Resume() was building VMConfig without TemplateID, so Firecracker MMDS
received an empty string. envd's PostInit then wrote that empty value to
/run/wrenn/.WRENN_TEMPLATE_ID. Fix by persisting the template ID in
snapshot metadata during Pause and reading it back during Resume.
Always use Firecracker Diff snapshots (fast, only changed pages) and
merge diff files at the file level when the generation cap is reached.
The previous approach used Firecracker's Full snapshot type which dumps
all memory to disk and can timeout, losing all snapshot data on failure.
Add snapshot.MergeDiffs() which reads each block from the appropriate
generation's diff file via the header mapping and writes them into a
single consolidated file with a fresh generation-0 header.
Use Firecracker's Diff snapshot type when re-pausing a previously
resumed sandbox, capturing only dirty pages instead of a full memory
dump. Chains up to 10 incremental generations before collapsing back
to a Full snapshot. Multi-generation diff files (memfile.{buildID})
are supported alongside the legacy single-file format in resume,
template creation, and snapshot existence checks.
- Replace reflink rootfs copy with device-mapper snapshots (shared
read-only loop device per base template, per-sandbox sparse CoW file)
- Add devicemapper package with create/restore/remove/flatten operations
and refcounted LoopRegistry for base image loop devices
- Fix pause ordering: destroy VM before removing dm-snapshot to avoid
"device busy" error (FC must release the dm device first)
- Add test UI at GET /test for sandbox lifecycle management (create,
pause, resume, destroy, exec, snapshot create/list/delete)
- Fix DirSize to report actual disk usage (stat.Blocks * 512) instead
of apparent size, so sparse CoW files report correctly
- Add timing logs to pause flow for performance diagnostics
- Fix all lint errors across api, network, vm, uffd, and sandbox packages
- Remove obsolete internal/filesystem package (replaced by devicemapper)
- Update CLAUDE.md with device-mapper architecture documentation
Implement full snapshot lifecycle: pause (snapshot + free resources),
resume (UFFD-based lazy restore), and named snapshot templates that
can spawn new sandboxes from frozen VM state.
Key changes:
- Snapshot header system with generational diff mapping (inspired by e2b)
- UFFD server for lazy page fault handling during snapshot restore
- Stable rootfs symlink path (/tmp/fc-vm/) for snapshot compatibility
- Templates DB table and CRUD API endpoints (POST/GET/DELETE /v1/snapshots)
- CreateSnapshot/DeleteSnapshot RPCs in hostagent proto
- Reconciler excludes paused sandboxes (expected absent from host agent)
- Snapshot templates lock vcpus/memory to baked-in values
- Proper cleanup of uffd sockets and pause snapshot files on destroy
- REST API (chi router): sandbox CRUD, exec, pause/resume, file write/read
- PostgreSQL persistence via pgx/v5 + sqlc (sandboxes table with goose migration)
- Connect RPC client to host agent for all VM operations
- Reconciler syncs host agent state with DB every 30s (detects TTL-reaped sandboxes)
- OpenAPI 3.1 spec served at /openapi.yaml, Swagger UI at /docs
- Added WriteFile/ReadFile RPCs to hostagent proto and implementations
- File upload via multipart form, download via JSON body POST
- sandbox_id propagated from control plane to host agent on create
