Add namespaced variables for cross-compilation in libblkid-rs

[jbaublitz]

Related to stratis-storage/project#583

Summary by CodeRabbit

• New Features

  • Build now honors three LIBBLKID_RS_PKG_CONFIG_* environment variables to influence pkg-config discovery (path, libdir, sysroot) during builds.

• Bug Fixes

  • More reliable detection of libblkid in nonstandard prefixes and cross-compilation or custom build environments, reducing build failures.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 10ae829a-53fa-4ca9-b16f-2424d86ee517

📥 Commits

Reviewing files that changed from the base of the PR and between a2cd1b8 and 8552131.

📒 Files selected for processing (1)

• libblkid-rs-sys/build.rs

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

• libblkid-rs-sys/build.rs

---

Walkthrough

The build script now maps three custom environment variables to their pkg-config counterparts before invoking pkg_config::probe("blkid"), which can alter how libblkid is discovered. No public APIs or other control flow were changed.

Changes

Cohort / File(s)	Summary of changes
Build script: pkg-config env propagation libblkid-rs-sys/build.rs	Reads LIBBLKID_RS_PKG_CONFIG_PATH, LIBBLKID_RS_PKG_CONFIG_LIBDIR, LIBBLKID_RS_PKG_CONFIG_SYSROOT_DIR and, if set, assigns them to PKG_CONFIG_PATH, PKG_CONFIG_LIBDIR, PKG_CONFIG_SYSROOT_DIR respectively before calling pkg_config::probe("blkid"). Missing variables are ignored.

Sequence Diagram(s)

sequenceDiagram
    autonumber
    actor Dev as Cargo Build
    participant B as build.rs
    participant Env as Environment
    participant PC as pkg-config
    participant Sys as System linker

    Dev->>B: Run build script
    B->>Env: Read LIBBLKID_RS_PKG_CONFIG_* vars
    alt Vars present
        B->>Env: Set PKG_CONFIG_* accordingly
        note right of B: Mapping occurs only if present
    else Vars absent
        note right of B: No changes to environment
    end
    B->>PC: probe("blkid")
    PC->>Env: Use PKG_CONFIG_* for search
    PC-->>B: blkid metadata (include/lib paths)
    B-->>Dev: Emit cargo:rustc-link-* directives
    Dev->>Sys: Link with discovered libblkid

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Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

I nudge the paths with gentle paws,
Three whispers guide pkg-config’s laws.
From burrowed env to linker’s light,
blkid is found—ears perked, just right.
A hop, a probe, a tidy trace—
Carrots secured, builds fall in place. 🥕

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	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 'Add namespaced variables for cross-compilation in libblkid-rs' directly and accurately reflects the main change: introducing LIBBLKID_RS_PKG_CONFIG_* environment variables for cross-compilation purposes.
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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• Create PR with unit tests

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[mulkieran]

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[packit-as-a-service]

Congratulations! One of the builds has completed. 🍾

You can install the built RPMs by following these steps:

• sudo yum install -y dnf-plugins-core on RHEL 8
• sudo dnf install -y dnf-plugins-core on Fedora
• dnf copr enable packit/stratis-storage-libblkid-rs-220
• And now you can install the packages.

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

[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/stratis-storage-libblkid-rs-220
• And now you can install the packages.

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

[jbaublitz]

@mulkieran After reviewing this issue, I believe that this may still be a useful PR to let people cross-compile these dependencies. Currently, I believe there's no way to specify the cross-compilation options for libblkid as a dependency as the environment variable would apply to all dependencies that use pkg-config. This change should allow specifically targeting libblkid. I intend to expand the pattern to other binding libraries.

[mulkieran]

I'm fine w/ the code, but I realized we should really document this for users.

[mulkieran]

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[mulkieran]

@jbaublitz I think all that needs to be done is to add a note in the README explaining what those particular environment variables are for and then we can merge.