#!/bin/sh
#
# overlayroot-chroot - chroot wrapper script for overlayroot
# Copyright (C) 2012 Dustin Kirkland <kirkland@ubuntu.com>
#
# Authors: Dustin Kirkland <kirkland@ubuntu.com>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, version 3 of the License.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
set -e
set -f # disable path expansion
REMOUNTS=""
error() {
printf "ERROR: $@\n" 1>&2
}
fail() { [ $# -eq 0 ] || error "$@"; exit 1; }
info() {
printf "INFO: $@\n" 1>&2
}
get_lowerdir() {
local overlay=""
overlay=$(awk \
'$1 == "overlayroot" && $2 == "/" { print $0 }' /proc/mounts)
if [ -n "${overlay}" ]; then
lowerdir=${overlay##*lowerdir=}
lowerdir=${lowerdir%%,*}
if mountpoint "${lowerdir}" >/dev/null; then
_RET="${lowerdir}"
else
fail "Unable to find the overlayroot lowerdir"
fi
else
fail "Unable to find an overlayroot filesystem"
fi
}
clean_exit() {
local mounts="$1" rc=0 d="" lowerdir="" mp=""
for d in ${mounts}; do
if mountpoint ${d} >/dev/null; then
umount ${d} || rc=1
fi
done
for mp in $REMOUNTS; do
mount -o remount,ro "${mp}" ||
error "Note that [${mp}] is still mounted read/write"
done
[ "$2" = "return" ] && return ${rc} || exit ${rc}
}
# Try to find the overlayroot filesystem
get_lowerdir
lowerdir=${_RET}
recurse_mps=$(awk '$1 ~ /^\/dev\// && $2 ~ starts { print $2 }' \
starts="^$lowerdir/" /proc/mounts)
mounts=
for d in proc run sys; do
if ! mountpoint "${lowerdir}/${d}" >/dev/null; then
mount -o bind "/${d}" "${lowerdir}/${d}" || fail "Unable to bind /${d}"
mounts="$mounts $lowerdir/$d"
trap "clean_exit \"${mounts}\" || true" EXIT HUP INT QUIT TERM
fi
done
# Remount with read/write
for mp in "$lowerdir" $recurse_mps; do
mount -o remount,rw "${mp}" &&
REMOUNTS="$mp $REMOUNTS" ||
fail "Unable to remount [$mp] writable"
done
info "Chrooting into [${lowerdir}]"
chroot ${lowerdir} "$@"
# Clean up mounts on exit
clean_exit "${mounts}" "return"
trap "" EXIT HUP INT QUIT TERM
# vi: ts=4 noexpandtab
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