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

[Thomas Huth <thuth@redhat.com>]

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?)

  Thomas