migration, xen: Fix block image lock issue on live migration

When doing a live migration of a Xen guest with libxl, the images for block devices are locked by the original QEMU process, and this prevent the QEMU at the destination to take the lock and the migration fail. >From QEMU point of view, once the RAM of a domain is migrated, there is two QMP commands, "stop" then "xen-save-devices-state", at which point a new QEMU is spawned at the destination. Release locks in "xen-save-devices-state" so the destination can takes them, if it's a live migration. This patch add the "live" parameter to "xen-save-devices-state" which default to true so older version of libxenlight can work with newer version of QEMU. Signed-off-by: Anthony PERARD <[email protected]> Reviewed-by: Dr. David Alan Gilbert <[email protected]> Reviewed-by: Juan Quintela <[email protected]> Signed-off-by: Juan Quintela <[email protected]>
Thaodan · Nov 21, 2017 · 5d6c599 · 5d6c599
1 parent a15d835
commit 5d6c599
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diff --git a/migration/savevm.c b/migration/savevm.c
@@ -2242,13 +2242,20 @@ int save_snapshot(const char *name, Error **errp)
     return ret;
 }
 
-void qmp_xen_save_devices_state(const char *filename, Error **errp)
+void qmp_xen_save_devices_state(const char *filename, bool has_live, bool live,
+                                Error **errp)
 {
     QEMUFile *f;
     QIOChannelFile *ioc;
     int saved_vm_running;
     int ret;
 
+    if (!has_live) {
+        /* live default to true so old version of Xen tool stack can have a
+         * successfull live migration */
+        live = true;
+    }
+
     saved_vm_running = runstate_is_running();
     vm_stop(RUN_STATE_SAVE_VM);
     global_state_store_running();
@@ -2263,6 +2270,20 @@ void qmp_xen_save_devices_state(const char *filename, Error **errp)
     qemu_fclose(f);
     if (ret < 0) {
         error_setg(errp, QERR_IO_ERROR);
+    } else {
+        /* libxl calls the QMP command "stop" before calling
+         * "xen-save-devices-state" and in case of migration failure, libxl
+         * would call "cont".
+         * So call bdrv_inactivate_all (release locks) here to let the other
+         * side of the migration take controle of the images.
+         */
+        if (live && !saved_vm_running) {
+            ret = bdrv_inactivate_all();
+            if (ret) {
+                error_setg(errp, "%s: bdrv_inactivate_all() failed (%d)",
+                           __func__, ret);
+            }
+        }
     }
 
  the_end:

diff --git a/qapi/migration.json b/qapi/migration.json
@@ -1075,6 +1075,9 @@
 # data. See xen-save-devices-state.txt for a description of the binary
 # format.
 #
+# @live: Optional argument to ask QEMU to treat this command as part of a live
+# migration. Default to true. (since 2.11)
+#
 # Returns: Nothing on success
 #
 # Since: 1.1
@@ -1086,7 +1089,8 @@
 # <- { "return": {} }
 #
 ##
-{ 'command': 'xen-save-devices-state', 'data': {'filename': 'str'} }
+{ 'command': 'xen-save-devices-state',
+  'data': {'filename': 'str', '*live':'bool' } }
 
 ##
 # @xen-set-replication: