vcontainer: add vdkr Docker support

Add vdkr - Docker CLI wrapper for cross-architecture container operations:

Scripts:
- vdkr.sh: Docker CLI entry point (vdkr-x86_64, vdkr-aarch64)
- vdkr-init.sh: Docker init script for QEMU guest

Recipes:
- vdkr-native: Installs vdkr CLI wrappers
- vdkr-rootfs-image: Builds Docker rootfs with containerd, runc, skopeo
- vdkr-initramfs-create: Creates bootable initramfs blob

The vdkr CLI provides Docker-compatible commands executed inside a
QEMU-emulated environment, enabling cross-architecture container
operations during Yocto builds.

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>

1 files changed, 74 insertions, 0 deletions

diff --git a/recipes-containers/vcontainer/vdkr-rootfs-image.bb b/recipes-containers/vcontainer/vdkr-rootfs-image.bb
new file mode 100644
index 00000000..a9bbb9fa
--- /dev/null
+++ b/recipes-containers/vcontainer/vdkr-rootfs-image.bb
@@ -0,0 +1,74 @@
+# SPDX-FileCopyrightText: Copyright (C) 2025 Bruce Ashfield
+#
+# SPDX-License-Identifier: MIT
+#
+# vdkr-rootfs-image.bb
+# Minimal Docker-capable image for vdkr QEMU environment
+#
+# This image is built via multiconfig and used by vdkr-initramfs-create
+# to provide a proper rootfs for running Docker in QEMU.
+#
+# Build with:
+#   bitbake mc:vdkr-aarch64:vdkr-rootfs-image
+#   bitbake mc:vdkr-x86-64:vdkr-rootfs-image
+
+SUMMARY = "Minimal Docker rootfs for vdkr"
+DESCRIPTION = "A minimal image containing Docker tools for use with vdkr. \
+               This image runs inside QEMU to provide Docker command execution."
+
+LICENSE = "MIT"
+LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"
+
+# Track init script changes via file-checksums
+# This adds the file content hash to the task signature
+do_rootfs[file-checksums] += "${THISDIR}/files/vdkr-init.sh:True"
+do_rootfs[file-checksums] += "${THISDIR}/files/vcontainer-init-common.sh:True"
+
+# Force do_rootfs to always run (no stamp caching)
+# Combined with file-checksums, this ensures init script changes are picked up
+do_rootfs[nostamp] = "1"
+
+# Inherit from core-image-minimal for a minimal base
+inherit core-image
+
+# We need Docker and container tools
+IMAGE_INSTALL = " \
+    packagegroup-core-boot \
+    docker-moby \
+    containerd \
+    runc \
+    skopeo \
+    busybox \
+    iproute2 \
+    util-linux \
+"
+
+# No extra features needed
+IMAGE_FEATURES = ""
+
+# Keep the image small
+IMAGE_ROOTFS_SIZE = "524288"
+IMAGE_ROOTFS_EXTRA_SPACE = "0"
+
+# Use squashfs for smaller size (~3x compression)
+# The preinit mounts squashfs read-only with tmpfs overlay for writes
+IMAGE_FSTYPES = "squashfs"
+
+# Install our init script
+ROOTFS_POSTPROCESS_COMMAND += "install_vdkr_init;"
+
+install_vdkr_init() {
+    # Install vdkr-init.sh as /init and vcontainer-init-common.sh alongside it
+    install -m 0755 ${THISDIR}/files/vdkr-init.sh ${IMAGE_ROOTFS}/init
+    install -m 0755 ${THISDIR}/files/vcontainer-init-common.sh ${IMAGE_ROOTFS}/vcontainer-init-common.sh
+
+    # Create required directories
+    install -d ${IMAGE_ROOTFS}/mnt/input
+    install -d ${IMAGE_ROOTFS}/mnt/state
+    install -d ${IMAGE_ROOTFS}/var/lib/docker
+    install -d ${IMAGE_ROOTFS}/run/containerd
+
+    # Create skopeo policy
+    install -d ${IMAGE_ROOTFS}/etc/containers
+    echo '{"default":[{"type":"insecureAcceptAnything"}]}' > ${IMAGE_ROOTFS}/etc/containers/policy.json
+}