Re: [PATCH] docs/about: Automatically deprecate versioned machine types older than 6 years

[Daniel P . Berrangé]

On Tue, Apr 30, 2024 at 12:29:14PM +0200, Thomas Huth wrote:
> On 30/04/2024 11.55, Daniel P. Berrangé wrote:
> > On Tue, Apr 30, 2024 at 08:45:29AM +0200, Thomas Huth wrote:
> > > Old machine types often have bugs or work-arounds that affect our
> > > possibilities to move forward with the QEMU code base (see for example
> > > https://gitlab.com/qemu-project/qemu/-/issues/2213 for a bug that likely
> > > cannot be fixed without breaking live migration with old machine types,
> > > or https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04516.html or
> > > commit ea985d235b86). So instead of going through the process of manually
> > > deprecating old machine types again and again, let's rather add an entry
> > > that can stay, which declares that machine types older than 6 years are
> > > considered as deprecated automatically. Six years should be sufficient to
> > > support the release cycles of most Linux distributions.
> > 
> > Reading this again, I think we're mixing two concepts here.
> > 
> > With this 6 year cut off, we're declaring the actual *removal* date,
> > not the deprecation date.
> > 
> > A deprecation is something that happens prior to removal normally,
> > to give people a warning of /future/ removal, as a suggestion
> > that they stop using it.
> > 
> > If we never set the 'deprecation_reason' on a machine type, then
> > unless someone reads this doc, they'll never realize they are on
> > a deprecated machine.
> > 
> > When it comes to machine types, I see deprecation as a way to tell
> > people they should not deploy a /new/ VM on a machine type, only
> > use it for back compat (incoming migration / restore from saved
> > image) with existing deployed VMs.
> > 
> > If we delete a machine on the 6 year anniversary, then users
> > don't want to be deploying /new/ VMs using that on the
> > 5 year anniversary as it only gives a 1 year upgrade window.
> > 
> > So how long far back do we consider it reasonable for a user
> > to deploy a /new/ VM on an old machine type ? 1 year, 2 years,
> > 3 years ?
> > 
> > 
> > How about picking the half way point ?  3 years ?
> > 
> > ie, set deprecation_reason for any machine that is 3 years
> > old, but declare that our deprecation cycle lasts for
> > 3 years, instead of the normal 1 year, when applied to
> > machine types.
> > 
> > This would give a strong hint that users should get off the
> > old machine type, several years before its finally deleted.
> 
> Sounds like a good idea, too! Since I have to drop this patch here anyway,
> could you maybe write such a new patch? (or do you want me to try to
> formulate this?)

Yes, I'll send something for discussion soon.

With regards,
Daniel
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