Re: Migrations to xorriso

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

i sent this message 4 hours ago but it did
not show up yet. So i send it again on the risk
to produce a duplicate.

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While my local bzr upgrade problems still persist
i can view grub-mkrescue.in at 
  https://code.launchpad.net/~vcs-imports/grub/grub2-bzr


> xorriso -pathspecs on -as mkisofs

I would make this
  xorriso -report_about HINT -as mkisofs -graft-points

Option -report_about HINT will reduce verbosity
to the level of messages about unusual events
and remedy proposals.

Since xorriso is run in mkisofs emulation, it
seems clearer to use -graft-points rather than
xorriso option -pathspecs.


> -as mkisofs ${grub_mkisofs_arguments} --protective-msdos-label
> -o ${output_image} -r ${iso9660_dir} ${source}

The potential content of ${grub_mkisofs_arguments}
looks good so far.
I assume you have already tested your use cases.


There remain opportunities for result size
reduction:

The result will be up to 426 kB larger than the
one of grub-mkisofs. (Modern mkisofs or
genisoimage would give you 300 kB extra.)

------------------------------------------------

You may add mkisofs option
  -no-pad
to avoid trailing padding of 300 kB which is only
needed if you later burn the image to a CD in
write mode TAO.
Alternatively you could allow option -no-pad in
the option interpreter of grub-mkrescue rather
than issueing:
    -*) 
        echo "Unrecognized option \`$option'" 1>&2

The burn program can eventually add padding.
xorriso -as cdrecord will by default use write
mode SAO if the file size is detectable.

------------------------------------------------

Another 64 to 126 kB can be saved by hiding the
fact that the target is a random access file.
One would replace
    -o ${output_image}
by
    | cat >${output_image}
This deprives the result of the capability to
show on overwriteable media a table-of-content
with older sessions.

------------------------------------------------

In my tests the size reduced result was 4 kB
smaller than the result from grub-mkisofs.


Have a nice day :)

Thomas