HLD for Shutdown and Startup Fabric module

Signed-off-by: mlok <marty.lok@nokia.com>

doc/pmon/shutdown_and_startup_fabric_design.md

@@ -0,0 +1,66 @@
+# PMON Enhancement -- Shutdown/Startup SFM module
+# High Level Design Document
+### Rev 1.0
+- [About this Manual](#about-this-manual)
+- [Scope](#scope)
+- [Background](#background)
+- [1 Requirements Overview](#1-requirements-overview)
+  * [1.1 Functional Requirements](#11-functional-requirements)
+- [2 Design Details](#2-design-details)
+  * [2.1 Using the existing CLI command "sudo config chassis module shutdown/startup <module_name>" by modifying/enhancing the chassis_module.py](#21-using-the-existing-cli-command--sudo-config-chassis-module-shutdown-startup--module-name---by-modifying-enhancing-the-chassis-modulepy)
+  * [2.2 Modify the vendor specified set_admin_state() in the module.py](#22-modify-the-vendor-specified-set-admin-state---in-the-modulepy)
+  * [2.3 Modify the ModuleUpdater in chassisd.](#23-modify-the-moduleupdater-in-chassisd)
+- [3 Test Considerations](#3-test-considerations)
+- [4 References](#4-references)
+
+<small><i><a href='http://ecotrust-canada.github.io/markdown-toc/'>Table of contents generated with markdown-toc</a></i></small>
+###### Revision
+| Rev |     Date    |       Author                                                                       | Change Description                |
+|:---:|:-----------:|:----------------------------------------------------------------------------------:|-----------------------------------|
+| 1.0 | 05/03/2024  | Marty Lok                                                                   | Initial public version            |
+
+# About this Manual
+This document describes the requirements for reset System Fabric Module (SFM)  on a Chassis and the planned design/code changes for supporting this enhancement.
+
+# Scope
+This scope of this specification is using the existing module shutdown/startup commands and the modification supports resetting of the SFM Module
+
+# Background
+In order to avoid the crash of the Swss/Syncd processes of a SFM module, when a SFM module in a chassis is required to be reseated or hot swapped, a proper shutdown and startup procedure needs to be followed.  
+
+
+# 1 Requirements Overview
+## 1.1 Functional Requirements
+This section describes the requirement for using existing CLI command shutdown/startup a SFM module on a Chassis system.  
+1. Using the existing CLI command "sudo config chassis module shutdown/startup <module_name>" to shutdown/startup a SFM module
+2. Module remains down state if system is booting up with a configuration file which contains a module is set to down state
+
+# 2 Design Details
+The following changes are implementation and modification.
+## 2.1 Using the existing CLI command "sudo config chassis module shutdown/startup <module_name>" by modifying/enhancing the chassis_module.py 
+1. Define and create a new method fabric_module_set_admin_status() with the following actions
+  * Derive a list of ASIC number (asic_list) which is assoicated with this module_name from the CHASSIS_FABRIC_ASIC_TABLE in the CHASSIS_STATE_DB
+  * For shutdown case:
+    - Loop this asic_list and call the "systemctl stop" to stop the related swss@ and syncd@ services.
+    - Delete the related CHASSIS_FABRIC_ASIC_TABLE entries in the CHASSIS_STATE_DB
+    - Loop this asic_list and call the "systemctl start" to start the related swss@ and syncd@ service.
+  * For startup case:
+    - Loop the asic_list and call the "systemctl start" to start the related swss@ and syncd@ service
+2. Modify the existing shutdown_chassis_module() and startup_chassis_module() method to all the fabric_module_set_admin_status()
+  * In order to avoid the raised condition of the chassisd re-populates CHASSIS_FABRIC_ASIC_TABLE entry while the shutdown command is executing, the implementation needs to make sure the new admin_status has been set to Redis DB before proceeds to stop related swss/syncd service and remove the CHASSIS_FABRIC_ASIC_TABLE  entry. The get_config_module_state_timeout() function is introduced to verify the config value setting in Redis DB.
+
+## 2.2 Modify the vendor specified set_admin_state() in the module.py
+Modify the set_admin_state() in module.py for SFM module to shutdown/startup a SFM module. This function is already called by the existing ConfigManagerTask class which subscribes the CHASSIS_MODULE in the CONFIG_DB to shutdown/startup a module when user issues the CLI command "sudo config chassis module shutdown/startup <module_name>" on the Supervisor. 
+
+## 2.3 Modify the ModuleUpdater in chassisd.
+Modify the ModuleUpdater class in chassisd to keep a SFM module in the down state when system is booting up with a configuration which contains a shutdown of a SMF module.
+1. Create and add a new fucntion get_module_admin_status() to get the admin_status from CHASSIS_CONFIG_TABLE in CONFIG_DB
+2. Modify the module_db_update() to call get_module_admin_status() to check the config module. If the module_cfg_status is not set to down, then populate the CH-TBDASSIS_FABRIC_ASIC_TABLE. Otherwise, just ignore it even the SFM module is present. This mechanism prevents the event is triggered in the swss.sh when admin_status is set to down state.
+
+# 3 Test Considerations
+UTs are also added to simulate the Fabric shutdown and startup 
+
+# 4 References
+-TBD
+
+