Add immediate log output for early kernel

src/libraries/kutil/include/kutil/logger.h

@@ -30,6 +30,12 @@ public:
 	/// \arg verbosity What level of logs to print for this area
 	void register_area(area_t area, const char *name, level verbosity);
 
+	/// Callback type for immediate-mode logging
+	typedef void (*immediate)(area_t, level, const char *);
+
+	/// Register an immediate-mode log callback
+	inline void set_immediate(immediate cb) { m_immediate = cb; }
+
 	/// Get the default logger.
 	inline logger & get() { return *s_log; }
 
@@ -85,6 +91,7 @@ private:
 	static const unsigned num_areas = 1 << (sizeof(area_t) * 8);
 	uint8_t m_levels[num_areas / 2];
 	const char *m_names[num_areas];
+	immediate m_immediate;
 
 	uint8_t m_sequence;
 

src/libraries/kutil/logger.cpp

@@ -14,6 +14,7 @@ const char *logger::s_level_names[] = {"", "debug", " info", " warn", "error", "
 
 logger::logger() :
 	m_buffer(nullptr, 0),
+	m_immediate(nullptr),
 	m_sequence(0)
 {
 	memset(&m_levels, 0, sizeof(m_levels));
@@ -23,6 +24,7 @@ logger::logger() :
 
 logger::logger(uint8_t *buffer, size_t size) :
 	m_buffer(buffer, size),
+	m_immediate(nullptr),
 	m_sequence(0)
 {
 	memset(&m_levels, 0, sizeof(m_levels));
@@ -73,6 +75,12 @@ logger::output(level severity, area_t area, const char *fmt, va_list args)
 	header->bytes +=
 		vsnprintf(header->message, sizeof(buffer) - sizeof(entry), fmt, args);
 
+	if (m_immediate) {
+		buffer[header->bytes] = 0;
+		m_immediate(area, severity, header->message);
+		return;
+	}
+
 	uint8_t *out;
 	size_t n = m_buffer.reserve(header->bytes, reinterpret_cast<void**>(&out));
 	if (n < sizeof(entry)) {