tstest/integration/vms: test on stable nixos (21.11)

I would like to do some more customized integration tests in the future,
(specifically, bringing up a mitm proxy and testing tailscaled through that)
so hoping to bring back the nixos wiring to support that.

Signed-off-by: Tom DNetto <tom@tailscale.com>

tstest/integration/vms/README.md

@@ -35,7 +35,7 @@ If you are using [Nix](https://nixos.org), you can run all of the tests with the
 correct command line tools using this command:
 
 ```console
-$ nix-shell -p openssh -p go -p qemu -p cdrkit --run "go test . --run-vm-tests --v --timeout 30m --no-s3"
+$ nix-shell -p nixos-generators -p openssh -p go -p qemu -p cdrkit --run "go test . --run-vm-tests --v --timeout 30m --no-s3"
 ```
 
 Keep the timeout high for the first run, especially if you are not downloading

tstest/integration/vms/distros.go

@@ -20,6 +20,7 @@ type Distro struct {
 	MemoryMegs     int    // VM memory in megabytes
 	PackageManager string // yum/apt/dnf/zypper
 	InitSystem     string // systemd/openrc
+	HostGenerated  bool   // generated image rather than downloaded
 }
 
 func (d *Distro) InstallPre() string {

tstest/integration/vms/distros.hujson

@@ -27,4 +27,13 @@
         "PackageManager": "apt",
         "InitSystem": "systemd"
     },
+    {
+        "Name": "nixos-21-11",
+        "URL": "channel:nixos-21.11",
+        "SHA256Sum": "lolfakesha",
+        "MemoryMegs": 512,
+        "PackageManager": "nix",
+        "InitSystem": "systemd",
+        "HostGenerated": true
+    },
 ]

tstest/integration/vms/top_level_test.go

@@ -18,3 +18,9 @@ func TestRunUbuntu2004(t *testing.T) {
 	setupTests(t)
 	testOneDistribution(t, 1, Distros[1])
 }
+
+func TestRunNixos2111(t *testing.T) {
+	t.Parallel()
+	setupTests(t)
+	testOneDistribution(t, 2, Distros[2])
+}

tstest/integration/vms/vm_setup_test.go

@@ -49,6 +49,13 @@ func (vm *vmInstance) running() bool {
 	}
 }
 
+func (h *Harness) makeImage(t *testing.T, d Distro, cdir string) string {
+	if !strings.HasPrefix(d.Name, "nixos") {
+		t.Fatal("image generation for non-nixos is not implemented")
+	}
+	return h.makeNixOSImage(t, d, cdir)
+}
+
 // mkVM makes a KVM-accelerated virtual machine and prepares it for introduction
 // to the testcontrol server. The function it returns is for killing the virtual
 // machine when it is time for it to die.
@@ -67,7 +74,14 @@ func (h *Harness) mkVM(t *testing.T, n int, d Distro, sshKey, hostURL, tdir stri
 		t.Fatal(err)
 	}
 
-	mkLayeredQcow(t, tdir, d, fetchDistro(t, d))
+	var qcowPath string
+	if d.HostGenerated {
+		qcowPath = h.makeImage(t, d, cdir)
+	} else {
+		qcowPath = fetchDistro(t, d)
+	}
+
+	mkLayeredQcow(t, tdir, d, qcowPath)
 	mkSeed(t, d, sshKey, hostURL, tdir, port)
 
 	driveArg := fmt.Sprintf("file=%s,if=virtio", filepath.Join(tdir, d.Name+".qcow2"))