From: Li Zhang <zhlcindy@gmail.com>
To: "Daniel P. Berrangé" <berrange@redhat.com>
Cc: lukasstraub2@web.de, alexandr.iarygin@profitbricks.com,
Markus Armbruster <armbru@redhat.com>,
qemu-devel@nongnu.org, Li Zhang <li.zhang@cloud.ionos.com>,
pankaj.gupta@cloud.ionos.com, marcandre.lureau@redhat.com
Subject: Re: [PATCH 2/2] Support monitor chardev hotswap with QMP
Date: Tue, 13 Apr 2021 11:33:31 +0200 [thread overview]
Message-ID: <CAD8of+pJU1Qdg256LKfTOQDL=hNy6Z=gQQdPWY53WbkQPJRAtQ@mail.gmail.com> (raw)
In-Reply-To: <YHVdFndkaj0bltcE@redhat.com>
On Tue, Apr 13, 2021 at 10:58 AM Daniel P. Berrangé <berrange@redhat.com> wrote:
>
> On Tue, Apr 13, 2021 at 08:40:59AM +0200, Markus Armbruster wrote:
> > Li Zhang <zhlcindy@gmail.com> writes:
> >
> > > From: Li Zhang <li.zhang@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 ?
>
Hi Daniel,
I would like to use this solution first because we'd like to use it as
soon as possible.
It's the best solution to implement the hot-add feature and it may
need more effort to do it.
I will consider it.
> > >
> > > So this patch is to support monitor chardev hotswap with QMP.
> > >
> > > Signed-off-by: Li Zhang <li.zhang@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
> --
> |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :|
> |: https://libvirt.org -o- https://fstop138.berrange.com :|
> |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
>
--
Best Regards
-Li
next prev parent reply other threads:[~2021-04-13 9:35 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-15 17:06 [PATCH 1/2] Fix the segment fault when calling yank_register_instance Li Zhang
2021-03-15 17:06 ` [PATCH 2/2] Support monitor chardev hotswap with QMP Li Zhang
2021-03-23 13:14 ` Li Zhang
2021-03-26 14:40 ` Markus Armbruster
2021-03-26 15:19 ` Li Zhang
2021-04-12 12:41 ` Li Zhang
2021-04-12 13:10 ` Markus Armbruster
2021-04-12 13:41 ` Li Zhang
2021-04-12 14:19 ` Pankaj Gupta
2021-04-13 6:40 ` Markus Armbruster
2021-04-13 8:51 ` Li Zhang
2021-04-16 9:33 ` Markus Armbruster
2021-04-16 9:52 ` Li Zhang
2021-04-13 8:57 ` Daniel P. Berrangé
2021-04-13 9:33 ` Li Zhang [this message]
2021-03-15 18:51 ` [PATCH 1/2] Fix the segment fault when calling yank_register_instance Marc-André Lureau
2021-03-16 9:45 ` Li Zhang
2021-03-16 14:46 ` Li Zhang
2021-03-16 15:24 ` Marc-André Lureau
2021-03-16 15:36 ` Li Zhang
2021-03-17 21:06 ` Lukas Straub
2021-03-26 14:41 ` Markus Armbruster
2021-03-26 16:02 ` Lukas Straub
2021-03-26 16:13 ` Markus Armbruster
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