UpdateVirtualSensor uses information from signals

UpdateVirtualSensor uses information obtained from signals to avoid
extensive dbus queries.

Tested:
1:Execute DBus cmd to see if VirtualSensor can correctly obtain the
value of DbusSensor
    busctl tree xyz.openbmc_project.VirtualSensor
    busctl introspect xyz.openbmc_project.VirtualSensor xxx
2:Waiting for the value change of DbusSensor,Check if the value of
the virtual sensor has changed after the dbusSensor changes.

Fixes openbmc/phosphor-virtual-sensor#1

Change-Id: If11f9017b31ce5cf06f910a38c65637c55d74b24
Signed-off-by: Tao Lin <lintao.lc@ieisystem.com>
diff --git a/dbusUtils.cpp b/dbusUtils.cpp
new file mode 100644
index 0000000..ea3879a
--- /dev/null
+++ b/dbusUtils.cpp
@@ -0,0 +1,81 @@
+#include "dbusUtils.hpp"
+
+#include <xyz/openbmc_project/ObjectMapper/common.hpp>
+
+const char* propIntf = "org.freedesktop.DBus.Properties";
+const char* mapperBusName = "xyz.openbmc_project.ObjectMapper";
+const char* mapperPath = "/xyz/openbmc_project/object_mapper";
+const char* mapperIntf =
+    sdbusplus::common::xyz::openbmc_project::ObjectMapper::interface;
+
+const char* methodGetObject = "GetObject";
+const char* methodGet = "Get";
+const char* methodSet = "Set";
+
+using namespace sdbusplus::xyz::openbmc_project::Common::Error;
+
+std::string getService(sdbusplus::bus_t& bus, const std::string& path,
+                       const char* intf)
+{
+    /* Get mapper object for sensor path */
+    auto mapper = bus.new_method_call(mapperBusName, mapperPath, mapperIntf,
+                                      methodGetObject);
+
+    mapper.append(path.c_str());
+    mapper.append(std::vector<std::string>({intf}));
+
+    std::unordered_map<std::string, std::vector<std::string>> resp;
+
+    try
+    {
+        auto msg = bus.call(mapper);
+        msg.read(resp);
+    }
+    catch (const sdbusplus::exception_t& ex)
+    {
+        if (ex.name() == std::string(sdbusplus::xyz::openbmc_project::Common::
+                                         Error::ResourceNotFound::errName))
+        {
+            // The service isn't on D-Bus yet.
+            return std::string{};
+        }
+        else if (ex.name() == std::string("org.freedesktop.DBus.Error.Timeout"))
+        {
+            lg2::info("Mapper timeout while looking up {PATH}", "PATH", path);
+            return std::string{};
+        }
+
+        throw;
+    }
+
+    if (resp.begin() == resp.end())
+    {
+        // Shouldn't happen, if the mapper can't find it it is handled above.
+        throw std::runtime_error("Unable to find Object: " + path);
+    }
+
+    return resp.begin()->first;
+}
+
+int setDbusProperty(sdbusplus::bus_t& bus, const std::string& service,
+                    const std::string& path, const std::string& intf,
+                    const std::string& property, const Value& value)
+{
+    try
+    {
+        auto method = bus.new_method_call(service.c_str(), path.c_str(),
+                                          propIntf, methodSet);
+        method.append(intf, property, value);
+        auto msg = bus.call(method);
+    }
+    catch (const sdbusplus::exception_t& e)
+    {
+        lg2::error(
+            "Faild to set dbus property. service:{SERVICE} path:{PATH} intf:{INTF} Property:{PROP},{ERROR}",
+            "SERVICE", service, "PATH", path, "INTF", intf, "PROP", property,
+            "ERROR", e);
+        return -1;
+    }
+
+    return 0;
+}