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]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yml

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📥 Commits

Reviewing files that changed from the base of the PR and between fbcddc8 and cfc8a73.

📒 Files selected for processing (1)

• fact/src/config/mod.rs

🚧 Files skipped from review as they are similar to previous changes (1)

• 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.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch mauro/chore/configurable-d-instantiate-ctx

---

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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 34.45%. Comparing base (40459ba) to head (cfc8a73).

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                           34.18%   34.45%   +0.26%     
==================================================================
  Files                                  22       22              
  Lines                                3358     3373      +15     
  Branches                             3358     3373      +15     
==================================================================
+ Hits                                 1148     1162      +14     
- Misses                               2205     2206       +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.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Enterprise

Run ID: 30975ee3-84da-4b56-bd53-8dd8227eb1a5

📥 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