EGL support for the Nvidia proprietary driver

Good news: we did not have to patch libglvnd for the EGL support. All
the low-level machinery was already here (but sadly undocumented).

Bad news: properly supporting the EGL stack turned out being more
involving than its GLX counterpart on the wrapper side. Not only you
need the main EGL lib in charge of implementing the
primitives (libEGL_nvidia.so), but also two other libraries
implementing the wayland and gbm bindings.

These DSOs in turn depend on some non-glibc but open source shared
libraries. I decided to use the ones coming from the host system
rather than the ones provided by Nixpkgs: it's best to assume that the
host system did its homework to determine which version of these
libraries the Nvidia driver is expecting to work with.

nixglhost-wrapper.py

@@ -1,10 +1,11 @@
 #!/usr/bin/env python3
 
 import argparse
+import json
 import os
 import re
-import subprocess
 import shutil
+import subprocess
 import sys
 
 IN_NIX_STORE = False
@@ -54,12 +55,37 @@ NVIDIA_DSO_NAMES = [
     "libnvidia-vulkan-producer\.so.*$",
     "libnvidia-wayland-client\.so.*$",
     "libnvoptix\.so.*$",
+
+    # Host dependencies required by the nvidia DSOs to properly
+    # operate
+
+    # libdrm
+    "libdrm\.so.*$",
+    # libffi
+    "libffi\.so.*$",
+    # libgbm
+    "libgbm\.so.*$",
+    # Cannot find that one :(
+    "libnvtegrahv\.so.*$",
+    # libexpat
+    "libexpat\.so.*$",
+    # libxcb
+    "libxcb-glx\.so.*$",
+    # Coming from libx11
+    "libX11-xcb\.so.*$",
+    "libX11\.so.*$",
+    "libXext\.so.*$",
+    # libwayland
+    "libwayland-server\.so.*$",
+    "libwayland-client\.so.*$",
+
 ]
 
 def find_nvidia_dsos(path):
     """Scans the PATH directory looking for the Nvidia driver shared
-    libraries. A shared library is considered as a Nvidia one if its
-    name maches a pattern contained in NVIDIA_DSO_NAMES.
+    libraries and their dependencies. A shared library is considered
+    as a Nvidia one if its name maches a pattern contained in
+    NVIDIA_DSO_NAMES.
 
     Returns the list of the DSOs absolute paths."""
 
@@ -79,7 +105,7 @@ def find_nvidia_dsos(path):
     return files
 
 
-def copy_and_patch_dsos_to_cache_dir(dsos, cache_dir):
+def copy_and_patch_dsos_to_libs_dir(dsos, libs_dir):
     """Copies the graphic vendor DSOs to the cache directory before
     patchelf-ing them.
 
@@ -94,11 +120,11 @@ def copy_and_patch_dsos_to_cache_dir(dsos, cache_dir):
     runpath to point to the cache directory."""
     for dso in dsos:
         basename = os.path.basename(dso)
-        newpath = os.path.join(cache_dir, basename)
+        newpath = os.path.join(libs_dir, basename)
         log_info(f"Copying {basename} to {newpath}")
         shutil.copyfile(dso, newpath)
         shutil.copymode(dso, newpath)
-        patch_dso(newpath, cache_dir)
+        patch_dso(newpath, libs_dir)
 
 
 def log_info(string):
@@ -109,15 +135,41 @@ def log_info(string):
 
 
 def patch_dso(dsoPath, rpath):
-    """Call patchelf to change the DSOPATH runpath with RPATH"""
+    """Call patchelf to change the DSOPATH runpath with RPATH."""
     log_info(f"Patching {dsoPath}")
     log_info(f"Exec: {PATCHELF_PATH} --set-rpath {rpath} {dsoPath}")
     res = subprocess.run([PATCHELF_PATH, "--set-rpath", rpath, dsoPath])
     if res.returncode != 0:
         raise (f"Cannot patch {dsoPath}. Patchelf exited with {res.returncode}")
 
+def generate_nvidia_egl_config_files(cache_dir, libs_dir):
+    """Generates a set of JSON files describing the EGL exec
+    envirnoment to libglvnd.
 
-def exec_binary(bin_path, args, cache_dir):
+    These configuration files will point to the EGL, wayland and GBM
+    Nvidia DSOs."""
+
+    def generate_egl_conf_json(dso):
+        return json.dumps({
+            "file_format_version": "1.0.0",
+            "ICD": {
+                "library_path": dso
+            }})
+
+    egl_conf_dir = os.path.join(cache_dir, "egl-confs")
+    os.makedirs(egl_conf_dir, exist_ok=True)
+    dso_paths = [ ("10_nvidia.json", f"{libs_dir}/libEGL_nvidia.so.0"),
+                  ("10_nvidia_wayland.json", f"{libs_dir}/libnvidia-egl-wayland.so.1"),
+                  ("15_nvidia_gbm.json", f"{libs_dir}/libnvidia-egl-gbm.so.1") ]
+
+    for (conf_file_name, dso_path) in dso_paths:
+        with open(os.path.join(egl_conf_dir, conf_file_name), "w", encoding = "utf-8") as f:
+            log_info(f"Writing {dso_path} conf to {egl_conf_dir}")
+            f.write(generate_egl_conf_json(dso_path))
+
+    return egl_conf_dir
+
+def exec_binary(bin_path, args, cache_dir, libs_dir):
     """Replace the current python program with the program pointed by
     BIN_PATH.
 
@@ -127,8 +179,11 @@ def exec_binary(bin_path, args, cache_dir):
     # The following two env variables are required by our patched libglvnd
     # implementation to figure out what kind of driver the host
     # machine is using.
-    os.environ["NIX_GLVND_GLX_PATH"] = cache_dir
+    os.environ["NIX_GLVND_GLX_PATH"] = libs_dir
     os.environ["__GLX_VENDOR_LIBRARY_NAME"] = "nvidia"
+    # The following env variable is pointing to the directory
+    # containing the EGL configuration.
+    os.environ["__EGL_VENDOR_LIBRARY_DIRS"] = generate_nvidia_egl_config_files(cache_dir, libs_dir)
     os.execv(bin_path, [bin_path] + args)
 
 
@@ -140,15 +195,17 @@ def main(args):
     home = os.path.expanduser("~")
     xdg_cache_home = os.environ.get("XDG_CACHE_HOME", os.path.join(home, ".cache"))
     cache_dir = os.path.join(xdg_cache_home, "nix-gl-host")
+    libs_dir = os.path.join(cache_dir, "lib")
     os.makedirs(cache_dir, exist_ok=True)
+    os.makedirs(libs_dir, exist_ok=True)
     log_info(f'Using "{cache_dir}" as cache dir.')
     log_info(f'Scanning "{args.GL_VENDOR_PATH}" for DSOs.')
     dsos = find_nvidia_dsos(args.GL_VENDOR_PATH)
     log_info(f"Found the following DSOs:")
     [log_info(dso) for dso in dsos]
     log_info("Patching the DSOs.")
-    copy_and_patch_dsos_to_cache_dir(dsos, cache_dir)
-    exec_binary(args.NIX_BINARY, args.ARGS, cache_dir)
+    copy_and_patch_dsos_to_libs_dir(dsos, libs_dir)
+    exec_binary(args.NIX_BINARY, args.ARGS, cache_dir, libs_dir)
     return 0