MXS-421 Add maxscale::event concept

MaxScale now defines events for which the syslog
facility and level can explicitly be defined by the
administrator. Currently there is only one such
event, namelt AUTHENTICATION_FAILURE.

In a subsequent commit, config.cc will be modified so
that event-related configuration parameters are passed
to event::configure() and in another subsequent commit
the authenticators will be modifed to use this mechanism.

In practice a line like:

   MXS_WARNING("%s: login attempt for user '%s'@[%s]:%s, "
               "authentication failed.",
               dcb->service->name, client_data->user,
               dcb->remote, dcb->path);

will be changed to

    MXS_LOG_EVENT(event::AUTHENTICATION_FAILURE,
                  "%s: login attempt for user '%s'@[%s]:%s, "
                  "authentication failed.",
                  dcb->service->name, client_data->user,
                  dcb->remote, dcb->path);

include/maxscale/event.hh

@@ -0,0 +1,174 @@
+#pragma once
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2020-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include <maxscale/cppdefs.hh>
+#include <syslog.h>
+#include <string>
+
+namespace maxscale
+{
+
+/**
+ * @brief Convert a syslog level into a string
+ *
+ * @param level  One of LOG_WARNING, LOG_ERR, ...
+ *
+ * @return The corresponding string; "LOG_WARNING", "LOG_ERR", ...
+ */
+const char* log_level_to_string(int32_t level);
+
+/**
+ * @brief Convert a string to a syslog level
+ *
+ * @param pLevel  [out] A syslog level.
+ * @param zValue  A syslog value as string; "LOG_WARNING", "LOG_ERR", ...
+ *
+ * @return True, if the string corresponds to a syslog level, false otherwise.
+ */
+bool log_level_from_string(int32_t* pLevel, const char* zValue);
+
+/**
+ * @brief Convert a syslog facility into a string
+ *
+ * @param level  One of LOG_USER, LOG_LOCAL0, ...
+ *
+ * @return The corresponding string; "LOG_USER", "LOG_LOCAL0", ...
+ */
+const char* log_facility_to_string(int32_t facility);
+
+/**
+ * @brief Convert a string to a syslog facility
+ *
+ * @param pFacility  [out] A syslog facility.
+ * @param zValue     A syslog facility as string; "LOG_USER", "LOG_LOCAL0", ...
+ *
+ * @return True, if the string corresponds to a syslog facility, false otherwise.
+ */
+bool log_facility_from_string(int32_t* pFacility, const char* zValue);
+
+namespace event
+{
+
+enum id_t
+{
+    AUTHENTICATION_FAILURE  /**< Authentication failure */
+};
+
+enum
+{
+    DEFAULT_FACILITY = LOG_USER,
+    DEFAULT_LEVEL = LOG_WARNING
+};
+
+/**
+ * @brief Convert an event id to a string.
+ *
+ * The string corresponding to an event id is the symbolic constant
+ * converted to all lower-case.
+ *
+ * @param id  An event id.
+ *
+ * @return The corresponding string.
+ */
+const char* to_string(id_t id);
+
+/**
+ * @brief Convert a string to an event id
+ *
+ * @param pId     [out] An event id.
+ * @param zValue  An event id a string; "authentication_failure", ...
+ *
+ * @return True, if the string could be converted, false otherwise.
+ */
+bool from_string(id_t* pId, const char* zValue);
+bool from_string(id_t* pId, const std::string& value)
+{
+    return from_string(pId, value.c_str());
+}
+
+/**
+ * @brief Set the syslog facility of an event.
+ *
+ * @param id        The id of the event.
+ * @param facility  One of LOG_USER, LOG_LOCAL0, ...
+ *
+ * @note If @c facility contains other bits than facility bits, they
+ *       will silently be ignored.
+ */
+void set_log_facility(id_t id, int32_t facility);
+
+/**
+ * @brief Get the syslog facility of an event.
+ *
+ * @param id  An event id.
+ *
+ * @return The facility of the event.
+ */
+int32_t get_log_facility(id_t id);
+
+/**
+ * @brief Set the syslog level of an event.
+ *
+ * @param id     The id of the event.
+ * @param level  One of LOG_WARNING, LOG_ERR, ...
+ *
+ * @note If @c level contains other bits than level bits, they
+ *       will silently be ignored.
+ */
+void set_log_level(id_t id, int32_t level);
+
+/**
+ * @brief Get the syslog level of an event.
+ *
+ * @param id  An event id.
+ *
+ * @return The level of the event.
+ */
+int32_t get_log_level(id_t id);
+
+
+/**
+ * @brief Log an event.
+ *
+ * Usually this function should not be used, but the macro
+ * @c MXS_LOG_EVENT should be used in its stead.
+ *
+ * @param event_id  The id of the event.
+ * @param modname   The module where the event is logged.
+ * @param file      The file where the event is logged.
+ * @param line      The line where the event is logged.
+ * @param function  The function where the event is logged.
+ * @param format    Printf formatting string.
+ * @param ...       Formatting string specific additional arguments.
+ *
+ */
+void log(id_t event_id,
+         const char* modname,
+         const char* file, int line, const char* function,
+         const char* format, ...) mxs_attribute((format(printf, 6, 7)));
+
+}
+
+}
+
+/**
+ * @brief Log an event.
+ *
+ * @param event_id  The id of the event.
+ * @param format    Printf formatting string.
+ * @param ...       Formatting string specific additional arguments.
+ *
+ */
+#define MXS_LOG_EVENT(event_id, format, ...)\
+    maxscale::event::log(event_id, MXS_MODULE_NAME, __FILE__, __LINE__, __func__, format, ##__VA_ARGS__)