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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
EOF
}
log() {
fmt=$1
shift
printf "tmpoverlay: $fmt\n" "$@" >&2
}
logv() {
if [ -n "$verbose" ]; then
log "$@"
fi
}
die() {
log "$@"
exit 1
}
canon() {
if [ -n "$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 no_mtab extra_overlayfs_opts tmpfs_opts tmpdir verbose
while true; do
case "$1" in
-c|--no-canonicalize) no_canon=-c; shift;;
-h|--help) usage; exit 0;;
-o|--overlayfs)
[ -n "$2" ] && extra_overlayfs_opts="$extra_overlayfs_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 "$1")
echo lowerdir=$lowerdir dest=$dest
[ -d "$dest" ] || die 'destination "%s" is not a directory' "$dest"
[ "$dest" != / ] || log 'overmounting root, use with caution'
if [ -z "$lowerdir" ]; then
lowerdir=$dest
fi
err() {
r=$?
trap - INT TERM QUIT
logv 'an error occurred, cleaning up'
if [ -d "$tmpdir" ]; then
if mountpoint -q "$tmpdir"; then
logv 'unmounting tmpdir'
umount $no_mtab "$tmpdir"
fi
logv 'deleting tmpdir'
rmdir "$tmpdir"
fi
case $1 in
[A-Z]*) logv 'reraising SIG%s' $1; kill -$1 $$ && read _
esac
logv 'exiting'
if [ $r = 0 ]; then
exit 1
fi
exit $r
}
trap 'err INT' INT
trap 'err TERM' TERM
trap 'err QUIT' QUIT
if [ -z "$tmpdir" ]; then
logv 'creating tmpdir'
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" || err
upperdir="$tmpdir/upper"
workdir="$tmpdir/work"
logv 'creating upper/work dirs'
mkdir "$upperdir" "$workdir" || err
# 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") || err
chown $owner "$upperdir" || err
logv 'copying lowerdir perms to upperdir'
mode=$(stat -c %a "$lastlowerdir") || err
chmod $mode "$upperdir" || err
# -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 attrs'
if attr=$(cd "$lastlowerdir" && getfattr -d -m - . 2>/dev/null); then
if [ -n "$attr" ]; then
printf '%s\n' "$attr" | (cd "$upperdir"; setfattr --restore=-) || err
fi
else
log 'getfattr not found or failed, skipping xattrs'
fi
logv 'mounting overlay'
overlayfs_opts="lowerdir=$lowerdir,upperdir=$upperdir,workdir=$workdir,volatile$extra_overlayfs_opts"
mount -t overlay -o "$overlayfs_opts" $no_canon $no_mtab $verbose ${mount_name-overlay} "$dest" || err
logv 'cleaning up'
umount "$tmpdir" || exit
rmdir "$tmpdir" || exit
logv 'done, exiting'
|
