Re: [PATCH v3 3/8] migration/savevm: Allow immutable device state to be migrated early (i.e., before RAM)

[David Hildenbrand <david@redhat.com>]

On 13.01.23 16:27, Peter Xu wrote:
> On Fri, Jan 13, 2023 at 10:20:31AM -0500, Peter Xu wrote:
>> On Fri, Jan 13, 2023 at 02:47:24PM +0100, David Hildenbrand wrote:
>>> I'd prefer to not go down that path for now. QEMU_VM_SECTION_START without
>>> QEMU_VM_SECTION_PART and QEMU_VM_SECTION_END feels pretty incomplete and
>>> wrong to me.
>>
>> That's fine.
>>
>>>
>>> If we want to do that in the future, we should conditionally send
>>> QEMU_VM_SECTION_START only if we have se->ops I assume?
>>
>> Yes.  START/FULL frames are mostly replaceable afaiu in the stream ABI, so
>> we always have space to change no matter what.  Let's leave that as-is.
> 
> If so, please consider adding one more paragraph describing the difference
> in vmsd early_setup comments (on using FULL for early vmsd and START for
> save_setup), hopefully it'll make things clearer.

What about the following:

diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index 7bc0cd9de9..cc910cab0f 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -188,6 +188,11 @@ struct VMStateDescription {
       * One SaveStateEntry should either have the save_setup() specified or
       * the vmsd with early_setup set to true. It should never have both
       * things set.
+     *
+     * Note that for now, a SaveStateEntry cannot have a VMSD and
+     * operations (e.g., save_setup()) set at the same time. For this reason,
+     * also early_setup VMSDs are migrated in a QEMU_VM_SECTION_FULL section,
+     * while save_setup() data is migrated in a QEMU_VM_SECTION_START section.
       */
      bool early_setup;
      int version_id;

Thanks!

-- 
Thanks,

David / dhildenb