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Re: dpkg question: preinst run before Depends:?

On Fri, 5 Sep 1997, Ian Jackson wrote:

> So you should not make tetex's preinst depend on dpkg-perl.  Only
> Essential packages are guaranteed to be available in preinst scripts.


So we are still looking for the best solution. The situation is the
following: The current preinst scripts of the tetex-* packages use
`dpkg -s' to search for the old tex packages.

If I remember right, this is because dpkg does not support mulitple
"Replaces:" and simple "Conflicts" would leave the user without
information in dselect. The preinst script checks for the old packages and
refuses to install, together with a note how to remove the old packages
before proceeding.

Thus, if dpkg could handle multiple Conflicts, all this would be a lot
easier. (Ian, please don't take this as an accusation.)

Since the call there are three (or more) tetex packages which have such a
preinst script, and each of them calls `dpkg -s' 37 times, that will make
3*37=111 calls, which takes to long even on fast computers.

(Note, that this check is done even on completely up-to-date system
whenever a new tetex package comes out. But we can't drop the preinst 
scripts, since that would make upgrades from older systems harder.)

As a possible speed up, I considered using Klee's nice dpkg-perl
programming interface to dpkg's db.

I see the following possibilities now:

   a) remove the preinst scripts completely and add "Conflicts:"

      (This makes the assumption that most people have 1.3 system--I 
      don't really think that this is the case.)

   b) make tetex-* packages "Pre-Depend" on dpkg-perl

      (not a good solution)

   c) move dpkg-perl into base system

      (Note, that there will be a new "perl-base" package which will be
      marked "Essential"--if I recall right. We could merge "dpkg-perl"
      and "perl-base".)

   d) include the (very small) modules from dpkg-perl in the preinst

      (This solution is not very nice but would work.)

Please note, that a programming interface to dpkg (i.e. dpkg-perl) is
valuable and it would be good if it can be using in such situations. Also
note, that the "Installed-Size" of dpkg-perl is only 32k.



--                 Christian Schwarz
                    schwarz@monet.m.isar.de, schwarz@schwarz-online.com,
Don't know Perl?     schwarz@debian.org, schwarz@mathematik.tu-muenchen.de
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http://www.perl.com     http://fatman.mathematik.tu-muenchen.de/~schwarz/

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