lvm2: add debug logging for all LVM2 command lines

[tasleson]

Introduce two new debug subsystems for LVM2 command tracing:

--debug=lvm2 Log every command line and its stdout on success.
--debug=lvm2err Log only commands that fail, with their stderr.

All logging is centralised in _Lvm2._run() so every subprocess invocation is covered. Command lines are formatted with shlex.join(). Both subsystems are included in --debug=all but can be enabled independently for fine-grained control.

Resolves: #979

Assisted-by: Claude noreply@anthropic.com

Summary by CodeRabbit

Release Notes

New Features

• Added new LVM2-specific debug flags and logging subsystems for extended debugging capabilities
• Extended debug support to include "lvm2" and "lvm2err" debug categories
• Implemented automatic capture and logging of LVM2 command details including execution information, output, and error diagnostics

[packit-as-a-service]

Congratulations! One of the builds has completed. 🍾

You can install the built RPMs by following these steps:

• sudo dnf install -y 'dnf*-command(copr)'
• dnf copr enable packit/snapshotmanager-snapm-994
• And now you can install the packages.

Please note that the RPMs should be used only in a testing environment.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: cdfd0900-e37d-4d32-bff8-d1923de220b8

📥 Commits

Reviewing files that changed from the base of the PR and between 05645ca and 29b14e4.

📒 Files selected for processing (4)

• snapm/_snapm.py
• snapm/command.py
• snapm/manager/plugins/lvm2.py
• tests/test_command.py

Walkthrough

The pull request extends the debugging infrastructure by introducing two new debug mask flags (SNAPM_DEBUG_LVM2 and SNAPM_DEBUG_LVM2_ERR) and corresponding logging subsystems. These flags are wired into the command-line debug selector and used in the LVM2 plugin to emit debug logs for executed commands and captured error output.

Changes

Cohort / File(s)	Summary
Debug Infrastructure snapm/_snapm.py, snapm/command.py	Added constants SNAPM_DEBUG_LVM2, SNAPM_DEBUG_LVM2_ERR and subsystem names SNAPM_SUBSYSTEM_LVM2, SNAPM_SUBSYSTEM_LVM2_ERR; updated global debug mask and subsystem mapping; extended command-line debug selector to recognise "lvm2" and "lvm2err" options.
LVM2 Plugin Logging snapm/manager/plugins/lvm2.py	Added module-level logger and debug logging in _Lvm2._run() to emit command-line strings on execution, decode and log stderr on errors, and conditionally emit failure details to "lvm2err" subsystem based on debug mask.
Test Updates tests/test_command.py	Updated test_set_debug_list to include "lvm2" and "lvm2err" in the debug selector list assertion.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• snapm: fix masked debug logging to be independent of module load order #524: Refactors debug subsystem API by introducing subsystem name constants and updating the debug mask mapping infrastructure that this PR builds upon.
• snapm: add fsdiff snapshot set comparison facility #620: Adds analogous debug constants and subsystem strings for a different subsystem, following the same pattern extended here.

Suggested labels

enhancement, Debugging, Plugin Integration

Poem

🐰 Hops with glee

New debug flags hop into view,
LVM2 commands now logged too,
When errors arise, they're captured with care,
A rabbit's delight—transparency everywhere! 🔍

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and clearly describes the primary change: adding debug logging for LVM2 command lines, which matches the core objective of centralising LVM2 command logging.
Linked Issues check	✅ Passed	The pull request fully addresses issue #979 by implementing central debug logging for all LVM2 command lines in the _Lvm2._run() method, with controllable subsystems (--debug=lvm2 and --debug=lvm2err).
Out of Scope Changes check	✅ Passed	All changes are within scope: new debug constants, debug subsystem support in command handling, logging implementation in lvm2.py, and corresponding test updates are all directly related to the central LVM2 debug logging objective.
Docstring Coverage	✅ Passed	Docstring coverage is 83.33% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[bmr-cymru]

Rebased to current main to pick up GitHub CI fix.