Re: [PATCH v5 7/8] virtio-mem: Migrate immutable properties early

[Juan Quintela <quintela@redhat.com>]

David Hildenbrand <david@redhat.com> wrote:
> The bitmap and the size are immutable while migration is active: see
> virtio_mem_is_busy(). We can migrate this information early, before
> migrating any actual RAM content. Further, all information we need for
> sanity checks is immutable as well.
>
> Having this information in place early will, for example, allow for
> properly preallocating memory before touching these memory locations
> during RAM migration: this way, we can make sure that all memory was
> actually preallocated and that any user errors (e.g., insufficient
> hugetlb pages) can be handled gracefully.
>
> In contrast, usable_region_size and requested_size can theoretically
> still be modified on the source while the VM is running. Keep migrating
> these properties the usual, late, way.
>
> Use a new device property to keep behavior of compat machines
> unmodified.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Juan Quintela <quintela@redhat.com>


> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 616f3a207c..29b57f6448 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -41,7 +41,9 @@
>  #include "hw/virtio/virtio-pci.h"
>  #include "qom/object_interfaces.h"
>  
> -GlobalProperty hw_compat_7_2[] = {};
> +GlobalProperty hw_compat_7_2[] = {
> +    { "virtio-mem", "x-early-migration", "false" },
> +};

We can stop prettending that we don't support this kind of properties O:-)