reset-build.sh

#!/usr/bin/env bash
#
# reset-build.sh — recreate the LFS disk image and prepare it for a fresh build.
#
# Does the mechanical, easy-to-get-wrong part of resetting an LFS 12.0 build:
#   1. (re)create the raw disk image
#   2. attach it to a loop device
#   3. partition it (msdos: /boot + /)
#   4. make ext4 filesystems
#   5. mount them at $LFS
#   6. rewrite etc/fstab in this repo with the REAL new UUIDs
#
# It stops there. The chapter work (host check, sources, jhalfs or the manual
# book steps) is up to you afterwards — see README / the build scripts.
#
# DESTRUCTIVE: partitioning + mkfs wipe the target image. Creating a new image
# over an existing one requires FORCE=1 so you can't nuke a good build by accident.
#
# Usage:
#   sudo ./reset-build.sh                 # refuses if the image already exists
#   sudo FORCE=1 ./reset-build.sh         # recreate even if the image exists
#   sudo IMG=/path/to.img LFS=/mnt/lfs SIZE=20G ./reset-build.sh
#
set -euo pipefail

# ---- config (override via env) ---------------------------------------------
IMG="${IMG:-$HOME/lfs-build/lfs-disk.img}"
LFS="${LFS:-/mnt/lfs}"
SIZE="${SIZE:-20G}"
BOOT_MIB_END="${BOOT_MIB_END:-512}"     # /boot = 1MiB .. BOOT_MIB_END
REPO_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
FSTAB="$REPO_DIR/etc/fstab"

# ---- preflight --------------------------------------------------------------
if [[ $EUID -ne 0 ]]; then
  echo "FATAL: must run as root (losetup/parted/mkfs/mount need it). Use: sudo $0" >&2
  exit 1
fi
for t in qemu-img losetup parted mkfs.ext4 blkid mountpoint; do
  command -v "$t" >/dev/null 2>&1 || { echo "FATAL: missing required tool: $t" >&2; exit 1; }
done

echo ">>> Target image : $IMG"
echo ">>> Mount point   : $LFS"
echo ">>> Image size    : $SIZE"
echo ">>> /boot end     : ${BOOT_MIB_END}MiB"
echo

# ---- 0. guard against clobbering a good image -------------------------------
if [[ -e "$IMG" && "${FORCE:-0}" != "1" ]]; then
  echo "REFUSING: $IMG already exists. Re-run with FORCE=1 to recreate it (this ERASES it)." >&2
  exit 1
fi

# ---- cleanup trap: always detach the loop device on exit --------------------
LOOP=""
cleanup() { [[ -n "$LOOP" ]] && losetup -d "$LOOP" 2>/dev/null || true; }
# only detach on ERROR; on success we leave filesystems mounted for the build.
trap '[[ $? -ne 0 ]] && cleanup' EXIT

# ---- 1. create the image ----------------------------------------------------
mkdir -p "$(dirname "$IMG")"
# make sure nothing from a previous run is still mounted under $LFS
if mountpoint -q "$LFS/boot"; then umount "$LFS/boot"; fi
if mountpoint -q "$LFS";      then umount "$LFS";      fi
echo ">>> Creating raw image ($SIZE) ..."
rm -f "$IMG"
qemu-img create -f raw "$IMG" "$SIZE"

# ---- 2. attach --------------------------------------------------------------
LOOP="$(losetup -fP --show "$IMG")"
echo ">>> Attached at $LOOP"

# ---- 3. partition (msdos: p1=/boot, p2=/) -----------------------------------
echo ">>> Partitioning ..."
parted -s "$LOOP" mklabel msdos
parted -s "$LOOP" -- mkpart primary ext4 1MiB "${BOOT_MIB_END}MiB"
parted -s "$LOOP" -- mkpart primary ext4 "${BOOT_MIB_END}MiB" 100%
parted -s "$LOOP" set 1 boot on
partprobe "$LOOP" 2>/dev/null || true
sleep 1
BOOT_PART="${LOOP}p1"
ROOT_PART="${LOOP}p2"
[[ -b "$BOOT_PART" && -b "$ROOT_PART" ]] || { echo "FATAL: partitions did not appear" >&2; exit 1; }

# ---- 4. filesystems ---------------------------------------------------------
echo ">>> Formatting ext4 ..."
mkfs.ext4 -q -L lfsboot "$BOOT_PART"
mkfs.ext4 -q -L lfsroot "$ROOT_PART"

# ---- 5. mount ---------------------------------------------------------------
echo ">>> Mounting at $LFS ..."
mkdir -p "$LFS"
mount "$ROOT_PART" "$LFS"
mkdir -p "$LFS/boot"
mount "$BOOT_PART" "$LFS/boot"

# ---- 6. rewrite repo etc/fstab with real UUIDs ------------------------------
ROOT_UUID="$(blkid -s UUID -o value "$ROOT_PART")"
BOOT_UUID="$(blkid -s UUID -o value "$BOOT_PART")"
echo ">>> root UUID = $ROOT_UUID"
echo ">>> boot UUID = $BOOT_UUID"

if [[ -f "$FSTAB" ]]; then cp -a "$FSTAB" "$FSTAB.bak.$(date +%s)"; fi
cat > "$FSTAB" <<EOF
# Begin /etc/fstab
# Regenerated by reset-build.sh on $(date -u +%Y-%m-%dT%H:%M:%SZ)

# file system   mount-point  type   options             dump  fsck
UUID=$ROOT_UUID   /            ext4   defaults            1     1
UUID=$BOOT_UUID   /boot        ext4   defaults            1     2

proc            /proc          proc     nosuid,noexec,nodev 0     0
sysfs           /sys           sysfs    nosuid,noexec,nodev 0     0
devpts          /dev/pts       devpts   gid=5,mode=620      0     0
tmpfs           /run           tmpfs    defaults            0     0
devtmpfs        /dev           devtmpfs mode=0755,nosuid    0     0
tmpfs           /dev/shm       tmpfs    nosuid,nodev        0     0
cgroup2         /sys/fs/cgroup cgroup2  nosuid,noexec,nodev 0     0

# End /etc/fstab
EOF
echo ">>> Wrote $FSTAB (backup saved alongside)"

cat <<EOF

================================================================================
Disk reset complete.

  image : $IMG
  loop  : $LOOP   (left attached)
  root  : $ROOT_PART  -> $LFS        (ext4, UUID $ROOT_UUID)
  boot  : $BOOT_PART  -> $LFS/boot   (ext4, UUID $BOOT_UUID)

Next steps:
  export LFS=$LFS
  # host sanity check:
  bash packages/checkfiles.sh
  # then: create sources dir, download LFS 12.0 wget-list, and build
  # (jhalfs with boot/config-6.4.12 as the kernel .config, or the manual book).

When done building, detach with:
  umount $LFS/boot && umount $LFS && losetup -d $LOOP
================================================================================
EOF