migration: Introduce capability 'x-colo' to migration

We add helper function colo_supported() to indicate whether
colo is supported or not, with which we use to control whether or not
showing 'x-colo' string to users, they can use qmp command
'query-migrate-capabilities' or hmp command 'info migrate_capabilities'
to learn if colo is supported.

The default value for COLO (COarse-Grain LOck Stepping) is disabled.

Cc: Juan Quintela <quintela@redhat.com>
Cc: Amit Shah <amit.shah@redhat.com>
Cc: Eric Blake <eblake@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
Signed-off-by: Gonglei <arei.gonglei@huawei.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Amit Shah <amit@amitshah.net>

docs/qmp-commands.txt

@@ -2861,6 +2861,7 @@ Enable/Disable migration capabilities
 - "compress": use multiple compression threads to accelerate live migration
 - "events": generate events for each migration state change
 - "postcopy-ram": postcopy mode for live migration
+- "x-colo": COarse-Grain LOck Stepping (COLO) for Non-stop Service
 
 Arguments:
 
@@ -2882,6 +2883,7 @@ Query current migration capabilities
          - "compress": Multiple compression threads state (json-bool)
          - "events": Migration state change event state (json-bool)
          - "postcopy-ram": postcopy ram state (json-bool)
+         - "x-colo": COarse-Grain LOck Stepping for Non-stop Service (json-bool)
 
 Arguments:
 
@@ -2895,7 +2897,8 @@ Example:
      {"state": false, "capability": "zero-blocks"},
      {"state": false, "capability": "compress"},
      {"state": true, "capability": "events"},
-     {"state": false, "capability": "postcopy-ram"}
+     {"state": false, "capability": "postcopy-ram"},
+     {"state": false, "capability": "x-colo"}
    ]}
 
 migrate-set-parameters

include/migration/colo.h

@@ -0,0 +1,20 @@
+/*
+ * COarse-grain LOck-stepping Virtual Machines for Non-stop Service (COLO)
+ * (a.k.a. Fault Tolerance or Continuous Replication)
+ *
+ * Copyright (c) 2016 HUAWEI TECHNOLOGIES CO., LTD.
+ * Copyright (c) 2016 FUJITSU LIMITED
+ * Copyright (c) 2016 Intel Corporation
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * later.  See the COPYING file in the top-level directory.
+ */
+
+#ifndef QEMU_COLO_H
+#define QEMU_COLO_H
+
+#include "qemu-common.h"
+
+bool colo_supported(void);
+
+#endif

include/migration/migration.h

@@ -298,6 +298,7 @@ int xbzrle_decode_buffer(uint8_t *src, int slen, uint8_t *dst, int dlen);
 
 int migrate_use_xbzrle(void);
 int64_t migrate_xbzrle_cache_size(void);
+bool migrate_colo_enabled(void);
 
 int64_t xbzrle_cache_resize(int64_t new_size);
 

migration/Makefile.objs

@@ -1,5 +1,6 @@
 common-obj-y += migration.o socket.o fd.o exec.o
 common-obj-y += tls.o
+common-obj-$(CONFIG_COLO) += colo.o
 common-obj-y += vmstate.o
 common-obj-y += qemu-file.o
 common-obj-y += qemu-file-channel.o

migration/colo.c

@@ -0,0 +1,19 @@
+/*
+ * COarse-grain LOck-stepping Virtual Machines for Non-stop Service (COLO)
+ * (a.k.a. Fault Tolerance or Continuous Replication)
+ *
+ * Copyright (c) 2016 HUAWEI TECHNOLOGIES CO., LTD.
+ * Copyright (c) 2016 FUJITSU LIMITED
+ * Copyright (c) 2016 Intel Corporation
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * later.  See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "migration/colo.h"
+
+bool colo_supported(void)
+{
+    return false;
+}

migration/migration.c

@@ -36,6 +36,7 @@
 #include "exec/address-spaces.h"
 #include "io/channel-buffer.h"
 #include "io/channel-tls.h"
+#include "migration/colo.h"
 
 #define MAX_THROTTLE  (32 << 20)      /* Migration transfer speed throttling */
 
@@ -531,6 +532,9 @@ MigrationCapabilityStatusList *qmp_query_migrate_capabilities(Error **errp)
 
     caps = NULL; /* silence compiler warning */
     for (i = 0; i < MIGRATION_CAPABILITY__MAX; i++) {
+        if (i == MIGRATION_CAPABILITY_X_COLO && !colo_supported()) {
+            continue;
+        }
         if (head == NULL) {
             head = g_malloc0(sizeof(*caps));
             caps = head;
@@ -733,6 +737,14 @@ void qmp_migrate_set_capabilities(MigrationCapabilityStatusList *params,
     }
 
     for (cap = params; cap; cap = cap->next) {
+        if (cap->value->capability == MIGRATION_CAPABILITY_X_COLO) {
+            if (!colo_supported()) {
+                error_setg(errp, "COLO is not currently supported, please"
+                             " configure with --enable-colo option in order to"
+                             " support COLO feature");
+                continue;
+            }
+        }
         s->enabled_capabilities[cap->value->capability] = cap->value->state;
     }
 
@@ -1713,6 +1725,12 @@ fail:
                       MIGRATION_STATUS_FAILED);
 }
 
+bool migrate_colo_enabled(void)
+{
+    MigrationState *s = migrate_get_current();
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_X_COLO];
+}
+
 /*
  * Master migration thread on the source VM.
  * It drives the migration and pumps the data down the outgoing channel.

qapi-schema.json

@@ -574,11 +574,16 @@
 #          been migrated, pulling the remaining pages along as needed. NOTE: If
 #          the migration fails during postcopy the VM will fail.  (since 2.6)
 #
+# @x-colo: If enabled, migration will never end, and the state of the VM on the
+#        primary side will be migrated continuously to the VM on secondary
+#        side, this process is called COarse-Grain LOck Stepping (COLO) for
+#        Non-stop Service. (since 2.8)
+#
 # Since: 1.2
 ##
 { 'enum': 'MigrationCapability',
   'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks',
-           'compress', 'events', 'postcopy-ram'] }
+           'compress', 'events', 'postcopy-ram', 'x-colo'] }
 
 ##
 # @MigrationCapabilityStatus

stubs/Makefile.objs

@@ -48,3 +48,4 @@ stub-obj-y += iohandler.o
 stub-obj-y += smbios_type_38.o
 stub-obj-y += ipmi.o
 stub-obj-y += pc_madt_cpu_entry.o
+stub-obj-y += migration-colo.o

stubs/migration-colo.c

@@ -0,0 +1,19 @@
+/*
+ * COarse-grain LOck-stepping Virtual Machines for Non-stop Service (COLO)
+ * (a.k.a. Fault Tolerance or Continuous Replication)
+ *
+ * Copyright (c) 2016 HUAWEI TECHNOLOGIES CO., LTD.
+ * Copyright (c) 2016 FUJITSU LIMITED
+ * Copyright (c) 2016 Intel Corporation
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * later.  See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "migration/colo.h"
+
+bool colo_supported(void)
+{
+    return false;
+}