Re: [RFC PATCH] virtio-net: introduce strict peer feature check

[Thomas Huth <thuth@redhat.com>]

On 13/11/2025 20.32, Peter Xu wrote:
> On Thu, Nov 13, 2025 at 12:46:55PM -0500, Michael S. Tsirkin wrote:
>> failing to start a perfectly good qemu which used to work
>> because you changed kernels is better than failing to migrate how?
>>
> 
> I agree this is not pretty.
> 
> The very original proposal was having extra features to be OFF by default,
> only allow explicit selections to enable them when the mgmt / user is aware
> of the possible hosts to run on top.

Could it maybe be tied to the "-nodefaults" option of QEMU? If you run QEMU 
with "-nodefaults" (which you should do when planning a migration later), 
these extra features that depend on the kernel version stay OFF. If you run 
QEMU without "-nodefaults", QEMU could enable them if supported by the 
kernel. So that would benefit both, the people running QEMU via management 
layers (using -nodefaults), and the people who just want to quickly launch 
QEMU on the command line. WDYT?

  Thomas