qmp: support out-of-band (oob) execution

Having "allow-oob":true for a command does not mean that this command
will always be run in out-of-band mode.  The out-of-band quick path will
only be executed if we specify the extra "run-oob" flag when sending the
QMP request:

    { "execute":   "command-that-allows-oob",
      "arguments": { ... },
      "control":   { "run-oob": true } }

The "control" key is introduced to store this extra flag.  "control"
field is used to store arguments that are shared by all the commands,
rather than command specific arguments.  Let "run-oob" be the first.

Note that in the patch I exported qmp_dispatch_check_obj() to be used to
check the request earlier, and at the same time allowed "id" field to be
there since actually we always allow that.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180309090006.10018-19-peterx@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[eblake: rebase to qobject_to(), spelling fix]
Signed-off-by: Eric Blake <eblake@redhat.com>

1 files changed, 75 insertions, 9 deletions

diff --git a/monitor.c b/monitor.c
index 017ddca6e2..405476fd09 100644
--- a/monitor.c
+++ b/monitor.c
@@ -1113,6 +1113,44 @@ static void qmp_caps_apply(Monitor *mon, QMPCapabilityList *list)
     }
 }
 
+/*
+ * Return true if check successful, or false otherwise.  When false is
+ * returned, detailed error will be in errp if provided.
+ */
+static bool qmp_cmd_oob_check(Monitor *mon, QDict *req, Error **errp)
+{
+    const char *command;
+    QmpCommand *cmd;
+
+    command = qdict_get_try_str(req, "execute");
+    if (!command) {
+        error_setg(errp, "Command field 'execute' missing");
+        return false;
+    }
+
+    cmd = qmp_find_command(mon->qmp.commands, command);
+    if (!cmd) {
+        error_set(errp, ERROR_CLASS_COMMAND_NOT_FOUND,
+                  "The command %s has not been found", command);
+        return false;
+    }
+
+    if (qmp_is_oob(req)) {
+        if (!qmp_oob_enabled(mon)) {
+            error_setg(errp, "Please enable Out-Of-Band first "
+                       "for the session during capabilities negotiation");
+            return false;
+        }
+        if (!(cmd->options & QCO_ALLOW_OOB)) {
+            error_setg(errp, "The command %s does not support OOB",
+                       command);
+            return false;
+        }
+    }
+
+    return true;
+}
+
 void qmp_qmp_capabilities(bool has_enable, QMPCapabilityList *enable,
                           Error **errp)
 {
@@ -4004,6 +4042,7 @@ static void monitor_qmp_bh_dispatcher(void *data)
     QMPRequest *req_obj = monitor_qmp_requests_pop_one();
 
     if (req_obj) {
+        trace_monitor_qmp_cmd_in_band(qobject_get_try_str(req_obj->id) ?: "");
         monitor_qmp_dispatch_one(req_obj);
         /* Reschedule instead of looping so the main loop stays responsive */
         qemu_bh_schedule(mon_global.qmp_dispatcher_bh);
@@ -4027,17 +4066,31 @@ static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
         error_setg(&err, QERR_JSON_PARSING);
     }
     if (err) {
-        monitor_qmp_respond(mon, NULL, err, NULL);
-        qobject_decref(req);
-        return;
+        goto err;
+    }
+
+    /* Check against the request in general layout */
+    qdict = qmp_dispatch_check_obj(req, &err);
+    if (!qdict) {
+        goto err;
     }
 
-    qdict = qobject_to(QDict, req);
-    if (qdict) {
-        id = qdict_get(qdict, "id");
-        qobject_incref(id);
-        qdict_del(qdict, "id");
-    } /* else will fail qmp_dispatch() */
+    /* Check against OOB specific */
+    if (!qmp_cmd_oob_check(mon, qdict, &err)) {
+        goto err;
+    }
+
+    id = qdict_get(qdict, "id");
+
+    /* When OOB is enabled, the "id" field is mandatory. */
+    if (qmp_oob_enabled(mon) && !id) {
+        error_setg(&err, "Out-Of-Band capability requires that "
+                   "every command contains an 'id' field");
+        goto err;
+    }
+
+    qobject_incref(id);
+    qdict_del(qdict, "id");
 
     req_obj = g_new0(QMPRequest, 1);
     req_obj->mon = mon;
@@ -4045,6 +4098,14 @@ static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
     req_obj->req = req;
     req_obj->need_resume = false;
 
+    if (qmp_is_oob(qdict)) {
+        /* Out-Of-Band (OOB) requests are executed directly in parser. */
+        trace_monitor_qmp_cmd_out_of_band(qobject_get_try_str(req_obj->id)
+                                          ?: "");
+        monitor_qmp_dispatch_one(req_obj);
+        return;
+    }
+
     /* Protect qmp_requests and fetching its length. */
     qemu_mutex_lock(&mon->qmp.qmp_queue_lock);
 
@@ -4081,6 +4142,11 @@ static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
 
     /* Kick the dispatcher routine */
     qemu_bh_schedule(mon_global.qmp_dispatcher_bh);
+    return;
+
+err:
+    monitor_qmp_respond(mon, NULL, err, NULL);
+    qobject_decref(req);
 }
 
 static void monitor_qmp_read(void *opaque, const uint8_t *buf, int size)