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multi-asic_aware_module_requirements.md

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Requirements for designing a customized ansible module to support multi-ASIC

PR sonic-net/SONiC#644 introduced the HLD to support multi ASIC. In the future, multi DUT or Chassis will be supported by SONiC as well. Some of the customized ansible modules need to be updated to support testing of the upcoming new architectures. This document tries to propose some requirements for designing customized ansible modules that need to deal with multi-ASIC. The target is to have a clean and easy to use interface for calling these ansible modules in scripts testing multi DUT and multi ASIC system. Meanwhile, the ansible modules need to maintain backward compatibility for single DUT and single ASIC testing.

Requirements

To support multi-ASIC SONiC testing, some of the customized ansible modules need to be updated to support ASIC/namespace. Based on the design of MultiAsicSonicHost and SonicAsic, the ASIC/namespace aware modules must follow below requirements:

  • The module must take optional argument for specifying ASIC index or namespace.
  • When ASIC index or namespace is specified, return the the ansible_facts of the specified ASIC/namespace.
  • When ASIC index is not specified, return the ansible_facts for the global ASIC/namespace, do not return ansible_facts for ASIC 0.

Why not return a list of results for all ASICs when ASIC index or namespace is not specified? There are 2 reasons:

  • Ansible requires that the returned ansible_facts must be a dictionary. It cannot be a list.
  • For multi-ASIC SONiC, there is global namespace. It makes more sense to return result of the global namespace. The object holding the list of ASICs can take care of getting results for all ASICs.
  • Just return result of the global ASIC/namespace can maintain backward compatibility for single ASIC SONiC device.

Why not return result for ASIC0 when ASIC/namespace is not specified?

  • For multi-ASIC SONiC, the global namespace is not equivalent to namespace of ASIC 0.

There is no strict require of argument name for specifying ASIC index or namespace. The argument name can be like: instance_id, asic_index, namespace_id,etc. Which argument to be use should be taken care of by methods in new class for ASIC/namespace specific operations. More details will be covered in upcoming design documents to support multi-DUT and multi-ASIC testing.

Possible interfaces for calling the modules

This section tries to add some dummy examples for how to call the multi ASCI aware ansible modules in test scripts. Assume:

  • module foo is a multi ASIC aware customized ansible module
  • module xyz is a none-multi-ASIC aware ansible module
  • fixture duthost is an instance representing single host with single or multiple ASIC. It should be an instance of new class like MultiAsicSonicHost. This new class delegates all none-multi-ASIC related calls to the existing SonicHost class.
  • fixture duthosts is an instance representing a testbed with multi DUTs or a Chassis. The duthosts have attributes like:
    • duthosts.nodes: A list of all the hosts in the testbed.
    • duthosts.frontend_nodes: A list of all the frontend hosts in the testbed.

Call ordinary ansible module on single host

duthost.xyz()  # No behavior change, for backward compatibility

Call ASIC/namespace aware module on single host

duthost.foo()  # Run `foo` for the global ASIC/namespace.

duthost.foo(asic_index=0)  # Run `foo` for asic_index=0, and return a single result.

duthost.foo(asic_index="all")  # Run `foo` for all ASICs, and return a list of results.

Call the module for multiple hosts support multiple ASICs

# Run `foo` for global ASIC/namespace for each of the frontend nodes. Return results in a dict like:
#     {'node1': global_foo_result, 'node2': global_foo_result}
duthosts.foo()

# Equivalent to
{node.hostname: node.foo() for node in duthosts.frontend_nodes}

# Run `foo` for asic_index=0 for each of the frontend nodes. Return results in a dict like:
#     {'node1': asic0_foo_result, 'node2': asic0_foo_result}
duthosts.foo(asic_index=0)

# Equivalent to
{node.hostname: node.foo(asic_index=0) for node in duthosts.frontend_nodes}

# Run `foo` for all ASICs on all frontend nodes. Return results in a dict like:
#     {'node1': [asic0_foo_result, asic1_foo_result, ...], 'node2': [asic0_foo_result, asic1_foo_result, ...]}
duthosts.foo(asic_index="all")

# Equivalent to
{node.hostname: node.foo(asic_index="all") for node in duthosts.frontend_nodes}

How to detect a multi ASIC system

According to sonic-net/SONiC#644, multi ASIC system should have file /usr/share/sonic/device/<platform>/asic.conf:

Sample asic.conf:

NUM_ASIC=3
DEV_ID_ASIC_0=03:00.0
DEV_ID_ASIC_1=06:00.0
DEV_ID_ASIC_2=11:00.0

Ansible module can check existence of this file to tell the current host is a multi ASIC system or single ASIC system.

Content like NUM_ASIC=3 in asic.conf indicates the number of ASICs the current system has.

The ansible module also can take advantage of the sonic_py_common package on the SONiC image. This package has modules like device_info and multi_asic that can be handy.

admin@sonic-host1:~$ python
Python 2.7.16 (default, Oct 10 2019, 22:02:15)
[GCC 8.3.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from sonic_py_common import device_info, multi_asic
>>> dir(device_info)
['ASIC_CONF_FILENAME', 'BACKEND_ASIC_SUB_ROLE', 'CONTAINER_PLATFORM_PATH', 'ConfigDBConnector', 'FRONTEND_ASIC_SUB_ROLE', 'HOST_DEVICE_PATH', 'MACHINE_CONF_PATH', 'NAMESPACE_PATH_GLOB', 'NPU_NAME_PREFIX', 'PLATFORM_JSON_FILE', 'PORT_CONFIG_FILE', 'SONIC_VERSION_YAML_PATH', 'SonicDBConfig', 'USR_SHARE_SONIC_PATH', '__builtins__', '__doc__', '__file__', '__name__', '__package__', '_valid_mac_address', 'get_all_namespaces', 'get_asic_conf_file_path', 'get_hwsku', 'get_machine_info', 'get_namespaces', 'get_npu_id_from_name', 'get_num_npus', 'get_path_to_port_config_file', 'get_paths_to_platform_and_hwsku_dirs', 'get_platform', 'get_platform_and_hwsku', 'get_sonic_version_info', 'get_system_mac', 'get_system_routing_stack', 'glob', 'is_multi_npu', 'natsorted', 'os', 're', 'subprocess', 'yaml']
>>> device_info.get_num_npus()
1
>>> device_info.is_multi_npu()
False
>>> dir(multi_asic)
['ASIC_CONF_FILENAME', 'ASIC_NAME_PREFIX', 'BACKEND_ASIC_SUB_ROLE', 'BGP_NEIGH_CFG_DB_TABLE', 'CONTAINER_PLATFORM_PATH', 'ConfigDBConnector', 'DEFAULT_NAMESPACE', 'EXTERNAL_PORT', 'FRONTEND_ASIC_SUB_ROLE', 'HOST_DEVICE_PATH', 'INTERNAL_PORT', 'NAMESPACE_PATH_GLOB', 'NEIGH_DEVICE_METADATA_CFG_DB_TABLE', 'PORT_CFG_DB_TABLE', 'PORT_CHANNEL_CFG_DB_TABLE', 'PORT_ROLE', 'SonicDBConfig', 'SonicV2Connector', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'connect_config_db_for_ns', 'connect_to_all_dbs_for_ns', 'get_all_namespaces', 'get_asic_conf_file_path', 'get_asic_id_from_name', 'get_external_ports', 'get_namespace_for_port', 'get_namespace_list', 'get_namespaces_from_linux', 'get_num_asics', 'get_platform', 'get_port_role', 'get_port_table', 'get_port_table_for_asic', 'glob', 'is_bgp_session_internal', 'is_multi_asic', 'is_port_channel_internal', 'is_port_internal', 'natsorted', 'os']
>>> multi_asic.is_multi_asic()
False
>>> multi_asic.get_num_asics()
1