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Re: Migrations to xorriso

From: Thomas Schmitt
Subject: Re: Migrations to xorriso
Date: Wed, 19 May 2010 15:23:26 +0200


> > - Option --diet saves about 400 kB of image
> >   size without losing much benefit.
> If it doesn't lose much,
> why would it not be the default?

Maybe one should revert the default and offer
an option
instead ?

>  Or, put another way, why would
> somebody want to turn this option off?

I could want a bootable multi-session backup
on USB stick with the opportunity to mount the
backup state of two weeks ago.
For that i'd start with a rescue system created
by grub-mkrescue, add my base backup as second
session and daily updates as further sessions.

The extra 64 kB to 126 kB make sure that the
older sessions of a multi-session ISO image can
be detected and mounted. Useful with incremental
backups on regular files, USB sticks, DVD+RW or
BD-RE media.
But not so much of interest with a single session
rescue image.

Without this extra space one can still add new
sessions but will always see the youngest one as
the only session of the image. (growisofs does
it that way.)
If the first session ends up on sequential media
(CD-R[W], DVD-R, DVD+R, BD-R) then further
multi-session will be managed by the drive

> Useless use of cat.

Not in this case. xorriso calls fstat(2) to
determine the semantics of the given output file.
Option -o "${output_image}" or a redirection
by >"${output_image}" would both reveil type
But for the diet case i want S_ISCHR or S_IFIFO
so that the output "media" appears as sequential
rather than as overwriteable.

Have a nice day :)


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