monitor/qmp.c

   1 /*
   2  * QEMU monitor
   3  *
   4  * Copyright (c) 2003-2004 Fabrice Bellard
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to deal
   8  * in the Software without restriction, including without limitation the rights
   9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10  * copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  22  * THE SOFTWARE.
  23  */
  24
  25 #include "qemu/osdep.h"
  26
  27 #include "chardev/char-io.h"
  28 #include "monitor-internal.h"
  29 #include "qapi/error.h"
  30 #include "qapi/qapi-commands-control.h"
  31 #include "qapi/qmp/qdict.h"
  32 #include "qapi/qmp/qjson.h"
  33 #include "qapi/qmp/qlist.h"
  34 #include "trace.h"
  35
  36 /*
  37  * qmp_dispatcher_co_busy is used for synchronisation between the
  38  * monitor thread and the main thread to ensure that the dispatcher
  39  * coroutine never gets scheduled a second time when it's already
  40  * scheduled (scheduling the same coroutine twice is forbidden).
  41  *
  42  * It is true if the coroutine will process at least one more request
  43  * before going to sleep.  Either it has been kicked already, or it
  44  * is active and processing requests.  Additional requests may therefore
  45  * be pushed onto mon->qmp_requests, and @qmp_dispatcher_co_shutdown may
  46  * be set without further ado.  @qmp_dispatcher_co must not be woken up
  47  * in this case.
  48  *
  49  * If false, you have to wake up @qmp_dispatcher_co after pushing new
  50  * requests. You also have to set @qmp_dispatcher_co_busy to true
  51  * before waking up the coroutine.
  52  *
  53  * The coroutine will automatically change this variable back to false
  54  * before it yields.  Nobody else may set the variable to false.
  55  *
  56  * Access must be atomic for thread safety.
  57  */
  58 static bool qmp_dispatcher_co_busy = true;
  59
  60 struct QMPRequest {
  61     /* Owner of the request */
  62     MonitorQMP *mon;
  63     /*
  64      * Request object to be handled or Error to be reported
  65      * (exactly one of them is non-null)
  66      */
  67     QObject *req;
  68     Error *err;
  69 };
  70 typedef struct QMPRequest QMPRequest;
  71
  72 QmpCommandList qmp_commands, qmp_cap_negotiation_commands;
  73
  74 static bool qmp_oob_enabled(MonitorQMP *mon)
  75 {
  76     return mon->capab[QMP_CAPABILITY_OOB];
  77 }
  78
  79 static void monitor_qmp_caps_reset(MonitorQMP *mon)
  80 {
  81     memset(mon->capab_offered, 0, sizeof(mon->capab_offered));
  82     memset(mon->capab, 0, sizeof(mon->capab));
  83     mon->capab_offered[QMP_CAPABILITY_OOB] = mon->common.use_io_thread;
  84 }
  85
  86 static void qmp_request_free(QMPRequest *req)
  87 {
  88     qobject_unref(req->req);
  89     error_free(req->err);
  90     g_free(req);
  91 }
  92
  93 /* Caller must hold mon->qmp.qmp_queue_lock */
  94 static void monitor_qmp_cleanup_req_queue_locked(MonitorQMP *mon)
  95 {
  96     while (!g_queue_is_empty(mon->qmp_requests)) {
  97         qmp_request_free(g_queue_pop_head(mon->qmp_requests));
  98     }
  99 }
 100
 101 static void monitor_qmp_cleanup_queue_and_resume(MonitorQMP *mon)
 102 {
 103     QEMU_LOCK_GUARD(&mon->qmp_queue_lock);
 104
 105     /*
 106      * Same condition as in monitor_qmp_dispatcher_co(), but before
 107      * removing an element from the queue (hence no `- 1`).
 108      * Also, the queue should not be empty either, otherwise the
 109      * monitor hasn't been suspended yet (or was already resumed).
 110      */
 111     bool need_resume = (!qmp_oob_enabled(mon) ||
 112         mon->qmp_requests->length == QMP_REQ_QUEUE_LEN_MAX)
 113         && !g_queue_is_empty(mon->qmp_requests);
 114
 115     monitor_qmp_cleanup_req_queue_locked(mon);
 116
 117     if (need_resume) {
 118         /*
 119          * handle_qmp_command() suspended the monitor because the
 120          * request queue filled up, to be resumed when the queue has
 121          * space again.  We just emptied it; resume the monitor.
 122          *
 123          * Without this, the monitor would remain suspended forever
 124          * when we get here while the monitor is suspended.  An
 125          * unfortunately timed CHR_EVENT_CLOSED can do the trick.
 126          */
 127         monitor_resume(&mon->common);
 128     }
 129
 130 }
 131
 132 void qmp_send_response(MonitorQMP *mon, const QDict *rsp)
 133 {
 134     const QObject *data = QOBJECT(rsp);
 135     GString *json;
 136
 137     json = qobject_to_json_pretty(data, mon->pretty);
 138     assert(json != NULL);
 139     trace_monitor_qmp_respond(mon, json->str);
 140
 141     g_string_append_c(json, '\n');
 142     monitor_puts(&mon->common, json->str);
 143
 144     g_string_free(json, true);
 145 }
 146
 147 /*
 148  * Emit QMP response @rsp to @mon.
 149  * Null @rsp can only happen for commands with QCO_NO_SUCCESS_RESP.
 150  * Nothing is emitted then.
 151  */
 152 static void monitor_qmp_respond(MonitorQMP *mon, QDict *rsp)
 153 {
 154     if (rsp) {
 155         qmp_send_response(mon, rsp);
 156     }
 157 }
 158
 159 /*
 160  * Runs outside of coroutine context for OOB commands, but in
 161  * coroutine context for everything else.
 162  */
 163 static void monitor_qmp_dispatch(MonitorQMP *mon, QObject *req)
 164 {
 165     QDict *rsp;
 166     QDict *error;
 167
 168     rsp = qmp_dispatch(mon->commands, req, qmp_oob_enabled(mon),
 169                        &mon->common);
 170
 171     if (mon->commands == &qmp_cap_negotiation_commands) {
 172         error = qdict_get_qdict(rsp, "error");
 173         if (error
 174             && !g_strcmp0(qdict_get_try_str(error, "class"),
 175                     QapiErrorClass_str(ERROR_CLASS_COMMAND_NOT_FOUND))) {
 176             /* Provide a more useful error message */
 177             qdict_del(error, "desc");
 178             qdict_put_str(error, "desc", "Expecting capabilities negotiation"
 179                           " with 'qmp_capabilities'");
 180         }
 181     }
 182
 183     monitor_qmp_respond(mon, rsp);
 184     qobject_unref(rsp);
 185 }
 186
 187 /*
 188  * Pop a QMP request from a monitor request queue.
 189  * Return the request, or NULL all request queues are empty.
 190  * We are using round-robin fashion to pop the request, to avoid
 191  * processing commands only on a very busy monitor.  To achieve that,
 192  * when we process one request on a specific monitor, we put that
 193  * monitor to the end of mon_list queue.
 194  *
 195  * Note: if the function returned with non-NULL, then the caller will
 196  * be with qmp_mon->qmp_queue_lock held, and the caller is responsible
 197  * to release it.
 198  */
 199 static QMPRequest *monitor_qmp_requests_pop_any_with_lock(void)
 200 {
 201     QMPRequest *req_obj = NULL;
 202     Monitor *mon;
 203     MonitorQMP *qmp_mon;
 204
 205     QTAILQ_FOREACH(mon, &mon_list, entry) {
 206         if (!monitor_is_qmp(mon)) {
 207             continue;
 208         }
 209
 210         qmp_mon = container_of(mon, MonitorQMP, common);
 211         qemu_mutex_lock(&qmp_mon->qmp_queue_lock);
 212         req_obj = g_queue_pop_head(qmp_mon->qmp_requests);
 213         if (req_obj) {
 214             /* With the lock of corresponding queue held */
 215             break;
 216         }
 217         qemu_mutex_unlock(&qmp_mon->qmp_queue_lock);
 218     }
 219
 220     if (req_obj) {
 221         /*
 222          * We found one request on the monitor. Degrade this monitor's
 223          * priority to lowest by re-inserting it to end of queue.
 224          */
 225         QTAILQ_REMOVE(&mon_list, mon, entry);
 226         QTAILQ_INSERT_TAIL(&mon_list, mon, entry);
 227     }
 228
 229     return req_obj;
 230 }
 231
 232 static QMPRequest *monitor_qmp_dispatcher_pop_any(void)
 233 {
 234     while (true) {
 235         /*
 236          * To avoid double scheduling, busy is true on entry to
 237          * monitor_qmp_dispatcher_co(), and must be set again before
 238          * aio_co_wake()-ing it.
 239          */
 240         assert(qatomic_read(&qmp_dispatcher_co_busy) == true);
 241
 242         /*
 243          * Mark the dispatcher as not busy already here so that we
 244          * don't miss any new requests coming in the middle of our
 245          * processing.
 246          *
 247          * Clear qmp_dispatcher_co_busy before reading request.
 248          */
 249         qatomic_set_mb(&qmp_dispatcher_co_busy, false);
 250
 251         WITH_QEMU_LOCK_GUARD(&monitor_lock) {
 252             QMPRequest *req_obj;
 253
 254             /* On shutdown, don't take any more requests from the queue */
 255             if (qmp_dispatcher_co_shutdown) {
 256                 return NULL;
 257             }
 258
 259             req_obj = monitor_qmp_requests_pop_any_with_lock();
 260             if (req_obj) {
 261                 return req_obj;
 262             }
 263         }
 264
 265         /*
 266          * No more requests to process.  Wait to be reentered from
 267          * handle_qmp_command() when it pushes more requests, or
 268          * from monitor_cleanup() when it requests shutdown.
 269          */
 270         qemu_coroutine_yield();
 271     }
 272 }
 273
 274 void coroutine_fn monitor_qmp_dispatcher_co(void *data)
 275 {
 276     QMPRequest *req_obj;
 277     QDict *rsp;
 278     bool oob_enabled;
 279     MonitorQMP *mon;
 280
 281     while ((req_obj = monitor_qmp_dispatcher_pop_any()) != NULL) {
 282         trace_monitor_qmp_in_band_dequeue(req_obj,
 283                                           req_obj->mon->qmp_requests->length);
 284
 285         /*
 286          * @req_obj has a request, we hold req_obj->mon->qmp_queue_lock
 287          */
 288
 289         mon = req_obj->mon;
 290
 291         /*
 292          * We need to resume the monitor if handle_qmp_command()
 293          * suspended it.  Two cases:
 294          * 1. OOB enabled: mon->qmp_requests has no more space
 295          *    Resume right away, so that OOB commands can get executed while
 296          *    this request is being processed.
 297          * 2. OOB disabled: always
 298          *    Resume only after we're done processing the request,
 299          * We need to save qmp_oob_enabled() for later, because
 300          * qmp_qmp_capabilities() can change it.
 301          */
 302         oob_enabled = qmp_oob_enabled(mon);
 303         if (oob_enabled
 304             && mon->qmp_requests->length == QMP_REQ_QUEUE_LEN_MAX - 1) {
 305             monitor_resume(&mon->common);
 306         }
 307
 308         /*
 309          * Drop the queue mutex now, before yielding, otherwise we might
 310          * deadlock if the main thread tries to lock it.
 311          */
 312         qemu_mutex_unlock(&mon->qmp_queue_lock);
 313
 314         if (qatomic_xchg(&qmp_dispatcher_co_busy, true) == true) {
 315             /*
 316              * Someone rescheduled us (probably because a new requests
 317              * came in), but we didn't actually yield. Do that now,
 318              * only to be immediately reentered and removed from the
 319              * list of scheduled coroutines.
 320              */
 321             qemu_coroutine_yield();
 322         }
 323
 324         /* Process request */
 325         if (req_obj->req) {
 326             if (trace_event_get_state(TRACE_MONITOR_QMP_CMD_IN_BAND)) {
 327                 QDict *qdict = qobject_to(QDict, req_obj->req);
 328                 QObject *id = qdict ? qdict_get(qdict, "id") : NULL;
 329                 GString *id_json;
 330
 331                 id_json = id ? qobject_to_json(id) : g_string_new(NULL);
 332                 trace_monitor_qmp_cmd_in_band(id_json->str);
 333                 g_string_free(id_json, true);
 334             }
 335             monitor_qmp_dispatch(mon, req_obj->req);
 336         } else {
 337             assert(req_obj->err);
 338             trace_monitor_qmp_err_in_band(error_get_pretty(req_obj->err));
 339             rsp = qmp_error_response(req_obj->err);
 340             req_obj->err = NULL;
 341             monitor_qmp_respond(mon, rsp);
 342             qobject_unref(rsp);
 343         }
 344
 345         if (!oob_enabled) {
 346             monitor_resume(&mon->common);
 347         }
 348
 349         qmp_request_free(req_obj);
 350     }
 351     qatomic_set(&qmp_dispatcher_co, NULL);
 352 }
 353
 354 void qmp_dispatcher_co_wake(void)
 355 {
 356     /* Write request before reading qmp_dispatcher_co_busy.  */
 357     smp_mb__before_rmw();
 358
 359     if (!qatomic_xchg(&qmp_dispatcher_co_busy, true)) {
 360         aio_co_wake(qmp_dispatcher_co);
 361     }
 362 }
 363
 364 static void handle_qmp_command(void *opaque, QObject *req, Error *err)
 365 {
 366     MonitorQMP *mon = opaque;
 367     QDict *qdict = qobject_to(QDict, req);
 368     QMPRequest *req_obj;
 369
 370     assert(!req != !err);
 371
 372     if (req && trace_event_get_state_backends(TRACE_HANDLE_QMP_COMMAND)) {
 373         GString *req_json = qobject_to_json(req);
 374         trace_handle_qmp_command(mon, req_json->str);
 375         g_string_free(req_json, true);
 376     }
 377
 378     if (qdict && qmp_is_oob(qdict)) {
 379         /* OOB commands are executed immediately */
 380         if (trace_event_get_state(TRACE_MONITOR_QMP_CMD_OUT_OF_BAND)) {
 381             QObject *id = qdict_get(qdict, "id");
 382             GString *id_json;
 383
 384             id_json = id ? qobject_to_json(id) : g_string_new(NULL);
 385             trace_monitor_qmp_cmd_out_of_band(id_json->str);
 386             g_string_free(id_json, true);
 387         }
 388         monitor_qmp_dispatch(mon, req);
 389         qobject_unref(req);
 390         return;
 391     }
 392
 393     req_obj = g_new0(QMPRequest, 1);
 394     req_obj->mon = mon;
 395     req_obj->req = req;
 396     req_obj->err = err;
 397
 398     /* Protect qmp_requests and fetching its length. */
 399     WITH_QEMU_LOCK_GUARD(&mon->qmp_queue_lock) {
 400
 401         /*
 402          * Suspend the monitor when we can't queue more requests after
 403          * this one.  Dequeuing in monitor_qmp_dispatcher_co() or
 404          * monitor_qmp_cleanup_queue_and_resume() will resume it.
 405          * Note that when OOB is disabled, we queue at most one command,
 406          * for backward compatibility.
 407          */
 408         if (!qmp_oob_enabled(mon) ||
 409             mon->qmp_requests->length == QMP_REQ_QUEUE_LEN_MAX - 1) {
 410             monitor_suspend(&mon->common);
 411         }
 412
 413         /*
 414          * Put the request to the end of queue so that requests will be
 415          * handled in time order.  Ownership for req_obj, req,
 416          * etc. will be delivered to the handler side.
 417          */
 418         trace_monitor_qmp_in_band_enqueue(req_obj, mon,
 419                                           mon->qmp_requests->length);
 420         assert(mon->qmp_requests->length < QMP_REQ_QUEUE_LEN_MAX);
 421         g_queue_push_tail(mon->qmp_requests, req_obj);
 422     }
 423
 424     /* Kick the dispatcher routine */
 425     qmp_dispatcher_co_wake();
 426 }
 427
 428 static void monitor_qmp_read(void *opaque, const uint8_t *buf, int size)
 429 {
 430     MonitorQMP *mon = opaque;
 431
 432     json_message_parser_feed(&mon->parser, (const char *) buf, size);
 433 }
 434
 435 static QDict *qmp_greeting(MonitorQMP *mon)
 436 {
 437     QList *cap_list = qlist_new();
 438     QObject *ver = NULL;
 439     QDict *args;
 440     QMPCapability cap;
 441
 442     args = qdict_new();
 443     qmp_marshal_query_version(args, &ver, NULL);
 444     qobject_unref(args);
 445
 446     for (cap = 0; cap < QMP_CAPABILITY__MAX; cap++) {
 447         if (mon->capab_offered[cap]) {
 448             qlist_append_str(cap_list, QMPCapability_str(cap));
 449         }
 450     }
 451
 452     return qdict_from_jsonf_nofail(
 453         "{'QMP': {'version': %p, 'capabilities': %p}}",
 454         ver, cap_list);
 455 }
 456
 457 static void monitor_qmp_event(void *opaque, QEMUChrEvent event)
 458 {
 459     QDict *data;
 460     MonitorQMP *mon = opaque;
 461
 462     switch (event) {
 463     case CHR_EVENT_OPENED:
 464         mon->commands = &qmp_cap_negotiation_commands;
 465         monitor_qmp_caps_reset(mon);
 466         data = qmp_greeting(mon);
 467         qmp_send_response(mon, data);
 468         qobject_unref(data);
 469         break;
 470     case CHR_EVENT_CLOSED:
 471         /*
 472          * Note: this is only useful when the output of the chardev
 473          * backend is still open.  For example, when the backend is
 474          * stdio, it's possible that stdout is still open when stdin
 475          * is closed.
 476          */
 477         monitor_qmp_cleanup_queue_and_resume(mon);
 478         json_message_parser_destroy(&mon->parser);
 479         json_message_parser_init(&mon->parser, handle_qmp_command,
 480                                  mon, NULL);
 481         monitor_fdsets_cleanup();
 482         break;
 483     case CHR_EVENT_BREAK:
 484     case CHR_EVENT_MUX_IN:
 485     case CHR_EVENT_MUX_OUT:
 486         /* Ignore */
 487         break;
 488     }
 489 }
 490
 491 void monitor_data_destroy_qmp(MonitorQMP *mon)
 492 {
 493     json_message_parser_destroy(&mon->parser);
 494     qemu_mutex_destroy(&mon->qmp_queue_lock);
 495     monitor_qmp_cleanup_req_queue_locked(mon);
 496     g_queue_free(mon->qmp_requests);
 497 }
 498
 499 static void monitor_qmp_setup_handlers_bh(void *opaque)
 500 {
 501     MonitorQMP *mon = opaque;
 502     GMainContext *context;
 503
 504     assert(mon->common.use_io_thread);
 505     context = iothread_get_g_main_context(mon_iothread);
 506     assert(context);
 507     qemu_chr_fe_set_handlers(&mon->common.chr, monitor_can_read,
 508                              monitor_qmp_read, monitor_qmp_event,
 509                              NULL, &mon->common, context, true);
 510     monitor_list_append(&mon->common);
 511 }
 512
 513 void monitor_init_qmp(Chardev *chr, bool pretty, Error **errp)
 514 {
 515     MonitorQMP *mon = g_new0(MonitorQMP, 1);
 516
 517     if (!qemu_chr_fe_init(&mon->common.chr, chr, errp)) {
 518         g_free(mon);
 519         return;
 520     }
 521     qemu_chr_fe_set_echo(&mon->common.chr, true);
 522
 523     /* Note: we run QMP monitor in I/O thread when @chr supports that */
 524     monitor_data_init(&mon->common, true, false,
 525                       qemu_chr_has_feature(chr, QEMU_CHAR_FEATURE_GCONTEXT));
 526
 527     mon->pretty = pretty;
 528
 529     qemu_mutex_init(&mon->qmp_queue_lock);
 530     mon->qmp_requests = g_queue_new();
 531
 532     json_message_parser_init(&mon->parser, handle_qmp_command, mon, NULL);
 533     if (mon->common.use_io_thread) {
 534         /*
 535          * Make sure the old iowatch is gone.  It's possible when
 536          * e.g. the chardev is in client mode, with wait=on.
 537          */
 538         remove_fd_in_watch(chr);
 539         /*
 540          * We can't call qemu_chr_fe_set_handlers() directly here
 541          * since chardev might be running in the monitor I/O
 542          * thread.  Schedule a bottom half.
 543          */
 544         aio_bh_schedule_oneshot(iothread_get_aio_context(mon_iothread),
 545                                 monitor_qmp_setup_handlers_bh, mon);
 546         /* The bottom half will add @mon to @mon_list */
 547     } else {
 548         qemu_chr_fe_set_handlers(&mon->common.chr, monitor_can_read,
 549                                  monitor_qmp_read, monitor_qmp_event,
 550                                  NULL, &mon->common, NULL, true);
 551         monitor_list_append(&mon->common);
 552     }
 553 }