libcamera/base: Move extended base functionality

Move the functionality for the following components to the new
base support library:

 - BoundMethod
 - EventDispatcher
 - EventDispatcherPoll
 - Log
 - Message
 - Object
 - Signal
 - Semaphore
 - Thread
 - Timer

While it would be preferable to see these split to move one component
per commit, these components are all interdependent upon each other,
which leaves us with one big change performing the move for all of them.

Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

1 files changed, 998 insertions, 0 deletions

diff --git a/src/libcamera/base/log.cpp b/src/libcamera/base/log.cpp
new file mode 100644
index 00000000..1801ae26
--- /dev/null
+++ b/src/libcamera/base/log.cpp
@@ -0,0 +1,998 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2018, Google Inc.
+ *
+ * log.cpp - Logging infrastructure
+ */
+
+#include <libcamera/base/log.h>
+
+#include <array>
+#if HAVE_BACKTRACE
+#include <execinfo.h>
+#endif
+#include <fstream>
+#include <iostream>
+#include <list>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <syslog.h>
+#include <time.h>
+#include <unordered_set>
+
+#include <libcamera/logging.h>
+
+#include <libcamera/base/thread.h>
+#include <libcamera/base/utils.h>
+
+/**
+ * \file base/log.h
+ * \brief Logging infrastructure
+ *
+ * libcamera includes a logging infrastructure used through the library that
+ * allows inspection of internal operation in a user-configurable way. The log
+ * messages are grouped in categories that represent areas of libcamera, and
+ * output of messages for each category can be controlled by independent log
+ * levels.
+ *
+ * The levels are configurable through the LIBCAMERA_LOG_LEVELS environment
+ * variable that contains a comma-separated list of 'category:level' pairs.
+ *
+ * The category names are strings and can include a wildcard ('*') character at
+ * the end to match multiple categories.
+ *
+ * The level are either numeric values, or strings containing the log level
+ * name. The available log levels are DEBUG, INFO, WARN, ERROR and FATAL. Log
+ * message with a level higher than or equal to the configured log level for
+ * their category are output to the log, while other messages are silently
+ * discarded.
+ *
+ * By default log messages are output to stderr. They can be redirected to a log
+ * file by setting the LIBCAMERA_LOG_FILE environment variable to the name of
+ * the file. The file must be writable and is truncated if it exists. If any
+ * error occurs when opening the file, the file is ignored and the log is output
+ * to stderr.
+ */
+
+/**
+ * \file logging.h
+ * \brief Logging management
+ *
+ * API to change the logging output destination and log levels programatically.
+ */
+
+namespace libcamera {
+
+static int log_severity_to_syslog(LogSeverity severity)
+{
+	switch (severity) {
+	case LogDebug:
+		return LOG_DEBUG;
+	case LogInfo:
+		return LOG_INFO;
+	case LogWarning:
+		return LOG_WARNING;
+	case LogError:
+		return LOG_ERR;
+	case LogFatal:
+		return LOG_ALERT;
+	default:
+		return LOG_NOTICE;
+	}
+}
+
+static const char *log_severity_name(LogSeverity severity)
+{
+	static const char *const names[] = {
+		"DEBUG",
+		" INFO",
+		" WARN",
+		"ERROR",
+		"FATAL",
+	};
+
+	if (static_cast<unsigned int>(severity) < std::size(names))
+		return names[severity];
+	else
+		return "UNKWN";
+}
+
+/**
+ * \brief Log output
+ *
+ * The LogOutput class models a log output destination
+ */
+class LogOutput
+{
+public:
+	LogOutput(const char *path);
+	LogOutput(std::ostream *stream);
+	LogOutput();
+	~LogOutput();
+
+	bool isValid() const;
+	void write(const LogMessage &msg);
+	void write(const std::string &msg);
+
+private:
+	void writeSyslog(LogSeverity severity, const std::string &msg);
+	void writeStream(const std::string &msg);
+
+	std::ostream *stream_;
+	LoggingTarget target_;
+};
+
+/**
+ * \brief Construct a log output based on a file
+ * \param[in] path Full path to log file
+ */
+LogOutput::LogOutput(const char *path)
+	: target_(LoggingTargetFile)
+{
+	stream_ = new std::ofstream(path);
+}
+
+/**
+ * \brief Construct a log output based on a stream
+ * \param[in] stream Stream to send log output to
+ */
+LogOutput::LogOutput(std::ostream *stream)
+	: stream_(stream), target_(LoggingTargetStream)
+{
+}
+
+/**
+ * \brief Construct a log output to syslog
+ */
+LogOutput::LogOutput()
+	: stream_(nullptr), target_(LoggingTargetSyslog)
+{
+	openlog("libcamera", LOG_PID, 0);
+}
+
+LogOutput::~LogOutput()
+{
+	switch (target_) {
+	case LoggingTargetFile:
+		delete stream_;
+		break;
+	case LoggingTargetSyslog:
+		closelog();
+		break;
+	default:
+		break;
+	}
+}
+
+/**
+ * \brief Check if the log output is valid
+ * \return True if the log output is valid
+ */
+bool LogOutput::isValid() const
+{
+	switch (target_) {
+	case LoggingTargetFile:
+		return stream_->good();
+	case LoggingTargetStream:
+		return stream_ != nullptr;
+	default:
+		return true;
+	}
+}
+
+/**
+ * \brief Write message to log output
+ * \param[in] msg Message to write
+ */
+void LogOutput::write(const LogMessage &msg)
+{
+	std::string str;
+
+	switch (target_) {
+	case LoggingTargetSyslog:
+		str = std::string(log_severity_name(msg.severity())) + " "
+		    + msg.category().name() + " " + msg.fileInfo() + " "
+		    + msg.msg();
+		writeSyslog(msg.severity(), str);
+		break;
+	case LoggingTargetStream:
+	case LoggingTargetFile:
+		str = "[" + utils::time_point_to_string(msg.timestamp()) + "] ["
+		    + std::to_string(Thread::currentId()) + "] "
+		    + log_severity_name(msg.severity()) + " "
+		    + msg.category().name() + " " + msg.fileInfo() + " "
+		    + msg.msg();
+		writeStream(str);
+		break;
+	default:
+		break;
+	}
+}
+
+/**
+ * \brief Write string to log output
+ * \param[in] str String to write
+ */
+void LogOutput::write(const std::string &str)
+{
+	switch (target_) {
+	case LoggingTargetSyslog:
+		writeSyslog(LogDebug, str);
+		break;
+	case LoggingTargetStream:
+	case LoggingTargetFile:
+		writeStream(str);
+		break;
+	default:
+		break;
+	}
+}
+
+void LogOutput::writeSyslog(LogSeverity severity, const std::string &str)
+{
+	syslog(log_severity_to_syslog(severity), "%s", str.c_str());
+}
+
+void LogOutput::writeStream(const std::string &str)
+{
+	stream_->write(str.c_str(), str.size());
+	stream_->flush();
+}
+
+/**
+ * \brief Message logger
+ *
+ * The Logger class handles log configuration.
+ */
+class Logger
+{
+public:
+	~Logger();
+
+	static Logger *instance();
+
+	void write(const LogMessage &msg);
+	void backtrace();
+
+	int logSetFile(const char *path);
+	int logSetStream(std::ostream *stream);
+	int logSetTarget(LoggingTarget target);
+	void logSetLevel(const char *category, const char *level);
+
+private:
+	Logger();
+
+	void parseLogFile();
+	void parseLogLevels();
+	static LogSeverity parseLogLevel(const std::string &level);
+
+	friend LogCategory;
+	void registerCategory(LogCategory *category);
+
+	std::unordered_set<LogCategory *> categories_;
+	std::list<std::pair<std::string, LogSeverity>> levels_;
+
+	std::shared_ptr<LogOutput> output_;
+};
+
+/**
+ * \enum LoggingTarget
+ * \brief Log destination type
+ * \var LoggingTargetNone
+ * \brief No logging destination
+ * \sa Logger::logSetTarget
+ * \var LoggingTargetSyslog
+ * \brief Log to syslog
+ * \sa Logger::logSetTarget
+ * \var LoggingTargetFile
+ * \brief Log to file
+ * \sa Logger::logSetFile
+ * \var LoggingTargetStream
+ * \brief Log to stream
+ * \sa Logger::logSetStream
+ */
+
+/**
+ * \brief Direct logging to a file
+ * \param[in] path Full path to the log file
+ *
+ * This function directs the log output to the file identified by \a path. The
+ * previous log target, if any, is closed, and all new log messages will be
+ * written to the new log file.
+ *
+ * If the function returns an error, the log target is not changed.
+ *
+ * \return Zero on success, or a negative error code otherwise
+ */
+int logSetFile(const char *path)
+{
+	return Logger::instance()->logSetFile(path);
+}
+
+/**
+ * \brief Direct logging to a stream
+ * \param[in] stream Stream to send log output to
+ *
+ * This function directs the log output to \a stream. The previous log target,
+ * if any, is closed, and all new log messages will be written to the new log
+ * stream.
+ *
+ * If the function returns an error, the log file is not changed
+ *
+ * \return Zero on success, or a negative error code otherwise.
+ */
+int logSetStream(std::ostream *stream)
+{
+	return Logger::instance()->logSetStream(stream);
+}
+
+/**
+ * \brief Set the logging target
+ * \param[in] target Logging destination
+ *
+ * This function sets the logging output to the target specified by \a target.
+ * The allowed values of \a target are LoggingTargetNone and
+ * LoggingTargetSyslog. LoggingTargetNone will send the log output to nowhere,
+ * and LoggingTargetSyslog will send the log output to syslog. The previous
+ * log target, if any, is closed, and all new log messages will be written to
+ * the new log destination.
+ *
+ * LoggingTargetFile and LoggingTargetStream are not valid values for \a target.
+ * Use logSetFile() and logSetStream() instead, respectively.
+ *
+ * If the function returns an error, the log file is not changed.
+ *
+ * \return Zero on success, or a negative error code otherwise.
+ */
+int logSetTarget(LoggingTarget target)
+{
+	return Logger::instance()->logSetTarget(target);
+}
+
+/**
+ * \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::instance()->logSetLevel(category, level);
+}
+
+Logger::~Logger()
+{
+	for (LogCategory *category : categories_)
+		delete category;
+}
+
+/**
+ * \brief Retrieve the logger instance
+ *
+ * The Logger is a singleton and can't be constructed manually. This function
+ * shall instead be used to retrieve the single global instance of the logger.
+ *
+ * \return The logger instance
+ */
+Logger *Logger::instance()
+{
+	static Logger instance;
+	return &instance;
+}
+
+/**
+ * \brief Write a message to the configured logger output
+ * \param[in] msg The message object
+ */
+void Logger::write(const LogMessage &msg)
+{
+	std::shared_ptr<LogOutput> output = std::atomic_load(&output_);
+	if (!output)
+		return;
+
+	output->write(msg);
+}
+
+/**
+ * \brief Write a backtrace to the log
+ */
+void Logger::backtrace()
+{
+#if HAVE_BACKTRACE
+	std::shared_ptr<LogOutput> output = std::atomic_load(&output_);
+	if (!output)
+		return;
+
+	void *buffer[32];
+	int num_entries = ::backtrace(buffer, std::size(buffer));
+	char **strings = backtrace_symbols(buffer, num_entries);
+	if (!strings)
+		return;
+
+	std::ostringstream msg;
+	msg << "Backtrace:" << std::endl;
+
+	/*
+	 * Skip the first two entries that correspond to this method and
+	 * ~LogMessage().
+	 */
+	for (int i = 2; i < num_entries; ++i)
+		msg << strings[i] << std::endl;
+
+	output->write(msg.str());
+
+	free(strings);
+#endif
+}
+
+/**
+ * \brief Set the log file
+ * \param[in] path Full path to the log file
+ *
+ * \sa libcamera::logSetFile()
+ *
+ * \return Zero on success, or a negative error code otherwise.
+ */
+int Logger::logSetFile(const char *path)
+{
+	std::shared_ptr<LogOutput> output = std::make_shared<LogOutput>(path);
+	if (!output->isValid())
+		return -EINVAL;
+
+	std::atomic_store(&output_, output);
+	return 0;
+}
+
+/**
+ * \brief Set the log stream
+ * \param[in] stream Stream to send log output to
+ *
+ * \sa libcamera::logSetStream()
+ *
+ * \return Zero on success, or a negative error code otherwise.
+ */
+int Logger::logSetStream(std::ostream *stream)
+{
+	std::shared_ptr<LogOutput> output = std::make_shared<LogOutput>(stream);
+	std::atomic_store(&output_, output);
+	return 0;
+}
+
+/**
+ * \brief Set the log target
+ * \param[in] target Log destination
+ *
+ * \sa libcamera::logSetTarget()
+ *
+ * \return Zero on success, or a negative error code otherwise.
+ */
+int Logger::logSetTarget(enum LoggingTarget target)
+{
+	std::shared_ptr<LogOutput> output;
+
+	switch (target) {
+	case LoggingTargetSyslog:
+		output = std::make_shared<LogOutput>();
+		std::atomic_store(&output_, output);
+		break;
+	case LoggingTargetNone:
+		output = nullptr;
+		std::atomic_store(&output_, std::shared_ptr<LogOutput>());
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/**
+ * \brief Set the log level
+ * \param[in] category Logging category
+ * \param[in] level Log level
+ *
+ * \sa libcamera::logSetLevel()
+ */
+void Logger::logSetLevel(const char *category, const char *level)
+{
+	LogSeverity severity = parseLogLevel(level);
+	if (severity == LogInvalid)
+		return;
+
+	for (LogCategory *c : categories_) {
+		if (!strcmp(c->name(), category)) {
+			c->setSeverity(severity);
+			break;
+		}
+	}
+}
+
+/**
+ * \brief Construct a logger
+ */
+Logger::Logger()
+{
+	parseLogFile();
+	parseLogLevels();
+}
+
+/**
+ * \brief Parse the log output file from the environment
+ *
+ * If the LIBCAMERA_LOG_FILE environment variable is set, open the file it
+ * points to and redirect the logger output to it. If the environment variable
+ * is set to "syslog", then the logger output will be directed to syslog. Errors
+ * are silently ignored and don't affect the logger output (set to stderr).
+ */
+void Logger::parseLogFile()
+{
+	const char *file = utils::secure_getenv("LIBCAMERA_LOG_FILE");
+	if (!file) {
+		logSetStream(&std::cerr);
+		return;
+	}
+
+	if (!strcmp(file, "syslog")) {
+		logSetTarget(LoggingTargetSyslog);
+		return;
+	}
+
+	logSetFile(file);
+}
+
+/**
+ * \brief Parse the log levels from the environment
+ *
+ * The log levels are stored in the LIBCAMERA_LOG_LEVELS environment variable
+ * as a list of "category:level" pairs, separated by commas (','). Parse the
+ * variable and store the levels to configure all log categories.
+ */
+void Logger::parseLogLevels()
+{
+	const char *debug = utils::secure_getenv("LIBCAMERA_LOG_LEVELS");
+	if (!debug)
+		return;
+
+	for (const char *pair = debug; *debug != '\0'; pair = debug) {
+		const char *comma = strchrnul(debug, ',');
+		size_t len = comma - pair;
+
+		/* Skip over the comma. */
+		debug = *comma == ',' ? comma + 1 : comma;
+
+		/* Skip to the next pair if the pair is empty. */
+		if (!len)
+			continue;
+
+		std::string category;
+		std::string level;
+
+		const char *colon = static_cast<const char *>(memchr(pair, ':', len));
+		if (!colon) {
+			/* 'x' is a shortcut for '*:x'. */
+			category = "*";
+			level = std::string(pair, len);
+		} else {
+			category = std::string(pair, colon - pair);
+			level = std::string(colon + 1, comma - colon - 1);
+		}
+
+		/* Both the category and the level must be specified. */
+		if (category.empty() || level.empty())
+			continue;
+
+		LogSeverity severity = parseLogLevel(level);
+		if (severity == LogInvalid)
+			continue;
+
+		levels_.push_back({ category, severity });
+	}
+}
+
+/**
+ * \brief Parse a log level string into a LogSeverity
+ * \param[in] level The log level string
+ *
+ * Log levels can be specified as an integer value in the range from LogDebug to
+ * LogFatal, or as a string corresponding to the severity name in uppercase. Any
+ * other value is invalid.
+ *
+ * \return The log severity, or LogInvalid if the string is invalid
+ */
+LogSeverity Logger::parseLogLevel(const std::string &level)
+{
+	static const char *const names[] = {
+		"DEBUG",
+		"INFO",
+		"WARN",
+		"ERROR",
+		"FATAL",
+	};
+
+	int severity;
+
+	if (std::isdigit(level[0])) {
+		char *endptr;
+		severity = strtoul(level.c_str(), &endptr, 10);
+		if (*endptr != '\0' || severity > LogFatal)
+			severity = LogInvalid;
+	} else {
+		severity = LogInvalid;
+		for (unsigned int i = 0; i < std::size(names); ++i) {
+			if (names[i] == level) {
+				severity = i;
+				break;
+			}
+		}
+	}
+
+	return static_cast<LogSeverity>(severity);
+}
+
+/**
+ * \brief Register a log category with the logger
+ * \param[in] category The log category
+ *
+ * Log categories must have unique names. If a category with the same name
+ * already exists this function performs no operation.
+ */
+void Logger::registerCategory(LogCategory *category)
+{
+	categories_.insert(category);
+
+	const std::string &name = category->name();
+	for (const std::pair<std::string, LogSeverity> &level : levels_) {
+		bool match = true;
+
+		for (unsigned int i = 0; i < level.first.size(); ++i) {
+			if (level.first[i] == '*')
+				break;
+
+			if (i >= name.size() ||
+			    name[i] != level.first[i]) {
+				match = false;
+				break;
+			}
+		}
+
+		if (match) {
+			category->setSeverity(level.second);
+			break;
+		}
+	}
+}
+
+/**
+ * \enum LogSeverity
+ * Log message severity
+ * \var LogDebug
+ * Debug message
+ * \var LogInfo
+ * Informational message
+ * \var LogWarning
+ * Warning message, signals a potential issue
+ * \var LogError
+ * Error message, signals an unrecoverable issue
+ * \var LogFatal
+ * Fatal message, signals an unrecoverable issue and aborts execution
+ */
+
+/**
+ * \class LogCategory
+ * \brief A category of log message
+ *
+ * The LogCategory class represents a category of log messages, related to an
+ * area of the library. It groups all messages belonging to the same category,
+ * and is used to control the log level per group.
+ */
+
+/**
+ * \brief Construct a log category
+ * \param[in] name The category name
+ */
+LogCategory::LogCategory(const char *name)
+	: name_(name), severity_(LogSeverity::LogInfo)
+{
+	Logger::instance()->registerCategory(this);
+}
+
+/**
+ * \fn LogCategory::name()
+ * \brief Retrieve the log category name
+ * \return The log category name
+ */
+
+/**
+ * \fn LogCategory::severity()
+ * \brief Retrieve the severity of the log category
+ * \sa setSeverity()
+ * \return Return the severity of the log category
+ */
+
+/**
+ * \brief Set the severity of the log category
+ *
+ * Messages of severity higher than or equal to the severity of the log category
+ * are printed, other messages are discarded.
+ */
+void LogCategory::setSeverity(LogSeverity severity)
+{
+	severity_ = severity;
+}
+
+/**
+ * \brief Retrieve the default log category
+ *
+ * The default log category is named "default" and is used by the LOG() macro
+ * when no log category is specified.
+ *
+ * \return A reference to the default log category
+ */
+const LogCategory &LogCategory::defaultCategory()
+{
+	static const LogCategory *category = new LogCategory("default");
+	return *category;
+}
+
+/**
+ * \class LogMessage
+ * \brief Internal log message representation.
+ *
+ * The LogMessage class models a single message in the log. It serves as a
+ * helper to provide the std::ostream API for logging, and must never be used
+ * directly. Use the LOG() macro instead access the log infrastructure.
+ */
+
+/**
+ * \brief Construct a log message for a given category
+ * \param[in] fileName The file name where the message is logged from
+ * \param[in] line The line number where the message is logged from
+ * \param[in] category The log message category, controlling how the message
+ * will be displayed
+ * \param[in] severity The log message severity, controlling how the message
+ * will be displayed
+ *
+ * Create a log message pertaining to line \a line of file \a fileName. The
+ * \a severity argument sets the message severity to control whether it will be
+ * output or dropped.
+ */
+LogMessage::LogMessage(const char *fileName, unsigned int line,
+		       const LogCategory &category, LogSeverity severity)
+	: category_(category), severity_(severity)
+{
+	init(fileName, line);
+}
+
+/**
+ * \brief Move-construct a log message
+ * \param[in] other The other message
+ *
+ * The move constructor is meant to support the _log() functions. Thanks to copy
+ * elision it will likely never be called, but C++11 only permits copy elision,
+ * it doesn't enforce it unlike C++17. To avoid potential link errors depending
+ * on the compiler type and version, and optimization level, the move
+ * constructor is defined even if it will likely never be called, and ensures
+ * that the destructor of the \a other message will not output anything to the
+ * log by setting the severity to LogInvalid.
+ */
+LogMessage::LogMessage(LogMessage &&other)
+	: msgStream_(std::move(other.msgStream_)), category_(other.category_),
+	  severity_(other.severity_)
+{
+	other.severity_ = LogInvalid;
+}
+
+void LogMessage::init(const char *fileName, unsigned int line)
+{
+	/* Log the timestamp, severity and file information. */
+	timestamp_ = utils::clock::now();
+
+	std::ostringstream ossFileInfo;
+	ossFileInfo << utils::basename(fileName) << ":" << line;
+	fileInfo_ = ossFileInfo.str();
+}
+
+LogMessage::~LogMessage()
+{
+	/* Don't print anything if we have been moved to another LogMessage. */
+	if (severity_ == LogInvalid)
+		return;
+
+	msgStream_ << std::endl;
+
+	if (severity_ >= category_.severity())
+		Logger::instance()->write(*this);
+
+	if (severity_ == LogSeverity::LogFatal) {
+		Logger::instance()->backtrace();
+		std::abort();
+	}
+}
+
+/**
+ * \fn std::ostream& LogMessage::stream()
+ *
+ * Data is added to a LogMessage through the stream returned by this function.
+ * The stream implements the std::ostream API and can be used for logging as
+ * std::cout.
+ *
+ * \return A reference to the log message stream
+ */
+
+/**
+ * \fn LogMessage::timestamp()
+ * \brief Retrieve the timestamp of the log message
+ * \return The timestamp of the message
+ */
+
+/**
+ * \fn LogMessage::severity()
+ * \brief Retrieve the severity of the log message
+ * \return The severity of the message
+ */
+
+/**
+ * \fn LogMessage::category()
+ * \brief Retrieve the category of the log message
+ * \return The category of the message
+ */
+
+/**
+ * \fn LogMessage::fileInfo()
+ * \brief Retrieve the file info of the log message
+ * \return The file info of the message
+ */
+
+/**
+ * \fn LogMessage::msg()
+ * \brief Retrieve the message text of the log message
+ * \return The message text of the message, as a string
+ */
+
+/**
+ * \class Loggable
+ * \brief Base class to support log message extensions
+ *
+ * The Loggable class allows classes to extend log messages without any change
+ * to the way the LOG() macro is invoked. By inheriting from Loggable and
+ * implementing the logPrefix() virtual method, a class can specify extra
+ * information to be automatically added to messages logged from class member
+ * methods.
+ */
+
+Loggable::~Loggable()
+{
+}
+
+/**
+ * \fn Loggable::logPrefix()
+ * \brief Retrieve a string to be prefixed to the log message
+ *
+ * This method allows classes inheriting from the Loggable class to extend the
+ * logger with an object-specific prefix output right before the log message
+ * contents.
+ *
+ * \return A string to be prefixed to the log message
+ */
+
+/**
+ * \brief Create a temporary LogMessage object to log a message
+ * \param[in] category The log message category
+ * \param[in] severity The log message severity
+ * \param[in] fileName The file name where the message is logged from
+ * \param[in] line The line number where the message is logged from
+ *
+ * This method is used as a backeng by the LOG() macro to create a log message
+ * for locations inheriting from the Loggable class.
+ *
+ * \return A log message
+ */
+LogMessage Loggable::_log(const LogCategory *category, LogSeverity severity,
+			  const char *fileName, unsigned int line) const
+{
+	LogMessage msg(fileName, line,
+		       category ? *category : LogCategory::defaultCategory(),
+		       severity);
+
+	msg.stream() << logPrefix() << ": ";
+	return msg;
+}
+
+/**
+ * \brief Create a temporary LogMessage object to log a message
+ * \param[in] category The log message category
+ * \param[in] severity The log message severity
+ * \param[in] fileName The file name where the message is logged from
+ * \param[in] line The line number where the message is logged from
+ *
+ * This function is used as a backeng by the LOG() macro to create a log
+ * message for locations not inheriting from the Loggable class.
+ *
+ * \return A log message
+ */
+LogMessage _log(const LogCategory *category, LogSeverity severity,
+		const char *fileName, unsigned int line)
+{
+	return LogMessage(fileName, line,
+			  category ? *category : LogCategory::defaultCategory(),
+			  severity);
+}
+
+/**
+ * \def LOG_DECLARE_CATEGORY(name)
+ * \hideinitializer
+ * \brief Declare a category of log messages
+ *
+ * This macro is used to declare a log category defined in another compilation
+ * unit by the LOG_DEFINE_CATEGORY() macro.
+ *
+ * The LOG_DECLARE_CATEGORY() macro must be used in the libcamera namespace.
+ *
+ * \sa LogCategory
+ */
+
+/**
+ * \def LOG_DEFINE_CATEGORY(name)
+ * \hideinitializer
+ * \brief Define a category of log messages
+ *
+ * This macro is used to define a log category that can then be used with the
+ * LOGC() macro. Category names shall be unique, if a category is shared between
+ * compilation units, it shall be defined in one compilation unit only and
+ * declared with LOG_DECLARE_CATEGORY() in the other compilation units.
+ *
+ * The LOG_DEFINE_CATEGORY() macro must be used in the libcamera namespace.
+ *
+ * \sa LogCategory
+ */
+
+/**
+ * \def LOG(category, severity)
+ * \hideinitializer
+ * \brief Log a message
+ * \param[in] category Category (optional)
+ * \param[in] severity Severity
+ *
+ * Return an std::ostream reference to which a message can be logged using the
+ * iostream API. The \a category, if specified, sets the message category. When
+ * absent the default category is used. The  \a severity controls whether the
+ * message is printed or discarded, depending on the log level for the category.
+ *
+ * If the severity is set to Fatal, execution is aborted and the program
+ * terminates immediately after printing the message.
+ *
+ * \warning Logging from the destructor of a global object, either directly or
+ * indirectly, results in undefined behaviour.
+ *
+ * \todo Allow logging from destructors of global objects to the largest
+ * possible extent
+ */
+
+/**
+ * \def ASSERT(condition)
+ * \hideinitializer
+ * \brief Abort program execution if assertion fails
+ *
+ * If \a condition is false, ASSERT() logs an error message with the Fatal log
+ * level and aborts program execution.
+ *
+ * If the macro NDEBUG is defined before including log.h, ASSERT() generates no
+ * code.
+ *
+ * Using conditions that have side effects with ASSERT() is not recommended, as
+ * these effects would depend on whether NDEBUG is defined or not. Similarly,
+ * ASSERT() should not be used to check for errors that can occur under normal
+ * conditions as those checks would then be removed when compiling with NDEBUG.
+ */
+
+} /* namespace libcamera */