microvm tests: stream OpenVMM transcripts to disk as they are read by jay23606 · Pull Request #588 · microsoft/nvx

Jay (jay23606) · 2026-10-16T20:15:57Z

Fixes #176.

Summary

OpenvmmProcess kept the transcript in memory and wrote it only from wait or close. A run that was terminated before cleanup left no transcript, or a truncated one, even though its output had been read.
The transcript is now opened before OpenVMM starts. Each consumed chunk is appended and flushed as it is read, and wait and close only close the file. Bytes are written in the order received, with no prefixes and no rewrite at cleanup, so nothing is duplicated.
A transcript that cannot be created stops the run before OpenVMM starts. Output still queued at close is written too.
In-memory output, marker search and timeout behavior are unchanged.
Scope: OpenvmmProcess only. TcpConsole has no transcript path, and the benchmark helpers in benchmark.py are not changed. Those are follow-ups.

Test

Three new tests: growth while the process runs (fails before the change, since the file did not exist until wait), a transcript that cannot be created (fails before the change), and output delivered after the last wait.
A real Windows child process printed BOOT, then LATE three seconds later. The transcript contained BOOT while the child was still running, and the final transcript matched the output.
test_microvm_tests: 193 tests. The dev baseline (190 tests) has the same nine failures and errors in host-loopback, private network ingress and SMP timer tests. They are unrelated to the transcript code and present on untouched dev.
ruff check and format are clean.
Not run: the PTY path on Linux, which needs a Linux host.

🤖 Generated with Claude Code

Copilot

🟡 Changes recommended

Cleanup ordering can lose final reader output and skip resource closure when transcript writes fail.

1 open finding

Final output is lost during close and transcript cleanup may be skipped · New

What changed in this PR

Streams consumed OpenVMM output to disk incrementally, improving microVM test diagnostics when runs end before cleanup.

Changes:

Opens the transcript before starting OpenVMM.
Writes and flushes each consumed chunk while preserving in-memory output.
Adds tests for transcript growth, creation failures, and queued cleanup output.

File	Description
scripts/test_microvm_tests.py	Adds three transcript persistence tests.
scripts/nvx_tools/openvmm_process.py	Replaces cleanup-time transcript rewrites with incremental writes.

🧠 Review effort: Balanced

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🟡 Changes recommended

Interaction shutdown errors skip queue draining, losing already-queued diagnostics.

1 open finding

Preserve queued output when interaction shutdown fails · New

1 resolved since last review

Final output is lost during close and transcript cleanup may be skipped

🧠 Review effort: Balanced

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🟢 Approval recommended

The focused changes address the prior cleanup issues and include regression coverage, with no unresolved findings.

0 open findings

2 resolved since last review

🧠 Review effort: Balanced

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🟢 Approval recommended

The scoped changes and regression tests have no identified blocking issues; runtime validation was not performed during this review.

No open issues 🎉

_{Review effort: Balanced}

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🟡 Changes recommended

Transcript I/O failures can prevent remaining queued bytes from reaching in-memory output.

1 open issue

Preserve all queued transcript chunks after write failure · New

_{Review effort: Balanced}

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Pedro Henrique Penna (ppenna) · 2026-10-20T20:01:58Z

Hello Jay (@jay23606) I would appreciate if you asked your agents to stop automatically rebasing this. The current workflow is preventing me to run your PRs on our CI and thus preventing them to be merged.

OpenvmmProcess kept the transcript in memory and wrote it only from wait or close, so a run terminated before cleanup left no transcript, or a truncated one, even though output had been read. Open the transcript before OpenVMM starts, append each consumed chunk and flush it, and close the file at wait or close. Bytes are written in the order received, with no prefixes and no duplication at cleanup. An error creating the transcript stops the run before OpenVMM starts. Output still queued at close is written too. The in-memory output and marker search are unchanged. Adds tests for growth while the process runs, a transcript that cannot be created, and output delivered after the last wait. Fixes microsoft#176 Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com> Signed-off-by: jay23606 <4602056+jay23606@users.noreply.github.com>

… release the transcript close drained the reader's queue before the interaction had stopped, so a final chunk queued during shutdown was lost from both output and transcript. A write failure during that drain also skipped closing the interaction and the transcript. Stop the interaction first, then drain, and release the transcript in a finally block. Adds regression tests for output queued during interaction close and for a transcript write failure. Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com> Signed-off-by: jay23606 <4602056+jay23606@users.noreply.github.com>

If InteractiveProcess.close raised, the drain was skipped and chunks still queued were missing from both output and the transcript. Drain in a finally around the interaction shutdown, so the transcript is complete whichever step fails. Adds a regression test with queued output and a failing interaction shutdown. Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com> Signed-off-by: jay23606 <4602056+jay23606@users.noreply.github.com>

_drain_available stopped at the first failed transcript write, so chunks still queued behind it never reached process.output. Keep collecting them in memory and re-raise the first error once the queue is empty. Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com> Signed-off-by: jay23606 <4602056+jay23606@users.noreply.github.com>

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Pedro Henrique Penna (ppenna) · 2026-10-20T20:29:49Z

Closing in favor of #659, which carries your commits unchanged (head 2634167ff) on a microsoft/nvx branch so that CI can run on a stable head. You remain the author of the commits, and further pushes to this branch will not affect #659. Thank you for the contribution!

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Pedro Henrique Penna (ppenna) mentioned this pull request Oct 20, 2026

microvm tests: stream OpenVMM transcripts to disk as they are read #659

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Pedro Henrique Penna (ppenna) closed this Oct 20, 2026

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Jay (jay23606) commented Oct 16, 2026

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