Implement new registration infrastructure under the "source" package.
This change loosens the coupling between label sources and the
nfd-worker, making it easier to refactor and move the code around.
Also, create a separate interface (ConfigurableSource) for configurable
feature sources in order to eliminate boilerplate code.
Add safety checks to the sources that they actually implement the
interfaces they should.
In sake of consistency and predictability (of behavior) change all
methods of the sources to use pointer receivers.
Add simple unit tests for the new functionality and include source/...
into make test target.
Extend the FeatureSource interface with new methods for configuration
handling. This enables easier on-the fly reconfiguration of the
feature sources. Further, it simplifies adding config support to feature
sources in the future. Stub methods are added to sources that do not
currently have any configurability.
The patch fixes some (corner) cases with the overrides (--options)
handling, too:
- Overrides were not applied if config file was missing or its parsing
failed
- Overrides for a certain source did not have effect if an empty config
for the source was specified in the config file. This was caused by
the first pass of parsing (config file) setting a nil pointer to the
source-specific config, effectively detaching it from the main config.
The second pass would then create a new instance of the source
specific config, but, this was not visible in the feature source, of
course.
* Arrange feature sources alphabetically
Just a cosmetic change, but, a small readability improvement.
* Implement detection of IOMMU (#136)
Add a new feature source, i.e. 'iommu', which detects if an IOMMU is
present and enabled in the kernel. The new node label is
node.alpha.kubernetes-incubator.io/nfd-iommu-present
