drm-buffer: Add API to export buffer file descriptor

Practically ends up in gbm_bo_get_fd(). For dumb buffer, an
'unsupported' error is returned.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1854>

src/backends/native/meta-drm-buffer-dumb.c

@@ -50,6 +50,15 @@ struct _MetaDrmBufferDumb
 
 G_DEFINE_TYPE (MetaDrmBufferDumb, meta_drm_buffer_dumb, META_TYPE_DRM_BUFFER)
 
+static int
+meta_drm_buffer_dumb_export_fd (MetaDrmBuffer  *buffer,
+                                GError        **error)
+{
+  g_set_error (error, G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED,
+               "Can't export fd for dumb buffer");
+  return -1;
+}
+
 static int
 meta_drm_buffer_dumb_get_width (MetaDrmBuffer *buffer)
 {
@@ -362,6 +371,7 @@ meta_drm_buffer_dumb_class_init (MetaDrmBufferDumbClass *klass)
 
   object_class->finalize = meta_drm_buffer_dumb_finalize;
 
+  buffer_class->export_fd = meta_drm_buffer_dumb_export_fd;
   buffer_class->get_width = meta_drm_buffer_dumb_get_width;
   buffer_class->get_height = meta_drm_buffer_dumb_get_height;
   buffer_class->get_stride = meta_drm_buffer_dumb_get_stride;

src/backends/native/meta-drm-buffer-gbm.c

@@ -57,6 +57,24 @@ meta_drm_buffer_gbm_get_bo (MetaDrmBufferGbm *buffer_gbm)
   return buffer_gbm->bo;
 }
 
+static int
+meta_drm_buffer_gbm_export_fd (MetaDrmBuffer  *buffer,
+                               GError        **error)
+{
+  MetaDrmBufferGbm *buffer_gbm = META_DRM_BUFFER_GBM (buffer);
+  int fd;
+
+  fd = gbm_bo_get_fd (buffer_gbm->bo);
+  if (fd == -1)
+    {
+      g_set_error (error, G_IO_ERROR, g_io_error_from_errno (errno),
+                   "Failed to export buffer fd: %s", g_strerror (errno));
+      return -1;
+    }
+
+  return fd;
+}
+
 static int
 meta_drm_buffer_gbm_get_width (MetaDrmBuffer *buffer)
 {
@@ -491,6 +509,7 @@ meta_drm_buffer_gbm_class_init (MetaDrmBufferGbmClass *klass)
 
   object_class->finalize = meta_drm_buffer_gbm_finalize;
 
+  buffer_class->export_fd = meta_drm_buffer_gbm_export_fd;
   buffer_class->get_width = meta_drm_buffer_gbm_get_width;
   buffer_class->get_height = meta_drm_buffer_gbm_get_height;
   buffer_class->get_stride = meta_drm_buffer_gbm_get_stride;

src/backends/native/meta-drm-buffer-import.c

@@ -44,6 +44,16 @@ struct _MetaDrmBufferImport
 G_DEFINE_TYPE (MetaDrmBufferImport, meta_drm_buffer_import,
                META_TYPE_DRM_BUFFER)
 
+static int
+meta_drm_buffer_import_export_fd (MetaDrmBuffer  *buffer,
+                                  GError        **error)
+{
+  MetaDrmBufferImport *buffer_import = META_DRM_BUFFER_IMPORT (buffer);
+
+  return meta_drm_buffer_export_fd (META_DRM_BUFFER (buffer_import->importee),
+                                    error);
+}
+
 static int
 meta_drm_buffer_import_get_width (MetaDrmBuffer *buffer)
 {
@@ -229,6 +239,7 @@ meta_drm_buffer_import_class_init (MetaDrmBufferImportClass *klass)
 
   object_class->finalize = meta_drm_buffer_import_finalize;
 
+  buffer_class->export_fd = meta_drm_buffer_import_export_fd;
   buffer_class->get_width = meta_drm_buffer_import_get_width;
   buffer_class->get_height = meta_drm_buffer_import_get_height;
   buffer_class->get_stride = meta_drm_buffer_import_get_stride;

src/backends/native/meta-drm-buffer.c

@@ -158,6 +158,13 @@ meta_drm_buffer_release_fb_id (MetaDrmBuffer *buffer)
   priv->fb_id = 0;
 }
 
+int
+meta_drm_buffer_export_fd (MetaDrmBuffer  *buffer,
+                           GError        **error)
+{
+  return META_DRM_BUFFER_GET_CLASS (buffer)->export_fd (buffer, error);
+}
+
 uint32_t
 meta_drm_buffer_get_fb_id (MetaDrmBuffer *buffer)
 {

src/backends/native/meta-drm-buffer.h

@@ -40,6 +40,9 @@ G_DECLARE_DERIVABLE_TYPE (MetaDrmBuffer,
                           META, DRM_BUFFER,
                           GObject)
 
+int meta_drm_buffer_export_fd (MetaDrmBuffer  *buffer,
+                               GError        **error);
+
 uint32_t meta_drm_buffer_get_fb_id (MetaDrmBuffer *buffer);
 
 int meta_drm_buffer_get_width (MetaDrmBuffer *buffer);