[sonic-py-common] get_platform(): Refactor method of retrieving platform identifier

platform/vs/docker-sonic-vs/Dockerfile.j2

@@ -145,4 +145,8 @@ RUN rm /etc/frr/frr.conf
 # Create /var/warmboot/teamd folder for teammgrd
 RUN mkdir -p /var/warmboot/teamd
 
+# Set an environment variable which applications can use to
+# determine that the environment is virtualized
+ENV SONIC_DOCKER_VIRTUAL_SWITCH=1
+
 ENTRYPOINT ["/usr/bin/supervisord"]

src/sonic-py-common/sonic_py_common/daemon_base.py

@@ -56,7 +56,7 @@ def load_platform_util(self, module_name, class_name):
         platform_util = None
 
         # Get path to platform and hwsku
-        (platform_path, hwsku_path) = device_info.get_paths_to_platform_and_hwsku()
+        (platform_path, hwsku_path) = device_info.get_paths_to_platform_and_hwsku_dirs()
 
         try:
             module_file = "/".join([platform_path, "plugins", module_name + ".py"])

src/sonic-py-common/sonic_py_common/device_info.py

@@ -29,6 +29,23 @@
 BACKEND_ASIC_SUB_ROLE = "BackEnd"
 
 
+def in_docker_container():
+    """
+    Returns:
+        True if running in a Docker container on a SONiC device, else False
+        Note that we also check if we are running in a SONiC virtual switch,
+        which itself is in a Docker container. In this case, we are technically
+        in the 'host OS', even though it is containerized.
+    """
+    with open("/proc/1/cgroup", "r") as f:
+        contents = f.read()
+        if "docker" in contents or "kubepods" in contents:
+            if os.getenv("SONIC_DOCKER_VIRTUAL_SWITCH", "0") == "0":
+                return True
+
+    return False
+
+
 def get_machine_info():
     """
     Retreives data from the machine configuration file
@@ -58,12 +75,28 @@ def get_platform():
     Returns:
         A string containing the device's platform identifier
     """
-    machine_info = get_machine_info()
-    if machine_info:
-        if 'onie_platform' in machine_info:
-            return machine_info['onie_platform']
-        elif 'aboot_platform' in machine_info:
-            return machine_info['aboot_platform']
+
+    # If we are running in a container, we won't have access
+    # to machine.conf, so instead we try reading the platform
+    # identifier from Config DB
+    if in_docker_container():
+        try:
+            config_db = ConfigDBConnector()
+            config_db.connect()
+
+            metadata = config_db.get_table('DEVICE_METADATA')
+
+            if 'localhost' in metadata and 'platform' in metadata['localhost']:
+                return metadata['localhost']['platform']
+        except Exception:
+            pass
+    else:
+        machine_info = get_machine_info()
+        if machine_info:
+            if 'onie_platform' in machine_info:
+                return machine_info['onie_platform']
+            elif 'aboot_platform' in machine_info:
+                return machine_info['aboot_platform']
 
     return None