QMP patches patches for 2021-02-04

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Merge remote-tracking branch 'remotes/armbru/tags/pull-qmp-2021-02-04' into staging

QMP patches patches for 2021-02-04

# gpg: Signature made Thu 04 Feb 2021 12:21:47 GMT
# gpg:                using RSA key 354BC8B3D7EB2A6B68674E5F3870B400EB918653
# gpg:                issuer "armbru@redhat.com"
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>" [full]
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>" [full]
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-qmp-2021-02-04:
  qmp: Resume OOB-enabled monitor before processing the request
  qmp: Add more tracepoints
  qmp: Fix up comments after commit 9ce44e2ce2
  docs/interop/qmp-spec: Document the request queue limit
  qobject: braces {} are necessary for all arms of this statement
  qobject: spaces required around that operators
  qobject: code indent should never use tabs
  qobject: open brace '{' following struct go on the same line
  monitor/qmp-cmds.c: Don't include ui/vnc.h

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

docs/interop/qmp-spec.txt

@@ -133,9 +133,11 @@ 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 stop reading the requests from the QMP
-channel until the request queue length is reduced to an acceptable
-range.
+execute them, the server will stop reading requests until the request
+queue length is reduced to an acceptable range.
+
+To ensure commands to be executed out-of-band get read and executed,
+the client should have at most eight in-band commands in flight.
 
 Only a few commands support out-of-band execution.  The ones that do
 have "allow-oob": true in output of query-qmp-schema.

monitor/qmp-cmds.c

@@ -23,7 +23,7 @@
 #include "qemu/uuid.h"
 #include "chardev/char.h"
 #include "ui/qemu-spice.h"
-#include "ui/vnc.h"
+#include "ui/console.h"
 #include "sysemu/kvm.h"
 #include "sysemu/runstate.h"
 #include "sysemu/runstate-action.h"

monitor/qmp.c

@@ -79,7 +79,7 @@ static void monitor_qmp_cleanup_queue_and_resume(MonitorQMP *mon)
     qemu_mutex_lock(&mon->qmp_queue_lock);
 
     /*
-     * Same condition as in monitor_qmp_bh_dispatcher(), but before
+     * Same condition as in monitor_qmp_dispatcher_co(), but before
      * removing an element from the queue (hence no `- 1`).
      * Also, the queue should not be empty either, otherwise the
      * monitor hasn't been suspended yet (or was already resumed).
@@ -113,6 +113,7 @@ void qmp_send_response(MonitorQMP *mon, const QDict *rsp)
 
     json = qobject_to_json_pretty(data, mon->pretty);
     assert(json != NULL);
+    trace_monitor_qmp_respond(mon, json->str);
 
     g_string_append_c(json, '\n');
     monitor_puts(&mon->common, json->str);
@@ -213,7 +214,7 @@ void coroutine_fn monitor_qmp_dispatcher_co(void *data)
 {
     QMPRequest *req_obj = NULL;
     QDict *rsp;
-    bool need_resume;
+    bool oob_enabled;
     MonitorQMP *mon;
 
     while (true) {
@@ -251,6 +252,9 @@ void coroutine_fn monitor_qmp_dispatcher_co(void *data)
             }
         }
 
+        trace_monitor_qmp_in_band_dequeue(req_obj,
+                                          req_obj->mon->qmp_requests->length);
+
         if (qatomic_xchg(&qmp_dispatcher_co_busy, true) == true) {
             /*
              * Someone rescheduled us (probably because a new requests
@@ -269,11 +273,32 @@ void coroutine_fn monitor_qmp_dispatcher_co(void *data)
         aio_co_schedule(qemu_get_aio_context(), qmp_dispatcher_co);
         qemu_coroutine_yield();
 
+        /*
+         * @req_obj has a request, we hold req_obj->mon->qmp_queue_lock
+         */
+
         mon = req_obj->mon;
-        /* qmp_oob_enabled() might change after "qmp_capabilities" */
-        need_resume = !qmp_oob_enabled(mon) ||
-            mon->qmp_requests->length == QMP_REQ_QUEUE_LEN_MAX - 1;
+
+        /*
+         * We need to resume the monitor if handle_qmp_command()
+         * suspended it.  Two cases:
+         * 1. OOB enabled: mon->qmp_requests has no more space
+         *    Resume right away, so that OOB commands can get executed while
+         *    this request is being processed.
+         * 2. OOB disabled: always
+         *    Resume only after we're done processing the request,
+         * We need to save qmp_oob_enabled() for later, because
+         * qmp_qmp_capabilities() can change it.
+         */
+        oob_enabled = qmp_oob_enabled(mon);
+        if (oob_enabled
+            && mon->qmp_requests->length == QMP_REQ_QUEUE_LEN_MAX - 1) {
+            monitor_resume(&mon->common);
+        }
+
         qemu_mutex_unlock(&mon->qmp_queue_lock);
+
+        /* Process request */
         if (req_obj->req) {
             if (trace_event_get_state(TRACE_MONITOR_QMP_CMD_IN_BAND)) {
                 QDict *qdict = qobject_to(QDict, req_obj->req);
@@ -287,16 +312,17 @@ void coroutine_fn monitor_qmp_dispatcher_co(void *data)
             monitor_qmp_dispatch(mon, req_obj->req);
         } else {
             assert(req_obj->err);
+            trace_monitor_qmp_err_in_band(error_get_pretty(req_obj->err));
             rsp = qmp_error_response(req_obj->err);
             req_obj->err = NULL;
             monitor_qmp_respond(mon, rsp);
             qobject_unref(rsp);
         }
 
-        if (need_resume) {
-            /* Pairs with the monitor_suspend() in handle_qmp_command() */
+        if (!oob_enabled) {
             monitor_resume(&mon->common);
         }
+
         qmp_request_free(req_obj);
 
         /*
@@ -349,7 +375,7 @@ static void handle_qmp_command(void *opaque, QObject *req, Error *err)
 
     /*
      * Suspend the monitor when we can't queue more requests after
-     * this one.  Dequeuing in monitor_qmp_bh_dispatcher() or
+     * this one.  Dequeuing in monitor_qmp_dispatcher_co() or
      * monitor_qmp_cleanup_queue_and_resume() will resume it.
      * Note that when OOB is disabled, we queue at most one command,
      * for backward compatibility.
@@ -364,6 +390,8 @@ static void handle_qmp_command(void *opaque, QObject *req, Error *err)
      * handled in time order.  Ownership for req_obj, req,
      * etc. will be delivered to the handler side.
      */
+    trace_monitor_qmp_in_band_enqueue(req_obj, mon,
+                                      mon->qmp_requests->length);
     assert(mon->qmp_requests->length < QMP_REQ_QUEUE_LEN_MAX);
     g_queue_push_tail(mon->qmp_requests, req_obj);
     qemu_mutex_unlock(&mon->qmp_queue_lock);

monitor/trace-events

@@ -10,6 +10,10 @@ monitor_protocol_event_queue(uint32_t event, void *qdict, uint64_t rate) "event=
 monitor_suspend(void *ptr, int cnt) "mon %p: %d"
 
 # qmp.c
+monitor_qmp_in_band_enqueue(void *req, void *mon, unsigned len) "%p mon %p len %u"
+monitor_qmp_in_band_dequeue(void *req, unsigned len) "%p len %u"
 monitor_qmp_cmd_in_band(const char *id) "%s"
+monitor_qmp_err_in_band(const char *desc) "%s"
 monitor_qmp_cmd_out_of_band(const char *id) "%s"
+monitor_qmp_respond(void *mon, const char *json) "mon %p resp: %s"
 handle_qmp_command(void *mon, const char *req) "mon %p req: %s"

qobject/json-parser.c

@@ -31,8 +31,7 @@ struct JSONToken {
     char str[];
 };
 
-typedef struct JSONParserContext
-{
+typedef struct JSONParserContext {
     Error *err;
     JSONToken *current;
     GQueue *buf;

qobject/qdict.c

@@ -39,12 +39,13 @@ QDict *qdict_new(void)
  */
 static unsigned int tdb_hash(const char *name)
 {
-    unsigned value;	/* Used to compute the hash value.  */
-    unsigned   i;	/* Used to cycle through random values. */
+    unsigned value;    /* Used to compute the hash value.  */
+    unsigned   i;      /* Used to cycle through random values. */
 
     /* Set the initial value from the key size. */
-    for (value = 0x238F13AF * strlen(name), i=0; name[i]; i++)
-        value = (value + (((const unsigned char *)name)[i] << (i*5 % 24)));
+    for (value = 0x238F13AF * strlen(name), i = 0; name[i]; i++) {
+        value = (value + (((const unsigned char *)name)[i] << (i * 5 % 24)));
+    }
 
     return (1103515243 * value + 12345);
 }
@@ -93,8 +94,9 @@ static QDictEntry *qdict_find(const QDict *qdict,
     QDictEntry *entry;
 
     QLIST_FOREACH(entry, &qdict->table[bucket], next)
-        if (!strcmp(entry->key, key))
+        if (!strcmp(entry->key, key)) {
             return entry;
+        }
 
     return NULL;
 }

qobject/qjson.c

@@ -22,8 +22,7 @@
 #include "qapi/qmp/qnum.h"
 #include "qapi/qmp/qstring.h"
 
-typedef struct JSONParsingState
-{
+typedef struct JSONParsingState {
     JSONMessageParser parser;
     QObject *result;
     Error *err;