Re: [PATCH 3/3] qapi: Add thread_status flag for iothreads

[Markus Armbruster <armbru@redhat.com>]

Zhang Chen <zhangckid@gmail.com> writes:

> On Thu, Jan 8, 2026 at 8:12 PM Markus Armbruster <armbru@redhat.com> wrote:
>>
>> Zhang Chen <zhangckid@gmail.com> writes:
>>
>> > The thread_status depends on struct IOThreadInfo's
>> > 'attached': 'bool'. Show in the qmp/hmp CMD with
>> > 'attached' or 'detached'.
>> >
>> > Signed-off-by: Zhang Chen <zhangckid@gmail.com>
>> > ---
>> >  iothread.c         | 1 +
>> >  monitor/hmp-cmds.c | 2 ++
>> >  qapi/misc.json     | 6 ++++++
>> >  3 files changed, 9 insertions(+)
>> >
>> > diff --git a/iothread.c b/iothread.c
>> > index 38e38fb44d..fb4898e491 100644
>> > --- a/iothread.c
>> > +++ b/iothread.c
>> > @@ -358,6 +358,7 @@ 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->attached = iothread->attached;
>> >      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 33a88ce205..84b01737cf 100644
>> > --- a/monitor/hmp-cmds.c
>> > +++ b/monitor/hmp-cmds.c
>> > @@ -197,6 +197,8 @@ void hmp_info_iothreads(Monitor *mon, const QDict *qdict)
>> >          value = info->value;
>> >          monitor_printf(mon, "%s:\n", value->id);
>> >          monitor_printf(mon, "  thread_id=%" PRId64 "\n", value->thread_id);
>> > +        monitor_printf(mon, "  thread_status=%s" "\n",
>> > +                       value->attached ? "attached" : "detached");
>> >          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 6153ed3d04..2eea920bd2 100644
>> > --- a/qapi/misc.json
>> > +++ b/qapi/misc.json
>> > @@ -76,6 +76,9 @@
>> >  #
>> >  # @thread-id: ID of the underlying host thread
>> >  #
>> > +# @attached: flag to show current iothread attached status
>>
>> What does "attached status" actually mean?
>
> This flag means weather the "-object iothread" already been used by a
> real device.
> In hotplug scenario, user can add multiple "-object iothread" and
> multiple devices (like virtio-blk).
> When user hotunplug the devices can keep the iothreads as a thread
> pool, following the new
> hotplug devices can attach to the released iothread.

Why would a management application or human user want to know this?

The answer should lead us to better doc text.

>>
>> > +#            (since 10.3.0)
>>
>> (since 12.0)
>
> OK.
>
>>
>> > +#
>> >  # @poll-max-ns: maximum polling time in ns, 0 means polling is
>> >  #     disabled (since 2.9)
>> >  #
>> > @@ -93,6 +96,7 @@
>> >  { 'struct': 'IOThreadInfo',
>> >    'data': {'id': 'str',
>> >             'thread-id': 'int',
>> > +           'attached': 'bool',
>> >             'poll-max-ns': 'int',
>> >             'poll-grow': 'int',
>> >             'poll-shrink': 'int',
>> > @@ -118,6 +122,7 @@
>> >  #              {
>> >  #                 "id":"iothread0",
>> >  #                 "thread-id":3134,
>> > +#                 'thread_status':"attached",
>>
>> I believe this is actually
>>
>>                      "attached": true
>>
>> and ...
>
> No, I changed it here for readability:
>
>> > +        monitor_printf(mon, "  thread_status=%s" "\n",
>> > +                       value->attached ? "attached" : "detached");
>
> But if you think ""attached": true" is more direct way, I can change
> it next version.

The example in the doc comment shows QMP.  Here's what I see in QMP:

    $ qemu-system-x86_64 -S -display none -qmp stdio -object iothread,id=iot0 -name debug-threads=on
    {"QMP": {"version": {"qemu": {"micro": 50, "minor": 2, "major": 10}, "package": "v10.2.0-521-g05115811fa"}, "capabilities": ["oob"]}}
    {"execute": "qmp_capabilities", "arguments": {"enable": ["oob"]}}
    {"return": {}}
    {"execute": "query-iothreads"}
    {"return": [{"attached": false, "poll-shrink": 0, "thread-id": 4031494, "aio-max-batch": 0, "poll-grow": 0, "poll-max-ns": 32768, "id": "iot0"}]}

This shows "attached": false, not 'thread_status': "attached".

The code you showed applies to HMP:

    $ qemu-system-x86_64 -S -display none -monitor stdio -object iothread,id=iot0 -name debug-threads=on
    QEMU 10.2.50 monitor - type 'help' for more information
    (qemu) info iothreads
    iot0:
      thread_id=4032011
      thread_status=detached
      poll-max-ns=32768
      poll-grow=0
      poll-shrink=0
      aio-max-batch=0

thread_status=detached might be slightly more readable than
attached=false, but it could also be confusing to people working with
both HMP and QMP.  I'd avoid the difference between the two.

>>
>> >  #                 'poll-max-ns':0,
>> >  #                 "poll-grow":0,
>> >  #                 "poll-shrink":0,
>> > @@ -126,6 +131,7 @@
>> >  #              {
>> >  #                 "id":"iothread1",
>> >  #                 "thread-id":3135,
>> > +#                 'thread_status':"detached",
>>
>>                      "attached": false
>>
>> Recommend to create example output by running a test instead of making
>> it up, because making it up likely screws it up :)
>
> Uh.... This output print is the real test in my machine, maybe you
> missed the previous description.

I can't see how QMP could possibly show 'thread_status':"detached:.

>
> Thanks
> Chen
>
>>
>> >  #                 'poll-max-ns':0,
>> >  #                 "poll-grow":0,
>> >  #                 "poll-shrink":0,
>>