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https://github.com/agent-substrate/substrate.git
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Lucky Abolorunke
ad830889ad
#### microvm: Exclude Overlay Workdirs from Rootfs Snapshots With `index=off` pinned on the merged rootfs mount, a restored workdir is inert: overlayfs wipes and rebuilds it at mount time, and staging recreates the directory regardless. Archiving `<cid>/work` was therefore dead weight on the suspend path—and not always trivial weight, since a copy-up in flight at pause can leave file-sized temporary data there. --- #### Key Changes: * **`tarutil.CreateFiltered`**: Added a skip predicate over `Create` (skipping a directory prunes its entire subtree). * **Workdir Pruning**: Drops exactly the second-level `work` entries during snapshot archive creation. * **Backward Compatibility**: Extraction logic remains unchanged; existing snapshots containing `workdir` entries will still restore without issue. --- > **Follow-up to #846 review note:** With `index=off` pinned, a restored workdir is inert and overlayfs rebuilds it at mount, making its archival unnecessary overhead on the suspend path.
88 lines
3.1 KiB
Go
88 lines
3.1 KiB
Go
//go:build linux
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// Copyright 2026 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package main
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import (
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"os"
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"path/filepath"
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"strings"
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"testing"
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)
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// upperDirWith returns a rootfs upper directory laid out the way the host
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// overlay staging builds one: <containerID>/{fs,work} per container, with the
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// given files created under it (paths relative to the directory).
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func upperDirWith(t *testing.T, files map[string]string) string {
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t.Helper()
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dir := t.TempDir()
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for rel, content := range files {
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p := filepath.Join(dir, rel)
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if err := os.MkdirAll(filepath.Dir(p), 0o755); err != nil {
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t.Fatalf("creating %q: %v", filepath.Dir(p), err)
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}
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if err := os.WriteFile(p, []byte(content), 0o644); err != nil {
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t.Fatalf("writing %q: %v", rel, err)
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}
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}
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return dir
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}
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func TestRootfsUpperRoundTrip(t *testing.T) {
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// Checkpoint: every container's upper, archived while the guest is paused.
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// The fs/ layout under the dir is exactly what find-paths re-opens; the
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// workdirs are deliberately left out of the archive (inert with index=off,
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// recreated at mount).
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files := map[string]string{
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"app_ovl/fs/home/agent/notes.txt": "rootfs write",
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"app_ovl/work/index": "",
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"app_ovl/work/#1/tmp.bin": "in-flight copy-up temp",
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"sidecar_ovl/fs/var/log/s.log": "sidecar write",
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}
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src := upperDirWith(t, files)
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checkpointDir := t.TempDir()
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if err := tarRootfsUpper(t.Context(), src, checkpointDir); err != nil {
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t.Fatalf("tarRootfsUpper: %v", err)
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}
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// Restore: onto a directory holding a stale previous activation's contents,
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// which must not leak into the restored overlay state.
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dst := upperDirWith(t, map[string]string{"app_ovl/fs/stale.txt": "stale"})
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if err := untarRootfsUpper(dst, checkpointDir); err != nil {
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t.Fatalf("untarRootfsUpper: %v", err)
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}
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for rel, want := range files {
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if strings.Contains(rel, "/work/") {
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continue // asserted absent below
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}
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got, err := os.ReadFile(filepath.Join(dst, rel))
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if err != nil {
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t.Errorf("reading restored %q: %v", rel, err)
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continue
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}
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if string(got) != want {
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t.Errorf("restored %q = %q, want %q", rel, got, want)
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}
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}
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// The workdirs must NOT survive the round trip: they are excluded from the
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// archive (dead weight; overlayfs rebuilds them at mount).
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if _, err := os.Stat(filepath.Join(dst, "app_ovl/work")); !os.IsNotExist(err) {
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t.Errorf("workdir survived the snapshot round trip (stat err = %v), want it excluded", err)
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}
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if _, err := os.Stat(filepath.Join(dst, "app_ovl/fs/stale.txt")); !os.IsNotExist(err) {
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t.Errorf("stale pre-restore content survived untarRootfsUpper (stat err = %v), want it wiped", err)
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}
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}
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