Layer Description and Status 10/22/2014

Overview: Layer libraries can be written to intercept or hook XGL entrypoints for various debug and validation purpose. One or more XGL entrypoints can be defined in your Layer library. Undefined entrypoints in the Layer library will be passed to the next Layer which may be the driver. Multiple layer libraries can be chained (actually a hierarchy) together. xglEnumerateLayer can be called to list the available layer libraries. xglGetProcAddr is used internally by the Layers and ICD Loader to initialize dispatch tables. Layers are activated at xglCreateDevice time. xglCreateDevice createInfo struct is extended to allow a list of layers to be activated. Layer libraries can alternatively be LD_PRELOADed.

Layer library example code: include/xglLayer.h - header file for layer code layer/basic_plugin.c - simple example wrapping three entrypoints. Single global dispatch table for either single gpu/device or multi-gpu with same activated layers for each device. Can be LD_PRELOADed individually. /layer/generic_layer.c - auto generated example wrapping all XGL entrypoints. Single global dispatch table. Can be LD_PRELOADed. /layer/api_dump.c - print out API calls along with parameter values /layer/object_track.c - Print object CREATE/USE/DESTROY stats

Using Layers:

1. Build XGL loader and i965 icd driver using normal steps (cmake and make)

2. Place libXGLLayer.so in the same directory as your XGL test or app: cp build/layer/libXGLLayerBasic.so build/layer/libXGLLayerGeneric.so build/tests This is required for the Icd loader to be able to scan and enumerate your library.

3. Specify which Layers to activate by using xglCreateDevice XGL_LAYER_CREATE_INFO struct or environment variable LIBXGL_LAYER_LIBS export LIBXGL_LAYER_LIBS=libXGLLayerBasic.so:LibXGLLayerGeneric.so cd build/tests; ./xglinfo

Status: Current Features: -scanning of available Layers during xglInitAndEnumerateGpus -xglEnumerateLayers and xglGetProcAddr supported APIs in xgl.h, ICD loader and i965 driver -multiple layers in a hierarchy supported -layer enumeration supported -layers activated per gpu and per icd driver: separate dispatch table and layer library list in loader for each gpu or icd driver -activation via xglCreateDevice extension struct in CreateInfo or via env var (LIBXGL_LAYER_LIBS) -layer libraries can be LD_PRELOADed

Current known issues: -layer libraries don't support multiple dispatch tables for multi-gpus -layers with extension APIs not yet tested or supported -layer libraries not yet include loader init functionality for full LD_PRELOAD of entire API including xglInitAndEnumerate -no support for apps registering layers, must be discovered via initial scan -no support for Loader discovering from layer and driver which layers support which gpus/drivers: any layer can be use any gpu right now -xglEnumerateLayers doesn't qualify Layers based on gpu, but enumerates all that were scanned