test PR

test/docker-in-docker/overlayfs_containerd_root.sh

@@ -0,0 +1,42 @@
+#!/bin/bash
+#
+# Regression test for devcontainers/features#1639 / PR #1645 follow-up:
+# verifies that when the dev container's root filesystem is overlayfs
+# (the default under Docker / containerd-backed hosts), the standalone
+# containerd started by the docker-in-docker Feature does NOT place its
+# overlayfs snapshotter data on an overlay rootfs (which would fail with
+# `invalid argument` when pulling images).
+#
+set -e
+
+source dev-container-features-test-lib
+
+# 1. Confirm we're really reproducing the affected condition:
+#    the dev container's / must be overlay.
+check "rootfs is overlay (precondition)" \
+    bash -c '[ "$(findmnt -no FSTYPE /)" = "overlay" ]'
+
+# 2. The Feature's volume mount must shadow /var/lib/containerd with a
+#    non-overlay filesystem. Without the mount, containerd's overlayfs
+#    snapshotter would be writing onto the overlay rootfs and fail at
+#    pull time.
+check "/var/lib/containerd is not overlay" \
+    bash -c '[ "$(findmnt -no FSTYPE /var/lib/containerd)" != "overlay" ]'
+
+check "/var/lib/docker is not overlay" \
+    bash -c '[ "$(findmnt -no FSTYPE /var/lib/docker)" != "overlay" ]'
+
+# 3. The actual symptom: pulling and running an image must succeed.
+#    Pre-PR-#1645 this fails with:
+#      failed to mount /tmp/containerd-mountXXXXX ... err: invalid argument
+check "docker run hello-world" \
+    docker run --rm hello-world
+
+# 4. Belt-and-braces: confirm dockerd is actually using the
+#    containerd-snapshotter path so we know this test exercises the
+#    affected code path, not the legacy overlay2 driver.
+check "containerd-snapshotter active" \
+    bash -c "docker info 2>/dev/null | grep -qiE 'driver-type: io.containerd.snapshotter.v1|Storage Driver: overlayfs'"
+
+reportResults
+

test/docker-in-docker/scenarios.json

@@ -1,4 +1,13 @@
 {
+    "overlayfs_containerd_root": {
+        "image": "mcr.microsoft.com/devcontainers/base:noble",
+        "features": {
+            "docker-in-docker": {
+                "version": "latest",
+                "moby": true
+            }
+        }
+    },    
     "docker_build_fallback_compose": {
         "image": "ubuntu:noble",
         "features": {