Re: [gentoo-catalyst] How is initrd built?

[Paul Smith]

%% Eric Edgar <rocket@g.o> writes:

  ee> Catalyst doesnt really support unionfs at the moment. 

  ee> You will need to add unionfs to your isolinux loader script to get
  ee> it to work.

Well, it pretty much works.  I wonder if anyone can be more clear about
in what way Catalyst doesn't support unionfs and what exactly "add
unionfs to my isolinux script" means?  I'm happy to continue moving
forward with this and even posting fixes etc. if I run into any.


What happens now: I'm booting a livecd image.  If I add --union to the
genkernel arguments when I build my livecd image with catalyst, then the
system does come up correctly.  I see it detect unionctl, I see it
create the tmpfs, I see it mount the tmpfs, etc.

However, after the system is booted there is one problem: all the
partitions that were mounted during the linuxrc are no longer visible
from within the unionfs.  Here are the unionfs-related steps genkernel
uses as far as I can determine them; I'm replacing variables with actual
values here to make things simpler to follow (I hope!):

   0) mkdir -p /newroot

   1) Create a tmpfs at /memory

   2) Create a unionfs at /union, where the only item in the union is
      /memory (mounted RW)

   3) Init /newroot (make directories, copy over /dev/null and /dev/console)

   4) Find the cdrom and mount it as /newroot/mnt/cdrom

   5) Mount the squashfs as /newroot/mnt/livecd (read-only)

   6) Add /newroot/mnt/livecd to the unionfs after the tmpfs (/memory)

   7) Create /union/proc and /union/sys

   8) Pivot_root to make /union the new /.

   9) Clean up the old root (in /tmp/.initrd)

  10) chroot . 'exec /sbin/init' (basically).

So, at the end of this our / is actually /union, and things are set up
properly, BUT if I run "df", for example, I get:

  Filesystme    1K-blocks       Used    Available   Use%    Mounted on
  df: `/memory': No such file or directory
  df: `/newroot/mnt/cdrom': No such file or directory
  df: `/newroot/mnt/livecd': No such file or directory
  udev             127724       2668       125056     3%    /dev

Is there a way to fix this?  Can we do some sort of fancy footwork
(maybe mount --move?) to get those things visible inside the union?
Creating these directories inside the union keeps df from complaining,
but those directories are still empty: you can't unmount them for
example (not that you'd be able to anyway for the unioned ones).

I'm mostly concerned with the cdrom mount.  I wonder if it would at
least be reasonable to mount /mnt/cdrom inside /union instead of inside
/newroot: that should be safe.  You can't do that with /memory since it
needs to exist before the union is created, and I doubt it would work to
do it with the livecd (union mount something that is mounted inside the
union...?  Hmm)

-- 
-------------------------------------------------------------------------------
 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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