server: allows to set maximum monitors

spice-server will attempt to limit number of monitors.
Guest machine can send monitor list it accepts. Limiting the number sent
by guest will limit the number of monitors client will try to enable.
The guest usually see client monitors enabled and start using it so
not seeing client monitor won't try to enable more monitor.
In this case the additional monitor guest can support will always be
seen as heads with no attached monitors.
This allows limiting monitors number without changing guest drivers.

Signed-off-by: Frediano Ziglio <fziglio@redhat.com>

server/red_dispatcher.c

@@ -66,6 +66,7 @@ struct RedDispatcher {
     Ring async_commands;
     pthread_mutex_t  async_lock;
     QXLDevSurfaceCreate surface_create;
+    unsigned int max_monitors;
 };
 
 extern uint32_t streaming_video;
@@ -693,6 +694,7 @@ static void red_dispatcher_monitors_config_async(RedDispatcher *dispatcher,
     payload.base.cmd = async_command_alloc(dispatcher, message, cookie);
     payload.monitors_config = monitors_config;
     payload.group_id = group_id;
+    payload.max_monitors = dispatcher->max_monitors;
 
     dispatcher_send_message(&dispatcher->dispatcher, message, &payload);
 }
@@ -986,6 +988,12 @@ void spice_qxl_monitors_config_async(QXLInstance *instance, QXLPHYSICAL monitors
     red_dispatcher_monitors_config_async(instance->st->dispatcher, monitors_config, group_id, cookie);
 }
 
+SPICE_GNUC_VISIBLE
+void spice_qxl_set_max_monitors(QXLInstance *instance, unsigned int max_monitors)
+{
+    instance->st->dispatcher->max_monitors = MAX(1u, max_monitors);
+}
+
 SPICE_GNUC_VISIBLE
 void spice_qxl_driver_unload(QXLInstance *instance)
 {
@@ -1110,6 +1118,8 @@ void red_dispatcher_init(QXLInstance *qxl)
     red_dispatcher->base.destroy_surface_wait = qxl_worker_destroy_surface_wait;
     red_dispatcher->base.loadvm_commands = qxl_worker_loadvm_commands;
 
+    red_dispatcher->max_monitors = UINT_MAX;
+
     qxl->st->qif->get_init_info(qxl, &init_info);
 
     init_data.memslot_id_bits = init_info.memslot_id_bits;

server/red_dispatcher.h

@@ -200,6 +200,7 @@ typedef struct RedWorkerMessageMonitorsConfigAsync {
     RedWorkerMessageAsync base;
     QXLPHYSICAL monitors_config;
     int group_id;
+    unsigned int max_monitors;
 } RedWorkerMessageMonitorsConfigAsync;
 
 typedef struct RedWorkerMessageDriverUnload {

server/red_worker.c

@@ -11217,11 +11217,13 @@ static inline void red_monitors_config_item_add(DisplayChannelClient *dcc)
 }
 
 static void worker_update_monitors_config(RedWorker *worker,
-                                          QXLMonitorsConfig *dev_monitors_config)
+                                          QXLMonitorsConfig *dev_monitors_config,
+                                          unsigned int max_monitors)
 {
     int heads_size;
     MonitorsConfig *monitors_config;
     int i;
+    unsigned int count = MIN(dev_monitors_config->count, max_monitors);
 
     monitors_config_decref(worker->monitors_config);
 
@@ -11235,13 +11237,13 @@ static void worker_update_monitors_config(RedWorker *worker,
                     dev_monitors_config->heads[i].width,
                     dev_monitors_config->heads[i].height);
     }
-    heads_size = dev_monitors_config->count * sizeof(QXLHead);
+    heads_size = count * sizeof(QXLHead);
     worker->monitors_config = monitors_config =
         spice_malloc(sizeof(*monitors_config) + heads_size);
     monitors_config->refs = 1;
     monitors_config->worker = worker;
-    monitors_config->count = dev_monitors_config->count;
-    monitors_config->max_allowed = dev_monitors_config->max_allowed;
+    monitors_config->count = count;
+    monitors_config->max_allowed = MIN(dev_monitors_config->max_allowed, max_monitors);
     memcpy(monitors_config->heads, dev_monitors_config->heads, heads_size);
 }
 
@@ -11651,7 +11653,7 @@ static void handle_dev_monitors_config_async(void *opaque, void *payload)
                       dev_monitors_config->max_allowed);
         return;
     }
-    worker_update_monitors_config(worker, dev_monitors_config);
+    worker_update_monitors_config(worker, dev_monitors_config, msg->max_monitors);
     red_worker_push_monitors_config(worker);
 }
 

server/spice-qxl.h

@@ -97,6 +97,9 @@ void spice_qxl_monitors_config_async(QXLInstance *instance, QXLPHYSICAL monitors
                                      int group_id, uint64_t cookie);
 /* since spice 0.12.3 */
 void spice_qxl_driver_unload(QXLInstance *instance);
+/* since spice 0.12.6 */
+void spice_qxl_set_max_monitors(QXLInstance *instance,
+                                unsigned int max_monitors);
 
 typedef struct QXLDrawArea {
     uint8_t *buf;

server/spice-server.syms

@@ -153,3 +153,8 @@ global:
     spice_server_get_best_record_rate;
     spice_server_set_record_rate;
 } SPICE_SERVER_0.12.4;
+
+SPICE_SERVER_0.12.6 {
+global:
+    spice_qxl_set_max_monitors;
+} SPICE_SERVER_0.12.5;