After Cliff Wright posted a patch for vnd(4) to handle compressed disk 
images some time ago[1] and Florian Stoehr wrote a userland tool to 
(de)compress disk images (using the cloop2 format also found on other 
systems)[2], I sat down to play with the two things tonight.

In short: very successfully!


What I basically did was build a kernel and vnconfig(8) with the patch in 
[1], and build Florian's tool (which I received in private from him).
After booting the patched kernel, I did the following steps:

Verify I was running the kernel I just built (this is all in qemu):

 	qemubsd# uname -a
 	NetBSD qemubsd 3.99.6 NetBSD 3.99.6 (GENERIC) #1: Mon Jun 13 01:12:47 MEST 2005  feyrer@miyu:/usr/cvs/src-cloop2/sys/arch/i386/compile/obj.i386/GENERIC i386


Create some toy filesystem:

 	qemubsd# /root/vndz/vnconfig -l
 	vnd0: not in use
 	vnd1: not in use
 	vnd2: not in use
 	vnd3: not in use
 	qemubsd# makefs
 	usage: makefs [-t fs-type] [-o fs-options] [-d debug-mask] [-B endian]
 		[-S sector-size] [-M minimum-size] [-m maximum-size] [-s image-size]
 		[-b free-blocks] [-f free-files] [-F mtree-specfile] [-x]
 		[-N userdb-dir] image-file directory
 	qemubsd#
 	qemubsd# makefs inc.fs /usr/include
 	Calculated size of `inc.fs': 11157504 bytes, 1273 inodes
 	Extent size set to 8192
 	inc.fs: 10.6MB (21792 sectors) block size 8192, fragment size 1024
 		using 1 cylinder groups of 10.64MB, 1362 blks, 1408 inodes.
 	super-block backups (for fsck -b #) at:
 	 32,
 	Populating `inc.fs'
 	Image `inc.fs' complete


Mount the filesystem the usual (uncompressed) way:

 	qemubsd# /root/vndz/vnconfig vnd0 /tmp/inc.fs
 	qemubsd# /root/vndz/vnconfig vnd0 -l
 	vnd0: / (/dev/wd0a) inode 10839
 	vnd1: not in use
 	vnd2: not in use
 	vnd3: not in use
 	qemubsd#
 	qemubsd# disklabel vnd0a
 	disklabel: Invalid signature in mbr record 0
 	# /dev/rvnd0a:
 	type: vnd
 	disk: vnd
 	label: fictitious
 	flags:
 	bytes/sector: 512
 	sectors/track: 32
 	tracks/cylinder: 64
 	sectors/cylinder: 2048
 	cylinders: 10
 	total sectors: 21792
 	rpm: 3600
 	interleave: 1
 	trackskew: 0
 	cylinderskew: 0
 	headswitch: 0		# microseconds
 	track-to-track seek: 0	# microseconds
 	drivedata: 0

 	4 partitions:
 	#        size    offset     fstype [fsize bsize cpg/sgs]
 	 a:     21792         0     4.2BSD      0     0     0  # (Cyl.      0 -     10*)
 	 d:     21792         0     unused      0     0        # (Cyl.      0 -     10*)
 	disklabel: boot block size 0
 	disklabel: super block size 0
 	qemubsd#
 	qemubsd# mount -o ro /dev/vnd0a /mnt/fs
 	qemubsd# ls -l /mnt/fs | head
 	total 788
 	-r--r--r--   1 root  wheel   3178 Jun  4 23:54 a.out.h
 	drwxr-xr-x   2 root  wheel    512 Jun  5 23:58 adosfs
 	drwxr-xr-x   2 root  wheel    512 Jun  5 23:58 altq
 	-r--r--r--   1 root  wheel   2721 Jun  4 23:54 ar.h
 	drwxr-xr-x   2 root  wheel    512 Jun  5 23:58 arpa
 	-r--r--r--   1 root  wheel   3993 Jun  4 23:54 assert.h
 	-r--r--r--   1 root  wheel   4439 Jun  4 23:54 bitstring.h
 	-r--r--r--   1 root  wheel   2265 Jun  4 23:54 bm.h
 	-r--r--r--   1 root  wheel   7897 Jun  4 23:55 bzlib.h


Now compress the filesystem image with Florian's clconfig tool:

 	qemubsd# ls -l
 	total 10926
 	-rwxr-xr-x   1 root  wheel  11157504 Jun 13 01:34 inc.fs
 	qemubsd#
 	qemubsd# /root/vndz/clconfig
 	usage: clconfig -c disk/fs-image compressed-image [blocksize]
 	       clconfig -d compressed-image disk/fs-image
 	qemubsd#
 	qemubsd# /root/vndz/clconfig -c inc.fs inc.fsz
 	Using blocksize: 65536 (170 complete and 1 zero-padded blocks)
 	qemubsd#
 	qemubsd# ls -l
 	total 13056
 	-rwxr-xr-x   1 root  wheel  11157504 Jun 13 01:34 inc.fs
 	-rw-r--r--   1 root  wheel   2164224 Jun 13 01:35 inc.fsz

clconfig shrank the image from ~11MB to ~2MB, i.e. down to ~19% of the 
original size. Assuming the same compression ration, this would fit about 
3.2GB of data on a 650MB CD. 'Nuff for KDE and OpenOffice. :-)


Next, mount the compressed image:

 	qemubsd# /root/vndz/vnconfig -z vnd1 inc.fsz
 	qemubsd# /root/vndz/vnconfig -l
 	vnd0: / (/dev/wd0a) inode 10839
 	vnd1: / (/dev/wd0a) inode 10840
 	vnd2: not in use
 	vnd3: not in use
 	qemubsd# ls -li inc*
 	10839 -rwxr-xr-x  1 root  wheel  11157504 Jun 13 01:34 inc.fs
 	10840 -rw-r--r--  1 root  wheel   2164224 Jun 13 01:35 inc.fsz
 	qemubsd#
 	qemubsd# disklabel vnd1
 	disklabel: Invalid signature in mbr record 0
 	# /dev/rvnd1d:
 	type: vnd
 	disk: vnd
 	label: fictitious
 	flags:
 	bytes/sector: 512
 	sectors/track: 32
 	tracks/cylinder: 64
 	sectors/cylinder: 2048
 	cylinders: 10
 	total sectors: 21888
 	rpm: 3600
 	interleave: 1
 	trackskew: 0
 	cylinderskew: 0
 	headswitch: 0		# microseconds
 	track-to-track seek: 0	# microseconds
 	drivedata: 0

 	4 partitions:
 	#        size    offset     fstype [fsize bsize cpg/sgs]
 	 a:     21888         0     4.2BSD      0     0     0  # (Cyl.      0 -     10*)
 	 d:     21888         0     unused      0     0        # (Cyl.      0 -     10*)
 	disklabel: boot block size 0
 	disklabel: super block size 0
 	qemubsd#
 	qemubsd# mount -o ro /dev/vnd1a /mnt/fsz
 	qemubsd# ls -l /mnt/fsz | head
 	total 788
 	-r--r--r--   1 root  wheel   3178 Jun  4 23:54 a.out.h
 	drwxr-xr-x   2 root  wheel    512 Jun  5 23:58 adosfs
 	drwxr-xr-x   2 root  wheel    512 Jun  5 23:58 altq
 	-r--r--r--   1 root  wheel   2721 Jun  4 23:54 ar.h
 	drwxr-xr-x   2 root  wheel    512 Jun  5 23:58 arpa
 	-r--r--r--   1 root  wheel   3993 Jun  4 23:54 assert.h
 	-r--r--r--   1 root  wheel   4439 Jun  4 23:54 bitstring.h
 	-r--r--r--   1 root  wheel   2265 Jun  4 23:54 bm.h
 	-r--r--r--   1 root  wheel   7897 Jun  4 23:55 bzlib.h


A very basic test to see if both file systems contain the same data:

 	qemubsd# diff -bur /mnt/fs /mnt/fsz
 	qemubsd#

No differences. Success!


Clean up everything:

 	qemubsd# umount /mnt/fs
 	qemubsd# umount /mnt/fsz
 	qemubsd#
 	qemubsd# /root/vndz/vnconfig -u vnd0
 	qemubsd# /root/vndz/vnconfig -u vnd1
 	qemubsd# /root/vndz/vnconfig -l
 	vnd0: not in use
 	vnd1: not in use
 	vnd2: not in use
 	vnd3: not in use
 	qemubsd#


Next steps?
  * find a better name for the "clconfig" tool, maybe with some input from
    Linux. (What's the equivalent tool named there?)
  * find someone who'll feel confident to commit the kernel code
  * find someone who'll feel confident to commit the userland code
  * find someone to write documentation ("how to create a live CD" :-)


Volunteers?


  - Hubert


[1] http://mail-index.netbsd.org/tech-kern/2005/03/29/0032.html
[2] http://mail-index.netbsd.org/tech-kern/2005/03/30/0004.html