diff options
Diffstat (limited to 'tmpoverlay')
| -rwxr-xr-x | tmpoverlay | 187 |
1 files changed, 122 insertions, 65 deletions
@@ -2,31 +2,24 @@ usage() { cat << EOF -usage: tmpoverlay [OPTIONS] SOURCE [DESTINATION] +usage: tmpoverlay [OPTIONS] [SOURCE...] DEST -Create a tmpfs-backed overlayfs for SOURCE, which is one or more directories -separated by colons. If DESTINATION is specified, mount the result at -DESTINATION. Otherwise, mount it on top of the last SOURCE. - -To free the memory, simply unmount the DESTINATION. - -tmpoverlay is not fully race-safe. It tries to match the ownership and -permissions of the tmpfs to the final SOURCE, but this is done in a step before -mounting. Therefore, any permission changes immediately before mounting may be -hidden by the mount. +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: - -h print this help - -k don't clean up temporary directory - -o additional overlayfs mount options - -n pass -n to mount (don't write to /etc/mtab) - -t additional tmpfs mount options - -T temporary directory - -v verbose mode + -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 / /tmp/my_root # make a thin copy of root + 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 } @@ -36,7 +29,7 @@ log() { printf "tmpoverlay: $fmt\n" "$@" >&2 } -verb() { +logv() { if [ -n "$verbose" ]; then log "$@" fi @@ -47,78 +40,142 @@ die() { exit 1 } -args=$(getopt -n tmpoverlay hko:nt:T:v "$@") || { usage >&2; 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_mtab extra_overlayfs_opts tmpfs_opts tmpdir verbose +unset no_canon no_mtab extra_overlayfs_opts tmpfs_opts tmpdir verbose while true; do case "$1" in - '-h') usage; exit 0;; - '-o') + -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=1; shift;; - '-t') + -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 ;; - '-T') - [ -d "$2" ] || die 'tmpdir "%s" is not a directory' "$2" - tmpdir=$2 - shift 2 - ;; - '-v') verbose=1; shift;; - '--') shift; break;; + -v|--verbose) verbose=-v; shift;; + --) shift; break;; *) die "getopt failure" esac done -case "$#" in - 1) lowerdir=$1 dir=${1##*:};; - 2) lowerdir=$1 dir=$2;; - *) usage >&2; exit 1;; -esac - -ld= -set -f -savedIFS=$IFS IFS=: -for d in $lowerdir; do - d=$(realpath -e "$d") - [ -d "$d" ] || die 'lowerdir "%s" is not a directory' "$d" - ld=$ld:$d +[ $# != 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 -IFS=$savedIFS -set +f -ld=${ld#:} -[ -d "$dir" ] || die 'destination "%s" is not a directory' "$dir" + +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() { - if [ -n "$mounted_tmpdir" ]; then - umount "$tmpdir" || exit 1 + 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 "$tmpdir" fi - if [ -n "$tmpdir" ] && [ -n "$created_tmpdir" ]; then - rm -r "$tmpdir" + case $1 in + [A-Z]*) logv 'reraising SIG%s' $1; kill -$1 $$ && read _ + esac + logv 'exiting' + if [ $r = 0 ]; then + exit 1 fi - exit 1 + exit $r } +trap 'err INT' INT +trap 'err TERM' TERM +trap 'err QUIT' QUIT + if [ -z "$tmpdir" ]; then - tmpdir=$(umask 077; mktemp -d --tmpdir tmpoverlay.XXXXXXXXXX) || exit 1 - created_tmpdir=1 - verb 'created tmpdir: %s' "$tmpdir" + 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 -mounted_tmpdir=1 + upperdir="$tmpdir/upper" workdir="$tmpdir/work" +logv 'creating upper/work dirs' mkdir "$upperdir" "$workdir" || err -chown --reference="${ld##*:}" "$upperdir" "$workdir" -chmod --reference="${ld##*:}" "$upperdir" "$workdir" -overlayfs_opts="lowerdir=$ld,upperdir=$upperdir,workdir=$workdir$extra_overlayfs_opts" -mount -t overlay -o "$overlayfs_opts" ${no_mtab:+-n} ${verbose:+-v} overlay "$dir" || 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 -umount "$tmpdir" || err -rm -r "$tmpdir" || err +logv 'done, exiting' |