[06/17] migration: Create x-multifd-threads parameter

diff --git a/hmp.c b/hmp.c
index 8522efe..8c7e302 100644
--- a/hmp.c
+++ b/hmp.c
@@ -322,6 +322,9 @@  void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict)
         monitor_printf(mon, " %s: %" PRId64,
             MigrationParameter_lookup[MIGRATION_PARAMETER_X_CHECKPOINT_DELAY],
             params->x_checkpoint_delay);
+        monitor_printf(mon, " %s: %" PRId64,
+            MigrationParameter_lookup[MIGRATION_PARAMETER_X_MULTIFD_THREADS],
+            params->x_multifd_threads);
         monitor_printf(mon, "\n");
     }

@@ -1394,6 +1397,10 @@  void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict)
                 p.has_x_checkpoint_delay = true;
                 use_int_value = true;
                 break;
+            case MIGRATION_PARAMETER_X_MULTIFD_THREADS:
+                p.has_x_multifd_threads = true;
+                use_int_value = true;
+                break;
             }

             if (use_int_value) {
@@ -1411,6 +1418,7 @@  void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict)
                 p.cpu_throttle_increment = valueint;
                 p.downtime_limit = valueint;
                 p.x_checkpoint_delay = valueint;
+                p.x_multifd_threads = valueint;
             }

             qmp_migrate_set_parameters(&p, &err);
diff --git a/include/migration/migration.h b/include/migration/migration.h
index 19245d6..b35044c 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -247,6 +247,8 @@  bool migration_in_postcopy(MigrationState *);
 bool migration_in_postcopy_after_devices(MigrationState *);
 MigrationState *migrate_get_current(void);

+int migrate_multifd_threads(void);
+
 void migrate_compress_threads_create(void);
 void migrate_compress_threads_join(void);
 void migrate_decompress_threads_create(void);
diff --git a/migration/migration.c b/migration/migration.c
index 1669e41..2fe03d8 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -67,6 +67,7 @@ 
  * Note: Please change this default value to 10000 when we support hybrid mode.
  */
 #define DEFAULT_MIGRATE_X_CHECKPOINT_DELAY 200
+#define DEFAULT_MIGRATE_MULTIFD_THREADS 2

 static NotifierList migration_state_notifiers =
     NOTIFIER_LIST_INITIALIZER(migration_state_notifiers);
@@ -101,6 +102,7 @@  MigrationState *migrate_get_current(void)
             .max_bandwidth = MAX_THROTTLE,
             .downtime_limit = DEFAULT_MIGRATE_SET_DOWNTIME,
             .x_checkpoint_delay = DEFAULT_MIGRATE_X_CHECKPOINT_DELAY,
+            .x_multifd_threads = DEFAULT_MIGRATE_MULTIFD_THREADS,
         },
     };

@@ -591,6 +593,8 @@  MigrationParameters *qmp_query_migrate_parameters(Error **errp)
     params->downtime_limit = s->parameters.downtime_limit;
     params->has_x_checkpoint_delay = true;
     params->x_checkpoint_delay = s->parameters.x_checkpoint_delay;
+    params->has_x_multifd_threads = true;
+    params->x_multifd_threads = s->parameters.x_multifd_threads;

     return params;
 }
@@ -854,6 +858,13 @@  void qmp_migrate_set_parameters(MigrationParameters *params, Error **errp)
                     "x_checkpoint_delay",
                     "is invalid, it should be positive");
     }
+    if (params->has_x_multifd_threads &&
+            (params->x_multifd_threads < 1 || params->x_multifd_threads > 255)) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                   "multifd_threads",
+                   "is invalid, it should be in the range of 1 to 255");
+        return;
+    }

     if (params->has_compress_level) {
         s->parameters.compress_level = params->compress_level;
@@ -892,6 +903,9 @@  void qmp_migrate_set_parameters(MigrationParameters *params, Error **errp)
     if (params->has_x_checkpoint_delay) {
         s->parameters.x_checkpoint_delay = params->x_checkpoint_delay;
     }
+    if (params->has_x_multifd_threads) {
+        s->parameters.x_multifd_threads = params->x_multifd_threads;
+    }
 }


@@ -1328,6 +1342,15 @@  bool migrate_use_multifd(void)
     return s->enabled_capabilities[MIGRATION_CAPABILITY_X_MULTIFD];
 }

+int migrate_multifd_threads(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters.x_multifd_threads;
+}
+
 int migrate_use_xbzrle(void)
 {
     MigrationState *s;
diff --git a/qapi-schema.json b/qapi-schema.json
index d34632e..2273864 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -981,13 +981,17 @@ 
 # @x-checkpoint-delay: The delay time (in ms) between two COLO checkpoints in
 #          periodic mode. (Since 2.8)
 #
+# @x-multifd-threads: Number of threads used to migrate data in parallel
+#                     The default value is 2 (since 2.9)
+#
 # Since: 2.4
 ##
 { 'enum': 'MigrationParameter',
   'data': ['compress-level', 'compress-threads', 'decompress-threads',
            'cpu-throttle-initial', 'cpu-throttle-increment',
            'tls-creds', 'tls-hostname', 'max-bandwidth',
-           'downtime-limit', 'x-checkpoint-delay' ] }
+           'downtime-limit', 'x-checkpoint-delay',
+           'x-multifd-threads'] }

 ##
 # @migrate-set-parameters:
@@ -1050,6 +1054,10 @@ 
 #
 # @x-checkpoint-delay: the delay time between two COLO checkpoints. (Since 2.8)
 #
+#
+# @x-multifd-threads: Number of threads used to migrate data in parallel
+#                     The default value is 1 (since 2.9)
+#
 # Since: 2.4
 ##
 { 'struct': 'MigrationParameters',
@@ -1062,7 +1070,8 @@ 
             '*tls-hostname': 'str',
             '*max-bandwidth': 'int',
             '*downtime-limit': 'int',
-            '*x-checkpoint-delay': 'int'} }
+            '*x-checkpoint-delay': 'int',
+            '*x-multifd-threads': 'int'} }

 ##
 # @query-migrate-parameters: