95rootfs-block: fix missing root when label contains slash

It is not clearly documented, but apparently fsck
(or, probably, getmntent) is using backslash as
escape character.

Label containing slash is converted to \x2f but '\'
is eaten by fsck later. Escape '\' before writing
into fstab.

v2:
- fix sed expression
- use printf instead of echo because echo eats '\' as well

Signed-off-by: Andrey Borzenkov <arvidjaar@gmail.com>

modules.d/95rootfs-block/mount-root.sh

@@ -106,7 +106,9 @@ if [ -n "$root" -a -z "${root%%block:*}" ]; then
             done
     fi
 
-    echo ${root#block:} "$NEWROOT" "$rootfs" ${rflags},${rootopts} 1 1 > /etc/fstab
+    # backslashes are treated as escape character in fstab
+    esc_root=$(echo ${root#block:} | sed 's,\\,\\\\,g')
+    printf "%s $NEWROOT $rootfs ${rflags},${rootopts} 1 1\n" "$esc_root" > /etc/fstab
 
     if [ -z "$fastboot" -a "$READONLY" != "yes" ]; then
         info "Checking filesystems"