AP_HAL: use ExpandingString class

libraries/AP_HAL/CANIface.h

@@ -20,6 +20,8 @@
 #include <stdint.h>
 #include "AP_HAL_Namespace.h"
 
+class ExpandingString;
+
 /**
  * Raw CAN frame, as passed to/from the CAN driver.
  */
@@ -191,10 +193,7 @@ public:
     }
 
     //Get status info of the interface
-    virtual uint32_t get_stats(char* data, uint32_t max_size)
-    {
-        return 0;
-    }
+    virtual void get_stats(ExpandingString &str) {}
 
     // return true if busoff was detected and not cleared
     virtual bool is_busoff() const

libraries/AP_HAL/Util.h

@@ -3,6 +3,8 @@
 #include <stdarg.h>
 #include "AP_HAL_Namespace.h"
 
+class ExpandingString;
+
 class AP_HAL::Util {
 public:
     int snprintf(char* str, size_t size,
@@ -183,10 +185,10 @@ public:
     virtual bool trap() const { return false; }
 
     // request information on running threads
-    virtual size_t thread_info(char *buf, size_t bufsize) { return 0; }
+    virtual void thread_info(ExpandingString &str) {}
 
     // request information on dma contention
-    virtual size_t dma_info(char *buf, size_t bufsize) { return 0; }
+    virtual void dma_info(ExpandingString &str) {}
 
 protected:
     // we start soft_armed false, so that actuators don't send any