Merge default into bug23554

9 files changed, 229 insertions, 150 deletions

diff --git a/docs/rabbitmqctl.1.xml b/docs/rabbitmqctl.1.xml
index 908ca97372..b825a1d0da 100644
--- a/docs/rabbitmqctl.1.xml
+++ b/docs/rabbitmqctl.1.xml
@@ -624,14 +624,31 @@
           </listitem>
         </varlistentry>
 
-        <varlistentry>
-          <term><cmdsynopsis><command>list_vhosts</command></cmdsynopsis></term>
+        <varlistentry role="usage-has-option-list">
+          <term><cmdsynopsis><command>list_vhosts</command> <arg choice="opt" role="usage-option-list"><replaceable>vhostinfoitem</replaceable> ...</arg></cmdsynopsis></term>
           <listitem>
             <para>
               Lists virtual hosts.
             </para>
+            <para>
+              The <command>vhostinfoitem</command> parameter is used to indicate which
+              virtual host information items to include in the results. The column order in the
+              results will match the order of the parameters.
+              <command>vhostinfoitem</command> can take any value from
+              the list that follows:
+            </para>
+            <variablelist>
+              <varlistentry>
+                <term>name</term>
+                <listitem><para>The name of the virtual host with non-ASCII characters escaped as in C.</para></listitem>
+              </varlistentry>
+              <varlistentry>
+                <term>tracing</term>
+                <listitem><para>Whether tracing is enabled for this virtual host.</para></listitem>
+              </varlistentry>
+            </variablelist>
             <para role="example-prefix">For example:</para>
-            <screen role="example">rabbitmqctl list_vhosts</screen>
+            <screen role="example">rabbitmqctl list_vhosts name tracing</screen>
             <para role="example">
               This command instructs the RabbitMQ broker to list all
               virtual hosts.
@@ -1266,59 +1283,34 @@
     </refsect2>
 
     <refsect2>
-      <title>Configuration variables</title>
-      <para>
-        Some configuration values can be changed at run time. Note
-        that this does not apply to all variables; many are only read
-        at startup - changing them will have no effect.
-      </para>
+      <title>Message Tracing</title>
       <variablelist>
         <varlistentry>
-          <term><cmdsynopsis><command>set_env</command> <arg choice="req"><replaceable>variable</replaceable></arg> <arg choice="req"><replaceable>value</replaceable></arg></cmdsynopsis></term>
+          <term><cmdsynopsis><command>trace_on</command> <arg choice="opt">-p <replaceable>vhost</replaceable></arg></cmdsynopsis></term>
           <listitem>
             <variablelist>
               <varlistentry>
-                <term>variable</term>
-                <listitem><para>The name of the variable to set, as the string form of an Erlang term.</para></listitem>
-              </varlistentry>
-              <varlistentry>
-                <term>value</term>
-                <listitem><para>The value to set it to, as the string form of an Erlang term.</para></listitem>
-              </varlistentry>
-            </variablelist>
-            <para>
-              Set the value of a configuration variable.
-            </para>
-          </listitem>
-        </varlistentry>
-
-        <varlistentry>
-          <term><cmdsynopsis><command>get_env</command> <arg choice="req"><replaceable>variable</replaceable></arg></cmdsynopsis></term>
-          <listitem>
-            <variablelist>
-              <varlistentry>
-                <term>variable</term>
-                <listitem><para>The name of the variable to get, as the string form of an Erlang term.</para></listitem>
+                <term>vhost</term>
+                <listitem><para>The name of the virtual host for which to start tracing.</para></listitem>
               </varlistentry>
             </variablelist>
             <para>
-              Get the value of a configuration variable, printing either
-              {ok,<command>Value</command>} or undefined.
+              Starts tracing.
             </para>
           </listitem>
         </varlistentry>
 
         <varlistentry>
-          <term><cmdsynopsis><command>unset_env</command> <arg choice="req"><replaceable>variable</replaceable></arg></cmdsynopsis></term>
+          <term><cmdsynopsis><command>trace_off</command> <arg choice="opt">-p <replaceable>vhost</replaceable></arg></cmdsynopsis></term>
           <listitem>
             <variablelist>
               <varlistentry>
-                <term>variable</term>
-                <listitem><para>The name of the variable to clear, as the string form of an Erlang term.</para></listitem>
+                <term>vhost</term>
+                <listitem><para>The name of the virtual host for which to stop tracing.</para></listitem>
               </varlistentry>
             </variablelist>
             <para>
-              Clear the value of a configuration variable.
+              Stops tracing.
             </para>
           </listitem>
         </varlistentry>
diff --git a/ebin/rabbit_app.in b/ebin/rabbit_app.in
index 014c18b0c6..7dabb8c346 100644
--- a/ebin/rabbit_app.in
+++ b/ebin/rabbit_app.in
@@ -36,6 +36,7 @@
          {auth_mechanisms, ['PLAIN', 'AMQPLAIN']},
          {auth_backends, [rabbit_auth_backend_internal]},
          {delegate_count, 16},
+         {trace_vhosts, []},
          {tcp_listen_options, [binary,
                                {packet,        raw},
                                {reuseaddr,     true},
diff --git a/src/rabbit_basic.erl b/src/rabbit_basic.erl
index 3cf73e80d2..fa7e3a5ac0 100644
--- a/src/rabbit_basic.erl
+++ b/src/rabbit_basic.erl
@@ -32,6 +32,9 @@
         ({ok, rabbit_router:routing_result(), [pid()]}
          | rabbit_types:error('not_found'))).
 
+-type(exchange_input() :: (rabbit_types:exchange() | rabbit_exchange:name())).
+-type(body_input() :: (binary() | [binary()])).
+
 -spec(publish/1 ::
         (rabbit_types:delivery()) -> publish_result()).
 -spec(delivery/5 ::
@@ -48,14 +51,14 @@
 -spec(properties/1 ::
         (properties_input()) -> rabbit_framing:amqp_property_record()).
 -spec(publish/4 ::
-        (rabbit_exchange:name(), rabbit_router:routing_key(),
-         properties_input(), binary()) -> publish_result()).
+        (exchange_input(), rabbit_router:routing_key(), properties_input(),
+         body_input()) -> publish_result()).
 -spec(publish/7 ::
-        (rabbit_exchange:name(), rabbit_router:routing_key(),
-         boolean(), boolean(), rabbit_types:maybe(rabbit_types:txn()),
-         properties_input(), binary()) -> publish_result()).
--spec(build_content/2 :: (rabbit_framing:amqp_property_record(), binary()) ->
-                              rabbit_types:content()).
+        (exchange_input(), rabbit_router:routing_key(), boolean(), boolean(),
+         rabbit_types:maybe(rabbit_types:txn()), properties_input(),
+         body_input()) -> publish_result()).
+-spec(build_content/2 :: (rabbit_framing:amqp_property_record(),
+                          binary() | [binary()]) -> rabbit_types:content()).
 -spec(from_content/1 :: (rabbit_types:content()) ->
                              {rabbit_framing:amqp_property_record(), binary()}).
 
@@ -66,18 +69,18 @@
 publish(Delivery = #delivery{
           message = #basic_message{exchange_name = ExchangeName}}) ->
     case rabbit_exchange:lookup(ExchangeName) of
-        {ok, X} ->
-            {RoutingRes, DeliveredQPids} = rabbit_exchange:publish(X, Delivery),
-            {ok, RoutingRes, DeliveredQPids};
-        Other ->
-            Other
+        {ok, X} -> publish(X, Delivery);
+        Other   -> Other
     end.
 
 delivery(Mandatory, Immediate, Txn, Message, MsgSeqNo) ->
     #delivery{mandatory = Mandatory, immediate = Immediate, txn = Txn,
               sender = self(), message = Message, msg_seq_no = MsgSeqNo}.
 
-build_content(Properties, BodyBin) ->
+build_content(Properties, BodyBin) when is_binary(BodyBin) ->
+    build_content(Properties, [BodyBin]);
+
+build_content(Properties, PFR) ->
     %% basic.publish hasn't changed so we can just hard-code amqp_0_9_1
     {ClassId, _MethodId} =
         rabbit_framing_amqp_0_9_1:method_id('basic.publish'),
@@ -85,7 +88,7 @@ build_content(Properties, BodyBin) ->
              properties = Properties,
              properties_bin = none,
              protocol = none,
-             payload_fragments_rev = [BodyBin]}.
+             payload_fragments_rev = PFR}.
 
 from_content(Content) ->
     #content{class_id = ClassId,
@@ -126,9 +129,9 @@ message(ExchangeName, RoutingKey,
         {error, _Reason} = Error -> Error
     end.
 
-message(ExchangeName, RoutingKey, RawProperties, BodyBin) ->
+message(ExchangeName, RoutingKey, RawProperties, Body) ->
     Properties = properties(RawProperties),
-    Content = build_content(Properties, BodyBin),
+    Content = build_content(Properties, Body),
     {ok, Msg} = message(ExchangeName, RoutingKey, Content),
     Msg.
 
@@ -153,18 +156,26 @@ indexof([_ | Rest], Element, N)        -> indexof(Rest, Element, N + 1).
 
 %% Convenience function, for avoiding round-trips in calls across the
 %% erlang distributed network.
-publish(ExchangeName, RoutingKeyBin, Properties, BodyBin) ->
-    publish(ExchangeName, RoutingKeyBin, false, false, none, Properties,
-            BodyBin).
+publish(Exchange, RoutingKeyBin, Properties, Body) ->
+    publish(Exchange, RoutingKeyBin, false, false, none, Properties,
+            Body).
 
 %% Convenience function, for avoiding round-trips in calls across the
 %% erlang distributed network.
-publish(ExchangeName, RoutingKeyBin, Mandatory, Immediate, Txn, Properties,
-        BodyBin) ->
-    publish(delivery(Mandatory, Immediate, Txn,
-                     message(ExchangeName, RoutingKeyBin,
-                             properties(Properties), BodyBin),
-                     undefined)).
+publish(X = #exchange{name = XName}, RKey, Mandatory, Immediate, Txn,
+        Props, Body) ->
+    publish(X, delivery(Mandatory, Immediate, Txn,
+                        message(XName, RKey, properties(Props), Body),
+                        undefined));
+publish(XName, RKey, Mandatory, Immediate, Txn, Props, Body) ->
+    case rabbit_exchange:lookup(XName) of
+        {ok, X} -> publish(X, RKey, Mandatory, Immediate, Txn, Props, Body);
+        Err     -> Err
+    end.
+
+publish(X, Delivery) ->
+    {RoutingRes, DeliveredQPids} = rabbit_exchange:publish(X, Delivery),
+    {ok, RoutingRes, DeliveredQPids}.
 
 is_message_persistent(#content{properties = #'P_basic'{
                                  delivery_mode = Mode}}) ->
diff --git a/src/rabbit_channel.erl b/src/rabbit_channel.erl
index f078886224..991b0b065c 100644
--- a/src/rabbit_channel.erl
+++ b/src/rabbit_channel.erl
@@ -23,7 +23,7 @@
 -export([start_link/10, do/2, do/3, flush/1, shutdown/1]).
 -export([send_command/2, deliver/4, flushed/2, confirm/2]).
 -export([list/0, info_keys/0, info/1, info/2, info_all/0, info_all/1]).
--export([emit_stats/1, ready_for_close/1]).
+-export([refresh_config_all/0, emit_stats/1, ready_for_close/1]).
 
 -export([init/1, terminate/2, code_change/3, handle_call/3, handle_cast/2,
          handle_info/2, handle_pre_hibernate/1, prioritise_call/3,
@@ -35,7 +35,7 @@
              user, virtual_host, most_recently_declared_queue,
              consumer_mapping, blocking, consumer_monitors, queue_collector_pid,
              stats_timer, confirm_enabled, publish_seqno, unconfirmed_mq,
-             unconfirmed_qm, confirmed, capabilities}).
+             unconfirmed_qm, confirmed, capabilities, trace_state}).
 
 -define(MAX_PERMISSION_CACHE_SIZE, 12).
 
@@ -89,6 +89,7 @@
 -spec(info/2 :: (pid(), rabbit_types:info_keys()) -> rabbit_types:infos()).
 -spec(info_all/0 :: () -> [rabbit_types:infos()]).
 -spec(info_all/1 :: (rabbit_types:info_keys()) -> [rabbit_types:infos()]).
+-spec(refresh_config_all/0 :: () -> 'ok').
 -spec(emit_stats/1 :: (pid()) -> 'ok').
 -spec(ready_for_close/1 :: (pid()) -> 'ok').
 
@@ -146,6 +147,11 @@ info_all() ->
 info_all(Items) ->
     rabbit_misc:filter_exit_map(fun (C) -> info(C, Items) end, list()).
 
+refresh_config_all() ->
+    rabbit_misc:upmap(
+      fun (C) -> gen_server2:call(C, refresh_config) end, list()),
+    ok.
+
 emit_stats(Pid) ->
     gen_server2:cast(Pid, emit_stats).
 
@@ -185,7 +191,8 @@ init([Channel, ReaderPid, WriterPid, ConnPid, Protocol, User, VHost,
                 unconfirmed_mq          = gb_trees:empty(),
                 unconfirmed_qm          = gb_trees:empty(),
                 confirmed               = [],
-                capabilities            = Capabilities},
+                capabilities            = Capabilities,
+                trace_state             = rabbit_trace:init(VHost)},
     rabbit_event:notify(channel_created, infos(?CREATION_EVENT_KEYS, State)),
     rabbit_event:if_enabled(StatsTimer,
                             fun() -> internal_emit_stats(State) end),
@@ -218,6 +225,9 @@ handle_call({info, Items}, _From, State) ->
     catch Error -> reply({error, Error}, State)
     end;
 
+handle_call(refresh_config, _From, State = #ch{virtual_host = VHost}) ->
+    reply(ok, State#ch{trace_state = rabbit_trace:init(VHost)});
+
 handle_call(_Request, _From, State) ->
     noreply(State).
 
@@ -263,8 +273,9 @@ handle_cast({deliver, ConsumerTag, AckRequired,
                     #basic_message{exchange_name = ExchangeName,
                                    routing_keys = [RoutingKey | _CcRoutes],
                                    content = Content}}},
-            State = #ch{writer_pid = WriterPid,
-                        next_tag = DeliveryTag}) ->
+            State = #ch{writer_pid  = WriterPid,
+                        next_tag    = DeliveryTag,
+                        trace_state = TraceState}) ->
     State1 = lock_message(AckRequired,
                           ack_record(DeliveryTag, ConsumerTag, Msg),
                           State),
@@ -281,7 +292,7 @@ handle_cast({deliver, ConsumerTag, AckRequired,
                          true  -> deliver;
                          false -> deliver_no_ack
                      end, State),
-    rabbit_trace:tap_trace_out(Msg),
+    rabbit_trace:tap_trace_out(Msg, TraceState),
     noreply(State1#ch{next_tag = DeliveryTag + 1});
 
 handle_cast(emit_stats, State = #ch{stats_timer = StatsTimer}) ->
@@ -591,7 +602,8 @@ handle_method(#'basic.publish'{exchange    = ExchangeNameBin,
                                immediate   = Immediate},
               Content, State = #ch{virtual_host    = VHostPath,
                                    transaction_id  = TxnKey,
-                                   confirm_enabled = ConfirmEnabled}) ->
+                                   confirm_enabled = ConfirmEnabled,
+                                   trace_state     = TraceState}) ->
     ExchangeName = rabbit_misc:r(VHostPath, exchange, ExchangeNameBin),
     check_write_permitted(ExchangeName, State),
     Exchange = rabbit_exchange:lookup_or_die(ExchangeName),
@@ -608,7 +620,7 @@ handle_method(#'basic.publish'{exchange    = ExchangeNameBin,
         end,
     case rabbit_basic:message(ExchangeName, RoutingKey, DecodedContent) of
         {ok, Message} ->
-            rabbit_trace:tap_trace_in(Message),
+            rabbit_trace:tap_trace_in(Message, TraceState),
             {RoutingRes, DeliveredQPids} =
                 rabbit_exchange:publish(
                   Exchange,
@@ -656,9 +668,10 @@ handle_method(#'basic.ack'{delivery_tag = DeliveryTag,
 
 handle_method(#'basic.get'{queue = QueueNameBin,
                            no_ack = NoAck},
-              _, State = #ch{writer_pid = WriterPid,
-                             conn_pid   = ConnPid,
-                             next_tag   = DeliveryTag}) ->
+              _, State = #ch{writer_pid  = WriterPid,
+                             conn_pid    = ConnPid,
+                             next_tag    = DeliveryTag,
+                             trace_state = TraceState}) ->
     QueueName = expand_queue_name_shortcut(QueueNameBin, State),
     check_read_permitted(QueueName, State),
     case rabbit_amqqueue:with_exclusive_access_or_die(
@@ -677,7 +690,7 @@ handle_method(#'basic.get'{queue = QueueNameBin,
                                  true  -> get_no_ack;
                                  false -> get
                              end, State),
-            rabbit_trace:tap_trace_out(Msg),
+            rabbit_trace:tap_trace_out(Msg, TraceState),
             ok = rabbit_writer:send_command(
                    WriterPid,
                    #'basic.get_ok'{delivery_tag = DeliveryTag,
diff --git a/src/rabbit_control.erl b/src/rabbit_control.erl
index b4b6255ebd..117496f561 100644
--- a/src/rabbit_control.erl
+++ b/src/rabbit_control.erl
@@ -221,9 +221,10 @@ action(delete_vhost, Node, Args = [_VHostPath], _Opts, Inform) ->
     Inform("Deleting vhost ~p", Args),
     call(Node, {rabbit_vhost, delete, Args});
 
-action(list_vhosts, Node, [], _Opts, Inform) ->
+action(list_vhosts, Node, Args, _Opts, Inform) ->
     Inform("Listing vhosts", []),
-    display_list(call(Node, {rabbit_vhost, list, []}));
+    ArgAtoms = default_if_empty(Args, [name]),
+    display_info_list(call(Node, {rabbit_vhost, info_all, []}), ArgAtoms);
 
 action(list_user_permissions, Node, Args = [_Username], _Opts, Inform) ->
     Inform("Listing permissions for user ~p", Args),
@@ -294,18 +295,15 @@ action(list_consumers, Node, _Args, Opts, Inform) ->
         Other             -> Other
     end;
 
-action(set_env, Node, [Var, Term], _Opts, Inform) ->
-    Inform("Setting control variable ~s for node ~p to ~s", [Var, Node, Term]),
-    rpc_call(Node, application, set_env, [rabbit, parse(Var), parse(Term)]);
-
-action(get_env, Node, [Var], _Opts, Inform) ->
-    Inform("Getting control variable ~s for node ~p", [Var, Node]),
-    Val = rpc_call(Node, application, get_env, [rabbit, parse(Var)]),
-    io:format("~p~n", [Val]);
+action(trace_on, Node, [], Opts, Inform) ->
+    VHost = proplists:get_value(?VHOST_OPT, Opts),
+    Inform("Starting tracing for vhost ~p", [VHost]),
+    rpc_call(Node, rabbit_trace, start, [list_to_binary(VHost)]);
 
-action(unset_env, Node, [Var], _Opts, Inform) ->
-    Inform("Clearing control variable ~s for node ~p", [Var, Node]),
-    rpc_call(Node, application, unset_env, [rabbit, parse(Var)]);
+action(trace_off, Node, [], Opts, Inform) ->
+    VHost = proplists:get_value(?VHOST_OPT, Opts),
+    Inform("Stopping tracing for vhost ~p", [VHost]),
+    rpc_call(Node, rabbit_trace, stop, [list_to_binary(VHost)]);
 
 action(set_permissions, Node, [Username, CPerm, WPerm, RPerm], Opts, Inform) ->
     VHost = proplists:get_value(?VHOST_OPT, Opts),
@@ -350,11 +348,6 @@ default_if_empty(List, Default) when is_list(List) ->
        true       -> [list_to_atom(X) || X <- List]
     end.
 
-parse(Str) ->
-    {ok, Tokens, _} = erl_scan:string(Str ++ "."),
-    {ok, Term} = erl_parse:parse_term(Tokens),
-    Term.
-
 display_info_list(Results, InfoItemKeys) when is_list(Results) ->
     lists:foreach(
       fun (Result) -> display_row(
diff --git a/src/rabbit_prelaunch.erl b/src/rabbit_prelaunch.erl
index 2512a60280..92829e4918 100644
--- a/src/rabbit_prelaunch.erl
+++ b/src/rabbit_prelaunch.erl
@@ -69,9 +69,13 @@ start() ->
     %% Write it out to $RABBITMQ_PLUGINS_EXPAND_DIR/rabbit.rel
     rabbit_misc:write_file(RootName ++ ".rel", io_lib:format("~p.~n", [RDesc])),
 
+    %% We exclude mochiweb due to its optional use of fdsrv.
+    XRefExclude = [mochiweb],
+
     %% Compile the script
     ScriptFile = RootName ++ ".script",
-    case systools:make_script(RootName, [local, silent, exref]) of
+    case systools:make_script(RootName, [local, silent,
+                                         {exref, AllApps -- XRefExclude}]) of
         {ok, Module, Warnings} ->
             %% This gets lots of spurious no-source warnings when we
             %% have .ez files, so we want to supress them to prevent
@@ -93,7 +97,8 @@ start() ->
                                  end]),
             case length(WarningStr) of
                 0 -> ok;
-                _ -> io:format("~s", [WarningStr])
+                _ -> S = string:copies("*", 80),
+                     io:format("~n~s~n~s~s~n~n", [S, WarningStr, S])
             end,
             ok;
         {error, Module, Error} ->
diff --git a/src/rabbit_trace.erl b/src/rabbit_trace.erl
index 2d15e7fc42..7d36856a9d 100644
--- a/src/rabbit_trace.erl
+++ b/src/rabbit_trace.erl
@@ -16,85 +16,104 @@
 
 -module(rabbit_trace).
 
--export([tap_trace_in/1, tap_trace_out/1]).
+-export([init/1, tracing/1, tap_trace_in/2, tap_trace_out/2, start/1, stop/1]).
 
 -include("rabbit.hrl").
 -include("rabbit_framing.hrl").
 
+-define(TRACE_VHOSTS, trace_vhosts).
+-define(XNAME, <<"amq.rabbitmq.trace">>).
+
 %%----------------------------------------------------------------------------
 
 -ifdef(use_specs).
 
--spec(tap_trace_in/1 :: (rabbit_types:basic_message()) -> 'ok').
--spec(tap_trace_out/1 :: (rabbit_amqqueue:qmsg()) -> 'ok').
+-type(state() :: rabbit_types:exchange() | 'none').
+
+-spec(init/1 :: (rabbit_types:vhost()) -> state()).
+-spec(tracing/1 :: (rabbit_types:vhost()) -> boolean()).
+-spec(tap_trace_in/2 :: (rabbit_types:basic_message(), state()) -> 'ok').
+-spec(tap_trace_out/2 :: (rabbit_amqqueue:qmsg(), state()) -> 'ok').
+
+-spec(start/1 :: (rabbit_types:vhost()) -> 'ok').
+-spec(stop/1 :: (rabbit_types:vhost()) -> 'ok').
 
 -endif.
 
 %%----------------------------------------------------------------------------
 
-tap_trace_in(Msg) ->
-    maybe_trace(Msg, <<"publish">>, xname(Msg), []).
+init(VHost) ->
+    case tracing(VHost) of
+        false -> none;
+        true  -> {ok, X} = rabbit_exchange:lookup(
+                             rabbit_misc:r(VHost, exchange, ?XNAME)),
+                 X
+    end.
+
+tracing(VHost) ->
+    {ok, VHosts} = application:get_env(rabbit, ?TRACE_VHOSTS),
+    lists:member(VHost, VHosts).
+
+tap_trace_in(Msg = #basic_message{exchange_name = #resource{name = XName}},
+             TraceX) ->
+    maybe_trace(TraceX, Msg, <<"publish">>, XName, []).
 
-tap_trace_out({#resource{name = QName}, _QPid, _QMsgId, Redelivered, Msg}) ->
+tap_trace_out({#resource{name = QName}, _QPid, _QMsgId, Redelivered, Msg},
+              TraceX) ->
     RedeliveredNum = case Redelivered of true -> 1; false -> 0 end,
-    maybe_trace(Msg, <<"deliver">>, QName,
+    maybe_trace(TraceX, Msg, <<"deliver">>, QName,
                 [{<<"redelivered">>, signedint, RedeliveredNum}]).
 
-xname(#basic_message{exchange_name = #resource{name         = XName}}) -> XName.
-vhost(#basic_message{exchange_name = #resource{virtual_host = VHost}}) -> VHost.
-
-maybe_trace(Msg, RKPrefix, RKSuffix, Extra) ->
-    XName = xname(Msg),
-    case trace_exchange(vhost(Msg)) of
-        none   -> ok;
-        XName  -> ok;
-        TraceX -> case catch trace(TraceX, Msg, RKPrefix, RKSuffix, Extra) of
-                      {'EXIT', R} -> rabbit_log:info("Trace died: ~p~n", [R]);
-                      ok          -> ok
-                  end
-    end.
+%%----------------------------------------------------------------------------
 
-trace_exchange(VHost) ->
-    case application:get_env(rabbit, trace_exchanges) of
-        undefined  -> none;
-        {ok, Xs}   -> proplists:get_value(VHost, Xs, none)
-    end.
+start(VHost) ->
+    update_config(fun (VHosts) -> [VHost | VHosts -- [VHost]] end).
+
+stop(VHost) ->
+    update_config(fun (VHosts) -> VHosts -- [VHost] end).
+
+update_config(Fun) ->
+    {ok, VHosts0} = application:get_env(rabbit, ?TRACE_VHOSTS),
+    VHosts = Fun(VHosts0),
+    application:set_env(rabbit, ?TRACE_VHOSTS, VHosts),
+    rabbit_channel:refresh_config_all(),
+    ok.
 
-trace(TraceX, Msg0, RKPrefix, RKSuffix, Extra) ->
-    Msg = ensure_content_decoded(Msg0),
-    rabbit_basic:publish(rabbit_misc:r(vhost(Msg), exchange, TraceX),
-                         <<RKPrefix/binary, ".", RKSuffix/binary>>,
-                         #'P_basic'{headers = msg_to_table(Msg) ++ Extra},
-                         payload(Msg)),
+%%----------------------------------------------------------------------------
+
+maybe_trace(none, _Msg, _RKPrefix, _RKSuffix, _Extra) ->
+    ok;
+maybe_trace(#exchange{name = Name}, #basic_message{exchange_name = Name},
+            _RKPrefix, _RKSuffix, _Extra) ->
+    ok;
+maybe_trace(X, Msg = #basic_message{content = #content{
+                                      payload_fragments_rev = PFR}},
+            RKPrefix, RKSuffix, Extra) ->
+    {ok, _, _} = rabbit_basic:publish(
+                   X, <<RKPrefix/binary, ".", RKSuffix/binary>>,
+                   #'P_basic'{headers = msg_to_table(Msg) ++ Extra}, PFR),
     ok.
 
 msg_to_table(#basic_message{exchange_name = #resource{name = XName},
                             routing_keys  = RoutingKeys,
-                            content       = #content{properties = Props}}) ->
+                            content       = Content}) ->
+    #content{properties = Props} =
+        rabbit_binary_parser:ensure_content_decoded(Content),
     {PropsTable, _Ix} =
-        lists:foldl(
-          fun (K, {L, Ix}) ->
-                  V = element(Ix, Props),
-                  NewL = case V of
-                             undefined -> L;
-                             _         -> [{a2b(K), type(V), V} | L]
-                         end,
-                  {NewL, Ix + 1}
-          end, {[], 2}, record_info(fields, 'P_basic')),
+        lists:foldl(fun (K, {L, Ix}) ->
+                            V = element(Ix, Props),
+                            NewL = case V of
+                                       undefined -> L;
+                                       _         -> [{a2b(K), type(V), V} | L]
+                                   end,
+                            {NewL, Ix + 1}
+                    end, {[], 2}, record_info(fields, 'P_basic')),
     [{<<"exchange_name">>, longstr, XName},
      {<<"routing_keys">>,  array,   [{longstr, K} || K <- RoutingKeys]},
      {<<"properties">>,    table,   PropsTable},
      {<<"node">>,          longstr, a2b(node())}].
 
-payload(#basic_message{content = #content{payload_fragments_rev = PFR}}) ->
-    list_to_binary(lists:reverse(PFR)).
-
-ensure_content_decoded(Msg = #basic_message{content = Content}) ->
-    Msg#basic_message{content = rabbit_binary_parser:ensure_content_decoded(
-                                  Content)}.
-
-a2b(A) ->
-    list_to_binary(atom_to_list(A)).
+a2b(A) -> list_to_binary(atom_to_list(A)).
 
 type(V) when is_list(V)    -> table;
 type(V) when is_integer(V) -> signedint;
diff --git a/src/rabbit_upgrade_functions.erl b/src/rabbit_upgrade_functions.erl
index 325156b1f3..a6f02a0e0a 100644
--- a/src/rabbit_upgrade_functions.erl
+++ b/src/rabbit_upgrade_functions.erl
@@ -28,6 +28,7 @@
 -rabbit_upgrade({topic_trie,            mnesia, []}).
 -rabbit_upgrade({semi_durable_route,    mnesia, []}).
 -rabbit_upgrade({exchange_event_serial, mnesia, []}).
+-rabbit_upgrade({trace_exchanges,       mnesia, []}).
 -rabbit_upgrade({mirror_pids,           mnesia, []}).
 
 %% -------------------------------------------------------------------
@@ -42,6 +43,7 @@
 -spec(topic_trie/0 :: () -> 'ok').
 -spec(exchange_event_serial/0 :: () -> 'ok').
 -spec(semi_durable_route/0 :: () -> 'ok').
+-spec(trace_exchanges/0 :: () -> 'ok').
 -spec(mirror_pids/0 :: () -> 'ok').
 
 -endif.
@@ -115,6 +117,12 @@ exchange_event_serial() ->
     create(rabbit_exchange_serial, [{record_name, exchange_serial},
                                     {attributes, [name, next]}]).
 
+trace_exchanges() ->
+    [declare_exchange(
+       rabbit_misc:r(VHost, exchange, <<"amq.rabbitmq.trace">>), topic) ||
+        VHost <- rabbit_vhost:list()],
+    ok.
+
 mirror_pids() ->
     Tables = [rabbit_queue, rabbit_durable_queue],
     AddMirrorPidsFun =
@@ -144,3 +152,16 @@ transform(TableName, Fun, FieldList, NewRecordName) ->
 create(Tab, TabDef) ->
     {atomic, ok} = mnesia:create_table(Tab, TabDef),
     ok.
+
+%% Dumb replacement for rabbit_exchange:declare that does not require
+%% the exchange type registry or worker pool to be running by dint of
+%% not validating anything and assuming the exchange type does not
+%% require serialisation.
+declare_exchange(XName, Type) ->
+    X = #exchange{name        = XName,
+                  type        = Type,
+                  durable     = true,
+                  auto_delete = false,
+                  internal    = false,
+                  arguments   = []},
+    ok = mnesia:dirty_write(rabbit_durable_exchange, X).
diff --git a/src/rabbit_vhost.erl b/src/rabbit_vhost.erl
index 24c130edd6..5270d80bd5 100644
--- a/src/rabbit_vhost.erl
+++ b/src/rabbit_vhost.erl
@@ -21,6 +21,7 @@
 %%----------------------------------------------------------------------------
 
 -export([add/1, delete/1, exists/1, list/0, with/2]).
+-export([info/1, info/2, info_all/0, info_all/1]).
 
 -ifdef(use_specs).
 
@@ -30,10 +31,18 @@
 -spec(list/0 :: () -> [rabbit_types:vhost()]).
 -spec(with/2 :: (rabbit_types:vhost(), rabbit_misc:thunk(A)) -> A).
 
+-spec(info/1 :: (rabbit_types:vhost()) -> rabbit_types:infos()).
+-spec(info/2 :: (rabbit_types:vhost(), rabbit_types:info_keys())
+                -> rabbit_types:infos()).
+-spec(info_all/0 :: () -> [rabbit_types:infos()]).
+-spec(info_all/1 :: (rabbit_types:info_keys()) -> [rabbit_types:infos()]).
+
 -endif.
 
 %%----------------------------------------------------------------------------
 
+-define(INFO_KEYS, [name, tracing]).
+
 add(VHostPath) ->
     R = rabbit_misc:execute_mnesia_transaction(
           fun () ->
@@ -51,12 +60,13 @@ add(VHostPath) ->
                      rabbit_misc:r(VHostPath, exchange, Name),
                      Type, true, false, false, []) ||
                       {Name,Type} <-
-                          [{<<"">>,            direct},
-                           {<<"amq.direct">>,  direct},
-                           {<<"amq.topic">>,   topic},
-                           {<<"amq.match">>,   headers}, %% per 0-9-1 pdf
-                           {<<"amq.headers">>, headers}, %% per 0-9-1 xml
-                           {<<"amq.fanout">>,  fanout}]],
+                          [{<<"">>,                   direct},
+                           {<<"amq.direct">>,         direct},
+                           {<<"amq.topic">>,          topic},
+                           {<<"amq.match">>,          headers}, %% per 0-9-1 pdf
+                           {<<"amq.headers">>,        headers}, %% per 0-9-1 xml
+                           {<<"amq.fanout">>,         fanout},
+                           {<<"amq.rabbitmq.trace">>, topic}]],
                   ok
           end),
     rabbit_log:info("Added vhost ~p~n", [VHostPath]),
@@ -104,3 +114,17 @@ with(VHostPath, Thunk) ->
                     Thunk()
             end
     end.
+
+%%----------------------------------------------------------------------------
+
+infos(Items, X) -> [{Item, i(Item, X)} || Item <- Items].
+
+i(name,    VHost) -> VHost;
+i(tracing, VHost) -> rabbit_trace:tracing(VHost);
+i(Item, _)        -> throw({bad_argument, Item}).
+
+info(VHost)        -> infos(?INFO_KEYS, VHost).
+info(VHost, Items) -> infos(Items, VHost).
+
+info_all()      -> info_all(?INFO_KEYS).
+info_all(Items) -> [info(VHost, Items) || VHost <- list()].