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Re: rollback after software upgrade

On Tue, Jul 27, 2010 at 06:18:43PM +0200, Michael wrote:
>  Lennart,
> > On Tue, Jul 27, 2010 at 02:45:27AM +0200, Michael wrote:
> > > (i think you wanted to write "didn't" here ?)
> > > 
> > > Wouldn't it be funny to ask developers for a downgrade converter :)
> > > 
> > > It's an interesting question if there will be any 'standard' configuration syntax some day (maybe XML based?) and if up- and downgrades can convert them rather easily then, both hither and forth...
> > 
> > XML does not help anything.  It is just something that lets you store a
> > tree of config in a flat text file.  Nothing more.  The meaning of the
> > tree is still a problem.  Anyone that thinks XML solves all config
> > parsing problems and makes files underversal and supported clearly has
> > no idea what XML is.  That would make Microsoft very happy however.
> > 
> > A downgrade quite simply requires a time machine.  After all the
> > developer has to write support for converting a future format into a
> > current format when you downgrade.  The new version has the ability to
> > upgrade old versions to new, and that is of course tested.  It does not
> > have the ability to convert back (and to what version)?  At least in
> > debian packages, it is the package being installed that is responsible
> > for any conversions, not the one being removed, so on a downgrade the
> > newer package doesn't do the conversion, and it would be the only one
> > that could know how to do it (although it would probably have very little
> > testing, if it was done at all).
> True. 
> It is not really about XML, it is about a standard for configurations and the file format is only a start, the real work starts beyond that,. But with not even that start...
> Theoretically there could be an upgrade/downgrade manager which would be called by the new or the downgraded (to be removed) package. As is aid, it's a technical problem and as such it could be solved. It's just a huge effort. That's why one would start thinking of a solution, if at all, then only if it would apply to all packages, not only a few.
> But hey this not a devel list and maybe my point is getting slightly off topic. Perhaps we should talk about real world solutions instead...for example, i would be interested if that system roll back works in M$, i've never tried it.

There's a discussion on the monotone-devel mailing list about putting /etc 
under revision control.  Of course one of the problems there is that Debian 
packages do some configuring when being installed, so there aren't files 
for a vendor branch anywhere in sight.

-- hendrik

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