migration: Make events a capability

Make check fails with events.  THis is due to the parser/lexer that it
uses.  Just in case that they are more broken parsers, just only send
events when there are capabilities.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

include/migration/migration.h

@@ -177,6 +177,7 @@ bool migrate_use_compression(void);
 int migrate_compress_level(void);
 int migrate_compress_threads(void);
 int migrate_decompress_threads(void);
+bool migrate_use_events(void);
 
 void ram_control_before_iterate(QEMUFile *f, uint64_t flags);
 void ram_control_after_iterate(QEMUFile *f, uint64_t flags);

migration/migration.c

@@ -205,6 +205,14 @@ void register_global_state(void)
     vmstate_register(NULL, 0, &vmstate_globalstate, &global_state);
 }
 
+static void migrate_generate_event(int new_state)
+{
+    if (migrate_use_events()) {
+        qapi_event_send_migration(new_state, &error_abort);
+        trace_migrate_set_state(new_state);
+    }
+}
+
 /*
  * Called on -incoming with a defer: uri.
  * The migration can be started later after any parameters have been
@@ -511,8 +519,7 @@ void qmp_migrate_set_parameters(bool has_compress_level,
 static void migrate_set_state(MigrationState *s, int old_state, int new_state)
 {
     if (atomic_cmpxchg(&s->state, old_state, new_state) == old_state) {
-        qapi_event_send_migration(new_state, &error_abort);
-        trace_migrate_set_state(new_state);
+        migrate_generate_event(new_state);
     }
 }
 
@@ -862,6 +869,15 @@ int migrate_decompress_threads(void)
     return s->parameters[MIGRATION_PARAMETER_DECOMPRESS_THREADS];
 }
 
+bool migrate_use_events(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_EVENTS];
+}
+
 int migrate_use_xbzrle(void)
 {
     MigrationState *s;

qapi-schema.json

@@ -523,6 +523,9 @@
 #          minimize migration traffic. The feature is disabled by default.
 #          (since 2.4 )
 #
+# @events: generate events for each migration state change
+#          (since 2.4 )
+#
 # @auto-converge: If enabled, QEMU will automatically throttle down the guest
 #          to speed up convergence of RAM migration. (since 1.6)
 #
@@ -530,7 +533,7 @@
 ##
 { 'enum': 'MigrationCapability',
   'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks',
-           'compress'] }
+           'compress', 'events'] }
 
 ##
 # @MigrationCapabilityStatus