CI

Overview of the GitHub Actions workflows in .github/workflows/.

E2E Test (system-test.yml)

The workflow display name is E2E Test (end-to-end): it boots real mac80211_hwsim + hostapd + dnsmasq processes and exercises the full stack, not just units. The file keeps the name system-test.yml because renaming it changes no behavior but churns git history and breaks deep links.

The PR trigger label stays system-test: it is user-facing, referenced in docs and existing PR workflows, so renaming it would break current usage. No required checks reference this workflow by name, so no branch-protection changes are needed. Artifact name: e2e-debug-logs. Concurrency group prefix: e2e-. For the same history/link reasons, tests/system_test.sh also keeps its filename.

hwsim module cache and branch scoping

The workflow caches compiled wireless stack modules (/tmp/hwsim) under key:

hwsim-modules-<os>-kernel-<uname -r>-<hash of .github/actions/build-hwsim-modules/action.yml>

Investigation of recent runs (32895001316, 32895972430, 32918439480, 32918739512, 32959609213) showed all used an identical cache key (hwsim-modules-Linux-kernel-6.17.0-1022-azure-<same hash>), yet most reported “Cache not found”. This ruled out:

• Runner kernel churn: 6.17.0-1022-azure was stable across all runs.
• Build recipe drift: the hashFiles() portion never changed.

Root cause: GitHub Actions branch cache isolation. The workflow runs on pull_request, so each run executes in its own PR branch’s cache scope. A cache entry saved during PR A’s run is invisible to PR B and to master, and vice versa. restore-keys cannot cross branch scopes either, which is why they are not used (in addition to the stale-module risk already noted in the workflow).

Mitigation: master-scope cache warming

Cache warming is a side effect of a manual workflow_dispatch run with no ref input (no push trigger, no cron schedule): such a run checks out master, so the e2e-test job’s post-step cache save lands in master’s scope. This is typically done after a runner kernel bump that invalidates old entries via the uname -r key segment; it also runs the full system test, which is exactly what you want before cutting a release. PR runs restore from whatever warm entry exists in master’s scope; until a dispatch is run they simply rebuild the modules locally.

The shared build recipe lives in the composite action .github/actions/build-hwsim-modules/.