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

[Daniel P . Berrangé]

On Tue, Apr 30, 2024 at 11:40:42AM +0200, Philippe Mathieu-Daudé wrote:
> Hi Thomas,
> 
> On 30/4/24 08:45, 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.
> 
> Thanks for taking that out of my plate :)
> 
> IIRC 6 years was because of some old RHEL version, otherwise could
> 5 years be enough? (maybe it could be good enough for this old RHEL
> version as of QEMU v10.0).

With my RHEL hat on, 6 years gives an approximate alignment with
RHEL lifecycles, which have ended up being roughly 3 years apart.
RHEL-N, wants to support all machine types from RHEL-(N-1), so
in the worst case that gives up to 6 years worth of QEMU versions.

5 years could well be enough in many cases, depending on how
frequently RHEL rebases QEMU, but could also trip us up if the
timelines do something unexpected. So 6 years is a bit safer
from Red Hat's POV, if the community is willing.

> > 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
> 
> Why can't we start with QEMU 9.1?
> 
> > +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.
> 
> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> 

With regards,
Daniel
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