Re: [PATCH v3 2/8] migration/savevm: Prepare vmdesc json writer in qemu_savevm_state_setup()

[David Hildenbrand]

On 12.01.23 18:43, Dr. David Alan Gilbert wrote:
> * David Hildenbrand (david@redhat.com) wrote:
> > ... and store it in the migration state. This is a preparation for
> > storing selected vmds's already in qemu_savevm_state_setup().
> >
> > Signed-off-by: David Hildenbrand <david@redhat.com>
> > ---
> >   migration/migration.c |  4 ++++
> >   migration/migration.h |  4 ++++
> >   migration/savevm.c    | 18 ++++++++++++------
> >   3 files changed, 20 insertions(+), 6 deletions(-)

[1]

> > diff --git a/migration/migration.c b/migration/migration.c
> > index 52b5d39244..1d33a7efa0 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -2170,6 +2170,9 @@ void migrate_init(MigrationState *s)
> >       s->vm_was_running = false;
> >       s->iteration_initial_bytes = 0;
> >       s->threshold_size = 0;
> > +
> > +    json_writer_free(s->vmdesc);
> > +    s->vmdesc = NULL;
> >   }

[...]

> >       trace_savevm_state_setup();
> >       QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
> >           if (!se->ops || !se->ops->save_setup) {
> > @@ -1390,15 +1395,12 @@ int 
> > qemu_savevm_state_complete_precopy_non_iterable(QEMUFile *f,
> >                                                       bool in_postcopy,
> >                                                       bool inactivate_disks)
> >   {
> > -    g_autoptr(JSONWriter) vmdesc = NULL;
> > +    MigrationState *ms = migrate_get_current();
> > +    JSONWriter *vmdesc = ms->vmdesc;
> >       int vmdesc_len;
> >       SaveStateEntry *se;
> >       int ret;
> >   
> > -    vmdesc = json_writer_new(false);
> > -    json_writer_start_object(vmdesc, NULL);
> > -    json_writer_int64(vmdesc, "page_size", qemu_target_page_size());
> > -    json_writer_start_array(vmdesc, "devices");
> >       QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
> >           ret = vmstate_save(f, se, vmdesc);
> >           if (ret) {
> > @@ -1433,6 +1435,10 @@ int 
> > qemu_savevm_state_complete_precopy_non_iterable(QEMUFile *f,
> >           qemu_put_buffer(f, (uint8_t *)json_writer_get(vmdesc), vmdesc_len);
> >       }
> >   
> > +    /* Free it now to detect any inconsistencies. */
> > +    json_writer_free(vmdesc);
> > +    ms->vmdesc = NULL;
>
> and this only happens when this succesfully exits;  so if this errors
> out, and then you retry an outwards migration, I think you've leaked a
> writer.

Shouldn't the change [1] to migrate_init() cover that?

--
Thanks,

David / dhildenb