qmp: add query-iothreads command

The "query-iothreads" command returns a list of information about
iothreads.  See the patch for API documentation.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

iothread.c

@@ -17,6 +17,7 @@
 #include "qemu/thread.h"
 #include "block/aio.h"
 #include "sysemu/iothread.h"
+#include "qmp-commands.h"
 
 #define IOTHREADS_PATH "/objects"
 
@@ -140,3 +141,38 @@ AioContext *iothread_get_aio_context(IOThread *iothread)
 {
     return iothread->ctx;
 }
+
+static int query_one_iothread(Object *object, void *opaque)
+{
+    IOThreadInfoList ***prev = opaque;
+    IOThreadInfoList *elem;
+    IOThreadInfo *info;
+    IOThread *iothread;
+
+    iothread = (IOThread *)object_dynamic_cast(object, TYPE_IOTHREAD);
+    if (!iothread) {
+        return 0;
+    }
+
+    info = g_new0(IOThreadInfo, 1);
+    info->id = iothread_get_id(iothread);
+    info->thread_id = iothread->thread_id;
+
+    elem = g_new0(IOThreadInfoList, 1);
+    elem->value = info;
+    elem->next = NULL;
+
+    **prev = elem;
+    *prev = &elem->next;
+    return 0;
+}
+
+IOThreadInfoList *qmp_query_iothreads(Error **errp)
+{
+    IOThreadInfoList *head = NULL;
+    IOThreadInfoList **prev = &head;
+    Object *container = container_get(object_get_root(), IOTHREADS_PATH);
+
+    object_child_foreach(container, query_one_iothread, &prev);
+    return head;
+}

qapi-schema.json

@@ -882,6 +882,35 @@
 ##
 { 'command': 'query-cpus', 'returns': ['CpuInfo'] }
 
+##
+# @IOThreadInfo:
+#
+# Information about an iothread
+#
+# @id: the identifier of the iothread
+#
+# @thread-id: ID of the underlying host thread
+#
+# Since: 2.0
+##
+{ 'type': 'IOThreadInfo',
+  'data': {'id': 'str', 'thread-id': 'int'} }
+
+##
+# @query-iothreads:
+#
+# Returns a list of information about each iothread.
+#
+# Note this list excludes the QEMU main loop thread, which is not declared
+# using the -object iothread command-line option.  It is always the main thread
+# of the process.
+#
+# Returns: a list of @IOThreadInfo for each iothread
+#
+# Since: 2.0
+##
+{ 'command': 'query-iothreads', 'returns': ['IOThreadInfo'] }
+
 ##
 # @BlockDeviceInfo:
 #

qmp-commands.hx

@@ -2326,6 +2326,45 @@ EQMP
         .mhandler.cmd_new = qmp_marshal_input_query_cpus,
     },
 
+SQMP
+query-iothreads
+---------------
+
+Returns a list of information about each iothread.
+
+Note this list excludes the QEMU main loop thread, which is not declared
+using the -object iothread command-line option.  It is always the main thread
+of the process.
+
+Return a json-array. Each iothread is represented by a json-object, which contains:
+
+- "id": name of iothread (json-str)
+- "thread-id": ID of the underlying host thread (json-int)
+
+Example:
+
+-> { "execute": "query-iothreads" }
+<- {
+      "return":[
+         {
+            "id":"iothread0",
+            "thread-id":3134
+         },
+         {
+            "id":"iothread1",
+            "thread-id":3135
+         }
+      ]
+   }
+
+EQMP
+
+    {
+        .name       = "query-iothreads",
+        .args_type  = "",
+        .mhandler.cmd_new = qmp_marshal_input_query_iothreads,
+    },
+
 SQMP
 query-pci
 ---------