Re: [PATCH 5/6] vfio/migration: Block VFIO migration with postcopy migration

[Peter Xu <peterx@redhat.com>]

On Mon, Aug 28, 2023 at 06:18:41PM +0300, Avihai Horon wrote:
> diff --git a/migration/options.c b/migration/options.c
> index 1d1e1321b0..e201053563 100644
> --- a/migration/options.c
> +++ b/migration/options.c
> @@ -499,6 +499,11 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp)
>              error_setg(errp, "Postcopy is not yet compatible with multifd");
>              return false;
>          }
> +
> +        if (migration_vfio_mig_active()) {
> +            error_setg(errp, "Postcopy is not compatible with VFIO migration");
> +            return false;
> +        }

Hmm.. this will add yet another vfio hard-coded line into migration/..

What will happen if the vfio device is hot plugged after enabling
postcopy-ram here?

Is it possible to do it in a generic way?

I was thinking the only unified place to do such check is when migration
starts, as long as we switch to SETUP all caps are locked and doesn't allow
any change until it finishes or fails.

So, can we do this check inside vfio_save_setup(), allow vfio_save_setup()
to fail the whole migration early?  For example, maybe we should have an
Error** passed in, then if it fails it calls migrate_set_error, so
reflected in query-migrate later too.

Thanks,

>      }
>  
>      if (new_caps[MIGRATION_CAPABILITY_BACKGROUND_SNAPSHOT]) {
> @@ -612,6 +617,16 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp)
>      return true;
>  }

-- 
Peter Xu