On 03/20/2013 08:20 PM, Yair Zaslavsky wrote:
----- Original Message -----
From: "Shireesh Anjal" <[email protected]>
To: "Mike Kolesnik" <[email protected]>
Cc: [email protected]
Sent: Wednesday, March 20, 2013 4:47:08 PM
Subject: Re: [Engine-devel] FeatureSupported and compatibility versions
On 03/18/2013 01:11 PM, Shireesh Anjal wrote:
On 03/18/2013 12:59 PM, Mike Kolesnik wrote:
----- Original Message -----
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:
You can "merge" the configs into a single config when older
versions
go out of the supported versions for the system.
i.e. in 4.0 you can have upgrade script that merges all
GlusterFeatureSupported to one entry instead of several.
Why are we even storing this information in config? Is this something
that can be "configured" at customer site?
As previously explained (but off list :) ) , Config gives you the ability to have a cachable
"map" of entry (i.e - "feature name") per version and value.
I guess it was convinient for the developers to use that.
I also mentioned that customers/oVirt users should config the entries of
vdc_options using engine-config tool only.
Not all entries are exposed via engine-config.properties (and no, not just "is
feature supported" entries are hidden).
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'm not sure why we would want to complicate this simple
mechanism?
Is there much to gain?
I think option 1 suggested above is simpler - to implement as well
as
to understand.
Let me give you an example of why I don't like current mechanism. I
introduce a version check for a feature that was introduced in 3.1.
I'm being asked now to add three entries in config
3.0 - false
3.1 - true
3.2 - true
It will also mean that when 3.3 goes out, someone has to make sure
that another entry is added for 3.3-true. I think it is not logical
as
well as scalable if you have more versions. And it sounds far more
complex (to maintain) than just having
<Feature>SupportedFrom = 3.1
So I would like to know if there are any objections to my proposal.
I
intend to use this for at least the gluster related features.
I've sent a patch (http://gerrit.ovirt.org/12970) with following changes:
1) Introduced CompatibilityUtils that provides utility methods for
checking if a given feature is supported in the config. One method to
check based on boolean values (as is being done today for virt
features), and nother to check based on a range (from, to) which I would
like to use for gluster features.
2) Renamed FeatureSupported to VirtFeatureSupported, and made it use the
first utility method from CompatibilityUtils
3) Introduced GlusterFeatureSupported for gluster features, which uses
the second utility method from CompatibilityUtils
Key advantage here is that
- we don't have to touch any virt specifc source for adding
compatibility checks for gluster features
- virt features continue to use the existing boolean config check
Any comments / suggestions / reviews will be highly appreciated :)
Thoughts?
Regards,
Shireesh
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