[Mesa-dev] [PATCH 07/14] dri: Implement a DRI vtable extension to replace the global driDriverAPI.

[Eric Anholt]

As we move to megadrivers, we are unable to build multiple drivers with
the same public global symbol per driver (Think an X Server with an intel
and a nouveau driver, and the X Server implementing indirect for both --
we have to actually talk to the right driver).  By slipping the
driDriverAPI vtable into the driver's extension list, we can replace the
usage of the global symbol with usage of the loader-dlsym()ed driver
information.
---
 include/GL/internal/dri_interface.h    | 17 +++++++++++++++++
 src/mesa/drivers/dri/common/dri_util.c | 11 +++++++++++
 2 files changed, 28 insertions(+)

diff --git a/include/GL/internal/dri_interface.h b/include/GL/internal/dri_interface.h
index e07f669..957dd8c 100644
--- a/include/GL/internal/dri_interface.h
+++ b/include/GL/internal/dri_interface.h
@@ -1268,4 +1268,21 @@ typedef struct __DRIconfigOptionsExtensionRec {
    const char *xml;
 } __DRIconfigOptionsExtension;
 
+/**
+ * This extension provides a driver vtable to a set of common driver helper
+ * functions (driCoreExtension, driDRI2Extension) within the driver
+ * implementation, as opposed to having to pass them through a global
+ * variable.
+ *
+ * It is not intended to be public API to the actual loader, and the vtable
+ * layout may change at any time.
+ */
+#define __DRI_DRIVER_VTABLE "DRI_DriverVtable"
+#define __DRI_DRIVER_VTABLE_VERSION 1
+
+typedef struct __DRIDriverVtableExtensionRec {
+    __DRIextension base;
+    const struct __DriverAPIRec *vtable;
+} __DRIDriverVtableExtension;
+
 #endif
diff --git a/src/mesa/drivers/dri/common/dri_util.c b/src/mesa/drivers/dri/common/dri_util.c
index 283e158..9a99ea9 100644
--- a/src/mesa/drivers/dri/common/dri_util.c
+++ b/src/mesa/drivers/dri/common/dri_util.c
@@ -100,8 +100,19 @@ dri2CreateNewScreen2(int scrn, int fd,
     if (!psp)
 	return NULL;
 
+    /* By default, use the global driDriverAPI symbol (non-megadrivers). */
     psp->driver = &driDriverAPI;
 
+    /* If the driver exposes its vtable through its extensions list
+     * (megadrivers), use that instead.
+     */
+    for (int i = 0; driver_extensions[i]; i++) {
+       if (strcmp(driver_extensions[i]->name, __DRI_DRIVER_VTABLE) == 0) {
+          psp->driver =
+             ((__DRIDriverVtableExtension *)driver_extensions[i])->vtable;
+       }
+    }
+
     setupLoaderExtensions(psp, extensions);
 
 #ifndef SWRAST_NO_DRM
-- 
1.8.4.rc3