On Thu, Aug 07, 2025 at 08:50:38AM -0400, Jonah Palmer wrote:
>
>
> On 8/6/25 11:58 AM, Peter Xu wrote:
> > On Tue, Jul 22, 2025 at 12:41:22PM +0000, Jonah Palmer wrote:
> > > Adds a new migration capability 'virtio-iterative' that will allow
> > > virtio devices, where supported, to iteratively migrate configuration
> > > changes that occur during the migration process.
> > >
> > > This capability is added to the validated capabilities list to ensure
> > > both the source and destination support it before enabling.
> > >
> > > The capability defaults to off to maintain backward compatibility.
> > >
> > > To enable the capability via HMP:
> > > (qemu) migrate_set_capability virtio-iterative on
> > >
> > > To enable the capability via QMP:
> > > {"execute": "migrate-set-capabilities", "arguments": {
> > > "capabilities": [
> > > { "capability": "virtio-iterative", "state": true }
> > > ]
> > > }
> > > }
> > >
> > > Signed-off-by: Jonah Palmer <jonah.pal...@oracle.com>
> > > ---
> > > migration/savevm.c | 1 +
> > > qapi/migration.json | 7 ++++++-
> > > 2 files changed, 7 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/migration/savevm.c b/migration/savevm.c
> > > index bb04a4520d..40a2189866 100644
> > > --- a/migration/savevm.c
> > > +++ b/migration/savevm.c
> > > @@ -279,6 +279,7 @@ static bool should_validate_capability(int capability)
> > > switch (capability) {
> > > case MIGRATION_CAPABILITY_X_IGNORE_SHARED:
> > > case MIGRATION_CAPABILITY_MAPPED_RAM:
> > > + case MIGRATION_CAPABILITY_VIRTIO_ITERATIVE:
> > > return true;
> > > default:
> > > return false;
> > > diff --git a/qapi/migration.json b/qapi/migration.json
> > > index 4963f6ca12..8f042c3ba5 100644
> > > --- a/qapi/migration.json
> > > +++ b/qapi/migration.json
> > > @@ -479,6 +479,11 @@
> > > # each RAM page. Requires a migration URI that supports seeking,
> > > # such as a file. (since 9.0)
> > > #
> > > +# @virtio-iterative: Enable iterative migration for virtio devices, if
> > > +# the device supports it. When enabled, and where supported, virtio
> > > +# devices will track and migrate configuration changes that may
> > > +# occur during the migration process. (Since 10.1)
> > > +#
> >
> > Having a migration capability to enable iterative support for a specific
> > type of device sounds wrong.
> >
> > If virtio will be able to support iterative saves, it could provide the
> > save_live_iterate() function. Any explanation why it needs to be a
> > migration capability?
> >
>
> It certainly doesn't have to be a migration capability. Perhaps it's better
> as a per-device compatibility property? E.g.:
>
> -device virtio-net-pci,x-iterative-migration=on,...
>
> I was just thinking along the lines of not having this feature enabled by
> default for backwards-compatibility (and something to toggle to compare
> performance during development).
>
> Totally open to suggestions though. I wasn't really sure how best a
> feature/capability like this should be introduced.
Yep, for RFC is fine, if there'll be a formal patch please propose it as a
device property whenever needed, thanks.
--
Peter Xu
