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Re: Migrations to xorriso

From: Seth Goldberg
Subject: Re: Migrations to xorriso
Date: Wed, 19 May 2010 14:35:56 -0700 (PDT)
User-agent: Alpine 2.00 (GSO 1167 2008-08-23)

Quoting Vladimir 'φ-coder/phcoder' Serbinenko, who wrote the following on...:

Thomas Schmitt wrote:

Isaac Dupree wrote:

What size range are the whole images?

The minimum output of grub-mkrescue 1.98 with
xorriso is 1544192 bytes.
grub-mkisofs: 1550336
genisoimage:  1859584 (-307200 with -no-pad)

One may add lots of other files, of course.

Also I guess no one compresses whole ISOs

It makes few sense to compress the ISO as a
whole. But one could compress some files in it.

One could implement a reader for H. Peter Anvin's
zisofs format in GRUB's ISO 9660 reader - if not
present already.
zisofs is a transparent content compression of
single files. A reader is implemented in the
Linux kernel. See macro CONFIG_ZISOFS in
An authorised description is given in
doc/zisofs_format.txt of xorriso resp. in
The ISO 9660 directory tree stays uncompressed.
Compressed and uncompressed files can be mixed.

xorriso can produce zisofs compressed data files
on the fly (needs zlib).
A grub-mkrescue 1.98 image with all files
compressed has 884736 bytes. But one would have
to leave those files uncompressed which are
needed for reading ISO 9660 and zisofs

I'm not sure that zisofs is useful for grub. We already have support for
.gz files. xz support is coming. Compressing explicitly we would avoid
to accidently compressing files we need uncompressed. Also we're more
Implementing zisofs reader may have some value but isn't a priority.

For the record, Solaris uses a ISO9660 filesystem image with individual compressed files, but this is mainly useful for being able to have a boot archive that grub2 does not have to completely decompress before loading into memory (so we get the benefit of a nearly-compressed filesystem image) without the overhead (taking the overhead on read operations). The value to grub2, though, is unknown.


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