diff options
| -rw-r--r-- | README.rst | 10 | ||||
| -rwxr-xr-x | tmpoverlay | 116 |
2 files changed, 82 insertions, 44 deletions
@@ -2,7 +2,9 @@ tmpoverlay ========== tmpoverlay is a small, almost-POSIX shell script to create tmpfs-backed -overlayfs mounts. See tmpoverlay --help for usage information. +overlayfs mounts. tmpoverlay automatically detects and uses index=on and +volatile, as well as redirect_dir and metacopy if only a single lowerdir is +used. See tmpoverlay --help for usage information. One important thing to note is that like any other Linux mount, an overlayfs mount only affects new directory lookups. If a process has its current @@ -21,9 +23,9 @@ POSIX compliance With the following exceptions, tmpoverlay is intended to be functional on POSIX-only shells: -- ``getopt --`` is required for proper handling of options containing spaces - ``mount -t overlay`` is obviously required +- ``getopt --`` is required for proper handling of options containing spaces +- ``stat -c`` is required to obtain upperdir owner and permissions, because + parsing ls -l is ridiculous. - ``getfattr`` is used for xattr copying but in case of failure, the system is assumed to not support xattrs and setfattr is skipped. -- ``stat -c`` is used to obtain upperdir owner and permissions, because parsing - ls -l is nonsense. @@ -36,8 +36,32 @@ logv() { } die() { - log "$@" - exit 1 + r=$? + 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' + umount $no_mtab "$tmpdir" + fi + logv 'deleting tmpdir' + rmdir "$tmpdir" + fi + if [ -n "$sig" ]; then + logv 'reraising SIG%s' $1 + kill -$1 $$ && read _ + fi + logv 'exiting' + if [ $r = 0 ]; then + exit 1 + fi + exit $r } canon() { @@ -63,17 +87,19 @@ my_getopt() { "$@" } +unset own_tmpdir + args=$(my_getopt "$@") || { usage >&2; exit 1; } eval set -- "$args" unset args -unset no_canon no_mtab extra_overlayfs_opts tmpfs_opts tmpdir verbose +unset no_canon extra_ovl_opts no_mtab mount_name tmpfs_opts verbose while true; do case "$1" in -c|--no-canonicalize) no_canon=-c; shift;; -h|--help) usage; exit 0;; -o|--overlayfs) - [ -n "$2" ] && extra_overlayfs_opts="$extra_overlayfs_opts,$2" + [ -n "$2" ] && extra_ovl_opts="$extra_ovl_opts,$2" shift 2 ;; -n|--no-mtab) no_mtab=-n; shift;; @@ -101,7 +127,6 @@ while [ -n "$2" ]; do done dest=$(canon "$1") -echo lowerdir=$lowerdir dest=$dest [ -d "$dest" ] || die 'destination "%s" is not a directory' "$dest" [ "$dest" != / ] || log 'overmounting root, use with caution' @@ -109,54 +134,64 @@ if [ -z "$lowerdir" ]; then lowerdir=$dest fi -err() { - r=$? - trap - INT TERM QUIT - logv 'an error occurred, cleaning up' - if [ -d "$tmpdir" ]; then - if mountpoint -q "$tmpdir"; then - logv 'unmounting tmpdir' - umount $no_mtab "$tmpdir" - fi - logv 'deleting tmpdir' - rmdir "$tmpdir" - fi - case $1 in - [A-Z]*) logv 'reraising SIG%s' $1; kill -$1 $$ && read _ - esac - logv 'exiting' - if [ $r = 0 ]; then - exit 1 - fi - exit $r -} - -trap 'err INT' INT -trap 'err TERM' TERM -trap 'err QUIT' QUIT +trap 'die -INT' INT +trap 'die -TERM' TERM +trap 'die -QUIT' QUIT if [ -z "$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" || err +mount -t tmpfs ${tmpfs_opts:+-o "$tmpfs_opts"} ${verbose:+-v} tmpfs "$tmpdir" || die upperdir="$tmpdir/upper" workdir="$tmpdir/work" -logv 'creating upper/work dirs' -mkdir "$upperdir" "$workdir" || err +testdir="$tmpdir/test" +tmpmnt="$tmpdir/tmpmnt" +logv 'creating dirs' +mkdir "$upperdir" "$workdir" "$testdir" "$tmpmnt" || die + +our_ovl_opts= +test_ovl_opts="lowerdir=$testdir,upperdir=$upperdir,workdir=$workdir" +logv 'testing overlay options' +mount -n -t overlay -o "$test_ovl_opts" overlay "$tmpmnt" || die "overlayfs is not supported" +umount "$tmpmnt" +if [ -n "$extra_ovl_opts" ]; then + mount -n -t overlay -o "$test_ovl_opts$extra_ovl_opts" overlay "$tmpmnt" || die "invalid extra overlayfs options" + umount "$tmpmnt" +fi +try_ovl_opt() { + case ",$extra_ovl_opts," in + *",$1[=,]"*) return + esac + logv 'checking if %s is supported' "$1${2+=$2}" + ovl_opts="$test_ovl_opts,$1${2+=$2}$extra_ovl_opts" + mount -n -t overlay -o "$ovl_opts" "overlay" "$tmpmnt" 2>/dev/null || return + umount "$tmpmnt" || die + rm -r "$workdir" "$upperdir" || die + mkdir "$upperdir" "$workdir" || die + our_ovl_opts="$our_ovl_opts,$1${2+=$2}" +} +case $lowerdir in + *:*) ;; + *) try_ovl_opt redirect_dir on + try_ovl_opt metacopy on +esac +try_ovl_opt index on +try_ovl_opt volatile # try to match perms/attrs. this is not race-free but it's impossible without # atomic (CAS) chown/chmod/setfattr. chown --from is not atomic, not portable, # and also doesn't cover chmod/setfattr. lastlowerdir=${lowerdir##*:} logv 'copying lowerdir owner to upperdir' -owner=$(stat -c %u:%g "$lastlowerdir") || err -chown $owner "$upperdir" || err +owner=$(stat -c %u:%g "$lastlowerdir") || die +chown $owner "$upperdir" || die logv 'copying lowerdir perms to upperdir' -mode=$(stat -c %a "$lastlowerdir") || err -chmod $mode "$upperdir" || err +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 @@ -164,15 +199,16 @@ chmod $mode "$upperdir" || err logv 'copying root attrs' if attr=$(cd "$lastlowerdir" && getfattr -d -m - . 2>/dev/null); then if [ -n "$attr" ]; then - printf '%s\n' "$attr" | (cd "$upperdir"; setfattr --restore=-) || err + printf '%s\n' "$attr" | (cd "$upperdir"; setfattr --restore=-) || die fi else log 'getfattr not found or failed, skipping xattrs' fi logv 'mounting overlay' -overlayfs_opts="lowerdir=$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 +mount_opts="$no_canon $no_mtab $verbose" +ovl_opts="lowerdir=$lowerdir,upperdir=$upperdir,workdir=$workdir$our_ovl_opts$extra_ovl_opts" +mount $mount_opts -t overlay -o "$ovl_opts" "${mount_name-overlay}" "$dest" || die logv 'cleaning up' umount "$tmpdir" || exit |