Detect perf capabilities for kernel tracing

[Abhishek21g]

Summary

• detect effective cap_perfmon / cap_sys_admin file capabilities on the configured perf executable
• keep root as the fast path for kernel tracing permissions
• fall back to the previous root-only behavior when getcap is unavailable or cannot inspect perf
• update the kernel tracing permission error to mention file capabilities
• update the README wording around kernel tracing permissions
• add expect tests for getcap output parsing

Fixes #94.

Notes

This keeps the existing capability detection structure and only broadens the kernel-tracing permission check. If getcap is unavailable or cannot inspect the configured perf, magic-trace keeps the previous root-only behavior.

Validation

• git diff --check
• DCO check is passing on GitHub
• Linux validation on fork branch with this patch plus a temporary workflow file: https://github.com/Abhishek21g/magic-trace/actions/runs/28693698343
  • dune build @fmt
  • make PROFILE=static
  • dune runtest --profile=static

Optional non-root capability smoke test on a disposable Linux machine:

sudo setcap cap_perfmon,cap_sys_ptrace,cap_syslog=ep "$(command -v perf)"
getcap "$(command -v perf)"

MAGIC_TRACE_PERF_PATH="$(command -v perf)" \
  ./_build/default/bin/magic_trace_bin.exe run -trace-include-kernel true

[Abhishek21g]

I noticed the older related PR #254 after opening this. Since that PR appears stale and #94 is still open, I put together a smaller version that keeps the existing capability detection structure, falls back to the current root-only behavior when getcap is unavailable, and adds focused expect tests for the parser. Happy to adjust direction if maintainers prefer reviving #254.