libxl: MigrateBegin: Dont call EndAPI in helper function

The libxlDomainMigrateBegin3Params API locks and ref counts the associated
virDomainObj but relies on the helper function libxlDomainMigrationBegin
to unref/unlock the object. libxlDomainMigrationBegin is also used by
libxlDomainMigratePerform3Params for p2p migration, but in that case the
lock/ref and unref/unlock are properly handled in the API entry point. So
p2p migrations suffer a double unref/unlock in the Perform API.

Remove the unref/unlock (virDomainObjEndAPI) from libxlDomainMigrationBegin
and adjust libxlDomainMigrateBegin3Params to properly unref/unlock
the virDomainObj on success and error paths.
Signed-off-by: NJim Fehlig <jfehlig@suse.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>

src/libxl/libxl_driver.c

@@ -5887,6 +5887,7 @@ libxlDomainMigrateBegin3Params(virDomainPtr domain,
 {
     const char *xmlin = NULL;
     virDomainObjPtr vm = NULL;
+    char *xmlout = NULL;
 
 #ifdef LIBXL_HAVE_NO_SUSPEND_RESUME
     virReportUnsupportedError();
@@ -5906,25 +5907,26 @@ libxlDomainMigrateBegin3Params(virDomainPtr domain,
         return NULL;
 
     if (STREQ_NULLABLE(vm->def->name, "Domain-0")) {
-            virReportError(VIR_ERR_OPERATION_INVALID, "%s",
-                           _("Domain-0 cannot be migrated"));
-            return NULL;
+        virReportError(VIR_ERR_OPERATION_INVALID, "%s",
+                       _("Domain-0 cannot be migrated"));
+        goto cleanup;
     }
 
-    if (virDomainMigrateBegin3ParamsEnsureACL(domain->conn, vm->def) < 0) {
-        virObjectUnlock(vm);
-        return NULL;
-    }
+    if (virDomainMigrateBegin3ParamsEnsureACL(domain->conn, vm->def) < 0)
+        goto cleanup;
 
     if (!virDomainObjIsActive(vm)) {
         virReportError(VIR_ERR_OPERATION_INVALID,
                        "%s", _("domain is not running"));
-        virObjectUnlock(vm);
-        return NULL;
+        goto cleanup;
     }
 
-    return libxlDomainMigrationBegin(domain->conn, vm, xmlin,
-                                     cookieout, cookieoutlen);
+    xmlout = libxlDomainMigrationBegin(domain->conn, vm, xmlin,
+                                       cookieout, cookieoutlen);
+
+ cleanup:
+    virDomainObjEndAPI(&vm);
+    return xmlout;
 }
 
 static int

src/libxl/libxl_migration.c

@@ -443,7 +443,6 @@ libxlDomainMigrationBegin(virConnectPtr conn,
 
  cleanup:
     libxlMigrationCookieFree(mig);
-    virDomainObjEndAPI(&vm);
     virDomainDefFree(tmpdef);
     virObjectUnref(cfg);
     return xml;