On Tue, Apr 13, 2021 at 08:40:59AM +0200, Markus Armbruster wrote:
> Li Zhang <zhlci...@gmail.com> writes:
>
> > From: Li Zhang <li.zh...@cloud.ionos.com>
> >
> > For some scenarios, it needs to hot-add a monitor device.
> > But QEMU doesn't support hotplug yet. It also works by adding
> > a monitor with null backend by default and then change its
> > backend to socket by QMP command "chardev-change".
If you need ability to hot-add monitor instances, why not just
implement that feature directly, instead of pre-creating monitors
with null backends and then later changing the backend ?
> >
> > So this patch is to support monitor chardev hotswap with QMP.
> >
> > Signed-off-by: Li Zhang <li.zh...@cloud.ionos.com>
>
> I think what what you're trying to say is that chardev-change does not
> work when the character device changes is used by a QMP monitor.
> Correct?
>
> If yes, how exactly does it misbehave?
>
> Does it work with an HMP monitor?
>
> > ---
> > monitor/monitor-internal.h | 3 +++
> > monitor/monitor.c | 2 +-
> > monitor/qmp.c | 42 +++++++++++++++++++++++++++++++++++---
> > 3 files changed, 43 insertions(+), 4 deletions(-)
> >
> > diff --git a/monitor/monitor-internal.h b/monitor/monitor-internal.h
> > index 40903d6386..2df6dd21de 100644
> > --- a/monitor/monitor-internal.h
> > +++ b/monitor/monitor-internal.h
> > @@ -186,4 +186,7 @@ int hmp_compare_cmd(const char *name, const char *list);
> > void qmp_query_qmp_schema(QDict *qdict, QObject **ret_data,
> > Error **errp);
> >
> > +gboolean monitor_unblocked(GIOChannel *chan, GIOCondition cond,
> > + void *opaque);
> > +
> > #endif
> > diff --git a/monitor/monitor.c b/monitor/monitor.c
> > index e94f532cf5..2d255bab18 100644
> > --- a/monitor/monitor.c
> > +++ b/monitor/monitor.c
> > @@ -157,7 +157,7 @@ static inline bool monitor_is_hmp_non_interactive(const
> > Monitor *mon)
> >
> > static void monitor_flush_locked(Monitor *mon);
> >
> > -static gboolean monitor_unblocked(GIOChannel *chan, GIOCondition cond,
> > +gboolean monitor_unblocked(GIOChannel *chan, GIOCondition cond,
> > void *opaque)
> > {
> > Monitor *mon = opaque;
> > diff --git a/monitor/qmp.c b/monitor/qmp.c
> > index 2326bd7f9b..55cfb230d9 100644
> > --- a/monitor/qmp.c
> > +++ b/monitor/qmp.c
> > @@ -44,6 +44,7 @@ struct QMPRequest {
> > Error *err;
> > };
> > typedef struct QMPRequest QMPRequest;
> > +static void monitor_qmp_set_handlers_bh(void *opaque);
> >
> > QmpCommandList qmp_commands, qmp_cap_negotiation_commands;
> >
> > @@ -480,7 +481,35 @@ void monitor_data_destroy_qmp(MonitorQMP *mon)
> > g_queue_free(mon->qmp_requests);
> > }
> >
> > -static void monitor_qmp_setup_handlers_bh(void *opaque)
> > +static int monitor_qmp_change(void *opaque)
> > +{
> > + MonitorQMP *mon = opaque;
> > +
> > + mon->common.use_io_thread =
> > + qemu_chr_has_feature(mon->common.chr.chr,
> > QEMU_CHAR_FEATURE_GCONTEXT);
> > +
> > + if (mon->common.use_io_thread) {
> > + aio_bh_schedule_oneshot(iothread_get_aio_context(mon_iothread),
> > + monitor_qmp_set_handlers_bh, mon);
> > + } else {
> > + qemu_chr_fe_set_handlers(&mon->common.chr, monitor_can_read,
> > + monitor_qmp_read, monitor_qmp_event,
> > + monitor_qmp_change, &mon->common, NULL,
> > true);
> > + }
> > +
> > + if (mon->common.out_watch) {
> > + g_source_remove(mon->common.out_watch);
>
> All other updates of @out_watch are under @mon_lock. Why not this one?
>
> I have no idea whether g_source_remove() is the right function to call.
> Its documentation says "You must use g_source_destroy() for sources
> added to a non-default main context." The qemu_chr_fe_set_handlers()
> contract is of no help.
>
> Documentation of g_source_destroy() confuses some more: "This does not
> unref the GSource: if you still hold a reference, use g_source_unref()
> to drop it.
>
> Marc-André, can you help?
>
> > + qemu_mutex_lock(&mon->common.mon_lock);
> > + mon->common.out_watch =
> > + qemu_chr_fe_add_watch(&mon->common.chr, G_IO_OUT | G_IO_HUP,
> > + monitor_unblocked, &mon->common);
>
> Bad indentation. Better:
>
> mon->common.out_watch =
> qemu_chr_fe_add_watch(&mon->common.chr, G_IO_OUT | G_IO_HUP,
> monitor_unblocked, &mon->common);
>
> or
>
> mon->common.out_watch = qemu_chr_fe_add_watch(&mon->common.chr,
> G_IO_OUT | G_IO_HUP,
> monitor_unblocked,
> &mon->common);
>
> or
>
> mon->common.out_watch = qemu_chr_fe_add_watch(&mon->common.chr,
> G_IO_OUT | G_IO_HUP,
> monitor_unblocked, &mon->common);
>
> > + qemu_mutex_unlock(&mon->common.mon_lock);
> > + }
> > +
> > + return 0;
> > +}
>
> This function copies from monitor_data_init(), monitor_init_qmp(), and
> monitor_flush_locked(). Feels like a refactoring would be in order.
> Possibly on top.
>
> > +
> > +static void monitor_qmp_set_handlers_bh(void *opaque)
> > {
> > MonitorQMP *mon = opaque;
> > GMainContext *context;
> > @@ -490,7 +519,14 @@ static void monitor_qmp_setup_handlers_bh(void *opaque)
> > assert(context);
> > qemu_chr_fe_set_handlers(&mon->common.chr, monitor_can_read,
> > monitor_qmp_read, monitor_qmp_event,
> > - NULL, &mon->common, context, true);
> > + monitor_qmp_change, &mon->common, context,
> > true);
> > +
> > +}
> > +
> > +static void monitor_qmp_setup_handlers_bh(void *opaque)
> > +{
> > + MonitorQMP *mon = opaque;
> > + monitor_qmp_set_handlers_bh(mon);
> > monitor_list_append(&mon->common);
> > }
> >
> > @@ -531,7 +567,7 @@ void monitor_init_qmp(Chardev *chr, bool pretty, Error
> > **errp)
> > } else {
> > qemu_chr_fe_set_handlers(&mon->common.chr, monitor_can_read,
> > monitor_qmp_read, monitor_qmp_event,
> > - NULL, &mon->common, NULL, true);
> > + monitor_qmp_change, &mon->common, NULL,
> > true);
> > monitor_list_append(&mon->common);
> > }
> > }
>
>
Regards,
Daniel
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