From 16d25f4fa690d2c6a22aff7b6b5d351fec13db13 Mon Sep 17 00:00:00 2001
From: Franz Pletz <fpletz@fnordicwalking.de>
Date: Mon, 6 Apr 2015 09:14:54 +0200
Subject: [PATCH] Check if /proc/sys/kernel/hotplug exists before writing

If a kernel without CONFIG_UEVENT_HELPER set is used with NixOS, the file
/proc/sys/kernel/hotplug does not exist. Before writing to it to disable
this deprecated mechanism, we have to ensure it actually exists because
otherwise the activation script will fail.
---
 nixos/modules/services/hardware/udev.nix | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/nixos/modules/services/hardware/udev.nix b/nixos/modules/services/hardware/udev.nix
index a775aed0fda..50588e44958 100644
--- a/nixos/modules/services/hardware/udev.nix
+++ b/nixos/modules/services/hardware/udev.nix
@@ -237,7 +237,10 @@ in
 
     system.activationScripts.udevd =
       ''
-        echo "" > /proc/sys/kernel/hotplug
+        # The deprecated hotplug uevent helper is not used anymore
+        if [ -e /proc/sys/kernel/hotplug ]; then
+          echo "" > /proc/sys/kernel/hotplug
+        fi
 
         # Regenerate the hardware database /var/lib/udev/hwdb.bin
         # whenever systemd changes.