AP_HAL_Linux: add function to check if path is chardev

Utility function to allow checking if a certain path is a character
device.

libraries/AP_HAL_Linux/Util.cpp

@@ -2,6 +2,7 @@
 #if CONFIG_HAL_BOARD == HAL_BOARD_LINUX
 #include <stdio.h>
 #include <stdarg.h>
+#include <sys/stat.h>
 #include <unistd.h>
 #include <stdlib.h>
 #include <errno.h>
@@ -62,4 +63,14 @@ void LinuxUtil::set_system_clock(uint64_t time_utc_usec)
 #endif    
 }
 
+bool LinuxUtil::is_chardev_node(const char *path)
+{
+    struct stat st;
+
+    if (!path || lstat(path, &st) < 0)
+        return false;
+
+    return S_ISCHR(st.st_mode);
+}
+
 #endif // CONFIG_HAL_BOARD == HAL_BOARD_LINUX

libraries/AP_HAL_Linux/Util.h

@@ -31,6 +31,8 @@ public:
      */
     void set_system_clock(uint64_t time_utc_usec);
 
+    bool is_chardev_node(const char *path);
+
 private:
 	static Linux::ToneAlarm _toneAlarm;
     int saved_argc;