#!/bin/sh
# prepare-linux-initramfs.sh
#
# Checks (default) or adds (--apply) the storage and network drivers a Linux guest
# needs in its initramfs to boot on the target hypervisor, BEFORE the conversion.
#   hyperv : hv_vmbus hv_storvsc hv_netvsc
#   virtio : virtio_pci virtio_blk virtio_scsi virtio_net   (Nutanix AHV, Proxmox VE, KVM)
#
# Supports dracut (RHEL, Rocky, Alma, SUSE, Fedora) and initramfs-tools (Debian, Ubuntu).
# Drivers built into the kernel (=y) need nothing and are reported as such.
#
# Usage:  sudo sh prepare-linux-initramfs.sh hyperv            # check only
#         sudo sh prepare-linux-initramfs.sh virtio --apply    # add missing drivers, rebuild
#
# Take a snapshot or a backup first. Rebuilding the initramfs of the running kernel is a
# boot-critical change: keep the previous kernel entry available in the boot menu.
# Source: ANYSYS ICT, https://www.anysys.be/articles/

set -eu

TARGET="${1:-}"
MODE="${2:-check}"
KVER="${KVER:-$(uname -r)}"

case "$TARGET" in
  hyperv) MODULES="hv_vmbus hv_storvsc hv_netvsc" ;;
  virtio) MODULES="virtio_pci virtio_blk virtio_scsi virtio_net" ;;
  *) echo "usage: $0 hyperv|virtio [--apply]" >&2; exit 2 ;;
esac

if command -v dracut >/dev/null 2>&1 && [ ! -d /etc/initramfs-tools ]; then
  TOOL=dracut
elif [ -d /etc/initramfs-tools ]; then
  TOOL=initramfs-tools
else
  echo "Neither dracut nor initramfs-tools found: prepare this guest manually." >&2
  exit 3
fi

BUILTIN="/lib/modules/$KVER/modules.builtin"

# RHEL family names the image initramfs-<kver>.img, Debian family initrd.img-<kver>.
if [ -f "/boot/initramfs-$KVER.img" ]; then
  IMG="/boot/initramfs-$KVER.img"
else
  IMG="/boot/initrd.img-$KVER"
fi

list_initramfs() {
  if [ "$TOOL" = dracut ]; then
    lsinitrd "$IMG" 2>/dev/null
  else
    lsinitramfs "$IMG" 2>/dev/null
  fi
}

CONTENT="$(list_initramfs || true)"
MISSING=""
for m in $MODULES; do
  if [ -f "$BUILTIN" ] && grep -q "/$m.ko" "$BUILTIN"; then
    echo "builtin   $m"
  elif printf '%s\n' "$CONTENT" | grep -q "/$m.ko"; then
    echo "present   $m"
  else
    echo "MISSING   $m"
    MISSING="$MISSING $m"
  fi
done

echo "kernel=$KVER tool=$TOOL image=$IMG target=$TARGET"

if [ -z "$MISSING" ]; then
  echo "Nothing to do."
  exit 0
fi

if [ "$MODE" != "--apply" ]; then
  echo "Run again with --apply to add:$MISSING"
  exit 1
fi

if [ "$TOOL" = dracut ]; then
  CONF="/etc/dracut.conf.d/90-migration-$TARGET.conf"
  echo "add_drivers+=\"$MISSING \"" > "$CONF"
  echo "wrote $CONF"
  dracut -f "$IMG" "$KVER"
else
  for m in $MISSING; do
    grep -qx "$m" /etc/initramfs-tools/modules || echo "$m" >> /etc/initramfs-tools/modules
  done
  echo "updated /etc/initramfs-tools/modules"
  update-initramfs -u -k "$KVER"
fi

echo "Rebuilt. Verify with: $0 $TARGET"