colo: Remove ENABLE_COLO savevm command and mark it as deprecated

No need for it anymore now that x-colo capability is required
on incoming side. There is also no need to send it for backwards
compatibility since we only support COLO with the same version on
both sides.

We mark the command code as deprecated and now error out if such
a unhandled command is encountered in loadvm_process_command().

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Lukas Straub <lukasstraub2@web.de>
Link: https://lore.kernel.org/qemu-devel/20260302-colo_unit_test_multifd-v11-5-d653fb3b1d80@web.de
Signed-off-by: Fabiano Rosas <farosas@suse.de>

include/migration/colo.h

@@ -25,8 +25,6 @@ void migrate_start_colo_process(MigrationState *s);
 bool migration_in_colo_state(void);
 
 /* loadvm */
-int migration_incoming_enable_colo(Error **errp);
-void migration_incoming_disable_colo(void);
 bool migration_incoming_in_colo_state(void);
 
 COLOMode get_colo_mode(void);

migration/migration.c

@@ -604,31 +604,6 @@ int migrate_send_rp_req_pages(MigrationIncomingState *mis,
     return migrate_send_rp_message_req_pages(mis, rb, start);
 }
 
-static bool migration_colo_enabled;
-void migration_incoming_disable_colo(void)
-{
-    ram_block_discard_disable(false);
-    migration_colo_enabled = false;
-}
-
-int migration_incoming_enable_colo(Error **errp)
-{
-#ifndef CONFIG_REPLICATION
-    error_setg(errp, "ENABLE_COLO command come in migration stream, but the "
-               "replication module is not built in");
-    return -ENOTSUP;
-#endif
-
-    if (!migrate_colo()) {
-        error_setg(errp, "ENABLE_COLO command come in migration stream"
-                   ", but x-colo capability is not set");
-        return -EINVAL;
-    }
-
-    migration_colo_enabled = true;
-    return 0;
-}
-
 void migrate_add_address(SocketAddress *address)
 {
     MigrationIncomingState *mis = migration_incoming_get_current();
@@ -735,7 +710,6 @@ static void process_incoming_migration_bh(void *opaque)
             runstate_set(RUN_STATE_PAUSED);
         }
     } else if (migrate_colo()) {
-        migration_incoming_disable_colo();
         vm_start();
     } else {
         runstate_set(global_state_get_runstate());
@@ -3542,11 +3516,6 @@ static void *migration_thread(void *opaque)
         qemu_savevm_send_postcopy_advise(s->to_dst_file);
     }
 
-    if (migrate_colo()) {
-        /* Notify migration destination that we enable COLO */
-        qemu_savevm_send_colo_enable(s->to_dst_file);
-    }
-
     if (migrate_auto_converge()) {
         /* Start RAMBlock dirty bitmap sync timer */
         cpu_throttle_dirty_sync_timer(true);

migration/savevm.c

@@ -90,7 +90,7 @@ enum qemu_vm_cmd {
                                       were previously sent during
                                       precopy but are dirty. */
     MIG_CMD_PACKAGED,          /* Send a wrapped stream within this stream */
-    MIG_CMD_ENABLE_COLO,       /* Enable COLO */
+    MIG_CMD_DEPRECATED_0,      /* Prior to 10.2, used as MIG_CMD_ENABLE_COLO */
     MIG_CMD_POSTCOPY_RESUME,   /* resume postcopy on dest */
     MIG_CMD_RECV_BITMAP,       /* Request for recved bitmap on dst */
     MIG_CMD_SWITCHOVER_START,  /* Switchover start notification */
@@ -1103,12 +1103,6 @@ static void qemu_savevm_command_send(QEMUFile *f,
     qemu_fflush(f);
 }
 
-void qemu_savevm_send_colo_enable(QEMUFile *f)
-{
-    trace_savevm_send_colo_enable();
-    qemu_savevm_command_send(f, MIG_CMD_ENABLE_COLO, 0, NULL);
-}
-
 void qemu_savevm_send_ping(QEMUFile *f, uint32_t value)
 {
     uint32_t buf;
@@ -2423,13 +2417,6 @@ static int loadvm_handle_recv_bitmap(MigrationIncomingState *mis,
     return 0;
 }
 
-static int loadvm_process_enable_colo(MigrationIncomingState *mis,
-                                      Error **errp)
-{
-    ERRP_GUARD();
-    return migration_incoming_enable_colo(errp);
-}
-
 static int loadvm_postcopy_handle_switchover_start(Error **errp)
 {
     SaveStateEntry *se;
@@ -2513,7 +2500,7 @@ static int loadvm_process_command(QEMUFile *f, Error **errp)
                 return ret;
             }
         }
-        break;
+        return 0;
 
     case MIG_CMD_PING:
         tmp32 = qemu_get_be32(f);
@@ -2524,7 +2511,7 @@ static int loadvm_process_command(QEMUFile *f, Error **errp)
             return -1;
         }
         migrate_send_rp_pong(mis, tmp32);
-        break;
+        return 0;
 
     case MIG_CMD_PACKAGED:
         return loadvm_handle_cmd_packaged(mis, errp);
@@ -2548,14 +2535,12 @@ static int loadvm_process_command(QEMUFile *f, Error **errp)
     case MIG_CMD_RECV_BITMAP:
         return loadvm_handle_recv_bitmap(mis, len, errp);
 
-    case MIG_CMD_ENABLE_COLO:
-        return loadvm_process_enable_colo(mis, errp);
-
     case MIG_CMD_SWITCHOVER_START:
         return loadvm_postcopy_handle_switchover_start(errp);
     }
 
-    return 0;
+    error_setg(errp, "MIG_CMD 0x%x deprecated (len 0x%x)", cmd, len);
+    return -EINVAL;
 }
 
 /*

migration/savevm.h

@@ -65,7 +65,6 @@ void qemu_savevm_send_postcopy_ram_discard(QEMUFile *f, const char *name,
                                            uint16_t len,
                                            uint64_t *start_list,
                                            uint64_t *length_list);
-void qemu_savevm_send_colo_enable(QEMUFile *f);
 int qemu_save_device_state(QEMUFile *f, Error **errp);
 int qemu_loadvm_state(QEMUFile *f, Error **errp);
 void qemu_loadvm_state_cleanup(MigrationIncomingState *mis);

migration/trace-events

@@ -37,7 +37,6 @@ savevm_send_ping(uint32_t val) "0x%x"
 savevm_send_postcopy_listen(void) ""
 savevm_send_postcopy_run(void) ""
 savevm_send_postcopy_resume(void) ""
-savevm_send_colo_enable(void) ""
 savevm_send_recv_bitmap(char *name) "%s"
 savevm_send_switchover_start(void) ""
 savevm_state_setup(void) ""