Implement fstab-like addon config

For now all it handles is bind mounting and squashfs
images that have to overlay at the root. The config
file syntax is obviously borrowed from fstab. This
is far from final, much of it could use some cleanup.

Signed-off-by: Simo Leone <simo@archlinux.org>

hooks/archiso

@@ -31,14 +31,38 @@ run_hook ()
 
     msg ":: Mounting root (union) filesystem"
     /bin/modprobe -q unionfs >/dev/null 2>&1
-    /bin/mount -t unionfs -o dirs=/tmpfs=rw:/tmpfs/squashfs_root=ro none /real_root
+    /bin/mount -t unionfs -o dirs=/tmpfs=rw none /real_root
 
-    addon_conf="${BOOT_MOUNT}/addons/config"
-    if [ -e "${addon_conf}" ]; then
+    # TODO: some of this could be broken into functions
+    LOOP_NUM="1"
+    addon_dir="${BOOT_MOUNT}/addons"
+    if [ -e "${addon_dir}/config" ]; then
         msg ":: Mounting addons"
-        . $addon_conf
+        while read img mountpoint type; do
+            # check if this line is a comment (starts with #)
+            [ "${img#'#'}" != "${img}" ] && continue
+
+            if [ "${type}" = "bind" ]; then
+                msg "   Binding ${img} to ${mountpoint}"
+                mkdir -p /real_root${mountpoint}
+                /bin/mount -o bind ${addon_dir}/$img /real_root${mountpoint}
+            elif [ "${type}" = "squashfs" ]; then
+                msg "   Adding new union branch: ${img}"
+                mkdir -p "/tmpfs/mnt/loop${LOOP_NUM}"
+                if ! /bin/losetup "/dev/loop${LOOP_NUM}" ${addon_dir}/$img > /dev/null 2>&1; then
+                    echo "ERROR: Cannot mount loop device /dev/loop${LOOP_NUM}"
+                    echo "       Couldn't mount all addons"
+                    break
+                fi
+                /bin/mount -r -t squashfs "/dev/loop${LOOP_NUM}" "/tmpfs/mnt/loop${LOOP_NUM}"
+                /bin/mount -t unionfs -o remount,add=:/tmpfs/mnt/loop${LOOP_NUM}=ro none "/real_root"
+                LOOP_NUM=$(( $LOOP_NUM + 1 ))
+            fi
+        done < ${addon_dir}/config
     fi
 
+    /bin/mount -t unionfs -o remount,add=:/tmpfs/squashfs_root=ro none /real_root
+
     if [ -d /proc/sys/dev/cdrom ]; then
         echo 0 > /proc/sys/dev/cdrom/lock
         echo 1 > /proc/sys/dev/cdrom/autoeject