Re: [Qemu-devel] [PATCH 2/4] e1000e: No need to validate configuration on migration

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Eduardo Habkost (ehabkost@redhat.com) wrote:
> On Thu, Oct 27, 2016 at 09:42:53AM +0300, Dmitry Fleytman wrote:
> > 
> > > On 26 Oct 2016, at 22:21 PM, Eduardo Habkost <ehabkost@redhat.com> wrote:
> > > 
> > > The user (or management software) is responsible for keeping the
> > > same configuration on both sides while migrating. Remove the
> > > configuration validation code at e1000e_post_load, and the
> > > unnecessary subsys_used/subsys_ven_used fields.
> > 
> > Migration with different subsys/subsys_ven may have a
> > really cumbersome consequences that are very hard to debug,
> > so I believe such a verification may save a lot of time,
> > however it’s a matter of convention.
> 
> The same issues apply to almost every other property on every
> other device. But the convention is to not expect devices to
> validate configuration changes on migration.
> 
> (It would be nice to have a more generic mechanism that detects
> configuration mismatch on migration, though. Having each device
> manually checking each of its properties wouldn't work).

Without knowing the e1000e code, isn't the easy way to do this
to change the:

        VMSTATE_UINT16(subsys, E1000EState),
        VMSTATE_UINT16(subsys_ven, E1000EState),
to

        VMSTATE_UINT16_EQUAL(subsys, E1000EState),
        VMSTATE_UINT16_EQUAL(subsys_ven, E1000EState),

and the migration code will flag if they don't match for you.

Dave

> 
> -- 
> Eduardo
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK