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monitor: separate QMP parser and dispatcher

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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 follow 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 <stefanha@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180309090006.10018-15-peterx@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[eblake: grammar tweaks, rebase to qobject_to()]
Signed-off-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Peter Xu 2018-03-09 16:59:57 +08:00 committed by Eric Blake
parent e3e977d45b
commit 71da4667db
1 changed files with 178 additions and 23 deletions
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201
monitor.c
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@ -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,
@ -1059,6 +1072,16 @@ 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)
{
@ -3869,30 +3892,39 @@ 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);
bool need_resume;
Error *err = NULL;
req = req_obj->req;
mon = req_obj->mon;
id = req_obj->id;
need_resume = req_obj->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;
}
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);
@ -3903,7 +3935,7 @@ 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;
@ -3919,12 +3951,122 @@ 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 commands only on a very busy monitor. To achieve that,
* when we process one request on a 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 the current monitor, we'll emulate the
* old behavior that we won't process the current monitor any more
* until it has 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,
* 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;
@ -4137,6 +4279,15 @@ 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)
@ -4288,6 +4439,10 @@ 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;
}