From 60e731d1ceb7343b1d137afe6b09f3f6409d701b Mon Sep 17 00:00:00 2001
From: Maximilian Bosch <maximilian@mbosch.me>
Date: Wed, 6 Oct 2021 14:06:12 +0200
Subject: [PATCH 1/2] nixos/qemu-vm: fix running VM with `QEMU_NET_OPTS`

I realized quite recently that running a test VM - as documented in the
manual - like

    QEMU_NET_OPTS='hostfwd=tcp::8080-:80'  ./result/bin/nixos-run-vms

doesn't work anymore on `master`. After bisecting I realized that the
introduction of a forward-port option[1] is the problem since it adds a
trailing comma even if no forwarding options are specified via
`virtualisation.forwardPorts`. In that case, the networking options
would look like `-netdev user,id=user.0,,hostfwd=tcp::8080-:80' which
confused QEMU and thus the VM refused to start.

Now, the trailing comma is only added if additional port forwards are
specified declaratively.

[1] b8bfc81d5b2d88b734a311f712fc0ba2b267f9e0
---
 nixos/modules/virtualisation/qemu-vm.nix | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/nixos/modules/virtualisation/qemu-vm.nix b/nixos/modules/virtualisation/qemu-vm.nix
index 69d67685f559..8f33ba4c5e04 100644
--- a/nixos/modules/virtualisation/qemu-vm.nix
+++ b/nixos/modules/virtualisation/qemu-vm.nix
@@ -780,7 +780,7 @@ in
       in
       [
         "-net nic,netdev=user.0,model=virtio"
-        "-netdev user,id=user.0,${forwardingOptions}\${QEMU_NET_OPTS:+,$QEMU_NET_OPTS}"
+        "-netdev user,id=user.0,${forwardingOptions}$QEMU_NET_OPTS"
       ];
 
     # FIXME: Consolidate this one day.

From f700a92d5c2b307c14ff2610ebfdfa0e98df2e16 Mon Sep 17 00:00:00 2001
From: Maximilian Bosch <maximilian@mbosch.me>
Date: Wed, 6 Oct 2021 23:12:53 +0200
Subject: [PATCH 2/2] nixos/qemu-vm: quote QEMU_NET_OPTS

Co-authored-by: Michele Guerini Rocco <rnhmjoj@users.noreply.github.com>
---
 nixos/modules/virtualisation/qemu-vm.nix | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/nixos/modules/virtualisation/qemu-vm.nix b/nixos/modules/virtualisation/qemu-vm.nix
index 8f33ba4c5e04..c5f71b249a6d 100644
--- a/nixos/modules/virtualisation/qemu-vm.nix
+++ b/nixos/modules/virtualisation/qemu-vm.nix
@@ -780,7 +780,7 @@ in
       in
       [
         "-net nic,netdev=user.0,model=virtio"
-        "-netdev user,id=user.0,${forwardingOptions}$QEMU_NET_OPTS"
+        "-netdev user,id=user.0,${forwardingOptions}\"$QEMU_NET_OPTS\""
       ];
 
     # FIXME: Consolidate this one day.