Monitor patches for 2018-12-12

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Merge remote-tracking branch 'remotes/armbru/tags/pull-monitor-2018-12-12' into staging

Monitor patches for 2018-12-12

# gpg: Signature made Wed 12 Dec 2018 10:08:15 GMT
# gpg:                using RSA key 3870B400EB918653
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>"
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>"
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-monitor-2018-12-12:
  tests: add oob functional test for test-qmp-cmds
  Revert "tests: Add parameter to qtest_init_without_qmp_handshake"
  monitor: Remove "x-oob", offer capability "oob" unconditionally
  monitor: Suspend monitor instead dropping commands
  monitor: avoid potential dead-lock when cleaning up
  monitor: prevent inserting new monitors after cleanup
  colo: check chardev can switch context
  monitor: check if chardev can switch gcontext for OOB
  char: add a QEMU_CHAR_FEATURE_GCONTEXT flag
  monitor: accept chardev input from iothread
  monitor: inline ambiguous helper functions

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

chardev/char.c

@@ -193,6 +193,8 @@ void qemu_chr_be_update_read_handlers(Chardev *s,
 {
     ChardevClass *cc = CHARDEV_GET_CLASS(s);
 
+    assert(qemu_chr_has_feature(s, QEMU_CHAR_FEATURE_GCONTEXT)
+           || !context);
     s->gcontext = context;
     if (cc->chr_update_read_handler) {
         cc->chr_update_read_handler(s);
@@ -240,6 +242,15 @@ static void char_init(Object *obj)
 
     chr->logfd = -1;
     qemu_mutex_init(&chr->chr_write_lock);
+
+    /*
+     * Assume if chr_update_read_handler is implemented it will
+     * take the updated gcontext into account.
+     */
+    if (CHARDEV_GET_CLASS(chr)->chr_update_read_handler) {
+        qemu_chr_set_feature(chr, QEMU_CHAR_FEATURE_GCONTEXT);
+    }
+
 }
 
 static int null_chr_write(Chardev *chr, const uint8_t *buf, int len)

docs/interop/qmp-spec.txt

@@ -130,8 +130,9 @@ to pass "id" with out-of-band commands.  Passing it with all commands
 is recommended for clients that accept capability "oob".
 
 If the client sends in-band commands faster than the server can
-execute them, the server will eventually drop commands to limit the
+execute them, the server will stop reading the requests from the QMP
-queue length.  The sever sends event COMMAND_DROPPED then.
+channel until the request queue length is reduced to an acceptable
+range.
 
 Only a few commands support out-of-band execution.  The ones that do
 have "allow-oob": true in output of query-qmp-schema.

include/chardev/char.h

@@ -47,6 +47,9 @@ typedef enum {
     QEMU_CHAR_FEATURE_FD_PASS,
     /* Whether replay or record mode is enabled */
     QEMU_CHAR_FEATURE_REPLAY,
+    /* Whether the gcontext can be changed after calling
+     * qemu_chr_be_update_read_handlers() */
+    QEMU_CHAR_FEATURE_GCONTEXT,
 
     QEMU_CHAR_FEATURE_LAST,
 } ChardevFeature;

include/monitor/monitor.h

@@ -13,7 +13,8 @@ extern __thread Monitor *cur_mon;
 #define MONITOR_USE_READLINE  0x02
 #define MONITOR_USE_CONTROL   0x04
 #define MONITOR_USE_PRETTY    0x08
-#define MONITOR_USE_OOB       0x10
+
+#define QMP_REQ_QUEUE_LEN_MAX 8
 
 bool monitor_cur_is_qmp(void);
 

monitor.c

@@ -263,10 +263,11 @@ typedef struct QMPRequest QMPRequest;
 /* QMP checker flags */
 #define QMP_ACCEPT_UNKNOWNS 1
 
-/* Protects mon_list, monitor_qapi_event_state.  */
+/* Protects mon_list, monitor_qapi_event_state, monitor_destroyed.  */
 static QemuMutex monitor_lock;
 static GHashTable *monitor_qapi_event_state;
 static QTAILQ_HEAD(mon_list, Monitor) mon_list;
+static bool monitor_destroyed;
 
 /* Protects mon_fdsets */
 static QemuMutex mon_fdsets_lock;
@@ -4109,8 +4110,12 @@ static void monitor_qmp_dispatch(Monitor *mon, QObject *req, QObject *id)
  * 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.
+ *
+ * Note: if the function returned with non-NULL, then the caller will
+ * be with mon->qmp.qmp_queue_lock held, and the caller is responsible
+ * to release it.
  */
-static QMPRequest *monitor_qmp_requests_pop_any(void)
+static QMPRequest *monitor_qmp_requests_pop_any_with_lock(void)
 {
     QMPRequest *req_obj = NULL;
     Monitor *mon;
@@ -4120,10 +4125,11 @@ static QMPRequest *monitor_qmp_requests_pop_any(void)
     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) {
+            /* With the lock of corresponding queue held */
             break;
         }
+        qemu_mutex_unlock(&mon->qmp.qmp_queue_lock);
     }
 
     if (req_obj) {
@@ -4142,30 +4148,34 @@ static QMPRequest *monitor_qmp_requests_pop_any(void)
 
 static void monitor_qmp_bh_dispatcher(void *data)
 {
-    QMPRequest *req_obj = monitor_qmp_requests_pop_any();
+    QMPRequest *req_obj = monitor_qmp_requests_pop_any_with_lock();
     QDict *rsp;
     bool need_resume;
+    Monitor *mon;
 
     if (!req_obj) {
         return;
     }
 
+    mon = req_obj->mon;
     /*  qmp_oob_enabled() might change after "qmp_capabilities" */
-    need_resume = !qmp_oob_enabled(req_obj->mon);
+    need_resume = !qmp_oob_enabled(mon) ||
+        mon->qmp.qmp_requests->length == QMP_REQ_QUEUE_LEN_MAX - 1;
+    qemu_mutex_unlock(&mon->qmp.qmp_queue_lock);
     if (req_obj->req) {
         trace_monitor_qmp_cmd_in_band(qobject_get_try_str(req_obj->id) ?: "");
-        monitor_qmp_dispatch(req_obj->mon, req_obj->req, req_obj->id);
+        monitor_qmp_dispatch(mon, req_obj->req, req_obj->id);
     } else {
         assert(req_obj->err);
         rsp = qmp_error_response(req_obj->err);
         req_obj->err = NULL;
-        monitor_qmp_respond(req_obj->mon, rsp, NULL);
+        monitor_qmp_respond(mon, rsp, NULL);
         qobject_unref(rsp);
     }
 
     if (need_resume) {
         /* Pairs with the monitor_suspend() in handle_qmp_command() */
-        monitor_resume(req_obj->mon);
+        monitor_resume(mon);
     }
     qmp_request_free(req_obj);
 
@@ -4173,8 +4183,6 @@ static void monitor_qmp_bh_dispatcher(void *data)
     qemu_bh_schedule(qmp_dispatcher_bh);
 }
 
-#define  QMP_REQ_QUEUE_LEN_MAX  (8)
-
 static void handle_qmp_command(void *opaque, QObject *req, Error *err)
 {
     Monitor *mon = opaque;
@@ -4216,28 +4224,14 @@ static void handle_qmp_command(void *opaque, QObject *req, Error *err)
     qemu_mutex_lock(&mon->qmp.qmp_queue_lock);
 
     /*
-     * If OOB is not enabled on the current monitor, we'll emulate the
+     * Suspend the monitor when we can't queue more requests after
-     * old behavior that we won't process the current monitor any more
+     * this one.  Dequeuing in monitor_qmp_bh_dispatcher() will resume
-     * until it has responded.  This helps make sure that as long as
+     * it.  Note that when OOB is disabled, we queue at most one
-     * OOB is not enabled, the server will never drop any command.
+     * command, for backward compatibility.
      */
-    if (!qmp_oob_enabled(mon)) {
+    if (!qmp_oob_enabled(mon) ||
+        mon->qmp.qmp_requests->length == QMP_REQ_QUEUE_LEN_MAX - 1) {
         monitor_suspend(mon);
-    } else {
-        /* Drop the request if queue is full. */
-        if (mon->qmp.qmp_requests->length >= QMP_REQ_QUEUE_LEN_MAX) {
-            qemu_mutex_unlock(&mon->qmp.qmp_queue_lock);
-            /*
-             * FIXME @id's scope is just @mon, and broadcasting it is
-             * wrong.  If another monitor's client has a command with
-             * the same ID in flight, the event will incorrectly claim
-             * that command was dropped.
-             */
-            qapi_event_send_command_dropped(id,
-                                            COMMAND_DROP_REASON_QUEUE_FULL);
-            qmp_request_free(req_obj);
-            return;
-        }
     }
 
     /*
@@ -4245,6 +4239,7 @@ static void handle_qmp_command(void *opaque, QObject *req, Error *err)
      * handled in time order.  Ownership for req_obj, req, id,
      * etc. will be delivered to the handler side.
      */
+    assert(mon->qmp.qmp_requests->length < QMP_REQ_QUEUE_LEN_MAX);
     g_queue_push_tail(mon->qmp.qmp_requests, req_obj);
     qemu_mutex_unlock(&mon->qmp.qmp_queue_lock);
 
@@ -4297,7 +4292,7 @@ int monitor_suspend(Monitor *mon)
 
     atomic_inc(&mon->suspend_cnt);
 
-    if (monitor_is_qmp(mon) && mon->use_io_thread) {
+    if (mon->use_io_thread) {
         /*
          * Kick I/O thread to make sure this takes effect.  It'll be
          * evaluated again in prepare() of the watch object.
@@ -4309,6 +4304,13 @@ int monitor_suspend(Monitor *mon)
     return 0;
 }
 
+static void monitor_accept_input(void *opaque)
+{
+    Monitor *mon = opaque;
+
+    qemu_chr_fe_accept_input(&mon->chr);
+}
+
 void monitor_resume(Monitor *mon)
 {
     if (monitor_is_hmp_non_interactive(mon)) {
@@ -4316,20 +4318,22 @@ void monitor_resume(Monitor *mon)
     }
 
     if (atomic_dec_fetch(&mon->suspend_cnt) == 0) {
-        if (monitor_is_qmp(mon)) {
+        AioContext *ctx;
-            /*
+
-             * For QMP monitors that are running in the I/O thread,
+        if (mon->use_io_thread) {
-             * let's kick the thread in case it's sleeping.
+            ctx = iothread_get_aio_context(mon_iothread);
-             */
-            if (mon->use_io_thread) {
-                aio_notify(iothread_get_aio_context(mon_iothread));
-            }
         } else {
+            ctx = qemu_get_aio_context();
+        }
+
+        if (!monitor_is_qmp(mon)) {
             assert(mon->rs);
             readline_show_prompt(mon->rs);
         }
-        qemu_chr_fe_accept_input(&mon->chr);
+
+        aio_bh_schedule_oneshot(ctx, monitor_accept_input, mon);
     }
+
     trace_monitor_suspend(mon, -1);
 }
 
@@ -4453,16 +4457,6 @@ static void sortcmdlist(void)
     qsort((void *)info_cmds, array_num, elem_size, compare_mon_cmd);
 }
 
-static GMainContext *monitor_get_io_context(void)
-{
-    return iothread_get_g_main_context(mon_iothread);
-}
-
-static AioContext *monitor_get_aio_context(void)
-{
-    return iothread_get_aio_context(mon_iothread);
-}
-
 static void monitor_iothread_init(void)
 {
     mon_iothread = iothread_create("mon_iothread", &error_abort);
@@ -4539,8 +4533,21 @@ void error_vprintf_unless_qmp(const char *fmt, va_list ap)
 static void monitor_list_append(Monitor *mon)
 {
     qemu_mutex_lock(&monitor_lock);
-    QTAILQ_INSERT_HEAD(&mon_list, mon, entry);
+    /*
+     * This prevents inserting new monitors during monitor_cleanup().
+     * A cleaner solution would involve the main thread telling other
+     * threads to terminate, waiting for their termination.
+     */
+    if (!monitor_destroyed) {
+        QTAILQ_INSERT_HEAD(&mon_list, mon, entry);
+        mon = NULL;
+    }
     qemu_mutex_unlock(&monitor_lock);
+
+    if (mon) {
+        monitor_data_destroy(mon);
+        g_free(mon);
+    }
 }
 
 static void monitor_qmp_setup_handlers_bh(void *opaque)
@@ -4549,7 +4556,7 @@ static void monitor_qmp_setup_handlers_bh(void *opaque)
     GMainContext *context;
 
     assert(mon->use_io_thread);
-    context = monitor_get_io_context();
+    context = iothread_get_g_main_context(mon_iothread);
     assert(context);
     qemu_chr_fe_set_handlers(&mon->chr, monitor_can_read, monitor_qmp_read,
                              monitor_qmp_event, NULL, mon, context, true);
@@ -4560,21 +4567,12 @@ void monitor_init(Chardev *chr, int flags)
 {
     Monitor *mon = g_malloc(sizeof(*mon));
     bool use_readline = flags & MONITOR_USE_READLINE;
-    bool use_oob = flags & MONITOR_USE_OOB;
 
-    if (use_oob) {
+    /* Note: we run QMP monitor in I/O thread when @chr supports that */
-        if (CHARDEV_IS_MUX(chr)) {
+    monitor_data_init(mon, false,
-            error_report("Monitor out-of-band is not supported with "
+                      (flags & MONITOR_USE_CONTROL)
-                         "MUX typed chardev backend");
+                      && qemu_chr_has_feature(chr,
-            exit(1);
+                                              QEMU_CHAR_FEATURE_GCONTEXT));
-        }
-        if (use_readline) {
-            error_report("Monitor out-of-band is only supported by QMP");
-            exit(1);
-        }
-    }
-
-    monitor_data_init(mon, false, use_oob);
 
     qemu_chr_fe_init(&mon->chr, chr, &error_abort);
     mon->flags = flags;
@@ -4601,7 +4599,7 @@ void monitor_init(Chardev *chr, int flags)
              * since chardev might be running in the monitor I/O
              * thread.  Schedule a bottom half.
              */
-            aio_bh_schedule_oneshot(monitor_get_aio_context(),
+            aio_bh_schedule_oneshot(iothread_get_aio_context(mon_iothread),
                                     monitor_qmp_setup_handlers_bh, mon);
             /* The bottom half will add @mon to @mon_list */
             return;
@@ -4634,10 +4632,14 @@ void monitor_cleanup(void)
 
     /* Flush output buffers and destroy monitors */
     qemu_mutex_lock(&monitor_lock);
+    monitor_destroyed = true;
     QTAILQ_FOREACH_SAFE(mon, &mon_list, entry, next) {
         QTAILQ_REMOVE(&mon_list, mon, entry);
+        /* Permit QAPI event emission from character frontend release */
+        qemu_mutex_unlock(&monitor_lock);
         monitor_flush(mon);
         monitor_data_destroy(mon);
+        qemu_mutex_lock(&monitor_lock);
         g_free(mon);
     }
     qemu_mutex_unlock(&monitor_lock);
@@ -4665,9 +4667,6 @@ QemuOptsList qemu_mon_opts = {
         },{
             .name = "pretty",
             .type = QEMU_OPT_BOOL,
-        },{
-            .name = "x-oob",
-            .type = QEMU_OPT_BOOL,
         },
         { /* end of list */ }
     },

net/colo-compare.c

@@ -957,6 +957,12 @@ static int find_and_check_chardev(Chardev **chr,
         return 1;
     }
 
+    if (!qemu_chr_has_feature(*chr, QEMU_CHAR_FEATURE_GCONTEXT)) {
+        error_setg(errp, "chardev \"%s\" cannot switch context",
+                   chr_name);
+        return 1;
+    }
+
     return 0;
 }
 

qapi/misc.json

@@ -3444,46 +3444,6 @@
 ##
 { 'command': 'query-sev-capabilities', 'returns': 'SevCapability' }
 
-##
-# @CommandDropReason:
-#
-# Reasons that caused one command to be dropped.
-#
-# @queue-full: the command queue is full. This can only occur when
-#              the client sends a new non-oob command before the
-#              response to the previous non-oob command has been
-#              received.
-#
-# Since: 2.12
-##
-{ 'enum': 'CommandDropReason',
-  'data': [ 'queue-full' ] }
-
-##
-# @COMMAND_DROPPED:
-#
-# Emitted when a command is dropped due to some reason.  Commands can
-# only be dropped when the oob capability is enabled.
-#
-# @id: The dropped command's "id" field.
-# FIXME Broken by design.  Events are broadcast to all monitors.  If
-# another monitor's client has a command with the same ID in flight,
-# the event will incorrectly claim that command was dropped.
-#
-# @reason: The reason why the command is dropped.
-#
-# Since: 2.12
-#
-# Example:
-#
-# { "event": "COMMAND_DROPPED",
-#   "data": {"result": {"id": "libvirt-102",
-#                       "reason": "queue-full" } } }
-#
-##
-{ 'event': 'COMMAND_DROPPED' ,
-  'data': { 'id': 'any', 'reason': 'CommandDropReason' } }
-
 ##
 # @set-numa-node:
 #

tests/libqtest.c

@@ -187,8 +187,7 @@ static const char *qtest_qemu_binary(void)
     return qemu_bin;
 }
 
-QTestState *qtest_init_without_qmp_handshake(bool use_oob,
+QTestState *qtest_init_without_qmp_handshake(const char *extra_args)
-                                             const char *extra_args)
 {
     QTestState *s;
     int sock, qmpsock, i;
@@ -219,12 +218,12 @@ QTestState *qtest_init_without_qmp_handshake(bool use_oob,
                               "-qtest unix:%s,nowait "
                               "-qtest-log %s "
                               "-chardev socket,path=%s,nowait,id=char0 "
-                              "-mon chardev=char0,mode=control%s "
+                              "-mon chardev=char0,mode=control "
                               "-machine accel=qtest "
                               "-display none "
                               "%s", qemu_binary, socket_path,
                               getenv("QTEST_LOG") ? "/dev/fd/2" : "/dev/null",
-                              qmp_socket_path, use_oob ? ",x-oob=on" : "",
+                              qmp_socket_path,
                               extra_args ?: "");
 
     g_test_message("starting QEMU: %s", command);
@@ -266,7 +265,7 @@ QTestState *qtest_init_without_qmp_handshake(bool use_oob,
 
 QTestState *qtest_init(const char *extra_args)
 {
-    QTestState *s = qtest_init_without_qmp_handshake(false, extra_args);
+    QTestState *s = qtest_init_without_qmp_handshake(extra_args);
     QDict *greeting;
 
     /* Read the QMP greeting and then do the handshake */

tests/libqtest.h

@@ -55,14 +55,12 @@ QTestState *qtest_init(const char *extra_args);
 
 /**
  * qtest_init_without_qmp_handshake:
- * @use_oob: true to have the server advertise OOB support
  * @extra_args: other arguments to pass to QEMU.  CAUTION: these
  * arguments are subject to word splitting and shell evaluation.
  *
  * Returns: #QTestState instance.
  */
-QTestState *qtest_init_without_qmp_handshake(bool use_oob,
+QTestState *qtest_init_without_qmp_handshake(const char *extra_args);
-                                             const char *extra_args);
 
 /**
  * qtest_quit:

tests/qmp-test.c

@@ -108,7 +108,7 @@ static void test_qmp_protocol(void)
     QList *capabilities;
     QTestState *qts;
 
-    qts = qtest_init_without_qmp_handshake(false, common_args);
+    qts = qtest_init_without_qmp_handshake(common_args);
 
     /* Test greeting */
     resp = qtest_qmp_receive(qts);
@@ -116,7 +116,7 @@ static void test_qmp_protocol(void)
     g_assert(q);
     test_version(qdict_get(q, "version"));
     capabilities = qdict_get_qlist(q, "capabilities");
-    g_assert(capabilities && qlist_empty(capabilities));
+    g_assert(capabilities);
     qobject_unref(resp);
 
     /* Test valid command before handshake */
@@ -219,7 +219,7 @@ static void test_qmp_oob(void)
     QList *capabilities;
     QString *qstr;
 
-    qts = qtest_init_without_qmp_handshake(true, common_args);
+    qts = qtest_init_without_qmp_handshake(common_args);
 
     /* Check the greeting message. */
     resp = qtest_qmp_receive(qts);

tests/test-qmp-cmds.c

@@ -126,6 +126,21 @@ static void test_dispatch_cmd(void)
     qobject_unref(req);
 }
 
+static void test_dispatch_cmd_oob(void)
+{
+    QDict *req = qdict_new();
+    QDict *resp;
+
+    qdict_put_str(req, "exec-oob", "test-flags-command");
+
+    resp = qmp_dispatch(&qmp_commands, QOBJECT(req), true);
+    assert(resp != NULL);
+    assert(!qdict_haskey(resp, "error"));
+
+    qobject_unref(resp);
+    qobject_unref(req);
+}
+
 /* test commands that return an error due to invalid parameters */
 static void test_dispatch_cmd_failure(void)
 {
@@ -302,6 +317,7 @@ int main(int argc, char **argv)
     g_test_init(&argc, &argv, NULL);
 
     g_test_add_func("/qmp/dispatch_cmd", test_dispatch_cmd);
+    g_test_add_func("/qmp/dispatch_cmd_oob", test_dispatch_cmd_oob);
     g_test_add_func("/qmp/dispatch_cmd_failure", test_dispatch_cmd_failure);
     g_test_add_func("/qmp/dispatch_cmd_io", test_dispatch_cmd_io);
     g_test_add_func("/qmp/dispatch_cmd_success_response",

vl.c

@@ -2322,11 +2322,6 @@ static int mon_init_func(void *opaque, QemuOpts *opts, Error **errp)
     if (qemu_opt_get_bool(opts, "pretty", 0))
         flags |= MONITOR_USE_PRETTY;
 
-    /* OOB is off by default */
-    if (qemu_opt_get_bool(opts, "x-oob", 0)) {
-        flags |= MONITOR_USE_OOB;
-    }
-
     chardev = qemu_opt_get(opts, "chardev");
     if (!chardev) {
         error_report("chardev is required");