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

[Paul Smith]

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

  ee> Catalyst doesnt really support unionfs at the moment.  You will
  ee> need to add unionfs to your isolinux loader script to get it to
  ee> work.

"isolinux loader script"?

  ee> unionfs=/path/to/block device will let you use a formatted device
  ee> as the place to store changes.  This code is VERY experimental and
  ee> is currently just starting to be supported.  It will not be in
  ee> official cds for sometime as no one has tested it all besides
  ee> myself.

Hm.  I had it working with the previous genkernel/catalyst, with a
custom linuxrc, but took out what I had in favor of the new support;
maybe I was too hasty :-).


The way I had it working was twofold: first, I used it even in the
livecd situation where there was no formatted device; in this case the
"top" filesystem in the union, the RW one, was a ramdisk.  The advantage
here is that I could avoid the long tmpfs copy step (by far the slowest
step) during boot: instead of copying all the modifiable directory
structures (/etc, /var, etc.) to a ramdisk I just used the unionfs to
overlay the RO partition and I was done.

Secondly, as you say, it could be used as a persistent storage.  In this
case I had the linuxrc try to mount disk devices (using /sys/block/...)
until I found one with a special token file in the root of the
filesystem.  I had it hardcoded to ext3 so I didn't need to worry about
different filesystem types.  If I found an ext3 filesystem with that
token file in the root I would use that as the top (RW) element in the
unionfs.


Anyway, for the time being I'm mostly interested in the first item:
speeding up the boot.  As things are turning out it's going to be more
important in my project to be able to install the whole thing to disk
and boot off of disk, than to boot off of CD with a persistent storage.
However, unionfs really helps me in two ways anyway: first is the boot
time from CD as I mentioned above.  Second is the copy time to the HD
partition, which can also benefit.

-- 
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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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