feat(memtrack): fail early when the kernel has no BTF

[not-matthias]

Problem

Memory mode fails on runners whose kernel is built without CONFIG_DEBUG_INFO_BTF.

libbpf resolves CO-RE relocations against the running kernel's own BTF, and the kernel resolves the attach target of every fentry/tp_btf program against it as well. Without /sys/kernel/btf/vmlinux the programs cannot load at all — and libbpf surfaces this as a bare -ESRCH, which says nothing about the actual cause.

Change

Preflight check in MemtrackBpf::with_variant, where the load would otherwise fail:

pub struct KernelBtf;

impl KernelBtf {
    pub fn is_available() -> bool;
    pub fn ensure_available() -> Result<()>;
}

The error names the running kernel and the config option to look for:

Memory profiling is not supported on this runner: its kernel (7.2.0) was built
without BTF, so /sys/kernel/btf/vmlinux does not exist. Use a runner whose kernel
is built with CONFIG_DEBUG_INFO_BTF=y.

The first commit is a pure refactor extracting the /proc/sys/kernel/osrelease read out of KernelVersion::current, so the message can report the running release.

Verification

• cargo test --release -p memtrack — 19 passed, remainder are the pre-existing root/eBPF-gated ignored tests.
• cargo fmt --check, cargo clippy --all-targets clean.
• Detection exercised on a BTF-having host: is_available() returns true, ensure_available() returns Ok, and the failure message renders with the real kernel release.

Notes for review

is_available is not unit-testable as written because the path is a hardcoded const. If coverage is wanted, it can take the path as a parameter behind a private helper.

COD-3417

[codspeed-hq]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 17 untouched benchmarks

---

_{Comparing cod-3417-depot-runner-migration-breaks-memtrack (03a0288) with main (6ecb3c0)}

[greptile-apps]

Greptile Summary

The PR adds an early kernel-BTF availability check before loading the memory-tracking eBPF programs and improves diagnostics for unsupported or inaccessible runner environments.

• Extracts kernel-release lookup for reuse in diagnostics.
• Distinguishes a missing BTF file from other filesystem access errors.
• Exposes the new kernel-BTF capability API from the memtrack crate.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains; the active memory-tracker initialization path now preserves non-NotFound BTF access errors instead of misreporting them as missing kernel support.

Important Files Changed

Filename	Overview
crates/memtrack/src/ebpf/memtrack/mod.rs	Adds the BTF preflight to the eBPF initialization path before program loading.
crates/memtrack/src/kernel.rs	Adds kernel-BTF detection with distinct diagnostics for missing files and other access failures, resolving the prior review issue.
crates/memtrack/src/lib.rs	Re-exports the new KernelBtf API alongside KernelVersion.

_{Reviews (3): Last reviewed commit: "feat(memtrack): fail early when the kern..." | Re-trigger Greptile}

[GuillaumeLagrange]

ogltm