migration: Don't activate block devices if using -S

Activating the block devices causes the locks to be taken on
the backing file.  If we're running with -S and the destination libvirt
hasn't started the destination with 'cont', it's expecting the locks are
still untaken.

Don't activate the block devices if we're not going to autostart the VM;
'cont' already will do that anyway.

bz: https://bugzilla.redhat.com/show_bug.cgi?id=1560854Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20180328170207.49512-1-dgilbert@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>

migration/migration.c

@@ -306,13 +306,21 @@ static void process_incoming_migration_bh(void *opaque)
     Error *local_err = NULL;
     MigrationIncomingState *mis = opaque;
 
-    /* Make sure all file formats flush their mutable metadata.
-     * If we get an error here, just don't restart the VM yet. */
-    bdrv_invalidate_cache_all(&local_err);
-    if (local_err) {
-        error_report_err(local_err);
-        local_err = NULL;
-        autostart = false;
+    /* Only fire up the block code now if we're going to restart the
+     * VM, else 'cont' will do it.
+     * This causes file locking to happen; so we don't want it to happen
+     * unless we really are starting the VM.
+     */
+    if (autostart && (!global_state_received() ||
+        global_state_get_runstate() == RUN_STATE_RUNNING)) {
+        /* Make sure all file formats flush their mutable metadata.
+         * If we get an error here, just don't restart the VM yet. */
+        bdrv_invalidate_cache_all(&local_err);
+        if (local_err) {
+            error_report_err(local_err);
+            local_err = NULL;
+            autostart = false;
+        }
     }
 
     /*