Previously withVMLockByRef held the per-VM mutex across InspectRepo,
waitForGuestSSH, dialGuest, ImportRepoToGuest (the tar stream!), and
the readonly chmod. A large repo could block `vm stop` / `vm delete`
/ `vm restart` on the same VM for however long the import took.
Split into two phases:
1. VM mutex held briefly to validate state (running + PID alive)
and snapshot the fields needed for SSH (guest IP, api sock).
2. VM mutex released. Acquire workspaceLocks[id] — a separate
per-VM mutex scoped to workspace.prepare / workspace.export —
for the guest I/O phase.
Lifecycle ops (stop/delete/restart/set) only take vmLocks, so they
no longer queue behind a slow import. Two concurrent prepares on the
same VM still serialise via workspaceLocks so tar streams don't
interleave. ExportVMWorkspace also acquires workspaceLocks to avoid
snapshotting a half-streamed import.
Two regression tests (sequential — they swap package-level seams):
ReleasesVMLockDuringGuestIO: stall the import fake, assert the VM
mutex is acquirable from another goroutine during the stall.
SerialisesConcurrentPreparesOnSameVM: 3 concurrent prepares, assert
Import is only ever invoked 1-at-a-time per VM.
ARCHITECTURE.md documents the split + updated lock ordering.
Thales Maciel
6cd52d12f4