[v1] hw: Mark the device with no migratable fields

[PATCH 02/18] migration/vmstate: Introduce vmstate_no_state_to_migrate

Posted by Philippe Mathieu-Daudé 5 years, 3 months ago

Introduce a special state to indicate when an object doesn't
have anything in its state to migrate.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 include/migration/vmstate.h | 1 +
 migration/vmstate.c         | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index af7d80cd4e..0922bc8efa 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -195,6 +195,7 @@ struct VMStateDescription {
 };
 
 extern const VMStateDescription vmstate_dummy; /* Exclusively for linux-user */
+extern const VMStateDescription vmstate_no_state_to_migrate;
 
 extern const VMStateInfo vmstate_info_bool;
 
diff --git a/migration/vmstate.c b/migration/vmstate.c
index bafa890384..d640cafad3 100644
--- a/migration/vmstate.c
+++ b/migration/vmstate.c
@@ -20,6 +20,13 @@
 #include "trace.h"
 #include "qjson.h"
 
+const VMStateDescription vmstate_no_state_to_migrate = {
+    .name = "empty-state",
+    .fields = (VMStateField[]) {
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 static int vmstate_subsection_save(QEMUFile *f, const VMStateDescription *vmsd,
                                    void *opaque, QJSON *vmdesc);
 static int vmstate_subsection_load(QEMUFile *f, const VMStateDescription *vmsd,
-- 
2.21.3

Re: [PATCH 02/18] migration/vmstate: Introduce vmstate_no_state_to_migrate

Posted by Peter Maydell 5 years, 2 months ago

On Fri, 3 Jul 2020 at 21:19, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>
> Introduce a special state to indicate when an object doesn't
> have anything in its state to migrate.
>
> Suggested-by: Peter Maydell <peter.maydell@linaro.org>
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
>  include/migration/vmstate.h | 1 +
>  migration/vmstate.c         | 7 +++++++
>  2 files changed, 8 insertions(+)
>
> diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
> index af7d80cd4e..0922bc8efa 100644
> --- a/include/migration/vmstate.h
> +++ b/include/migration/vmstate.h
> @@ -195,6 +195,7 @@ struct VMStateDescription {
>  };
>
>  extern const VMStateDescription vmstate_dummy; /* Exclusively for linux-user */
> +extern const VMStateDescription vmstate_no_state_to_migrate;
>
>  extern const VMStateInfo vmstate_info_bool;
>
> diff --git a/migration/vmstate.c b/migration/vmstate.c
> index bafa890384..d640cafad3 100644
> --- a/migration/vmstate.c
> +++ b/migration/vmstate.c
> @@ -20,6 +20,13 @@
>  #include "trace.h"
>  #include "qjson.h"
>
> +const VMStateDescription vmstate_no_state_to_migrate = {
> +    .name = "empty-state",
> +    .fields = (VMStateField[]) {
> +        VMSTATE_END_OF_LIST()
> +    }
> +};

Does this definitely not put any data into the migration stream?
We don't want to change what's on the wire for machines that
use devices that start using this. (If it does by default, it
would be easy to make the migration code special case the
magic symbol to act like "no vmsd specified").

thanks
-- PMM

Re: [PATCH 02/18] migration/vmstate: Introduce vmstate_no_state_to_migrate

Posted by Dr. David Alan Gilbert 5 years, 2 months ago

* Peter Maydell (peter.maydell@linaro.org) wrote:
> On Fri, 3 Jul 2020 at 21:19, Philippe Mathieu-DaudÃ© <f4bug@amsat.org> wrote:
> >
> > Introduce a special state to indicate when an object doesn't
> > have anything in its state to migrate.
> >
> > Suggested-by: Peter Maydell <peter.maydell@linaro.org>
> > Signed-off-by: Philippe Mathieu-DaudÃ© <f4bug@amsat.org>
> > ---
> >  include/migration/vmstate.h | 1 +
> >  migration/vmstate.c         | 7 +++++++
> >  2 files changed, 8 insertions(+)
> >
> > diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
> > index af7d80cd4e..0922bc8efa 100644
> > --- a/include/migration/vmstate.h
> > +++ b/include/migration/vmstate.h
> > @@ -195,6 +195,7 @@ struct VMStateDescription {
> >  };
> >
> >  extern const VMStateDescription vmstate_dummy; /* Exclusively for linux-user */
> > +extern const VMStateDescription vmstate_no_state_to_migrate;
> >
> >  extern const VMStateInfo vmstate_info_bool;
> >
> > diff --git a/migration/vmstate.c b/migration/vmstate.c
> > index bafa890384..d640cafad3 100644
> > --- a/migration/vmstate.c
> > +++ b/migration/vmstate.c
> > @@ -20,6 +20,13 @@
> >  #include "trace.h"
> >  #include "qjson.h"
> >
> > +const VMStateDescription vmstate_no_state_to_migrate = {
> > +    .name = "empty-state",
> > +    .fields = (VMStateField[]) {
> > +        VMSTATE_END_OF_LIST()
> > +    }
> > +};
> 
> Does this definitely not put any data into the migration stream?
> We don't want to change what's on the wire for machines that
> use devices that start using this. (If it does by default, it
> would be easy to make the migration code special case the
> magic symbol to act like "no vmsd specified").

I'd need to test it to be sure, but I think if we added a .needed
to vmstate_no_state_to_migrate with a function that always returned
false, then I think the stream would stay unchanged.

Dave

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