#!/bin/sh
# genfstab <target-root>  -  print an /etc/fstab for whatever is mounted
# under <target-root> right now, reading /proc/mounts from the caller's
# own environment (this has to run before chroot, not after - a chroot
# has no view of the outer mount table without proc bind-mounted first).
#
#   genfstab /mnt >> /mnt/etc/fstab
#
# shellcheck shell=sh disable=SC2039

set -u
_t=${1:?usage: genfstab <target-root>}

printf '# ScrapLinux - /etc/fstab\n'
printf '# <device>\t<mount>\t<type>\t<options>\t<dump>\t<pass>\n'

# Longest paths last so /boot/efi is written after /boot, which is the
# order mount(8) needs to be able to replay them at boot.
awk -v t="$_t" '
	$2 == t            { print $1, "/",                  $3, $4; next }
	index($2, t"/")==1 { print $1, substr($2, length(t)+1), $3, $4 }
' /proc/mounts | sort -k2,2 | while read -r dev mnt type opts; do
	case "$type" in
	autofs|proc|sysfs|devtmpfs|devpts|tmpfs|cgroup*|securityfs|debugfs|\
	tracefs|mqueue|hugetlbfs|configfs|fusectl|pstore|bpf|ramfs|squashfs|overlay)
		continue ;;
	esac
	case "$dev" in /dev/*) ;; *) continue ;; esac

	# UUID before PARTUUID: the initramfs resolves root= with busybox
	# findfs, which only understands LABEL=/UUID=, never PARTUUID=.
	uuid=$(blkid -s UUID -o value "$dev" 2>/dev/null)
	if [ -n "$uuid" ]; then
		spec="UUID=$uuid"
	else
		partuuid=$(blkid -s PARTUUID -o value "$dev" 2>/dev/null)
		spec=${partuuid:+PARTUUID=$partuuid}; spec=${spec:-$dev}
	fi

	# Keep only the mount options worth persisting. The kernel reports
	# plenty that are either defaults or meaningless in fstab.
	keep=""
	OIFS=$IFS; IFS=,
	for o in $opts; do
		case "$o" in
		rw|ro|noatime|relatime|nodiratime|nosuid|nodev|noexec|discard*|\
		compress=*|compress-force=*|subvol=*|subvolid=*|space_cache*|\
		ssd|autodefrag|commit=*|fmask=*|dmask=*|utf8*|iocharset=*|\
		shortname=*|errors=*|data=*|barrier*|journal_checksum)
			keep="${keep:+$keep,}$o" ;;
		esac
	done
	IFS=$OIFS
	[ -n "$keep" ] || keep=defaults

	# fsck pass: root first, other real filesystems after, never for
	# btrfs (which has no fsck to run at boot) or vfat ESPs.
	case "$type" in
	btrfs)     pass=0 ;;
	vfat)      pass=2 ;;
	*) [ "$mnt" = / ] && pass=1 || pass=2 ;;
	esac
	[ "$mnt" = / ] && [ "$type" = btrfs ] && pass=0

	printf '%s\t%s\t%s\t%s\t0\t%s\n' "$spec" "$mnt" "$type" "$keep" "$pass"
done

printf 'tmpfs\t/tmp\ttmpfs\trw,nosuid,nodev,size=50%%\t0\t0\n'
printf 'proc\t/proc\tproc\trw,nosuid,nodev,noexec\t0\t0\n'
printf 'sysfs\t/sys\tsysfs\trw,nosuid,nodev,noexec\t0\t0\n'
printf 'devpts\t/dev/pts\tdevpts\trw,nosuid,noexec,gid=5,mode=620\t0\t0\n'