v4l2allocator: Add a method to read number of allocated group

sys/v4l2/gstv4l2allocator.c

@@ -1361,3 +1361,17 @@ gst_v4l2_allocator_reset_group (GstV4l2Allocator * allocator,
       break;
   }
 }
+
+gsize
+gst_v4l2_allocator_num_allocated (GstV4l2Allocator * allocator)
+{
+  gsize num_allocated;
+
+  GST_OBJECT_LOCK (allocator);
+
+  num_allocated = allocator->count;
+
+  GST_OBJECT_UNLOCK (allocator);
+
+  return num_allocated;
+}

sys/v4l2/gstv4l2allocator.h

@@ -149,6 +149,8 @@ GstV4l2MemoryGroup*  gst_v4l2_allocator_dqbuf          (GstV4l2Allocator * alloc
 void                 gst_v4l2_allocator_reset_group    (GstV4l2Allocator * allocator,
                                                         GstV4l2MemoryGroup * group);
 
+gsize                gst_v4l2_allocator_num_allocated  (GstV4l2Allocator * allocator);
+
 G_END_DECLS
 
 #endif /* __GST_V4L2_ALLOCATOR_H__ */