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

[Peter Xu]

On Wed, Jul 10, 2024 at 04:48:23PM -0300, Fabiano Rosas wrote:
> 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.

I'd say that "i.e." implies n->n+1 is not the only forward migration we
would support.

I _think_ we should support all forward migration as long as the machine
type matches.

> 
> >
> > 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

It's an example to show what I meant! :) Nothing else. Definitely not
saying that everyone should use an upstream released QEMU (but in reality,
it's not a problem, I think, and I do feel like people use them, perhaps
more with the stable releases).

> 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.

No matter what we test in CI, I don't think we should break that for >1
versions..  I hope 2.7->9.1 keeps working, otherwise I think it's legal to
file a bug by anyone.

For example, I randomly fetched a bug report:

https://gitlab.com/qemu-project/qemu/-/issues/1937

QEMU version:                6.2 and 7.2.5

And I believe that's the common case even for upstream.  If we don't do
that right for upstream, it can be impossible tasks for downstream and for
all of us to maintain.

-- 
Peter Xu