From cf13eaa30700d3f3c7f43b3e842cf15bea96e3aa Mon Sep 17 00:00:00 2001
From: Kir Kolyshkin <kolyshkin@gmail.com>
Date: Fri, 25 Jul 2025 15:52:30 -0700
Subject: [PATCH 1/2] dbus: add AttachProcessesToUnit

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
---
 dbus/methods.go | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/dbus/methods.go b/dbus/methods.go
index 074148cb..285eaddb 100644
--- a/dbus/methods.go
+++ b/dbus/methods.go
@@ -862,3 +862,8 @@ func (c *Conn) FreezeUnit(ctx context.Context, unit string) error {
 func (c *Conn) ThawUnit(ctx context.Context, unit string) error {
 	return c.sysobj.CallWithContext(ctx, "org.freedesktop.systemd1.Manager.ThawUnit", 0, unit).Store()
 }
+
+// AttachProcessesToUnit moves existing processes, identified by pids, into an existing systemd unit.
+func (c *Conn) AttachProcessesToUnit(ctx context.Context, unit, subcgroup string, pids []uint32) error {
+	return c.sysobj.CallWithContext(ctx, "org.freedesktop.systemd1.Manager.AttachProcessesToUnit", 0, unit, subcgroup, pids).Store()
+}

From 190804470dbe9200b58abe09f35559a6f9152373 Mon Sep 17 00:00:00 2001
From: Kir Kolyshkin <kolyshkin@gmail.com>
Date: Mon, 28 Jul 2025 19:26:53 -0700
Subject: [PATCH 2/2] dbus: add unit tests for AttachProcessesToUnit

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
---
 dbus/methods_test.go              | 88 +++++++++++++++++++++++++++++++
 fixtures/attach-processes.service |  6 +++
 2 files changed, 94 insertions(+)
 create mode 100644 fixtures/attach-processes.service

diff --git a/dbus/methods_test.go b/dbus/methods_test.go
index 30cc1324..79ad6809 100644
--- a/dbus/methods_test.go
+++ b/dbus/methods_test.go
@@ -1689,3 +1689,91 @@ func TestFreezer(t *testing.T) {
 
 	runStopUnit(t, conn, TrUnitProp{target, nil})
 }
+
+func testAttachProcessesToUnit(t *testing.T, subcgroup string) {
+	target := "attach-processes.service"
+	conn := setupConn(t)
+	defer conn.Close()
+
+	setupUnit(target, conn, t)
+	linkUnit(target, conn, t)
+
+	// Start the unit first.
+	reschan := make(chan string)
+	_, err := conn.StartUnit(target, "replace", reschan)
+	if err != nil {
+		t.Fatal(err)
+	}
+	job := <-reschan
+	if job != "done" {
+		t.Fatal("Job is not done:", job)
+	}
+
+	// Cleanup.
+	defer func() {
+		_, err = conn.StopUnit(target, "replace", reschan)
+		if err != nil {
+			t.Fatal(err)
+		}
+		<-reschan
+	}()
+
+	if subcgroup != "" {
+		// Pre-create a sub-cgroup.
+		prop, err := conn.GetServiceProperty(target, "ControlGroup")
+		if err != nil {
+			t.Fatal(err)
+		}
+		path := prop.Value.Value().(string)
+		err = os.Mkdir(filepath.Join("/sys/fs/cgroup", path, subcgroup), 0777)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+	}
+
+	// Start a test process that we can attach.
+	cmd := exec.Command("/bin/sleep", "400")
+	err = cmd.Start()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		cmd.Process.Kill()
+		cmd.Wait()
+	}()
+
+	pid := uint32(cmd.Process.Pid)
+
+	// Test attaching the process to the unit.
+	ctx := context.Background()
+	err = conn.AttachProcessesToUnit(ctx, target, subcgroup, []uint32{pid})
+	if err != nil {
+		// AttachProcessesToUnit might not be supported on all systemd versions.
+		e, ok := err.(dbus.Error)
+		if ok && (e.Name == "org.freedesktop.DBus.Error.UnknownMethod" ||
+			e.Name == "org.freedesktop.DBus.Error.NotSupported") {
+			t.SkipNow()
+		}
+		t.Fatalf("failed to attach process %d to unit %s: %s", pid, target, err)
+	}
+
+	// Verify the process was attached by getting the unit it belongs to.
+	attachedPath, err := conn.GetUnitByPID(ctx, pid)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	attachedUnit := unitName(attachedPath)
+	if attachedUnit != target {
+		t.Fatalf("process was not attached to correct unit: got %s, want %s", attachedUnit, target)
+	}
+}
+
+func TestAttachProcessesToUnit(t *testing.T) {
+	testAttachProcessesToUnit(t, "")
+}
+
+func TestAttachProcessesToUnitWithSubcgroup(t *testing.T) {
+	testAttachProcessesToUnit(t, "/test-subcgroup")
+}
diff --git a/fixtures/attach-processes.service b/fixtures/attach-processes.service
new file mode 100644
index 00000000..c82197c7
--- /dev/null
+++ b/fixtures/attach-processes.service
@@ -0,0 +1,6 @@
+[Unit]
+Description=attach processes test
+
+[Service]
+Delegate=yes
+ExecStart=/bin/sleep 400