%config files and upgrade to F11 - consider noreplace

[Tomas Mraz]

On Wed, 2009-02-25 at 23:12 +0100, Miloslav Trmač wrote:
> Bill Nottingham píše v St 25. 02. 2009 v 17:01 -0500:
> > Miloslav Trmač (mitr at volny.cz) said: 
> > > Because the Fedora 11 RPM packages will use SHA-256 for file digests in
> > > the RPM headers, upgrades from earlier releases to Fedora 11 will
> > > replace user-modified %config files (without noreplace) by their
> > > original versions, and rename the user-modified files to *.rpmsave.
> > > 
> > > The Fedora packaging guidelines already suggest using %config(noreplace)
> > > in most cases:
> > > https://fedoraproject.org/wiki/PackagingGuidelines#Configuration_files .
> > > 
> > > Please review use of %config without noreplace in your packages, and add
> > > noreplace if appropriate.  The list of affected packages is below.
> > 
> > Given that it's comparing hashes, and the old hash is *obviously* of a
> > different type than the new hash, why can't these sorts of conflicts
> > be caught?
> rpm recognizes that the hash changed, but what can it do?
> 
> - there is a config file
> - the config file was modified by the user
> - the update package may or may not contain a different version
>   of the config file than the old package.
> => the only things rpm can do is:
> - leave the modified config file as is
>   (this is what rpm does if the hashes are equal, i.e. the update 
>    doesn't change the config file)
>   X if the update did update the config file, the updated config file
>     would not be installed - but %config means the updated config file
>     should be installed
>   X this loses data (user would have to dig into the updated rpm package
>     manually to get the updated config file, and would get no
>     notification about the unused updated config file)
> - save the updated config file as .rpmnew
>   X there would be no difference between %config and %config(noreplace),
>     changing the semantics
> - save the modified config file as .rpmsave
>   X moves modified files to .rpmsave even if the update doesn't change
>     the config file

As already pointed out by someone else before. RPM could compute
on-the-fly the old (MD5) hash of the new config file being installed and
use that for the comparsion. Except this may not be easily hackable into
the RPM code I suppose because the file is possibly not yet extracted
from the cpio at the time the hashes are compared.
-- 
Tomas Mraz
No matter how far down the wrong road you've gone, turn back.
                                              Turkish proverb