HAL_SITL: implement get_system_id()

libraries/AP_HAL_SITL/Util.cpp

@@ -8,3 +8,51 @@ uint64_t HALSITL::Util::get_hw_rtc() const
     const uint64_t nanoseconds = ts.tv_nsec;
     return (seconds * 1000000ULL + nanoseconds/1000ULL);
 }
+
+/*
+  get a (hopefully unique) machine ID
+ */
+bool HALSITL::Util::get_system_id_unformatted(uint8_t buf[], uint8_t &len)
+{
+    char *cbuf = (char *)buf;
+
+    // try first to use machine-id file. Most systems will have this
+    const char *paths[] = { "/etc/machine-id", "/var/lib/dbus/machine-id" };
+    for (uint8_t i=0; i<ARRAY_SIZE(paths); i++) {
+        int fd = open(paths[i], O_RDONLY);
+        if (fd == -1) {
+            continue;
+        }
+        ssize_t ret = read(fd, buf, len);
+        close(fd);
+        if (ret <= 0) {
+            continue;
+        }
+        len = ret;
+        char *p = strchr(cbuf, '\n');
+        if (p) {
+            *p = 0;
+        }
+        len = strnlen(cbuf, len);
+        return true;
+    }
+
+    // fallback to hostname
+    if (gethostname(cbuf, len) != 0) {
+        // use a default name so this always succeeds. Without it we can't
+        // implement some features (such as UAVCAN)
+        strncpy(cbuf, "sitl-unknown", len);
+    }
+    len = strnlen(cbuf, len);
+    return true;
+}
+
+/*
+  as get_system_id_unformatted will already be ascii, we use the same
+  ID here
+ */
+bool HALSITL::Util::get_system_id(char buf[40])
+{
+    uint8_t len = 40;
+    return get_system_id_unformatted((uint8_t *)buf, len);
+}

libraries/AP_HAL_SITL/Util.h

@@ -29,6 +29,9 @@ public:
 
     uint64_t get_hw_rtc() const override;
 
+    bool get_system_id(char buf[40]) override;
+    bool get_system_id_unformatted(uint8_t buf[], uint8_t &len) override;
+    
 private:
     SITL_State *sitlState;
 };