On Mon, Mar 9, 2026 at 3:49 PM Stefan Hajnoczi <stefanha@redhat.com> wrote:
>
> On Thu, Mar 05, 2026 at 10:24:48PM +0800, Zhang Chen wrote:
> > Currently, IOThreads do not maintain a record of which devices are
> > associated with them. This makes it difficult to monitor the
> > workload distribution of IOThreads, especially in complex
> > hotplug scenarios involving multiple virtio-blk or virtio-scsi devices.
> >
> > This patch introduces a reference counting and tracking mechanism
> > within the IOThread object:
> >
> > - iothread_ref(): Prepends the device's QOM path to a list.
> > Note: The IOThread takes ownership of the passed 'holder' string.
>
> This is outdated, the patch duplicates the string and the caller still
> owns the holder argument:
>
> iothread->holders = g_list_prepend(iothread->holders, g_strdup(holder));
>
Yes, will remove this "Note" comments.
> > - iothread_unref(): Searches for the device path using a custom
> > string comparison (g_strcmp0), releases the associated memory
> > upon a successful match.
> > - holders: A GList storing the QOM paths of attached devices
> > for runtime introspection.
> >
> > This infrastructure allows management tools and QMP commands to
> > query the attachment status of IOThreads.
> >
> > Signed-off-by: Zhang Chen <zhangckid@gmail.com>
> > ---
> > include/system/iothread.h | 1 +
> > iothread.c | 28 ++++++++++++++++++++++++++++
> > 2 files changed, 29 insertions(+)
> >
> > diff --git a/include/system/iothread.h b/include/system/iothread.h
> > index e26d13c6c7..21a76bd70d 100644
> > --- a/include/system/iothread.h
> > +++ b/include/system/iothread.h
> > @@ -33,6 +33,7 @@ struct IOThread {
> > bool stopping; /* has iothread_stop() been called? */
> > bool running; /* should iothread_run() continue? */
> > int thread_id;
> > + GList *holders; /* an array of QOM paths for attached devices */
> >
> > /* AioContext poll parameters */
> > int64_t poll_max_ns;
> > diff --git a/iothread.c b/iothread.c
> > index caf68e0764..80a8cf4b32 100644
> > --- a/iothread.c
> > +++ b/iothread.c
> > @@ -36,6 +36,34 @@
> > #define IOTHREAD_POLL_MAX_NS_DEFAULT 0ULL
> > #endif
> >
> > +/*
> > + * Add holder device path to the list.
> > + */
> > +static void iothread_ref(IOThread *iothread, const char *holder)
> > +{
> > + iothread->holders = g_list_prepend(iothread->holders, g_strdup(holder));
> > +}
> > +
> > +/*
> > + * Delete holder device path from the list.
> > + */
> > +static void iothread_unref(IOThread *iothread, const char *holder)
> > +{
> > + if (iothread->holders) {
>
> g_list_find_customer(NULL, ...) returns NULL rather than crashing, so
> there is no need for if (iothread->holders).
OK.
>
> > + GList *link = g_list_find_custom(iothread->holders, holder,
> > + (GCompareFunc)g_strcmp0);
> > +
> > + if (link) {
>
> assert(link) is usually used in QEMU instead. If the reference has
> already been released then the program is in an invalid state and it's
> not safe to continue running.
>
> Please also add assert(iothread->holders == NULL) to
> iothread_instance_finalize() so that leaked references are caught.
OK. will update in next version.
>
> > + g_free(link->data);
> > + iothread->holders = g_list_delete_link(iothread->holders, link);
> > + } else {
> > + error_report("iothread_unref can't find the holder %s", holder);
> > + }
> > + } else {
> > + error_report("iohtread_unref iothread is not held by any devices");
>
> iohtread -> iothread
Thanks
Chen