Re: Unionfs (was: Re: [gentoo-catalyst] Keeping a test environment using catalyst)

[Paul Smith]

%% Chris Gianelloni <wolf31o2@g.o> writes:

  cg> That's a good point.  I was just thinking that by holding off
  cg> until a bit later, it allows us to have our full module list,
  cg> rather than the limited subset provided in the initrd.

Well, you still can have your full module list during linuxrc.  After
you mount the cdrom you can just change /lib to point to the version on
the cdrom partition (whether you do it directly or through the unionfs,
it doesn't really matter).

Now, making this change involves a little bit of fancy footwork, since
some applications, even in the initrd, will be dynamically linked and
trying to swap out /lib can give them a migraine.  However, taking a
page from the Knoppix linuxrc I got it to work by invoking the runtime
linker from the cdrom directly; here's a snippet:

  # Run a command using "safe" paths to the ORIGFS.  Only valid once
  # that's been mounted!  Note that the command MUST have a
  # fully-qualified path!
  runit() {
    cmd="$1"
    shift
    "${ORIGFS}/lib/ld-linux.so.2" --library-path "${ORIGFS}/lib" \
      "${ORIGFS}$cmd" "$@"
  }

  cd /
  mkdir -p /.old
  for f in etc lib bin boot sbin var opt root usr; do
    runit /usr/bin/test -e "/$f" \
      && runit /bin/mv "/$f" /.old \
      && runit /bin/ln -snf "${UNIONFS}/$f" "/$f"
  done
  $DEBUG || rm -rf /.old

Here, ORIGFS would be the mount point for the cdrom.  Of course you can
change this into two loops easily enough if you don't want all of these
to go through the unionfs.


Anyway, once you get this done your "/" contains the fully-expressed
squashfs contents, not just the stuff in the initrd, so you can load up
any other modules you think are necessary, that might not exist in the
initrd filesystem.


Cheers!

-- 
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 Paul D. Smith <psmith@××××××.com>           HASMAT--HA Software Mthds & Tools
 "Please remain calm...I may be mad, but I am a professional." --Mad Scientist
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   These are my opinions---Nortel Networks takes no responsibility for them.
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