Enabled when building monolithically and statically.
This should allow us to work around the -whole-archive issue with
libtool. If the libraries register the plugin constructors they provide
they reference the constructors and will therefore prevent the linker from
removing these seemingly unused symbols from the final executable.
For use cases where dlsym() can be used, e.g. because the static libraries
are manually linked with -whole-archive (Linux) or -force-load (Apple),
this can be disabled by passing ss_cv_static_plugin_constructors=no to
the configure script.
This strangely never caused any noticeable issues, but was the reason for
build failures in certain test cases (mostly BLISS) due to missing plugin
features when built with specific options on Travis (was not reproducible
locally).
This change allows selectively modifying the default plugin list by setting
the `load` setting of individual plugins (e.g. to disable them or to change
their priority) without enabling charon.load_modular and having to configure
a section and a load statement for every plugin.
This can be useful when writing custom plugins as typos or missing
linker flags that result in unresolved symbols in the shared object
could otherwise cause late crashes. In particular, if such a symbol
is used in a code path that is rarely executed. During development
and testing using RTLD_NOW instead of RTLD_LAZY will prevent the
plugin from getting loaded and makes the error visible immediately.
Since we can't get rid of all unmet dependencies (at least not in every
possible plugin configuration) the message is more confusing than
helpful. In particular because a detailed warning about plugin features
that failed to load due to unmet dependencies is only logged on level 2.
Unloading libraries calls any library constructor/destructor functions. Some
libraries can't handle that in our excessive unit test use. GnuTLS leaks
a /dev/urandom file descriptor, letting unit tests fail with arbitrary
out-of-resources errors.
This now works because all plugins use the same config namespace.
If <ns>.load_modular is true, the list of plugins to load is determined
via the value of the <ns>.plugins.<name>.load options.
Using includes the following is possible:
charon {
load_modular = yes
plugins {
include strongswan.d/charon/*.conf
}
}
charon-cmd {
load_modular = yes
plugins {
include strongswan.d/charon-cmd/*.conf
}
}
Where each .conf file would contain something like:
<name> {
load = yes
<option> = <value>
}
To increase the priority of individual plugins load = <priority> can be
used (the default is 1). For instance, to use openssl instead of the
built-in crypto plugins set in strongswan.d/charon/openssl.conf:
openssl {
load = 10
}
If two plugins have the same priority their order in the default plugin
list is preserved. Plugins not found in that list are ordered
alphabetically before other plugins with the same priority.
Still log an error message if critical features fail, as loaded
plugins/features are not logged in that case.
This way loaded plugins are printed before failed features and
the relation is easier to make for users. It also allows programs
to log this message on a different level.
With the new implementation the plugins don't have to be listed in any
special order, dependencies are properly resolved. The order only
matters if two plugins provide the same feature.
This allows daemons and other components to register plugin features
like those provided by plugins (following the same lifecycle).
The added features are internally handled like they were added by a
plugin.
Tobias Brunner