[PATCH] migration: add optional capabilities field to migrate and migrate-incoming

[Trieu Huynh <vikingtc4@gmail.com>]

From: Trieu Huynh <vikingtc4@gmail.com>

When invoking migration, user must call migrate-set-capabilities as a
separate QMP command before calling migrate or migrate-incoming.

Add an optional 'capabilities' field to both commands. When provided,
the capabilities are applied before the migration starts, in the same
order as a migrate-set-capabilities call would apply them. Existing
callers that do not pass the field are unaffected.

This is particularly useful, eg. for snapshot-load workflows where a
single migrate-incoming call should express the full migration
configuration:

  { "execute": "migrate-incoming",
    "arguments": {
      "uri": "file:/tmp/snapshot",
      "capabilities": [{"capability": "mapped-ram", "state": true}]
    }}

Internal callers (HMP migrate-incoming, vl.c -incoming) pass
has_capabilities=false so their behaviour is unchanged.

Related-to: https://wiki.qemu.org/ToDo/LiveMigration#Allow_QMP_command_%22migrate[_incoming]%22_to_take_capabilities_and_parameters

Signed-off-by: Trieu Huynh <vikingtc4@gmail.com>
---
 migration/migration-hmp-cmds.c |  4 ++--
 migration/migration.c          | 19 +++++++++++++++++++
 qapi/migration.json            | 12 ++++++++++++
 system/vl.c                    |  3 ++-
 4 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/migration/migration-hmp-cmds.c b/migration/migration-hmp-cmds.c
index 0a193b8f54..32c338103d 100644
--- a/migration/migration-hmp-cmds.c
+++ b/migration/migration-hmp-cmds.c
@@ -522,7 +522,7 @@ void hmp_migrate_incoming(Monitor *mon, const QDict *qdict)
     }
     QAPI_LIST_PREPEND(caps, g_steal_pointer(&channel));
 
-    qmp_migrate_incoming(NULL, true, caps, true, false, &err);
+    qmp_migrate_incoming(NULL, true, caps, false, NULL, true, false, &err);
     qapi_free_MigrationChannelList(caps);
 
 end:
@@ -829,7 +829,7 @@ void hmp_migrate(Monitor *mon, const QDict *qdict)
     }
     QAPI_LIST_PREPEND(caps, g_steal_pointer(&channel));
 
-    qmp_migrate(NULL, true, caps, true, resume, &err);
+    qmp_migrate(NULL, true, caps, false, NULL, true, resume, &err);
     if (hmp_handle_error(mon, err)) {
         return;
     }
diff --git a/migration/migration.c b/migration/migration.c
index 5c9aaa6e58..eb1a734dd9 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1752,6 +1752,8 @@ void migrate_del_blocker(Error **reasonp)
 
 void qmp_migrate_incoming(const char *uri, bool has_channels,
                           MigrationChannelList *channels,
+                          bool has_capabilities,
+                          MigrationCapabilityStatusList *capabilities,
                           bool has_exit_on_error, bool exit_on_error,
                           Error **errp)
 {
@@ -1772,6 +1774,14 @@ void qmp_migrate_incoming(const char *uri, bool has_channels,
         return;
     }
 
+    if (has_capabilities) {
+        qmp_migrate_set_capabilities(capabilities, errp);
+        if (*errp) {
+            yank_unregister_instance(MIGRATION_YANK_INSTANCE);
+            return;
+        }
+    }
+
     mis->exit_on_error =
         has_exit_on_error ? exit_on_error : INMIGRATE_DEFAULT_EXIT_ON_ERROR;
 
@@ -2020,6 +2030,8 @@ static gboolean migration_connect_outgoing_cb(QIOChannel *channel,
 
 void qmp_migrate(const char *uri, bool has_channels,
                  MigrationChannelList *channels,
+                 bool has_capabilities,
+                 MigrationCapabilityStatusList *capabilities,
                  bool has_resume, bool resume, Error **errp)
 {
     MigrationState *s = migrate_get_current();
@@ -2036,6 +2048,13 @@ void qmp_migrate(const char *uri, bool has_channels,
         return;
     }
 
+    if (has_capabilities) {
+        qmp_migrate_set_capabilities(capabilities, errp);
+        if (*errp) {
+            return;
+        }
+    }
+
     if (!migrate_prepare(s, has_resume && resume, errp)) {
         /* Error detected, put into errp */
         return;
diff --git a/qapi/migration.json b/qapi/migration.json
index 7134d4ce47..58d934f8fe 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -1388,6 +1388,11 @@
 # @channels: list of migration stream channels with each stream in the
 #     list connected to a destination interface endpoint.
 #
+# @capabilities: list of migration capabilities to set before
+#     starting the migration.  Equivalent to calling
+#     `migrate-set-capabilities` before `migrate`, but more
+#     convenient.
+#
 # @resume: when set, use the new uri/channels specified to resume
 #     paused postcopy migration.  This flag should only be used if
 #     the previous postcopy migration was interrupted.  The command
@@ -1453,6 +1458,7 @@
 { 'command': 'migrate',
   'data': {'*uri': 'str',
            '*channels': [ 'MigrationChannel' ],
+           '*capabilities': ['MigrationCapabilityStatus'],
            '*resume': 'bool' } }
 
 ##
@@ -1467,6 +1473,11 @@
 # @channels: list of migration stream channels with each stream in the
 #     list connected to a destination interface endpoint.
 #
+# @capabilities: list of migration capabilities to set before
+#     starting the migration.  Equivalent to calling
+#     `migrate-set-capabilities` before `migrate-incoming`, but more
+#     convenient.
+#
 # @exit-on-error: Exit on incoming migration failure.  Default true.
 #     When set to false, the failure triggers a
 #     :qapi:event:`MIGRATION` event, and error details could be
@@ -1525,6 +1536,7 @@
 { 'command': 'migrate-incoming',
              'data': {'*uri': 'str',
                       '*channels': [ 'MigrationChannel' ],
+                      '*capabilities': ['MigrationCapabilityStatus'],
                       '*exit-on-error': 'bool' } }
 
 ##
diff --git a/system/vl.c b/system/vl.c
index 246623b319..ed569d75e7 100644
--- a/system/vl.c
+++ b/system/vl.c
@@ -2826,7 +2826,8 @@ void qmp_x_exit_preconfig(Error **errp)
                 g_new0(MigrationChannelList, 1);
 
             channels->value = incoming_channels[MIGRATION_CHANNEL_TYPE_MAIN];
-            qmp_migrate_incoming(NULL, true, channels, true, true, &local_err);
+            qmp_migrate_incoming(NULL, true, channels, false, NULL, true,
+                                 true, &local_err);
             if (local_err) {
                 error_reportf_err(local_err, "-incoming %s: ", incoming);
                 exit(1);
-- 
2.43.0