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

[Daniel P . Berrangé]

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.

> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  docs/about/deprecated.rst | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
> index 6d595de3b6..fe69e2d44c 100644
> --- a/docs/about/deprecated.rst
> +++ b/docs/about/deprecated.rst
> @@ -220,6 +220,17 @@ is a chance the code will bitrot without anyone noticing.
>  System emulator machines
>  ------------------------
>  
> +Versioned machine types older than 6 years
> +''''''''''''''''''''''''''''''''''''''''''
> +
> +Starting with the release of QEMU 10.0, versioned machine types older than
> +6 years will automatically be considered as deprecated and might be due to
> +removal without furthor notice. For example, this affects machine types like
> +pc-i440fx-X.Y, pc-q35-X.Y, pseries-X.Y, s390-ccw-virtio-X.Y or virt-X.Y where
> +X is the major number and Y is the minor number of the old QEMU version.
> +If you are still using machine types from QEMU versions older than 6 years,
> +please update your setting to use a newer versioned machine type instead.
> +
>  Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1)
>  ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
>  
> -- 
> 2.44.0
> 

With regards,
Daniel
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