Re: [PATCH V1 1/3] migration: check mode in notifiers

[Steven Sistare <steven.sistare@oracle.com>]

On 1/10/2024 2:09 AM, Peter Xu wrote:
> On Wed, Dec 13, 2023 at 10:11:31AM -0800, Steve Sistare wrote:
>> The existing notifiers should only apply to normal mode.
>>
>> No functional change.
> 
> Instead of adding such check in every notifier, why not make CPR a separate
> list of notifiers?  Just like the blocker lists.

Sure.   I proposed minimal changes in this current series, but extending the 
api to take migration mode would be nicer.

> Aside of this patch, I just started to look at this "notifier" code, I
> really don't think we should pass in MigrationState* into the notifiers.
> IIUC we only need the "state" as an enum.  Then with two separate
> registers, the device code knows the migration mode.
> 
> What do you think?

If we pass state, the notifier must either compare to enum values such as
MIGRATION_STATUS_COMPLETED instead of calling migration_has_finished(s), or
we must define new accessors such as migration_state_is_finished(state).

IMO passing MigrationState is the best approach.
MigrationState is an incomplete type in most notifiers, and the client can
pass it to a limited set of accessors to get more information -- exactly what 
we want to hide migration internals.  However, we could further limit the
allowed accessors, eg move these to a new file "include/migration/notifier.h".

----------------------------------------
#include "qemu/notify.h"
void migration_add_notifier(Notifier *notify,
                            void (*func)(Notifier *notifier, void *data));
void migration_remove_notifier(Notifier *notify);
bool migration_is_active(MigrationState *);
bool migration_in_setup(MigrationState *);
bool migration_has_finished(MigrationState *);
bool migration_has_failed(MigrationState *);
-----------------------------------------------

- Steve