chore: make d_instantiate_ctx size configurable

[Molter73]

Description

With the changes introduced by #1440, the d_instantiate_ctx map has grown considerably in size. This patch reduces the default size and exposes a method for setting the size at runtime for fine-tweaking.

Checklist

• Patch has a change log entry OR does not need one.
• Investigated and inspected CI test results
• Updated documentation accordingly

Automated testing

• Added unit tests
• Added integration tests
• Added regression tests

If any of these don't apply, please comment below.

Testing Performed

Run fact with --d-inst-size 65535 and use bpftool map show to check the map max_entries is properly set:

31236: lru_hash name d_instantiate_c flags 0x0
key 8B value 12320B max_entries 655535 memlock 8129679272B
btf_id 13108
pids fact(751156)

Summary by CodeRabbit

• New Features

  • Added configuration support for tuning the BPF context map capacity.
  • The setting can be specified through configuration files, environment variables, and command-line options.
  • Defaults to 512 entries when not configured.
  • Invalid or out-of-range values are rejected with an error.

• Bug Fixes

  • Ensured the configured capacity is applied when loading BPF components.

[coderabbitai]

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• fact/src/config/mod.rs

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• fact/src/config/mod.rs

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📝 Walkthrough

Walkthrough

Changes

The PR adds bpf.d_instantiate_ctx_size configuration through YAML, CLI, and environment variables. It validates positive values below u32::MAX, defaults to 512, and applies the value to the eBPF map loader. Tests cover parsing, precedence, updates, defaults, and invalid values.

D-instantiate context map configuration

Layer / File(s)	Summary
Configuration sources and validation fact/src/config/mod.rs	BpfConfig stores and exposes d_instantiate_ctx_size. YAML, CLI, and environment configuration support the setting. Higher-precedence values update the configuration.
Configuration behavior tests fact/src/config/tests.rs	Tests cover parsing, validation, updates, defaults, environment variables, precedence, and invalid values.
Loader and eBPF map wiring fact/src/bpf/mod.rs, fact-ebpf/src/bpf/maps.h	The loader applies the configured map size. The eBPF map declaration defaults to 512 entries.

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

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: making the d_instantiate_ctx map size configurable.
Description check	✅ Passed	The description explains the change, records testing steps, and identifies unit tests, with only non-critical checklist items left unchecked.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 34.23%. Comparing base (fead948) to head (14aba93).

Files with missing lines	Patch %	Lines
fact/src/bpf/mod.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## mauro/ROX-34920/track-symlinks #1453 +/- ##
==================================================================
+ Coverage 33.97% 34.23% +0.26% 
==================================================================
Files 22 22 Lines 3379 3394 +15 Branches 3379 3394 +15 ==================================================================
+ Hits 1148 1162 +14 - Misses 2226 2227 +1 
Partials 5 5 

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.
Inline comments:
In `@fact/src/config/mod.rs`:
- Around line 866-873: Update the d_instantiate_ctx_size argument definition and
its parsing path to reject 0 and u32::MAX, accepting only values in the YAML
range 1..u32::MAX before they reach map_max_entries. Add CLI and
environment-variable tests covering both rejected boundaries, using the existing
configuration test patterns and symbols.

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📥 Commits

Reviewing files that changed from the base of the PR and between bb01edc and fbcddc8.

📒 Files selected for processing (4)

• fact-ebpf/src/bpf/maps.h
• fact/src/bpf/mod.rs
• fact/src/config/mod.rs
• fact/src/config/tests.rs

[Molter73]

/retest

[Molter73]

/retest