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[] zisofs test looks unsuitable

From: Thomas Schmitt
Subject: [] zisofs test looks unsuitable
Date: Wed, 25 Aug 2021 12:29:48 +0200


the xorriso run for testing zisofs in


looks not like it would cause any zisofs compression in the ISO.

Line 1024:

      xorriso -compliance rec_mtime -set_filter_r --zisofs -- -zisofs default
              -as mkisofs ... some options ... --
              -set_filter_r --zisofs -- -zisofs default -add /="$MASTER" ;;

should probably become

      xorriso -compliance rec_mtime \
              -as mkisofs ... same options as above ... -- \
              -add /="$MASTER" -- \
              -zisofs default \
              -set_filter_r --zisofs / --

In the current run, both times when "-set_filter_r --zisofs" is executed
in xorriso's native command mode, the emerging root directory is still empty.
So -set_filter_r cannot yet affect the files of "$MASTER" which get added
only later.

Command -zisofs sets parameters for -set_filter_r. So it must be executed
before any successful -set_filter_r. Only the lack of any installed
compression filters keeps the existing run from failing with
  libisofs: FAILURE : Cannot set global zisofs parameters while filters exist

Command -set_filter_r expects one or more paths in the ISO as parameters.
The empty path list defaults to "/" indeed, but that's not a documented
Command -add has a variable length parameter list and should thus be
terminated by '--'. In my proposal it has to be terminated because more
commands follow.


Currently the run is essentially like

  xorriso -compliance rec_mtime \
          -as mkisofs -o test.iso --graft-points -- \
          -add /=test -- -set_filter_r --zisofs / --

My test directory contains

  -rw-r--r-- 1 thomas thomas 51200 Aug 25 11:51 zeros
  -rw-r--r-- 1 thomas thomas     6 Aug 25 09:37 ÄÖÜß

No zisofs compression gets applied by above run to the files, as can be
seen by a subsequent run of

  xorriso -indev test.iso -find / -exec show_stream --

which reports

  '/zeros' < image:'/zeros'
  '/ÄÖÜß' < image:'/ÄÖÜß'

In contrast, my proposed xorriso run causes compression of file "zeros",
which then causes the xorriso run with -indev to install a decompression
filter to that file:

  '/zeros' < --zisofs-decode:pz:32k < image:'/zeros'
  '/ÄÖÜß' < image:'/ÄÖÜß'

The small "ÄÖÜß" staid uncompressed, because compression yielded no gain in
terms of 2048 byte blocks.

Have a nice day :)


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