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|
#!/bin/sh
usage() {
cat << EOF
usage: tmpoverlay [OPTIONS] [SOURCE...] DEST
Create a tmpfs-backed overlayfs at DEST starting with SOURCEs. If no SOURCE is
specified, use DEST as the source. To free the memory, simply umount DEST.
options:
-c, --no-canonicalize don't canonicalize paths
-h, --help print this help
-o, --overlayfs OPTS add overlayfs mount options, e.g. redirect_dir/metacopy
-n, --no-mtab don't write to /etc/mtab
-N, --mount-name NAME source name for mount (default "overlay")
-t, --tmpfs OPTS add tmpfs mount options, e.g. size
-v, --verbose verbose mode
examples:
tmpoverlay / /new_root # make a thin copy of root
tmpoverlay /etc # make read-only /etc writable
tmpoverlay /a /b /c /merged # merge /a, /b, /c, and a fresh tmpfs
tmpoverlay / # USE WITH CAUTION, see docs
EOF
}
log() {
fmt=$1
shift
printf 'tmpoverlay: ' >&2
# shellcheck disable=SC2059
printf "$fmt" "$@" >&2
printf '\n' >&2
}
logv() {
if [ -n "$verbose" ]; then
log "$@"
fi
}
cmdv() {
logv '%s ' "$@"
"$@"
}
unset own_tmpdir
die() {
r=$?
trap - INT TERM QUIT
unset sig
case $1 in
-[A-Z]*) sig=${1#-};;
'') ;;
*) log "$@"
esac
logv 'an error occurred, cleaning up'
if [ -d "$tmpdir" ] && [ -n "$own_tmpdir" ]; then
if mountpoint -q "$tmpdir"; then
logv 'unmounting tmpdir'
# shellcheck disable=SC2086
umount $no_mtab "$tmpdir"
fi
logv 'deleting tmpdir'
rmdir "$tmpdir"
fi
if [ -n "$sig" ]; then
logv 'reraising SIG%s' "$1"
kill "-$1" "$$" && read -r _
fi
logv 'exiting'
if [ $r = 0 ]; then
exit 1
fi
exit $r
}
canon() {
if [ -n "$no_canon" ]; then
printf '%s\n' "$1"
else
realpath "$1"
fi
}
my_getopt() {
getopt \
-l no-canonicalize \
-l help \
-l overlayfs: \
-l no-mtab \
-l mount-name: \
-l tmpfs: \
-l verbose \
-n tmpoverlay \
-- \
cho:nN:t:v \
"$@"
}
args=$(my_getopt "$@") || { usage >&2; exit 1; }
eval set -- "$args"
unset args
unset no_canon extra_ovl_opts no_mtab mount_name tmpfs_opts verbose
while true; do
case "$1" in
-c|--no-canonicalize) no_canon=-c; shift;;
-h|--help) usage; exit 0;;
-o|--overlayfs)
[ -n "$2" ] && extra_ovl_opts="$extra_ovl_opts,$2"
shift 2
;;
-n|--no-mtab) no_mtab=-n; shift;;
-N|--mount-name) mount_name=$2; shift 2;;
-t|--tmpfs)
[ -n "$2" ] && tmpfs_opts="${tmpfs_opts:+$tmpfs_opts,}$2"
shift 2
;;
-v|--verbose) verbose=-v; shift;;
--) shift; break;;
*) die "getopt failure"
esac
done
[ $# != 0 ] || { log 'no paths specified'; usage >&2; exit 1; }
unset lowerdir
while [ -n "$2" ]; do
d=$(canon "$1")
if [ -h "$d" ] || ! [ -d "$d" ]; then
die 'source "%s" is not a directory' "$d"
fi
lowerdir=${lowerdir+:}$d
shift
done
dest=$(canon "$1")
[ -d "$dest" ] || die 'destination "%s" is not a directory' "$dest"
[ "$dest" != / ] || log 'overmounting root, use with caution'
if [ -z "$lowerdir" ]; then
lowerdir=$dest
fi
trap 'die -INT' INT
trap 'die -TERM' TERM
trap 'die -QUIT' QUIT
if [ -z "$tmpdir" ]; then
logv 'creating tmpdir'
own_tmpdir=1
tmpdir=$(umask 077; mktemp -dt tmpoverlay.XXXXXXXXXX) || exit 1
logv 'created tmpdir: %s' "$tmpdir"
fi
mount -t tmpfs ${tmpfs_opts:+-o "$tmpfs_opts"} ${verbose:+-v} tmpfs "$tmpdir" || die
upperdir="$tmpdir/upper"
workdir="$tmpdir/work"
tmpmnt="$tmpdir/tmpmnt"
logv 'creating dirs'
mkdir "$upperdir" "$workdir" "$tmpmnt" || die
ovl_opts="lowerdir=$lowerdir,upperdir=$upperdir,workdir=$workdir"
logv 'testing overlay options'
mount -n -t overlay -o "$ovl_opts" overlay "$tmpmnt" || die "overlayfs is not supported"
umount "$tmpmnt"
if [ -n "$extra_ovl_opts" ]; then
ovl_opts="$ovl_opts,$extra_ovl_opts"
mount -n -t overlay -o "$ovl_opts" overlay "$tmpmnt" || die "invalid extra overlayfs options"
umount "$tmpmnt"
fi
chk_ovl_opt() {
if [ -n "$2" ]; then
case ",$ovl_opts," in
*",$1=$2,"*) return 0
esac
[ "$2" = on ] && val=Y || val=N
else
val=Y
fi
f=/sys/module/overlay/parameters/$1
[ -e "$f" ] && [ "$(cat "$f")" = "$val" ]
}
try_ovl_opt() {
# returns 0 iff option is/gets enabled
case ",$ovl_opts," in
*",$1=off,"*) return 1;;
*",$1[=,]"*) return 0
esac
if chk_ovl_opt "$1"; then
logv 'skipping %s'
return
fi
logv 'trying %s' "$1${2+=$2}"
new_ovl_opts="$ovl_opts,$1${2+=$2}"
mount -n -t overlay -o "$new_ovl_opts" "overlay" "$tmpmnt" 2>/dev/null || return
umount "$tmpmnt" || die
# clear out workdir/work/incompat/volatile and upperdir index
rm -r "$workdir" "$upperdir" || die
mkdir "$upperdir" "$workdir" || die
ovl_opts="$new_ovl_opts"
}
try_ovl_opt index on
# redirect_dir/metacopy are unsafe with untrusted non-bottom layers
[ "${lowerdir#*:}" = "$lowerdir" ] && \
! chk_ovl_opt userxattr on && \
try_ovl_opt redirect_dir on && \
{ chk_ovl_opt nfs_export on || try_ovl_opt metacopy on; }
try_ovl_opt volatile
# try to match perms/attrs. this is not race-free but it's impossible without
# atomic (CAS) chown/chmod/setfattr. chown --from is not atomic, not portable,
# and also doesn't cover chmod/setfattr.
lastlowerdir=${lowerdir##*:}
logv 'copying lowerdir owner to upperdir'
owner=$(stat -c %u:%g "$lastlowerdir") || die
chown "$owner" "$upperdir" || die
logv 'copying lowerdir perms to upperdir'
mode=$(stat -c %a "$lastlowerdir") || die
chmod "$mode" "$upperdir" || die
# -m - covers ACLs (system.posix_acl_access) and file caps
# (security.capability). theoretically someone might have get/setcap and/or
# get/setfacl but not get/setxattr, but this is unlikely since libcap/acl
# require attr.
logv 'copying root xattrs'
if attrs=$(cd "$lastlowerdir" && getfattr -d -m - . 2>/dev/null); then
if [ -n "$attrs" ]; then
printf '%s\n' "$attrs" | (cd "$upperdir"; setfattr --restore=-) || die
fi
else
log 'getfattr not found or failed, skipping xattrs'
fi
logv 'mounting overlay'
mount_opts="$no_canon $no_mtab $verbose"
# shellcheck disable=SC2086
cmdv mount $mount_opts -t overlay -o "$ovl_opts" "${mount_name-overlay}" "$dest" || die
logv 'cleaning up'
umount "$tmpdir" || exit
rmdir "$tmpdir" || exit
logv 'done'
|
