larch-5

larch-5 uses a simpler live-medium structure than larch-4, using a union-root.

Session saving on CD/DVD is dropped, but is retained and enhanced on USB-stick.

Basic session saving is now simply a matter of compressing the overlay layer
of the union. That should speed up session saving a bit. There is also a
second stage of session saving, more akin to the old version, where a
read-only (squashfs) layer between the main system and the top overlay
is rewritten, merging in the top overlay.

To further increase speed I am trying tar and lzo-compression instead of
squashfs for the top overlay.

If the total overlay size gets big, there should be support for recreating
the live system (using larchify).


system.sqf: The main squashed system, mounted to union root in initramfs

overlay.ovl: The saved state of the writable union layer, unpacked in initramfs

mods.sqf: A union layer (between system and overlay). Can be updated by
          merging in overlay. Doesn't contain changes in /etc.


Building:
=========

Export from svn:
   svn export svn://svn.berlios.de/larch/branches/larch5.3

Then run 'mklarchrepo'. This will create a repository of the larch
packages, at larchrepo.

Copy this directory to an empty working directory (or make a symlink
from 'larchrepo' in the empty directory to the repository).

Then copy 'larch-setup' to the working directory and edit it so that
the local 'REPO=' entry becomes operative. Then run it.
Alternatively, install the larch package with 'pacman -U'.


tar / lzo:
==========

Compress:
tar -cf - src | lzop > src.tar.lzo

Uncompress:
lzop -d < src.tar.lzo | tar -xf -

Could use lzf (liblzf) instead of lzo, but lzo may be slightly better?
lzf is much smaller, and easy to compile - can also use klcc.
Both seem a lot faster at compressing than squashfs or gzip (more than
twice as fast?), decompression is similar in all cases, but gzip may be
very slightly slower. squashfs looks better than gzip - smaller file,
slightly faster - but it may just be the settings. lzf/lzo lose a few
percent of compression (squashfs ~10% smaller?).