Add acceptable_buffer_backends field in rmw_subscription_options_s

rmw/include/rmw/types.h

@@ -184,6 +184,17 @@ typedef struct RMW_PUBLIC_TYPE rmw_subscription_options_s
 
   /// Used to create a content filter options during subscription creation.
   rmw_subscription_content_filter_options_t * content_filter_options;
+
+  /// Comma-separated list of acceptable buffer backend names for this endpoint.
+  /**
+   * NULL, empty string, or "cpu" all mean CPU-only (default for backward compat).
+   * "any" means all installed backends are acceptable.
+   * Comma-separated for specific backends, e.g. "cuda,demo".
+   * CPU is always implicitly acceptable regardless of this value.
+   * The RMW will validate that each specified backend is installed and will
+   * report an error if any are not available.
+   */
+  const char * acceptable_buffer_backends;
 } rmw_subscription_options_t;
 
 typedef struct RMW_PUBLIC_TYPE rmw_subscription_s

rmw/src/subscription_options.c

@@ -27,6 +27,7 @@ rmw_get_default_subscription_options(void)
     .ignore_local_publications = false,
     .require_unique_network_flow_endpoints = RMW_UNIQUE_NETWORK_FLOW_ENDPOINTS_NOT_REQUIRED,
     .content_filter_options = NULL,
+    .acceptable_buffer_backends = NULL,
   };
   return subscription_options;
 }

rmw/test/test_subscription_options.cpp

@@ -25,4 +25,5 @@ TEST(rmw_subscription_options, get_default_subscription_options)
     options.require_unique_network_flow_endpoints,
     RMW_UNIQUE_NETWORK_FLOW_ENDPOINTS_NOT_REQUIRED);
   EXPECT_EQ(options.content_filter_options, nullptr);
+  EXPECT_EQ(options.acceptable_buffer_backends, nullptr);
 }