" needed the plugins to decode received data, even if it couldn't collect data on its own. Since this is no longer true, plugins such as apple_sensors only need to be build when they can actually collect the values. Thus, the dependency checking has been moved into the configure script with version 4.1. The plugins are automatically enabled or disabled, depending on wether their dependencies are met (or not) and the --enable-plugin argument can be used to force the plugin to be enabled or disabled.

autoconf

There is a macro that will add

the --enable-plugin argument to the configure script,
the BUILD_PLUGIN_PLUGIN conditional to the Makefile, and
the HAVE_PLUGIN_PLUGIN define to config.h.

The macro needs to be called like this:

AC_PLUGIN([name], $with_dependency, [description])

The second argument is the value of a variable which decides wether the plugin should be built or not. This is, of course, the tricky part. The first argument is simply the name of the plugin, the third is only a description for ./configure --help.

automake

The AC_PLUGIN (see above) sets a conditional to be used in the Makefile.am, named BUILD_PLUGIN_PLUGIN. This conditional surrounds the block that defines the plugin so that it's only build if the conditional is true. A typical block looks like this:

if BUILD_PLUGIN_FOOBAR
pkglib_LTLIBRARIES += foobar.la
foobar_la_SOURCES = foobar.c
foobar_la_LDFLAGS = -module -avoid-version
collectd_LDADD += "-dlopen" foobar.la
collectd_DEPENDENCIES += foobar.la
endif

Generate `configure` and `Makefile.in`

After you have made your changes you need to generate the configure-script and some Makefile.in's. This can be done by simply typing make if you already have a configure script (the genereated Makefile will check if it needs to re-generate the auto{conf,make} stuff) or by running the build.sh script from the Git repository. After that you should be ready to go.