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Re: FHS: Wholesale conversion is wrong

Yann Dirson wrote:
> Richard Braakman writes:
>  >   3. Ensure that dpkg can handle a package upgrade that moves a 
>  >      directory and replaces it with a symlink to the new location.
>  >      Brandon Robinson ran into problems when he did this in xbase.
> He's not the only one.  I was hit by this with 2 packages, which ended
> in `rm -rf's in preinst script to turn around this.  I sent a simple
> test-case in a bug-report, and got positive feedback from Ian or Klee
> (don't remember), telling they were already investigating this
> problem.
> I'd add that both replacing a plain dir with a symlink, and replacing
> a symlink with a plain dir cause problems to dpkg 1.4.0.x.  Never
> tried 1.4.1.x.  You've been warned ;)

I've tried to think of a way around this, but it may well be fatal for
my proposal.  I see two ways to deal with the dpkg issue:

  - Fix the bug in dpkg, and have FHS-compliant packages assume the
    bug is fixed.  This means everyone has to upgrade dpkg before
    installing anything else from slink.
    (This can't be captured in package relationships.  Even a Pre-Depends
     on the fixed dpkg will not affect a running dpkg.  We'd have to
     handle it just like the introduction of epochs.)

  - Put code in the preinst to move directories and install symlinks,
    for every package that needs to.  (And code in the postrm to unwind
    this, when downgrading!)
    Disadvantage: This is icky code, and I don't have confidence that
    every package will do it right.  If we provide a tool for it, then
    everyone will have to install the tool before installing anything
    else from slink.  That would be about equivalent to having every
    package depend on a "fhs" package, so we might as well go that way

Either way, I think the disadvantages will outweigh the advantages
that can be gained from my proposal.  I regretfully retract it.

Richard Braakman

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