Re: [PATCH V13 02/15] iothread: introduce holder tracking

[Markus Armbruster <armbru@redhat.com>]

Zhang Chen <zhangckid@gmail.com> writes:

> On Tue, Aug 25, 2026 at 4:17 PM Markus Armbruster <armbru@redhat.com> wrote:
>>
>> Zhang Chen <zhangckid@gmail.com> writes:
>>
>> > IOThreads do not record the QOM objects and block exports that use
>> > them, making runtime introspection and hotplug debugging difficult.
>> >
>> > Add:
>> >
>> > - holders: a list describing what is holding an iothread
>> > - iothread_ref(): add a holder to the list
>> > - iothread_unref(): remove a holder from the list
>> >
>> > A holder can identify either a QOM object or a block export. A later
>> > patch will expose this information through query-iothreads.
>> >
>> > Signed-off-by: Zhang Chen <zhangckid@gmail.com>
>> > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
>> > Reviewed-by: Markus Armbruster <armbru@redhat.com>
>>
>> I'm suspending my R-by, see below why.

I'm now reinstating it.

>> [...]
>>
>> > diff --git a/iothread.c b/iothread.c
>> > index 3558535b40..66dfde626e 100644
>> > --- a/iothread.c
>> > +++ b/iothread.c
>> > @@ -21,10 +21,71 @@
>> >  #include "system/iothread.h"
>> >  #include "qapi/error.h"
>> >  #include "qapi/qapi-commands-misc.h"
>> > +#include "qapi/clone-visitor.h"
>> > +#include "qapi/qapi-visit-misc.h"
>> >  #include "qemu/error-report.h"
>> >  #include "qemu/rcu.h"
>> >  #include "qemu/main-loop.h"
>> >
>> > +/* Add a deep copy of @holder to @iothread's list of holders. */
>> > +void iothread_ref(IOThread *iothread, const IOThreadHolder *holder)
>> > +{
>> > +    assert(holder);
>> > +
>> > +    QAPI_LIST_PREPEND(iothread->holders, QAPI_CLONE(IOThreadHolder, holder));
>> > +}
>> > +
>> > +static int iothread_holder_compare(const IOThreadHolder *holder_a,
>> > +                                   const IOThreadHolder *holder_b)
>> > +{
>> > +    const char *name_a, *name_b;
>> > +
>> > +    if (holder_a->type != holder_b->type) {
>> > +        return holder_a->type - holder_b->type;
>>
>> Why did you swap the operands in v13?  Not mentioned in the cover
>> letter's change log.  I requested the other order in review of v8[*] and
>> v9, and you complied in v10.  Unless you have a compelling reason, swap
>> them right back, please.
>>
>> In general, rocking the boat like this when you're at v13 is
>> inadvisable.  It risks delaying the series even more and annoying
>> reviewers.
>
> Please allow me to explain the details, I have always respected the
> opinions of the community.
> Yes, I remember your comments in V9 and I fixed it. This change wasn't
> something I made secretly or accidentally.
> However, Stefan gave the opposite opinion in the V12, and I see you
> didn't object,

I didn't see it.  Sadly, I can't follow the entire discussion of every
version of every series I comment on.

When reviewer A asks you to change something, and reviewer B later asks
you to change it again, there's a conflict.  If A is aware and remains
silent, that may be taken as assent.  But is A aware?  Better ask to
make sure.

> so it was changed according to his suggestion. This might be a misunderstanding.

It is.  Go with your current version.

> https://lists.gnu.org/archive/html/qemu-devel/2026-08/msg05089.html
>
> I look forward to your reply so we can discuss this issue clearly.
>
> Thanks
> Chen

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