Global configuration is accessed via a GlobalConfiguration instance.
The instance is conceptually a singleton, but singletons are not welcome
in libcamera so we must store the (preferably single) instance
somewhere.
This patch creates a GlobalConfiguration instance in CameraManager and
defines the corresponding access method. CameraManager is typically
instantiated only once or a few times, it is accessible in many places
in libcamera and the configuration can be retrieved from it and passed
to other places if needed (it's read-only once created). Using
CameraManager for the purpose is still suboptimal and we use it only due
to lack of better options. An alternative could be Logger, which is
still a singleton and it's accessible from everywhere. But with Logger,
we have a chicken and egg problem -- GlobalConfiguration should log
contingent problems with the configuration when it's loaded but if it is
created in the logger then there are mutual infinite recursive calls.
One possible way to deal with this is to look at the environment
variables only during logging initialisation and apply the logging
configuration when a CameraManager is constructed. Considering there
are intentions to remove the Logger singleton, let's omit logging
configuration for now.
If there are multiple CameraManager instances, there are also multiple
GlobalConfiguration instances, each CameraManager instance is meant to
be fully independent, including configuration. They may or may not
contain the same data, depending on whether the global configuration
file in the file system was changed in the meantime.
The configuration is stored in the private CameraManager. It's
accessible within libcamera (via CameraManager) but it's not meant to be
accessed by applications.
Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
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