Re: [PATCH v3 06/17] hw/sd/sdcard: Do not store vendor data on block drive (CMD56)

[Fabiano Rosas <farosas@suse.de>]

Peter Xu <peterx@redhat.com> writes:

> On Wed, Jul 10, 2024 at 01:21:51PM -0300, Fabiano Rosas wrote:
>> It's not about trust, we simply don't support migrations other than
>> n->n+1 and (maybe) n->n-1. So QEMU from 2016 is certainly not included.
>
> Where does it come from?  I thought we suppport that..

I'm taking that from:

docs/devel/migration/main.rst:
  "In general QEMU tries to maintain forward migration compatibility
  (i.e. migrating from QEMU n->n+1) and there are users who benefit from
  backward compatibility as well."

But of course it doesn't say whether that comes with a transitive rule
allowing n->n+2 migrations.

>
> The same question would be: are we requesting an OpenStack cluster to
> always upgrade QEMU with +1 versions, otherwise migration will fail?

Will an OpenStack cluster be using upstream QEMU? If not, then that's a
question for the distro. In a very practical sense, we're not requesting
anything. We barely test n->n+1/n->n-1, even if we had a strong support
statement I wouldn't be confident saying migration from QEMU 2.7 -> QEMU
9.1 should succeed.