Multiple "cloop" application :LiveDVD 3.8GB burned

Question

The following is copied from Knoppix DVD forum on this date;
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If you use Linux 2.6 with driver mapper support you can go around 2Gb limit a little bit differently - split your uncompressed image into chunks (on a block boundary) which would compressed into under 2Gb sized images, use separate cloop devices for each of them and then use 'linear' target to put them all together. Try something like this (assuming 65536 block size and 16Gb uncompressed image):
split -b 4294967296 KNOPPIX-UNCOMPRESSED.iso KNOPPIX.iso.
create_compressed_fs KNOPPIX.iso.aa 65536 > KNOPPIX0-gz.iso
create_compressed_fs KNOPPIX.iso.ab 65536 > KNOPPIX1-gz.iso
create_compressed_fs KNOPPIX.iso.ac 65536 > KNOPPIX2-gz.iso
create_compressed_fs KNOPPIX.iso.ad 65536 > KNOPPIX3-gz.iso
modprobe cloop
losetup /dev/loop0 KNOPPIX0-gz.iso
losetup /dev/loop1 KNOPPIX1-gz.iso
losetup /dev/loop2 KNOPPIX2-gz.iso
losetup /dev/loop3.KNOPPIX3-gz.iso
dmsetup create knoppix <<EOF
0 8388608 linear /dev/loop0 0
8388608 8388608 linear /dev/loop1 0
16777216 8388608 linear /dev/loop2 0
25165824 8388608 linear /dev/loop3 0
mount -r -t iso9660 /dev/mapper/knoppix /KNOPPIX
So, here - you'll have your under 2Gb file sizes on iso9660 and a nice 16Gb uncompressed file system. 
The only problems are that Linux 2.4 does not have device mapper and you need to adjust your mounting schema for /KNOPPIX during boot.
Hope it helps,
Cheers,
Igor
P.S. It may not work with the current create_compressed_fs due to a small bug - it adds an extra block if uncompressed image size is evenly divided by the block size. It doesn't show up when you have just one image, but with many it will show up in the middle of your file system.
If you have python installed you can use "my cloop python utilities"  ftp://belyi.ac93.org/pub/cloop-pyutils.tar.gz as a workaround. Otherwise, you should apply a tiny patch provided with a debian bug report: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=296179
lilsirecho
Joined: 13 Jul 2004
Posts: 166
Location: Ca
Posted: Sat Feb 26, 2005 3:44 am
belyi;
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The above describes a possible application to establish a 16GB (uncompressed) filesystem by applying cloop technique multiple times.

Answer 1

The author of the multi cloop procedure has provided his details for a split-knoppix DVD boot of Knoppix26.  These are reprinted below;
=================================================================================For a proof of concept I've created a new minirt26.gz which recognizes KNOPPIX.0 .. KNOPPIX.3 images as a split KNOPPIX image. I've tried it on KNOPPIX 3.7 CD by spliting its compressed image in half.
You can get this 1.4Mb minirt26.gz from ftp://belyi.ac93.org/pub/KNOPPIX/minirt26.gz but I have very small upload speed so it may be easier if I tell you what I did.
1. Mounted the original minirt26:
modprobe cloop
mount -o loop KNOPPIX-3.7.iso /mnt/src
losetup /dev/cloop0 /mnt/src/KNOPPIX/KNOPPIX
mount /dev/cloop0 /mnt/root
gzip -c /mnt/src/boot/isolinux/minirt26.gz > minirt26
mount -o loop minirt26 /mnt/minirt
2. Edited /mnt/minirt/linuxrc (here's the patch: ftp://belyi.ac93.org/pub/KNOPPIX/linuxrc-dm.patch)
3. Statically compiled losetup and dmsetup utils (simply added -static switch to the linker) and copied them into /mnt/minirt/static
4. Statically compiled a small program dmtables (ftp://belyi.ac93.org/pub/KNOPPIX/dmtables.c and copied it into static as well.
gcc -static -o dmtables dmtables.c
cp dmtables /mnt/minirt/static
5. Copied driver mapper kernel module:
cp /mnt/root/lib/modules/2.6.9/kernel/drivers/md/dm-mod.ko /mnt/minirt/modules/dm-mod.o
6. Created additional cloop nodes:
pushd /mnt/minirt/dev
mv cloop cloop0
ln -s cloop0 cloop
mknod cloop1 b 240 1
mknod cloop2 b 240 2
mknod cloop3 b 240 3
popd
7. Unmount and compress minirt26 back:
umount /mnt/minirt
gzip minirt26
8. Create your splitted KNOPPIX image:
rsync -a --exclude=KNOPPIX/KNOPPIX /mnt/src/ newimage
extract_compressed_fs /mnt/src/KNOPPIX/KNOPPIX | split -d -a 1 -b 973696k - knoppix.decomp.
create_compressed_fs knoppix.decomp.0 > newimage/KNOPPIX/KNOPPIX.0
create_compressed_fs knoppix.decomp.1 > newimage/KNOPPIX/KNOPPIX.1
cp minirt26.gz newimage/boot/isolinux
mkisofs -pad -l -r -J -v -V "KNOPPIX" -no-emul-boot -boot-load-size 4 -boot-info-table -b boot/isolinux/isolinux.bin -c boot/isolinux/boot.cat -hide-rr-moved -o KNOPPIX-3.7-splited.iso newimage
9. Burn the image and then boot it using knoppix26
10. If it works you can start fill KNOPPIX with your favorite programs without worry for 2Gb limitation of iso9660. 
Note 1. dmtables just simulates the job of blockdev --getsz, plus some arithmetics to align those split images nicely for driver mapper. I suspect you can do its job easily with some other methods.
Note 2. This is just quick-and-dirty work - it is not intended for mass production.
Note 3. I didn't use extrace_compressed_fs and create_compressed_fs programs - I used my own utils but it shouldn't be matter as long as you use the patched version.
I appologize for being too verbose... Spending 20 minutes to create an image and then finding a typo in linuxrc during boot (repeated number of times) do get on my nerves. I thought I should spill it on somebody else too. 
Cheers,
Igor
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The knoppix forum for DVD has the original reference in the first DVD posting.  The minirt26.gz file is available at 1.4MB from the link provided therein.
I am not expert enough to be able to try this out, but someone will!!!