[outputs] Fix gcc 10 complaining about multiple definitions

outputs_master_volume, output_device_list and output_buffer were defined in
outputs.h, but should only have been declared with extern.

Solve it by making output_buffer static/non-global (wasn't used anyway), and
the two others are now returned by functions.

src/outputs.c

@@ -105,6 +105,12 @@ struct output_quality_subscription
   struct encode_ctx *encode_ctx;
 };
 
+// Buffer used to pass data to the backends
+static struct output_buffer output_buffer;
+
+static struct output_device *outputs_device_list;
+static int outputs_master_volume;
+
 static struct outputs_callback_register outputs_cb_register[OUTPUTS_MAX_CALLBACKS];
 static struct event *outputs_deferredev;
 static struct timeval outputs_stop_timeout = { OUTPUTS_STOP_TIMEOUT, 0 };
@@ -392,14 +398,14 @@ device_list_sort(void)
     {
       swaps = 0;
       prev = NULL;
-      for (device = output_device_list; device && device->next; device = device->next)
+      for (device = outputs_device_list; device && device->next; device = device->next)
 	{
 	  next = device->next;
 	  if ( (outputs_priority(device) > outputs_priority(next)) ||
 	       (outputs_priority(device) == outputs_priority(next) && strcasecmp(device->name, next->name) > 0) )
 	    {
-	      if (device == output_device_list)
+	      if (device == outputs_device_list)
-		output_device_list = next;
+		outputs_device_list = next;
 	      if (prev)
 		prev->next = next;
 
@@ -513,7 +519,7 @@ vol_adjust(void)
   int selected_highest = -1;
   int all_highest = -1;
 
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_device_list; device; device = device->next)
     {
       if (OUTPUTS_DEVICE_DISPLAY_SELECTED(device) && (device->volume > selected_highest))
 	selected_highest = device->volume;
@@ -524,7 +530,7 @@ vol_adjust(void)
 
   outputs_master_volume = (selected_highest >= 0) ? selected_highest : all_highest;
 
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_device_list; device; device = device->next)
     {
       if (!OUTPUTS_DEVICE_DISPLAY_SELECTED(device) && (device->volume > outputs_master_volume))
 	device->volume = outputs_master_volume;
@@ -535,7 +541,7 @@ vol_adjust(void)
 #ifdef DEBUG_VOLUME
   DPRINTF(E_DBG, L_PLAYER, "*** Master: %d\n", outputs_master_volume);
 
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_device_list; device; device = device->next)
     {
       DPRINTF(E_DBG, L_PLAYER, "*** %s: abs %d rel %d selected %d\n", device->name, device->volume, device->relvol, OUTPUTS_DEVICE_DISPLAY_SELECTED(device));
     }
@@ -549,7 +555,7 @@ outputs_device_get(uint64_t device_id)
 {
   struct output_device *device;
 
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_device_list; device; device = device->next)
     {
       if (device_id == device->id)
 	return device;
@@ -692,7 +698,7 @@ outputs_device_add(struct output_device *add, bool new_deselect)
   char *keep_name;
   int ret;
 
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_device_list; device; device = device->next)
     {
       if (device->id == add->id)
 	break;
@@ -719,8 +725,8 @@ outputs_device_add(struct output_device *add, bool new_deselect)
       if (new_deselect)
 	device->selected = 0;
 
-      device->next = output_device_list;
+      device->next = outputs_device_list;
-      output_device_list = device;
+      outputs_device_list = device;
     }
   // Update to a device already in the list
   else
@@ -780,7 +786,7 @@ outputs_device_remove(struct output_device *remove)
     outputs_device_stop(remove, device_stop_cb);
 
   prev = NULL;
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_device_list; device; device = device->next)
     {
       if (device == remove)
 	break;
@@ -799,7 +805,7 @@ outputs_device_remove(struct output_device *remove)
   DPRINTF(E_INFO, L_PLAYER, "Removing %s device '%s'; stopped advertising\n", remove->type_name, remove->name);
 
   if (!prev)
-    output_device_list = remove->next;
+    outputs_device_list = remove->next;
   else
     prev->next = remove->next;
 
@@ -1006,7 +1012,7 @@ outputs_start(output_status_cb started_cb, output_status_cb stopped_cb, bool onl
   int pending = 0;
   int ret = -1;
 
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_device_list; device; device = device->next)
     {
       if (device->selected)
 	ret = outputs_device_start(device, started_cb, only_probe);
@@ -1029,7 +1035,7 @@ outputs_stop(output_status_cb cb)
   int pending = 0;
   int ret;
 
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_device_list; device; device = device->next)
     {
       if (!device->session)
 	continue;
@@ -1049,7 +1055,7 @@ outputs_stop_delayed_cancel(void)
 {
   struct output_device *device;
 
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_device_list; device; device = device->next)
     event_del(device->stop_timer);
 
   return 0;
@@ -1062,7 +1068,7 @@ outputs_flush(output_status_cb cb)
   int pending = 0;
   int ret;
 
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_device_list; device; device = device->next)
     {
       ret = outputs_device_flush(device, cb);
       if (ret < 0)
@@ -1074,6 +1080,12 @@ outputs_flush(output_status_cb cb)
   return pending;
 }
 
+int
+outputs_volume_get(void)
+{
+  return outputs_master_volume;
+}
+
 int
 outputs_volume_set(int volume, output_status_cb cb)
 {
@@ -1086,7 +1098,7 @@ outputs_volume_set(int volume, output_status_cb cb)
 
   outputs_master_volume = volume;
 
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_device_list; device; device = device->next)
     {
       if (!device->selected)
 	continue;
@@ -1109,7 +1121,7 @@ outputs_sessions_count(void)
   struct output_device *device;
   int count = 0;
 
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_device_list; device; device = device->next)
     if (device->session)
       count++;
 
@@ -1175,6 +1187,12 @@ outputs_name(enum output_types type)
   return outputs[type]->name;
 }
 
+struct output_device *
+outputs_list(void)
+{
+  return outputs_device_list;
+}
+
 int
 outputs_init(void)
 {

src/outputs.h

@@ -182,7 +182,7 @@ struct output_buffer
   // holds the original, untranscoded, data (which might not have any
   // subscribers, and the last element is a zero terminator.
   struct output_data data[OUTPUTS_MAX_QUALITY_SUBSCRIPTIONS + 2];
-} output_buffer;
+};
 
 struct output_definition
 {
@@ -256,9 +256,6 @@ struct output_definition
   void (*metadata_purge)(void);
 };
 
-// Our main list of devices, not for use by backend modules
-struct output_device *output_device_list;
-
 /* ------------------------------- General use ------------------------------ */
 
 struct output_device *
@@ -283,9 +280,6 @@ outputs_cb(int callback_id, uint64_t device_id, enum output_device_state);
 
 /* ---------------------------- Called by player ---------------------------- */
 
-int
-outputs_master_volume;
-
 // Ownership of *add is transferred, so don't address after calling. Instead you
 // can address the return value (which is not the same if the device was already
 // in the list.
@@ -343,6 +337,9 @@ outputs_stop(output_status_cb cb);
 int
 outputs_flush(output_status_cb cb);
 
+int
+outputs_volume_get(void);
+
 int
 outputs_volume_set(int volume, output_status_cb cb);
 
@@ -367,6 +364,9 @@ outputs_priority(struct output_device *device);
 const char *
 outputs_name(enum output_types type);
 
+struct output_device *
+outputs_list(void);
+
 int
 outputs_init(void);
 

src/player.c

@@ -1437,7 +1437,7 @@ device_auth_kickoff(void *arg, int *retval)
   struct output_device *device;
 
   // First find the device requiring verification
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_list(); device; device = device->next)
     {
       if (device->type == cmdarg->auth.type && device->state == OUTPUT_STATE_PASSWORD)
 	break;
@@ -1858,7 +1858,7 @@ get_status(void *arg, int *retval)
   status->consume = consume;
   status->repeat = repeat;
 
-  status->volume = outputs_master_volume;
+  status->volume = outputs_volume_get();
 
   status->plid = cur_plid;
 
@@ -2055,7 +2055,7 @@ playback_start_item(void *arg, int *retval)
       DPRINTF(E_LOG, L_PLAYER, "All selected speakers failed to start\n");
 
       // All selected devices failed, autoselect an unselected (if enabled)
-      for (device = output_device_list; (*retval < 0) && speaker_autoselect && device; device = device->next)
+      for (device = outputs_list(); (*retval < 0) && speaker_autoselect && device; device = device->next)
 	{
 	  if (!device->selected && outputs_priority(device) != 0 && !device->session)
 	    *retval = outputs_device_start(device, device_activate_cb, false);
@@ -2474,7 +2474,7 @@ speaker_enumerate(void *arg, int *retval)
   struct output_device *device;
   struct player_speaker_info spk;
 
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_list(); device; device = device->next)
     {
       device_to_speaker_info(&spk, device);
       spk_enum->cb(&spk, spk_enum->arg);
@@ -2490,7 +2490,7 @@ speaker_get_byid(void *arg, int *retval)
   struct speaker_get_param *spk_param = arg;
   struct output_device *device;
 
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_list(); device; device = device->next)
     {
       if ((device->advertised || device->selected)
 	  && device->id == spk_param->spk_id)
@@ -2512,7 +2512,7 @@ speaker_get_byactiveremote(void *arg, int *retval)
   struct speaker_get_param *spk_param = arg;
   struct output_device *device;
 
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_list(); device; device = device->next)
     {
       if ((uint32_t)device->id == spk_param->active_remote)
 	{
@@ -2547,7 +2547,7 @@ speaker_set(void *arg, int *retval)
 
   DPRINTF(E_DBG, L_PLAYER, "Speaker set: %d speakers\n", nspk);
 
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_list(); device; device = device->next)
     {
       for (i = 1; i <= nspk; i++)
 	{
@@ -3495,7 +3495,7 @@ player(void *arg)
 
   db_speaker_clear_all();
 
-  for (device = output_device_list; device; device = device->next)
+  for (device = outputs_list(); device; device = device->next)
     {
       ret = db_speaker_save(device);
       if (ret < 0)