[PATCH V9 15/17] qapi: examine IOThread attachment status via query-iothreads

[Zhang Chen <zhangckid@gmail.com>]

Extend the 'IOThreadInfo' structure to include attachment metrics.
This allows users to monitor the associated devices by identify them
by their QOM paths, block nodes or monitors.

New fields added to IOThreadInfo:
 @holders: IOThreadHolder of the devices currently associated with
     this iothread.  Users can pre-allocate multiple iothread objects
     to serve as a persistent thread pool.  When a device is hot-unplugged,
     it is detached from its iothread, but the iothread remains available,
     allowing future hot-plugged devices to attach to it.  (Since 11.1)

These fields are also exposed via the Human Monitor Interface (HMP)
command 'info iothreads' to assist with manual debugging and
performance tuning.

Signed-off-by: Zhang Chen <zhangckid@gmail.com>
---
 iothread.c         | 22 ++++++++++++++++++++++
 monitor/hmp-cmds.c | 26 ++++++++++++++++++++++++++
 qapi/misc.json     |  9 +++++++++
 3 files changed, 57 insertions(+)

diff --git a/iothread.c b/iothread.c
index a85e960e45..5949785b32 100644
--- a/iothread.c
+++ b/iothread.c
@@ -24,6 +24,8 @@
 #include "qemu/error-report.h"
 #include "qemu/rcu.h"
 #include "qemu/main-loop.h"
+#include "qapi/clone-visitor.h"
+#include "qapi/qapi-visit-misc.h"
 
 /*
  * iothread_ref:
@@ -119,6 +121,25 @@ static void iothread_unref(IOThread *iothread, const IOThreadHolder *holder)
     object_unref(OBJECT(iothread));
 }
 
+static IOThreadHolderList *iothread_get_holders_list(IOThread *iothread)
+{
+    IOThreadHolderList *head = NULL;
+    IOThreadHolderList **prev = &head;
+    GList *l;
+
+    for (l = iothread->holders; l; l = l->next) {
+        IOThreadHolder *src = l->data;
+        IOThreadHolderList *entry = g_new0(IOThreadHolderList, 1);
+
+        entry->value = QAPI_CLONE(IOThreadHolder, src);
+
+        *prev = entry;
+        prev = &entry->next;
+    }
+
+    return head;
+}
+
 static void *iothread_run(void *opaque)
 {
     IOThread *iothread = opaque;
@@ -488,6 +509,7 @@ static int query_one_iothread(Object *object, void *opaque)
     info = g_new0(IOThreadInfo, 1);
     info->id = iothread_get_id(iothread);
     info->thread_id = iothread->thread_id;
+    info->holders = iothread_get_holders_list(iothread);
     info->poll_max_ns = iothread->poll_max_ns;
     info->poll_grow = iothread->poll_grow;
     info->poll_shrink = iothread->poll_shrink;
diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
index 443b8c785d..1b5883147b 100644
--- a/monitor/hmp-cmds.c
+++ b/monitor/hmp-cmds.c
@@ -237,11 +237,37 @@ void hmp_info_iothreads(Monitor *mon, const QDict *qdict)
     IOThreadInfoList *info_list = qmp_query_iothreads(NULL);
     IOThreadInfoList *info;
     IOThreadInfo *value;
+    IOThreadHolderList *h;
 
     for (info = info_list; info; info = info->next) {
         value = info->value;
         monitor_printf(mon, "%s:\n", value->id);
         monitor_printf(mon, "  thread_id=%" PRId64 "\n", value->thread_id);
+        monitor_printf(mon, "  holders=");
+        if (value->holders) {
+            for (h = value->holders; h; h = h->next) {
+                IOThreadHolder *holder = h->value;
+
+                switch (holder->type) {
+                case IO_THREAD_HOLDER_KIND_BLOCK_NODE:
+                    monitor_printf(mon, "[block-node: %s]",
+                                   holder->u.block_node.node_name);
+                    break;
+                case IO_THREAD_HOLDER_KIND_QOM_OBJECT:
+                    monitor_printf(mon, "[qom-path: %s]",
+                                   holder->u.qom_object.qom_path);
+                    break;
+                case IO_THREAD_HOLDER_KIND_MONITOR_NAME:
+                    monitor_printf(mon, "[monitor-name: %s]",
+                                   holder->u.monitor_name.monitor_name);
+                    break;
+                default:
+                    monitor_printf(mon, "[unknown]");
+                    break;
+                }
+            }
+            monitor_printf(mon, "\n");
+        }
         monitor_printf(mon, "  poll-max-ns=%" PRId64 "\n", value->poll_max_ns);
         monitor_printf(mon, "  poll-grow=%" PRId64 "\n", value->poll_grow);
         monitor_printf(mon, "  poll-shrink=%" PRId64 "\n", value->poll_shrink);
diff --git a/qapi/misc.json b/qapi/misc.json
index d9f82f0922..6486c62ab5 100644
--- a/qapi/misc.json
+++ b/qapi/misc.json
@@ -137,6 +137,11 @@
 #
 # @thread-id: ID of the underlying host thread
 #
+# @holders: the QOM objects, block nodes or monitors currently
+#     associated with this iothread.  When an associated component is
+#     detached or destroyed, it is removed from this list.
+#     (Since 11.1)
+#
 # @poll-max-ns: maximum polling time in ns, 0 means polling is
 #     disabled (since 2.9)
 #
@@ -159,6 +164,7 @@
 { 'struct': 'IOThreadInfo',
   'data': {'id': 'str',
            'thread-id': 'int',
+           'holders': ['IOThreadHolder'],
            'poll-max-ns': 'int',
            'poll-grow': 'int',
            'poll-shrink': 'int',
@@ -185,6 +191,8 @@
 #              {
 #                 "id":"iothread0",
 #                 "thread-id":3134,
+#                 "holders":[{"qom-path": "/machine/peripheral/blk1/virtio-backend", "type": "qom-object"},
+#                            {"monitor-name": "compat_monitor0", "type": "monitor-name"}],
 #                 "poll-max-ns":32768,
 #                 "poll-grow":0,
 #                 "poll-shrink":0,
@@ -193,6 +201,7 @@
 #              {
 #                 "id":"iothread1",
 #                 "thread-id":3135,
+#                 "holders":[{"node-name": "fmt_qcow2", "type": "block-node"}],
 #                 "poll-max-ns":32768,
 #                 "poll-grow":0,
 #                 "poll-shrink":0,
-- 
2.49.0