Making loop-device flexible in the script mkbimage

[Mats Erik Andersson]

  Dear Maintainers,

since several months there has been a bugreport
#352731
in the BTS of Debian, to the effect that 

      mkbimage      of grub 0.95 and 0.97

uses a fixed loop-device /dev/loop1 and could
potentially
be harmful by destrying anything that already involves
this particular device. The elementary solution is to
prepare oneself with "temp=`losetup -f`". This very
same method is implemented in the attached patch.
Please,consider incorporating it. I see only one
minor timing problem with this solution: between

         temp_loop=$(losetup -f)
   and
         losetup $lo_options $temp_loop $image

there is a minute time window available to steal
the allotted loop-device. The danger of prescribing
/dev/loop1 seems, however, to be more serious.

The Debian maintainers of grub have not mentioned
any reason not to let you people have a first
opportunity to implement a remedy, hence this email.

I would at this time like to point out a true bug:
there is no texinfo on the grub-shell command "dump",
although it is used in some script of the grub-source.

      Best regards
                     Mats Erik Andersson
                     address@hidden





# dev-loop_indep_mkbimage.diff
#
# The dependency of a loop-device is made dynamic,
# instead of statically using /dev/loop1.
#
# Mats Erik Andersson <address@hidden>
#
diff -Naur grub-0.97.orig/util/mkbimage grub-0.97.patched/util/mkbimage
--- grub-0.97.orig/util/mkbimage        2004-07-24 20:57:31.000000000 +0200
+++ grub-0.97.patched/util/mkbimage     2006-10-06 12:57:21.609356256 +0200
@@ -149,9 +149,10 @@
   if [ "$offset" = "0" ] ; then
     mkfs.$fs -F $image
   elif [ `id -u` = "0" ] ; then
-    losetup $lo_options /dev/loop1 $image
-    mkfs.$fs /dev/loop1
-    losetup -d /dev/loop1
+    temp_loop=$(losetup -f)
+    losetup $lo_options $temp_loop $image
+    mkfs.$fs $temp_loop
+    losetup -d $temp_loop
   else
     error must_be_root
   fi
@@ -185,13 +186,14 @@
        $cp ${image}1/$file ${image}:$file
     done
   elif [ "`id -u`" = "0" ] ; then
-    losetup $lo_options /dev/loop1 $image
+    temp_loop=$(losetup -f)
+    losetup $lo_options $temp_loop $image
     mkdir ${image}.mnt
-    mount -t $fs /dev/loop1 ${image}.mnt
+    mount -t $fs $temp_loop ${image}.mnt
     cp -a ${image}1/* ${image}.mnt/ && sync
     umount ${image}.mnt
     rmdir ${image}.mnt
-    losetup -d /dev/loop1
+    losetup -d $temp_loop
   else
     error must_be_root
   fi