[Engine-devel] FeatureSupported and compatibility versions

[Omer Frenkel]

----- Original Message -----
> From: "Shireesh Anjal" <sanjal at redhat.com>
> To: engine-devel at ovirt.org
> Sent: Monday, March 18, 2013 8:28:14 AM
> Subject: [Engine-devel] FeatureSupported and compatibility versions
> 
> Hi all,
> 
> The current mechanism in oVirt to check whether a feature is
> supported
> in a particular compatibility version is to use the FeatureSupported
> class. e.g.
> 
> FeatureSupported.networkLinking(getVm().getVdsGroupCompatibilityVersion())
> 
> Checks whether the "network linking" feature is supported for the the
> VM's cluster compatibility version. This internally checks whether
> the
> value of the corresponding config (NetworkLinkingSupported) for the
> given compatibility version is true/false.
> 
> I'm not sure if this is a good idea, since a feature is typically
> supported "from" a particular version. E.g. Gluster support was
> introduced in 3.1, and it continues to be available in all subsequent
> versions. So I see no point in adding configuration for every version
> indicating whether the feature is supported in that version or not. I
> suggest to use either of the following options:
> 
> 1) Instead of using a boolean config for each version, use a single
> string config that indicates the "supported from" version e.g.
> GlusterSupportedFrom = 3.1. There could be rare  cases where a
> feature,
> for some reason, is removed in some release. In such cases, we could
> use
> one additional config for the "supported to" version.
> 
> 2) Continue with the boolean approach, but do not have entries for
> every
> version; rather make use of the "default value" for majority of
> cases,
> and add the explicit version mapping for the minority e.g.
> GlusterSupported = true by default, and false in case of 3.0 (only
> one
> config required for 3.0)
> 

i like this approach better,
if one add new feature for 3.3 he should add it as 'true' in the config to be used as default,
and explicitly add it as false for other unsupported versions.
if we do go this way, we need to make sure it works because i vaguely remember we had a bug in configuration,
making us explicitly specify value for all versions.

> Thoughts?
> 
> Regards,
> Shireesh
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