vxn: add Xen DomU container runtime with OCI image support

vxn runs OCI containers as Xen DomU guests — the VM IS the container.
No Docker/containerd runs inside the guest; the init script directly
mounts the container rootfs and execs the entrypoint via chroot.

Host-side (Dom0):
- vxn.sh: Docker-like CLI wrapper (sets HYPERVISOR=xen)
- vrunner-backend-xen.sh: Xen xl backend for vrunner
  - hv_prepare_container(): pulls OCI images via skopeo,
    resolves entrypoint from OCI config using jq on host
  - xl create for VM lifecycle (PVH on aarch64, PV on x86_64)
  - Bridge networking with iptables DNAT for port forwards
  - Console capture via xl console for ephemeral mode

Guest-side (DomU):
- vxn-init.sh: mounts container rootfs from input disk,
  extracts OCI layers, execs entrypoint via chroot
  - Supports containers with or without /bin/sh
  - grep/sed fallback for OCI config parsing (no jq needed)
  - Daemon mode with command loop on hvc1
- vcontainer-init-common.sh: hypervisor detection, head -n fix
- vcontainer-preinit.sh: init selection via vcontainer.init=

Build system:
- vxn-initramfs-create.inc: assembles boot blobs from vruntime
  multiconfig, injects vxn-init.sh into rootfs squashfs
- vxn_1.0.bb: Dom0 package with scripts + blobs
  - nostamp on install/package chain (blobs from DEPLOY_DIR
    are untracked by sstate)
- vxn.cfg: Xen PV kernel config fragment

Tested: vxn -it --no-daemon run --rm hello-world

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

1 files changed, 24 insertions, 0 deletions

diff --git a/recipes-kernel/linux/linux-yocto/vxn.cfg b/recipes-kernel/linux/linux-yocto/vxn.cfg
new file mode 100644
index 00000000..932732dc
--- /dev/null
+++ b/recipes-kernel/linux/linux-yocto/vxn.cfg
@@ -0,0 +1,24 @@
+# Xen PV guest support for vxn (vcontainer on Xen)
+# These configs enable a kernel to run as a Xen PV or PVHVM guest
+# with virtio-equivalent functionality via Xen paravirtualized drivers.
+
+# Core Xen guest support
+CONFIG_XEN=y
+CONFIG_XEN_PV=y
+CONFIG_XEN_PVHVM=y
+
+# Block device frontend (guest sees /dev/xvd*)
+CONFIG_XEN_BLKDEV_FRONTEND=y
+
+# Network frontend (guest sees eth0 via xennet)
+CONFIG_XEN_NETDEV_FRONTEND=y
+
+# PV console (guest sees /dev/hvc0, /dev/hvc1)
+CONFIG_HVC_XEN=y
+CONFIG_HVC_XEN_FRONTEND=y
+
+# Framebuffer frontend (not strictly required but useful)
+CONFIG_XEN_FBDEV_FRONTEND=y
+
+# 9pfs frontend for file sharing (trans=xen)
+CONFIG_XEN_9PFS_FRONTEND=y