MXS-2592 Add configuration for session specific in-memory log

When enabled each session will write log messages in the in-memory log.
If session ends in error this log is written to the actual log in disk.

maxutils/maxbase/include/maxbase/log.h

@@ -85,6 +85,8 @@ typedef struct MXB_LOG_THROTTLING
  */
 typedef size_t (* mxb_log_context_provider_t)(char* buffer, size_t len);
 
+typedef void (* mxb_in_memory_log_t)(const char* buffer, size_t len);
+
 /**
  * @brief Initialize the log
  *
@@ -105,7 +107,8 @@ bool mxb_log_init(const char* ident,
                   const char* logdir,
                   const char* filename,
                   mxb_log_target_t target,
-                  mxb_log_context_provider_t context_provider);
+                  mxb_log_context_provider_t context_provider,
+                  mxb_in_memory_log_t in_memory_log);
 
 /**
  * @brief Finalize the log
@@ -150,6 +153,8 @@ const char* mxb_log_get_filename();
  */
 bool mxb_log_set_priority_enabled(int priority, bool enabled);
 
+bool mxb_log_get_session_trace();
+
 /**
  * Query whether a particular syslog priority is enabled.
  *
@@ -233,6 +238,14 @@ void mxb_log_get_throttling(MXB_LOG_THROTTLING* throttling);
  */
 void mxs_log_redirect_stdout(bool redirect);
 
+/**
+ * Set session specific in-memory log
+ *
+ * @param enabled True or false to enable or disable session in-memory logging
+ */
+void mxb_log_set_session_trace(bool enabled);
+
+
 /**
  * Log a message of a particular priority.
  *
@@ -278,7 +291,7 @@ int mxb_log_oom(const char* message);
  *            MXB_ERROR, MXB_WARNING, etc. macros instead.
  */
 #define MXB_LOG_MESSAGE(priority, format, ...) \
-    (mxb_log_is_priority_enabled(priority)   \
+    (mxb_log_is_priority_enabled(priority) || mxb_log_get_session_trace()  \
      ? mxb_log_message(priority, MXB_MODULE_NAME, __FILE__, __LINE__, __func__, format, ##__VA_ARGS__)  \
      : 0)
 

maxutils/maxbase/include/maxbase/log.hh

@@ -30,7 +30,7 @@
  */
 inline bool mxb_log_init(mxb_log_target_t target = MXB_LOG_TARGET_FS)
 {
-    return mxb_log_init(nullptr, ".", nullptr, target, nullptr);
+    return mxb_log_init(nullptr, ".", nullptr, target, nullptr, nullptr);
 }
 
 namespace maxbase
@@ -52,16 +52,17 @@ public:
         const char* logdir,
         const char* filename,
         mxb_log_target_t target,
-        mxb_log_context_provider_t context_provider)
+        mxb_log_context_provider_t context_provider,
+        mxb_in_memory_log_t in_memory_log)
     {
-        if (!mxb_log_init(ident, logdir, filename, target, context_provider))
+        if (!mxb_log_init(ident, logdir, filename, target, context_provider, in_memory_log))
         {
             throw std::runtime_error("Failed to initialize the log.");
         }
     }
 
     Log(mxb_log_target_t target = MXB_LOG_TARGET_FS)
-        : Log(nullptr, ".", nullptr, target, nullptr)
+        : Log(nullptr, ".", nullptr, target, nullptr, nullptr)
     {
     }
 

maxutils/maxbase/include/maxbase/maxbase.hh

@@ -78,7 +78,8 @@ public:
             const char* zLogdir,
             const char* zFilename,
             mxb_log_target_t target,
-            mxb_log_context_provider_t context_provider);
+            mxb_log_context_provider_t context_provider,
+            mxb_in_memory_log_t in_memory_log);
 
     /**
      * @brief Initializes MaxBase and the MaxBase log.
@@ -88,7 +89,7 @@ public:
      * @throws std::runtime_error if the initialization failed.
      */
     MaxBase(mxb_log_target_t target)
-        : MaxBase(nullptr, ".", nullptr, target, nullptr)
+        : MaxBase(nullptr, ".", nullptr, target, nullptr, nullptr)
     {
     }