Kernel/USB: Refactor USB Pipe

Decompose the current monolithic USBD Pipe interface into several
subclasses, one for each pair of endpoint type & direction. This is to
make it more clear what data and functionality belongs to which Pipe
type, and prevent nonsensical things like trying to execute a control
transfer on a non-control pipe. This is important, because the Pipe
class is the interface by which USB device drivers will interact with
the HCD, so the clearer and more explicit this interface is the better.

Kernel/Bus/USB/USBDevice.cpp

@@ -18,7 +18,7 @@ namespace Kernel::USB {
 
 ErrorOr<NonnullLockRefPtr<Device>> Device::try_create(USBController const& controller, u8 port, DeviceSpeed speed)
 {
-    auto pipe = TRY(Pipe::try_create_pipe(controller, Pipe::Type::Control, Pipe::Direction::Bidirectional, 0, 8, 0));
+    auto pipe = TRY(ControlPipe::create(controller, 0, 8, 0));
     auto device = TRY(adopt_nonnull_lock_ref_or_enomem(new (nothrow) Device(controller, port, speed, move(pipe))));
     auto sysfs_node = TRY(SysFSUSBDeviceInformation::create(*device));
     device->m_sysfs_device_info_node = move(sysfs_node);
@@ -26,7 +26,7 @@ ErrorOr<NonnullLockRefPtr<Device>> Device::try_create(USBController const& contr
     return device;
 }
 
-Device::Device(USBController const& controller, u8 port, DeviceSpeed speed, NonnullOwnPtr<Pipe> default_pipe)
+Device::Device(USBController const& controller, u8 port, DeviceSpeed speed, NonnullOwnPtr<ControlPipe> default_pipe)
     : m_device_port(port)
     , m_device_speed(speed)
     , m_address(0)
@@ -35,7 +35,7 @@ Device::Device(USBController const& controller, u8 port, DeviceSpeed speed, Nonn
 {
 }
 
-Device::Device(NonnullLockRefPtr<USBController> controller, u8 address, u8 port, DeviceSpeed speed, NonnullOwnPtr<Pipe> default_pipe)
+Device::Device(NonnullLockRefPtr<USBController> controller, u8 address, u8 port, DeviceSpeed speed, NonnullOwnPtr<ControlPipe> default_pipe)
     : m_device_port(port)
     , m_device_speed(speed)
     , m_address(address)
@@ -44,7 +44,7 @@ Device::Device(NonnullLockRefPtr<USBController> controller, u8 address, u8 port,
 {
 }
 
-Device::Device(Device const& device, NonnullOwnPtr<Pipe> default_pipe)
+Device::Device(Device const& device, NonnullOwnPtr<ControlPipe> default_pipe)
     : m_device_port(device.port())
     , m_device_speed(device.speed())
     , m_address(device.address())

Kernel/Bus/USB/USBDevice.h

@@ -36,8 +36,8 @@ public:
 
     static ErrorOr<NonnullLockRefPtr<Device>> try_create(USBController const&, u8, DeviceSpeed);
 
-    Device(USBController const&, u8, DeviceSpeed, NonnullOwnPtr<Pipe> default_pipe);
+    Device(USBController const&, u8, DeviceSpeed, NonnullOwnPtr<ControlPipe> default_pipe);
-    Device(Device const& device, NonnullOwnPtr<Pipe> default_pipe);
+    Device(Device const& device, NonnullOwnPtr<ControlPipe> default_pipe);
     virtual ~Device();
 
     ErrorOr<void> enumerate_device();
@@ -59,7 +59,7 @@ public:
     SysFSUSBDeviceInformation& sysfs_device_info_node(Badge<USB::Hub>) { return *m_sysfs_device_info_node; }
 
 protected:
-    Device(NonnullLockRefPtr<USBController> controller, u8 address, u8 port, DeviceSpeed speed, NonnullOwnPtr<Pipe> default_pipe);
+    Device(NonnullLockRefPtr<USBController> controller, u8 address, u8 port, DeviceSpeed speed, NonnullOwnPtr<ControlPipe> default_pipe);
 
     u8 m_device_port { 0 };     // What port is this device attached to. NOTE: This is 1-based.
     DeviceSpeed m_device_speed; // What speed is this device running at
@@ -72,7 +72,7 @@ protected:
     Vector<USBConfiguration> m_configurations;  // Configurations for this device
 
     NonnullLockRefPtr<USBController> m_controller;
-    NonnullOwnPtr<Pipe> m_default_pipe; // Default communication pipe (endpoint0) used during enumeration
+    NonnullOwnPtr<ControlPipe> m_default_pipe; // Default communication pipe (endpoint0) used during enumeration
 
 private:
     IntrusiveListNode<Device, NonnullLockRefPtr<Device>> m_hub_child_node;

Kernel/Bus/USB/USBHub.cpp

@@ -18,25 +18,25 @@ namespace Kernel::USB {
 ErrorOr<NonnullLockRefPtr<Hub>> Hub::try_create_root_hub(NonnullLockRefPtr<USBController> controller, DeviceSpeed device_speed)
 {
     // NOTE: Enumeration does not happen here, as the controller must know what the device address is at all times during enumeration to intercept requests.
-    auto pipe = TRY(Pipe::try_create_pipe(controller, Pipe::Type::Control, Pipe::Direction::Bidirectional, 0, 8, 0));
+    auto pipe = TRY(ControlPipe::create(controller, 0, 8, 0));
     auto hub = TRY(adopt_nonnull_lock_ref_or_enomem(new (nothrow) Hub(controller, device_speed, move(pipe))));
     return hub;
 }
 
 ErrorOr<NonnullLockRefPtr<Hub>> Hub::try_create_from_device(Device const& device)
 {
-    auto pipe = TRY(Pipe::try_create_pipe(device.controller(), Pipe::Type::Control, Pipe::Direction::Bidirectional, 0, device.device_descriptor().max_packet_size, device.address()));
+    auto pipe = TRY(ControlPipe::create(device.controller(), 0, device.device_descriptor().max_packet_size, device.address()));
     auto hub = TRY(adopt_nonnull_lock_ref_or_enomem(new (nothrow) Hub(device, move(pipe))));
     TRY(hub->enumerate_and_power_on_hub());
     return hub;
 }
 
-Hub::Hub(NonnullLockRefPtr<USBController> controller, DeviceSpeed device_speed, NonnullOwnPtr<Pipe> default_pipe)
+Hub::Hub(NonnullLockRefPtr<USBController> controller, DeviceSpeed device_speed, NonnullOwnPtr<ControlPipe> default_pipe)
     : Device(move(controller), 1 /* Port 1 */, device_speed, move(default_pipe))
 {
 }
 
-Hub::Hub(Device const& device, NonnullOwnPtr<Pipe> default_pipe)
+Hub::Hub(Device const& device, NonnullOwnPtr<ControlPipe> default_pipe)
     : Device(device, move(default_pipe))
 {
 }

Kernel/Bus/USB/USBHub.h

@@ -96,9 +96,9 @@ public:
 
 private:
     // Root Hub constructor
-    Hub(NonnullLockRefPtr<USBController>, DeviceSpeed, NonnullOwnPtr<Pipe> default_pipe);
+    Hub(NonnullLockRefPtr<USBController>, DeviceSpeed, NonnullOwnPtr<ControlPipe> default_pipe);
 
-    Hub(Device const&, NonnullOwnPtr<Pipe> default_pipe);
+    Hub(Device const&, NonnullOwnPtr<ControlPipe> default_pipe);
 
     USBHubDescriptor m_hub_descriptor {};
 

Kernel/Bus/USB/USBPipe.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com>
+ * Copyright (c) 2022, blackcat <b14ckcat@protonmail.com>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -12,48 +13,33 @@
 
 namespace Kernel::USB {
 
-ErrorOr<NonnullOwnPtr<Pipe>> Pipe::try_create_pipe(USBController const& controller, Type type, Direction direction, u8 endpoint_address, u16 max_packet_size, i8 device_address, size_t buffer_size, u8 poll_interval)
+Pipe::Pipe(USBController const& controller, Type type, Direction direction, u8 endpoint_address, u16 max_packet_size, i8 device_address, NonnullOwnPtr<Memory::Region> dma_buffer)
-{
-    auto dma_region = TRY(MM.allocate_dma_buffer_pages(TRY(Memory::page_round_up(buffer_size)), "USB device DMA buffer"sv, Memory::Region::Access::ReadWrite));
-    return adopt_nonnull_own_or_enomem(new (nothrow) Pipe(controller, type, direction, endpoint_address, max_packet_size, poll_interval, device_address, move(dma_region)));
-}
-
-Pipe::Pipe(USBController const& controller, Type type, Pipe::Direction direction, u16 max_packet_size, NonnullOwnPtr<Memory::Region> dma_buffer)
-    : m_controller(controller)
-    , m_type(type)
-    , m_direction(direction)
-    , m_endpoint_address(0)
-    , m_max_packet_size(max_packet_size)
-    , m_poll_interval(0)
-    , m_data_toggle(false)
-    , m_dma_buffer(move(dma_buffer))
-{
-}
-
-Pipe::Pipe(USBController const& controller, Type type, Direction direction, USBEndpointDescriptor& endpoint [[maybe_unused]], NonnullOwnPtr<Memory::Region> dma_buffer)
-    : m_controller(controller)
-    , m_type(type)
-    , m_direction(direction)
-    , m_dma_buffer(move(dma_buffer))
-{
-    // TODO: decode endpoint structure
-}
-
-Pipe::Pipe(USBController const& controller, Type type, Direction direction, u8 endpoint_address, u16 max_packet_size, u8 poll_interval, i8 device_address, NonnullOwnPtr<Memory::Region> dma_buffer)
     : m_controller(controller)
     , m_type(type)
     , m_direction(direction)
     , m_device_address(device_address)
     , m_endpoint_address(endpoint_address)
     , m_max_packet_size(max_packet_size)
-    , m_poll_interval(poll_interval)
     , m_data_toggle(false)
     , m_dma_buffer(move(dma_buffer))
 {
 }
 
-ErrorOr<size_t> Pipe::control_transfer(u8 request_type, u8 request, u16 value, u16 index, u16 length, void* data)
+ErrorOr<NonnullOwnPtr<ControlPipe>> ControlPipe::create(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, size_t buffer_size)
 {
+    auto dma_buffer = TRY(MM.allocate_dma_buffer_pages(TRY(Memory::page_round_up(buffer_size)), "USB device DMA buffer"sv, Memory::Region::Access::ReadWrite));
+    return adopt_nonnull_own_or_enomem(new (nothrow) ControlPipe(controller, endpoint_address, max_packet_size, device_address, move(dma_buffer)));
+}
+
+ControlPipe::ControlPipe(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, NonnullOwnPtr<Memory::Region> dma_buffer)
+    : Pipe(controller, Type::Control, Direction::Bidirectional, endpoint_address, max_packet_size, device_address, move(dma_buffer))
+{
+}
+
+ErrorOr<size_t> ControlPipe::control_transfer(u8 request_type, u8 request, u16 value, u16 index, size_t length, void* data)
+{
+    VERIFY(length <= m_dma_buffer->size());
+
     MutexLocker lock(m_dma_buffer_lock);
 
     USBRequestData usb_request;
@@ -67,7 +53,7 @@ ErrorOr<size_t> Pipe::control_transfer(u8 request_type, u8 request, u16 value, u
     auto transfer = TRY(Transfer::try_create(*this, length, *m_dma_buffer));
     transfer->set_setup_packet(usb_request);
 
-    dbgln_if(USB_DEBUG, "Pipe: Transfer allocated @ {}", transfer->buffer_physical());
+    dbgln_if(USB_DEBUG, "ControlPipe: Transfer allocated @ {}", transfer->buffer_physical());
     auto transfer_length = TRY(m_controller->submit_control_transfer(*transfer));
 
     // TODO: Check transfer for completion and copy data from transfer buffer into data
@@ -78,26 +64,90 @@ ErrorOr<size_t> Pipe::control_transfer(u8 request_type, u8 request, u16 value, u
     return transfer_length;
 }
 
-ErrorOr<size_t> Pipe::bulk_transfer(u16 length, void* data)
+ErrorOr<NonnullOwnPtr<BulkInPipe>> BulkInPipe::create(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, size_t buffer_size)
 {
+    VERIFY(buffer_size >= max_packet_size);
+    auto dma_buffer = TRY(MM.allocate_dma_buffer_pages(TRY(Memory::page_round_up(buffer_size)), "USB pipe DMA buffer"sv, Memory::Region::Access::ReadWrite));
+    return adopt_nonnull_own_or_enomem(new (nothrow) BulkInPipe(controller, endpoint_address, max_packet_size, device_address, move(dma_buffer)));
+}
+
+BulkInPipe::BulkInPipe(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, NonnullOwnPtr<Memory::Region> dma_buffer)
+    : Pipe(controller, Pipe::Type::Bulk, Direction::In, endpoint_address, max_packet_size, device_address, move(dma_buffer))
+{
+}
+
+ErrorOr<size_t> BulkInPipe::bulk_in_transfer(size_t length, void* data)
+{
+    VERIFY(length <= m_dma_buffer->size());
+
+    MutexLocker lock(m_dma_buffer_lock);
+
+    size_t transfer_length = 0;
+
+    auto transfer = TRY(Transfer::try_create(*this, length, *m_dma_buffer));
+
+    dbgln_if(USB_DEBUG, "Pipe: Bulk in transfer allocated @ {}", transfer->buffer_physical());
+    transfer_length = TRY(m_controller->submit_bulk_transfer(*transfer));
+    memcpy(data, transfer->buffer().as_ptr(), min(length, transfer_length));
+    dbgln_if(USB_DEBUG, "Pipe: Bulk in transfer complete!");
+
+    return transfer_length;
+}
+
+ErrorOr<NonnullOwnPtr<BulkOutPipe>> BulkOutPipe::create(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, size_t buffer_size)
+{
+    VERIFY(buffer_size >= max_packet_size);
+    auto dma_buffer = TRY(MM.allocate_dma_buffer_pages(TRY(Memory::page_round_up(buffer_size)), "USB pipe DMA buffer"sv, Memory::Region::Access::ReadWrite));
+    return adopt_nonnull_own_or_enomem(new (nothrow) BulkOutPipe(controller, endpoint_address, max_packet_size, device_address, move(dma_buffer)));
+}
+
+BulkOutPipe::BulkOutPipe(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, NonnullOwnPtr<Memory::Region> dma_buffer)
+    : Pipe(controller, Type::Bulk, Direction::Out, endpoint_address, max_packet_size, device_address, move(dma_buffer))
+
+{
+}
+
+ErrorOr<size_t> BulkOutPipe::bulk_out_transfer(size_t length, void* data)
+{
+    VERIFY(length <= m_dma_buffer->size());
+
     MutexLocker lock(m_dma_buffer_lock);
 
     size_t transfer_length = 0;
     auto transfer = TRY(Transfer::try_create(*this, length, *m_dma_buffer));
 
-    if (m_direction == Direction::In) {
-        dbgln_if(USB_DEBUG, "Pipe: Bulk in transfer allocated @ {}", transfer->buffer_physical());
-        transfer_length = TRY(m_controller->submit_bulk_transfer(*transfer));
-        memcpy(data, transfer->buffer().as_ptr(), min(length, transfer_length));
-        dbgln_if(USB_DEBUG, "Pipe: Bulk in transfer complete!");
-    } else if (m_direction == Direction::Out) {
     TRY(transfer->write_buffer(length, data));
     dbgln_if(USB_DEBUG, "Pipe: Bulk out transfer allocated @ {}", transfer->buffer_physical());
     transfer_length = TRY(m_controller->submit_bulk_transfer(*transfer));
     dbgln_if(USB_DEBUG, "Pipe: Bulk out transfer complete!");
-    }
 
     return transfer_length;
 }
 
+ErrorOr<NonnullOwnPtr<InterruptInPipe>> InterruptInPipe::create(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, u16 poll_interval, size_t buffer_size)
+{
+    VERIFY(buffer_size >= max_packet_size);
+    auto dma_buffer = TRY(MM.allocate_dma_buffer_pages(TRY(Memory::page_round_up(buffer_size)), "USB pipe DMA buffer"sv, Memory::Region::Access::ReadWrite));
+    return adopt_nonnull_own_or_enomem(new (nothrow) InterruptInPipe(controller, endpoint_address, max_packet_size, device_address, poll_interval, move(dma_buffer)));
+}
+
+InterruptInPipe::InterruptInPipe(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, u16 poll_interval, NonnullOwnPtr<Memory::Region> dma_buffer)
+    : Pipe(controller, Type::Interrupt, Direction::In, endpoint_address, max_packet_size, device_address, move(dma_buffer))
+    , m_poll_interval(poll_interval)
+{
+}
+
+ErrorOr<NonnullOwnPtr<InterruptOutPipe>> InterruptOutPipe::create(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, u16 poll_interval, size_t buffer_size)
+{
+    VERIFY(buffer_size >= max_packet_size);
+    auto dma_buffer = TRY(MM.allocate_dma_buffer_pages(TRY(Memory::page_round_up(buffer_size)), "USB pipe DMA buffer"sv, Memory::Region::Access::ReadWrite));
+    return adopt_nonnull_own_or_enomem(new (nothrow) InterruptOutPipe(controller, endpoint_address, max_packet_size, device_address, poll_interval, move(dma_buffer)));
+}
+
+InterruptOutPipe::InterruptOutPipe(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, u16 poll_interval, NonnullOwnPtr<Memory::Region> dma_buffer)
+    : Pipe(controller, Type::Interrupt, Direction::In, endpoint_address, max_packet_size, device_address, move(dma_buffer))
+    , m_poll_interval(poll_interval)
+{
+}
+
 }

Kernel/Bus/USB/USBPipe.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com>
+ * Copyright (c) 2022, blackcat <b14ckcat@protonmail.com>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -15,6 +16,7 @@
 namespace Kernel::USB {
 
 class USBController;
+class Transfer;
 
 //
 // A pipe is the logical connection between a memory buffer on the PC (host) and
@@ -41,8 +43,6 @@ public:
         FullSpeed
     };
 
-    static ErrorOr<NonnullOwnPtr<Pipe>> try_create_pipe(USBController const& controller, Type type, Direction direction, u8 endpoint_address, u16 max_packet_size, i8 device_address, size_t buffer_size = PAGE_SIZE, u8 poll_interval = 0);
-
     Type type() const { return m_type; }
     Direction direction() const { return m_direction; }
     DeviceSpeed device_speed() const { return m_speed; }
@@ -50,23 +50,17 @@ public:
     i8 device_address() const { return m_device_address; }
     u8 endpoint_address() const { return m_endpoint_address; }
     u16 max_packet_size() const { return m_max_packet_size; }
-    u8 poll_interval() const { return m_poll_interval; }
     bool data_toggle() const { return m_data_toggle; }
 
     void set_max_packet_size(u16 max_size) { m_max_packet_size = max_size; }
     void set_toggle(bool toggle) { m_data_toggle = toggle; }
     void set_device_address(i8 addr) { m_device_address = addr; }
 
-    ErrorOr<size_t> control_transfer(u8 request_type, u8 request, u16 value, u16 index, u16 length, void* data);
+protected:
-    ErrorOr<size_t> bulk_transfer(u16 length, void* data);
-
-    Pipe(USBController const& controller, Type type, Direction direction, u16 max_packet_size, NonnullOwnPtr<Memory::Region> dma_buffer);
-    Pipe(USBController const& controller, Type type, Direction direction, USBEndpointDescriptor& endpoint, NonnullOwnPtr<Memory::Region> dma_buffer);
-    Pipe(USBController const& controller, Type type, Direction direction, u8 endpoint_address, u16 max_packet_size, u8 poll_interval, i8 device_address, NonnullOwnPtr<Memory::Region> dma_buffer);
-
-private:
     friend class Device;
 
+    Pipe(USBController const& controller, Type type, Direction direction, u8 endpoint_address, u16 max_packet_size, i8 device_address, NonnullOwnPtr<Memory::Region> dma_buffer);
+
     NonnullLockRefPtr<USBController> m_controller;
 
     Type m_type;
@@ -76,11 +70,77 @@ private:
     i8 m_device_address { 0 };    // Device address of this pipe
     u8 m_endpoint_address { 0 };  // Corresponding endpoint address for this pipe
     u16 m_max_packet_size { 0 };  // Max packet size for this pipe
-    u8 m_poll_interval { 0 };     // Polling interval (in frames)
     bool m_data_toggle { false }; // Data toggle for stuffing bit
 
     Mutex m_dma_buffer_lock { "USB pipe mutex"sv };
 
     NonnullOwnPtr<Memory::Region> m_dma_buffer;
 };
+
+class ControlPipe : public Pipe {
+public:
+    static ErrorOr<NonnullOwnPtr<ControlPipe>> create(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, size_t buffer_size = PAGE_SIZE);
+
+    ErrorOr<size_t> control_transfer(u8 request_type, u8 request, u16 value, u16 index, size_t length, void* data);
+
+private:
+    ControlPipe(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, NonnullOwnPtr<Memory::Region> dma_buffer);
+};
+
+class BulkInPipe : public Pipe {
+public:
+    static ErrorOr<NonnullOwnPtr<BulkInPipe>> create(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, size_t buffer_size = PAGE_SIZE);
+
+    ErrorOr<size_t> bulk_in_transfer(size_t length, void* data);
+
+private:
+    BulkInPipe(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, NonnullOwnPtr<Memory::Region> dma_buffer);
+};
+
+class BulkOutPipe : public Pipe {
+public:
+    static ErrorOr<NonnullOwnPtr<BulkOutPipe>> create(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, size_t buffer_size = PAGE_SIZE);
+
+    ErrorOr<size_t> bulk_out_transfer(size_t length, void* data);
+
+private:
+    BulkOutPipe(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, NonnullOwnPtr<Memory::Region> dma_buffer);
+};
+
+class InterruptInPipe : public Pipe {
+public:
+    static ErrorOr<NonnullOwnPtr<InterruptInPipe>> create(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, u16 poll_interval, size_t buffer_size = PAGE_SIZE);
+
+    u16 poll_interval() const { return m_poll_interval; }
+
+private:
+    InterruptInPipe(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, u16 poll_interval, NonnullOwnPtr<Memory::Region> dma_pool);
+
+    u16 m_poll_interval;
+};
+
+class InterruptOutPipe : public Pipe {
+public:
+    static ErrorOr<NonnullOwnPtr<InterruptOutPipe>> create(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, u16 poll_interval, size_t buffer_size = PAGE_SIZE);
+
+    u16 poll_interval() const { return m_poll_interval; }
+
+private:
+    InterruptOutPipe(USBController const& controller, u8 endpoint_address, u16 max_packet_size, i8 device_address, u16 poll_interval, NonnullOwnPtr<Memory::Region> dma_pool);
+
+    u16 m_poll_interval;
+};
+
+class IsochronousInPipe : public Pipe {
+    // TODO
+public:
+private:
+};
+
+class IsochronousOutPipe : public Pipe {
+    // TODO
+public:
+private:
+};
+
 }