Padding and filesystem size in debian-live-9.2.0-amd64-cinnamon.iso

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

Hi,

while inspecting debian-live-9.2.0-amd64-cinnamon.iso i wondered why its
ISO 9660 filesystem size is smaller than its image file size.
That's a problem with the advise how to verify ISOs on DVD or USB stick
   https://www.debian.org/CD/faq/#verify
because programs "isosize" or "./check_debian_iso" will use the filesystem
size for computing checksums.

The file /.disk/mkisofs in the ISO tells the reason:
xorriso was used in its native command mode, not in its mkisofs emulation.
This mode by default does not count the padding as part of the filesystem.

To change to the desired behavior one would have to give command

  -padding included

or, because the image will never fit on a CD, it is safe to disable padding
and to save 300 KiB of image file size:

  -padding 0

The command may be given at any position in the xorriso command list.


Padding is only needed if the image gets written with CD write type TAO.
The Linux kernel believes too much in the reply of SCSI command READ CAPACITY
and then makes up a false theory about the reason for consequential read
errors.
(If anybody is here with a kernel standing, i am sure it could be fixed:
  https://www.spinics.net/lists/linux-scsi/msg94638.html
)


Have a nice day :)

Thomas