[mssonicbld]

Description of PR

Summary:
Fixes a self-match bug in bmc_log_zgrep (tests/common/platform/bmc_utils.py).

bmc_log_zgrep runs its zgrep via duthost.shell(...). Ansible logs every shell/command module invocation to syslog, echoing the full command line (including the search pattern) in a line like:

<date> sonic INFO python3.13[725497]: ansible-ansible.legacy.command Invoked with _raw_params=zgrep -hI -E 'Mirroring TEMPERATURE_INFO to BMC STATE_DB' /var/log/syslog* ...

Because that line contains the search pattern verbatim, zgrep matches its OWN command-invocation syslog entry (a self-match), so the function returns a non-empty string even when the real daemon log line is absent. In test_thermalctld_chassis_thermal_monitoring this defeats the if not mirror_init_log: pytest.skip(...) guard, so the test proceeds, finds 0 real TEMPERATURE_INFO|* keys in STATE_DB, and FAILS instead of SKIPPING.

Fixes # (issue)

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• New Test case
  • Skipped for non-supported platforms
• Test case improvement

Back port request

• 202205
• 202305
• 202311
• 202405
• 202411
• 202505
• 202511
• 202608

Approach

What is the motivation for this PR?

Prevent bmc_log_zgrep from matching Ansible's own command-invocation syslog line, which produced false-positive non-empty results and caused tests relying on the empty-result skip guard to fail incorrectly.

How did you do it?

In bmc_log_zgrep, the zgrep output is now piped through grep -vE 'ansible-ansible\.legacy\.(command|shell)' before tail, dropping Ansible's command/shell invocation lines so the function cannot self-match.

Because the pipeline's rc is now grep -v's / tail's rc (and grep -v returns rc=1 when it legitimately filters away all lines), the previous if r.get('rc') == 0 gate would wrongly discard valid empty results. The return logic now simply returns the stripped stdout regardless of rc (empty stdout already means "no match"). module_ignore_errors=True is retained, and the docstring documents the filtering.

How did you verify/test it?

• python -c "import ast; ast.parse(open('tests/common/platform/bmc_utils.py').read())" — parses OK.
• python -m flake8 --max-line-length=120 tests/common/platform/bmc_utils.py — no findings.

Any platform specific information?

No. This is a SmartSwitch/BMC test utility change; no platform-specific behavior.

Supported testbed topology if it's a new test case?

N/A — not a new test case.

Documentation

N/A — updated the function docstring to note that Ansible's command-invocation syslog lines are filtered out to avoid self-matching.

Signed-off-by: Sonic Build Admin sonicbld@microsoft.com

[mssonicbld]

Original PR: sonic-net/sonic-mgmt#28530

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