docs: add container bundling and vdkr/vpdmn documentation

Add comprehensive documentation for the container cross-install system:

- Choosing between BUNDLED_CONTAINERS and container-bundle packages
- Decision guide table for selecting the right approach
- Component relationships (app recipe -> container image -> bundle)
- BUNDLED_CONTAINERS format and examples
- container-bundle.bbclass usage
- Container autostart configuration
- vdkr/vpdmn virtual container runtime usage
- Architecture overview and how it works
- Testing instructions

This provides a single reference for users wanting to bundle containers
into Yocto images at build time.

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

2 files changed, 342 insertions, 0 deletions

diff --git a/docs/00-INDEX b/docs/00-INDEX
index 6659fbee..dfcc8bda 100644
--- a/docs/00-INDEX
+++ b/docs/00-INDEX
@@ -8,6 +8,9 @@ alphabetical order as well.
 00-README
         - info on the goals of meta-virtualization and this docs subdir
 
+container-bundling.md
+        - container bundling, cross-install, and vdkr/vpdmn documentation.
+
 openvswitch.txt
         - example on how to setup openvswitch with qemu/kvm.
 
diff --git a/docs/container-bundling.md b/docs/container-bundling.md
new file mode 100644
index 00000000..ee2b5e31
--- /dev/null
+++ b/docs/container-bundling.md
@@ -0,0 +1,339 @@
+Container Bundling and Cross-Architecture Deployment
+=====================================================
+
+This document describes how to bundle containers into Yocto images at build
+time using the container-cross-install system. This enables deploying Docker
+and Podman containers from x86_64 build systems to ARM64/x86_64 targets
+without requiring container runtimes on the build host.
+
+Prerequisites
+-------------
+
+Enable the vcontainer distro feature in local.conf:
+
+    DISTRO_FEATURES:append = " virtualization vcontainer"
+
+Enable multiconfig for blob builds:
+
+    BBMULTICONFIG = "vruntime-aarch64 vruntime-x86-64"
+
+
+Choosing How to Bundle Containers
+---------------------------------
+
+There are two ways to bundle containers into a host image:
+
+1. **BUNDLED_CONTAINERS variable** (simpler, no extra recipe needed)
+
+       # In local.conf or image recipe
+       BUNDLED_CONTAINERS = "container-base:docker myapp-container:docker:autostart"
+
+2. **container-bundle packages** (more flexible)
+
+       # Create a bundle recipe, then add to IMAGE_INSTALL
+       inherit container-bundle
+       CONTAINER_BUNDLES = "myapp-container:autostart"
+
+### Decision Guide
+
+    Use Case                                    | BUNDLED_CONTAINERS | Bundle Recipe
+    --------------------------------------------|--------------------|--------------
+    Simple: containers in one host image        | recommended        | overkill
+    Reuse containers across multiple images     | repetitive         | recommended
+    Remote containers (docker.io/library/...)   | not supported      | required
+    Package versioning and dependencies         | not supported      | supported
+    Distribute pre-built container set          | not supported      | supported
+
+**For most single-image use cases, BUNDLED_CONTAINERS is simpler:**
+- No bundle recipe needed
+- Dependencies auto-generated at parse time
+- vrunner batch-import runs once for all containers
+
+**Use container-bundle.bbclass when you need:**
+- Remote container fetching via skopeo
+- A distributable/versioned package of containers
+- To share the same bundle across multiple different host images
+
+
+Component Relationships
+-----------------------
+
+To bundle a local container like "myapp:autostart", three recipe types
+work together:
+
+1. **Application Recipe** (builds the software)
+
+       recipes-demo/myapp/myapp_1.0.bb
+       - Compiles application binaries
+       - Creates installable package (myapp)
+
+2. **Container Image Recipe** (creates OCI image containing the app)
+
+       recipes-demo/images/myapp-container.bb
+       - inherit image image-oci
+       - IMAGE_INSTALL = "myapp"
+       - Produces: ${DEPLOY_DIR_IMAGE}/myapp-container-latest-oci/
+
+3. **Bundle Recipe** (packages container images for deployment) - OPTIONAL
+
+       recipes-demo/bundles/my-bundle_1.0.bb
+       - inherit container-bundle
+       - CONTAINER_BUNDLES = "myapp-container:autostart"
+       - Creates installable package with OCI data
+
+### Flow Diagram
+
+    myapp_1.0.bb                    myapp-container.bb
+    (application)                   (container image)
+         │                               │
+         │ IMAGE_INSTALL="myapp"         │ inherit image-oci
+         └──────────────┬────────────────┘
+                        │
+                        ▼
+               myapp-container-latest-oci/
+               (OCI directory in DEPLOY_DIR_IMAGE)
+                        │
+                        │ BUNDLED_CONTAINERS or CONTAINER_BUNDLES
+                        ▼
+               container-image-host
+               (target host image with containers pre-installed)
+
+### Concrete Example (from meta-virtualization)
+
+- Application: `recipes-demo/autostart-test/autostart-test_1.0.bb`
+- Container image: `recipes-demo/images/autostart-test-container.bb`
+- Usage: `BUNDLED_CONTAINERS = "autostart-test-container:docker:autostart"`
+
+
+Using BUNDLED_CONTAINERS
+------------------------
+
+Set in local.conf or image recipe:
+
+    BUNDLED_CONTAINERS = "container-base:docker myapp-container:podman:autostart"
+
+### Format
+
+    name:runtime[:autostart][:external]
+
+- **name**: Container image recipe name or OCI directory name
+- **runtime**: `docker` or `podman`
+- **autostart**: Optional - `autostart`, `always`, `unless-stopped`, `on-failure`
+- **external**: Optional - skip dependency generation for third-party blobs
+
+### Examples
+
+    # Yocto-built containers (dependencies auto-generated)
+    BUNDLED_CONTAINERS = "container-base:docker"
+    BUNDLED_CONTAINERS = "myapp-container:podman:autostart"
+
+    # Third-party blobs (no dependency generated)
+    BUNDLED_CONTAINERS = "vendor-image:docker:external"
+
+    # Legacy format (still supported)
+    BUNDLED_CONTAINERS = "container-base-latest-oci:docker"
+
+
+Using container-bundle.bbclass
+------------------------------
+
+Create a bundle recipe:
+
+    # recipes-demo/bundles/my-bundle_1.0.bb
+    inherit container-bundle
+
+    CONTAINER_BUNDLES = "\
+        myapp-container:autostart \
+        mydb-container \
+        docker.io/library/redis:7 \
+    "
+
+    # Required for remote containers:
+    CONTAINER_DIGESTS[docker.io_library_redis_7] = "sha256:..."
+
+To get the digest for a remote container, use skopeo:
+
+    skopeo inspect docker://docker.io/library/redis:7 | jq -r '.Digest'
+
+Install in your host image:
+
+    IMAGE_INSTALL:append:pn-container-image-host = " my-bundle"
+
+
+Container Autostart
+-------------------
+
+Containers can be configured to start automatically on boot:
+
+| Policy | Description |
+|--------|-------------|
+| `autostart` | Alias for unless-stopped (recommended) |
+| `always` | Always restart container |
+| `unless-stopped` | Restart unless manually stopped |
+| `on-failure` | Restart only on non-zero exit code |
+
+**Generated files:**
+- Docker: `/lib/systemd/system/container-<name>.service`
+- Podman: `/etc/containers/systemd/<name>.container` (Quadlet format)
+
+
+vdkr and vpdmn - Virtual Container Runtimes
+===========================================
+
+vdkr (virtual docker) and vpdmn (virtual podman) are tools that execute
+container commands inside a QEMU-emulated environment. They enable
+cross-architecture container operations during Yocto builds.
+
+| Tool | Runtime | State Directory |
+|------|---------|-----------------|
+| `vdkr` | Docker (dockerd + containerd) | `~/.vdkr/<arch>/` |
+| `vpdmn` | Podman (daemonless) | `~/.vpdmn/<arch>/` |
+
+Quick Start
+-----------
+
+    # Build and install the standalone SDK
+    MACHINE=qemux86-64 bitbake vcontainer-tarball
+    ./tmp/deploy/sdk/vcontainer-standalone.sh -d /tmp/vcontainer -y
+    source /tmp/vcontainer/init-env.sh
+
+    # List images
+    vdkr images
+
+    # Import an OCI container
+    vdkr vimport ./my-container-oci/ myapp:latest
+
+    # Export storage for deployment
+    vdkr --storage /tmp/docker-storage.tar vimport ./container-oci/ myapp:latest
+
+    # Clean persistent state
+    vdkr clean
+
+Architecture Selection
+----------------------
+
+vdkr/vpdmn detect target architecture automatically. Override with:
+
+| Method | Example | Priority |
+|--------|---------|----------|
+| `--arch` / `-a` flag | `vdkr -a aarch64 images` | Highest |
+| Executable name | `vdkr-x86_64 images` | 2nd |
+| `VDKR_ARCH` env var | `export VDKR_ARCH=aarch64` | 3rd |
+| Config file | `~/.config/vdkr/arch` | 4th |
+| Host architecture | `uname -m` | Lowest |
+
+Memory Resident Mode
+--------------------
+
+Keep QEMU VM running for fast command execution (~1s vs ~30s):
+
+    vdkr vmemres start              # Start daemon
+    vdkr images                    # Fast!
+    vdkr pull alpine:latest        # Fast!
+    vdkr vmemres stop               # Stop daemon
+
+Commands
+--------
+
+### Docker-Compatible
+
+    images, run, import, load, save, pull, tag, rmi, ps, rm, logs, start, stop, exec
+
+### Extended (vdkr-specific)
+
+| Command | Description |
+|---------|-------------|
+| `vimport <path> [name:tag]` | Import OCI directory or tarball |
+| `vrun [opts] <image> [cmd]` | Run with entrypoint cleared |
+| `clean` | Remove persistent state |
+| `vmemres start/stop/status` | Memory resident VM control |
+
+
+How It Works
+============
+
+The container-cross-install system uses QEMU to run container tools
+(Docker/Podman) for the target architecture during the build. This solves
+the "pseudo problem" where container tools fail under Yocto's fakeroot.
+
+Architecture:
+
+    ┌─────────────────────────────────────────────────────────────────┐
+    │  QEMU VM (target architecture)                                  │
+    │  ┌───────────────────────────────────────────────────────────┐  │
+    │  │  rootfs.img (squashfs, ~100-130MB)                        │  │
+    │  │  - Docker or Podman tools                                 │  │
+    │  │  - Processes OCI containers                               │  │
+    │  │  - Outputs storage tar via console                        │  │
+    │  └───────────────────────────────────────────────────────────┘  │
+    │                                                                 │
+    │  Drive Layout:                                                  │
+    │    /dev/vda = rootfs.img (tools)                               │
+    │    /dev/vdb = input disk (OCI containers)                      │
+    │    /dev/vdc = state disk (Docker/Podman storage)               │
+    └─────────────────────────────────────────────────────────────────┘
+
+Blobs are built via multiconfig and deployed to:
+
+    tmp-vruntime-aarch64/deploy/images/qemuarm64/vdkr/
+    tmp-vruntime-x86-64/deploy/images/qemux86-64/vdkr/
+
+
+Testing
+=======
+
+    cd /opt/bruce/poky/meta-virtualization
+    
+    # Run container-cross-install tests
+    pytest tests/test_container_cross_install.py -v
+    
+    # Run vdkr/vpdmn CLI tests
+    pytest tests/test_vdkr.py tests/test_vpdmn.py -v --vdkr-dir /tmp/vcontainer
+
+
+Quick Reference Commands
+========================
+
+Build host image with bundled containers:
+
+    cd /opt/bruce/poky
+    source oe-init-build-env build
+
+    # Ensure local.conf has:
+    #   DISTRO_FEATURES:append = " virtualization vcontainer"
+    #   BBMULTICONFIG = "vruntime-aarch64 vruntime-x86-64"
+    #   BUNDLED_CONTAINERS = "container-base:docker autostart-test-container:docker:autostart"
+
+    MACHINE=qemux86-64 bitbake container-image-host
+
+Build the vdkr/vpdmn SDK tarball:
+
+    # Build blobs for desired architectures (sequentially to avoid deadlocks)
+    bitbake mc:vruntime-x86-64:vdkr-initramfs-create mc:vruntime-x86-64:vpdmn-initramfs-create
+    bitbake mc:vruntime-aarch64:vdkr-initramfs-create mc:vruntime-aarch64:vpdmn-initramfs-create
+
+    # Build SDK tarball
+    MACHINE=qemux86-64 bitbake vcontainer-tarball
+
+    # Output: tmp/deploy/sdk/vcontainer-standalone.sh
+
+Install and test SDK:
+
+    ./tmp/deploy/sdk/vcontainer-standalone.sh -d /tmp/vcontainer -y
+    source /tmp/vcontainer/init-env.sh
+
+    vdkr images
+    vdkr vimport /path/to/container-base-latest-oci/ test:latest
+    vdkr vmemres start
+    vdkr images
+    vdkr vmemres stop
+    vdkr clean
+
+
+See Also
+========
+
+- `classes/container-cross-install.bbclass` - Main bundling class
+- `classes/container-bundle.bbclass` - Package-based bundling
+- `recipes-containers/vcontainer/README.md` - vdkr/vpdmn detailed documentation
+- `tests/README.md` - Test documentation