Optionally mount custom mounts as unions.

This can potentially save a lot of space, and this type of persistence
doesn't hide changes to the read-only filesystem which can be both
good and bad.

diff --git a/scripts/live b/scripts/live
index abdc87c..fad7107 100755 (executable)
--- a/scripts/live
+++ b/scripts/live
@@ -1564,6 +1564,34 @@ setup_unionfs ()
        mkdir -p "${rootmnt}/live"
        mount -t tmpfs tmpfs ${rootmnt}/live
 
+       live_rofs_list=""
+       # SHOWMOUNTS is necessary for custom mounts with the union option
+       if [ -n "${SHOWMOUNTS}" ] || ( [ -n "${PERSISTENT}" ] && [ -z "${NOPERSISTENT}" ] )
+       then
+               # XXX: is the for loop really necessary? rofslist can only contain one item (see above XXX about EXPOSEDROOT) and this is also assumed elsewhere above (see use of $rofs above).
+               for d in ${rofslist}
+               do
+                       live_rofs="${rootmnt}/live/${d##*/}"
+                       live_rofs_list="${live_rofs_list} ${live_rofs}"
+                       mkdir -p "${live_rofs}"
+                       case d in
+                               *.dir)
+                                       # do nothing # mount -o bind "${d}" "${live_rofs}"
+                                       ;;
+                               *)
+                                       case "${UNIONTYPE}" in
+                                               unionfs-fuse)
+                                                       mount -o bind "${d}" "${live_rofs}"
+                                                       ;;
+                                               *)
+                                                       mount -o move "${d}" "${live_rofs}"
+                                                       ;;
+                                       esac
+                                       ;;
+                       esac
+               done
+       fi
+
        # Adding other custom mounts
        if [ -n "${PERSISTENT}" ] && [ -z "${NOPERSISTENT}" ]
        then
@@ -1628,7 +1656,7 @@ setup_unionfs ()
                                for opt in $(echo ${options} | tr ',' ' ');
                                do
                                        case "${opt}" in
-                                               "linkfiles")
+                                               linkfiles|union)
                                                        ;;
                                                *)
                                                        log_warning_msg "Skipping custom mount with unkown option: ${opt}"
@@ -1677,12 +1705,16 @@ setup_unionfs ()
                while read source dest options  # < ${custom_mounts}
                do
                        local opt_linkfiles=""
+                       local opt_union=""
                        for opt in $(echo ${options} | tr ',' ' ');
                        do
                                 case "${opt}" in
-                                       "linkfiles")
+                                       linkfiles)
                                                opt_linkfiles="yes"
                                                ;;
+                                       union)
+                                               opt_union="yes"
+                                               ;;
                                esac
                        done
 
@@ -1716,8 +1748,6 @@ setup_unionfs ()
                                fi
                        fi
 
-                       # FIXME: could we instead only save the aufs-diff in the persistent media? implications? What about when there's changes in the live image?
-
                        # if ${source} doesn't exist on our persistent media we
                        # bootstrap it with $dest from the live filesystem.
                        # this both makes sense and is critical if we're
@@ -1727,18 +1757,38 @@ setup_unionfs ()
                                if [ -n "${PERSISTENT_READONLY}" ] || [ -n "${opt_linkfiles}" ]
                                then
                                        continue
+                               elif [ -n "${opt_union}" ]
+                               then
+                                       # union's don't need to be bootstrapped
+                                       mkdir "${source}"
+                               else
+                                       # ensure that $dest is not copied *into* $source
+                                       mkdir -p "$(dirname ${source})"
+                                       cp -a "${dest}" "${source}"
                                fi
-                               # ensure that $dest is not copied *into* $source
-                               mkdir -p "$(dirname ${source})"
-                               cp -a "${dest}" "${source}"
                        fi
 
+                       rofs_dest_backing=""
+                       for d in ${live_rofs_list}
+                       do
+                               rofs_dest_backing="${d}/$(echo ${dest} | sed -e "s|${rootmnt}||")"
+                               if [ -d "${rofs_dest_backing}" ]
+                               then
+                                       break
+                               else
+                                       rofs_dest_backing=""
+                               fi
+                       done
+
                        if [ -z "${PERSISTENT_READONLY}" ]
                        then
                                if [ -n "${opt_linkfiles}" ]
                                then
                                        links_source="${source}"
                                        links_dest="${dest}"
+                               elif [ -n "${opt_union}" ]
+                               then
+                                       do_union ${dest} ${source} ${rofs_dest_backing}
                                else
                                        mount --bind "${source}" "${dest}"
                                fi
@@ -1751,8 +1801,7 @@ setup_unionfs ()
                                fi
                                cow_dir="$(echo ${dest} | sed -e "s|${rootmnt}|/cow/|")"
                                mkdir -p ${cow_dir}
-                               # XXX: broken! will be fixed in the next few commits...
-                               do_union ${dest} ${cow_dir} ${source}
+                               do_union ${dest} ${cow_dir} ${source} ${rofs_dest_backing}
                        fi
 
                        if [ -n "${opt_linkfiles}" ]
@@ -1771,32 +1820,6 @@ setup_unionfs ()
                try_snap "${home_snapdata}" "${rootmnt}" "HOME" "/home"
        fi
 
-       if [ -n "${SHOWMOUNTS}" ]
-       then
-               for d in ${rofslist}
-               do
-                       mkdir -p "${rootmnt}/live/${d##*/}"
-
-                       case d in
-                               *.dir)
-                                       # do nothing # mount -o bind "${d}" "${rootmnt}/live/${d##*/}"
-                                       ;;
-
-                               *)
-                                       case "${UNIONTYPE}" in
-                                               unionfs-fuse)
-                                                       mount -o bind "${d}" "${rootmnt}/live/${d##*/}"
-                                                       ;;
-
-                                               *)
-                                                       mount -o move "${d}" "${rootmnt}/live/${d##*/}"
-                                                       ;;
-                                       esac
-                                       ;;
-                       esac
-               done
-       fi
-
        # shows cow fs on /cow for use by live-snapshot
        mkdir -p "${rootmnt}/live/cow"
        mount -o move /cow "${rootmnt}/live/cow" >/dev/null 2>&1 || mount -o bind /cow "${rootmnt}/live/cow" || log_warning_msg "Unable to move or bind /cow to ${rootmnt}/live/cow"