libutil: Introduce multi-level message logging

The goal of util_log is to provide a facility for a multi-level message
logging on stderr. This allows to selectively enable/disable log messages
via a log level which can be adjusted at runtime.

Signed-off-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Reviewed-by: Jan Hoeppner <hoeppner@linux.ibm.com>
Reviewed-by: Philipp Rudo <prudo@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

include/lib/util_log.h

@@ -0,0 +1,28 @@
+/**
+ * @defgroup util_log_h util_file: Multi-level message logging interface
+ * @{
+ * @brief Multi-level message logging
+ *
+ * Copyright IBM Corp. 2021
+ *
+ * s390-tools is free software; you can redistribute it and/or modify
+ * it under the terms of the MIT license. See LICENSE for details.
+ */
+
+#ifndef LIB_UTIL_LOG_H
+#define LIB_UTIL_LOG_H
+
+enum util_log_level {
+	UTIL_LOG_ERROR,
+	UTIL_LOG_WARN,
+	UTIL_LOG_INFO,
+	UTIL_LOG_DEBUG,
+	UTIL_LOG_TRACE,
+	UTIL_LOG_NUM_LEVELS	/* Must be the last one. */
+};
+
+void util_log_set_level(int log_level);
+
+void util_log_print(int log_level, const char *fmt, ...);
+
+#endif /** LIB_UTIL_LOG_H @} */

libutil/Makefile

@@ -22,6 +22,7 @@ objects =	util_base.o \
 		util_file.o \
 		util_libc.o \
 		util_list.o \
+		util_log.o \
 		util_opt.o \
 		util_panic.o \
 		util_part.o \

libutil/util_log.c

@@ -0,0 +1,70 @@
+/*
+ * Multi-level message logging
+ *
+ * Copyright IBM Corp. 2021
+ *
+ * s390-tools is free software; you can redistribute it and/or modify
+ * it under the terms of the MIT license. See LICENSE for details.
+ */
+
+#include <stdio.h>
+#include <stdarg.h>
+
+#include "lib/util_log.h"
+
+static int current_log_level = UTIL_LOG_INFO;
+
+static const char *log_level_to_str(int log_level)
+{
+	switch (log_level) {
+	case UTIL_LOG_ERROR:
+		return "ERROR";
+	case UTIL_LOG_WARN:
+		return "WARN";
+	case UTIL_LOG_INFO:
+		return "INFO";
+	case UTIL_LOG_DEBUG:
+		return "DEBUG";
+	case UTIL_LOG_TRACE:
+		return "TRACE";
+	default:
+		return "UNKNW";
+	}
+}
+
+static void log_helper(FILE *fp, int log_level, const char *fmt, va_list args)
+{
+	if (current_log_level < log_level)
+		return;
+
+	fprintf(fp, "%5s: ", log_level_to_str(log_level));
+	vfprintf(fp, fmt, args);
+}
+
+/**
+ * Changes the current log level
+ *
+ * @param[in] log_level A new log level to be set as the current one
+ */
+void util_log_set_level(int log_level)
+{
+	current_log_level = log_level;
+}
+
+/**
+ * Outputs the given message on stderr
+ *
+ * The given message is printed only if the current log level is >= than the given one.
+ *
+ * @param[in] log_level Log level starting from which the given message shall be printed
+ * @param[in] fmt       Format string for generation of the log message
+ * @param[in] ...       Parameters for format string
+ */
+void util_log_print(int log_level, const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	log_helper(stderr, log_level, fmt, args);
+	va_end(args);
+}