internal-logging: Fix issues with file logging

This commit fixes the following issues if access
to the internal log file is not possible (logging_mode = DLT_LOG_TO_FILE)
* dlt_log_free tried to call fclose on a nullptr
  Added a nullcheck for this
* Access to log file might be denied but access to logs is still wanted
  Add a new CMake option WITH_DLT_FILE_LOGGING_SYSLOG_FALLBACK
  If this is set to ON and the logging moe is set to file,
  the dlt-daemon will fall back to syslog if opening the internal log
  file failed

Author: alexmohr

CMakeLists.txt

@@ -73,6 +73,7 @@ option(WITH_DLT_DBUS          "Set to ON to build src/dbus binaries"
 option(WITH_DLT_TESTS         "Set to ON to build src/test binaries"                                             ON)
 option(WITH_DLT_UNIT_TESTS    "Set to ON to build gtest framework and tests/binaries"                            OFF)
 option(WITH_DLT_QNX_SYSTEM    "Set to ON to build QNX system binary dlt-qnx-system"                              OFF)
+option(WITH_DLT_FILE_LOGGING_SYSLOG_FALLBACK "Set to ON to enable fallback to syslog if dlt logging to file fails" OFF)
 
 set(DLT_IPC "FIFO" CACHE STRING "UNIX_SOCKET,FIFO")
 set(DLT_USER "genivi" CACHE STRING "Set user for process not run as root")
@@ -169,6 +170,10 @@ if(WITH_DLT_QNX_SYSTEM AND NOT "${CMAKE_C_COMPILER}" MATCHES "nto-qnx|qcc")
     message(FATAL_ERROR "Can only compile for QNX with a QNX compiler.")
 endif()
 
+if (WITH_DLT_FILE_LOGGING_SYSLOG_FALLBACK)
+    add_definitions(-DWITH_DLT_FILE_LOGGING_SYSLOG_FALLBACK)
+endif()
+
 if(WITH_GPROF)
     add_compile_options(-pg)
 endif()
@@ -336,6 +341,7 @@ message(STATUS "WITH_LIB_SHORT_VERSION = ${WITH_LIB_SHORT_VERSION}")
 message(STATUS "WITH_LEGACY_INCLUDE_PATH = ${WITH_LEGACY_INCLUDE_PATH}")
 message(STATUS "WITH_EXTENDED_FILTERING = ${WITH_EXTENDED_FILTERING}")
 message(STATUS "WITH_DLT_DISABLE_MACRO = ${WITH_DLT_DISABLE_MACRO}")
+message(STATUS "WITH_DLT_FILE_LOGGING_SYSLOG_FALLBACK = ${WITH_DLT_FILE_LOGGING_SYSLOG_FALLBACK}" )
 message(STATUS "Change a value with: cmake -D<Variable>=<Value>")
 message(STATUS "-------------------------------------------------------------------------------")
 message(STATUS)

include/dlt/dlt_common.h

@@ -1195,7 +1195,7 @@ void dlt_print_with_attributes(bool state);
  * Initialize (external) logging facility
  * @param mode positive, 0 = log to stdout, 1 = log to syslog, 2 = log to file, 3 = log to stderr
  */
-void dlt_log_init(int mode);
+DltReturnValue dlt_log_init(int mode);
 /**
  * Print with variable arguments to specified file descriptor by DLT_LOG_MODE environment variable (like fprintf)
  * @param format format string for message

src/daemon/dlt-daemon.c

@@ -940,7 +940,25 @@ int main(int argc, char *argv[])
     /* Initialize internal logging facility */
     dlt_log_set_filename(daemon_local.flags.loggingFilename);
     dlt_log_set_level(daemon_local.flags.loggingLevel);
-    dlt_log_init(daemon_local.flags.loggingMode);
+    DltReturnValue log_init_result =
+        dlt_log_init(daemon_local.flags.loggingMode);
+
+    if (log_init_result != DLT_RETURN_OK) {
+      fprintf(stderr, "Failed to init internal logging\n");
+
+#if WITH_DLT_FILE_LOGGING_SYSLOG_FALLBACK
+        if (daemon_local.flags.loggingMode == DLT_LOG_TO_FILE) {
+          fprintf(stderr, "Falling back to syslog mode\n");
+
+          daemon_local.flags.loggingMode = DLT_LOG_TO_SYSLOG;
+          log_init_result = dlt_log_init(daemon_local.flags.loggingMode);
+          if (log_init_result != DLT_RETURN_OK) {
+            fprintf(stderr, "Failed to setup syslog logging, internal logs will "
+                            "not be available\n");
+          }
+      }
+#endif
+    }
 
     /* Print version information */
     dlt_get_version(version, DLT_DAEMON_TEXTBUFSIZE);
@@ -955,7 +973,7 @@ int main(int argc, char *argv[])
     if (dlt_mkdir_recursive(dltFifoBaseDir) != 0) {
         dlt_vlog(LOG_ERR, "Base dir %s cannot be created!\n", dltFifoBaseDir);
         return -1;
-    }
+  }
 
 #else
     if (dlt_mkdir_recursive(DLT_USER_IPC_PATH) != 0) {

src/daemon/dlt.conf

@@ -46,6 +46,8 @@ LoggingMode = 0
 LoggingLevel = 6
 
 # The logging filename if internal logging mode is log to file (Default: /tmp/dlt.log)
+# If access to the file is not possible, the daemon will fall back to syslog
+# if WITH_DLT_FILE_LOGGING_SYSLOG_FALLBACK is set as compile flag
 LoggingFilename = /tmp/dlt.log
 
 # Timeout on send to client (sec)

src/shared/dlt_common.c

@@ -1803,11 +1803,11 @@ void dlt_print_with_attributes(bool state)
     print_with_attributes = state;
 }
 
-void dlt_log_init(int mode)
+DltReturnValue dlt_log_init(int mode)
 {
     if ((mode < DLT_LOG_TO_CONSOLE) || (mode > DLT_LOG_DROPPED)) {
         dlt_vlog(LOG_WARNING, "Wrong parameter for mode: %d\n", mode);
-        return;
+        return DLT_RETURN_WRONG_PARAMETER;
     }
 
     logging_mode = mode;
@@ -1818,14 +1818,16 @@ void dlt_log_init(int mode)
 
         if (logging_handle == NULL) {
             dlt_user_printf("Internal log file %s cannot be opened!\n", logging_filename);
-            return;
+            return DLT_RETURN_ERROR;
         }
     }
+
+    return DLT_RETURN_OK;
 }
 
 void dlt_log_free(void)
 {
-    if (logging_mode == DLT_LOG_TO_FILE)
+    if (logging_mode == DLT_LOG_TO_FILE && logging_handle)
         fclose(logging_handle);
 }