meta/selection-source-memory: Use memfd instead of GBytes

MetaSelectionSourceMemory currently uses GBytes for its underlying data.
This can cause memory overhead when large items, such as HD images, are
stored in the clipboard. This commit changes the underlying data
structure to a MetaAnonymousFile object, which writes to memfd instead
of heap. When reading, MetaSelectionSourceMemory will create a
Gio.UnixInputStream from the file descriptor generated by
MetaAnonymousFile. We subclass the UnixInputStream as
MetaUnixInputStream, to override the stream's close_fn function so
that it invokes meta_anonymous_file_close_fd when the stream terminates.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3551>

src/core/meta-clipboard-manager.c

@@ -146,12 +146,22 @@ owner_changed_cb (MetaSelection       *selection,
     }
   else if (!new_owner && display->saved_clipboard)
     {
+      g_autoptr (GError) error = NULL;
+      g_autoptr (MetaSelectionSource) new_source = NULL;
+
       /* Old owner is gone, time to take over */
-      new_owner = meta_selection_source_memory_new (display->saved_clipboard_mimetype,
+      new_source = meta_selection_source_memory_new (display->saved_clipboard_mimetype,
-                                                    display->saved_clipboard);
+                                                     display->saved_clipboard,
-      g_set_object (&display->selection_source, new_owner);
+                                                     &error);
-      meta_selection_set_owner (selection, selection_type, new_owner);
+      if (!new_source)
-      g_object_unref (new_owner);
+        {
+          g_warning ("MetaClipboardManager failed to create new MetaSelectionSourceMemory: %s",
+                     error->message);
+          return;
+        }
+
+      g_set_object (&display->selection_source, new_source);
+      meta_selection_set_owner (selection, selection_type, new_source);
     }
 }
 

src/core/meta-selection-source-memory.c

@@ -21,17 +21,75 @@
 
 #include "meta/meta-selection-source-memory.h"
 
+#include <gio/gunixinputstream.h>
+
+#include "core/meta-anonymous-file.h"
+
 struct _MetaSelectionSourceMemory
 {
   MetaSelectionSource parent_instance;
   char *mimetype;
-  GBytes *content;
+  MetaAnonymousFile *content;
 };
 
 G_DEFINE_TYPE (MetaSelectionSourceMemory,
                meta_selection_source_memory,
                META_TYPE_SELECTION_SOURCE)
 
+struct _MetaUnixInputStream
+{
+  GUnixInputStream parent_instance;
+};
+
+#define META_TYPE_UNIX_INPUT_STREAM (meta_unix_input_stream_get_type ())
+G_DECLARE_FINAL_TYPE (MetaUnixInputStream,
+                      meta_unix_input_stream,
+                      META, UNIX_INPUT_STREAM,
+                      GUnixInputStream)
+
+G_DEFINE_FINAL_TYPE (MetaUnixInputStream,
+                     meta_unix_input_stream,
+                     G_TYPE_UNIX_INPUT_STREAM)
+
+static gboolean
+meta_unix_input_stream_close_fn (GInputStream  *input_stream,
+                                 GCancellable  *cancellable,
+                                 GError       **error)
+{
+  GUnixInputStream *stream = G_UNIX_INPUT_STREAM (input_stream);
+  int fd;
+
+  if (!g_unix_input_stream_get_close_fd (stream))
+    return TRUE;
+
+  fd = g_unix_input_stream_get_fd (stream);
+  meta_anonymous_file_close_fd (fd);
+
+  return TRUE;
+}
+
+static void
+meta_unix_input_stream_class_init (MetaUnixInputStreamClass *klass)
+{
+  GInputStreamClass *input_stream_class = G_INPUT_STREAM_CLASS (klass);
+
+  input_stream_class->close_fn = meta_unix_input_stream_close_fn;
+}
+
+static void
+meta_unix_input_stream_init (MetaUnixInputStream *stream)
+{
+}
+
+static GInputStream *
+meta_unix_input_stream_new (int fd)
+{
+  return G_INPUT_STREAM (g_object_new (META_TYPE_UNIX_INPUT_STREAM,
+                                       "fd", fd,
+                                       "close-fd", true,
+                                       NULL));
+}
+
 static void
 meta_selection_source_memory_read_async (MetaSelectionSource *source,
                                          const char          *mimetype,
@@ -42,6 +100,7 @@ meta_selection_source_memory_read_async (MetaSelectionSource *source,
   MetaSelectionSourceMemory *source_mem = META_SELECTION_SOURCE_MEMORY (source);
   GInputStream *stream;
   g_autoptr (GTask) task = NULL;
+  int fd;
 
   if (g_strcmp0 (mimetype, source_mem->mimetype) != 0)
     {
@@ -55,7 +114,20 @@ meta_selection_source_memory_read_async (MetaSelectionSource *source,
   task = g_task_new (source, cancellable, callback, user_data);
   g_task_set_source_tag (task, meta_selection_source_memory_read_async);
 
-  stream = g_memory_input_stream_new_from_bytes (source_mem->content);
+  fd = meta_anonymous_file_open_fd (source_mem->content,
+                                    META_ANONYMOUS_FILE_MAPMODE_SHARED);
+
+  if (fd == -1)
+    {
+      g_task_report_new_error (source, callback, user_data,
+                               meta_selection_source_memory_read_async,
+                               G_IO_ERROR, G_IO_ERROR_FAILED,
+                               "Failed to open MetaAnonymousFile");
+      return;
+    }
+
+  stream = meta_unix_input_stream_new (fd);
+
   g_task_return_pointer (task, stream, g_object_unref);
 }
 
@@ -85,7 +157,7 @@ meta_selection_source_memory_finalize (GObject *object)
 {
   MetaSelectionSourceMemory *source_mem = META_SELECTION_SOURCE_MEMORY (object);
 
-  g_clear_pointer (&source_mem->content, g_bytes_unref);
+  g_clear_pointer (&source_mem->content, meta_anonymous_file_free);
   g_free (source_mem->mimetype);
 
   G_OBJECT_CLASS (meta_selection_source_memory_parent_class)->finalize (object);
@@ -111,16 +183,30 @@ meta_selection_source_memory_init (MetaSelectionSourceMemory *source)
 
 MetaSelectionSource *
 meta_selection_source_memory_new (const char  *mimetype,
-                                  GBytes      *content)
+                                  GBytes      *content,
+                                  GError     **error)
 {
   MetaSelectionSourceMemory *source;
+  MetaAnonymousFile *anon_file;
+  const uint8_t *data;
+  size_t size;
 
   g_return_val_if_fail (mimetype != NULL, NULL);
   g_return_val_if_fail (content != NULL, NULL);
 
+  data = g_bytes_get_data (content, &size);
+  anon_file = meta_anonymous_file_new (size, data);
+
+  if (anon_file == NULL)
+    {
+      g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                   "Failed to create MetaAnonymousFile");
+      return NULL;
+    }
+
   source = g_object_new (META_TYPE_SELECTION_SOURCE_MEMORY, NULL);
   source->mimetype = g_strdup (mimetype);
-  source->content = g_bytes_ref (content);
+  source->content = anon_file;
 
   return META_SELECTION_SOURCE (source);
 }

src/meta/meta-selection-source-memory.h

@@ -31,4 +31,5 @@ G_DECLARE_FINAL_TYPE (MetaSelectionSourceMemory,
 
 META_EXPORT
 MetaSelectionSource * meta_selection_source_memory_new (const char  *mimetype,
-                                                        GBytes     *content);
+                                                        GBytes      *content,
+                                                        GError     **error);