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Re: How to prepare an ISO 9660 CD for booting via GRUB ?

From: Thomas Schmitt
Subject: Re: How to prepare an ISO 9660 CD for booting via GRUB ?
Date: Sat, 10 Apr 2010 00:28:10 +0200


> Now it's enough to replace grub-mkisofs with xorrisofs.

What about operating systems other than GNU/Linux
and FreeBSD ?

I have running a version of grub-mkrescue which
can deal with grub-mkisofs, genisoimage, and
xorriso. (genisoimage without
--protective-msdos-label and --modification-date)

Maybe it would offer a softer migration path
than flatly urging people to port xorrisofs to
their favorite exotic OS.
Of course i would gladly support any porting
effort, which should be easy as long as one does
not want to use it for burning optical media.

> Do you know when debian will follow? When
> this version is in Debian sid I plan to remove grub-mkisofs

I informed George Danchev about our progress
today. Like so many people he is very occupied
In charge are the Debian Libburnia packagers.

Since Debian covers our dynamic compilations
i will first have to release a new
libisofs-0.6.30 and a new libisoburn-0.5.4.
That should be possible in the next days.
I just have to do some more tests.

Maybe one could try to find testers for
GNU xorriso-0.5.3 on some of the other OSes in
the meantime ?

> Unfortunately floppies are of interest. Moreover our modules put
> together result in 1146880 bytes tar file.

Then you should in any case let xorrisofs
write into a sequential pipe
  | cat > ${output_image}
rather than into a random access file
  -o ${output_image}
  (or  > ${output_image} without cat)
in order to save the overhead of 64 to 126 kB.

Would read support for zisofs be in your reach ?
It is implemented in the Linux kernel iso9660
code since a while. See CONFIG_ZISOFS in

If zlib is provided, then xorriso can produce
zisofs on-the-fly on normal input file trees.
No need to run the mkzftree utility.
(But it can recognize and use the mkzftree
 prepared files too.)

The mkisofs emulation cannot do the on-the-fly
stunt, yet. So this has to look a bit ugly:

  "${mkisofs_prog}" ...
                    ${source} \
                    -- -set_filter_r --zisofs / -- \
                    | cat > ${output_image}

But the result has only 884736 bytes.

We would have to keep some modules uncompressed
i assume.

It can also produce gzipped files on the fly:

   ${mkisofs_prog}" ...
                    ${source} \
                    -- -set_filter_r --gzip / -- \
                    | cat > ${output_image}

Result again has 884736 bytes. Files have suffix
.gz now. Small files may stay uncompressed:

  $ ls -l /mnt/boot/grub/i386-pc
  -r--r--r-- 1 root root  2675 2010-04-10 00:17 afs.mod.gz
  -r--r--r-- 1 root root  1052 2010-04-10 00:17 aout.mod

One could of course apply mkzftree or gzip to
the temporary tree during the grub-mkrescue run.

Have a nice day :)


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