From dcaabe4d4a8589e1bd73c506dc6f03c8302787fc Mon Sep 17 00:00:00 2001
From: Alex Crawford <alex.crawford@coreos.com>
Date: Mon, 24 Nov 2014 16:42:31 -0800
Subject: [PATCH 1/5] system: clean up UnitManager interface

---
 initialize/config.go      | 38 ++++++++++++++++----------------
 initialize/config_test.go | 20 ++++++++---------
 system/file.go            |  9 +++++---
 system/networkd.go        |  3 ++-
 system/systemd.go         | 46 +++++++++++++++------------------------
 system/systemd_test.go    | 14 ++++++------
 system/unit.go            | 18 +++++++--------
 7 files changed, 70 insertions(+), 78 deletions(-)

diff --git a/initialize/config.go b/initialize/config.go
index a2024ce..9e169ce 100644
--- a/initialize/config.go
+++ b/initialize/config.go
@@ -195,66 +195,66 @@ func Apply(cfg config.CloudConfig, env *Environment) error {
 // commands against units. It returns any error encountered.
 func processUnits(units []system.Unit, root string, um system.UnitManager) error {
 	type action struct {
-		unit    string
+		unit    system.Unit
 		command string
 	}
 	actions := make([]action, 0, len(units))
 	reload := false
 	for _, unit := range units {
-		dst := unit.Destination(root)
 		if unit.Content != "" {
-			log.Printf("Writing unit %s to filesystem at path %s", unit.Name, dst)
-			if err := um.PlaceUnit(&unit, dst); err != nil {
+			log.Printf("Writing unit %q to filesystem", unit.Name)
+			if err := um.PlaceUnit(unit); err != nil {
 				return err
 			}
-			log.Printf("Placed unit %s at %s", unit.Name, dst)
+			log.Printf("Wrote unit %q", unit.Name)
 			reload = true
 		}
 
 		if unit.Mask {
-			log.Printf("Masking unit file %s", unit.Name)
-			if err := um.MaskUnit(&unit); err != nil {
+			log.Printf("Masking unit file %q", unit.Name)
+			if err := um.MaskUnit(unit); err != nil {
 				return err
 			}
 		} else if unit.Runtime {
-			log.Printf("Ensuring runtime unit file %s is unmasked", unit.Name)
-			if err := um.UnmaskUnit(&unit); err != nil {
+			log.Printf("Ensuring runtime unit file %q is unmasked", unit.Name)
+			if err := um.UnmaskUnit(unit); err != nil {
 				return err
 			}
 		}
 
 		if unit.Enable {
 			if unit.Group() != "network" {
-				log.Printf("Enabling unit file %s", unit.Name)
-				if err := um.EnableUnitFile(unit.Name, unit.Runtime); err != nil {
+				log.Printf("Enabling unit file %q", unit.Name)
+				if err := um.EnableUnitFile(unit); err != nil {
 					return err
 				}
-				log.Printf("Enabled unit %s", unit.Name)
+				log.Printf("Enabled unit %q", unit.Name)
 			} else {
-				log.Printf("Skipping enable for network-like unit %s", unit.Name)
+				log.Printf("Skipping enable for network-like unit %q", unit.Name)
 			}
 		}
 
 		if unit.Group() == "network" {
-			actions = append(actions, action{"systemd-networkd.service", "restart"})
+			networkd := system.Unit{Unit: config.Unit{Name: "systemd-networkd.service"}}
+			actions = append(actions, action{networkd, "restart"})
 		} else if unit.Command != "" {
-			actions = append(actions, action{unit.Name, unit.Command})
+			actions = append(actions, action{unit, unit.Command})
 		}
 	}
 
 	if reload {
 		if err := um.DaemonReload(); err != nil {
-			return errors.New(fmt.Sprintf("failed systemd daemon-reload: %v", err))
+			return errors.New(fmt.Sprintf("failed systemd daemon-reload: %s", err))
 		}
 	}
 
 	for _, action := range actions {
-		log.Printf("Calling unit command '%s %s'", action.command, action.unit)
-		res, err := um.RunUnitCommand(action.command, action.unit)
+		log.Printf("Calling unit command %q on %q'", action.command, action.unit.Name)
+		res, err := um.RunUnitCommand(action.unit, action.command)
 		if err != nil {
 			return err
 		}
-		log.Printf("Result of '%s %s': %s", action.command, action.unit, res)
+		log.Printf("Result of %q on %q': %s", action.command, action.unit.Name, res)
 	}
 
 	return nil
diff --git a/initialize/config_test.go b/initialize/config_test.go
index fd67d7e..10a5ae3 100644
--- a/initialize/config_test.go
+++ b/initialize/config_test.go
@@ -32,29 +32,29 @@ type TestUnitManager struct {
 	reload   bool
 }
 
-func (tum *TestUnitManager) PlaceUnit(unit *system.Unit, dst string) error {
-	tum.placed = append(tum.placed, unit.Name)
+func (tum *TestUnitManager) PlaceUnit(u system.Unit) error {
+	tum.placed = append(tum.placed, u.Name)
 	return nil
 }
-func (tum *TestUnitManager) EnableUnitFile(unit string, runtime bool) error {
-	tum.enabled = append(tum.enabled, unit)
+func (tum *TestUnitManager) EnableUnitFile(u system.Unit) error {
+	tum.enabled = append(tum.enabled, u.Name)
 	return nil
 }
-func (tum *TestUnitManager) RunUnitCommand(command, unit string) (string, error) {
+func (tum *TestUnitManager) RunUnitCommand(u system.Unit, c string) (string, error) {
 	tum.commands = make(map[string]string)
-	tum.commands[unit] = command
+	tum.commands[u.Name] = c
 	return "", nil
 }
 func (tum *TestUnitManager) DaemonReload() error {
 	tum.reload = true
 	return nil
 }
-func (tum *TestUnitManager) MaskUnit(unit *system.Unit) error {
-	tum.masked = append(tum.masked, unit.Name)
+func (tum *TestUnitManager) MaskUnit(u system.Unit) error {
+	tum.masked = append(tum.masked, u.Name)
 	return nil
 }
-func (tum *TestUnitManager) UnmaskUnit(unit *system.Unit) error {
-	tum.unmasked = append(tum.unmasked, unit.Name)
+func (tum *TestUnitManager) UnmaskUnit(u system.Unit) error {
+	tum.unmasked = append(tum.unmasked, u.Name)
 	return nil
 }
 
diff --git a/system/file.go b/system/file.go
index f56ab10..ad8673f 100644
--- a/system/file.go
+++ b/system/file.go
@@ -19,6 +19,7 @@ package system
 import (
 	"fmt"
 	"io/ioutil"
+	"log"
 	"os"
 	"os/exec"
 	"path"
@@ -47,13 +48,14 @@ func (f *File) Permissions() (os.FileMode, error) {
 }
 
 func WriteFile(f *File, root string) (string, error) {
+	fullpath := path.Join(root, f.Path)
+	dir := path.Dir(fullpath)
+	log.Printf("Writing file to %q", fullpath)
+
 	if f.Encoding != "" {
 		return "", fmt.Errorf("Unable to write file with encoding %s", f.Encoding)
 	}
 
-	fullpath := path.Join(root, f.Path)
-	dir := path.Dir(fullpath)
-
 	if err := EnsureDirectoryExists(dir); err != nil {
 		return "", err
 	}
@@ -94,6 +96,7 @@ func WriteFile(f *File, root string) (string, error) {
 		return "", err
 	}
 
+	log.Printf("Wrote file to %q", fullpath)
 	return fullpath, nil
 }
 
diff --git a/system/networkd.go b/system/networkd.go
index 528aaa2..056eb6a 100644
--- a/system/networkd.go
+++ b/system/networkd.go
@@ -96,7 +96,8 @@ func maybeProbeBonding(interfaces []network.InterfaceGenerator) error {
 
 func restartNetworkd() error {
 	log.Printf("Restarting networkd.service\n")
-	_, err := NewUnitManager("").RunUnitCommand("restart", "systemd-networkd.service")
+	networkd := Unit{config.Unit{Name: "systemd-networkd.service"}}
+	_, err := NewUnitManager("").RunUnitCommand(networkd, "restart")
 	return err
 }
 
diff --git a/system/systemd.go b/system/systemd.go
index 8200333..2c346a5 100644
--- a/system/systemd.go
+++ b/system/systemd.go
@@ -23,7 +23,6 @@ import (
 	"os"
 	"os/exec"
 	"path"
-	"path/filepath"
 	"strings"
 
 	"github.com/coreos/coreos-cloudinit/Godeps/_workspace/src/github.com/coreos/go-systemd/dbus"
@@ -42,49 +41,38 @@ type systemd struct {
 // never be used as a true MachineID
 const fakeMachineID = "42000000000000000000000000000042"
 
-// PlaceUnit writes a unit file at the provided destination, creating
-// parent directories as necessary.
-func (s *systemd) PlaceUnit(u *Unit, dst string) error {
-	dir := filepath.Dir(dst)
-	if _, err := os.Stat(dir); os.IsNotExist(err) {
-		if err := os.MkdirAll(dir, os.FileMode(0755)); err != nil {
-			return err
-		}
-	}
-
+// PlaceUnit writes a unit file at its desired destination, creating parent
+// directories as necessary.
+func (s *systemd) PlaceUnit(u Unit) error {
 	file := File{config.File{
-		Path:               filepath.Base(dst),
+		Path:               u.Destination(s.root),
 		Content:            u.Content,
 		RawFilePermissions: "0644",
 	}}
 
-	_, err := WriteFile(&file, dir)
-	if err != nil {
-		return err
-	}
-
-	return nil
+	_, err := WriteFile(&file, "/")
+	return err
 }
 
-func (s *systemd) EnableUnitFile(unit string, runtime bool) error {
+func (s *systemd) EnableUnitFile(u Unit) error {
 	conn, err := dbus.New()
 	if err != nil {
 		return err
 	}
 
-	units := []string{unit}
-	_, _, err = conn.EnableUnitFiles(units, runtime, true)
+	units := []string{u.Name}
+	_, _, err = conn.EnableUnitFiles(units, u.Runtime, true)
 	return err
 }
 
-func (s *systemd) RunUnitCommand(command, unit string) (string, error) {
+func (s *systemd) RunUnitCommand(u Unit, c string) (string, error) {
 	conn, err := dbus.New()
 	if err != nil {
 		return "", err
 	}
 
 	var fn func(string, string) (string, error)
-	switch command {
+	switch c {
 	case "start":
 		fn = conn.StartUnit
 	case "stop":
@@ -100,10 +88,10 @@ func (s *systemd) RunUnitCommand(command, unit string) (string, error) {
 	case "reload-or-try-restart":
 		fn = conn.ReloadOrTryRestartUnit
 	default:
-		return "", fmt.Errorf("Unsupported systemd command %q", command)
+		return "", fmt.Errorf("Unsupported systemd command %q", c)
 	}
 
-	return fn(unit, "replace")
+	return fn(u.Name, "replace")
 }
 
 func (s *systemd) DaemonReload() error {
@@ -119,8 +107,8 @@ func (s *systemd) DaemonReload() error {
 // /dev/null, analogous to `systemctl mask`.
 // N.B.: Unlike `systemctl mask`, this function will *remove any existing unit
 // file at the location*, to ensure that the mask will succeed.
-func (s *systemd) MaskUnit(unit *Unit) error {
-	masked := unit.Destination(s.root)
+func (s *systemd) MaskUnit(u Unit) error {
+	masked := u.Destination(s.root)
 	if _, err := os.Stat(masked); os.IsNotExist(err) {
 		if err := os.MkdirAll(path.Dir(masked), os.FileMode(0755)); err != nil {
 			return err
@@ -134,8 +122,8 @@ func (s *systemd) MaskUnit(unit *Unit) error {
 // UnmaskUnit is analogous to systemd's unit_file_unmask. If the file
 // associated with the given Unit is empty or appears to be a symlink to
 // /dev/null, it is removed.
-func (s *systemd) UnmaskUnit(unit *Unit) error {
-	masked := unit.Destination(s.root)
+func (s *systemd) UnmaskUnit(u Unit) error {
+	masked := u.Destination(s.root)
 	ne, err := nullOrEmpty(masked)
 	if os.IsNotExist(err) {
 		return nil
diff --git a/system/systemd_test.go b/system/systemd_test.go
index 2d4f1d5..1a728f6 100644
--- a/system/systemd_test.go
+++ b/system/systemd_test.go
@@ -51,7 +51,7 @@ Address=10.209.171.177/19
 		t.Fatalf("unit.Destination returned %s, expected %s", dst, expectDst)
 	}
 
-	if err := sd.PlaceUnit(&u, dst); err != nil {
+	if err := sd.PlaceUnit(u); err != nil {
 		t.Fatalf("PlaceUnit failed: %v", err)
 	}
 
@@ -128,7 +128,7 @@ Where=/media/state
 		t.Fatalf("unit.Destination returned %s, expected %s", dst, expectDst)
 	}
 
-	if err := sd.PlaceUnit(&u, dst); err != nil {
+	if err := sd.PlaceUnit(u); err != nil {
 		t.Fatalf("PlaceUnit failed: %v", err)
 	}
 
@@ -180,7 +180,7 @@ func TestMaskUnit(t *testing.T) {
 	sd := &systemd{dir}
 
 	// Ensure mask works with units that do not currently exist
-	uf := &Unit{config.Unit{Name: "foo.service"}}
+	uf := Unit{config.Unit{Name: "foo.service"}}
 	if err := sd.MaskUnit(uf); err != nil {
 		t.Fatalf("Unable to mask new unit: %v", err)
 	}
@@ -194,7 +194,7 @@ func TestMaskUnit(t *testing.T) {
 	}
 
 	// Ensure mask works with unit files that already exist
-	ub := &Unit{config.Unit{Name: "bar.service"}}
+	ub := Unit{config.Unit{Name: "bar.service"}}
 	barPath := path.Join(dir, "etc", "systemd", "system", "bar.service")
 	if _, err := os.Create(barPath); err != nil {
 		t.Fatalf("Error creating new unit file: %v", err)
@@ -220,12 +220,12 @@ func TestUnmaskUnit(t *testing.T) {
 
 	sd := &systemd{dir}
 
-	nilUnit := &Unit{config.Unit{Name: "null.service"}}
+	nilUnit := Unit{config.Unit{Name: "null.service"}}
 	if err := sd.UnmaskUnit(nilUnit); err != nil {
 		t.Errorf("unexpected error from unmasking nonexistent unit: %v", err)
 	}
 
-	uf := &Unit{config.Unit{Name: "foo.service", Content: "[Service]\nExecStart=/bin/true"}}
+	uf := Unit{config.Unit{Name: "foo.service", Content: "[Service]\nExecStart=/bin/true"}}
 	dst := uf.Destination(dir)
 	if err := os.MkdirAll(path.Dir(dst), os.FileMode(0755)); err != nil {
 		t.Fatalf("Unable to create unit directory: %v", err)
@@ -245,7 +245,7 @@ func TestUnmaskUnit(t *testing.T) {
 		t.Errorf("unmask of non-empty unit mutated unit contents unexpectedly")
 	}
 
-	ub := &Unit{config.Unit{Name: "bar.service"}}
+	ub := Unit{config.Unit{Name: "bar.service"}}
 	dst = ub.Destination(dir)
 	if err := os.Symlink("/dev/null", dst); err != nil {
 		t.Fatalf("Unable to create masked unit: %v", err)
diff --git a/system/unit.go b/system/unit.go
index 26e9bbc..b48db7b 100644
--- a/system/unit.go
+++ b/system/unit.go
@@ -27,12 +27,12 @@ import (
 const cloudConfigDropIn = "20-cloudinit.conf"
 
 type UnitManager interface {
-	PlaceUnit(unit *Unit, dst string) error
-	EnableUnitFile(unit string, runtime bool) error
-	RunUnitCommand(command, unit string) (string, error)
+	PlaceUnit(unit Unit) error
+	EnableUnitFile(unit Unit) error
+	RunUnitCommand(unit Unit, command string) (string, error)
+	MaskUnit(unit Unit) error
+	UnmaskUnit(unit Unit) error
 	DaemonReload() error
-	MaskUnit(unit *Unit) error
-	UnmaskUnit(unit *Unit) error
 }
 
 // Unit is a top-level structure which embeds its underlying configuration,
@@ -41,10 +41,10 @@ type Unit struct {
 	config.Unit
 }
 
-// Destination builds the appropriate absolute file path for
-// the Unit. The root argument indicates the effective base
-// directory of the system (similar to a chroot).
-func (u *Unit) Destination(root string) string {
+// Destination builds the appropriate absolute file path for the Unit. The root
+// argument indicates the effective base directory of the system (similar to a
+// chroot).
+func (u Unit) Destination(root string) string {
 	dir := "etc"
 	if u.Runtime {
 		dir = "run"

From 75ed8dacf997220248e261306f1dfe07fede5650 Mon Sep 17 00:00:00 2001
From: Alex Crawford <alex.crawford@coreos.com>
Date: Mon, 24 Nov 2014 17:05:36 -0800
Subject: [PATCH 2/5] initialize: clean up TestProcessUnits()

---
 initialize/config_test.go | 136 ++++++++++++++++++++------------------
 1 file changed, 71 insertions(+), 65 deletions(-)

diff --git a/initialize/config_test.go b/initialize/config_test.go
index 10a5ae3..cf8f80e 100644
--- a/initialize/config_test.go
+++ b/initialize/config_test.go
@@ -17,6 +17,7 @@
 package initialize
 
 import (
+	"reflect"
 	"testing"
 
 	"github.com/coreos/coreos-cloudinit/config"
@@ -59,72 +60,77 @@ func (tum *TestUnitManager) UnmaskUnit(u system.Unit) error {
 }
 
 func TestProcessUnits(t *testing.T) {
-	tum := &TestUnitManager{}
-	units := []system.Unit{
-		system.Unit{Unit: config.Unit{
-			Name: "foo",
-			Mask: true,
-		}},
-	}
-	if err := processUnits(units, "", tum); err != nil {
-		t.Fatalf("unexpected error calling processUnits: %v", err)
-	}
-	if len(tum.masked) != 1 || tum.masked[0] != "foo" {
-		t.Errorf("expected foo to be masked, but found %v", tum.masked)
+	tests := []struct {
+		units []system.Unit
+
+		result TestUnitManager
+	}{
+		{
+			units: []system.Unit{
+				system.Unit{Unit: config.Unit{
+					Name: "foo",
+					Mask: true,
+				}},
+			},
+			result: TestUnitManager{
+				masked: []string{"foo"},
+			},
+		},
+		{
+			units: []system.Unit{
+				system.Unit{Unit: config.Unit{
+					Name: "bar.network",
+				}},
+			},
+			result: TestUnitManager{
+				commands: map[string]string{
+					"systemd-networkd.service": "restart",
+				},
+			},
+		},
+		{
+			units: []system.Unit{
+				system.Unit{Unit: config.Unit{
+					Name:    "baz.service",
+					Content: "[Service]\nExecStart=/bin/true",
+				}},
+			},
+			result: TestUnitManager{
+				placed: []string{"baz.service"},
+				reload: true,
+			},
+		},
+		{
+			units: []system.Unit{
+				system.Unit{Unit: config.Unit{
+					Name:    "locksmithd.service",
+					Runtime: true,
+				}},
+			},
+			result: TestUnitManager{
+				unmasked: []string{"locksmithd.service"},
+			},
+		},
+		{
+			units: []system.Unit{
+				system.Unit{Unit: config.Unit{
+					Name:   "woof",
+					Enable: true,
+				}},
+			},
+			result: TestUnitManager{
+				enabled: []string{"woof"},
+			},
+		},
 	}
 
-	tum = &TestUnitManager{}
-	units = []system.Unit{
-		system.Unit{Unit: config.Unit{
-			Name: "bar.network",
-		}},
-	}
-	if err := processUnits(units, "", tum); err != nil {
-		t.Fatalf("unexpected error calling processUnits: %v", err)
-	}
-	if _, ok := tum.commands["systemd-networkd.service"]; !ok {
-		t.Errorf("expected systemd-networkd.service to be reloaded!")
-	}
-
-	tum = &TestUnitManager{}
-	units = []system.Unit{
-		system.Unit{Unit: config.Unit{
-			Name:    "baz.service",
-			Content: "[Service]\nExecStart=/bin/true",
-		}},
-	}
-	if err := processUnits(units, "", tum); err != nil {
-		t.Fatalf("unexpected error calling processUnits: %v", err)
-	}
-	if len(tum.placed) != 1 || tum.placed[0] != "baz.service" {
-		t.Fatalf("expected baz.service to be written, but got %v", tum.placed)
-	}
-
-	tum = &TestUnitManager{}
-	units = []system.Unit{
-		system.Unit{Unit: config.Unit{
-			Name:    "locksmithd.service",
-			Runtime: true,
-		}},
-	}
-	if err := processUnits(units, "", tum); err != nil {
-		t.Fatalf("unexpected error calling processUnits: %v", err)
-	}
-	if len(tum.unmasked) != 1 || tum.unmasked[0] != "locksmithd.service" {
-		t.Fatalf("expected locksmithd.service to be unmasked, but got %v", tum.unmasked)
-	}
-
-	tum = &TestUnitManager{}
-	units = []system.Unit{
-		system.Unit{Unit: config.Unit{
-			Name:   "woof",
-			Enable: true,
-		}},
-	}
-	if err := processUnits(units, "", tum); err != nil {
-		t.Fatalf("unexpected error calling processUnits: %v", err)
-	}
-	if len(tum.enabled) != 1 || tum.enabled[0] != "woof" {
-		t.Fatalf("expected woof to be enabled, but got %v", tum.enabled)
+	for _, tt := range tests {
+		tum := &TestUnitManager{}
+		if err := processUnits(tt.units, "", tum); err != nil {
+			t.Errorf("bad error (%+v): want nil, got %s", tt.units, err)
+		}
+		if !reflect.DeepEqual(tt.result, *tum) {
+			t.Errorf("bad result (%+v): want %+v, got %+v", tt.units, tt.result, tum)
+		}
 	}
 }

From 624df676d06e5f1a54d671a2667ffb07f05f87c2 Mon Sep 17 00:00:00 2001
From: Alex Crawford <alex.crawford@coreos.com>
Date: Tue, 25 Nov 2014 17:41:26 -0800
Subject: [PATCH 3/5] config/unit: move Type() and Group() out of config

---
 config/config_test.go  |   3 --
 config/unit.go         |  19 --------
 system/systemd_test.go |  32 -------------
 system/unit.go         |  23 +++++++++-
 system/unit_test.go    | 100 +++++++++++++++++++++++++++++++++++++++++
 5 files changed, 122 insertions(+), 55 deletions(-)
 create mode 100644 system/unit_test.go

diff --git a/config/config_test.go b/config/config_test.go
index e4c322d..d858cfa 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -261,9 +261,6 @@ Address=10.209.171.177/19
 		if u.Name != "50-eth0.network" {
 			t.Errorf("Unit has incorrect name %s", u.Name)
 		}
-		if u.Type() != "network" {
-			t.Errorf("Unit has incorrect type '%s'", u.Type())
-		}
 	}
 
 	if cfg.Coreos.OEM.ID != "rackspace" {
diff --git a/config/unit.go b/config/unit.go
index 1f56a1e..93ed3f1 100644
--- a/config/unit.go
+++ b/config/unit.go
@@ -16,11 +16,6 @@
 
 package config
 
-import (
-	"path/filepath"
-	"strings"
-)
-
 type Unit struct {
 	Name    string `yaml:"name"`
 	Mask    bool   `yaml:"mask"`
@@ -34,17 +29,3 @@ type Unit struct {
 	// until the correct behaviour for multiple drop-in units is determined.
 	DropIn bool `yaml:"-"`
 }
-
-func (u *Unit) Type() string {
-	ext := filepath.Ext(u.Name)
-	return strings.TrimLeft(ext, ".")
-}
-
-func (u *Unit) Group() string {
-	switch u.Type() {
-	case "network", "netdev", "link":
-		return "network"
-	default:
-		return "system"
-	}
-}
diff --git a/system/systemd_test.go b/system/systemd_test.go
index 1a728f6..a728efd 100644
--- a/system/systemd_test.go
+++ b/system/systemd_test.go
@@ -46,10 +46,6 @@ Address=10.209.171.177/19
 	sd := &systemd{dir}
 
 	dst := u.Destination(dir)
-	expectDst := path.Join(dir, "run", "systemd", "network", "50-eth0.network")
-	if dst != expectDst {
-		t.Fatalf("unit.Destination returned %s, expected %s", dst, expectDst)
-	}
 
 	if err := sd.PlaceUnit(u); err != nil {
 		t.Fatalf("PlaceUnit failed: %v", err)
@@ -80,30 +76,6 @@ Address=10.209.171.177/19
 	}
 }
 
-func TestUnitDestination(t *testing.T) {
-	dir := "/some/dir"
-	name := "foobar.service"
-
-	u := Unit{config.Unit{
-		Name:   name,
-		DropIn: false,
-	}}
-
-	dst := u.Destination(dir)
-	expectDst := path.Join(dir, "etc", "systemd", "system", "foobar.service")
-	if dst != expectDst {
-		t.Errorf("unit.Destination returned %s, expected %s", dst, expectDst)
-	}
-
-	u.DropIn = true
-
-	dst = u.Destination(dir)
-	expectDst = path.Join(dir, "etc", "systemd", "system", "foobar.service.d", cloudConfigDropIn)
-	if dst != expectDst {
-		t.Errorf("unit.Destination returned %s, expected %s", dst, expectDst)
-	}
-}
-
 func TestPlaceMountUnit(t *testing.T) {
 	u := Unit{config.Unit{
 		Name:    "media-state.mount",
@@ -123,10 +95,6 @@ Where=/media/state
 	sd := &systemd{dir}
 
 	dst := u.Destination(dir)
-	expectDst := path.Join(dir, "etc", "systemd", "system", "media-state.mount")
-	if dst != expectDst {
-		t.Fatalf("unit.Destination returned %s, expected %s", dst, expectDst)
-	}
 
 	if err := sd.PlaceUnit(u); err != nil {
 		t.Fatalf("PlaceUnit failed: %v", err)
diff --git a/system/unit.go b/system/unit.go
index b48db7b..897a853 100644
--- a/system/unit.go
+++ b/system/unit.go
@@ -19,6 +19,8 @@ package system
 import (
 	"fmt"
 	"path"
+	"path/filepath"
+	"strings"
 
 	"github.com/coreos/coreos-cloudinit/config"
 )
@@ -36,11 +38,30 @@ type UnitManager interface {
 }
 
 // Unit is a top-level structure which embeds its underlying configuration,
-// config.Unit, and provides the system-specific Destination().
+// config.Unit, and provides the system-specific Destination(), Type(), and
+// Group().
 type Unit struct {
 	config.Unit
 }
 
+// Type returns the extension of the unit (everything that follows the final
+// period).
+func (u Unit) Type() string {
+	ext := filepath.Ext(u.Name)
+	return strings.TrimLeft(ext, ".")
+}
+
+// Group returns "network" or "system" depending on whether or not the unit is
+// a network unit or otherwise.
+func (u Unit) Group() string {
+	switch u.Type() {
+	case "network", "netdev", "link":
+		return "network"
+	default:
+		return "system"
+	}
+}
+
 // Destination builds the appropriate absolute file path for the Unit. The root
 // argument indicates the effective base directory of the system (similar to a
 // chroot).
diff --git a/system/unit_test.go b/system/unit_test.go
new file mode 100644
index 0000000..0303694
--- /dev/null
+++ b/system/unit_test.go
@@ -0,0 +1,100 @@
+/*
+   Copyright 2014 CoreOS, Inc.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package system
+
+import (
+	"testing"
+
+	"github.com/coreos/coreos-cloudinit/config"
+)
+
+func TestType(t *testing.T) {
+	tests := []struct {
+		name string
+
+		typ string
+	}{
+		{},
+		{"test.service", "service"},
+		{"hello", ""},
+		{"lots.of.dots", "dots"},
+	}
+
+	for _, tt := range tests {
+		u := Unit{config.Unit{
+			Name: tt.name,
+		}}
+		if typ := u.Type(); tt.typ != typ {
+			t.Errorf("bad type (%+v): want %q, got %q", tt, tt.typ, typ)
+		}
+	}
+}
+
+func TestGroup(t *testing.T) {
+	tests := []struct {
+		name string
+
+		group string
+	}{
+		{"test.service", "system"},
+		{"test.link", "network"},
+		{"test.network", "network"},
+		{"test.netdev", "network"},
+		{"test.conf", "system"},
+	}
+
+	for _, tt := range tests {
+		u := Unit{config.Unit{
+			Name: tt.name,
+		}}
+		if group := u.Group(); tt.group != group {
+			t.Errorf("bad group (%+v): want %q, got %q", tt, tt.group, group)
+		}
+	}
+}
+
+func TestDestination(t *testing.T) {
+	tests := []struct {
+		root    string
+		name    string
+		runtime bool
+
+		destination string
+	}{
+		{
+			root:        "/some/dir",
+			name:        "foobar.service",
+			destination: "/some/dir/etc/systemd/system/foobar.service",
+		},
+		{
+			root:        "/some/dir",
+			name:        "foobar.service",
+			runtime:     true,
+			destination: "/some/dir/run/systemd/system/foobar.service",
+		},
+	}
+
+	for _, tt := range tests {
+		u := Unit{config.Unit{
+			Name:    tt.name,
+			Runtime: tt.runtime,
+		}}
+		if d := u.Destination(tt.root); tt.destination != d {
+			t.Errorf("bad destination (%+v): want %q, got %q", tt, tt.destination, d)
+		}
+	}
+}

From 420f7cf2025d3d881711848acf7839ccd81267cf Mon Sep 17 00:00:00 2001
From: Alex Crawford <alex.crawford@coreos.com>
Date: Tue, 25 Nov 2014 17:42:37 -0800
Subject: [PATCH 4/5] system: clean up TestPlaceUnit()

---
 system/systemd_test.go | 123 +++++++++++++----------------------------
 1 file changed, 37 insertions(+), 86 deletions(-)

diff --git a/system/systemd_test.go b/system/systemd_test.go
index a728efd..ba0be4d 100644
--- a/system/systemd_test.go
+++ b/system/systemd_test.go
@@ -17,6 +17,7 @@
 package system
 
 import (
+	"fmt"
 	"io/ioutil"
 	"os"
 	"path"
@@ -25,101 +26,51 @@ import (
 	"github.com/coreos/coreos-cloudinit/config"
 )
 
-func TestPlaceNetworkUnit(t *testing.T) {
-	u := Unit{config.Unit{
-		Name:    "50-eth0.network",
-		Runtime: true,
-		Content: `[Match]
-Name=eth47
-
-[Network]
-Address=10.209.171.177/19
-`,
-	}}
-
-	dir, err := ioutil.TempDir(os.TempDir(), "coreos-cloudinit-")
-	if err != nil {
-		t.Fatalf("Unable to create tempdir: %v", err)
-	}
-	defer os.RemoveAll(dir)
-
-	sd := &systemd{dir}
-
-	dst := u.Destination(dir)
-
-	if err := sd.PlaceUnit(u); err != nil {
-		t.Fatalf("PlaceUnit failed: %v", err)
+func TestPlaceUnit(t *testing.T) {
+	tests := []config.Unit{
+		{
+			Name:    "50-eth0.network",
+			Runtime: true,
+			Content: "[Match]\nName=eth47\n\n[Network]\nAddress=10.209.171.177/19\n",
+		},
+		{
+			Name:    "media-state.mount",
+			Content: "[Mount]\nWhat=/dev/sdb1\nWhere=/media/state\n",
+		},
 	}
 
-	fi, err := os.Stat(dst)
-	if err != nil {
-		t.Fatalf("Unable to stat file: %v", err)
-	}
+	for _, tt := range tests {
+		dir, err := ioutil.TempDir(os.TempDir(), "coreos-cloudinit-")
+		if err != nil {
+			panic(fmt.Sprintf("Unable to create tempdir: %v", err))
+		}
 
-	if fi.Mode() != os.FileMode(0644) {
-		t.Errorf("File has incorrect mode: %v", fi.Mode())
-	}
+		u := Unit{tt}
+		sd := &systemd{dir}
 
-	contents, err := ioutil.ReadFile(dst)
-	if err != nil {
-		t.Fatalf("Unable to read expected file: %v", err)
-	}
+		if err := sd.PlaceUnit(u); err != nil {
+			t.Fatalf("PlaceUnit(): bad error (%+v): want nil, got %s", tt, err)
+		}
 
-	expectContents := `[Match]
-Name=eth47
+		fi, err := os.Stat(u.Destination(dir))
+		if err != nil {
+			t.Fatalf("Stat(): bad error (%+v): want nil, got %s", tt, err)
+		}
 
-[Network]
-Address=10.209.171.177/19
-`
-	if string(contents) != expectContents {
-		t.Fatalf("File has incorrect contents '%s'.\nExpected '%s'", string(contents), expectContents)
-	}
-}
+		if mode := fi.Mode(); mode != os.FileMode(0644) {
+			t.Errorf("bad filemode (%+v): want %v, got %v", tt, os.FileMode(0644), mode)
+		}
 
-func TestPlaceMountUnit(t *testing.T) {
-	u := Unit{config.Unit{
-		Name:    "media-state.mount",
-		Runtime: false,
-		Content: `[Mount]
-What=/dev/sdb1
-Where=/media/state
-`,
-	}}
+		c, err := ioutil.ReadFile(u.Destination(dir))
+		if err != nil {
+			t.Fatalf("ReadFile(): bad error (%+v): want nil, got %s", tt, err)
+		}
 
-	dir, err := ioutil.TempDir(os.TempDir(), "coreos-cloudinit-")
-	if err != nil {
-		t.Fatalf("Unable to create tempdir: %v", err)
-	}
-	defer os.RemoveAll(dir)
+		if string(c) != tt.Content {
+			t.Errorf("bad contents (%+v): want %q, got %q", tt, tt.Content, string(c))
+		}
 
-	sd := &systemd{dir}
-
-	dst := u.Destination(dir)
-
-	if err := sd.PlaceUnit(u); err != nil {
-		t.Fatalf("PlaceUnit failed: %v", err)
-	}
-
-	fi, err := os.Stat(dst)
-	if err != nil {
-		t.Fatalf("Unable to stat file: %v", err)
-	}
-
-	if fi.Mode() != os.FileMode(0644) {
-		t.Errorf("File has incorrect mode: %v", fi.Mode())
-	}
-
-	contents, err := ioutil.ReadFile(dst)
-	if err != nil {
-		t.Fatalf("Unable to read expected file: %v", err)
-	}
-
-	expectContents := `[Mount]
-What=/dev/sdb1
-Where=/media/state
-`
-	if string(contents) != expectContents {
-		t.Fatalf("File has incorrect contents '%s'.\nExpected '%s'", string(contents), expectContents)
+		os.RemoveAll(dir)
 	}
 }
 

From ffc54b028cb9ebe60a2353ea322b3f7b5caad6f9 Mon Sep 17 00:00:00 2001
From: Alex Crawford <alex.crawford@coreos.com>
Date: Tue, 25 Nov 2014 16:57:15 -0800
Subject: [PATCH 5/5] drop-in: add support for drop-ins

This allows a list of drop-ins for a unit to be declared inline within a
cloud-config. For example:

  #cloud-config
  coreos:
    units:
      - name: docker.service
        drop-ins:
          - name: 50-insecure-registry.conf
            content: |
              [Service]
              Environment=DOCKER_OPTS='--insecure-registry="10.0.1.0/24"'
---
 Documentation/cloud-config.md | 80 +++++++++++++++++++++--------------
 config/config_test.go         | 20 ---------
 config/unit.go                | 23 +++++-----
 initialize/config.go          | 16 +++++++
 initialize/config_test.go     | 67 +++++++++++++++++++++++++++++
 system/env.go                 | 15 +------
 system/env_test.go            |  4 +-
 system/etcd.go                |  9 +++-
 system/etcd_test.go           | 18 +++++---
 system/flannel.go             |  9 +++-
 system/flannel_test.go        | 16 ++++---
 system/fleet.go               |  9 +++-
 system/fleet_test.go          | 16 ++++---
 system/systemd.go             | 13 ++++++
 system/systemd_test.go        | 58 +++++++++++++++++++++++++
 system/unit.go                | 23 ++++++----
 system/unit_test.go           | 38 +++++++++++++++++
 17 files changed, 329 insertions(+), 105 deletions(-)

diff --git a/Documentation/cloud-config.md b/Documentation/cloud-config.md
index e36778c..aab6746 100644
--- a/Documentation/cloud-config.md
+++ b/Documentation/cloud-config.md
@@ -16,7 +16,7 @@ We've designed our implementation to allow the same cloud-config file to work ac
 
 The cloud-config file uses the [YAML][yaml] file format, which uses whitespace and new-lines to delimit lists, associative arrays, and values.
 
-A cloud-config file should contain `#cloud-config`, followed by an associative array which has zero or more of the following keys:
+A cloud-config file must contain `#cloud-config`, followed by an associative array which has zero or more of the following keys:
 
 - `coreos`
 - `ssh_authorized_keys`
@@ -46,13 +46,13 @@ If the platform environment supports the templating feature of coreos-cloudinit
 #cloud-config
 
 coreos:
-    etcd:
-        name: node001
-	# generate a new token for each unique cluster from https://discovery.etcd.io/new
-        discovery: https://discovery.etcd.io/<token>
-	# multi-region and multi-cloud deployments need to use $public_ipv4
-        addr: $public_ipv4:4001
-        peer-addr: $private_ipv4:7001
+  etcd:
+      name: node001
+      # generate a new token for each unique cluster from https://discovery.etcd.io/new
+      discovery: https://discovery.etcd.io/<token>
+      # multi-region and multi-cloud deployments need to use $public_ipv4
+      addr: $public_ipv4:4001
+      peer-addr: $private_ipv4:7001
 ```
 
 ...will generate a systemd unit drop-in like this:
@@ -66,7 +66,6 @@ Environment="ETCD_PEER_ADDR=192.0.2.13:7001"
 ```
 
 For more information about the available configuration parameters, see the [etcd documentation][etcd-config].
-Note that hyphens in the coreos.etcd.* keys are mapped to underscores.
 
 _Note: The `$private_ipv4` and `$public_ipv4` substitution variables referenced in other documents are only supported on Amazon EC2, Google Compute Engine, OpenStack, Rackspace, DigitalOcean, and Vagrant._
 
@@ -80,9 +79,9 @@ The `coreos.fleet.*` parameters work very similarly to `coreos.etcd.*`, and allo
 #cloud-config
 
 coreos:
-    fleet:
-        public-ip: $public_ipv4
-        metadata: region=us-west
+  fleet:
+      public-ip: $public_ipv4
+      metadata: region=us-west
 ```
 
 ...will generate a systemd unit drop-in like this:
@@ -105,8 +104,8 @@ The `coreos.flannel.*` parameters also work very similarly to `coreos.etcd.*` an
 #cloud-config
 
 coreos:
-    flannel:
-        etcd-prefix: /coreos.com/network2
+  flannel:
+      etcd-prefix: /coreos.com/network2
 ```
 
 ...will generate systemd unit drop-in like so:
@@ -158,6 +157,10 @@ Each item is an object with the following fields:
 - **content**: Plaintext string representing entire unit file. If no value is provided, the unit is assumed to exist already.
 - **command**: Command to execute on unit: start, stop, reload, restart, try-restart, reload-or-restart, reload-or-try-restart. The default behavior is to not execute any commands.
 - **mask**: Whether to mask the unit file by symlinking it to `/dev/null` (analogous to `systemctl mask <name>`). Note that unlike `systemctl mask`, **this will destructively remove any existing unit file** located at `/etc/systemd/system/<unit>`, to ensure that the mask succeeds. The default value is false.
+- **drop-ins**: A list of unit drop-ins with the following fields:
+  - **name**: String representing unit's name. Required.
+  - **content**: Plaintext string representing entire file. Required.
+
 
 **NOTE:** The command field is ignored for all network, netdev, and link units. The systemd-networkd.service unit will be restarted in their place.
 
@@ -169,19 +172,34 @@ Write a unit to disk, automatically starting it.
 #cloud-config
 
 coreos:
-    units:
-      - name: docker-redis.service
-        command: start
-        content: |
-          [Unit]
-          Description=Redis container
-          Author=Me
-          After=docker.service
+  units:
+    - name: docker-redis.service
+      command: start
+      content: |
+        [Unit]
+        Description=Redis container
+        Author=Me
+        After=docker.service
 
-          [Service]
-          Restart=always
-          ExecStart=/usr/bin/docker start -a redis_server
-          ExecStop=/usr/bin/docker stop -t 2 redis_server
+        [Service]
+        Restart=always
+        ExecStart=/usr/bin/docker start -a redis_server
+        ExecStop=/usr/bin/docker stop -t 2 redis_server
+```
+
+Add the DOCKER_OPTS environment variable to docker.service.
+
+```yaml
+#cloud-config
+
+coreos:
+  units:
+    - name: docker.service
+      drop-ins:
+        - name: 50-insecure-registry.conf
+          content: |
+            [Service]
+            Environment=DOCKER_OPTS='--insecure-registry="10.0.1.0/24"'
 ```
 
 Start the built-in `etcd` and `fleet` services:
@@ -190,11 +208,11 @@ Start the built-in `etcd` and `fleet` services:
 #cloud-config
 
 coreos:
-    units:
-      - name: etcd.service
-        command: start
-      - name: fleet.service
-        command: start
+  units:
+    - name: etcd.service
+      command: start
+    - name: fleet.service
+      command: start
 ```
 
 ### ssh_authorized_keys
diff --git a/config/config_test.go b/config/config_test.go
index d858cfa..29171ad 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -335,26 +335,6 @@ func TestCloudConfigSerializationHeader(t *testing.T) {
 	}
 }
 
-// TestDropInIgnored asserts that users are unable to set DropIn=True on units
-func TestDropInIgnored(t *testing.T) {
-	contents := `
-coreos:
-  units:
-    - name: test
-      dropin: true
-`
-	cfg, err := NewCloudConfig(contents)
-	if err != nil || len(cfg.Coreos.Units) != 1 {
-		t.Fatalf("Encountered unexpected error: %v", err)
-	}
-	if len(cfg.Coreos.Units) != 1 || cfg.Coreos.Units[0].Name != "test" {
-		t.Fatalf("Expected 1 unit, but got %d: %v", len(cfg.Coreos.Units), cfg.Coreos.Units)
-	}
-	if cfg.Coreos.Units[0].DropIn {
-		t.Errorf("dropin option on unit in cloud-config was not ignored!")
-	}
-}
-
 func TestCloudConfigUsers(t *testing.T) {
 	contents := `
 users:
diff --git a/config/unit.go b/config/unit.go
index 93ed3f1..3a09bbb 100644
--- a/config/unit.go
+++ b/config/unit.go
@@ -17,15 +17,16 @@
 package config
 
 type Unit struct {
-	Name    string `yaml:"name"`
-	Mask    bool   `yaml:"mask"`
-	Enable  bool   `yaml:"enable"`
-	Runtime bool   `yaml:"runtime"`
-	Content string `yaml:"content"`
-	Command string `yaml:"command" valid:"start,stop,restart,reload,try-restart,reload-or-restart,reload-or-try-restart"`
-
-	// For drop-in units, a cloudinit.conf is generated.
-	// This is currently unbound in YAML (and hence unsettable in cloud-config files)
-	// until the correct behaviour for multiple drop-in units is determined.
-	DropIn bool `yaml:"-"`
+	Name    string       `yaml:"name"`
+	Mask    bool         `yaml:"mask"`
+	Enable  bool         `yaml:"enable"`
+	Runtime bool         `yaml:"runtime"`
+	Content string       `yaml:"content"`
+	Command string       `yaml:"command" valid:"start,stop,restart,reload,try-restart,reload-or-restart,reload-or-try-restart"`
+	DropIns []UnitDropIn `yaml:"drop_ins"`
+}
+
+type UnitDropIn struct {
+	Name    string `yaml:"name"`
+	Content string `yaml:"content"`
 }
diff --git a/initialize/config.go b/initialize/config.go
index 9e169ce..660f00b 100644
--- a/initialize/config.go
+++ b/initialize/config.go
@@ -201,6 +201,11 @@ func processUnits(units []system.Unit, root string, um system.UnitManager) error
 	actions := make([]action, 0, len(units))
 	reload := false
 	for _, unit := range units {
+		if unit.Name == "" {
+			log.Printf("Skipping unit without name")
+			continue
+		}
+
 		if unit.Content != "" {
 			log.Printf("Writing unit %q to filesystem", unit.Name)
 			if err := um.PlaceUnit(unit); err != nil {
@@ -210,6 +215,17 @@ func processUnits(units []system.Unit, root string, um system.UnitManager) error
 			reload = true
 		}
 
+		for _, dropin := range unit.DropIns {
+			if dropin.Name != "" && dropin.Content != "" {
+				log.Printf("Writing drop-in unit %q to filesystem", dropin.Name)
+				if err := um.PlaceUnitDropIn(unit, dropin); err != nil {
+					return err
+				}
+				log.Printf("Wrote drop-in unit %q", dropin.Name)
+				reload = true
+			}
+		}
+
 		if unit.Mask {
 			log.Printf("Masking unit file %q", unit.Name)
 			if err := um.MaskUnit(unit); err != nil {
diff --git a/initialize/config_test.go b/initialize/config_test.go
index cf8f80e..ed95d58 100644
--- a/initialize/config_test.go
+++ b/initialize/config_test.go
@@ -37,6 +37,10 @@ func (tum *TestUnitManager) PlaceUnit(u system.Unit) error {
 	tum.placed = append(tum.placed, u.Name)
 	return nil
 }
+func (tum *TestUnitManager) PlaceUnitDropIn(u system.Unit, d config.UnitDropIn) error {
+	tum.placed = append(tum.placed, u.Name+".d/"+d.Name)
+	return nil
+}
 func (tum *TestUnitManager) EnableUnitFile(u system.Unit) error {
 	tum.enabled = append(tum.enabled, u.Name)
 	return nil
@@ -122,6 +126,69 @@ func TestProcessUnits(t *testing.T) {
 				enabled: []string{"woof"},
 			},
 		},
+		{
+			units: []system.Unit{
+				system.Unit{Unit: config.Unit{
+					Name:    "hi.service",
+					Runtime: true,
+					Content: "[Service]\nExecStart=/bin/echo hi",
+					DropIns: []config.UnitDropIn{
+						{
+							Name:    "lo.conf",
+							Content: "[Service]\nExecStart=/bin/echo lo",
+						},
+						{
+							Name:    "bye.conf",
+							Content: "[Service]\nExecStart=/bin/echo bye",
+						},
+					},
+				}},
+			},
+			result: TestUnitManager{
+				placed:   []string{"hi.service", "hi.service.d/lo.conf", "hi.service.d/bye.conf"},
+				unmasked: []string{"hi.service"},
+				reload:   true,
+			},
+		},
+		{
+			units: []system.Unit{
+				system.Unit{Unit: config.Unit{
+					DropIns: []config.UnitDropIn{
+						{
+							Name:    "lo.conf",
+							Content: "[Service]\nExecStart=/bin/echo lo",
+						},
+					},
+				}},
+			},
+			result: TestUnitManager{},
+		},
+		{
+			units: []system.Unit{
+				system.Unit{Unit: config.Unit{
+					Name: "hi.service",
+					DropIns: []config.UnitDropIn{
+						{
+							Content: "[Service]\nExecStart=/bin/echo lo",
+						},
+					},
+				}},
+			},
+			result: TestUnitManager{},
+		},
+		{
+			units: []system.Unit{
+				system.Unit{Unit: config.Unit{
+					Name: "hi.service",
+					DropIns: []config.UnitDropIn{
+						{
+							Name: "lo.conf",
+						},
+					},
+				}},
+			},
+			result: TestUnitManager{},
+		},
 	}
 
 	for _, tt := range tests {
diff --git a/system/env.go b/system/env.go
index 152b977..993d583 100644
--- a/system/env.go
+++ b/system/env.go
@@ -25,7 +25,7 @@ import (
 
 // dropinContents generates the contents for a drop-in unit given the config.
 // The argument must be a struct from the 'config' package.
-func dropinContents(e interface{}) string {
+func serviceContents(e interface{}) string {
 	et := reflect.TypeOf(e)
 	ev := reflect.ValueOf(e)
 
@@ -42,16 +42,3 @@ func dropinContents(e interface{}) string {
 	}
 	return "[Service]\n" + out
 }
-
-func dropinFromConfig(cfg interface{}, name string) []Unit {
-	content := dropinContents(cfg)
-	if content == "" {
-		return nil
-	}
-	return []Unit{{config.Unit{
-		Name:    name,
-		Runtime: true,
-		DropIn:  true,
-		Content: content,
-	}}}
-}
diff --git a/system/env_test.go b/system/env_test.go
index 0623186..7a02ca2 100644
--- a/system/env_test.go
+++ b/system/env_test.go
@@ -4,7 +4,7 @@ import (
 	"testing"
 )
 
-func TestDropinContents(t *testing.T) {
+func TestServiceContents(t *testing.T) {
 	tests := []struct {
 		Config   interface{}
 		Contents string
@@ -48,7 +48,7 @@ Environment="D=0.1"
 	}
 
 	for _, tt := range tests {
-		if c := dropinContents(tt.Config); c != tt.Contents {
+		if c := serviceContents(tt.Config); c != tt.Contents {
 			t.Errorf("bad contents (%+v): want %q, got %q", tt, tt.Contents, c)
 		}
 	}
diff --git a/system/etcd.go b/system/etcd.go
index a80b091..0e898b1 100644
--- a/system/etcd.go
+++ b/system/etcd.go
@@ -28,5 +28,12 @@ type Etcd struct {
 
 // Units creates a Unit file drop-in for etcd, using any configured options.
 func (ee Etcd) Units() []Unit {
-	return dropinFromConfig(ee.Etcd, "etcd.service")
+	return []Unit{{config.Unit{
+		Name:    "etcd.service",
+		Runtime: true,
+		DropIns: []config.UnitDropIn{{
+			Name:    "20-cloudinit.conf",
+			Content: serviceContents(ee.Etcd),
+		}},
+	}}}
 }
diff --git a/system/etcd_test.go b/system/etcd_test.go
index 879eb8f..a161abc 100644
--- a/system/etcd_test.go
+++ b/system/etcd_test.go
@@ -30,7 +30,11 @@ func TestEtcdUnits(t *testing.T) {
 	}{
 		{
 			config.Etcd{},
-			nil,
+			[]Unit{{config.Unit{
+				Name:    "etcd.service",
+				Runtime: true,
+				DropIns: []config.UnitDropIn{{Name: "20-cloudinit.conf"}},
+			}}},
 		},
 		{
 			config.Etcd{
@@ -40,11 +44,13 @@ func TestEtcdUnits(t *testing.T) {
 			[]Unit{{config.Unit{
 				Name:    "etcd.service",
 				Runtime: true,
-				DropIn:  true,
-				Content: `[Service]
+				DropIns: []config.UnitDropIn{{
+					Name: "20-cloudinit.conf",
+					Content: `[Service]
 Environment="ETCD_DISCOVERY=http://disco.example.com/foobar"
 Environment="ETCD_PEER_BIND_ADDR=127.0.0.1:7002"
 `,
+				}},
 			}}},
 		},
 		{
@@ -56,12 +62,14 @@ Environment="ETCD_PEER_BIND_ADDR=127.0.0.1:7002"
 			[]Unit{{config.Unit{
 				Name:    "etcd.service",
 				Runtime: true,
-				DropIn:  true,
-				Content: `[Service]
+				DropIns: []config.UnitDropIn{{
+					Name: "20-cloudinit.conf",
+					Content: `[Service]
 Environment="ETCD_DISCOVERY=http://disco.example.com/foobar"
 Environment="ETCD_NAME=node001"
 Environment="ETCD_PEER_BIND_ADDR=127.0.0.1:7002"
 `,
+				}},
 			}}},
 		},
 	} {
diff --git a/system/flannel.go b/system/flannel.go
index d6559a5..3e97f18 100644
--- a/system/flannel.go
+++ b/system/flannel.go
@@ -13,5 +13,12 @@ type Flannel struct {
 // Units generates a Unit file drop-in for flannel, if any flannel options were
 // configured in cloud-config
 func (fl Flannel) Units() []Unit {
-	return dropinFromConfig(fl.Flannel, "flanneld.service")
+	return []Unit{{config.Unit{
+		Name:    "flanneld.service",
+		Runtime: true,
+		DropIns: []config.UnitDropIn{{
+			Name:    "20-cloudinit.conf",
+			Content: serviceContents(fl.Flannel),
+		}},
+	}}}
 }
diff --git a/system/flannel_test.go b/system/flannel_test.go
index 943382e..2e20c46 100644
--- a/system/flannel_test.go
+++ b/system/flannel_test.go
@@ -14,7 +14,11 @@ func TestFlannelUnits(t *testing.T) {
 	}{
 		{
 			config.Flannel{},
-			nil,
+			[]Unit{{config.Unit{
+				Name:    "flanneld.service",
+				Runtime: true,
+				DropIns: []config.UnitDropIn{{Name: "20-cloudinit.conf"}},
+			}}},
 		},
 		{
 			config.Flannel{
@@ -22,13 +26,15 @@ func TestFlannelUnits(t *testing.T) {
 				EtcdPrefix:   "/coreos.com/network/tenant1",
 			},
 			[]Unit{{config.Unit{
-				Name: "flanneld.service",
-				Content: `[Service]
+				Name:    "flanneld.service",
+				Runtime: true,
+				DropIns: []config.UnitDropIn{{
+					Name: "20-cloudinit.conf",
+					Content: `[Service]
 Environment="FLANNELD_ETCD_ENDPOINT=http://12.34.56.78:4001"
 Environment="FLANNELD_ETCD_PREFIX=/coreos.com/network/tenant1"
 `,
-				Runtime: true,
-				DropIn:  true,
+				}},
 			}}},
 		},
 	} {
diff --git a/system/fleet.go b/system/fleet.go
index 45def39..84cb378 100644
--- a/system/fleet.go
+++ b/system/fleet.go
@@ -29,5 +29,12 @@ type Fleet struct {
 // Units generates a Unit file drop-in for fleet, if any fleet options were
 // configured in cloud-config
 func (fe Fleet) Units() []Unit {
-	return dropinFromConfig(fe.Fleet, "fleet.service")
+	return []Unit{{config.Unit{
+		Name:    "fleet.service",
+		Runtime: true,
+		DropIns: []config.UnitDropIn{{
+			Name:    "20-cloudinit.conf",
+			Content: serviceContents(fe.Fleet),
+		}},
+	}}}
 }
diff --git a/system/fleet_test.go b/system/fleet_test.go
index bf3c77e..f3e3284 100644
--- a/system/fleet_test.go
+++ b/system/fleet_test.go
@@ -30,19 +30,25 @@ func TestFleetUnits(t *testing.T) {
 	}{
 		{
 			config.Fleet{},
-			nil,
+			[]Unit{{config.Unit{
+				Name:    "fleet.service",
+				Runtime: true,
+				DropIns: []config.UnitDropIn{{Name: "20-cloudinit.conf"}},
+			}}},
 		},
 		{
 			config.Fleet{
 				PublicIP: "12.34.56.78",
 			},
 			[]Unit{{config.Unit{
-				Name: "fleet.service",
-				Content: `[Service]
+				Name:    "fleet.service",
+				Runtime: true,
+				DropIns: []config.UnitDropIn{{
+					Name: "20-cloudinit.conf",
+					Content: `[Service]
 Environment="FLEET_PUBLIC_IP=12.34.56.78"
 `,
-				Runtime: true,
-				DropIn:  true,
+				}},
 			}}},
 		},
 	} {
diff --git a/system/systemd.go b/system/systemd.go
index 2c346a5..f9651b1 100644
--- a/system/systemd.go
+++ b/system/systemd.go
@@ -54,6 +54,19 @@ func (s *systemd) PlaceUnit(u Unit) error {
 	return err
 }
 
+// PlaceUnitDropIn writes a unit drop-in file at its desired destination,
+// creating parent directories as necessary.
+func (s *systemd) PlaceUnitDropIn(u Unit, d config.UnitDropIn) error {
+	file := File{config.File{
+		Path:               u.DropInDestination(s.root, d),
+		Content:            d.Content,
+		RawFilePermissions: "0644",
+	}}
+
+	_, err := WriteFile(&file, "/")
+	return err
+}
+
 func (s *systemd) EnableUnitFile(u Unit) error {
 	conn, err := dbus.New()
 	if err != nil {
diff --git a/system/systemd_test.go b/system/systemd_test.go
index ba0be4d..2794c88 100644
--- a/system/systemd_test.go
+++ b/system/systemd_test.go
@@ -74,6 +74,64 @@ func TestPlaceUnit(t *testing.T) {
 	}
 }
 
+func TestPlaceUnitDropIn(t *testing.T) {
+	tests := []config.Unit{
+		{
+			Name:    "false.service",
+			Runtime: true,
+			DropIns: []config.UnitDropIn{
+				{
+					Name:    "00-true.conf",
+					Content: "[Service]\nExecStart=\nExecStart=/usr/bin/true\n",
+				},
+			},
+		},
+		{
+			Name: "true.service",
+			DropIns: []config.UnitDropIn{
+				{
+					Name:    "00-false.conf",
+					Content: "[Service]\nExecStart=\nExecStart=/usr/bin/false\n",
+				},
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		dir, err := ioutil.TempDir(os.TempDir(), "coreos-cloudinit-")
+		if err != nil {
+			panic(fmt.Sprintf("Unable to create tempdir: %v", err))
+		}
+
+		u := Unit{tt}
+		sd := &systemd{dir}
+
+		if err := sd.PlaceUnitDropIn(u, u.DropIns[0]); err != nil {
+			t.Fatalf("PlaceUnit(): bad error (%+v): want nil, got %s", tt, err)
+		}
+
+		fi, err := os.Stat(u.DropInDestination(dir, u.DropIns[0]))
+		if err != nil {
+			t.Fatalf("Stat(): bad error (%+v): want nil, got %s", tt, err)
+		}
+
+		if mode := fi.Mode(); mode != os.FileMode(0644) {
+			t.Errorf("bad filemode (%+v): want %v, got %v", tt, os.FileMode(0644), mode)
+		}
+
+		c, err := ioutil.ReadFile(u.DropInDestination(dir, u.DropIns[0]))
+		if err != nil {
+			t.Fatalf("ReadFile(): bad error (%+v): want nil, got %s", tt, err)
+		}
+
+		if string(c) != u.DropIns[0].Content {
+			t.Errorf("bad contents (%+v): want %q, got %q", tt, u.DropIns[0].Content, string(c))
+		}
+
+		os.RemoveAll(dir)
+	}
+}
+
 func TestMachineID(t *testing.T) {
 	dir, err := ioutil.TempDir(os.TempDir(), "coreos-cloudinit-")
 	if err != nil {
diff --git a/system/unit.go b/system/unit.go
index 897a853..e7152ec 100644
--- a/system/unit.go
+++ b/system/unit.go
@@ -25,11 +25,9 @@ import (
 	"github.com/coreos/coreos-cloudinit/config"
 )
 
-// Name for drop-in service configuration files created by cloudconfig
-const cloudConfigDropIn = "20-cloudinit.conf"
-
 type UnitManager interface {
 	PlaceUnit(unit Unit) error
+	PlaceUnitDropIn(unit Unit, dropIn config.UnitDropIn) error
 	EnableUnitFile(unit Unit) error
 	RunUnitCommand(unit Unit, command string) (string, error)
 	MaskUnit(unit Unit) error
@@ -66,14 +64,21 @@ func (u Unit) Group() string {
 // argument indicates the effective base directory of the system (similar to a
 // chroot).
 func (u Unit) Destination(root string) string {
+	return path.Join(u.prefix(root), u.Name)
+}
+
+// DropInDestination builds the appropriate absolute file path for the
+// UnitDropIn. The root argument indicates the effective base directory of the
+// system (similar to a chroot) and the dropIn argument is the UnitDropIn for
+// which the destination is being calculated.
+func (u Unit) DropInDestination(root string, dropIn config.UnitDropIn) string {
+	return path.Join(u.prefix(root), fmt.Sprintf("%s.d", u.Name), dropIn.Name)
+}
+
+func (u Unit) prefix(root string) string {
 	dir := "etc"
 	if u.Runtime {
 		dir = "run"
 	}
-
-	if u.DropIn {
-		return path.Join(root, dir, "systemd", u.Group(), fmt.Sprintf("%s.d", u.Name), cloudConfigDropIn)
-	} else {
-		return path.Join(root, dir, "systemd", u.Group(), u.Name)
-	}
+	return path.Join(root, dir, "systemd", u.Group())
 }
diff --git a/system/unit_test.go b/system/unit_test.go
index 0303694..10cb883 100644
--- a/system/unit_test.go
+++ b/system/unit_test.go
@@ -98,3 +98,41 @@ func TestDestination(t *testing.T) {
 		}
 	}
 }
+
+func TestDropInDestination(t *testing.T) {
+	tests := []struct {
+		root       string
+		unitName   string
+		dropInName string
+		runtime    bool
+
+		destination string
+	}{
+		{
+			root:        "/some/dir",
+			unitName:    "foo.service",
+			dropInName:  "bar.conf",
+			destination: "/some/dir/etc/systemd/system/foo.service.d/bar.conf",
+		},
+		{
+			root:        "/some/dir",
+			unitName:    "foo.service",
+			dropInName:  "bar.conf",
+			runtime:     true,
+			destination: "/some/dir/run/systemd/system/foo.service.d/bar.conf",
+		},
+	}
+
+	for _, tt := range tests {
+		u := Unit{config.Unit{
+			Name:    tt.unitName,
+			Runtime: tt.runtime,
+			DropIns: []config.UnitDropIn{{
+				Name: tt.dropInName,
+			}},
+		}}
+		if d := u.DropInDestination(tt.root, u.DropIns[0]); tt.destination != d {
+			t.Errorf("bad destination (%+v): want %q, got %q", tt, tt.destination, d)
+		}
+	}
+}