lavu/hwcontext_vaapi: Use vaMapBuffer2 for mapping image buffers

This allows some optimizations in driver, such as not having to read
back the data if write-only mapping is requested.

libavutil/hwcontext_vaapi.c

@@ -809,6 +809,9 @@ static int vaapi_map_frame(AVHWFramesContext *hwfc,
     VAStatus vas;
     void *address = NULL;
     int err, i;
+#if VA_CHECK_VERSION(1, 21, 0)
+    uint32_t vaflags = 0;
+#endif
 
     surface_id = (VASurfaceID)(uintptr_t)src->data[3];
     av_log(hwfc, AV_LOG_DEBUG, "Map surface %#x.\n", surface_id);
@@ -892,7 +895,16 @@ static int vaapi_map_frame(AVHWFramesContext *hwfc,
         }
     }
 
+#if VA_CHECK_VERSION(1, 21, 0)
+    if (flags & AV_HWFRAME_MAP_READ)
+        vaflags |= VA_MAPBUFFER_FLAG_READ;
+    if (flags & AV_HWFRAME_MAP_WRITE)
+        vaflags |= VA_MAPBUFFER_FLAG_WRITE;
+    // On drivers not implementing vaMapBuffer2 libva calls vaMapBuffer instead.
+    vas = vaMapBuffer2(hwctx->display, map->image.buf, &address, vaflags);
+#else
     vas = vaMapBuffer(hwctx->display, map->image.buf, &address);
+#endif
     if (vas != VA_STATUS_SUCCESS) {
         av_log(hwfc, AV_LOG_ERROR, "Failed to map image from surface "
                "%#x: %d (%s).\n", surface_id, vas, vaErrorStr(vas));