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Re: [Libcdio-devel] [RFC/PATCH] add multi extent ISO9660 file support to

From: Thomas Schmitt
Subject: Re: [Libcdio-devel] [RFC/PATCH] add multi extent ISO9660 file support to libcdio
Date: Wed, 06 Jun 2018 20:13:17 +0200


Pete Batard wrote:
> - I'm not entirely sure that the sector size array is entirely necessary

The specs say that extents of the same file must be neighbors and in sequence.
But they do not outrule that an extent's size is not aligned to block size.
So there could be invalid bytes between extents. 

> - Not sure about adding a test for this one, even if I'd like to. There's
> Thomas' very helpful multiextent compressed ISO image, from:
> However, since that image uncompresses to 4 GB, and then we might have to
> process another 4GB file, it looks like a tricky sale...

In the course of
i provided 73 KB of

It contains two files which can be combined to form a sparse ISO image
of only a few hundred KB of weight:


To be unpacked and combined by

  uudecode -o - < cd9660/cd9660_rgr.image.at0.bz2.uue | bunzip2 > test.iso

  uudecode -o - < cd9660/cd9660_rgr.image.at2114008.bz2.uue | bunzip2 | \
    dd bs=2048 seek=2114008 of=test.iso

(uuencode is a demand of NetBSD regression testing system.
 bunzip2 does not offer an option to create a sparse file. But dd seek=
 hopping over a large unwritten range causes a lightweight range of

Then you will see on a filesystem that can store sparse files (here ext4):

  $ ls -l test.iso
  -rw-r--r-- 1 thomas thomas 4329758720 Jun  6 19:42 test.iso
  $ du test.iso
  388     test.iso

  # mount test.iso /mnt/iso
  mount: /dev/loop0 is write-protected, mounting read-only

  $ find  /mnt/iso -exec ls -ld '{}' ';'
  dr-x------ 1 thomas root 2048 May  6  2014 /mnt/iso
  dr-x------ 1 thomas root 2048 May  3  2014 /mnt/iso/dev
  prw------- 1 thomas root 0 May 25  2014 /mnt/iso/dev/test.fifo
  br-------- 1 thomas tty 0, 12 May 14  2014 /mnt/iso/dev/wd1e
  dr-x------ 1 thomas thomas 2048 May  6  2014 /mnt/iso/my
  -r-------- 1 thomas thomas 4329375744 May  6  2014 /mnt/iso/my/large_file
  dr-x------ 1 thomas root 2048 Jan 19  2014 /mnt/iso/reg
  -r-x------ 1 thomas root 133411 Jan 19  2014 /mnt/iso/reg/tar
  lr-x------ 1 thomas root 3 May 26  2014 /mnt/iso/reg/to_regfile -> tar
  -r-------- 1 thomas thomas 6 May  6  2014 /mnt/iso/small_file
  $ wc /mnt/iso/my/large_file
         0          0 4329375744 /mnt/iso/my/large_file

(Note: No i/o errors on wc.)

Have a nice day :)


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