#!/bin/bash
# Kernel-lane spike (R-836, `09` §3 decision 164) — set up on a Proxmox host WITHOUT rebooting. Reversible: spike-undo.sh.
# Usage: spike-setup.sh <old-kver> <new-kver>     e.g. spike-setup.sh 7.0.2-6-pve 7.0.14-20-pve
set -euo pipefail
OLD=$1 NEW=$2
ROOTUUID=$(findmnt -n -o UUID /)
ESPUUID=$(findmnt -n -o UUID /boot/efi)
ROOTDEV=$(findmnt -n -o SOURCE /)
ADV="gnulinux-advanced-$ROOTUUID"
[ -f /etc/default/grub.felhom-spike-orig ] || cp -p /etc/default/grub /etc/default/grub.felhom-spike-orig
# 1. the OLD kernel is the default (an install of a new kernel made the NEW one default — R-836)
sed -i "s|^GRUB_DEFAULT=.*|GRUB_DEFAULT=\"$ADV>gnulinux-$OLD-advanced-$ROOTUUID\"|" /etc/default/grub
# 2. candidate 2: a one-shot flag in a GRUB environment block on the ESP (vfat — GRUB can rewrite it in place)
grub-editenv /boot/efi/EFI/proxmox/felhom-oneshot.env create
cat > /etc/grub.d/01_felhom_oneshot <<SNIP
#!/bin/sh
cat <<'G'
# felhom kernel-lane spike: a one-shot default read from (and cleared in) an env block on the ESP
insmod part_gpt
insmod fat
search --no-floppy --fs-uuid --set=felhom_esp $ESPUUID
if [ -f (\$felhom_esp)/EFI/proxmox/felhom-oneshot.env ]; then
  load_env -f (\$felhom_esp)/EFI/proxmox/felhom-oneshot.env felhom_next
  if [ "\${felhom_next}" ]; then
    set default="\${felhom_next}"
    set felhom_next=
    save_env -f (\$felhom_esp)/EFI/proxmox/felhom-oneshot.env felhom_next
  fi
fi
G
SNIP
chmod 0755 /etc/grub.d/01_felhom_oneshot
# 3. the test entries: the NEW kernel healthy, and two simulated hangs before userspace (no init → kernel panic)
entry() { # id title extra-cmdline
cat <<G
menuentry '$2' --id $1 {
  insmod gzio
  insmod part_gpt
  insmod lvm
  insmod ext2
  search --no-floppy --fs-uuid --set=root $ROOTUUID
  linux /boot/vmlinuz-$NEW root=$ROOTDEV ro quiet $3
  initrd /boot/initrd.img-$NEW
}
G
}
{ echo '#!/bin/sh'; echo "cat <<'G'"
  entry felhom-spike-good  "felhom spike: $NEW healthy"            "panic=10"
  entry felhom-spike-panic "felhom spike: $NEW, panic, restart 10s" "rdinit=/felhom-spike-no-rdinit init=/felhom-spike-no-init panic=10"
  entry felhom-spike-freeze "felhom spike: $NEW, panic, NO restart" "rdinit=/felhom-spike-no-rdinit init=/felhom-spike-no-init panic=0"
  echo G; } > /etc/grub.d/41_felhom_spike
chmod 0755 /etc/grub.d/41_felhom_spike
update-grub 2>&1 | tail -2
grub-script-check /boot/grub/grub.cfg && echo "grub.cfg syntax OK"
grep -n 'felhom_next\|felhom-spike-\|^set default' /boot/grub/grub.cfg | head -20
grub-editenv /boot/efi/EFI/proxmox/felhom-oneshot.env list; echo "(env listed above; empty = no one-shot)"