[Morphix-devel] UnionFS branches precedence and MiniModule root/ directory

[<ne...@ne...>]

First of all, sorry for the wrong post on the "cvs" mailing list!

The message was:

Ciao all.

I think that MiniModule unionfs overlaying is conceptually wrong.

in the base module we have 2 init script that mount main and mini
modules by using unionfs.

While Mainmodule is overlayed in morphix-start in this way:

     mount -t unionfs -o dirs=3D/mnt/main${UNIONFS_MOUNT_OPT},debug=3D$DEBU=
GOVERLAY none /mnt/main
     unionctl /mnt/main --add --mode ro /mnt/main_ro
     unionctl /mnt/main --add --mode rw $DIR2/root

MiniModules are overlayed in load-minimodules.sh with:

   if [ -d /mnt/main/mnt/mini/mod$count/root ]; then
       unionctl /mnt/main --add --after 0 --mode ro /mnt/main/mnt/mini/mod$=
count/root
   fi

This make the root file system on the resulting live cd booted like
this:

root@Medianix:~# unionctl / --list
        /mnt/.hidden_base/ramdisk/var/tmp/overlay/root (rw-)
        /mnt/mini/mod2/root (r--)
        /mnt/.hidden_base/mnt/main_ro (r--)
root@Medianix:~#


as the "0" branch is the rw mounted ramdisk, so, when add to the unionfs
the MiniModule, it will go after this and before the Main that is
/mnt/.hidden_base/mnt/main_ro.

In this way if we have 2 files (let me say for an example, /etc/passwd)
both in main *and* minimodule, the main one take precedence over the
minimodule one.

While having multiple minimodule with the same file can open some
issues, i think that it will be better to permit to minimodules
to take precedence over the mainmodule, so, i think that in
load-minimodules.sh the unionctl line shuld be
   unionctl /mnt/main --add --mode ro /mnt/main/mnt/mini/mod$count/root
without the --after 0 switch.

Another idea is to use a file inside the minimodule, something like
"unionfsposition" that contain the position to insert the minimodule
branch, letting us configure this from the minimodule itself. Something
like:

if [ -d /mnt/main/mnt/mini/mod$count/root ]; then
  if [ -f /mnt/main/mnt/mini/mod$count/unionfspos ]; then
    ufsafter=3D"--after `cat /mnt/main/mnt/mini/mod$count/unionfspos`"
  fi
  unionctl /mnt/main --add $ufsafter --mode ro /mnt/main/mnt/mini/mod$count=
/root
fi


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Franco (nextime) Lanza
Busto Arsizio - Italy
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