libcamera: pipeline: Add a platform configuration file helper

Add a new helper function PipelineHandler::configurationFile() that returns
the full path of a named configuration file. This configuration file may be read
by pipeline handlers for platform specific configuration parameters on
initialisation.

The mechanism for searching for the configuration file is similar to the IPA
configuration file:

- In the source tree if libcamera is not installed
- Otherwise in standard system locations (etc and share directories).

When stored in the source tree, configuration files shall be located in a 'data'
subdirectory of their respective pipeline handler directory.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/internal/pipeline_handler.h

@@ -65,6 +65,9 @@ public:
 	bool completeBuffer(Request *request, FrameBuffer *buffer);
 	void completeRequest(Request *request);
 
+	std::string configurationFile(const std::string &subdir,
+				      const std::string &name) const;
+
 	const char *name() const { return name_; }
 
 protected:

src/libcamera/pipeline_handler.cpp

@@ -8,6 +8,7 @@
 #include "libcamera/internal/pipeline_handler.h"
 
 #include <chrono>
+#include <sys/stat.h>
 #include <sys/sysmacros.h>
 
 #include <libcamera/base/log.h>
@@ -534,6 +535,62 @@ void PipelineHandler::completeRequest(Request *request)
 	}
 }
 
+/**
+ * \brief Retrieve the absolute path to a platform configuration file
+ * \param[in] subdir The pipeline handler specific subdirectory name
+ * \param[in] name The configuration file name
+ *
+ * This function locates a named platform configuration file and returns
+ * its absolute path to the pipeline handler. It searches the following
+ * directories, in order:
+ *
+ * - If libcamera is not installed, the src/libcamera/pipeline/\<subdir\>/data/
+ *   directory within the source tree ; otherwise
+ * - The system data (share/libcamera/pipeline/\<subdir\>) directory.
+ *
+ * The system directories are not searched if libcamera is not installed.
+ *
+ * \return The full path to the pipeline handler configuration file, or an empty
+ * string if no configuration file can be found
+ */
+std::string PipelineHandler::configurationFile(const std::string &subdir,
+					       const std::string &name) const
+{
+	std::string confPath;
+	struct stat statbuf;
+	int ret;
+
+	std::string root = utils::libcameraSourcePath();
+	if (!root.empty()) {
+		/*
+		 * When libcamera is used before it is installed, load
+		 * configuration files from the source directory. The
+		 * configuration files are then located in the 'data'
+		 * subdirectory of the corresponding pipeline handler.
+		 */
+		std::string confDir = root + "src/libcamera/pipeline/";
+		confPath = confDir + subdir + "/data/" + name;
+
+		LOG(Pipeline, Info)
+			<< "libcamera is not installed. Loading platform configuration file from '"
+			<< confPath << "'";
+	} else {
+		/* Else look in the system locations. */
+		confPath = std::string(LIBCAMERA_DATA_DIR)
+				+ "/pipeline/" + subdir + '/' + name;
+	}
+
+	ret = stat(confPath.c_str(), &statbuf);
+	if (ret == 0 && (statbuf.st_mode & S_IFMT) == S_IFREG)
+		return confPath;
+
+	LOG(Pipeline, Error)
+		<< "Configuration file '" << confPath
+		<< "' not found for pipeline handler '" << PipelineHandler::name() << "'";
+
+	return std::string();
+}
+
 /**
  * \brief Register a camera to the camera manager and pipeline handler
  * \param[in] camera The camera to be added