chimera-chroot

#!/bin/sh
#
# Chimera Linux chroot script
#
# Copyright 2023-2024 q66 <q66@chimera-linux.org>
#
# License: BSD-2-Clause
#

readonly PROGNAME=$(basename "$0")

MOUNTED_PSEUDO=
ROOT_DIR=
RESOLV_SAVED=
RESOLV_REPLACED=

do_trymount() {
    if mountpoint -q "${ROOT_DIR}/$1" > /dev/null 2>&1; then
        return 0
    fi
    mount --rbind "/$1" "${ROOT_DIR}/$1" || die "Failed to mount ${1}fs"
    mount --make-rslave "${ROOT_DIR}/$1" || die "Failed to make ${1} rslave"
    MOUNTED_PSEUDO="${MOUNTED_PSEUDO} $1"
}

mount_pseudo() {
    do_trymount dev
    do_trymount proc
    do_trymount sys
    do_trymount tmp
}

umount_pseudo() {
    sync
    for mnt in ${MOUNTED_PSEUDO}; do
        [ -n "$mnt" ] || continue
        umount -R -f "${ROOT_DIR}/$mnt" > /dev/null 2>&1
    done
}

replace_resolv() {
    # do not touch if target /etc is missing or if we do not have resolv.conf
    [ -d "${ROOT_DIR}/etc" -a -f /etc/resolv.conf ] || return 0
    RESOLV_REPLACED="${ROOT_DIR}/etc/resolv.conf"
    # save the existing one if needed
    if [ -e "$RESOLV_REPLACED" -o -L "$RESOLV_REPLACED" ]; then
        RESOLV_SAVED="${ROOT_DIR}/etc/resolv.conf.chimera-chroot.$$"
        # make space, this should not do anything
        rm -f "$RESOLV_SAVED" > /dev/null 2>&1
        # try moving, on failure unset saved
        if ! mv "$RESOLV_REPLACED" "$RESOLV_SAVED" > /dev/null 2>&1; then
            RESOLV_SAVED=
            RESOLV_REPLACED=
            return 0
        fi
    fi
    # now replace it
    cp /etc/resolv.conf "$RESOLV_REPLACED" > /dev/null 2>&1
}

restore_resolv() {
    # restore best we can
    [ -n "$RESOLV_REPLACED" ] && \
        rm -f "$RESOLV_REPLACED" > /dev/null 2>&1
    [ -n "$RESOLV_SAVED" ] && \
        mv "$RESOLV_SAVED" "$RESOLV_REPLACED" > /dev/null 2>&1
    RESOLV_SAVED=
    RESOLV_REPLACED=
}

msg() {
    printf "\033[1m$@\n\033[m"
}

error_sig() {
    restore_resolv
    umount_pseudo
    [ -n "$REPOSF" ] && rm -f "$REPOSF"
    [ -n "$EREPOSF" ] && rm -f "$EREPOSF"
    exit ${1:=0}
}

trap 'error_sig $? $LINENO' INT TERM 0

die() {
    echo "ERROR: $@"
    error_sig 1 $LINENO
}

usage() {
    cat << EOF
Usage: $PROGNAME [opts] root [command] [args]...

This script chroots into the given root, much like the actual chroot
command. However, it also ensures that pseudo-filesystems are mounted
and other things necessary for remote installation manipulation.

Options:
  -r  Do not touch resolv.conf.
  -h  Print this message.
EOF
    exit ${1:=1}
}

# ensure we run as root
if [ "$(id -u)" != "0" ]; then
    die "Must run this as root."
fi

REPLACE_RESOLV=1

while getopts "rh" opt; do
    case "$opt" in
        r) REPLACE_RESOLV=0 ;;
        h) usage 0 ;;
        *) usage 1 ;;
    esac
done

shift $((OPTIND - 1))

ROOT_DIR="$1"
shift

# ensure the target exists
[ -d "$ROOT_DIR" ] || die "root directory does not exist"

mount_pseudo

if [ "$REPLACE_RESOLV" -eq 1 ]; then
    replace_resolv
fi

if [ -f "${ROOT_DIR}/etc/chimera-release" ]; then
    export SHELL=/bin/sh
fi
PS1="(chroot) $PS1" chroot "$ROOT_DIR" "$@"
RC=$?

restore_resolv
umount_pseudo

exit $RC