DataFlash: simplify dataflash initialisation

libraries/DataFlash/DataFlash.cpp

@@ -4,6 +4,7 @@
 
 #include "DataFlash_File.h"
 #include "DataFlash_MAVLink.h"
+#include <GCS_MAVLink/GCS.h>
 
 DataFlash_Class *DataFlash_Class::_instance;
 
@@ -49,6 +50,7 @@ const AP_Param::GroupInfo DataFlash_Class::var_info[] = {
 
 void DataFlash_Class::Init(const struct LogStructure *structures, uint8_t num_types)
 {
+    GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_INFO, "Preparing log system");
 #if CONFIG_HAL_BOARD == HAL_BOARD_SITL
     validate_structures(structures, num_types);
     dump_structures(structures, num_types);
@@ -104,6 +106,10 @@ void DataFlash_Class::Init(const struct LogStructure *structures, uint8_t num_ty
     for (uint8_t i=0; i<_next_backend; i++) {
         backends[i]->Init();
     }
+
+    Prep();
+
+    GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_INFO, "Prepared log system");
 }
 
 #if CONFIG_HAL_BOARD == HAL_BOARD_SITL

libraries/DataFlash/DataFlash.h

@@ -74,10 +74,6 @@ public:
     bool NeedErase(void);
     void EraseAll();
 
-    // possibly expensive calls to start log system:
-    bool NeedPrep();
-    void Prep();
-
     // get a pointer to structures
     const struct LogStructure *get_structures(uint8_t &num_types) {
         num_types = _num_types;
@@ -286,4 +282,8 @@ private:
     void dump_structures(const struct LogStructure *structures, const uint8_t num_types);
 
     void Log_Write_EKF_Timing(const char *name, uint64_t time_us, const struct ekf_timing &timing);
+
+    // possibly expensive calls to start log system:
+    void Prep();
+    bool NeedPrep();
 };

libraries/DataFlash/DataFlash_File.cpp

@@ -397,6 +397,9 @@ void DataFlash_File::Prep_MinSpace()
 #endif
 
 void DataFlash_File::Prep() {
+    if (!NeedPrep()) {
+        return;
+    }
     if (hal.util->get_soft_armed()) {
         // do not want to do any filesystem operations while we are e.g. flying
         return;