[PATCH 6/8] plugins: implement QPP import function

[Andrew Fasano <fasano@mit.edu>]

From: Elysia Witham <elysia.witham@ll.mit.edu>

Plugins can export functions or import functions from other
plugins using their name and the function name. This is also
described in <qemu-plugin.h>.

Signed-off-by: Elysia Witham <elysia.witham@ll.mit.edu>
Signed-off-by: Andrew Fasano <fasano@mit.edu>
---
 include/qemu/qemu-plugin.h   | 10 ++++++++++
 plugins/api.c                | 21 +++++++++++++++++++++
 plugins/qemu-plugins.symbols |  1 +
 3 files changed, 32 insertions(+)

diff --git a/include/qemu/qemu-plugin.h b/include/qemu/qemu-plugin.h
index 4221545015..a0516e9a0e 100644
--- a/include/qemu/qemu-plugin.h
+++ b/include/qemu/qemu-plugin.h
@@ -354,6 +354,16 @@ size_t qemu_plugin_tb_n_insns(const struct qemu_plugin_tb *tb);
  */
 uint64_t qemu_plugin_tb_vaddr(const struct qemu_plugin_tb *tb);
 
+/**
+ * qemu_plugin_import_function() - return pointer to a function in another
+ * plugin
+ * @plugin: plugin name
+ * @function: function name
+ *
+ * Returns: NULL on failure, function pointer on success
+ */
+gpointer qemu_plugin_import_function(const char *plugin, const char *function);
+
 /**
  * qemu_plugin_create_callback() - create a new cb with given name
  * @id: unique plugin id
diff --git a/plugins/api.c b/plugins/api.c
index 1f7ea718dc..a998df6942 100644
--- a/plugins/api.c
+++ b/plugins/api.c
@@ -400,6 +400,27 @@ bool qemu_plugin_bool_parse(const char *name, const char *value, bool *ret)
     return name && value && qapi_bool_parse(name, value, ret, NULL);
 }
 
+/*
+ * QPP: inter-plugin function resolution and callbacks
+ */
+
+gpointer qemu_plugin_import_function(const char *target_plugin,
+                                     const char *function) {
+    gpointer function_pointer = NULL;
+    struct qemu_plugin_ctx *ctx = plugin_name_to_ctx_locked(target_plugin);
+    if (ctx == NULL) {
+        error_report("Unable to load plugin %s by name", target_plugin);
+    } else if (g_module_symbol(ctx->handle, function,
+               (gpointer *)&function_pointer)) {
+        return function_pointer;
+    } else {
+      error_report("function: %s not found in plugin: %s", function,
+                   target_plugin);
+    }
+    abort();
+    return NULL;
+}
+
 bool qemu_plugin_create_callback(qemu_plugin_id_t id, const char *cb_name)
 {
     struct qemu_plugin_ctx *ctx = plugin_id_to_ctx_locked(id);
diff --git a/plugins/qemu-plugins.symbols b/plugins/qemu-plugins.symbols
index b7013980cf..70a518839d 100644
--- a/plugins/qemu-plugins.symbols
+++ b/plugins/qemu-plugins.symbols
@@ -3,6 +3,7 @@
   qemu_plugin_end_code;
   qemu_plugin_entry_code;
   qemu_plugin_get_hwaddr;
+  qemu_plugin_import_function;
   qemu_plugin_create_callback;
   qemu_plugin_run_callback;
   qemu_plugin_reg_callback;
-- 
2.34.1