dm: Add bd_dm_get_thin_pool_stats for generic thin pools

[vojtechtrefny]

Adds a way to query physical space usage of a device mapper thin pool directly via libdevmapper, without requiring the pool to be managed by LVM. The new BDDMThinPoolStats struct reports used/total data and metadata block counts together with the pool status flags.

Resolves: #444

Summary by CodeRabbit

• New Features

  • Added an API to retrieve device-mapper thin-pool statistics, including metadata and data usage, capacity, and pool status indicators.
  • Added support for copying and freeing thin-pool statistics data.

• Documentation

  • Documented the new thin-pool statistics API and data type.

• Tests

  • Added coverage for successful statistics retrieval and expected errors for invalid or unsupported device maps.

[coderabbitai]

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 7ce6c6e and b951858.

📒 Files selected for processing (5)

• docs/libblockdev-sections.txt
• src/lib/plugin_apis/dm.api
• src/plugins/dm.c
• src/plugins/dm.h
• tests/dm_test.py

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📝 Walkthrough

Walkthrough

The dm plugin adds a boxed BDDMThinPoolStats type and bd_dm_get_thin_pool_stats. The implementation queries and parses device-mapper thin-pool status. Tests cover valid statistics and invalid map types. Gtk-doc sections list the new symbols.

Changes

Thin-pool statistics

Layer / File(s)	Summary
Public statistics contract src/lib/plugin_apis/dm.api, src/plugins/dm.h	Defines BDDMThinPoolStats, boxed type helpers, copy/free functions, and the bd_dm_get_thin_pool_stats declaration.
Device-mapper status implementation src/plugins/dm.c	Queries map status, verifies the thin-pool target, parses status values, populates statistics, and reports errors.
Validation and API documentation tests/dm_test.py, docs/libblockdev-sections.txt	Creates test thin pools, validates statistics and error cases, and adds gtk-doc entries for the new symbols.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: 🟡 Moderate · up to b9518

The PR adds thin-pool statistics support, but the standalone DM header currently advertises a type helper that the standalone plugin does not provide, creating a bounded integration risk for consumers and potentially causing link failures. This should be corrected before merging.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 72.73% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 11 functions across 3 files. (2 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the device-mapper change and names the primary API, bd_dm_get_thin_pool_stats, for generic thin pools.
Linked Issues check	✅ Passed	The pull request satisfies issue #444 by adding bd_dm_get_thin_pool_stats and BDDMThinPoolStats to report used and total data and metadata blocks for generic device-mapper thin pools. It also adds err…
Out of Scope Changes check	✅ Passed	The changes are limited to the API declaration, implementation, public header, documentation, and tests required to retrieve and manage thin-pool statistics. No unrelated changes are present.

Full details: Linked Issues check

Explanation

The pull request satisfies issue #444 by adding bd_dm_get_thin_pool_stats and BDDMThinPoolStats to report used and total data and metadata blocks for generic device-mapper thin pools. It also adds error handling, lifecycle helpers, documentation, and tests.

Full details: Docstring Coverage

Explanation

Docstring coverage is 72.73% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 11 functions across 3 files. (2 skipped: 2 unsupported.)

• Fix all pre-merge checks with AI

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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