Re: [PATCH v5 2/8] migration: add VMSTATE_VARRAY_OF_POINTER_TO_STRUCT_UINT{8, 32}_ALLOC

[Peter Xu <peterx@redhat.com>]

On Tue, Mar 17, 2026 at 11:27:02AM +0100, Alexander Mikhalitsyn wrote:
> From: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@futurfusion.io>
> 
> Add VMSTATE_VARRAY_OF_POINTER_TO_STRUCT_UINT{8, 32}_ALLOC, which
> helps to save/restore a dynamic array of pointers to
> structures.
> 
> Suggested-by: Peter Xu <peterx@redhat.com>
> Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@futurfusion.io>
> v2:
> - added VMSTATE_VARRAY_OF_POINTER_TO_STRUCT_UINT8_ALLOC
> v4:
> - almost completely reworked, new flag VMS_ARRAY_OF_POINTER_ALLOW_NULL
>   was introduced as suggested by Peter
> v5:
> - rebased on top of https://lore.kernel.org/all/20260304212303.667141-1-vsementsov@yandex-team.ru/
> ---
>  include/migration/vmstate.h | 77 ++++++++++++++++++++++++++++++-
>  migration/savevm.c          | 26 +++++++++++
>  migration/vmstate-types.c   | 91 +++++++++++++++++++++++++++++++++++++
>  migration/vmstate.c         | 54 ++++++++++++++++++----
>  4 files changed, 236 insertions(+), 12 deletions(-)

Hi, Alexander,

Sorry for a late reply, I didn't reply to your previous version on patch 2
because I didn't yet get time to really review this patch. It took me some
time to figure out what's the best way to do this.  I still think it'll be
good to avoid introducing yet another info like what this patch did.  In
general, I want to see if we can reduce get()/put()/save()/load() rather
than adding more.

Meanwhile, there're small issues here and there I saw.

E.g. reusing ->start to cache the object size sounds too tricky.  I am
trying to figure out if we can always stick with ->size to store the object
size; I'll need some even pre-requisite patches though to convert some
existing VMS_ARRAY_OF_POINTER users to reserve the ->size field for that,
though.

The other thing is I had a gut feeling this patch may have issue on the
JSON blob dumped in the migration stream, via the JSONWriter* object passed
into vmstate_save_vmsd_v().

All these made me feel like I'd better go prepare some RFC patches, because
commenting will be too slow.

I'll likely send something very soon just to show what I meant, it'll be
good if you can have a look at that when it comes.

Thanks,

-- 
Peter Xu