libcamera: logging: add logging API for applications

Currently the log file and the log level can only be set via environment
variables, but applications may also want to set the log file and the
log level at run time. Provide an API for this.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

include/libcamera/logging.h

@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * logging.h - Logging infrastructure
+ */
+#ifndef __LIBCAMERA_LOGGING_H__
+#define __LIBCAMERA_LOGGING_H__
+
+namespace libcamera {
+
+void logSetFile(const char *file);
+int logSetLevel(const char *category, const char *level);
+
+} /* namespace libcamera */
+
+#endif /* __LIBCAMERA_LOGGING_H__ */

include/libcamera/meson.build

@@ -9,6 +9,7 @@ libcamera_api = files([
     'geometry.h',
     'ipa/ipa_interface.h',
     'ipa/ipa_module_info.h',
+    'logging.h',
     'object.h',
     'request.h',
     'signal.h',

src/libcamera/log.cpp

@@ -69,6 +69,9 @@ private:
 	void parseLogLevels();
 	static LogSeverity parseLogLevel(const std::string &level);
 
+	friend int logSetFile(const char *file);
+	friend void logSetLevel(const char *category, const char *level);
+
 	friend LogCategory;
 	void registerCategory(LogCategory *category);
 	void unregisterCategory(LogCategory *category);
@@ -80,6 +83,68 @@ private:
 	std::ostream *output_;
 };
 
+/**
+ * \brief Set the log file
+ * \param[in] file Full path to the log file
+ *
+ * This function sets the logging output file to \a file. The previous log file,
+ * if any, is closed, and all new log messages will be written to the new log
+ * file.
+ *
+ * If \a file is a null pointer, the log is directed to stderr. If the
+ * function returns an error, the log file is not changed.
+ *
+ * \return Zero on success, or a negative error code otherwise.
+ */
+int logSetFile(const char *file)
+{
+	Logger *logger = Logger::instance();
+
+	if (!file) {
+		logger->output_ = &std::cerr;
+		logger->file_.close();
+		return 0;
+	}
+
+	std::ofstream logFile(file);
+	if (!logFile.good())
+		return -EINVAL;
+
+	if (logger->output_ != &std::cerr)
+		logger->file_.close();
+	logger->file_ = std::move(logFile);
+	logger->output_ = &logger->file_;
+	return 0;
+}
+
+/**
+ * \brief Set the log level
+ * \param[in] category Logging category
+ * \param[in] level Log level
+ *
+ * This function sets the log level of \a category to \a level.
+ * \a level shall be one of the following strings:
+ * - "DEBUG"
+ * - "INFO"
+ * - "WARN"
+ * - "ERROR"
+ * - "FATAL"
+ *
+ * "*" is not a valid \a category for this function.
+ */
+void logSetLevel(const char *category, const char *level)
+{
+	Logger *logger = Logger::instance();
+
+	LogSeverity severity = Logger::parseLogLevel(level);
+	if (severity == LogInvalid)
+		return;
+
+	for (LogCategory *c : logger->categories_)
+		if (!strcmp(c->name(), category))
+			c->setSeverity(severity);
+}
+
 /**
  * \brief Retrieve the logger instance
  *