[augeas-devel] OT: How do Augeas lenses deal with incompatible config file changes on upgrade?

[David Lutterkort]

On Fri, 2008-06-13 at 13:07 -0700, Jeff Schroeder wrote:
> How does Augeas deal with something like squid where the config file
> will change in incompatible ways?
> Some of the directives in the rhel4 squid vs rhel5 change and are not
> backwards compatible.

What exactly are the differences ? Is it possible to detect what version
a file is for just from looking at the config file ?

> This is a very difficult problem to solve. If Augeas has solved it, how?

It hasn't really; Augeas doesn't have a way (yet) to couple lens
definitions to versions of installed software. It simply looks for
certain files, and if they are there processes them according to a fixed
definition.

The simplest way to address it would be for squid to ship the
appropriate lens definition for each version. With that, the squid
package would install the right squid.aug into /usr/share/augeas/lenses.

Even more difficult is the question of how to get from an 'old' squid
config file to a 'new' squid config file. It would be possible to
address that with Augeas, and a bit of copying files around, but it's
not something anybody has looked at in much detail.

David