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.
The aim here is to add another way to specify labels using the local
source by reading files in a specific directory. That avoids us to
execute a hook when we just need to get the content of a file.
See https://github.com/kubernetes-sigs/node-feature-discovery/issues/226
Signed-off-by: Jordan Jacobelli <jjacobelli@nvidia.com>
Make it possible for the hooks to fully define the label name to be used
(i.e. without the '<hook name>-' prefix) by prefixing the printed
feature names with a slash ('/'). This makes it possible to e.g.
override labels create by other sources.
For example having the following output from a hook:
/override_source-override_bool
/override_source-override_value=my value
will translate into the following feature labels:
feature.node.kubernetes.io/override_source-override_bool = true
feature.node.kubernetes.io/override_source-override_value = my value
Make the feature detector hooks, run by the 'local' feature source,
support non-binary label values. Hooks can advertise non-binary value by
using <name>=<value> format.
For example, /etc/kubernetes/node-feature-discovery/source.d/myhook
having the following stdout:
LABEL_1
LABEL_2=foobar
Would translate into the following labels:
feature.node.kubernetes.io/myhook-LABEL_1 = true
feature.node.kubernetes.io/myhook-LABEL_2 = foobar
Implement a new feature source named 'local' whose only purpose is to
run feature source hooks found under
/etc/kubernetes/node-feature-discovery/source.d/ It tries to execute all
files found under the directory, in alphabetical order.
This feature source provides users a mechanism to implement custom
feature sources in a pluggable way, without modifying nfd source code or
Docker images.
The hooks are supposed to print all discovered features in stdout, one
feature per line. The output in stdout is used in the node label as is.
Full node label name will have the following format:
feature.node.kubernetes.io/<hook name>-<feature name>
Stderr from the hooks is propagated to nfd log.
