config interface breakout fails validation if a static IP is set on the management interface (eth0) without a corresponding MGMT_PORT block.

[univac490]

Severity: Major (Blocks port configuration)

Component: swssconfig, portmgrd (Configuration Validator)

Description:
On a clean install, if a static IP address is configured for the management port eth0, an entry is created in the MGMT_INTERFACE table of the database.

However, no corresponding entry is created in the MGMT_PORT table.

This causes the config interface breakout command to fail its validation check, as it seems to expect a MGMT_PORT entry for every MGMT_INTERFACE entry. The command fails with a ConfigMgmt Class creation failed error, preventing any port breakouts.

Steps to Reproduce:

1. Start with a clean, stable switch (management on DHCP).
2. Assign a static IP to the management port:
   sudo config interface ip add eth0 10.18.0.36/23 10.18.0.1
3. Save the configuration:
   sudo config save -y
4. Attempt to break out any data port:
   sudo config interface breakout Ethernet240 '1x100G(4)'

Expected Behavior:
The breakout command should succeed. The configuration of the management port (eth0) should be irrelevant to a data port (Ethernet240) breakout operation.

Actual Behavior:
The breakout command fails with a configuration validation error. The log shows ConfigMgmt Class creation failed and leafref errors, indicating the validator is unhappy with the MGMT_INTERFACE entry not having a MGMT_PORT counterpart.

Workaround:
The validation bug can be fixed by manually adding a MGMT_PORT block to /etc/sonic/config_db.json and reloading the config:

"MGMT_PORT": {
    "eth0": {
        "alias": "eth0",
        "admin_status": "up"
    }
}

After running sudo config reload, the breakout command works as expected.

Suggested Fix:
The configuration logic should be fixed in one of two ways:

1. Fix the Validator: The config validator should be modified to not require a MGMT_PORT entry when a MGMT_INTERFACE entry exists. The presence of eth0 in the MGMT_INTERFACE table should be sufficient.
2. Fix the config command: Alternatively, when the sudo config interface ip add eth0... command is executed, it should automatically create the corresponding default MGMT_PORT block (e.g., with "alias": "eth0") to ensure the configuration remains valid.