From 399db54e3514ceaee82ec217140975d77963359f Mon Sep 17 00:00:00 2001
From: Nikolay Amiantov <ab@fmap.me>
Date: Thu, 5 Mar 2015 17:21:57 +0300
Subject: [PATCH] nixos/qemu: don't recreate extra disks

---
 nixos/modules/virtualisation/qemu-vm.nix | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/nixos/modules/virtualisation/qemu-vm.nix b/nixos/modules/virtualisation/qemu-vm.nix
index 9d9b725a805d..b77b319f4a28 100644
--- a/nixos/modules/virtualisation/qemu-vm.nix
+++ b/nixos/modules/virtualisation/qemu-vm.nix
@@ -62,7 +62,9 @@ let
       idx=2
       extraDisks=""
       ${flip concatMapStrings cfg.emptyDiskImages (size: ''
-        ${pkgs.qemu_kvm}/bin/qemu-img create -f qcow2 "empty$idx.qcow2" "${toString size}M"
+        if ! test -e "empty$idx.qcow2"; then
+            ${pkgs.qemu_kvm}/bin/qemu-img create -f qcow2 "empty$idx.qcow2" "${toString size}M"
+        fi
         extraDisks="$extraDisks -drive index=$idx,file=$(pwd)/empty$idx.qcow2,if=${cfg.qemu.diskInterface},werror=report"
         idx=$((idx + 1))
       '')}