glamor: Add glamor_shareable_fd_from_pixmap()

Add glamor_shareable_fd_from_pixmap function to get dma-buf fds suitable
for sharing across GPUs (not using GPU specific tiling).

This is necessary for the modesetting driver to correctly implement
the DRI2 SharePixmapBacking callback.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Keith Packard <keithp@keithp.com>

glamor/glamor.c

@@ -821,6 +821,26 @@ glamor_fd_from_pixmap(ScreenPtr screen,
     return -1;
 }
 
+_X_EXPORT int
+glamor_shareable_fd_from_pixmap(ScreenPtr screen,
+                                PixmapPtr pixmap, CARD16 *stride, CARD32 *size)
+{
+    unsigned orig_usage_hint = pixmap->usage_hint;
+    int ret;
+
+    /*
+     * The actual difference between a sharable and non sharable buffer
+     * is decided 4 call levels deep in glamor_make_pixmap_exportable()
+     * based on pixmap->usage_hint == CREATE_PIXMAP_USAGE_SHARED
+     * 2 of those calls are also exported API, so we cannot just add a flag.
+     */
+    pixmap->usage_hint = CREATE_PIXMAP_USAGE_SHARED;
+    ret = glamor_fd_from_pixmap(screen, pixmap, stride, size);
+    pixmap->usage_hint = orig_usage_hint;
+
+    return ret;
+}
+
 int
 glamor_name_from_pixmap(PixmapPtr pixmap, CARD16 *stride, CARD32 *size)
 {

glamor/glamor.h

@@ -181,6 +181,26 @@ extern _X_EXPORT int glamor_fd_from_pixmap(ScreenPtr screen,
                                            PixmapPtr pixmap,
                                            CARD16 *stride, CARD32 *size);
 
+/* @glamor_shareable_fd_from_pixmap: Get a dma-buf fd suitable for sharing
+ *				     with other GPUs from a pixmap.
+ *
+ * @screen: Current screen pointer.
+ * @pixmap: The pixmap from which we want the fd.
+ * @stride, @size: Pointers to fill the stride and size of the
+ * 		   buffer associated to the fd.
+ *
+ * The returned fd will point to a buffer which is suitable for sharing
+ * across GPUs (not using GPU specific tiling).
+ * The pixmap and the buffer associated by the fd will share the same
+ * content.
+ * The pixmap's stride may be modified by this function.
+ * Returns the fd on success, -1 on error.
+ * */
+extern _X_EXPORT int glamor_shareable_fd_from_pixmap(ScreenPtr screen,
+                                                     PixmapPtr pixmap,
+                                                     CARD16 *stride,
+                                                     CARD32 *size);
+
 /**
  * @glamor_name_from_pixmap: Gets a gem name from a pixmap.
  *