Re: Final CDs being written for Stretch - 9.13 release - prior to LTS

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

Hi,

Stefan Monnier wrote:
> I was thinking of a scheme by which the ISO is constructed and streamed
> at the same time, so the complete ISO images aren't ever stored whole
> anywhere on the server.

Although there are no fundamental obstacles for stream production,
the current software uncompresses the .template file to a file on disk
and then fills the marked holes by the packages which it downloads from
the chosen mirror server.


I wrote:
> > The production of jigdo files is a linear effort only if the producer
> > knows where the filesystem stores file content data.

Stefan Monnier wrote:
> I'm not sure I understand what this means,

Indeed "linear" is not the right term. I apologize for being misleading.

Given the original description
  http://atterer.org/jigdo/debian-jigdo-mini-howto#PREPARINGTHEISOFORDOWNLOAD
of the production process it is more about "scientific" versus "magic":

  "Through magic, jigdo-file finds out which of the loose files are
   contained in the ISO image and their offsets within the ISO file.
   It outputs two files: a ".template" file and a ".jigdo" file."

All tools for creating .jigdo and .template get a list of MD5 sums and
package file paths (the "loose" files).

The original tool, jigdo-file, scans the readily prepared ISO image for
the content of the data files without knowing where their content starts.
This implies a large amount of try-and-error, even with a smart algorithm.
The mismatching efforts are wasted.

genisoimage and libjte (under libisofs and xorriso) get to see the content
data of each data file, compute the MD5 and look up this MD5 in the list.
They don't have to guess where the files are stored in the ISO.

On the other hand, jigdo-file can apply its magic to any filesystem which
stores file content unchanged in one byte string, whereas the non-guessing
approach needs help from the filesystem producer.


> it does sound like it
> implies that streaming production of ISOs is technically possible.

I actually meant production of .template and .jigdo, not re-assembly of
the .iso from them and Debian packages.

But yes, streaming re-assembly of .iso from .jigdo only needs structural
changes in the download software. (The problem is how to motivate the
change given that there hardly will be an official ISO-from-Jigdo server.)

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

Tixy wrote:
> > Debian's 'DVD' images are isohybrid and work for booting from USB flash
> > drives,

Stefan Monnier wrote:
> The discussion was about the creation of special ISOs for old Mac
> hardware whose firmware isn't able to boot from those hybrid ISOs.

The "mac" ISOs for i386 and amd64 are hybrid ISOs too. Just not for EFI.

They have legacy MBR boot code which hops on the boot image for CD booting
after it was started by legacy BIOS from USB stick.
But they don't have a second boot image for EFI from CD (which also
would serve as EFI System Partition on USB stick).


Have a nice day :)

Thomas