internal-logging: Fix issues with file logging (#378)

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

Signed-off-by: Alexander Mohr <alexander.m.mohr@mercedes-benz.com>

3 files changed, 28 insertions, 6 deletions

diff --git a/src/daemon/dlt-daemon.c b/src/daemon/dlt-daemon.c
index 35fb024..2c9ff6a 100644
--- a/src/daemon/dlt-daemon.c
+++ b/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) {
diff --git a/src/daemon/dlt.conf b/src/daemon/dlt.conf
index 7e19817..777aa82 100644
--- a/src/daemon/dlt.conf
+++ b/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)
diff --git a/src/shared/dlt_common.c b/src/shared/dlt_common.c
index adda5db..57455fa 100644
--- a/src/shared/dlt_common.c
+++ b/src/shared/dlt_common.c
@@ -1814,11 +1814,11 @@ 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;
@@ -1829,14 +1829,16 @@ 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);
 }