From abf81c8c676bb8997efe4d92a6e4369dcdd6961a Mon Sep 17 00:00:00 2001
From: Bruce Ashfield <bruce.ashfield@gmail.com>
Date: Fri, 23 Jan 2026 15:46:16 -0500
Subject: vcontainer: add tiny initramfs image infrastructure

Add proper Yocto image recipes for the tiny initramfs used by
vdkr/vpdmn in the switch_root boot flow:

- vcontainer-tiny-initramfs-image.inc: Shared image configuration
- vcontainer-preinit_1.0.bb: Preinit script package (shared)
- vdkr-tiny-initramfs-image.bb: Tiny initramfs for vdkr
- vpdmn-tiny-initramfs-image.bb: Tiny initramfs for vpdmn

The tiny initramfs contains only busybox and a preinit script that:
1. Mounts devtmpfs, proc, sysfs
2. Mounts the squashfs rootfs.img from /dev/vda
3. Creates tmpfs overlay for writes
4. Performs switch_root to the real rootfs

This replaces ad-hoc file extraction with proper image-based builds,
improving reproducibility and maintainability.

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
---
 .../vcontainer/files/vcontainer-preinit.sh         | 133 +++++++++++++++++++++
 .../vcontainer/files/vdkr-preinit.sh               | 133 ---------------------
 .../vcontainer/vcontainer-preinit_1.0.bb           |  43 +++++++
 .../vcontainer/vcontainer-tiny-initramfs-image.inc |  70 +++++++++++
 .../vcontainer/vdkr-tiny-initramfs-image.bb        |  13 ++
 .../vcontainer/vpdmn-tiny-initramfs-image.bb       |  13 ++
 6 files changed, 272 insertions(+), 133 deletions(-)
 create mode 100644 recipes-containers/vcontainer/files/vcontainer-preinit.sh
 delete mode 100644 recipes-containers/vcontainer/files/vdkr-preinit.sh
 create mode 100644 recipes-containers/vcontainer/vcontainer-preinit_1.0.bb
 create mode 100644 recipes-containers/vcontainer/vcontainer-tiny-initramfs-image.inc
 create mode 100644 recipes-containers/vcontainer/vdkr-tiny-initramfs-image.bb
 create mode 100644 recipes-containers/vcontainer/vpdmn-tiny-initramfs-image.bb

(limited to 'recipes-containers/vcontainer')

diff --git a/recipes-containers/vcontainer/files/vcontainer-preinit.sh b/recipes-containers/vcontainer/files/vcontainer-preinit.sh
new file mode 100644
index 00000000..6f1b7e09
--- /dev/null
+++ b/recipes-containers/vcontainer/files/vcontainer-preinit.sh
@@ -0,0 +1,133 @@
+#!/bin/sh
+# SPDX-FileCopyrightText: Copyright (C) 2025 Bruce Ashfield
+#
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# vcontainer-preinit.sh
+# Minimal init for initramfs - mounts rootfs and does switch_root
+#
+# This script runs from the initramfs and:
+# 1. Mounts essential filesystems
+# 2. Finds and mounts the rootfs.img (squashfs, read-only)
+# 3. Creates overlayfs with tmpfs for writes
+# 4. Executes switch_root to the overlay root filesystem
+#
+# The real init (/init or /sbin/init on rootfs) then continues boot
+
+# Mount essential filesystems first (needed to check cmdline)
+mount -t proc proc /proc
+mount -t sysfs sysfs /sys
+mount -t devtmpfs devtmpfs /dev
+
+# Check for quiet mode (interactive)
+QUIET=0
+for param in $(cat /proc/cmdline 2>/dev/null); do
+    case "$param" in
+        docker_interactive=1) QUIET=1 ;;
+    esac
+done
+
+log() {
+    [ "$QUIET" = "0" ] && echo "$@"
+}
+
+log "=== vcontainer preinit (squashfs) ==="
+
+# Wait for block devices to appear
+log "Waiting for block devices..."
+sleep 2
+
+# Show available block devices
+log "Block devices:"
+[ "$QUIET" = "0" ] && ls -la /dev/vd* 2>/dev/null || log "No virtio block devices found"
+
+# The rootfs.img is always the first virtio-blk device (/dev/vda)
+# Additional devices (input, state) come after
+ROOTFS_DEV="/dev/vda"
+
+if [ ! -b "$ROOTFS_DEV" ]; then
+    echo "ERROR: Rootfs device $ROOTFS_DEV not found!"
+    echo "Available devices:"
+    ls -la /dev/
+    sleep 10
+    reboot -f
+fi
+
+# Create mount points for overlay setup
+mkdir -p /mnt/lower    # squashfs (read-only)
+mkdir -p /mnt/upper    # tmpfs for overlay upper
+mkdir -p /mnt/work     # tmpfs for overlay work
+mkdir -p /mnt/root     # final overlayfs mount
+
+# Mount squashfs read-only
+log "Mounting squashfs rootfs from $ROOTFS_DEV..."
+
+if ! mount -t squashfs -o ro "$ROOTFS_DEV" /mnt/lower; then
+    # Fallback to ext4 for backwards compatibility
+    log "squashfs mount failed, trying ext4..."
+    if ! mount -t ext4 -o ro "$ROOTFS_DEV" /mnt/lower; then
+        echo "ERROR: Failed to mount rootfs (tried squashfs and ext4)!"
+        sleep 10
+        reboot -f
+    fi
+    # ext4 fallback - just use it directly without overlay
+    log "Using ext4 rootfs directly (no overlay)"
+    mount --move /mnt/lower /mnt/root
+else
+    log "Squashfs mounted successfully"
+
+    # Create tmpfs for overlay upper/work directories
+    # Size is generous since container operations need temp space
+    log "Creating tmpfs overlay..."
+    mount -t tmpfs -o size=1G tmpfs /mnt/upper
+    mkdir -p /mnt/upper/upper
+    mkdir -p /mnt/upper/work
+
+    # Create overlayfs combining squashfs (lower) + tmpfs (upper)
+    log "Mounting overlayfs..."
+    if ! mount -t overlay overlay -o lowerdir=/mnt/lower,upperdir=/mnt/upper/upper,workdir=/mnt/upper/work /mnt/root; then
+        echo "ERROR: Failed to mount overlayfs!"
+        sleep 10
+        reboot -f
+    fi
+
+    log "Overlayfs mounted successfully"
+fi
+
+if [ "$QUIET" = "0" ]; then
+    echo "Contents:"
+    ls -la /mnt/root/
+fi
+
+# Verify init exists on rootfs
+if [ ! -x /mnt/root/init ] && [ ! -x /mnt/root/sbin/init ]; then
+    echo "ERROR: No init found on rootfs!"
+    sleep 10
+    reboot -f
+fi
+
+# Move filesystems to new root before switch_root
+# This way they persist across switch_root and the new init doesn't need to remount
+mkdir -p /mnt/root/proc /mnt/root/sys /mnt/root/dev
+mount --move /proc /mnt/root/proc
+mount --move /sys /mnt/root/sys
+mount --move /dev /mnt/root/dev
+
+# Switch to real root
+# switch_root will:
+# 1. Mount the new root
+# 2. chroot into it
+# 3. Execute the new init
+# 4. Delete everything in the old initramfs
+log "Switching to real root..."
+
+if [ -x /mnt/root/init ]; then
+    exec switch_root /mnt/root /init
+elif [ -x /mnt/root/sbin/init ]; then
+    exec switch_root /mnt/root /sbin/init
+fi
+
+# If we get here, switch_root failed
+echo "ERROR: switch_root failed!"
+sleep 10
+reboot -f
diff --git a/recipes-containers/vcontainer/files/vdkr-preinit.sh b/recipes-containers/vcontainer/files/vdkr-preinit.sh
deleted file mode 100644
index 08738022..00000000
--- a/recipes-containers/vcontainer/files/vdkr-preinit.sh
+++ /dev/null
@@ -1,133 +0,0 @@
-#!/bin/sh
-# SPDX-FileCopyrightText: Copyright (C) 2025 Bruce Ashfield
-#
-# SPDX-License-Identifier: GPL-2.0-only
-#
-# vdkr-preinit.sh
-# Minimal init for initramfs - mounts rootfs and does switch_root
-#
-# This script runs from the initramfs and:
-# 1. Mounts essential filesystems
-# 2. Finds and mounts the rootfs.img (squashfs, read-only)
-# 3. Creates overlayfs with tmpfs for writes
-# 4. Executes switch_root to the overlay root filesystem
-#
-# The real init (/init or /sbin/init on rootfs) then runs vdkr-init.sh logic
-
-# Mount essential filesystems first (needed to check cmdline)
-mount -t proc proc /proc
-mount -t sysfs sysfs /sys
-mount -t devtmpfs devtmpfs /dev
-
-# Check for quiet mode (interactive)
-QUIET=0
-for param in $(cat /proc/cmdline 2>/dev/null); do
-    case "$param" in
-        docker_interactive=1) QUIET=1 ;;
-    esac
-done
-
-log() {
-    [ "$QUIET" = "0" ] && echo "$@"
-}
-
-log "=== vdkr preinit (squashfs) ==="
-
-# Wait for block devices to appear
-log "Waiting for block devices..."
-sleep 2
-
-# Show available block devices
-log "Block devices:"
-[ "$QUIET" = "0" ] && ls -la /dev/vd* 2>/dev/null || log "No virtio block devices found"
-
-# The rootfs.img is always the first virtio-blk device (/dev/vda)
-# Additional devices (input, state) come after
-ROOTFS_DEV="/dev/vda"
-
-if [ ! -b "$ROOTFS_DEV" ]; then
-    echo "ERROR: Rootfs device $ROOTFS_DEV not found!"
-    echo "Available devices:"
-    ls -la /dev/
-    sleep 10
-    reboot -f
-fi
-
-# Create mount points for overlay setup
-mkdir -p /mnt/lower    # squashfs (read-only)
-mkdir -p /mnt/upper    # tmpfs for overlay upper
-mkdir -p /mnt/work     # tmpfs for overlay work
-mkdir -p /mnt/root     # final overlayfs mount
-
-# Mount squashfs read-only
-log "Mounting squashfs rootfs from $ROOTFS_DEV..."
-
-if ! mount -t squashfs -o ro "$ROOTFS_DEV" /mnt/lower; then
-    # Fallback to ext4 for backwards compatibility
-    log "squashfs mount failed, trying ext4..."
-    if ! mount -t ext4 -o ro "$ROOTFS_DEV" /mnt/lower; then
-        echo "ERROR: Failed to mount rootfs (tried squashfs and ext4)!"
-        sleep 10
-        reboot -f
-    fi
-    # ext4 fallback - just use it directly without overlay
-    log "Using ext4 rootfs directly (no overlay)"
-    mount --move /mnt/lower /mnt/root
-else
-    log "Squashfs mounted successfully"
-
-    # Create tmpfs for overlay upper/work directories
-    # Size is generous since container operations need temp space
-    log "Creating tmpfs overlay..."
-    mount -t tmpfs -o size=1G tmpfs /mnt/upper
-    mkdir -p /mnt/upper/upper
-    mkdir -p /mnt/upper/work
-
-    # Create overlayfs combining squashfs (lower) + tmpfs (upper)
-    log "Mounting overlayfs..."
-    if ! mount -t overlay overlay -o lowerdir=/mnt/lower,upperdir=/mnt/upper/upper,workdir=/mnt/upper/work /mnt/root; then
-        echo "ERROR: Failed to mount overlayfs!"
-        sleep 10
-        reboot -f
-    fi
-
-    log "Overlayfs mounted successfully"
-fi
-
-if [ "$QUIET" = "0" ]; then
-    echo "Contents:"
-    ls -la /mnt/root/
-fi
-
-# Verify init exists on rootfs
-if [ ! -x /mnt/root/init ] && [ ! -x /mnt/root/sbin/init ]; then
-    echo "ERROR: No init found on rootfs!"
-    sleep 10
-    reboot -f
-fi
-
-# Move filesystems to new root before switch_root
-# This way they persist across switch_root and the new init doesn't need to remount
-mkdir -p /mnt/root/proc /mnt/root/sys /mnt/root/dev
-mount --move /proc /mnt/root/proc
-mount --move /sys /mnt/root/sys
-mount --move /dev /mnt/root/dev
-
-# Switch to real root
-# switch_root will:
-# 1. Mount the new root
-# 2. chroot into it
-# 3. Execute the new init
-# 4. Delete everything in the old initramfs
-log "Switching to real root..."
-
-if [ -x /mnt/root/init ]; then
-    exec switch_root /mnt/root /init
-elif [ -x /mnt/root/sbin/init ]; then
-    exec switch_root /mnt/root /sbin/init
-fi
-
-# If we get here, switch_root failed
-echo "ERROR: switch_root failed!"
-sleep 10
-reboot -f
diff --git a/recipes-containers/vcontainer/vcontainer-preinit_1.0.bb b/recipes-containers/vcontainer/vcontainer-preinit_1.0.bb
new file mode 100644
index 00000000..078a5617
--- /dev/null
+++ b/recipes-containers/vcontainer/vcontainer-preinit_1.0.bb
@@ -0,0 +1,43 @@
+# SPDX-FileCopyrightText: Copyright (C) 2025 Bruce Ashfield
+#
+# SPDX-License-Identifier: MIT
+#
+# vcontainer-preinit_1.0.bb
+# ===========================================================================
+# Package containing the preinit script for vcontainer tiny initramfs
+# ===========================================================================
+#
+# This package installs the preinit script as /init for use in a tiny
+# initramfs. The script:
+#   1. Mounts essential filesystems (/proc, /sys, /dev)
+#   2. Mounts the squashfs rootfs from /dev/vda with overlayfs
+#   3. Executes switch_root to the real root filesystem
+#
+# Used by: vdkr-tiny-initramfs-image.bb, vpdmn-tiny-initramfs-image.bb
+#
+
+SUMMARY = "Preinit script for vcontainer initramfs"
+DESCRIPTION = "Minimal init script that mounts squashfs rootfs with overlayfs \
+               and performs switch_root for vcontainer QEMU environment."
+HOMEPAGE = "https://git.yoctoproject.org/meta-virtualization/"
+LICENSE = "GPL-2.0-only"
+LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/GPL-2.0-only;md5=801f80980d171dd6425610833a22dbe6"
+
+SRC_URI = "file://vcontainer-preinit.sh"
+
+S = "${UNPACKDIR}"
+
+# This package only provides the init script - no dependencies
+# The initramfs image will pull in busybox separately
+RDEPENDS:${PN} = ""
+
+do_install() {
+    install -d ${D}
+    install -m 0755 ${S}/vcontainer-preinit.sh ${D}/init
+}
+
+# Package the /init script
+FILES:${PN} = "/init"
+
+# Prevent QA warnings about /init location
+INSANE_SKIP:${PN} += "file-rdeps"
diff --git a/recipes-containers/vcontainer/vcontainer-tiny-initramfs-image.inc b/recipes-containers/vcontainer/vcontainer-tiny-initramfs-image.inc
new file mode 100644
index 00000000..1fef7822
--- /dev/null
+++ b/recipes-containers/vcontainer/vcontainer-tiny-initramfs-image.inc
@@ -0,0 +1,70 @@
+# SPDX-FileCopyrightText: Copyright (C) 2025 Bruce Ashfield
+#
+# SPDX-License-Identifier: MIT
+#
+# vcontainer-tiny-initramfs-image.inc
+# ===========================================================================
+# Shared tiny initramfs image for vdkr/vpdmn switch_root boot flow
+# ===========================================================================
+#
+# This produces a minimal cpio.gz initramfs containing only:
+#   - busybox (for mount, switch_root, sh, etc.)
+#   - vcontainer-preinit (the /init script)
+#
+# Boot flow:
+#   QEMU boots kernel + this initramfs
+#   -> /init (vcontainer-preinit) mounts squashfs rootfs.img from /dev/vda
+#   -> switch_root into rootfs.img with overlayfs
+#   -> ${runtime}-init.sh runs with full container tools
+#
+
+SUMMARY = "Tiny initramfs for vcontainer switch_root"
+DESCRIPTION = "Minimal initramfs containing busybox and preinit script for \
+               mounting squashfs rootfs and performing switch_root."
+LICENSE = "MIT"
+LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"
+
+inherit core-image
+
+# Minimal packages: just busybox and the preinit script
+# busybox provides: mount, switch_root, sh, mkdir, sleep, cat, ls, echo, reboot
+PACKAGE_INSTALL = "busybox vcontainer-preinit"
+
+# No extra features - keep it tiny
+IMAGE_FEATURES = ""
+
+# Don't include kernel in initramfs
+PACKAGE_EXCLUDE = "kernel-image-*"
+
+# Output as cpio.gz (standard initramfs format)
+IMAGE_FSTYPES = "${INITRAMFS_FSTYPES}"
+
+# Keep the image small
+IMAGE_ROOTFS_SIZE = "8192"
+IMAGE_ROOTFS_EXTRA_SPACE = "0"
+
+# No locales needed
+IMAGE_LINGUAS = ""
+
+# Suppress the suffix for cleaner naming
+IMAGE_NAME_SUFFIX = ""
+
+# Compatible with x86_64 and aarch64 targets
+COMPATIBLE_HOST = "(x86_64|aarch64).*-linux"
+
+# Create required directories that busybox/preinit expect
+ROOTFS_POSTPROCESS_COMMAND += "create_initramfs_dirs;"
+
+create_initramfs_dirs() {
+    # Create mount points used by preinit
+    install -d ${IMAGE_ROOTFS}/proc
+    install -d ${IMAGE_ROOTFS}/sys
+    install -d ${IMAGE_ROOTFS}/dev
+    install -d ${IMAGE_ROOTFS}/mnt/lower
+    install -d ${IMAGE_ROOTFS}/mnt/upper
+    install -d ${IMAGE_ROOTFS}/mnt/work
+    install -d ${IMAGE_ROOTFS}/mnt/root
+
+    # Create console device node (needed before /dev is mounted)
+    mknod -m 622 ${IMAGE_ROOTFS}/dev/console c 5 1 2>/dev/null || true
+}
diff --git a/recipes-containers/vcontainer/vdkr-tiny-initramfs-image.bb b/recipes-containers/vcontainer/vdkr-tiny-initramfs-image.bb
new file mode 100644
index 00000000..42aa8637
--- /dev/null
+++ b/recipes-containers/vcontainer/vdkr-tiny-initramfs-image.bb
@@ -0,0 +1,13 @@
+# SPDX-FileCopyrightText: Copyright (C) 2025 Bruce Ashfield
+#
+# SPDX-License-Identifier: MIT
+#
+# vdkr-tiny-initramfs-image.bb - Tiny initramfs for vdkr
+#
+# Build with:
+#   bitbake mc:vruntime-aarch64:vdkr-tiny-initramfs-image
+#   bitbake mc:vruntime-x86-64:vdkr-tiny-initramfs-image
+#
+# Output: ${DEPLOY_DIR_IMAGE}/vdkr-tiny-initramfs-image-${MACHINE}.cpio.gz
+
+require vcontainer-tiny-initramfs-image.inc
diff --git a/recipes-containers/vcontainer/vpdmn-tiny-initramfs-image.bb b/recipes-containers/vcontainer/vpdmn-tiny-initramfs-image.bb
new file mode 100644
index 00000000..c407f013
--- /dev/null
+++ b/recipes-containers/vcontainer/vpdmn-tiny-initramfs-image.bb
@@ -0,0 +1,13 @@
+# SPDX-FileCopyrightText: Copyright (C) 2025 Bruce Ashfield
+#
+# SPDX-License-Identifier: MIT
+#
+# vpdmn-tiny-initramfs-image.bb - Tiny initramfs for vpdmn
+#
+# Build with:
+#   bitbake mc:vruntime-aarch64:vpdmn-tiny-initramfs-image
+#   bitbake mc:vruntime-x86-64:vpdmn-tiny-initramfs-image
+#
+# Output: ${DEPLOY_DIR_IMAGE}/vpdmn-tiny-initramfs-image-${MACHINE}.cpio.gz
+
+require vcontainer-tiny-initramfs-image.inc
-- 
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