Re: [PATCH 10/10] docs/about/deprecated: Deprecate the qemu-system-i386 binary

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, Apr 02, 2026 at 12:11:37PM +0200, Thomas Huth wrote:
> On 02/04/2026 12.06, Daniel P. Berrangé wrote:
> > On Thu, Apr 02, 2026 at 11:51:32AM +0200, Thomas Huth wrote:
> > > From: Thomas Huth <thuth@redhat.com>
> > > 
> > > Aside from not supporting KVM on 32-bit hosts, the qemu-system-x86_64
> > > binary is a proper superset of the qemu-system-i386 binary. And with
> > > the 32-bit x86 host support being removed now, it is possible to
> > > deprecate the qemu-system-i386 binary now, too.
> > > 
> > > With regards to 32-bit KVM support in the x86 Linux kernel,
> > > the developers confirmed that they do not need a recent
> > > qemu-system-i386 binary here:
> > > 
> > >   https://lore.kernel.org/kvm/Y%2ffkTs5ajFy0hP1U@google.com/
> > > 
> > > Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> > > Signed-off-by: Thomas Huth <thuth@redhat.com>
> > > ---
> > >   docs/about/deprecated.rst | 19 +++++++++++++++++++
> > >   1 file changed, 19 insertions(+)
> > > 
> > > diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
> > > index a6d6a713265..2de51337d75 100644
> > > --- a/docs/about/deprecated.rst
> > > +++ b/docs/about/deprecated.rst
> > > @@ -301,6 +301,25 @@ machine must ensure that they're setting the ``spike`` machine in the
> > >   command line (``-M spike``).
> > > +System emulator binaries
> > > +------------------------
> > > +
> > > +``qemu-system-i386`` binary (since 11.1)
> > > +''''''''''''''''''''''''''''''''''''''''
> > > +
> > > +The ``qemu-system-i386`` binary was mainly useful for running with KVM
> > > +on 32-bit x86 hosts, but most Linux distributions already removed their
> > > +support for 32-bit x86 kernels, so hardly anybody still needs this. The
> > > +``qemu-system-x86_64`` binary is a proper superset and can be used to
> > > +run 32-bit guests by selecting a 32-bit CPU model, including KVM support
> > > +on x86_64 hosts. Thus users are recommended to reconfigure their systems
> > > +to use the ``qemu-system-x86_64`` binary instead. If a 32-bit CPU guest
> > > +environment should be enforced, you can switch off the "long mode" CPU
> > > +flag with ``-cpu max,lm=off``, or rename/symlink ``qemu-system-x86_64``
> > > +to ``qemu-system-i386`` -- QEMU will then run with the 64-bit extensions
> > > +disabled.
> > 
> > Why don't we just have our install rules create the symlink from
> > qemu-system-x86_64 to qemu-system-i386. That gives us near zero
> > ongoing maint cost, without need to deprecate stuff / impact users
> 
> I think we should do that once the deprecation period is over and we don't
> allow to build QEMU in this mode anymore. I would rather not jump directly
> to that state to provide people some time for experimenting whether this new
> approach works as expected in all scenarios that are in use.

This feels a bit wierd as a deprecation though.  We're telling people
not to use  qemu-system-i386 and yet we intend to continue providing
it via a symlink and expect full back compatibility and people can
carry on with it forever.


I think this is probably something better handled via a build time
option & messages from

  * Step 1: full i686 binary by default but have --enable-i686-compat
            to switch to symlink. Issue hint message that symlink will
	    become the default in future & asking for feedback if
	    --enable-i686-compat is not given

  * Step 2: symlink i686 binary by default but have --disable-i686-compat
            to switch to full binary. Issue *WARNING* that full binary
	    will be soon removed if --disable-i686-compat is given

  * Step 3: remove full binary

With regards,
Daniel
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