From 8b1f1d93fa8e3524e0e01378dbe813e6eb06712e Mon Sep 17 00:00:00 2001
From: Linus Heckemann <git@sphalerite.org>
Date: Wed, 12 Jul 2017 22:03:53 +0100
Subject: [PATCH 1/2] nixos-install: only search for nixpkgs when needed

---
 nixos/modules/installer/tools/nixos-install.sh | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/nixos/modules/installer/tools/nixos-install.sh b/nixos/modules/installer/tools/nixos-install.sh
index 087fbcd4512f..7fae915871e4 100644
--- a/nixos/modules/installer/tools/nixos-install.sh
+++ b/nixos/modules/installer/tools/nixos-install.sh
@@ -106,8 +106,11 @@ extraBuildFlags+=(--option "build-users-group" "$buildUsersGroup")
 binary_caches="$(@perl@/bin/perl -I @nix@/lib/perl5/site_perl/*/* -e 'use Nix::Config; Nix::Config::readConfig; print $Nix::Config::config{"binary-caches"};')"
 extraBuildFlags+=(--option "binary-caches" "$binary_caches")
 
-nixpkgs="$(readlink -f "$(nix-instantiate --find-file nixpkgs)")"
-export NIX_PATH="nixpkgs=$nixpkgs:nixos-config=$mountPoint/$NIXOS_CONFIG"
+# We only need nixpkgs in the path if we don't already have a system closure to install
+if [[ -z "$closure" ]]; then
+    nixpkgs="$(readlink -f "$(nix-instantiate --find-file nixpkgs)")"
+    export NIX_PATH="nixpkgs=$nixpkgs:nixos-config=$mountPoint/$NIXOS_CONFIG"
+fi
 unset NIXOS_CONFIG
 
 # TODO: do I need to set NIX_SUBSTITUTERS here or is the --option binary-caches above enough?

From 77ce02201e1bc7facabb774d7e9996ab803145d2 Mon Sep 17 00:00:00 2001
From: Linus Heckemann <git@sphalerite.org>
Date: Wed, 12 Jul 2017 22:04:49 +0100
Subject: [PATCH 2/2] nixos-install: use FIFO for system closure

This avoids running out of space in space-constrained environments,
e.g. VMs with relatively small amounts of memory and tmp on tmpfs
---
 nixos/modules/installer/tools/nixos-install.sh | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/nixos/modules/installer/tools/nixos-install.sh b/nixos/modules/installer/tools/nixos-install.sh
index 7fae915871e4..79ed18c923c0 100644
--- a/nixos/modules/installer/tools/nixos-install.sh
+++ b/nixos/modules/installer/tools/nixos-install.sh
@@ -126,6 +126,9 @@ function closure() {
 }
 
 system_closure="$tmpdir/system.closure"
+# Use a FIFO for piping nix-store --export into nix-store --import, saving disk
+# I/O and space. nix-store --import is run by nixos-prepare-root.
+mkfifo $system_closure
 
 if [ -z "$closure" ]; then
     expr="(import <nixpkgs/nixos> {}).system"
@@ -135,7 +138,9 @@ else
     system_root=$closure
     # Create a temporary file ending in .closure (so nixos-prepare-root knows to --import it) to transport the store closure
     # to the filesytem we're preparing. Also delete it on exit!
-    nix-store --export $(nix-store -qR $closure) > $system_closure
+    # Run in background to avoid blocking while trying to write to the FIFO
+    # $system_closure refers to
+    nix-store --export $(nix-store -qR $closure) > $system_closure &
 fi
 
 channel_root="$(nix-env -p /nix/var/nix/profiles/per-user/root/channels -q nixos --no-name --out-path 2>/dev/null || echo -n "")"