migration: Introduce interface query-migrationthreads

Introduce interface query-migrationthreads. The interface is used
to query information about migration threads and returns with
migration thread's name and its id.
Introduce threadinfo.c to manage threads with migration.

Signed-off-by: Jiang Jiacheng <jiangjiacheng@huawei.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

migration/meson.build

@@ -26,6 +26,7 @@ softmmu_ss.add(files(
   'savevm.c',
   'socket.c',
   'tls.c',
+  'threadinfo.c',
 ), gnutls)
 
 softmmu_ss.add(when: rdma, if_true: files('rdma.c'))

migration/threadinfo.c

@@ -0,0 +1,51 @@
+/*
+ *  Migration Threads info
+ *
+ *  Copyright (c) 2022 HUAWEI TECHNOLOGIES CO., LTD.
+ *
+ *  Authors:
+ *  Jiang Jiacheng <jiangjiacheng@huawei.com>
+ *
+ *  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 "threadinfo.h"
+
+static QLIST_HEAD(, MigrationThread) migration_threads;
+
+MigrationThread *MigrationThreadAdd(const char *name, int thread_id)
+{
+    MigrationThread *thread =  g_new0(MigrationThread, 1);
+    thread->name = name;
+    thread->thread_id = thread_id;
+
+    QLIST_INSERT_HEAD(&migration_threads, thread, node);
+
+    return thread;
+}
+
+void MigrationThreadDel(MigrationThread *thread)
+{
+    if (thread) {
+        QLIST_REMOVE(thread, node);
+        g_free(thread);
+    }
+}
+
+MigrationThreadInfoList *qmp_query_migrationthreads(Error **errp)
+{
+    MigrationThreadInfoList *head = NULL;
+    MigrationThreadInfoList **tail = &head;
+    MigrationThread *thread = NULL;
+
+    QLIST_FOREACH(thread, &migration_threads, node) {
+        MigrationThreadInfo *info = g_new0(MigrationThreadInfo, 1);
+        info->name = g_strdup(thread->name);
+        info->thread_id = thread->thread_id;
+
+        QAPI_LIST_APPEND(tail, info);
+    }
+
+    return head;
+}

migration/threadinfo.h

@@ -0,0 +1,28 @@
+/*
+ *  Migration Threads info
+ *
+ *  Copyright (c) 2022 HUAWEI TECHNOLOGIES CO., LTD.
+ *
+ *  Authors:
+ *  Jiang Jiacheng <jiangjiacheng@huawei.com>
+ *
+ *  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/queue.h"
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "qapi/qapi-commands-migration.h"
+
+typedef struct MigrationThread MigrationThread;
+
+struct MigrationThread {
+    const char *name; /* the name of migration thread */
+    int thread_id; /* ID of the underlying host thread */
+    QLIST_ENTRY(MigrationThread) node;
+};
+
+MigrationThread *MigrationThreadAdd(const char *name, int thread_id);
+
+void MigrationThreadDel(MigrationThread *info);

qapi/migration.json

@@ -1958,6 +1958,35 @@
 { 'command': 'query-vcpu-dirty-limit',
   'returns': [ 'DirtyLimitInfo' ] }
 
+##
+# @MigrationThreadInfo:
+#
+# Information about migrationthreads
+#
+# @name: the name of migration thread
+#
+# @thread-id: ID of the underlying host thread
+#
+# Since: 7.2
+##
+{ 'struct': 'MigrationThreadInfo',
+  'data': {'name': 'str',
+           'thread-id': 'int'} }
+
+##
+# @query-migrationthreads:
+#
+# Returns information of migration threads
+#
+# data: migration thread name
+#
+# returns: information about migration threads
+#
+# Since: 7.2
+##
+{ 'command': 'query-migrationthreads',
+  'returns': ['MigrationThreadInfo'] }
+
 ##
 # @snapshot-save:
 #