[chassisd] Add script to initialize chassis info in STATE_DB (sonic-net#183)

#### Description
I added a new script `chassis_db_init` that uploads chassis hardware information such as serial number, model number and hardware revision to the STATE_DB under the CHASSIS_INFO table. 

#### Motivation and Context
I made this change in order to expose the chassis hardware information to SONiC user space and allow CLI utilities to access it in order to expose it to the user.

Author: alexrallen

sonic-chassisd/scripts/chassis_db_init

@@ -0,0 +1,105 @@
+#!/usr/bin/env python3
+
+"""
+    chassis_db_init
+    Chassis information update tool for SONiC
+    This tool runs one time at the launch of the platform monitor in order to populate STATE_DB with chassis information such as model, serial number, and revision.
+"""
+
+try:
+    import os
+    import sys
+
+    from sonic_py_common import daemon_base, logger
+
+    # If unit testing is occurring, mock swsscommon and module_base
+    if os.getenv("CHASSIS_DB_INIT_UNIT_TESTING") == "1":
+        from tests import mock_swsscommon as swsscommon
+    else:
+        from swsscommon import swsscommon
+except ImportError as e:
+    raise ImportError(str(e) + " - required module not found")
+
+#
+# Constants
+#
+
+SYSLOG_IDENTIFIER = "chassis_db_init"
+
+CHASSIS_INFO_TABLE = 'CHASSIS_INFO'
+CHASSIS_INFO_KEY_TEMPLATE = 'chassis {}'
+CHASSIS_INFO_CARD_NUM_FIELD = 'module_num'
+CHASSIS_INFO_SERIAL_FIELD = 'serial'
+CHASSIS_INFO_MODEL_FIELD = 'model'
+CHASSIS_INFO_REV_FIELD = 'revision'
+
+CHASSIS_LOAD_ERROR = 1
+
+NOT_AVAILABLE = 'N/A'
+
+#
+# Helper functions =============================================================
+#
+
+# try get information from platform API and return a default value if caught NotImplementedError
+
+
+def try_get(callback, *args, **kwargs):
+    """
+    Handy function to invoke the callback and catch NotImplementedError
+    :param callback: Callback to be invoked
+    :param args: Arguments to be passed to callback
+    :param kwargs: Default return value if exception occur
+    :return: Default return value if exception occur else return value of the callback
+    """
+    default = kwargs.get('default', NOT_AVAILABLE)
+    try:
+        ret = callback(*args)
+        if ret is None:
+            ret = default
+    except NotImplementedError:
+        ret = default
+
+    return ret
+
+#
+# Functions
+# 
+
+def provision_db(platform_chassis, log):
+    # Init state db connection
+    state_db = daemon_base.db_connect("STATE_DB")
+    chassis_table = swsscommon.Table(state_db, CHASSIS_INFO_TABLE)
+
+    # Populate DB with chassis hardware info 
+    fvs = swsscommon.FieldValuePairs([
+                                        (CHASSIS_INFO_SERIAL_FIELD, try_get(platform_chassis.get_serial)),
+                                        (CHASSIS_INFO_MODEL_FIELD, try_get(platform_chassis.get_model)),
+                                        (CHASSIS_INFO_REV_FIELD, try_get(platform_chassis.get_revision))
+                                    ])
+    chassis_table.set(CHASSIS_INFO_KEY_TEMPLATE.format(1), fvs)
+    log.log_info("STATE_DB provisioned with chassis info.")
+
+    return chassis_table
+
+
+#
+# Main
+#
+
+def main():
+    log = logger.Logger(SYSLOG_IDENTIFIER)
+    log.log_info("Provisioning Database with Chassis Info...")
+
+    # Load platform api class
+    try:
+        import sonic_platform.platform
+        platform_chassis = sonic_platform.platform.Platform().get_chassis()
+    except Exception as e:
+        log.log_error("Failed to load chassis due to {}".format(repr(e)))
+        sys.exit(CHASSIS_LOAD_ERROR)
+
+    provision_db(platform_chassis, log)
+
+if __name__ == '__main__':
+    main()

sonic-chassisd/setup.py

@@ -15,6 +15,7 @@
     ],
     scripts=[
         'scripts/chassisd',
+        'scripts/chassis_db_init'
     ],
     setup_requires=[
         'pytest-runner',

sonic-chassisd/tests/mock_platform.py

@@ -92,3 +92,12 @@ def get_module_index(self, module_name):
 
     def init_midplane_switch(self):
         return True
+
+    def get_serial(self):
+        return "Serial No"
+
+    def get_model(self):
+        return "Model A"
+
+    def get_revision(self):
+        return "Rev C"

sonic-chassisd/tests/test_chassis_db_init.py

@@ -0,0 +1,38 @@
+import os
+import sys
+from imp import load_source
+
+from mock import Mock, MagicMock, patch
+from sonic_py_common import daemon_base
+
+from .mock_platform import MockChassis, MockModule
+from .mock_module_base import ModuleBase
+
+SYSLOG_IDENTIFIER = 'chassis_db_init_test'
+NOT_AVAILABLE = 'N/A'
+
+daemon_base.db_connect = MagicMock()
+
+test_path = os.path.dirname(os.path.abspath(__file__))
+modules_path = os.path.dirname(test_path)
+scripts_path = os.path.join(modules_path, "scripts")
+sys.path.insert(0, modules_path)
+
+os.environ["CHASSIS_DB_INIT_UNIT_TESTING"] = "1"
+load_source('chassis_db_init', scripts_path + '/chassis_db_init')
+from chassis_db_init import *
+
+
+def test_provision_db():
+    chassis = MockChassis()
+    log = MagicMock()
+    serial = "Serial No"
+    model = "Model A"
+    revision = "Rev C"
+
+    chassis_table = provision_db(chassis, log)
+
+    fvs = chassis_table.get(CHASSIS_INFO_KEY_TEMPLATE.format(1))
+    assert serial == fvs[CHASSIS_INFO_SERIAL_FIELD]
+    assert model == fvs[CHASSIS_INFO_MODEL_FIELD]
+    assert revision == fvs[CHASSIS_INFO_REV_FIELD]