feat(setserial): support TIOCGSERIAL/TIOCSSERIAL

serial_setserial_linux.go

@@ -0,0 +1,78 @@
+//go:build linux
+// +build linux
+
+package serial
+
+import (
+	"fmt"
+	"os"
+	"syscall"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+// CSerialStruct is a C-interop struct for linux/serial.h: struct serial_struct
+// Field order and types must exactly match the C definition for binary compatibility.
+// See: https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/serial.h#L135
+type CSerialStruct struct {
+	Type          int32
+	Line          int32
+	Port          uint32
+	IRQ           int32
+	Flags         int32
+	XmitFifoSize  int32
+	CustomDivisor int32
+	BaudBase      int32
+	CloseDelay    uint16
+	IOType        byte
+	ReservedChar  byte
+	Hub6          int32
+	ClosingWait   uint16
+	ClosingWait2  uint16
+	IOMemBase     uintptr
+	IOMemRegShift uint16
+	PortHigh      uint32
+	// IOMapBase: In C, this is 'unsigned long'. Use uint64 for 64-bit systems.
+	// For 32-bit systems, you may need to use uint32 for binary compatibility.
+	IOMapBase uint64
+}
+
+// GetSerialStruct opens the device and retrieves the CSerialStruct using TIOCGSERIAL ioctl.
+func GetSerialStruct(device string) (*CSerialStruct, error) {
+	f, err := os.OpenFile(device, os.O_RDWR|syscall.O_NOCTTY|syscall.O_NONBLOCK, 0666)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open device: %w", err)
+	}
+	defer f.Close()
+
+	var ser CSerialStruct
+	_, _, errno := syscall.Syscall(syscall.SYS_IOCTL, f.Fd(), unix.TIOCGSERIAL, uintptr(unsafe.Pointer(&ser)))
+	if errno != 0 {
+		return nil, fmt.Errorf("ioctl TIOCGSERIAL failed: %v", errno)
+	}
+	return &ser, nil
+}
+
+// SetSerialPortMode sets the port mode using ioctl TIOCSSERIAL
+func SetSerialPortMode(device string, portMode uint32) error {
+	f, err := os.OpenFile(device, os.O_RDWR|syscall.O_NOCTTY|syscall.O_NONBLOCK, 0666)
+	if err != nil {
+		return fmt.Errorf("failed to open device: %w", err)
+	}
+	defer f.Close()
+
+	var ser CSerialStruct
+	_, _, errno := syscall.Syscall(syscall.SYS_IOCTL, f.Fd(), unix.TIOCGSERIAL, uintptr(unsafe.Pointer(&ser)))
+	if errno != 0 {
+		return fmt.Errorf("ioctl TIOCGSERIAL failed: %v", errno)
+	}
+
+	ser.Port = portMode
+
+	_, _, errno = syscall.Syscall(syscall.SYS_IOCTL, f.Fd(), unix.TIOCSSERIAL, uintptr(unsafe.Pointer(&ser)))
+	if errno != 0 {
+		return fmt.Errorf("ioctl TIOCSSERIAL failed: %v", errno)
+	}
+	return nil
+}

serial_setserial_linux_test.go

@@ -0,0 +1,52 @@
+//go:build linux
+// +build linux
+
+package serial
+
+import (
+	"context"
+	"os/exec"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func startSocatAndWaitForSetserialTest(t *testing.T, ctx context.Context) *exec.Cmd {
+	cmd := exec.CommandContext(ctx, "socat", "-D", "STDIO", "pty,link=/tmp/faketty_setserial")
+	r, err := cmd.StderrPipe()
+	require.NoError(t, err)
+	require.NoError(t, cmd.Start())
+	buf := make([]byte, 1024)
+	_, err = r.Read(buf)
+	require.NoError(t, err)
+	return cmd
+}
+
+func TestGetSerialStructOnFakeTty(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	cmd := startSocatAndWaitForSetserialTest(t, ctx)
+	go cmd.Wait()
+
+	ser, err := GetSerialStruct("/tmp/faketty_setserial")
+	// Note: socat's virtual TTY may not fully support TIOCGSERIAL.
+	// If not supported, skip the test (environment dependent).
+	if err != nil {
+		t.Skipf("ioctl TIOCGSERIAL not supported on socat pty: %v", err)
+	}
+	require.NotNil(t, ser)
+}
+
+func TestSetSerialPortModeOnFakeTty(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	cmd := startSocatAndWaitForSetserialTest(t, ctx)
+	go cmd.Wait()
+
+	err := SetSerialPortMode("/tmp/faketty_setserial", 0)
+	// Note: socat's virtual TTY may not fully support TIOCSSERIAL.
+	// If not supported, skip the test (environment dependent).
+	if err != nil {
+		t.Skipf("ioctl TIOCSSERIAL not supported on socat pty: %v", err)
+	}
+}