spa/support: add plugin loader interface

Add a SPA interface for loading SPA plugins, so that plugins can request
the host to load other plugins.

spa/include/spa/support/plugin-loader.h

@@ -0,0 +1,97 @@
+/* Simple Plugin API
+ *
+ * Copyright © 2021 Wim Taymans
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef SPA_PLUGIN_LOADER_H
+#define SPA_PLUGIN_LOADER_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <spa/utils/hook.h>
+#include <spa/utils/defs.h>
+
+/**
+ * \addtogroup spa_support
+ * \{
+ */
+
+#define SPA_TYPE_INTERFACE_PluginLoader	SPA_TYPE_INFO_INTERFACE_BASE "PluginLoader"
+
+#define SPA_VERSION_PLUGIN_LOADER		0
+struct spa_plugin_loader { struct spa_interface iface; };
+
+struct spa_plugin_loader_methods {
+#define SPA_VERSION_PLUGIN_LOADER_METHODS	0
+        uint32_t version;
+
+	/**
+	 * Load a SPA plugin.
+         *
+         * \param factory_name Plugin factory name
+         * \param info Info dictionary for plugin. NULL if none.
+         * \return plugin handle, or NULL on error
+	 */
+	struct spa_handle *(*load) (void *object, const char *factory_name, const struct spa_dict *info);
+
+	/**
+	 * Unload a SPA plugin.
+         *
+         * \param handle Plugin handle.
+         * \return 0 on success, < 0 on error
+	 */
+	int (*unload)(void *object, struct spa_handle *handle);
+};
+
+static inline struct spa_handle *
+spa_plugin_loader_load(struct spa_plugin_loader *loader, const char *factory_name, const struct spa_dict *info)
+{
+	struct spa_handle *res = NULL;
+	if (SPA_LIKELY(loader != NULL))
+		spa_interface_call_res(&loader->iface,
+				struct spa_plugin_loader_methods, res,
+				load, 0, factory_name, info);
+	return res;
+}
+
+static inline int
+spa_plugin_loader_unload(struct spa_plugin_loader *loader, struct spa_handle *handle)
+{
+	int res = -1;
+	if (SPA_LIKELY(loader != NULL))
+		spa_interface_call_res(&loader->iface,
+				struct spa_plugin_loader_methods, res,
+				unload, 0, handle);
+	return res;
+}
+
+/**
+ * \}
+ */
+
+#ifdef __cplusplus
+}  /* extern "C" */
+#endif
+
+#endif /* SPA_PLUGIN_LOADER_H */