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

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_{Comparing cod-3417-depot-runner-migration-breaks-memtrack (94ace38) with main (6ecb3c0)}

[greptile-apps]

Greptile Summary

The PR adds an early kernel-BTF availability check before loading memtrack’s eBPF programs and extracts kernel-release retrieval for a more actionable error message.

• Adds KernelBtf::is_available and KernelBtf::ensure_available.
• Runs the preflight from both BPF variants before page-size and rmap detection.
• Publicly re-exports the new kernel capability helper.

Confidence Score: 4/5

The PR appears safe to merge, with a non-blocking diagnostic issue when kernel BTF is present but hidden or inaccessible through sysfs.

The preflight correctly prevents an unsupported BPF load, but its boolean filesystem probe conflates genuine BTF absence with namespace, mount, and permission failures and consequently recommends the wrong remediation.

Files Needing Attention: crates/memtrack/src/kernel.rs

Important Files Changed

Filename	Overview
crates/memtrack/src/kernel.rs	Adds kernel release and BTF helpers; the availability probe produces misleading diagnostics when sysfs metadata cannot be accessed.
crates/memtrack/src/ebpf/memtrack/mod.rs	Adds the intended BTF preflight before either eBPF variant is loaded.
crates/memtrack/src/lib.rs	Publicly re-exports KernelBtf alongside KernelVersion, with no current compatibility issue identified.

Prompt To Fix All With AI

### Issue 1
crates/memtrack/src/kernel.rs:69-70
**BTF probe hides access errors**

If the tracker runs where sysfs is absent, masked, or inaccessible, `Path::exists` returns false and the diagnostic states that the kernel was built without BTF. This sends users toward replacing or rebuilding the kernel instead of correcting sysfs visibility or access.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

_{Reviews (1): Last reviewed commit: "feat(memtrack): fail early when the kern..." | Re-trigger Greptile}

[greptile-apps]

BTF probe hides access errors

If the tracker runs where sysfs is absent, masked, or inaccessible, Path::exists returns false and the diagnostic states that the kernel was built without BTF. This sends users toward replacing or rebuilding the kernel instead of correcting sysfs visibility or access.

Knowledge Base Used:

• Native profiling components
• eBPF memory tracker

Prompt To Fix With AI

This is a comment left during a code review.
Path: crates/memtrack/src/kernel.rs
Line: 69-70

Comment:
**BTF probe hides access errors**

If the tracker runs where sysfs is absent, masked, or inaccessible, `Path::exists` returns false and the diagnostic states that the kernel was built without BTF. This sends users toward replacing or rebuilding the kernel instead of correcting sysfs visibility or access.

**Knowledge Base Used:**
- [Native profiling components](https://app.greptile.com/codspeed/-/custom-context/knowledge-base/codspeedhq/codspeed/-/docs/native-profiling-components.md)
- [eBPF memory tracker](https://app.greptile.com/codspeed/-/custom-context/knowledge-base/codspeedhq/codspeed/-/docs/ebpf-memory-tracker.md)

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!