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Re: sunsite.org.uk - rsync access to cd-images

On Tue, 3 Aug 1999, Philip Hands wrote:

> In the mean time, cdimage.d.o has the drawbridge down (i.e. no
> passwords required) but as always I'd really appreciate it if people
> would make every effort to find the images on nearer mirrors before
> resorting to using this, because otherwise I'll probably have to haul

Hmmm. Before my vacation, only 2 rsync mirrors were up, and one (Japan??) was
_very_ slow (from the Netherlands). There should really be more rsync mirrors.

And cdimage.d.o is unreachable now. Well, no information is better than the
wrong information, as it keeps people from trying to access non-existant
mirrors. (Or did you finally update the page while I was away?)

But during my vacation, I got an idea that might be interesting. Some time
ago, I proposed to close FTP access to the fastest mirrors during release
time, and allow only rsync access. That would require fetching a pre-release
image which could be rsync-patched. 

There is however another easier and more robust way of making a pseudo-image
that can be rsync-patched.

ISO images store files in 2048-byte blocks. If all directories are located in
the beginning of the image, then the rest of the image would be a simple
concatenation of files that are zero-padded to a multiple of 2048 bytes.

So, if we know which files are in what sequence in the "files part" of the
image, then it would be very easy to get those files from the nearest
_packages_ mirror (many fast ones available), pad them to a multiple of 2048
bytes and cat >>pseudo-image. A very simple shell script using wget could do
it. No scaring debian_cd/yacs stuff. And it would not require any more
disk-space than the final image's size.

After this, rsync can be used to insert the directory structure, Packages.cd
files and possibly a few other things.

 - a sequence-listing of the files on the various CDs should be available on
   the cdimage sites. The `isoinfo' program from the "cdrecord suite"
   (http://www.fokus.gmd.de/nthp/employees/schilling/cdrecord.html) can
   generate such a listing from the ISO image;
 - a simple script for the "cd burner" that uses this listing to build a
   pseudo-image as described above;
 - understandable & correct instructions how to use rsync to patch
   the pseudo-image to an Official one.

Would this approach work?

At the moment, I've only limited net access, and loads of other things to do,
so I'll leave it to a volunteer to further explore this.

BTW, this works best if all directories are located at the beginning of the
image. `mkisofs' 1.12b3 as distributed in the "cdrecord suite" (see above)
does this; I'm not sure about `mkhybrid'. BTW, do you really still use
`mkhybrid'? The new `mkisofs' seems to be able to do anything `mkhybrid'

Another question: does rsync patch in-place or does it make a temporary
patched file (thus requiring twice the disk space)?

  Anne Bezemer

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