From cfdcce705291ebb4659dfaf8684f2cf950ecdebb Mon Sep 17 00:00:00 2001
From: Sam Stites <stites@users.noreply.github.com>
Date: Sun, 20 Oct 2019 17:05:35 -0400
Subject: [PATCH] openmpi: enable cuda support

---
 .../development/libraries/openmpi/default.nix | 22 +++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/pkgs/development/libraries/openmpi/default.nix b/pkgs/development/libraries/openmpi/default.nix
index 2a293e0b8562..5996dda1e74e 100644
--- a/pkgs/development/libraries/openmpi/default.nix
+++ b/pkgs/development/libraries/openmpi/default.nix
@@ -1,5 +1,8 @@
 { stdenv, fetchurl, fetchpatch, gfortran, perl, libnl
-, rdma-core, zlib, numactl, libevent, hwloc, pkgsTargetTarget
+, rdma-core, zlib, numactl, libevent, hwloc, pkgsTargetTarget, symlinkJoin
+
+# Enable CUDA support
+, cudaSupport ? false, cudatoolkit ? null
 
 # Enable the Sun Grid Engine bindings
 , enableSGE ? false
@@ -8,9 +11,15 @@
 , enablePrefix ? false
 }:
 
+assert !cudaSupport || cudatoolkit != null;
+
 let
   version = "4.0.2";
 
+  cudatoolkit_joined = symlinkJoin {
+    name = "${cudatoolkit.name}-unsplit";
+    paths = [ cudatoolkit.out cudatoolkit.lib ];
+  };
 in stdenv.mkDerivation rec {
   pname = "openmpi";
   inherit version;
@@ -33,15 +42,20 @@ in stdenv.mkDerivation rec {
 
   buildInputs = with stdenv; [ gfortran zlib ]
     ++ lib.optionals isLinux [ libnl numactl ]
+    ++ lib.optionals cudaSupport [ cudatoolkit ]
     ++ [ libevent hwloc ]
     ++ lib.optional (isLinux || isFreeBSD) rdma-core;
 
   nativeBuildInputs = [ perl ];
 
-  configureFlags = with stdenv; [ "--disable-mca-dso" ]
+  configureFlags = with stdenv; lib.optional (!cudaSupport) "--disable-mca-dso"
     ++ lib.optional isLinux  "--with-libnl=${libnl.dev}"
     ++ lib.optional enableSGE "--with-sge"
     ++ lib.optional enablePrefix "--enable-mpirun-prefix-by-default"
+    # TODO: add UCX support, which is recommended to use with cuda for the most robust OpenMPI build
+    # https://github.com/openucx/ucx
+    # https://www.open-mpi.org/faq/?category=buildcuda
+    ++ lib.optionals cudaSupport [ "--with-cuda=${cudatoolkit_joined}" "--enable-dlopen" ]
     ;
 
   enableParallelBuilding = true;
@@ -69,6 +83,10 @@ in stdenv.mkDerivation rec {
 
   doCheck = true;
 
+  passthru = {
+    inherit cudaSupport cudatoolkit;
+  };
+
   meta = with stdenv.lib; {
     homepage = https://www.open-mpi.org/;
     description = "Open source MPI-3 implementation";