udev-util: add wrapper for sd_device_get_property_value()

... that allows to pass additional properties to fall back to.

src/shared/udev-util.c

@@ -410,3 +410,30 @@ int device_get_model_string(sd_device *device, const char **ret) {
 
         return -ENOENT;
 }
+
+int device_get_property_value_with_fallback(
+                sd_device *device,
+                const char *prop,
+                Hashmap *extra_props,
+                const char **ret) {
+        const char *value;
+        int r;
+
+        assert(device);
+        assert(prop);
+        assert(ret);
+
+        r = sd_device_get_property_value(device, prop, &value);
+        if (r < 0) {
+                if (r != -ENOENT)
+                        return r;
+
+                value = hashmap_get(extra_props, prop);
+                if (!value)
+                        return -ENOENT;
+        }
+
+        *ret = value;
+
+        return 1;
+}

src/shared/udev-util.h

@@ -3,6 +3,7 @@
 
 #include "sd-device.h"
 
+#include "hashmap.h"
 #include "time-util.h"
 
 int udev_set_max_log_level(char *str);
@@ -25,3 +26,9 @@ bool udev_available(void);
 
 int device_get_vendor_string(sd_device *device, const char **ret);
 int device_get_model_string(sd_device *device, const char **ret);
+
+int device_get_property_value_with_fallback(
+                sd_device *device,
+                const char *prop,
+                Hashmap *extra_props,
+                const char **ret);