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A UDC unbind, disconnect or host retry makes FunctionFS cancel a SETUP that smoo has read but not yet answered. With gadgetry-most-foul 0.1.1 the following ep0 event read then fails once with EINVAL, and control_loop propagated that with `?` and returned. Dropping `Custom` closed every FunctionFS file, so the host could never reconnect, parked ublk I/O waited forever, and the main loop never noticed because it only joined control_task at exit. control_loop now retries ep0 read errors that leave ep0 usable, with a 10 ms to 1 s backoff and a budget of 20 consecutive failures. Errors that mean FunctionFS itself is gone (a closed ep0, EBADFD, EBADF, ENODEV) still end the loop. The main loop checks control_task on every iteration. If it finishes without a stop request, smoo-gadget logs an error, fails pending I/O and exits with an error through the usual teardown, so a supervisor such as systemd Restart= can act. It no longer idles with the FunctionFS files closed. gadgetry-most-foul 0.1.2 removes the spurious EINVAL itself; this change is still needed for the remaining non-fatal errors and for any future control loop exit. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Move StallingHttpSource and the device-read helpers out of link_replay into tests/common/stalling_http.rs so the UDC rebind scenario can hold a read in flight the same way. The source can now be re-armed on a different block: a generation counter makes each release() free only the requests that arrived before it, so re-arming right after a release cannot re-stall a request that has not woken up yet. link_replay and user_recovery_handover behave as before; expected bytes now come from the source's own RandomBlockSource instead of a second identical one. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
usb-signaller switches USB modes by unbinding the gadget's UDC and binding it again while smoo-gadget keeps running. No scenario covered that: link_replay kills the host with the device bound, and user_recovery_handover rebinds across a gadget process swap. udc_rebind holds a device read in flight at the HTTP source, unbinds the UDC, keeps it unbound for 0.1 s, 2 s and 10 s while asserting the read stays parked, rebinds, and waits for the reconnected host to replay the read before checking its bytes. udc_rebind_loop repeats a 0.1 s cycle 20 times. After every cycle the FunctionFS instance must still read ready, the UDC must be bound, and smoo-gadget must not have logged losing its control plane. Add it to the stable set run by `cargo xtask integration` and `cargo xtask vm-integration`. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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Included review availability: Your plan provides up to 10 included reviews per hour; 7 remain after this review. 📝 WalkthroughWalkthroughThe FunctionFS control loop retries selected event-read errors with bounded backoff and reports unexpected termination. Shared HTTP stalling helpers support link replay tests. The ignored UDC rebind tests cover scenario handling, and the integration task now selects that scenario. ChangesGadget recovery and UDC rebind
Priority: ⬇️ Low Estimated code review effort: 3 (Moderate) | ~25 minutes Change: Bug fix Merge Risk: ⚪ Minimal · up to No actionable merge-blocking issue is established; the change is mergeable after normal checks. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to The change aims to keep the gadget available through routine USB rebinds and to exit rather than leave I/O waiting if recovery fails. No new access path was established. Whether a deployed supervisor restarts the process remains unverified. Retained concerns Security review detailsSecurity Blast Radius
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In `@crates/smoo-test-harness/tests/udc_rebind.rs`:
- Line 111: Update configfs unbind handling used by unbind_udc to expose
write_sys failures through a fallible API, and handle the error with cycle
context before calling assert_device_read_pending. Ensure an unbind failure is
reported directly rather than allowing the test to continue.
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HACKING.mdcrates/smoo-gadget-app/src/lib.rscrates/smoo-test-harness/tests/common/stalling_http.rscrates/smoo-test-harness/tests/link_replay.rscrates/smoo-test-harness/tests/udc_rebind.rsxtask/src/main.rs
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GadgetConfigFs::unbind_udc wrote an empty string to the gadget's UDC file. std::fs::write with an empty buffer never issues write(2), so the configfs store never ran and the gadget stayed bound. The next bind_udc then failed with EBUSY, because configfs still held the UDC name. adopt_restart only appeared to work because the old gadget's exit closes ep0, and FunctionFS then unbinds the gadget itself. Teardown's unbind was a silent no-op for the same reason. Write "\n" instead, which the kernel strips to an empty name and treats as an unbind, like `echo > UDC`. ENODEV now means FunctionFS already unbound the gadget after its daemon exited, and is logged at debug instead of as a failure. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
A cycle that fails while the read is parked left the read in a tokio blocking-pool thread. The runtime's shutdown waited for that thread forever, because the gadget that would answer the read was gone. The test then never reported its error, and the VM harness only gave up at its 30 minute timeout. Read on a plain OS thread instead, which process exit kills. Also log the error as soon as a cycle fails, before scenario teardown. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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Actionable comments posted: 1
- 🪄 Fix CodeRabbit comments on this PR
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Inline comments:
In `@crates/smoo-test-harness/tests/udc_rebind.rs`:
- Line 52: Move failure logging into run_rebind_cycles so errors are logged
while sc is still alive, before its drop triggers configfs teardown; remove the
callers’ inspect_err(log_failure) handlers to avoid relying on logging after
teardown.
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The callers logged the error with inspect_err only after run_rebind_cycles returned, by which point `sc` had already been dropped and its configfs teardown had run synchronously. A teardown that blocked would still hide the original error. Run the cycles in drive_cycles, borrowing the scenario, and log a failure in run_rebind_cycles while `sc` is still alive. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
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Problem
usb-signaller switches USB modes by unbinding the gadget's UDC and binding it again while smoo-gadget keeps running. smoo is designed to park I/O across that, but the ep0 control plane had a latent wedge.
EINVAL.control_looppropagated that error with?and returned. DroppingCustomclosed every FunctionFS file, so:control_taskat exit.The window is sub-millisecond per unbind. Routine rebinds turn it from theoretical into a matter of time.
Change
control_loopretries ep0 read errors that leave ep0 usable, with a 10 ms to 1 s backoff and a budget of 20 consecutive failures.EBADFD,EBADForENODEV.control_taskon every iteration. If the task finishes without a stop request, smoo-gadget:Restart=can act instead of idling with dead FunctionFS files.StallingHttpSourceand the read helpers move totests/common/stalling_http.rs.GadgetConfigFs::unbind_udcwrote an empty string.std::fs::writewith an empty buffer never callswrite(2), so the gadget stayed bound and the nextbind_udcfailed withEBUSY.adopt_restartand teardown only appeared to work because FunctionFS unbinds the gadget once its daemon closes ep0."\n", likeecho > UDC.ENODEV(already unbound by FunctionFS) is logged at debug.udc_rebind.unbind_udc()in-process.bind_udc(), the test waits for the reconnected host to replay the read, then checks its bytes.udc_rebind_loopruns 20 cycles of 0.1 s.functions/ffs.*/readymust read 1, the UDC must be bound, and no control-plane loss may be logged.Dependency
This depends on gadgetry-most-foul 0.1.2 (samcday/gadgetry-most-foul#5). That release stops the spurious
EINVALat the source: a cancelled SETUP (EIDRM) no longer leaves the request marked as pending. The workspace still requires0.1.1here, because 0.1.2 is not published yet. After it is published, this PR getsgadgetry-most-foul = "0.1.2"plus aCargo.lockupdate. The smoo-side changes stand on their own: with 0.1.1, the single spurious error is now logged and retried instead of being fatal.Validation
cargo fmt --all -- --check,cargo clippy --workspace --all-targets(no warnings),cargo test --workspace --locked: all pass. New unit tests cover the ep0 error classification and the backoff.cargo xtask vm-integration, full stable set, local KVM with the published image for this input hash:[patch.crates-io]pointing at the PR branch): passed.udc_rebindcovered the 0.1 s, 2 s and 10 s gaps, andudc_rebind_loop20 cycles, in 147 s.rw_modestfailed once with "2 orphan bulk transfers", a pcap accounting check in a scenario with no rebind and no ep0 errors, and passed on the next run (flaky).udc_rebindhit theEBUSYdescribed above, which led to the two harness fixes.vm-integrationpassed, includingudc_rebind(2 passed, 152 s).Not in this PR
Design item S3, caching the endpoint max packet size per enable. The blocking
FUNCTIONFS_ENDPOINT_DESCioctl lives in gadgetry-most-foul'sEndpointSender/EndpointReceiver::chunk_size(), not in smoo. A per-enable cache needs:That is not a small, contained change, so it is left out. The practical impact is one tokio worker blocked in the ioctl while the gadget is unbound.
data_plane_epochis still never incremented (noted in review, unchanged).🤖 Generated with Claude Code
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