* Marc-André Lureau (marcandre.lur...@gmail.com) wrote:
> Hi
>
> On Fri, Mar 9, 2018 at 9:59 AM, Peter Xu <pet...@redhat.com> wrote:
> > Originally QMP goes through these steps:
> >
> > JSON Parser --> QMP Dispatcher --> Respond
> > /|\ (2) (3) |
> > (1) | \|/ (4)
> > +--------- main thread --------+
> >
> > This patch does this:
> >
> > JSON Parser QMP Dispatcher --> Respond
> > /|\ | /|\ (4) |
> > | | (2) | (3) | (5)
> > (1) | +-----> | \|/
> > +--------- main thread <-------+
> >
> > So the parsing job and the dispatching job is isolated now. It gives us
> > a chance in following up patches to totally move the parser outside.
> >
> > The isolation is done using one QEMUBH. Only one dispatcher QEMUBH is
> > used for all the monitors.
> >
> > Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
> > Signed-off-by: Peter Xu <pet...@redhat.com>
> > ---
> > monitor.c | 201
> > +++++++++++++++++++++++++++++++++++++++++++++++++++++++-------
> > 1 file changed, 178 insertions(+), 23 deletions(-)
> >
> > diff --git a/monitor.c b/monitor.c
> > index de9343be87..5104e5db07 100644
> > --- a/monitor.c
> > +++ b/monitor.c
> > @@ -172,6 +172,13 @@ typedef struct {
> > */
> > QmpCommandList *commands;
> > bool qmp_caps[QMP_CAPABILITY__MAX];
> > + /*
> > + * Protects qmp request/response queue. Please take monitor_lock
> > + * first when used together.
> > + */
> > + QemuMutex qmp_queue_lock;
> > + /* Input queue that holds all the parsed QMP requests */
> > + GQueue *qmp_requests;
> > } MonitorQMP;
> >
> > /*
> > @@ -218,6 +225,8 @@ struct Monitor {
> > /* Let's add monitor global variables to this struct. */
> > static struct {
> > IOThread *mon_iothread;
> > + /* Bottom half to dispatch the requests received from IO thread */
> > + QEMUBH *qmp_dispatcher_bh;
> > } mon_global;
> >
> > /* QMP checker flags */
> > @@ -600,11 +609,13 @@ static void monitor_data_init(Monitor *mon, bool
> > skip_flush,
> > {
> > memset(mon, 0, sizeof(Monitor));
> > qemu_mutex_init(&mon->out_lock);
> > + qemu_mutex_init(&mon->qmp.qmp_queue_lock);
> > mon->outbuf = qstring_new();
> > /* Use *mon_cmds by default. */
> > mon->cmd_table = mon_cmds;
> > mon->skip_flush = skip_flush;
> > mon->use_io_thr = use_io_thr;
> > + mon->qmp.qmp_requests = g_queue_new();
> > }
> >
> > static void monitor_data_destroy(Monitor *mon)
> > @@ -617,6 +628,8 @@ static void monitor_data_destroy(Monitor *mon)
> > readline_free(mon->rs);
> > QDECREF(mon->outbuf);
> > qemu_mutex_destroy(&mon->out_lock);
> > + qemu_mutex_destroy(&mon->qmp.qmp_queue_lock);
> > + g_queue_free(mon->qmp.qmp_requests);
> > }
> >
> > char *qmp_human_monitor_command(const char *command_line, bool
> > has_cpu_index,
> > @@ -1056,6 +1069,16 @@ static void monitor_init_qmp_commands(void)
> > qmp_marshal_qmp_capabilities, QCO_NO_OPTIONS);
> > }
> >
> > +static bool qmp_cap_enabled(Monitor *mon, QMPCapability cap)
> > +{
> > + return mon->qmp.qmp_caps[cap];
> > +}
> > +
> > +static bool qmp_oob_enabled(Monitor *mon)
> > +{
> > + return qmp_cap_enabled(mon, QMP_CAPABILITY_OOB);
> > +}
> > +
> > static void qmp_caps_check(Monitor *mon, QMPCapabilityList *list,
> > Error **errp)
> > {
> > @@ -3866,30 +3889,39 @@ static void monitor_qmp_respond(Monitor *mon,
> > QObject *rsp,
> > qobject_decref(rsp);
> > }
> >
> > -static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
> > +struct QMPRequest {
> > + /* Owner of the request */
> > + Monitor *mon;
> > + /* "id" field of the request */
> > + QObject *id;
> > + /* Request object to be handled */
> > + QObject *req;
> > + /*
> > + * Whether we need to resume the monitor afterward. This flag is
> > + * used to emulate the old QMP server behavior that the current
> > + * command must be completed before execution of the next one.
> > + */
> > + bool need_resume;
> > +};
> > +typedef struct QMPRequest QMPRequest;
> > +
> > +/*
> > + * Dispatch one single QMP request. The function will free the req_obj
> > + * and objects inside it before return.
> > + */
> > +static void monitor_qmp_dispatch_one(QMPRequest *req_obj)
> > {
> > - QObject *req, *rsp = NULL, *id = NULL;
> > + Monitor *mon, *old_mon;
> > + QObject *req, *rsp = NULL, *id;
> > QDict *qdict = NULL;
> > - MonitorQMP *mon_qmp = container_of(parser, MonitorQMP, parser);
> > - Monitor *old_mon, *mon = container_of(mon_qmp, Monitor, qmp);
> > -
> > - Error *err = NULL;
> > + bool need_resume;
> >
> > - req = json_parser_parse_err(tokens, NULL, &err);
> > - if (!req && !err) {
> > - /* json_parser_parse_err() sucks: can fail without setting @err */
> > - error_setg(&err, QERR_JSON_PARSING);
> > - }
> > - if (err) {
> > - goto err_out;
> > - }
> > + req = req_obj->req;
> > + mon = req_obj->mon;
> > + id = req_obj->id;
> > + need_resume = req_obj->need_resume;
> >
> > - qdict = qobject_to_qdict(req);
> > - if (qdict) {
> > - id = qdict_get(qdict, "id");
> > - qobject_incref(id);
> > - qdict_del(qdict, "id");
> > - } /* else will fail qmp_dispatch() */
> > + g_free(req_obj);
> >
> > if (trace_event_get_state_backends(TRACE_HANDLE_QMP_COMMAND)) {
> > QString *req_json = qobject_to_json(req);
> > @@ -3900,7 +3932,7 @@ static void handle_qmp_command(JSONMessageParser
> > *parser, GQueue *tokens)
> > old_mon = cur_mon;
> > cur_mon = mon;
> >
> > - rsp = qmp_dispatch(cur_mon->qmp.commands, req);
> > + rsp = qmp_dispatch(mon->qmp.commands, req);
> >
> > cur_mon = old_mon;
> >
> > @@ -3916,12 +3948,122 @@ static void handle_qmp_command(JSONMessageParser
> > *parser, GQueue *tokens)
> > }
> > }
> >
> > -err_out:
> > - monitor_qmp_respond(mon, rsp, err, id);
> > + /* Respond if necessary */
> > + monitor_qmp_respond(mon, rsp, NULL, id);
> > +
> > + /* This pairs with the monitor_suspend() in handle_qmp_command(). */
> > + if (need_resume) {
> > + monitor_resume(mon);
> > + }
> >
> > qobject_decref(req);
> > }
> >
> > +/*
> > + * Pop one QMP request from monitor queues, return NULL if not found.
> > + * We are using round-robin fashion to pop the request, to avoid
> > + * processing command only on a very busy monitor. To achieve that,
> > + * when we processed one request on specific monitor, we put that
> > + * monitor to the end of mon_list queue.
> > + */
> > +static QMPRequest *monitor_qmp_requests_pop_one(void)
> > +{
> > + QMPRequest *req_obj = NULL;
> > + Monitor *mon;
> > +
> > + qemu_mutex_lock(&monitor_lock);
> > +
> > + QTAILQ_FOREACH(mon, &mon_list, entry) {
> > + qemu_mutex_lock(&mon->qmp.qmp_queue_lock);
> > + req_obj = g_queue_pop_head(mon->qmp.qmp_requests);
> > + qemu_mutex_unlock(&mon->qmp.qmp_queue_lock);
> > + if (req_obj) {
> > + break;
> > + }
> > + }
> > +
> > + if (req_obj) {
> > + /*
> > + * We found one request on the monitor. Degrade this monitor's
> > + * priority to lowest by re-inserting it to end of queue.
> > + */
> > + QTAILQ_REMOVE(&mon_list, mon, entry);
> > + QTAILQ_INSERT_TAIL(&mon_list, mon, entry);
> > + }
> > +
> > + qemu_mutex_unlock(&monitor_lock);
> > +
> > + return req_obj;
> > +}
> > +
> > +static void monitor_qmp_bh_dispatcher(void *data)
> > +{
> > + QMPRequest *req_obj = monitor_qmp_requests_pop_one();
> > +
> > + if (req_obj) {
> > + monitor_qmp_dispatch_one(req_obj);
> > + /* Reschedule instead of looping so the main loop stays responsive
> > */
> > + qemu_bh_schedule(mon_global.qmp_dispatcher_bh);
> > + }
> > +}
> > +
> > +static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
> > +{
> > + QObject *req, *id = NULL;
> > + QDict *qdict = NULL;
> > + MonitorQMP *mon_qmp = container_of(parser, MonitorQMP, parser);
> > + Monitor *mon = container_of(mon_qmp, Monitor, qmp);
> > + Error *err = NULL;
> > + QMPRequest *req_obj;
> > +
> > + req = json_parser_parse_err(tokens, NULL, &err);
> > + if (!req && !err) {
> > + /* json_parser_parse_err() sucks: can fail without setting @err */
> > + error_setg(&err, QERR_JSON_PARSING);
> > + }
> > + if (err) {
> > + monitor_qmp_respond(mon, NULL, err, NULL);
> > + qobject_decref(req);
> > + return;
> > + }
> > +
> > + qdict = qobject_to_qdict(req);
> > + if (qdict) {
> > + id = qdict_get(qdict, "id");
> > + qobject_incref(id);
> > + qdict_del(qdict, "id");
> > + } /* else will fail qmp_dispatch() */
> > +
> > + req_obj = g_new0(QMPRequest, 1);
> > + req_obj->mon = mon;
> > + req_obj->id = id;
> > + req_obj->req = req;
> > + req_obj->need_resume = false;
> > +
> > + /*
> > + * If OOB is not enabled on current monitor, we'll emulate the old
> > + * behavior that we won't process current monitor any more until
> > + * it is responded. This helps make sure that as long as OOB is
> > + * not enabled, the server will never drop any command.
> > + */
> > + if (!qmp_oob_enabled(mon)) {
> > + monitor_suspend(mon);
> > + req_obj->need_resume = true;
> > + }
> > +
> > + /*
> > + * Put the request to the end of queue so that requests will be
> > + * handled in time order. Ownership for req_obj, req, id,
>
> I think the order is not respected if subsequent messages have errors
> (in either json parsing, dispatch_check_obj, oob_check). So if I
> enable oob, and queue a few command, then send a bad command/message,
> I won't be able to tell for which command.
Doesn't OOB insist on having an ID field with the command?
Dave
> > + * etc. will be delivered to the handler side.
> > + */
> > + qemu_mutex_lock(&mon->qmp.qmp_queue_lock);
> > + g_queue_push_tail(mon->qmp.qmp_requests, req_obj);
> > + qemu_mutex_unlock(&mon->qmp.qmp_queue_lock);
> > +
> > + /* Kick the dispatcher routine */
> > + qemu_bh_schedule(mon_global.qmp_dispatcher_bh);
> > +}
> > +
> > static void monitor_qmp_read(void *opaque, const uint8_t *buf, int size)
> > {
> > Monitor *mon = opaque;
> > @@ -4134,6 +4276,15 @@ static void monitor_iothread_init(void)
> > {
> > mon_global.mon_iothread = iothread_create("mon_iothread",
> > &error_abort);
> > +
> > + /*
> > + * This MUST be on main loop thread since we have commands that
> > + * have assumption to be run on main loop thread. It would be
> > + * nice that one day we can remove this assumption in the future.
> > + */
> > + mon_global.qmp_dispatcher_bh = aio_bh_new(qemu_get_aio_context(),
> > + monitor_qmp_bh_dispatcher,
> > + NULL);
> > }
> >
> > void monitor_init_globals(void)
> > @@ -4280,6 +4431,10 @@ void monitor_cleanup(void)
> > }
> > qemu_mutex_unlock(&monitor_lock);
> >
> > + /* QEMUBHs needs to be deleted before destroying the IOThread. */
> > + qemu_bh_delete(mon_global.qmp_dispatcher_bh);
> > + mon_global.qmp_dispatcher_bh = NULL;
> > +
> > iothread_destroy(mon_global.mon_iothread);
> > mon_global.mon_iothread = NULL;
> > }
> > --
> > 2.14.3
> >
> >
>
>
>
> --
> Marc-André Lureau
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
